B-cell Precursor Acute Lymphoblastic Leukemia Research Articles

Breaking Barriers in B-Acute Lymphoblastic Leukemia Treatment: Experience of a Tertiary Hospital with the Use of a Tandem Dual CAR-T 19/22 in Pediatric & AYA Patients

INTRODUCTION Anti-CD19 chimeric antigen receptor (CAR) autologous T-cell therapy tisagenlecleucel (CTL019) has shown efficacy in pivotal trials and real-world data in relapsed/refractory pediatric B-cell precursor acute lymphoblastic leukemia (r/r B-ALL). However, 30-50% of patients relapse, because of CD19 loss in leukemic cells, or persistence/function reduction of CTL019. To improve relapse free survival, multitargeting CAR-T cells, such as bicistronic anti-CD22 and anti-CD19 or single sequential infusion are being developed. We report the safety and efficacy of an in-house manufactured tandem anti-CD19/22 dual CAR-T cells in pediatric, adolescents and young adults (AYA) diagnosed with r/r B-ALL. MATERIAL AND METHODS Eight batches of the tandem anti-CD19/22 dual CAR-T cells were manufactured under Good Manufacturing Practices (GMP) and authorized under a compassionate use program by the Spanish Agency for Medicines and Health (AEMPS). The starting material in all cases was patient´s non mobilized apheresis. After, CD4 + and CD8 + T cells were immune selected, activated with CD3/CD28 beads and transduced with a CD19/CD22 lentiviral vector (from Miltenyi Biotec®). Cell expansion was performed in a CliniMACS Prodigy® device with TexMACs® culture medium supplemented with IL-7 and IL-15. During manufacturing, process and quality controls were carried out and the finished product was infused fresh or cryopreserved. RESULTS A total of 8 patients with a median age of 10.5 (range 6-25) years old received a median of 1 (range 1-3) doses of tandem anti-CD19/22 dual CAR-T cells containing a median of 1.13x106 (range 7.5x105-3x106) cells/kg infused. First 3 patients (37.5%) received cryopreserved product. Two patients (25%) were also diagnosed with Down syndrome (DS). The median time between apheresis and infusion was 10.5 days (range 9-14 ). Five patients (62.5%) received previously tisagenlecleucel and four of them (50%) had also received a hematopoietic stem cell transplantation (HSCT). Leukemia blasts did not express CD19 in 2 patients (25%). Both received tisagenlecleucel previously, and one of them also expressed low levels of CD22. Median pre-infusion minimal residual disease (MRD) was 4.91% (range 0.01-87). Bridging therapy was low dose chemotherapy in 7 patients (87.5%), using inotuzumab in 1 patient. Lymphodepletion regimen was individualized, in 5 patients (62.5%) consisted on fludarabine 30 mg/m2/day for 4 days and cyclophosphamide 600 mg/m2/day for 2 days. Regarding CAR cell product, mean transduction was 41.4 %. Similar CD4 +/CD8 + distribution was seen in most products generated (7/8, 88%), and central memory cells were the main subpopulation found, followed by naïve cells. Most CAR-T cell expansions (88%, median 7, range 7-28) were seen between day +7 and day +21 post-infusion. Regarding toxicity, 7 patients (87.5%) presented cytokine release syndrome (CRS). Three patients (37.5 %) with high pre CAR-T tumor burden (TB) (range 75-87 %) developed CRS grade 3-4 (ASBMT guidelines) followed by ICANS grade 3. On day +28 after infusion, 6 patients (75%) were in complete remission (CR), one of them with positive minimal residual disease (MRD). Two patients died because of disease progression (range 2-4.5 months) and a third one (with DS) because of toxicity before day +28 after CAR-T infusion. Consolidative HSCT was performed in 3 of 6 patients that achieved CR (50%) during the first 90 days after CAR-T cell infusion. During follow up of these transplanted patients (median 8.4 months, range 2.3-12.3), 1 patient (33.3%) relapsed after 11 months. One patient presented central nervous system relapse 1 month after CAR-T infusion and HSCT was performed and with 35 months of follow up, continues alive in CR. The last patient (with DS) relapsed 3 months after infusion and immunotherapy (inotuzumab) has been given in order to perform a second HSCT if CR is achieved. CONCLUSIONS In-house manufacturing of tandem anti-CD19/22 dual CAR-T cells is feasible and reproducible under GMP conditions in an academic institution. Product infusion seems to be well tolerated in most patients, although patients with high TB developed high grade toxicities. Setting bridging therapy, reducing TB and manufacturing time remains a challenge. Our experience suggests the efficacy of its use as a bridge to consolidative HSCT. Nevertheless, a larger number of patients in the context of a clinical trial would be necessary.

Frailty in Children and Adolescents with Lymphoblastic Leukemia or Lymphoma Receiving Maintenance Chemotherapy - a Pilot Study

Background: Increased survivorship of childhood cancer has revealed a number of long-term morbidities related to treatment. Evidence suggests that cancer and its treatment may accelerate normal loss of physiologic capacity that occurs during aging.The advanced physiologic aging and related morbidities often seen in childhood cancer survivors suggests that these patients may present with signs of early-onset frailty. Frailty is a measure of global infirmity and impaired physical function and has been correlated with adverse health outcomes and elevated incidence of mortality in the general population. Research into the incidence and applicability of the frailty phenotype in children being treated for cancer may aid in the identification of the most vulnerable patients and identify those who may require intervention. The purpose of this study is to explore the frailty phenotype in children and adolescents receiving maintenance chemotherapy for acute lymphoblastic leukemia or lymphoma. Methods: We prospectively recruited children and adolescents (aged 5-18 years-old) diagnosed with acute lymphoblastic leukemia or lymphoma in the first cycle of their maintenance chemotherapy. Frailty was assessed twice: at an initial visit in cycle 1 maintenance treatment (V1), and 6-months following the initial assessment (V2). The frailty phenotype consists of 5 domains, which were assessed using developmentally appropriate measures: 1) Slowness: 6-minute walk test; 2) Weakness: Handgrip strength dynamometry - calibrated to the size of the participant's hand; 3) Exhaustion/Fatigue: The PedsQL TM Multidimensional Fatigue Scale; 4) Body Composition: InBody 270 body composition analyzer; and 5) Physical activity/Energy expenditure: Self-administered physical activity questionnaire for older children (PAQ-C) and physical activity questionnaire for adolescents (PAQ-A).Each assessment was scored individually and “Frailty points” were assigned based on age and sex-based normative z-scores or survey scores, and a composite “Frailty Score” ranging from 0=least frail to 25=most frail. Wilcoxon signed-rank test was used to compare V1 and V2 frailty scores. Results:The analysis sample consisted of 19 participants (mean age 9.1 [SD=3.4] years old; 63% female) who completed V1 and 7 participants that completed V2. Diagnoses of participants who completed V1 include precursor B-Cell acute lymphoblastic leukemia (n=15), T-Cell acute lymphoblastic leukemia (n=3), and T-Cell lymphoblastic Lymphoma (n=1). Median V1 z-scores and survey scores per domain are as follows: Slowness: z-score -3.11 [-4.02, -2.48]; Weakness: z-score -1.48 [-2.06, -1.38]; Exhaustion/Fatigue: score 58.3 [46.5, 70.8]; Body composition: z-score (total body fat) 0.90 [0.47, 1.79]; Physical activity/Energy expenditure: score 2.26 [1.73, 2.54]. Domain specific frailty score for V1 are displayed in Figure 1. Of the 7 participants with a V2 frailty assessment, paired analysis demonstrated significant improvement in Exhaustion/Fatigue (median score V1=56.94, V2=70.83 [p=0.016]). However, improvements in weakness, body composition, and physical activity/energy expenditure did not reach statistical significance. Median slowness z-scores at V2 were similar to V1. Median composite frailty score improved from 12 to 11 in V2 but was not statistically significant (p=0.054). Comparison of V1 and V2 overall composite scores are displayed in Figure 2. Conclusion: Children and adolescents receiving maintenance chemotherapy for acute lymphoblastic leukemia or lymphoma scored poorly in all five domains of frailty. We observed some improvements in exhaustion/fatigue, and trending improvements in subdomain and composite frailty scores in the small sample of participants with V1 and V2 assessments. Given that frailty has been shown to persist into adulthood in survivors of childhood cancer, the frailty assessment may be an effective tool for identifying patients who may require additional intervention. Initial and follow-up frailty measurements for this study are currently ongoing.

Mitochondrial dsRNA from B-Precursor Acute Lymphoblastic Leukemia Cells Induce Formation of Cancer Associated Fibroblast in the Bone Marrow Leading to Formation of a Chemoprotective Bone Marrow Niche

Precursor B-cell Acute Lymphoblastic Leukemia (B-ALL) is typically a highly chemosensitive malignancy with the majority of children being cured by chemotherapy alone. Adult ALL is often chemosensitive at initial treatment, but long term disease free survival is less common. It is widely accepted that outcome in ALL closely relates to underlying genetic lesion (Moorman, Hematologica 2016) but no specific mechanisms by which ALL genetics influence outcome have been identified. We have previously demonstrated that an ‘activated mesenchymal stromal cell (MSC) niche’ develops in response to reactive oxygen species (ROS) -inducing chemotherapy in which mitochondria are actively transferred along tunnelling nanotubes to ‘rescue’ B-ALL cells from chemotherapy (Burt, et al Blood 2019). According to recent evidence that chemotherapy resistant ALL sub-clones may exist at diagnosis (Dobson et al Cancer Discovery 2020), we hypothesised that B-ALL cells may themselves directly activate bone marrow stromal cells to generate cancer associated fibroblasts (CAF) from MSC. To test this hypothesis, we first used our previously described in vitro niche model wherein either the HS27a MSC cell line or healthy donor (HD) MSCs are co-cultured with either B-ALL cell lines or primary patient B-ALL cells. Three of five B-ALL cell lines and 3 of 4 primary B-ALL samples tested, induced activation of the MSCs, as characterised by cytomorphological changes identified by confocal microscopy, up-regulation of CAF-relevant gene expression and increased IL6, IL8 and CCL2 protein secretion. The ability of the B-ALL cell lines to induce CAF correlated directly with the intrinsic ROS levels of the cell as determined by CellROX assay. In vivo, the CAF-inducing ALL cell lines also activated murine MSCs when established as xenografts in NOD-SCID gamma (NSG) mice. Immunohistochemistry of NSG murine femora revealed a very significant expansion in nestin+ cells after exposure to CAF-induing ALL cells compared to non-CAF-inducing controls. We established that the ALL cells activated MSC without contact, both from exposure of MSC to ALL cells in transwell and from exposure to B-ALL cell conditioned media (CM). RNA sequencing of HS27a stromal cells exposed to CAF-inducing B-ALL cell CM compared with non-CAF inducing controls unexpectedly showed that the most highly upregulated pathways were those involved in RNA sensing. Using a smaller gene panel selected from among the RNA-sensing pathway genes, we confirmed that this was also the case for primary, HD MSCs upon exposure to primary ALL patient samples. As a result, we sought evidence for the role of mitochondrial dsRNA, which has been shown to activate the anti-viral signalling pathway (Dhir et al, Nature 2018). Using the J2 anti-dsRNA monoclonal antibody in both confocal and flow cytometric assays, we observed very significantly higher levels of dsRNA in MSC which had been exposed to CAF inducing B-ALL cell CM than in non-CAF inducing B-ALL or MSC alone controls. We confirmed by RT-PCR for mitochondrial genes on dsRNA immunoprecipitated from CAF inducing B-ALL cell CM that the dsRNA was of mitochondrial origin. Using ELISA, we quantified dsRNA from total cell RNA extracted from paired primary B-ALL patient samples at diagnosis and in remission. We found significantly higher levels of dsRNA at diagnosis than in remission, with it being undetectable in most remission samples. Moreover, we confirmed by flow cytometry the presence of dsRNA in 6 B-ALL patient derived xenografts which was absent in the control NSG mice without leukemia. We used DMSO to degrade dsRNA from CAF inducing B-ALL cell CM, as is often done in Sanger sequencing and confirmed the degradation by ELISA. We then quantified gene expression of a selection of stromal cell activation marker genes, as well as genes in the RNA sensing pathway after exposure to either DMSO-treated B-ALL cell CM or non-treated control. There was a 2 to 4-fold reduction in expression of IL6, IL8 as well as of RIG-I, MX2, IFIH1, MAVS and OAS1 expression in DMSO-treated condition compared to control. We confirmed that IL6, IL8 and CCL2 protein secretion was also significantly abrogated in the test but not the control condition. We propose a model in which ROS-induced mitochondrial dysfunction in ALL cells leads to release of dsRNA which in turn activates bone marrow stromal cells leading to protective niche formation, despite lack of prior exposure to cytotoxic agents.

Genetic and Cytometric Characteristics of Pediatric B-Other Acute Lymphoblastic Leukemia Cohort

Background: According to WHO-HAEM5, the majority of precursor B-cell acute lymphoblastic leukemia (B-ALL) cases are classified based on cytogenetic testing according to ploidy changes or well-known chromosomal rearrangements. Approximately 30% of patients with B-ALL, however, display none of the major chromosomal abnormalities. This population is classified together as B-other-ALL, a highly diverse subgroup with heterogenous genetic profiles, clinical characteristics, and outcomes. Recent advances in gene expression profiling and sequencing allowed to identify multiple genetic drivers that confer distinct clinical and prognostic features in B-other ALL resulting in better understanding of this subgroup. Among them, B-ALL with specific gene expression signatures (i.e. BCR-ABL1-like and ETV6-RUNX1-like) have been described and included in the classification. However, due to the complex mechanisms underlying the phenotype, standard molecular and cytogenetic workup is not sufficient to make a diagnosis and there is still no universally accepted definition or diagnostic algorithm. Therefore, there is a need to improve our understanding of genetic aberrations driving B-other ALL, screen for unknown lesions, and associate these findings with clinical picture. Aims: Genetic and cytometric characteristics of pediatric B-other ALL cohort treated in a single center in Poland to evaluate population frequencies of known ALL subtypes, genetic aberrations, immunophenotypes, and evaluate their associations with outcome and clinical and demographic parameters. Methods The study included 54 consecutive children (aged 1-18 years) diagnosed in 2014-2022 with B-other ALL, i.e. excluding hyperdiploidy, hypodiploidy, ETV6-RUNX1, BCR-ABL1, TCF3-PBX1, and KMT2A-fusions. In all samples, targeted RNA sequencing using FusionPlex Acute Lymphoblastic Leukemia library preparation kit (ArcherDx) and digital MLPA using SALSA digital MLPA assay were performed. The samples were sequenced on Illumina MiSeq platform. RNAseq data were analyzed using Archer Analysis software v7.0 and aimed to identify fusions, point mutations and expression levels in 81 genes, including fusion transcripts with unknown partners. MLPA data were analyzed using Coffalyser digitalMLPA software. All novel in-frame fusion transcripts were confirmed with Sanger sequencing. Cytometric evaluation included both standard and extended panel of immunophenotypic markers, i.e. CD45, CD3, CD19, CD34, HLA-DR, phospho-TYR, phospho-STAT3, phospho-STAT5, phospho-CRKL, CRLF2 CD127, CD115, CD25, SOCS1, BLNK, CD97, CD99, CD140A, CD140B, and viability stains (FVS780 and/or 7AAD). Clinical data was obtained retrospectively from medical records. Results: The cohort included 35% of BCR-ABL1-like cases, 2% ETV6-RUNX-like, and 5,5% PAX5 rearranged (1 fusion, 2 mutations). Mutations activating RAS/RAF-MAPK signaling were observed in 64% of cases and spread across all subtypes. JAK-STAT class aberrations were observed in 37% cases whereas ABL-class aberrations - in 7,2%. Three novel in-frame fusion transcripts were detected, including two lesions affecting cytokine/kinase signaling related to BCR-ABL1-like phenotype (TCOF3/PDGFRB and CD74/PDGFRB) and one affecting DNA repair mechanisms (SSBP2/CHD1). Novel aberrations were associated with poor prognosis. In addition, HOOK3/FGFR1 fusion transcript previously described for other hematological malignancies, but not in ALL, was detected in a single subject. Except for CRLF2, none of the single markers alone allowed to distinguish new subtypes of ALL. However, multiparameter statistical analysis of the data allowed to build a Ph-like ALL predictor for the identification of Ph-like ALL cases Conclusion: Our study shows population-based frequencies of novel ALL subtypes, including both recurrent and novel genetic aberrations. This data widens our knowledge on the interplay between molecular aberrations and clinical course of the disease and provides clues for diagnostics optimization.

Venetoclax and Blinatumomab for Adult Patients with Relapsed/Refractory or MRD Positive Ph-Negative B-Precursor ALL: First Results of the GMALL-Bliven Trial

Introduction Prognosis of adult patients with relapsed/refractory (R/R) B-precursor acute lymphoblastic leukemia (BCP-ALL) remains poor. Monotherapy with Blinatumomab in ALL induced a complete remission (CR) in 44% of patients and measurable residual disease (MRD) negative molecular remission (MOL-CR) in 33%. Median overall survival of 7.7 months remains unsatisfactory. In the MRD setting, median survival was 36 months in the context of subsequent allogeneic stem cell transplantation (SCT). The combination of Blinatumomab with Venetoclax may be an effective option in ALL. Objectives In this multicenter phase 1 clinical trial the GMALL study group evaluates the safety of Blinatumomab in combination with Venetoclax in R/R or MRD positive BCP-ALL (NCT05182385). Using RNA sequencing, functional intracellular BH3 profiling, T cell immunomonitoring and effector cell cytotoxicity assays we aim to further elucidate synergy of this combination. Methods The BLIVEN trial includes patients with CD19-positive Ph-negative BCP-ALL aged 18 years and older, with no upper age limit. Eligible patients had either R/R ALL (bone marrow blasts >5%) or molecular failure/relapse (MRD >1xE-04). To assess safety, we determined maximum tolerated dose (MTD) as primary endpoint of the phase I part of the trial as designated recommended phase 2 dose (RP2D). Key secondary endpoint was the MOL-CR rate. Treatment consisted of oral Venetoclax in continuous dosing on day -7 to day 42 of target doses ranging between 200-800 mg once daily, and Blinatumomab as continuous intravenous infusion of 28 µg/d 4 weeks on and 2 weeks off, starting on day 1. For patients with R/R ALL, a cautionary dose step of 9 µg/d Blinatumomab was implemented for one week. MRD was analyzed in the reference laboratory using real-time quantitative PCR (RQ-PCR) of immunoglobulin and T-cell receptor (IG/TR) rearrangements. Results Between February 2022 and May 2023 a total of 7 patients were enrolled in the phase I part at four German centers (Figure 1). Venetoclax target doses were 400 mg (n=3), 600 mg (n=3), and 800 mg (n=1). Median age was 48.5 years (range 22 - 72 years). MRD assessment was available in 7/7 patients. Molecular BCP-ALL subtypes were identified by RNA sequencing in 5/5 analyzed patients, including ZNF384-rearranged ALL (n=2), BCR::ABL1-like (n=2; IGH::CRLF2 rearranged), and KMT2A-rearranged ALL (n=1). Three of seven patients were treated for hematological relapse, while 4/7 patients had molecular failure/relapse at time of enrolment. Among patients with R/R ALL, 2/3 were refractory to front-line therapy with intensive GMALL induction/consolidation therapy, while 1/3 suffered relapse shortly after failure of second allogeneic SCT. CTCAE grade IV neutropenia was identified as adverse reaction related to Venetoclax in one patient. Neutropenia resolved before dose limiting toxicity (DLT) evaluation time (i.e. 42 days after Venetoclax initiation). Overall, no DLT was identified throughout the trial and MTD was not reached. No treatment interruption was noted during cycle 1. Two of seven patients received one treatment cycle of BLIVEN only due to treatment failure, 5/7 patients received two treatment cycles. Response assessment was available for 7/7 patients. Treatment with Blinatumomab/Venetoclax of R/R ALL resulted in CR in 1/3 patients, with the responding patient showing a MOL-CR. The MOL-CR rate in molecular failure/relapse patients was 3/4. Conclusion Salvage therapy with Blinatumomab and Venetoclax exhibited good tolerability without treatment-related mortality. No treatment withdrawals were attributed to safety concerns. Two patients did not respond to BLIVEN combination therapy. Interestingly, both patients exhibited IGH::CRLF2 fusion transcripts.The remaining 5 patients obtained MRD responses, including complete MRD responses, of which 2/2 occurred in ZNF384 rearranged BCP-ALL. Further follow-up and larger patient numbers are needed to establish the potential benefit of this regimen in molecular driver subtypes of BCP-ALL. Enrollment to complete phase I of the BLIVEN trial is currently ongoing. Updated results including RP2D will be presented at the meeting. Acknowledgments This is an independent academic early phase I clinical trial conducted under the sponsor role of the Goethe University, Frankfurt, Germany. It received financial support and supply of Venetoclax by AbbVie Inc..

A Nationwide Clinical Trial ALL-B12: An Optimized Therapy for Pediatric B-Precursor Acute Lymphoblastic Leukemia with Excellent Overall Survival and Minimal Non-Relapse Mortality: A Report from the Japan Children's Cancer Group

Background: Advancements in treatment have significantly improved therapeutic outcomes for pediatric acute lymphoblastic leukemia (ALL) and relapsed ALL. However, there remains a need for therapies that minimize relapse in high-risk groups and avoid long-term complications. To address this gap. we conducted the nationwide clinical trial ALL-B12, aimed at newly diagnosed B-precursor ALL aged 1-18 years. Methods: ALL-B12 enrolled participants from November 2012 to November 2017. Patients were stratified based on the NCI classification (age and WBC count at diagnosis). Those with NCI-SR and NCI-HR were assigned to the standard risk group (SR) and the intermediate group (IR), respectively. Poor steroid responders and those with high-risk genomic abnormalities were assigned to the high risk group (HR). A treatment regimen, including 4-drug remission induction, early consolidation, HD-MTX-containing intensification, re-induction, and maintenance, was implemented. Anthracycline dose in the induction therapy was reduced in SR patients. In contrast, early consolidation was intensified with L-ASP for a part (randomized) of the IR and the entire HR. Patients classified as CNS3 were treated as high risk, receiving 12 Gy cranial irradiation; prophylactic cranial irradiation was avoided in non-CNS3 groups. Allogeneic hematopoietic cell transplantation (allo-HCT) during the first remission was restricted to those in the very high-risk group with specific genomic abnormalities (e.g., hypodiploid <44 and TCF3-HLF) and residual MRD above 10^-3 at the end of early consolidation. A randomized comparison was carried out within each risk group to identify the optimal treatment. We assessed the effectiveness of intensification with VCR/DEX pulses for the SR, the impact of L-ASP intensification for the IR, and compared block-type treatment and HD-MTX intensified with VCR and L-ASP (HD-MTX/VL) for the HR. The primary outcome measure was the 5-year event-free survival (EFS) rate. Results: In total, 1,936 patients were enrolled, with 1,804 patients receiving protocol treatment after excluding ineligible patients such as those with BCR-ABL1 positivity. The percentage of patients achieving remission at the end of early consolidation was 98.9%. The overall 5-year EFS and OS probability were 85.2% (95%CI 83.5-86.8%) and 94.3% (95%CI 93.1-95.3%), respectively. Only 1.7% of patients underwent allo-HCT during the first remission. The mortality rate during induction was just 0.6%, with non-relapse mortality (NRM) after remission at 0.6%. The overall relapse incidence was 13.2%, and the overall CNS relapse rate was 1.9%. Among patients assigned to risk groups, 1,107 (62.7%) were assigned to the SR, 459 (26.0%) to the IR, and 200 (11.3%) to the HR. The 5yEFS for the SR was 89.9%. The post-randomization EFS rates for those with and without VCR/DEX intensification were 90.7% and 90.1%, respectively, indicating nearly identical survival curves (p = 0.73). The EFS for the IR was 79.7%, but L-ASP intensification was expected to be effective, the EFS for groups with and without ASP intensification was 82.1% and 77.9%, respectively, failing to reach statistical significance (p = 0.31). The EFS for the HR was 75.5%, with overlapping survival curves for block treatment (75.7%) and HD-MTX/VL (74.2%) (p = 0.92). MRD dynamics were associated with prognosis, and early consolidation therapy enhanced by ASP resulted in better MRD clearance. MRD of 10^-4 was associated with poor prognosis at both the end of induction and the end of early consolidation. Conclusion: In our multi-center clinical trial, we observed excellent outcomes in a diverse group of patients nationwide. Using the NCI criteria for stratification, a significant number of patients were categorized into the SR. Additionally, introducing L-ASP during early consolidation decreased the number of MRD-positive patients, which subsequently reduced the subset needing allo-HCT. This strategic adjustment in treatment intensity resulted in both high EFS rates and low NRM. Given the rise of immunotherapy and its promising results for recovery even post-relapse, there's a pressing need to enhance overall outcomes while minimizing non-relapse mortality. We anticipate refining our stratification further and integrating immunotherapy and other innovative treatments into our approach.

Increased Environmental Temperature Is an Emerging Health Risk That Correlates with Rates of Acute Lymphoblastic Leukemia in Europe

Background: The World Meteorological Organization (WMO) has calculated that European temperatures have increased at more than double the global average over the last 30 years 1. Besides research in radiation, little research has focused on how this might connect to the mechanisms initiating mutations in ALL. Both latitude and solar irradiance are potential risk factors in the development of ALL 2,3. Latitude covaries with the intensity of solar irradiance and ambient temperature, and both could therefore influence the risk of ALL. Furthermore, high ambient temperature during pregnancy was found to be associated with increased likelihood of childhood ALL 4. Global increases in temperature escalate the likelihood of extreme heat events, which in mammals increases reactive oxygen species, increases DNA damage, and suppresses the immune system 5. Few studies have evaluated changes in ambient temperature as a risk factor for ALL in Europe. We also included chronic lymphocytic leukemia (CLL) for comparison. Objective:To investigate the relationship between population-weighted country centroids (location of greatest population density), average country yearly temperature, solar irradiance and ALL and CLL rates in 40 European countries between the years 2010 and 2019. Design/Method:Incidence and prevalence rates for ALL and CLL (Age-standardized data with males and females) were obtained from the Global Health Data Exchange (GHDx) database. Population-weighted latitude/longitude centroids for Europe 6 were obtained from Baylor University and input into the Global Solar Atlas to obtain the average yearly global horizontal irradiance values. European temperature data was obtained from the Climatic Research Unit at the University of East Anglia (Copernicus Climate Data Store) 7. ALL and CLL incidence and prevalence rates per 100,000 people for 40 European countries were compared by linear regression to each country's temperature or solar irradiance at the population centroids. Statistical analyses were performed using GraphPad Prism and Excel. Results:After2010, we detected a significant positive correlation between ALL incidence and prevalence rates with mean annual temperature across countries for each year of analysis (for example in 2014 the ALL prevalence p-value = 0.01 and R= 0.4, see Figure 1). There was also an increase in the significance of this relationship over time between 2010 and 2019 (Figure 1B). We also detected a significant positive correlation between the increase in mean annual temperature across Europe and an increase in ALL over the past decade (Figure 1B). However, no relationship was established in this study for solar irradiance or population-weighted latitude and CLL prevalence and incidence rates. Conclusions:Increasing mean annual temperatures may increase the risk of developing ALL. We speculate this may be connected through increases in extreme weather events impacting oxidative stress, DNA damage, and/or suppression of the immune system. Considering the global climate crisis, the WMO finding of higher European temperature increases and our finding of significance between temperature and ALL rates, these relationships should be functionally studied. Finally, these studies should be expanded to countries outside of Europe. References 1 World Meteorological Organization. Temperatures in Europe increase more than twice global average. (2022). 2 Pordanjani, S. R., Kavousi, A., Mirbagheri, B., Shahsavani, A. & Etemad, K. Temporal trend and spatial distribution of ALL in Iranian children during 2006-2014: a mixed ecological study. Epidemiol. Health42, (2020). 3 Coste, A. et al. Residential exposure to UV light and risk of precursor B-cell ALL: assessing the role of individual risk factors, the ESCALE and ESTELLE studies. Cancer Causes Control28, 1075-1083 (2017). 4 Rogne, T. et al. High Ambient Temperature in Pregnancy and Risk of Childhood ALL. medRxiv (2023) 5 Chauhan, S. S., Rashamol, V. P., Bagath, M., Sejian, V. & Dunshea, F. R. Impacts of heat stress on immune responses and oxidative stress in farm animals and nutritional strategies for amelioration. Int. J. Biometeorol.65, 1231-1244 (2021). 6 Hamerly, G. Population-weighted European state centers. (2006). 7 Climatic Research Unit, U. of E. A. Temperature and precipitation gridded data for global and regional domains derived from in-situ and satellite observations. (2023).

The Battle within: AML´s p53 Strategies to Evade T-Cell Attack

Bispecific T-cell recruiting antibody constructs (BsAb) have shown clinical efficacy with Blinatumomab, a CD3xCD19 BiTE ® construct used for the treatment of relapsed or refractory B-cell precursor ALL. Despite the success of BsAbs in B-cell malignancies, the translation to a myeloid setting has been unsuccessful, independently of the chosen target antigen. For example, targeting CD33 has failed to provide long-term benefits. Several reports have demonstrated that the diverse genetic makeup of AML confers resistance to T-cell based immunotherapy. Mutations of TP53 occur in 5-10% of patients with de novo AML and up to 50% in older patients with therapy related AML, thus highlighting its role as a potential resistance mechanism. We hypothesize, that genetic aberrations of TP53 in AML contribute to cell intrinsic and cell extrinsic resistance against T-cell based immunotherapy approaches. To study the impact of TP53 aberrations on T-cell based immunotherapy, MV4-11 p53 WT or MV4-11 p53 KD were cocultured with healthy donor T cells at an effector to target ratio of 1:6 with or without BsAbs. BsAb-mediated cytotoxicity was analyzed by specific lysis of the CD33 + target cells and T-cell proliferation was assessed by FarRed ® staining or CD2 + T-cell fold change calculated to day 0. Cytokine secretion was monitored in the coculture supernatants by cytometric beads arrays. To differentiate between secretome vs surfacome mediated differences, transwell assays were performed. To identify the T-cell immunosuppressive factor, secretome analysis were performed using the Olink® proteomics platform. To further dissect the effect of the p53 KD MV-411 on T cells, we performed RNA-Seq analysis of T cells after coculture with MV4-11 p53 KD vs p53 WT. As expected, BsAb-mediated cytotoxicity was reduced against p53 KD vs p53 WT MV4-11 (% specific lysis: p53 KD=47.86±7.37 vs p53 WT=76.42±3.82; p=0,0001). However, BsAb-mediated T-cell proliferation was also significantly decreased in cocultures with p53 KD vs p53 WT (% proliferated: 30.26±2.92 vs 44.25±4.08; p=0.002). In line with these findings, we observed a significant decrease in secretion of the proinflammatory cytokines IFNγ (p53 KD=2985,01±896,69 vs p53 WT=4009.15±764.97 pg/ml; p=0.068), TNF (29,38±8.16 vs 110.21±37.61 pg/ml; p=0.044) and IL-2 (1391.64±375.93 vs 2253.88±604.76 pg/ml; p=0.018). RNA-Seq analysis of T cells after coculture with MV4-11 p53 KD vs p53 WT revealed a decrease in the expression of genes associated with mitosis (such as E2F targets and mitotic spindle related genes). A lower mitotic rate provides a potential explanation for the reduction in T-cell proliferation after coculture with p53 KD. To dissect if the observed effects were due to the AML surfacome or the secretome, we performed transwell assays. Indeed, the negative impact of p53 KD AML cells on T-cell function was also observed without direct cell-cell contact. To gain further insights in the secretome of the AML cells, coculture supernatant was analysed using the Olink ® platform and demonstrated significantly higher secretion of IL-18 and LAP TGF-β1 (TGF-β1 latency associated protein) in the coculture with MV4-11 p53 KD vs MV4-11 p53 WT (normalized protein expression for IL-18: p53 KD=1.86±0.22 vs p53 WT=0.96±0.052; p=0.0153; for LAP TGF-β1: 6.52±0.18 vs 5.84±0.14; p=0.0394). The relevance of TGF-β on T-cell fitness was confirmed by the analysis of BsAb-mediated cytotoxicity with or without the addition of TGF-β. Addition of 3 ng/µl TGF-β to the coculture with p53 WT decreased the specific lysis significantly and was now comparable to the lysis of p53 KD. Confirmatory studies in primary AML samples with or without p53 aberrations further validated our findings with a clear reduction of BsAb-mediated cytotoxicity (% specific lysis: p53 KD=35.82±5.51 vs p53 WT=61.32±8.27; p=0.015), T-cell proliferation (CD2 + fold change: 3.17±0,61 vs 7.1±2.8; p=0.111) and secretion of proinflammatory cytokines. Taken together, we demonstrated that AML cells carrying a p53 aberration are less susceptible to BsAb-mediated cytotoxicity. Surprisingly, immune evasion was mediated by the AML secretome leading to a decrease in T-cell proliferation and cytokine secretion. Secretome analyses indicated TGF-β as a prominent cytokine leading to an impairment of T-cell function. Further studies are needed to understand the influence of p53 on the TGF-β pathway in AML cells.

Prognostic Value of MRD By Flow Cytometry in Adolescent and Adult Patients with Philadelphia Chromosome-Negative Acute Lymphoblastic Leukemia Treated with Pediatric-Inspired Regimen: A Post-Hoc Analysis from a Prospective Study of China

Background Minimal residual disease (MRD) is currently considered as one of the most powerful predictors in patients with Philadelphia chromosome-negative acute lymphoblastic leukemia (Ph - ALL).The time points and thresholds for MRD monitoring in pediatric Ph - ALL have been well established. However, surveillance strategy in adult ALL has not yet been standardized. In this study, we explored the prognostic value of MRD levels and monitoring time points by flow cytometry (FCM) in adolescent and adult patients with Ph - ALL treated with pediatric-inspired regimen. Methods This analysis includes adolescent and adult patients who were treated according to a pediatric-inspired regimen revised based on Children's Oncology Group protocol (CCG-1961). This prospective study was registered at Chinese Clinical Trial Registry Website with the registration number of ChiCTR-OOC-15006328. MRD was measured using bone marrow aspirates with eight-color multiparametric FCM on day 14 of induction, at end of induction (EOI, days 29-42) , post the first consolidation (post-C1), and throughout the treatment period. MRD was defined as the percentage of lymphoblasts present in the total nucleated cells counted. MRD levels of < 0.01% and ≥ 0.01% was considered as negative and positive, respectively.Patients who were MRD-positive were further stratified into three groups according to MRD level: MRD low positive (MRD-lp), ≥ 0.01% to < 0.1%; MRD high positive (MRD-hp), ≥ 0.1% to < 1%; and MRD very high positive (MRD-vhp), ≥ 1%. Results From 2014 to 2021, a total of 415 patients with a median age of 27 (range: 14-69) years were treated. Three hundred and twelve patients presented with B-precursor ALL and 103 with T-cell ALL. With a median follow-up time of 40.8 months, the median overall survival (OS) of the cohort has not yet been reached. There were 386, 389, and 346 BM samples available for MRD evaluation on day 14 of induction, at EOI, and post-C1, respectively. Figure 1A presents the distribution of MRD status over time. Figure 1B depicts the compositions of MRD levels at EOI stratified according to disease types. Notably, Ph-like ALL and early T-cell precursor (ETP) ALL were associated with extremely lower achievements of MRD negativity at EOI compared with other types. The 5-year OS rates of patients with MRD negativity, MRD-lp, MRD-hp, and MRD-vhp at EOI were 68.0% (95% CI: 60.2%-75.8%), 44.8% (95% CI: 28.9%-60.7%), 52.4% (95% CI: 34.2%-70.6%), and 36.7% (95% CI: 24.2%-49.2%), respectively ( P < 0.001) (Figure 2A). If patients were censored at the time of hematopoietic stem cell transplantation, the 5-year OS rates of these patients were 74.9% (95% CI: 65.1%-84.7%), 39.7% (95% CI: 18.7%-60.7%), 42.3% (95% CI: 11.7%-72.9%) and 0%, respectively ( P < 0.001) (Figure 2B). Patients with a negative MRD at EOI had a more favorable OS than those with a positive MRD at EOI. There was no statistically significant difference in terms of survival time between patients with MRD-lp and MRD-hp. Further, patients with MRD-vhp had the worst survival. The relapse probabilities had a similar pattern. Patients with MRD negativity at EOI had a lower 5-year CIR than those with MRD positivity at any levels. Compared to MRD-lp and MRD-hp patients, patients with MRD-vhp experienced a significantly higher rate of early relapse. However, with a longer follow-up, the 5-year cumulative incidence of relapse (CIR) did not differ significantly among patients with a positive MRD in any of the three groups, with a rate of 47.4%, 43.8%, and 49.1% in patients with MRD-lp, MRD-hp, and MRD-vhp, respectively (Figure 2C). Multivariate analysis showed that positive post-induction MRD was one of independent predictors of both OS and Disease-free survival. Conclusion Our study confirmed that MRD negativity at EOI is an independent prognostic factor of OS in adolescent and adult patients with Ph - ALL treated with pediatric-inspired regimen. Patients with MRD-lp and MRD-hp at EOI had a lower OS and a higher relapse incidence than those with MRD negativity. Therefore, an early and deep MRD clearance is important, and even extremely low MRD levels can predict poor prognosis.

Inotuzumab Use: A Single-Center Experience in B-Cell Acute Lymphoblastic Leukemia

Introduction: Inotuzumab Ozogamicin (InO) is a humanized anti-CD22 monoclonal antibody conjugated to calicheamicin, a cytotoxic antibiotic agent used in B-Acute Lymphoblastic Leukemia (B-ALL). The conjugate is internalized and produces DNA cleavage and subsequent apoptosis. InO has shown better results than conventional chemotherapy. Patients and methods: We present the results of a single-center experience with a small cohort of 13 patients diagnosed with ALL who received InO outside of clinical trials. Results: Of the 13 patients, 69% (9) were male. The median age was 38 years old (range 16-64). 10 patients younger than 55 years 9 patients had relapsed diseases, 3 refractory diseases and one patient was newly diagnosed. Regardless of relapsed disease, 7 patients used InO as a first line of salvage and 2 as a second line. In refractory disease, 1 patient used InO as the second salvage and 2 as third or more. White blood cells range from 1,500 to 285,000 mm3. Peripheral blood blast from 50-80%. Before InO administration, all the patients had bilirubin lower than 2 mg/DL (range 0.15-1.26 mg/dL), an ALT (alanine aminotransferase) medium value of 34 U/dl, and an AST (aspartate aminotransferase) medium value of 33 U/dL. The most common type of leukemia was CALLA in 8 patients: B-ALL Phi positive in 2, Lymphoid blast crisis in1, pre-B ALL 1, and t (8;22) 1 patient. 10 patients had CD-22 positivity in flow cytometry, and 3 had negative results. There was no relation between the intensity of CD 22 and the rate of response. 11 patients received InO as monotherapy, and 2 were associated with Mini-HyperCVAD-InO. 7 patients received 1 cycle and 6 patients received 2 cycles of InO; the average dose received was 2,7 mg/m2. 7 (53%) patients in complete response (CR) plus MDR (Minimal Residual disease) negative after treatment, 4 progressive diseases and 2 missing. Three patients received HCT (hematopoietic cell transplantation) post-InO, and two are waiting in complete remission. One patient relapsed while she was waiting for HCT and died. 4 patients received InO as a salvage after relapse post-HCT. All these patients had progressive diseases and died. In the patients that used InO as a bridge to HCT, the average time to transplant was 94 days. Regardless of Veno-Occlusive Disease (VOD), 1 patient developed it after InO treatment; no patients had VOD associated with HCT. Overall survival: 38 months; progression-free survival: 4.1 months. Mortality rate was 53% (7 patients). Causes were: 4 with progressive disease, 1 hemorrhagic stroke, 1 septic shock, and 1 suicide. Conclusion: We show our small local experience using this new drug in B-ALL patients. Patients who use InO as a bridge to HCT could have a good outcome. We had not found good results when InO was used in relapse post-HCT. There was no relation between the intensity of CD22 at flow cytometry and the rate of responses. The incidence of VOD was low. Rates of response are comparable to other real-world reports. This small experience could be the beginning of a multicenter Real-World study in Latin America.

The Different Impacts of an MRD-Guided Protocol on Relapse of Childhood Acute Lymphoblastic Leukemia: The Report of Taiwan Pediatric Oncology Group (TPOG)-ALL-2013

Taiwan Pediatric Oncology Group (TPOG)-ALL-2013 protocol (TPOG-2013), modifying from St. Jude Total Therapy XV Study and Total Therapy XVI Study, was launched since January 2013. This is the first nationwide minimal residual disease (MRD)-directed protocol for treatment of childhood acute lymphoblastic leukemia (ALL) in Taiwan. According to TPOG-2013, two MRD measurements were scheduled on days 15-19 of induction (MRD1 time point, TP1) and days 35-42, end of induction (MRD2 time point, TP2) to make the definitive risk stratification to guide subsequent therapy. As of April 30, 2023, 814 newly diagnosed ALLs treated with TPOG-2013 and followed up ≥3 years were enrolled in the study. The outcomes were compared with those of TPOG-ALL-2002 protocol (TPOG-2002) (N=1350, between January 2002 and December 2012), which did not integrate the MRD monitoring. The 5-year event-free survival and overall survival were significantly improved from 76% (95% CI, 74-78) and 81% (80-84) of TPOG-2002 to 86% (83-88) and 89% (87-92) of TPOG-2013, respectively ( P< 0.0001). For further analysis of TPOG-2013, 585 (72%) patients with exact adherence (EA) to both TPs were assigned as MRD EA group; 225 patients who were non-adherence (NA) to either one of TPs as MRD NA group; and four patients were excluded for the comparative outcome analysis. For B-cell precursor (BCP) ALL, the 5-year cumulative incidence of relapse (CIR) significantly decreased from TPOG-2002 (N=1194) to TPOG-2013 MRD EA (N=527) ( P <0.0001). However, there was no significant improvement of CIR between TPOG-2002 and MRD NA (N=202) ( P= 0.21) (Figure 1). In MRD EA of BCP-ALL, compared with TPOG-2002, patients with ETV6::RUNX1 or BCR::ABL1 appeared to have significantly lower CIR. Patients without the common genetic subtypes , denoted as “negative” group, also had significant inferior CIR. And the trend of CIR decrease did not attain significant difference in high hyperdiploidy. In contrast, patients with T CF3::PBX1 or infant with KMT2A-rearrangement did not show CIR improvement (Table 1). In T-ALL, compared with TPOG-2002 (N=156), there was a significant decrease of CIR in TPOG-2013 MRD EA (N=58)( P= 0.01)(Table 1), but not in MRD NA (N=23)( P= 0.86). There was a longer duration to relapse in MRD EA of BCP-ALL. However, a delay of relapse was only demonstrated in patients with BCR::ABL1, which could be addressed by the introduction of MRD-monitoring and TKI inhibitor in TPOG-2013 (Table 1). Further, in term of early relapse before 1.5 year of remission, there was no significant difference in MRD EA of BCP-ALL, compared with TPOG-2002. In conclusion, this study demonstrated diffident impacts on relapse according to genetic subtypes and MRD adherence. In the negative group of BCP-ALL without the discovery of novel genetic alternations, the relapse could be much decreased with the MRD-directed treatment protocol.

The Tetraspanin CD9 Shapes Glucocorticoid Sensitivity in Pediatric B-Precursor Acute Lymphoblastic Leukemia

Background: De novo or acquired resistance to glucocorticoids (GCs), the common therapeutic regimens for remission-induction in pediatric B-precursor acute lymphoblastic leukemia, confronts treatment success and is a strong predictor for disease relapse. Discovery of predictive markers and underlying mechanisms of GC resistance could lead to new treatment and prognostic modalities. Aims: This study aims: (1) to demonstrate the association between CD9 expression and GC sensitivity in childhood BCP-ALL; (2) to dissect the underlying mechanisms driving GC resistance; and (3) to discover the possible therapeutic modalities for restoring GC susceptibility. Methods: Ex vivo drug sensitivity profiling to prednisone (Pred) and dexamethasone (Dex) was performed on 6 BCP-ALL cell lines and 18 patient samples with differential CD9 expression. Association of CD9 expression with patient responses to Pred prophase was analyzed in a pediatric BCP-ALL cohort (n=182). Functional impact of CD9 on GC susceptibility was dissected by gain- and loss-of-function experiments in BCP-ALL cells. Mechanistic basis of CD9-driven GC response was investigated through genomics, transcriptomics, and proteomics. Reversal of GC resistance by pathway-targeted agents were explored on BCP-ALL cells and xenograft models. Results: Distinctive differences in the drug sensitivity pattern were found between CD9- and CD9+ BCP-ALL cell lines, with the former showing resistance to GCs but not other chemotherapeutic agents. Concurrently, CD9- primary lymphoblasts exhibited resistance to Dex (IC50s: 2,761 vs. 31 nM) and Pred (IC50s: 8,185 vs. 268 nM) compared with CD9+ samples (positivity defined by the presence of ≥ 20% CD9+ blasts). More Pred poor responders (defined by the presence of ≥ 1×10 9/L circulating lymphoblasts on day 8) were found in CD9- than CD9+ patients (19.4% vs. 6.2%, P=0.018). Subgroup analyses revealed more poor responders with CD9- phenotype were enriched in patients with older age (60% vs. 3.7%, P=0.008), male gender (21.7% vs. 6.7%, P=0.045), higher white blood cell count (66.7% vs. 15.4%, P=0.004), and in those with BCR-ABL1 translocation (100% vs. 12.5%, P=0.024), or not otherwise cytogenetically specified BCP-ALL (30.8% vs. 5.8%, P=0.019). Univariate and multivariate analyses further confirmed CD9 negativity as an independent predictor for GC resistance (OR=5.1, P=0.009). Overexpression of CD9 in CD9- cells (SEM, KOPN-8) by lentiviral transduction significantly enhanced GC sensitivity by 2.8-62.3-fold ( P<0.024), whereas CD9 knockout in CD9+ cells (697) using CRISPR-Cas9 decreased GC susceptibility ( P<0.003). No significant differences in mRNA or protein expression of the GC receptor NR3C1 were identified between CD9+ and CD9- cells, as well as its isoforms or mutants. The cytoplasm-to-nucleus translocation of GC receptor was consistent among cell lines regardless of CD9 expression status, but CD9 was physically interacted with NR3C1. Upon GC stimulation, the presence of CD9 increased the number of DEGs (110 vs. 82 DEGs) and magnitude of GC-responsive genes exclusively detected in the background of CD9 (1.3-18.6-fold; e.g. AKAP13, STAT5A, EZR). CD9- cells showed constitutive activation of the MAPK pathway and could be preferentially restored for GC susceptibility by the MEK1/2 inhibitor trametinib in vitro. BCP-ALL xenograft modeling revealed that, compared to single agent Dex treatment, combination with trametinib significantly reduced the leukemic load in animal transplanted with CD9- SEM but not CD9+ BV-173 cell lines. Ex vivo drug testing further showed that the resistance to GCs in some CD9+ cases could be partially reversed by combination of trametinib and the JAK inhibitor ruxolitinib due to the activation of STAT5. Conclusions: This study provides a definitive linkage of CD9 with GC sensitivity in childhood BCP-ALL mediated through a NR3C1-independent mechanism. CD9- cases could be prone to trametinib combination therapy, whereas CD9+ cases might need a third drug such as ruxolitinib to counteract GC resistance.

Identifying a core protein signature of small extracellular vesicles derived from B-cell precursor acute lymphoblastic leukaemia.

Acute paediatric leukaemia is diagnosed and monitored via bone marrow aspirate assessment of blasts as a measure of minimal residual disease. Liquid biopsies in the form of blood samples could greatly reduce the need for invasive bone marrow aspirations, but there are currently no blood markers that match the sensitivity of bone marrow diagnostics. Circulating extracellular vesicles (EVs) represent candidate biomarkers that may reflect the blast burden in bone marrow, and several studies have reported on the utility of EVs as biomarkers for adult haematological malignancies. Increased levels of EVs have been reported for several haematological malignancies, and we similarly report here elevated EV concentrations in plasma from paediatric BCP-ALL patients. Plasma EVs are very heterogeneous in terms of their cellular origin, thus identifying a cancer selective EV-marker is challenging. Here, we undertook a reductionistic approach to identify protein markers selectively associated to plasma EVs derived from BCP-ALL patients. The EV proteome of primary BCP-ALL cell-derived EVs were compared against EVs from healthy donor B cells and the BCP-ALL cell line REH, and further against EVs isolated from plasma of healthy paediatric donors and paediatric BCP-ALL patients. With this approach, we identified a signature of 6 proteins (CD317, CD38, IGF2BP1, PCNA, CSDE1, and GPR116) that were specifically identified in BCP-ALL derived EVs only and not in healthy control EVs, and that could be exploited as diagnostic biomarkers.

Glycosylation as regulator of human B-cell leukaemias in bone marrow

Leukemic B-cells are lodged in the bone marrow [BM], a complex organ composed of many cell types and extracellular matrix. Determining how the reciprocal interactions between these components are regulated is critical to our understanding of the factors that allow leukemia cells to survive, multiply and withstand treatment. All cells in the bone marrow are surrounded by a glycocalyx, a glycan-rich layer of high complexity, which regulates such cell-cell and cell-matrix interactions. However, the structure and function of the glycan components of the biomolecules that constitute this layer have not been explored in much detail. Gaps are difficult to fill due to technical limitations as well as the fact that the composition of the BM in health, disease and aging is not static. This also applies to B-lineage malignancies that develop or persist in BM such as B-cell precursor acute lymphoblastic leukemia and Multiple Myeloma, and the effects of their treatment. In contrast, the proteomes and transcriptomes of different human bone marrow cells have been studied more extensively. A combination of technologies now increasingly allows correlations to be made between the expression of glycosyltransferases and glycan structures in cell lines, which could be extrapolated to RNAseq data from primary cells. Glycopeptide analysis will also be invaluable in providing details of specific glycan occupancy on glycoproteins, even if only as a snapshot in time. Functional studies on CD19, CD138/SDC1 and BCMA/TNFRSF17 have already demonstrated the importance of their glycosylation. Additional studies using such approaches are likely to find many more other instances in which malignant B-cell homeostasis is regulated by glycosylation, and lead to the identification of new targets to treat B-cell malignancies.

Presence of leukemic clone-specific immunoglobulin heavy chain rearrangements in neonatal blood spots of children with B-cell precursor acute lymphoblastic leukemia.

Childhood B-cell precursor acute lymphoblastic leukemia (BCP-ALL) can be traced back to birth using leukemic clone-specific immunoglobulin heavy chain (IGH) rearrangements, implying prenatal origin of this disease. We retrospectively analyzed neonatal blood spots (Guthrie cards) of 24 patients with childhood BCP-ALL aged 1-9.6 years (median 3.1 years) for the presence of clonotypic IGH rearrangements identified in diagnostic bone marrow samples. Based on the sequences of IGH rearrangements, 2 patient-specific primers were designed for each patient and used in semi-nested polymerase chain reaction for the detection of preleukemic clones at birth. Clonotypic IGH rearrangements were detected in neonatal blood spots of 54.2% of patients (13/24). In two cases with double IGH rearrangements detected at diagnosis, only one rearrangement was present at birth, while in the third case both leukemic rearrangements were detected in neonatal blood. Guthrie card-positive findings were significantly more frequent in children ≤5 years of age than in older children (p = 0.011). Regarding patients' characteristics at birth and at diagnosis, Guthrie card-positivity was not associated with sex, birth weight and mother's age, as well as with white blood cell count, percentage of bone marrow blasts, immunophenotype and the presence of ETV6/RUNX1 and TCF3/PBX1 fusion genes at diagnosis. Our study confirms that a large proportion of childhood BCP-ALL originates in utero, regardless of the molecular subtype defined by chromosomal aberrations. The observed trend toward younger age at diagnosis in Guthrie card-positive versus Guthrie card-negative patients implies that the age at diagnosis depends on the presence of preleukemic clone at birth, as well as on the timing of postnatal transforming genetic events.

The Topoisomerase-I Inhibitor Gimatecan Exhibits Potent and Selective Activities Against B-Cell Precursor Acute Lymphoblastic Leukemia with a Favorable Cardiotoxicity Profile

Topoisomerase-II inhibitors such as daunorubicin have long been the standard chemotherapeutic agents for managing acute leukemias. Yet, severe complications could be resulted from their myelosuppressive and cardiotoxic nature. Here, we report preclinical evidence showing the exceptional activities of gimatecan, an orally available topoisomerase-I inhibitor currently being investigated in Phase II trials for solid cancers, on hematologic malignancies. Activity screening on leukemia cell lines revealed a substantially higher potency of gimatecan than frontline chemotherapeutics against B-cell precursor acute lymphoblastic leukemia (BCP-ALL) driven by on-target depletion of topoisomerase-I. Gimatecan had a median IC50 of 0.9 nM against BCP-ALL with profound selectivity over acute myeloid leukemia (AML, 3.6-fold, P< 0.01) or hematopoietic stem/progenitor cells (HSPCs, 75-fold, P< 0.001). In contrast, the four standard chemotherapeutics (cytarabine, daunorubicin, dexamethasone and vincristine) exhibited much higher median IC50s against BCP-ALL (18-2,201 nM). Following single-agent gimatecan treatment, complete dissolution of medullary and extramedullary leukemia (CNS and testis) by >95% inhibition concomitant with markedly extended survival (1.2 to 3.3-fold, P< 0.01) were demonstrated in animals grafted with cytogenetically distinct lymphoid leukemia cell lines (Reh, ETV6-RUNX1+; 697, TCF3-PBX1+; RS4;11, KMT2A-AFF1+; HAL-01, TCF3-HLF+) and in patient-derived xenografts from three cases of highly resistant BCP-ALL failing salvage chemotherapy or upfront immunotherapies. Splenocytes isolated from NSG mice relapsed from gimatecan treatment demonstrated recurrent drug sensitivity ex vivo comparing with vehicle controls and that gimatecan reinduction offered additional survival benefits in the xenograft model ( P< 0.05). The therapeutic efficacy was also observed at varied initial tumor load, together suggesting its potential for reinduction and flexibility on the administration schedule. In NSG mice reconstituted with cord blood HSPCs, gimatecan displayed a mild but transient suppression on normal hematopoiesis without bias on lineage output (63% reduction at 6 weeks, P=0.002; not statistically significant at 14 weeks). Importantly, gimatecan did not affect the viability of human iPSC-derived cardiomyocytes (hiPSC-CM) even at the highest tested dose (1,000 nM) as opposed to daunorubicin (IC50: 130 nM). Concordantly, no noticeable signs of DNA damage (by γ-H2AX staining) or apoptotic events (by enumeration of condensed nuclei) on hiPSC-CMs were observed after gimatecan exposure at doses at or above its Cmax (~130 nM). The gross structure of heart tissues harvested from gimatecan-treated mice was also intact without signs of cardiotoxicity at the dose effective to suppress leukemia (0.2 mg/kg). When compared with malignant B-lymphoblasts, there was a declined expression of topoisomerase-I in HSPCs (0.63-fold, P=0.025) and cardiomyocytes (0.24-fold, P<0.001), potentially explaining its selectivity against BCP-ALL. Mechanistically, gimatecan induced time- and dose-dependent cell death via intrinsic apoptosis coupled with G2/M cell cycle arrest. RNA-seq analysis of gimatecan-treated BCP-ALL cells showed activation of the tumor suppressive p53 pathway and suppression of the MYC pathway. Phosphorylation of p53 and appearance of DNA damage markers, including CHK1/2, PARP and H2AX, were robustly detected upon gimatecan treatment. In short, gimatecan possesses remarkable anti-leukemia activities and tolerable toxicity profiles compared to counterpart topoisomerase-II inhibitor. This study, therefore, puts forward a new agent for BCP-ALL and points towards randomized clinical trials to realize its potential on acute leukemias.

High-Hyperdiploid Acute Lymphoblastic Leukemia in Children with LZTR1 Germline Variants

Introduction Firstly described in 1967, hyperdiploidy (HD) is the most frequent genetic abnormality in B-cell- precursor acute lymphoblastic leukemia (BCP-ALL) in children, comprising about 25% of all cases. A not yet exactly defined proportion have predisposing pathogenic germline variants in DNA repair pathway genes, chromatin remodeling factors, transcription factors regulating B-cell development (particularly ETV6) or receptor tyrosine kinases pathway genes like RAS/RAF. Among the latter, mutations have mostly been described in PTPN11 and SOS1, but not yet in other components of this central regulatory hub of cellular communication. Germline loss-of-function (LOF) LZTR1 mutations are typically linked to hereditary nerve sheath tumors. However, it remains largely unknown, if other tumor entities are associated with LZTR1 LOF germline mutations, potentially broadening the spectrum of malignancies associated with RASopathies. Aim Our aim is to understand the frequency and the impact of LZTR1 germline variants in HD BCP-ALL of childhood. Material and Methods We analyzed WES data of 283 children with BCP-ALL for the presence of pathogenic variants in the LZTR1 cancer predisposition gene. For a part of the detected variants, we performed further functional analyses to investigate the effect of the alteration on protein function. We applied a Drosophila model that is particularly suited for functional evaluation of Ras pathway activity. Results We identified LZTR1 germline variants in 10/283 (3.5%) patients (Figure 1). Interestingly, in 6 out of 283 (2.1%) children the LZTR1 variants were classified as pathogenic/likely pathogenic (P/LP). The majority of patients (5/6) harboring a P/LP germline LZTR1 variant presented with a HD BCP-ALL. Only two of our patients showed concomitant phenotypic features indicative of an underlying syndromic condition. Patient P1 presented with a HD BCP-ALL at the age of 9 years and mild psychomotor delay. Sequencing revealed a likely pathogenic variant (p.Arg283Trp) that was not yet reported in association with RASopathy syndromes. The second child P8, also diagnosed with a HD BCP-ALL, carried a well-known autosomal dominant mutation described in Noonan syndrome (NS) variant (p.Gly248Arg). The child was characterized by facial dysmorphism, as well as mild developmental delay, although a diagnosis of NS was not established prior to development of the BCP-ALL. The other three patients had no clinical peculiarities other than HD BCP-ALL. We functionally characterized patient derived LZTR1 variants in dLztr1-depleted ISC. Like wild-type hLZTR1 wt, hLZTR1 p.Arg283Trp and hLZTR1 p.Lys761Arg restored control-like ISC lineage production, suggesting that hLZTR1 p.Arg283Trp and hLZTR1 p.Lys761Arg still regulate Ras ubiquitination. In contrast, hLZTR1 p.Tyr535Ter results in even 1.8-fold higher ISC lineage production than dLztr1-RNAi. Beyond ISC production as a readout, we employed a second experimental paradigm directly addressing Ras signalling activity with a translocating modified ERK sensor. In line with Ras activity control of LZTR1, hLZTR1 wt significantly reduced ERK activity, while the putatively LOF variant hLZTR1 p.Tyr535Ter variant significantly increased Ras pathway activation by 1.4-fold over controls. We also noticed that hLZTR1 p.Tyr535Ter induced extensive membrane blebbing and nuclear fragmentation of GFP positive cells likely indicating programmed cell death. Quantification of apoptotic cells revealed an 11.1-fold increase compared to controls, which was not observed for hLZTR1 p.Arg283Trp and hLZTR1 p.Lys761Arg. Most notably, forced expression of hLZTR1 p.Arg283Trp andhLZTR1 p.Tyr535Ter increased mitotic recombination by 4-fold and 3.4-fold, respectively, which was not observed for the hLZTR1 p. Lys761Arg variant. Conclusion In our cohort, approximately 2% of all children with BCP-ALL harboured a P/LP LZTR1 germline variation, not necessarily linked with clinical appearance of Noonan-syndrome-like features, but to the development of a high hyperdiploid karyotype. By applying a Drosophila model, we demonstrated that patient-derived LZTR1 germline variants affect RAS pathway activation, ERK accumulation, cell proliferation, DNA recombination and apoptosis. Figure 1: Depiction of the ten LZTR1 variants detected in an unselected pediatric cohort of 283 BCP-ALL patients

Pax5 Heterozygosity Affects B-Cell Differentiation and Generates a Deregulated Precursor Population in the Bone Marrow

Introduction: PAX5 is a well-known master regulator for B-cell development, commitment and identity. Hence, germline or somatic deregulation of PAX5 facilitates the development of B-cell precursor acute lymphoblastic leukemia (BCP-ALL). Previously, our group has described B-cell development abnormalities in three families carrying PAX5 germline variants ( Escudero et al., Leukemia, 2022) as well as established a link between Pax5 heterozygosity and infection exposure, thereby recapitulating the incomplete penetrance of the human BCP-ALL ( Martin-Lorenzo et al., Cancer Discovery, 2015). Nevertheless, the molecular single-cell characteristics of the susceptible precursor population mediated by reduced Pax5 levels is still poorly understood. Methods: Here, we deeply characterized the susceptible precursor population in Pax5+/- mice utilizing single-cell RNA Sequencing (scRNA-Seq), multicolor flow cytometry analyses and in-vivo transplantation models. Results: Our data show, that Pax5 heterozygosity leads to an aberrant pre-BII population (B220 +CD19 +IgM -CD25 +) in the bone marrow (BM) of Pax5+/- mice (p=0.0026, Student's t-test) (Fig. 1A). This population is stable over time and characterized by higher CD25 and IL-7-Receptor expression (p<0.0001, Student's t-test). Furthermore, bulk RNA-Sequencing of the pre-BII population revealed B-cell receptor (BCR) signaling as one of the top downregulated pathways (including CD79a/b, Lyn and CD72), while DNA replication and cell cycle signaling pathways were upregulated in Pax5+/- vs. Wildtype (WT) pre-BII cells. ScRNA-Seq analyses confirmed these results (Fig. 1B) and further showed that pre-BII cells of Pax5+/- mice are skewed toward the less commonly used lambda light chain BCR-rearrangements. The observed delay in the transition to IgM-positivity was additionally validated in a murine in-vivo transplantation model. Here, after 72 hours pre-BII cells from Pax5+/- mice preferably homed to the BM, while matured transplanted WT cells were predominantly found in the spleen (p=0.0023 and p=0.0140, respectively, Student's t-test). To depict the full spectrum of malignant transformation based on the described deregulated precursor B-cell population, we additionally performed scRNA-Seq on different stages of Pax5-mediated BCP-ALL evolution. Our data show that in a first step, arrested pre-leukemic cells of Pax5+/- mice lose their B-cell identity and display high Myc levels. Sequentially, full blown BCP-ALL arises in a second step after acquisition of additional oncogenic driver mutations (including Jak1 and Jak3). Interestingly, although the analyzed BCP-ALLs of Pax5+/- mice were all based on the same predisposition, they greatly varied in their transcriptional profile and cell-cycle state, depending on their oncogenic 2 nd hit. Conclusion: In summary, we deeply characterized how reduced Pax5 transcriptional activity in the BM generates a predisposed precursor B-cell environment, which is susceptibility for malignant transformation. These findings are important for understanding the molecular mechanisms to prevent or treat a significant proportion of childhood BCP-ALLs.

Accomplices in Cure: Blinatumomab + Dasatinib Reduces TCR Signaling and Effector Function Stronger Than Ponatinib and Ameliorates T-Cell Exhaustion

The tyrosine kinase inhibitors (TKIs) dasatinib (dasa) and ponatinib (pona) are being tested in clinical trials in philadelphia chromosome-positive (Ph +) B-cell precursor acute lymphoblastic leukemia (BCP-ALL) patients in combination with the CD19xCD3 bispecific blinatumomab (blina). Pona but not dasa is able to bind the BCR-ABL T315I mutation, which frequently occurs in BCP-ALL patients. Therefore, clinical studies are moving away from dasa and favor pona. Nevertheless, both TKIs in combination with blina have led to striking remission rates in Ph + BCP-ALL (complete response dasa: 98%, Foá 2020; pona: 92%, Jabbour 2023). Interestingly, increased lymphocyte frequencies were reported in patients under blina + dasa therapy (Puzzolo 2021), indicating that the effect of dasa is not limited to toxicity towards ALL cells conferred by BCR-ABL inhibition. Indeed, dasa modulates T-cell function by interfering with TCR signaling (Mestermann 2019). Also, we have shown that resting of T cells by high-dose dasa treatment ameliorates bispecific-induced T-cell exhaustion (Philipp 2022). In contrast, less is known about the effect of pona on T-cell function. Based on these data, we hypothesize that TKIs fine-tune TCR signaling, which ameliorates T-cell exhaustion during continuous blina infusion. Here, we systematically compared the influence of dasa and pona on blina-mediated TCR signaling and T-cell function. Inhibition of T-cell activation and function by dasa or pona at 0.3 - 100 nM was tested in vitro over 3 days: (1) CD69 expression, (2) blina-mediated killing as specific lysis of CD19 + tumor cells (3) T-cell expansion analyzed by dye dilution or CD2+ fold change (FC), (4) cytokine secretion measured by cytokine catch or cytometric bead array. Inhibition of TCR signaling was evaluated using a Jurkat-NFAT T-cell line stimulated for 6h with blina and CD19 + tumor cells. Phosphoflow of pAKT and pZAP70 was performed on CD3/CD28 activated primary human T cells. Toxicity of the TKIs against BCR-ABL +/- cell lines was evaluated after 3 days. T-cell exhaustion upon continuous blina + dasa stimulation was assessed in an in vitro long-term culture system for continuous bispecific exposure (Philipp 2022). Functional assays as described in (1)-(4) were performed every 7 days with isolated T cells from long-term cultures. Both TKIs inhibited T-cell function in a dose-dependent manner. Surprisingly, dasa was more potent than pona at low-intermediate doses in reducing T-cell function, shown by CD69 expression (mean % at TKI = 3 nM: basal = 70, dasa = 25, pona = 64, p<0.0001), cytotoxic function (mean % specific lysis at TKI = 12.5 nM: basal = 55, dasa = 0, pona = 54, p<0.0001), T-cell proliferation (mean % proliferated at TKI = 1.5 nM: basal = 62, dasa = 25, pona = 51, p<0.0001), as well as IFN secretion (normalized mean fluorescence intensity (MFI) at TKI = 12.5 nM: basal = 655, dasa = 0, pona = 924, p<0.0001). We also observed that NFAT engagement was significantly lower in dasa-treated Jurkat-NFAT cells (relative luminescence units at TKI 12.5 nM: basal = 1620, dasa = 392, pona = 996, p<0.001). Similarly, phosphoflow analyses revealed lower levels of pAKT and pZAP70 upon CD3/CD28 + dasa versus pona treatment (MFI of pAKT at TKI = 25 nM: basal = 2347, dasa = 1642, pona = 2045). Importantly, both TKIs induced cell death of BCR-ABL + but not BCR-ABL - cell lines at concentrations >3 nM. Interestingly, 14 days continuously stimulated T cells with blina + dasa (12.5 nM) did not lead to co-expression of inhibitory checkpoints (mean % of PD-1 +Tim-3 +LAG-3 + T cells on day 14: blina = 31, +dasa = 0.6, p<0.01). Furthermore, when isolated from long-term cultures and tested in functional assays, blina + dasa treated T cells maintained high cytokine secretion (mean IL-2 in pg/ml on day 14: blina = 730, blina + dasa = 5638, p<0.01), granzyme B expression (mean MFI ratio of CD8 + on day 14: blina = 96, blina + dasa = 335, p<0.01) and cytotoxic activity (mean % specific lysis on day 14: blina = 61, blina + dasa = 80). Together, these findings indicate that while both TKIs confer comparable toxicity to BCR-ABL + leukemia cells, dasa dampens TCR signaling and T-cell effector function more potently than pona. Strikingly, dasa can ameliorate T-cell exhaustion upon continuous blina exposure. Our data suggest that low-dose TKIs can fine-tune T-cell activity and might play a considerable role for the clinical success of combinatorial bispecific and TKI therapy in Ph + BCP-ALL.

Acquired Venetoclax Resistance in an In Vivo Model of B-Cell Precursor Acute Lymphoblastic Leukemia Is Characterized By Altered Functions of Apoptosis Regulators

Deregulation of cell death pathways such as apoptosis is a hallmark of cancer and contributes to leukemogenesis and treatment failure in B-cell precursor acute lymphoblastic leukemia (BCP-ALL). Apoptosis is controlled by different pro- and anti-apoptotic molecules either inducing or counteracting cell death signaling. Inhibition of anti-apoptotic molecules of BCL-2 family cell death inhibitors has been developed as therapeutic strategy. Venetoclax (VEN) binds selectively to BCL-2 resulting in apoptosis induction and has shown clinical activity in hematologic malignancies, but primary and secondary resistance have also been described. In this study, we aimed to identify resistance mechanisms acquired during VEN treatment leading to therapy failure of BCL-2 inhibition. In order to mimic a clinical situation with consecutive treatment cycles, we employed a patient-derived human BCP-ALL xenograft mouse model with subsequent courses of VEN administration to ALL bearing recipients in vivo. First, we estimated VEN-sensitivities in a series of BCP-ALL PDX samples (N=30) by ex vivo titration of individual VEN-EC 50 values and identified a range of heterogeneous VEN-activities. A VEN-sensitive (low VEN-EC50) PDX-ALL sample with a pro-B ALL phenotype carrying a KMT2A:: MLL1 gene fusion was selected and transplanted onto immunodeficient NOD/SCID recipient mice. Upon leukemia manifestation (presence of 5% human ALL cells in peripheral blood), mice were either treated with VEN (100 mg/kg, two times five days) or vehicle control. Recipients were sacrificed upon onset of leukemia-related morbidity and ALL cells isolated from spleens were transplanted onto secondary recipients, which were again treated with VEN or vehicle. ALL cells isolated from secondary recipients were retransferred onto tertiary mice and again exposed to in vivo VEN-treatment providing a total of three subsequent transplantation and in vivo VEN-therapy cycles. Assessing VEN sensitivities of the ALL cells initially transplanted and isolated after VEN-treatment cycles by using an ex vivo cytochrome c release assay showed increasing VEN-resistance. Accordingly, comparison of VEN to control in vivo treated cells showed significantly decreased sensitivities over treatment cycles. Importantly, also the time periods between treatment and leukemia re-occurrence in mice indicating decreasing VEN-sensitivity became shorter with every additional in vivo therapy course. Paired RNA- seq analysis revealed that transcript levels of the pro-apoptotic molecules BAX and BIM were significantly downregulated in VEN-exposed/resistant ALL as compared to vehicle control treated cells. Basal BH3 profiling analysis showed impaired apoptotic priming (significantly lower cytochrome c release after BIM and PUMA peptide exposure) and decreased dependence on anti-apoptotic BCL-2 and MCL-1 indicating a shift from a pro-apoptotic to a pro-survival state. This shift was also reflected in an e x vivo drug treatment assay showing decreased sensitivity to the MCL-1 inhibitor S63845 and the BCL-XL inhibitor A-1331852 in ALL cells from VEN- treated mice compared to control- treated mice (S63845 EC 50 1.5 vs. 2.2 µM, A-1331852 EC 50 9.3 vs. 15.3 µM). In line with the low BAX levels in ALL cells with acquired VEN-resistance, PDX BCP-ALL samples with intrinsic VEN resistance also showed lower BAX protein expression. Taken together, acquired VEN-resistance was recapitulated in a co-clinical trial model of BCP-ALL with repeated in vivo treatment cycles showing lower drug sensitivities along with increasingly reduced in vivo anti-ALL activity of VEN. Characterization of acquired VEN-resistance revealed decreased functional dependency on anti-apoptotic proteins and downregulation of pro-apoptotic BIM and BAX, thus pointing to an imbalance of pro- and anti-apoptotic molecules, which can be potentially targeted by directed compounds bypassing resistance to specific BCL-2 inhibition.