Transplantation Experiments Research Articles

Evidence for a selective link between cooperation and individual recognition

The ability to recognize others is a frequent assumption of models of the evolution of cooperation. At the same time, cooperative behavior has been proposed as a selective agent favoring the evolution of individual recognition abilities. Although theory predicts that recognition and cooperation may co-evolve, data linking recognition abilities and cooperative behavior with evidence of selection are elusive. Here, we provide evidence of a selective link between individual recognition and cooperation in the paper wasp Polistes fuscatus through a combination of clinal, common garden, and population genomics analyses. We identified latitudinal clines in both rates of cooperative nesting and color pattern diversity, consistent with a selective link between recognition and cooperation. In behavioral experiments, we replicated previous results demonstrating individual recognition in cooperative and phenotypically diverse P.fuscatus from New York. In contrast, wasps from a less cooperative and phenotypically uniform Louisiana population showed no evidence of individual recognition. In a common garden experiment, groups of wasps from northern populations formed more stable and individually biased associations, indicating that recognition facilitates group stability. The strength of recent positive selection on cognition-associated loci likely to mediate individual recognition is substantially greater in northern compared with southern P.fuscatus populations. Collectively, these data suggest that individual recognition and cooperative nesting behavior have co-evolved in P.fuscatus because recognition helps stabilize social groups. This work provides evidence of a specific cognitive phenotype under selection because of social interactions, supporting the idea that social behavior can be a key driver of cognitive evolution.

Assisted Migration of Sequoiadendron Genotypes for Conservation and Timber: Performance and Morphology in a Warmer Climate Outside of Their Range

Sequoiadendron giganteum (giant sequoia) has a fragmented distribution of 75 groves found along the western slope of the Sierra Nevada Mountains, California, USA. Outplanting and range expansion or assisted migration of this iconic species for the objectives of genetic conservation and timber production would be supported by information on growth and morphology to guide seed-collection decisions. We measured and assessed giant sequoia planted as seedlings and clonal stock originating from 22 groves in two common-garden experiments at Foresthill, California, north of the current species range, after 29 growing seasons. Traits examined were tree-size parameters, fluting and asymmetry of the lower stem, basal swelling, fullness of the live crown, epicormic sprouting, and heartwood decay resistance in cut stumps. Performance in terms of tree size after 29 years varied widely among genotypes with different grove origins. Morphology and decay resistance also exhibited some variation according to grove origins. The seedling stock outperformed the clonal stock of the same grove origins in terms of size and is therefore recommended when faster early growth is desired to outcompete other trees or for other management objectives. However, more fluting was exhibited by the larger fast-growing giant sequoia, while fewer seedlings had epicormic sprouts than the clonal stock of the same grove origins. At our warm low-elevation study site, giant sequoia from Mountain Home, Giant Forest, and Converse Basin consistently exhibited above-average growth among other giant sequoia in a pure planting and in an intimate mixture with five common conifer associates. Therefore, seed collected from these three groves should perform relatively well at other locations with a similar climate. When conservation of the species and its genetic diversity is the primary objective, we recommend collecting from a wide range of groves and undertaking assisted migration by planting at multiple locations inside and outside giant sequoia’s range as a hedge against the loss of native groves.

An in vitro comparison of intra-operative isohemagglutinin and human leukocyte antigen removal techniques in pediatric heart transplantation

Background: Highly sensitized pediatric patients awaiting heart transplantation experience longer wait times and thus higher waitlist mortality. Similarly, children less than 2 years of age have increased waitlist times and mortality when compared to their older peers. To improve the likelihood of successful transplantation in these patients, various strategies have been utilized, including peri-operative plasmapheresis. However, limited data exists comparing plasmapheresis techniques for antibody reduction. This study’s aim was to compare the in vitro magnitude of isohemagglutinin titers (IT) and human leukocyte antigen (HLA) antibody removal and the time required between membrane-based plasmapheresis (MP) and centrifuge-based plasmapheresis (CP) incorporated into the extracorporeal (EC) circuit. Methods: Two MP (Prismaflex) and two CP (Spectra Optia, Terumo BCT) circuits were incorporated into four separate EC circuits primed with high titer, highly sensitized type O donor whole blood. Assays were performed to determine baseline IT and anti-HLA antibodies and then at 30-minute increments until completion of the run (two plasma volume exchanges) at two hours. Results: There was a decrease in anti-A and anti-B IgM and IgG titers with both MP and CP. Mean anti-A and anti-B titer reduction was by 4.625 titers (93.7% change) and 4.375 titers (93.8% change) using MP and CP, respectively. At 2 h of apheresis, CP reduced 62.5% of all ITs to ≤ 1:4, while MP reduced 50% of ITs to ≤ 1:4. Additionally, reduction of anti-HLA class II antibody to mean fluorescence intensity (MFI) <3000 was achieved with both MP and CP. At 2 h of apheresis, CP reduced MFI by 2–3.5 fold and MP reduced MFI by 1.7–2.5 fold. Both demonstrated similar hemolytic and thrombotic profiles. Conclusions: In this in vitro plasmapheresis model of IT and anti-HLA antibody reduction, both MP and CP incorporated into the EC circuit can be used quickly and effectively to reduce circulating antibodies. While CP may have some greater efficiency, further study is necessary to verify this in vivo.

#380 : Clickbait in Uterine Transplant Surgery

Background and Aims: The proliferation of social media platforms has led to the emergence of diverse online communities, presenting unique challenges in terms of patient autonomy and quality of care within the field of uterine transplantation. This research delves into the psychosocial implications of social media communities throughout the uterine transplant patient journey. The absence of standardized guidelines in these virtual spaces presents a novel landscape for healthcare professionals to navigate. This study sheds light on the evolving nature of social media and its impact on the uterine transplant journey, emphasizing the need for healthcare providers to adapt to these unfamiliar territories. Moreover, social media communities introduce additional complexities by increasing the risk of undue influence and coercion on potential donors and transplant candidates. This study will highlight the importance of exploring these themes to ensure the integrity of the transplant process. This study aims to examine the social media discourse surrounding the experiences of both donors and recipients who have undergone uterine transplant surgery. Method: A qualitative research design was employed to observe and reflect on social media posts related to donor and recipient surgeries enrolled in our uterine transplant research study program. Thematic analysis was utilised to identify recurring themes and patterns within the data collected from both recipients and donors. Results: The analysis of social media posts revealed a range of experiences shared by donors and recipients undergoing uterine transplant surgery. Both recipients and donors often expressed mixed feelings associated with their unique transplant experience. Conclusion: Future research and guidelines are needed to navigate the evolving landscape of social media in the uterine transplantation field, safeguarding the well-being of all stakeholders.

Look at the future -perceptions of fertility counseling and decision-making among adolescents and their parents in the context of hematopoietic stem cell transplantation—experience of one major center for pediatric stem cell transplantation

IntroductionIncreasing survival rates after hematopoietic stem cell transplantation (HSCT) in childhood should put focus on improving the quality of life as adults. An essential aspect is fertility and its preservation. In order to take advantage of the possibility of fertility preservation, fertility counseling should be provided to patients and their parents prior to gonadotoxic therapies.MethodsThe aim of this survey was to analyze the impact of fertility counseling in pediatric stem cell transplantation in patients and their parents using questionnaires designed for the study questions. Fifty-one parents and 7 adolescent patients were interviewed between February 2019 and October 2021 about the counseling, their perceptions of fertility issues, and the nature of decision- making concerning fertility preservation. The study included patients with malignant (e.g., leukemia, lymphoma, neuroblastoma) and nonmalignant diseases (e.g., thalassemia, sickle cell disease, immunodeficiency) who received counseling on fertility preservation before HSCT based on an in-house standard and analysed the impact for both groups.ResultsTwo-thirds of the study participants were concerned about having children and grandchildren respectively; for half of all respondents, the topic of fertility and fertility preservation proved to be hopeful. Forty percent of the study participants were burdened by the risk of possible fertility limitations after HSCT. Concerns about fertility was particularly significant for parents whose children were advised to undergo fertility preservation. Parents of children <12 years found deciding on appropriate measures more difficult. Parents with children >7 years involved their children in the decision. All study participants agreed that fertility counseling had not negatively affected the parent-child relationship. More than 90% of all study participants were in favor of addressing fertility, its potential limitations and fertility preservation measures before HSCT. There was no significant difference between the malignant and the non-malignant cohort in all study questions.DiscussionOverall, the standardized fertility counseling provided in our center of pediatric stem cell transplantation resulted in high satisfaction among patients and their parents. Multiple counseling on infertility risk, including the younger patients in the decision-making and further options after gonadotoxic therapy may increase the satisfaction of the counseled patients and their parents.

Pathogenic Mechanisms of DDX41 Mutations in the Development of Myeloid Malignancies

DDX41 is a newly identified leukemia predisposition gene encoding an RNA helicase, whose germline mutations are tightly associated with late-onset myeloid malignancies. Importantly, germline DDX41 mutations were also found in as many as ~7 % of sporadic cases of high-risk MDS, conferring the largest germline risk for myeloid malignancies. In typical cases, a germline loss-of-function allele (most commonly p.A500fs or p.D140fs, depending on the ethnicity) is compounded by a somatic missense mutation affecting the helicase domain in the remaining allele (p.R525H). However, the molecular mechanism by which DDX41 mutations lead to myeloid neoplasms have not fully been elucidated. To clarify the role of these distinct DDX41 alleles, we generated mice models carrying either or both of conditional/constitutive Ddx41 knock-out (KO) and conditional R525H knock-in (KI) alleles. Vav1-Cre mediated homozygous deletion of Ddx41 resulted in embryonic lethality, suggesting that Ddx41 is indispensable for normal hematopoiesis. Next, by crossing these mice and further breeding with Rosa26-CreERT2 transgenic mice, we engineered mice that were wild-type for Ddx41 ( Ddx41 +/+), heterozygous Ddx41 KO( Ddx41 +/-), homozygous Ddx41 KO( Ddx41 -/-), heterozygous for the Ddx41 R525H mutation ( Ddx41 R525H/+), or hemizygous for the Ddx41 R525H mutation( Ddx41 R525H/-), in which expression of the mutant allele was induced by tamoxifen administration. First, we assessed cell intrinsic effects of these Ddx41 alleles, using noncompetitive transplantation experiments. Shortly after tamoxifen administration, most of the recipient mice that were transplanted with BM from Ddx41 -/- or Ddx41 R525H/- mice died within a month after CreERT2 induction due to severe BM failure (BMF), which was not observed in mice transplanted with BM from Ddx41 +/+, Ddx41 +/- or Ddx41 R525H/+ mice. By contrast, the mice transplanted with Ddx41 +/- or Ddx41 R525H/+ BM showed significantly reduced WBC counts and anemia in long-term observation in both primary and serial transplantations. Some of the Ddx41 +/- or Ddx41 R525H/+ BM-transplanted mice exhibited MDS-like phenotypes, showing ineffective hematopoiesis with evidence of erythroid dysplasia. Transcriptome analysis revealed that stem cells (Kit +Sca-1 -Lin low cells) derived from Ddx41 R525H/- BM-transplanted mice exhibited a significant upregulation of genes involved in innate immunity, including interferon stimulated genes, compared with stem cells derived from Ddx41 +/+ BM-transplanted mice. In addition, snoRNA and ribosomal genes were significantly deregulated in stem cells from Ddx41 -/- and Ddx41 R525H/- BM-transplanted mice, which could result in abnormal ribosome biogenesis and protein synthesis in Ddx41 mutant cells. We also assessed the reconstitution capacity of whole BM cells from different Ddx41 mutant mice in competitive transplantation experiments. The donor chimerism of Ddx41 -/- and Ddx41 R525H/- BM-transplanted mice in PB was markedly reduced compared to Ddx41 +/+ BM-transplanted mice. In contrast, Ddx41 +/- and Ddx41 R525H/+ BM-transplanted micedid not show significant changes in competitive bone marrow reconstitution compared to Ddx41 +/+ BM-transplanted mice. Given that the MDS clones bearing DDX41 R525H somatic alleles are typically observed as a small subclone in patients, we next co-transplanted Ddx41 +/+- and Ddx41 525H/--derived BM cells with Ddx41 +/+- or Ddx41 +/--derived BM cells at the ratio of 1:9. Recipient mice showed significantly reduced WBC counts when Ddx41 +/+- or Ddx41 +/- were co-transplanted with Ddx41 525H/- -derived BM, suggesting that Ddx41 525H/--derived hematopoietic cells have negative effect on normal hematopoiesis. In summary, compound biallelic loss-of function and R525 alleles led to severe BM failure. Monoallelic Ddx41 loss-of function and R525H knock-in alleles, by contrast, are compatible with hematopoiesis but associated with an impairment of hematopoiesis and the development of MDS with ageing, where activated innate immunity, impaired RNA metabolism and ribosome functions may play important roles.

NK-2 Homeobox Transcription Factor NKX2-3 Confers Differentiation Block in NPM1-Mutated in Acute Myeloid Leukaemia

Dysregulation of HOX homeobox family transcription factor (TF) gene expression is important in the pathogenesis of AML in particular in NPM1-mutated and MLL rearranged molecular subtypes. However, little is known about the role of NK2-homeobox (NKX2) family TF genes. NKX2 genes have critical roles in normal development of the central nervous system, thyroid, lung and pancreas. We observed high expression of NKX2-3 in patient AML samples and hypothesised the transcription factor might have a functional role in the disease. By qPCR, we found that NKX2-3 is highly expressed in normal HSCs but is rapidly down regulated as cells differentiate. In primary AML samples, it is highly expressed in 21-37% cases, including within the immunophenotypic LSC compartment, in particular in cases with NPM1 and/or FLT3-ITD mutations. Forced expression of NKX2-3 in normal murine KIT + bone marrow (BM) HSPCs transiently enhanced their clonogenic activity and impaired differentiation: NKX2-3-expressing HSPCs expressed higher levels of E2F or MYC target genes, and leukemia stem cell (LSC) maintenance genes. Congenic transplant experiments revealed that forced expression of NKX2-3 in normal BM HSPCs was sufficient to enhance multilineage engraftment across four months of follow up without inducing leukemia. In keeping with this, transplantation of Nkx2-3 -/- knockout BM cells led to significantly inferior engraftment compared with BM cells from litter mate control mice. Thus, while increased expression of Nkx2-3 enhances engraftment of normal stem cells in transplantation assays, loss of Nkx2-3 impairs it. Analysis of NKX2-3 high primary human AML cases demonstrated that HOXA9 was the most highly upregulated transcription factor gene compared with NKX2-3 low cases. We expressed both factors singly and together in murine KIT+ BM HSPCs: Hoxa9/NKX2-3 cells exhibited significantly higher clonogenic activity and reduced morphologic and immunophenotypic differentiation compared with Hoxa9/MTV cells. Congenic BM transplant experiments demonstrated that Hoxa9/NKX2-3 recipients developed leukemias significantly earlier than Hoxa9/MTV recipients (median 82 vs 155 days). BM morphology and immunophenotyping confirmed that Hoxa9/NKX2-3AMLs exhibited a greater degree of differentiation block than Hoxa9/MTV AMLs. Leukemia cells from Hoxa9/NKX2-3 recipients coordinately expressed higher levels of E2F or MYC target genes, and LSC maintenance genes. NKX2-3 KD to ~30% of control values reduced proliferation and induced morphologic and immunophenotypic differentiation in primary patient NPM1-mutated AML cells. NKX2-3 KD led to down regulation of E2F and MYC target genes and normal human CD34 + stem cell genes; and up regulation of myeloid differentiation genes. Using a CRISPR ribonucleofection approach to relocate NPM1c to the nucleus we confirmed that NKX2-3 expression in NPM1-mutant primary AML cells is sustained by mutant NPM1c. ChIPseq in NPM1-mutated primary patient and KO52 AML cells identified NKX2-3 binding peaks. As expected, DNA sequences under peak apices were strongly enriched for NKX2-3 binding motifs; there was also significant enrichment for RUNX and ETS family motifs, but not HOX/MEIS/PBX motifs. To identify genes potentially regulated by NKX2-3, genomic coordinates of strong binding peaks were mapped to the single nearest gene. Remarkably, among genes up regulated following NKX2-3 knockdown in primary human AML cells there was a highly significant enrichment of genes with putative regulatory elements bound by NKX2-3. Likewise, among genes down regulated in NKX2-3-expressing KIT+ murine HSPCs, there was a similar significant enrichment of genes with putative regulatory elements bound by NKX2-3. These data suggest that NKX2-3 functions as a transcription repressor at bound regulatory elements in primary AML cells. In summary, NKX2-3 is highly expressed in NPM1 & FLT3 mutated molecular subtypes of AML and serves to enhance self-renewal and the level of differentiation block through binding to and repressing regulatory elements of myeloid differentiation genes.

British Columbia Experience in Allogeneic Stem Cell Transplantation for Myelofibrosis with or without Pre-Transplant Ruxolitinib

Introduction Allogeneic stem cell transplantation (AlloHSCT) remains the only potentially curative treatment for myelofibrosis (MF). It confronts many challenges stemming from the older age of the typical patients and their age-related comorbidities, as well as disease-specific factors such as splenomegaly and hostile marrow microenvironment, which raise concerns for delayed engraftment and graft failure. Methods We performed a retrospective review of the 58 adult patients who received AlloHSCT for MF in British Columbia, Canada, in the 20-year period between January 2001 and December 2020. Data pertaining to patient demographics, disease characteristics, treatment/transplant details and clinical outcomes were gathered from the available paper and electronic records. Relapse-free survival (RFS) was defined as the time between the day of the transplant and the day of disease relapse or death from any cause. Overall survival (OS) was defined as the time between the day of the transplant and death from any cause. Patients who did not have an event during follow up were censored at the time of the last known follow up. Survival analysis was performed by Kaplan-Meier survival estimator and log-rank test, using Stata version 16.1 (Texas, USA). Results The median age of the cohort was 56 years (range 26-68), with 36% being 60 years old or older. The male to female ratio was 1.6:1. The median Karnofsky Performance Status index was 80 (range 70-100) and the median age-adjusted HCT-specific Comorbidity Index was 2 (range 0-5). The pre-transplant DIPPS plus risk category was: high in 13 patients (22%); intermediate-2 in 29 (50%); intermediate-1 in 15 (26%); and low in 1 (2%). 19/58 (33%) had a peripheral blast percentage greater than 2%. 51/58 (88%) had grade 3 fibrosis seen on the pre-AlloHSCT bone marrow biopsy. 27/57 (47%) patients were transfusion-dependent for pRBC and/or platelets. 28/54 (52%) evaluable patients had a normal karyotype and 6/54 (11%) a complex karyotype. Sixteen patients (28%) had a myeloid gene panel performed by PCR; the most commonly seen variants were ASXL1 (10 patients) and TET2 (5 patients). The median number of variants seen in a single patient was 3 (range 0-5). 42/58 (72%) patients received myeloablative conditioning before AlloHSCT. The donor type was: a volunteer unrelated donor in 54%; a matched sibling in 42%; and an alternative source (double cord or haploidentical donor) in 4%. Peripheral blood stem cells were used in 93% of the AlloHSCT. 24/58 (41%) patients received ruxolitinib pre-AlloHSCT (starting in June 2012) for a median duration of 10 months (range 1-44); 17/24 (71%) of the recipients had a clinical response to ruxolitinib but 3 had lost the response before their AlloHSCT. One patient had stopped ruxolitinib due to cytopenia. During a median follow up period of 41.7 months (range 0.5-260.7), 24/58 (41%) experienced acute graft-versus-host disease (GVHD) and 33/49 (67%) evaluable patients developed chronic GVHD. Graft failure was seen in 2 patients - one primary and the other secondary. MF relapse was seen in 13/58 (22%) after a median time of 1.1 years post-AlloHSCT (IQR 0.7-2.4). The transplant-related mortality (TRM) was 25% at 1 year and 28% at 3 years post-AlloHSCT. The most common causes of death were infection (7 patients), disease relapse (6 patients), and multiorgan failure (5 patients). Transfusion independence was achieved in 45/58 (78%) patients by day +100 and in 40/44 (90%) by 1-year post-AlloHSCT. 17/48 (35%) evaluable patients had persistent grade 3 fibrosis on their day+100 bone marrow biopsy. The estimated 1-year, 5-year and 10-year RFS rates were 66% (95% CI 52-76), 55% (95% CI 41-67) and 47% (95% CI 42-61) respectively. The estimated 1-year, 5-year and 10-year OS rates were 72% (95% CI 59-82), 63% (95% CI 49-74) and 54% (95% CI 37-68) respectively. There were no differences in RFS (p=0.40) and OS (p=0.23) between those who received ruxolitinib pre-transplant vs. those who did not. Conclusion In our cohort, approximately half the AlloHSCT recipients achieved long-term survival, many in remission (10-year OS 54%; 10-year RFS 47%). TRM was seen in 25% within the first year after AlloHSCT, with patients most commonly succumbing to infections. The graft failure rate was low at 3%. An increasing number of patients received pre-AlloHSCT ruxolitinib in the recent years but we were unable to demonstrate improved transplant outcomes with its use in this single centre cohort.

Allogeneic Hematopoietic Stem Cell Transplantation for Adult Metachromatic Leukodystrophy (MLD): A Case Series

Introduction Adult Metachromatic Leukodystrophy (MLD) is a rare neurological disorder leading to devastating and progressive cognitive impairment and motor impairment with ataxia, spasticity and neuropathy as well as incontinence resulting in complete disability and reduced life expectancy. MLD is caused by autosomal recessive mutations of the ARSA gene, resulting in reduced arylsulfatase A enzyme (ARSA) activity and consecutive accumulation of galactosylceramide-3-0-sulfate in the central nervous system (CNS). Potential therapies in infantile and juvenile MLD include allogeneic hematopoietic stem cell transplantation (allo-HCT), ex-vivo gene therapy (Atidarsagen autotemcel), and (intrathecal) enzyme replacement as tested in ongoing trials. Allo-HCT may slow down or stop MLD progression. However, the outcome in adult patients treated with allo-HCT has been only reported in a few case reports. In this case series, we report our experience of allogeneic transplantation in four patients with adult MLD. Methods Four patients (2 male and 2 female) with a genetically confirmed diagnosis of adult MLD, with enzyme deficiency detectable in peripheral blood (ARSA activity range 0.00-0.06 E514nm/10 -6), evidence of white matter lesions on MRI and demyelinating polyneuropathy in EMG were treated with allo-HCT. One patient was still clinically asymptomatic at the treatment timepoint. Allo-HCT was performed at an age between 18 and 37 years (mean 25.75 years) and within one year after diagnosis. Bone marrow (n=2) or mobilized peripheral blood stem cells (n=2) from 10/10 matched related (n=1) or unrelated (n=3) donors were infused at a dose of 2.2-7.82x10 6 CD34+/kg after a reduced intensity conditioning regime with Fludarabine (150 mg/m²) and Treosulfane (10 or 14 g/m²). Three patients received further infusions with allogeneic mesenchymal stem cells (MSCs) manufactured in the hospital´s own GMP laboratory around day 30 after transplantation. One patient received a second MSC infusion at day 182. MSCs are able to secrete ARSA and were used to consolidate enzyme levels. In case of transplant failure donor lymphocytes (DLI) were given. For posttransplant immunosuppression Tacrolimus, Methotrexate, Mycophenolate mofetil or Anti-thymocyte globulin (ATG, Grafalon®, Neovii 10 mg/kg) were used. Results All patients engrafted 16-21 days after HCT. Platelets regenerated within 14 to 21 days (mean 16 days), neutrophils recovered within 16 to 21 days (mean 18.5 days). In two patients hepatitis and exanthema associated with ATG administration were observed as transient adverse events. Other therapy-associated adverse events were innappetence, hyperkalemia and diarrhea. A mild Graft-versus-host disease of the skin occurred only in one patient with full resolution on a course of steroids and Tacrolimus. After allo-HCT, an increase in ARSA levels reaching normal range values within the first 12 months after treatment was already documented in 3 out of 4 patients; measurements are pending in the 4 th more recently transplanted patient. Three out of four patients developed consistent full donor chimerism within 11 (1-11 ) months after HCT. In the fourth 18-year-old patient autologous chimerism increased to 60-80%, while ARSA activity decreased from 1.05 to 0.61 E514nm/10 -6. Consequently, the patient received DLIs. However, an improvement in chimerism has not be achieved so far. Longer follow-up data will be reported at the meeting. Discussion and Conclusion Allo-HCT in patients with MLD can be used to restore normal range ARSA activity. Donor-derived macrophages with an adequate secretion of ARSA migrate to the central nervous system and release ARSA. To our knowledge, there have been only a few individual case reports on allo-HCT in adult MLD so far. Our case series indicates that allo-HCT can be performed with tolerable risks and evident efficacy in adult patients with MLD. Based on this experience and previously reported cohorts in juvenile and infantile MLD allo-HCT should be thus also considered as a therapeutic option for adult patients with MLD. Longer clinical follow-up, higher patient numbers and ultimately a prospective randomised trial containing an untreated group would be needed to evaluate allo-HCT as a treatment option for adult MLD.

Clinician and Administrator Perspectives on Chimeric Antigen Receptor (CAR) T-Cell Therapy Outpatient Administration in Relapsed or Refractory Multiple Myeloma (RRMM) in the United States (US): A Qualitative Study

Background: The use of CAR-T cell therapy has transformed treatment paradigms in B-cell malignancies. Ciltacabtagene autoleucel (cilta-cel) was approved for use in RRMM after four or more prior lines of therapy in 2022. While the pivotal studies exclusively treated patients in an inpatient setting, robust infrastructure planning at some centers across US has fostered outpatient administration of the commercially available product. Outpatient administration of CAR-T is more desirable due to superior financial sustainability, lower healthcare resource utilization, and greater patient autonomy during the treatment. Hence, we conducted a qualitative study to evaluate clinical and administrative perspectives and trends in outpatient administration of commercialized cilta-cel with an aim to understand best practices from certified CAR-T centers in the USA. Methods: A targeted literature review was conducted to better understand current practices around outpatient administration of CAR-T, and inform the development of primary research materials for designing subsequent interviews. Next, two 60-minute exploratory interviews were conducted with multi-stakeholder participants (n=5) from two certified cilta-cel centers, each with significant volume of outpatient administration of cilta-cel. Following the qualitative analysis of interviews, two 90-minute panels were conducted with multi-stakeholder participants (n=14) from six certified cilta-cel centers, including centers from exploratory interviews, focusing on clinical and administrative topics across the patient journey. Results: Each center in the study treated approximately 15-30 patients with cilta-cel in the outpatient setting. Using Likert scales, participants from all centers ranked space/capacity as the most important factor in decision-making process for outpatient cilta-cel administration, and ranked reimbursement incentives as a highly (67% of participants) or a moderately (33%) important factor. All participants agreed that having a dedicated outpatient infrastructure (dedicated space such as bed availability and internal processes including standard operating procedures (SOPs)), 24/7 support, outpatient bone marrow transplant (BMT) or cell therapy experience, and robust multidisciplinary teams were key to setting-up successful outpatient centers for cilta-cel therapy. The participants agreed that cilta-cel can be administered safely in an outpatient setting due to generally predictable, delayed onset of potential AEs, except in patients with significant comorbidities or organ dysfunction. Participants also considered caregiver support and lodging availability as factors of importance for outpatient administration. Institutionally established AE monitoring protocols are critical for safe use of cilta-cel in an outpatient setting. Over 50% of the centers interviewed have recently started to administer tocilizumab to treat mild grade 1 cytokine release syndrome (CRS) in an outpatient setting. Based on the findings across the phases of research, the patient journey for outpatient administration of cilta-cel was updated (Figure 1). While patients may be admitted for toxicity events, 100% of centers interviewed had 24-hour coverage and bed availability for these patients if needed. Conclusions: Overall, this study further supports the notion that centers can safely administer cilta-cel in an outpatient setting, if appropriate infrastructure is in place. Additional best practices for new outpatient sites include adequate infrastructure, SOPs, a well-trained and multidisciplinary team, and education of patients and caregivers (Table 1). Outpatient management and earlier intervention for low-grade AEs is currently evolving, with more real-world research required. Continued expert sharing of best practices can aid centers in implementing outpatient administration of CAR-T therapies. Funding: This analysis was supported by Janssen Research & Development, LLC and Legend Biotech USA, Inc

Efficacy of Treatment Options for Children with Steroid-Refractory Acute Gvhd

Background: Approximately half of patients with acute graft-versus-host disease (aGVHD) after allogeneic hematopoietic cell transplantation (alloHCT) experience steroid-refractory aGVHD (SR-aGVHD) disease. Patients with SR-aGVHD require intense and prolonged immunosuppression resulting in high risk of severe opportunistic infections and risk of relapse of malignancy which ultimately results in significant increase in short- and long-term morbidity and mortality, poor quality of life for children and their families and increases financial burden on families and health care system. Corticosteroids have been the mainstay of therapy for new onset acute GVHD. However, treatment for SR-GVHD in children is a serious unmet need. To date, few therapies have been investigated for SR-aGVHD in robust clinical trials for children. Moreover, long-term benefits and survival data from these trials are often lacking or unclear. A systematic literature review (SLR) was conducted to better understand the efficacy of therapies under investigation in this population. Methods: Literature database searches of Embase, MEDLINE, Cochrane, and Econlit, were performed on 22 May 2023 according to Cochrane guidelines to identify randomized and non-randomized clinical trials in which the pediatric population with SR-aGVHD represented at least 50% of the trial population. Clinical trials extensions and long-term follow-up reports were also included. Studies published in English from 2009 onwards were retrieved. Additional manual searches of relevant conference abstracts published in the past 3 years were performed. Results: Overall, 29 publications (23 unique studies) met the selection criteria, representing a total of 801 patients aged 18 years or younger with SR-aGVHD. A limited number of interventions were investigated in this population and most studies had a non-randomized design (19 out of 23 studies). Overall survival (OS) and response rates (ORR) were analyzed from studies enrolling more than 20 pediatric patients with SR-aGVHD (9 studies, Table), which investigated therapies such as mesenchymal stromal cells (MSC), remestemcel-L (MSC manufactured by Mesoblast), ruxolitinib, etanercept and extracorporeal photopheresis. At least 80% of patients treated with cellular therapies (remestemcel-L/MSC) and etanercept had grade III or IV disease. ORR on day 28 was 92% with etanercept, 77% to 91% with ruxolitinib, 61% to 92% with mesenchymal stromal cells, 61% to 70% with remestemcel-L, and 55% with extracorporeal photopheresis. Durable response rates of 69% at day 56 and 70% at day 100 and were noted for remestemcel-L and ruxolitinib, respectively. OS at 6 months was 69% with remestemcel-L, and 71% with mesenchymal stromal cells. OS at 1 year was reported for remestemcel-L (63%) and etanercept (59%). Long-term survival data beyond 1 year of patients enrolled in the clinical trial was available only for remestemcel-L and showed an OS rate of 51% at 2 years and 49% at 3 and 4 years. 4-year OS probability for patients with grade III or IV (48% in both cases) was similar to that for the overall population. Conclusions: Only a few small size clinical trials were conducted for children with SR-aGVHD which poses a unique challenge for FDA to approve new therapies for SR-aGVHD. Despite a small number (n=9: 5 ruxolitinib arm and 4 control arm) of children (12-18 years) enrolled in REACH II study, ruxolitinib was FDA approved for children>12 years of age. Long-term efficacy outcomes of children enrolled in clinical trials were reported only for remestemcel-L and showed that approximately half survived beyond 3 years. While other reports showed that grade III/IV disease is associated with poorer outcomes compared to grade I/II, similar survival rates were noted for patients with grade II, III and IV treated with remestemcel-L. In children with SR-aGVHD, other therapies such as ruxolitinib or etanercept demonstrated good response rates, however, the associated survival benefit is unclear.

Ferritinophagy Is a Druggable Vulnerability of Quiescent Leukemic Stem Cells

Acute myeloid leukemia (AML) poses significant challenges in terms of prognosis and treatment options. Leukemic stem cells (LSCs) contribute to therapy resistance, relapse and adverse outcomes. This study aimed to explore one of the major features of LSCs (e.g. quiescence) and its underlying molecular mechanisms, as well as identify potential targets for therapeutic intervention. Using in vivo cell labeling in patient-derived xenograft (PDX) assays, we identified a quiescent cell subpopulation with high LSC potential. Transcriptomics experiments conducted separately on quiescent and cycling cell subsets revealed gene signatures characteristic of quiescent (Q_AML_UP) and cycling cells (C_AML_UP). Using single-cell RNA sequencing, we identified clusters of quiescent leukemic cell that were highly enriched in gene signatures related to LSCs (Figure 1A). Through a machine learning approach, we identified a gene set highly specific of quiescent cells (named the QS35 gene signature) that emerged as a significant prognostic factor for poor outcomes in independent cohorts of AML patients (Figure 1B). Next, we aimed to identify new vulnerabilities of LSCs by investigating the quiescent subset of leukemic cells. Transcriptomics and proteomics approaches on quiescent vs cycling cells revealed enhanced autophagy within the quiescent subset. Additionally, the transferrin receptor TFRC and ferritin, two key regulators of iron metabolism, exhibited lower expression in the quiescent subpopulations. As intracellular iron availability is tightly regulated by ferritinophagy, a specific form of autophagy leading to the degradation of ferritin, we investigated the coordinated regulation of autophagy and iron metabolism in the quiescent LSC subset. Intriguingly, the intracellular iron pool was lower in quiescent LSCs, particularly in the CD34+CD38- compartment compared to more mature leukemic cells. Moreover, autophagy inhibition selectively induced cytotoxicity in the CD34+CD38- compartment and reduced the frequency of long-term culture-initiating cells (LTC-IC), and these effects were rescued by exogenous iron supply, underscoring the critical role of autophagy in iron bioavailability within the quiescent LSC subpopulation. To target ferritinophagy in this compartment, we depleted NCOA4, the main carrier in ferritinophagy responsible for delivering ferritin-bound iron to the autophagosome, using shRNAs in primary AML samples. Interestingly, NCOA4 was found more expressed in quiescent compared to cycling AML cells. In ex vivo assays, NCOA4 downregulation significantly reduced the frequency of LTC-IC and inhibited the clonogenic capacities of leukemic cells. Furthermore, NCOA4 invalidation abrogated leukemia initiation and self-renewal in serial transplantation experiments in vivo, particularly within the quiescent LSC population (Figure 2A). Additionally, treatment with a novel small molecule inhibitor named compound 9a that disrupts the NCOA4-ferritin interaction, depleted intracellular iron in primary AML cells, reduced their clonogenic potential and LTC-IC frequency ex vivo, and induced cell death specifically within the quiescent CD34+CD38- subset. Importantly, the viability of LSCs treated with compound 9a was rescued by the addition of iron, demonstrating that the cytotoxic effects of this compound were dependent on iron depletion. Notably, compound 9a exhibited minimal toxicity to normal hematopoietic cells ex vivo. In PDX models, in vivo short-term treatment with compound 9a decreased tumor burden and induced cell death within the CD34+CD38- LSC population (Figure 2B). Mechanistically, genetic of chemical inhibition of NCOA4 led to the accumulation of dysfunctional mitochondria, and to the generation of reactive oxygen species especially within the LSCs population. Furthermore, inhibition of NCOA4 by compound 9a decreased mitophagy, strongly suggesting that NCOA4 coordinates ferritinophagy and mitophagy pathways to increase intracellular iron, thereby specifically promoting the survival of LSCs. These findings highlight the critical vulnerability of quiescent LSCs to ferritinophagy. Thus, NCOA4 inhibition represents an innovative therapeutic approach for AML patients.

Using warming tolerances to predict understory plant responses to climate change.

Climate change is pushing species towards and potentially beyond their critical thermal limits. The extent to which species can cope with temperatures exceeding their critical thermal limits is still uncertain. To better assess species' responses to warming, we compute the warming tolerance (ΔTniche ) as a thermal vulnerability index, using species' upper thermal limits (the temperature at the warm limit of their distribution range) minus the local habitat temperature actually experienced at a given location. This metric is useful to predict how much more warming species can tolerate before negative impacts are expected to occur. Here we set up a cross-continental transplant experiment involving five regions distributed along a latitudinal gradient across Europe (43° N-61° N). Transplant sites were located in dense and open forests stands, and at forest edges and in interiors. We estimated the warming tolerance for 12 understory plant species common in European temperate forests. During 3 years, we examined the effects of the warming tolerance of each species across all transplanted locations on local plant performance, in terms of survival, height, ground cover, flowering probabilities and flower number. We found that the warming tolerance (ΔTniche ) of the 12 studied understory species was significantly different across Europe and varied by up to 8°C. In general, ΔTniche were smaller (less positive) towards the forest edge and in open stands. Plant performance (growth and reproduction) increased with increasing ΔTniche across all 12 species. Our study demonstrated that ΔTniche of understory plant species varied with macroclimatic differences among regions across Europe, as well as in response to forest microclimates, albeit to a lesser extent. Our findings support the hypothesis that plant performance across species decreases in terms of growth and reproduction as local temperature conditions reach or exceed the warm limit of the focal species.

Vascular Cell Adhesion Molecule-1 Regulates Bone Marrow Mesenchymal Stem Cell Maintenance and Niche Function

Bone marrow (BM) mesenchymal stem cells (MSCs) are rare non-hematopoietic perivascular stromal cells characterized by their unique ability to self-renew and differentiate into bone, cartilage, and fat, ensuring proper skeletal development and maintenance. Different subsets of BM MSCs associate with arteriolar and sinusoidal vessels to form specialized niches that regulate hematopoietic stem cell (HSC) function by secreting high levels of niche factors such as CXC-chemokine ligand 12 (CXCL12), stem cell factor (SCF), and Vascular Cell Adhesion Molecule-1 (VCAM1). VCAM1 is classically expressed on endothelial and stromal cells where it acts as an adhesion molecule that preferentially binds to α4β1 integrin on HSCs and progenitor cells (HSPCs). Deletion of Vcam1 in endothelial and hematopoietic cells induces HSPC mobilization into the peripheral blood without affecting endothelial cells homeostasis. Recent work from our lab further demonstrated that VCAM1 expression on HSCs and leukemic stem cells confers innate immune tolerance ( Nat Cell Biol 2022). While the contribution of HSC and endothelial-derived VCAM1 to homeostasis has been well studied, the role of MSC-derived VCAM1 on HSC and MSC maintenance and multilineage potency remains unknown. Our supporting data suggest that MSCs are the BM's main source of Vcam1 (p<0.0001) and that VCAM1 is critical for the maintenance, survival, and function of MSCs. Using a mouse model in which Vcam1 can be conditionally deleted in BM MSCs by a tamoxifen-inducible N-Cadherin-Cre ER line (referred to as Vcam1 N-CadCreER), we found that deletion of Vcam1 significantly reduces the number (4-fold, p=0.0030), frequency (4-fold, p=0.0042), and viability (2-fold, p=0.0039) of BM MSCs. Previous findings in breast cancer revealed that VCAM1 promotes PI3K/Akt survival signaling via Akt phosphorylation. Accordingly, Vcam1 deletion in N-Cadherin-Cre ER MSCs, demonstrated a significant reduction in phospho-Akt (Ser473) (p<0.05), supporting the role of VCAM1 in mediating PI3K/Akt survival signaling in MSCs. Intriguingly, the remaining viable VCAM1-null MSCs isolated from Vcam1 N-CadCreER mice exhibited reduced clonogenic potential (determined by CFU-F assays; 3-fold, p=0.0001). Furthermore, micro-CT analysis of 6-month-old Vcam1 N-CadCreER mice presented an altered bone phenotype compared to the control as evidenced by their significantly increased bone thickness and volume (p<0.05), yet significantly decreased tissue mineral density and medullary cavity area (p<0.05). Bulk RNA sequencing (RNAseq) of sorted viable MSCs revealed distinct grouping between Control and Vcam1 N-CadCreER MSCs. Gene ontology analysis demonstrated that deletion of Vcam1 caused an upregulation of pathways associated with inflammation and cytokine release while pathways associated with ossification, extracellular matrix organization, and skeletal development were all downregulated. Surprisingly, both bulk RNAseq and qPCR analysis confirmed a significant reduction in the expression of HSC niche factors ( Vcam1 Cxcl12 and Scf) following Vcam1 deletion, indicative of reduced niche activity. As expected, Vcam1 deletion in N-Cadherin-Cre ER MSCs, caused significant mobilization of HSCs into the blood (p<0.0001) and BM homing defects (p<0.05), however the number and repopulation capacity of BM HSCs remained unaltered, as seen by BM transplantation experiments. Surprisingly, imaging analysis of whole-mount bone marrow sternum of phenotypic HSCs revealed no differences in HSC niche localization between Vcam1-null and Control mice. Accordingly, ELISA analysis of BM extracellular fluid revealed no differences in overall CXCL12 and SCF levels suggesting that there may be some local or systemic niche compensation at play. Single-cell (sc)RNAseq of pooled BM and compact bone sorted non-hematopoietic stromal cells (DAPI -Lineage -CD45 -Ter119 -CD19 -CD71 -)from Vcam1 N-CadCreERand Control mice further confirmed the downregulation of HSC niche factors in MSCs, and overall remodeling of the BM stromal cell composition following Vcam1 deletion. Interestingly, our scRNAseq analysis revealed increased expression of Cxcl12 and Scf in specific vascular and stromal cell populations, supporting the notion of HSC niche compensation. Overall, these findings demonstrate that MSC-derived Vcam1 is critical for BM MSC survival and their HSC niche function.

Arid1b Loss Impairs Hematopoietic Stem Cell Function in Normal Hematopoiesis

Switch Sugar Non- Fermenting (SWI/SNF) nucleosome remodeling complexes are multi subunits complexes that utilize the energy from ATP to remodel chromatin, affecting cellular processes on chromatin including that of gene transcription. SWI/SNF complexes play important roles in normal development and differentiation as well as in oncogenesis. ARID1 proteins, ARID1A and ARID1B, are unique and mutually exclusive subunits of the canonical SWI/SNF complex BRG-1/BRM Associated Factor (BAF) complex. Arid1a is the most frequently mutated SWI/SNF subunit in cancers and plays a vital role in hematopoiesis. Arid1b is also frequently mutated in cancers, and its loss promotes Acute Myeloid Leukemia leukemogenesis. However, its role in normal hematopoiesis is not known. In this study we used hematopoietic specific Cre strains, VavCre and Mx1Cre, to delete Arid1b in a mouse genetic model to study its role in normal hematopoiesis. Analysis of steady state hematopoiesis in the VavCre model showed no significant differences in complete blood count (CBC) between Arid1b fl/flVavCre+ and VavCre+ mice. Further, bone marrow (BM) cellularity was not significantly different between control and experimental mice. Flow cytometry analysis of the percentage of mature myeloid, B cell, or T cell populations in the peripheral blood (PB), BM, or spleen (SPL) did not show significant differences between Arid1b fl/flVavCre+ and VavCre+ control mice. Further, we did not observe any significant differences in percentages of hematopoietic stem and progenitor cells (HSPCs), including HSCs, common myeloid progenitors (CMPs), granulocyte macrophage progenitors (GMPs), megakaryocyte/erythrocyte progenitors (MEPs), and common lymphoid progenitors (CLPs) in the BM of Arid1b fl/flVavCre+ mice versus VavCre+ controls. Analysis of Mx1Cre model showed similar results. Taken together, these results suggest that Arid1b is dispensable for steady state hematopoiesis. To assess the effect of loss Arid1b in a regenerative setting, we conducted non-competitive and competitive transplantation experiments in VavCre and Mx1Cre models. We transplanted BM cells from Arid1b fl/flCre+ or Cre+ mice (CD45.2) into lethally irradiated recipient CD45.1 mice with (CD45.1 at 1:1 ratio) or without competitor cells for competitive or non-competitive transplantations respectively. In Mx1Cre model, deletion of Arid1b was induced 4 weeks after transplantation. We monitored donor chimerism in PB over time as well as in the BM and SPL at end point. In both VavCre and Mx1Cre non-competitive transplants, we did not observe significant differences in CBC or donor chimerism in mature cells between Arid1b fl/flCre+ and control Cre+ mice in the PB over time. Further, no significant differences were observed between knockout and control mice in donor chimerism in mature cell populations in the BM or SPL, nor HSPC populations in the BM at end point (24-28 weeks). Deletion of Arid1b in the BM was confirmed. These results indicate that Arid1b loss does not affect regenerative potential of HSPCs in a non-competitive setting. In our competitive transplants, we observed significant decreases in PB donor chimerism for both myeloid and B cell populations over time in Arid1b fl/flVavCre+ compared to VavCre+ controls. Further, we observed significant decreases in donor chimerism of mature myeloid cells and B cells in the BM and SPL, as well as HSCs, CMPs, GMPs, and MEPs in the BM of Arid1b fl/flVavCre+ mice compared to VavCre+ controls at endpoint. However, there seemed to be incomplete penetrance as the observed phenotype varied in cohorts of different donor mice and was not significant in all cohorts. A similar phenotype was observed in the Mx1Cre model with the exception of a trend, albeit insignificant, towards a decrease in donor derived mature B cell populations in Arid1b fl/flMx1Cre+ compared to Mx1Cre+ mice in PB, SPL, and BM and no significant difference in HSCs in the BM at end point (20 weeks). Deletion of Arid1b in the BM was confirmed in both models. Overall, our results suggest that Arid1b deficient HSCs can regenerate the hematopoietic system but have defects in competitive transplantations with incomplete penetrance. Further work is needed to address the observed incomplete penetrance phenotype in competitive transplantations, and to understand the mechanism behind the requirement of Arid1b in normal hematopoiesis.

Mitochondrial tRNA Pseudouridylation Regulates Erythropoiesis Via the mTOR Signaling Pathway: Implications for Mlasa and Treatment Strategies

Pseudouridine, the most abundant RNA modification found in various RNA molecules, is crucial for cellular functions. Pseudouridylation is the process of converting uridine to pseudouridine, catalyzed by pseudouridine synthases (PUSs), and abnormal pseudouridylation has been linked to human diseases, including mitochondrial myopathy, lactic acidosis, and sideroblastic anemia syndrome (MLASA). MLASA is associated with genetic mutations in the PUS1 gene, leading to progressive exercise intolerance, sideroblastic anemia, hyperlactatemia, and muscle weakness. The underlying mechanism of anemia in MLASA remains unclear. In this study, we identified a novel homozygous frameshift deletion (c.523delC, p.P175fs*8) in the PUS1 gene in an MLASA patient with progressive anemia in our hospital. We investigated the role of pseudouridylation in erythropoiesis and its impact on MLASA using in vitro and in vivo approaches. We established an MLASA patient-derived inducible pluripotent stem cell (iPSC) line (referred to as MLASA-iPSCs) with the mutation, as well as a repaired line (MLASA-Res iPSC), and a corresponding mutant mouse model for the investigation. During erythroid differentiation, MLASA-iPSCs showed a significant decrease in the production of erythroblasts compared to the repaired line. Also, MLASA-iPSCs exhibited a lower ratio of mitochondrial membrane potential to mitochondrial mass, decreased oxygen consumption rates, reduced ATP production, and elevated levels of ROS. Attenuated activities of NADH dehydrogenase (Complex I) and cytochrome c reductase (Complex III) were also observed in MLASA-iPSCs, indicating compromised mitochondrial functions. Further analysis revealed a reduction in mitochondrial tRNA levels and abnormal mitochondrial translation in MLASA-iPSCs due to the specific loss of pseudouridylation. Screening of mitochondrial supplements, which could boost mitochondrial function or modulating protein synthesis, revealed that nicotinamide ribose (NR) and mitoquinone (MitoQ) improved mitochondrial function but failed to promote erythroid differentiation in MLASA-iPSCs. Interestingly, rapamycin, an mTOR inhibitor, improved erythroid differentiation in MLASA-iPSCs. Furthermore, MLASA-iPSCs showed activated mTOR signaling, increased protein synthesis and higher translation efficiency of mTOR1 targets, all of which could be rescued by rapamycin treatment, suggesting mTOR-associated translation stress. Consistently, the corresponding PUS1 mutant mouse model exhibited anemia with blocked erythropoiesis at four weeks of age. Serial competitive transplantation experiments revealed an intrinsic impairment in the reconstitution of red blood cells. Mutant erythroblasts showed impaired oxidative phosphorylation and aberrant activation of the mTOR signaling pathway. Rapamycin treatment partially alleviated the anemia phenotype in mice. Significantly, in the MLASA patient, sirolimus (rapamycin) administration under strict supervision and medical guidance effectively alleviated anemia symptoms and improved blood routine profile. In summary, our findings provide insights into the critical role of mitochondrial tRNA pseudouridylation in governing erythropoiesis via mTOR signaling pathway. We propose rapamycin as potential therapeutic strategies for anemia patients experiencing protein translation pressure, such as those with MLASA. #These authors contributed equally: Chu Y, Wang B, Shi D and Lian Y. Correspondence to: wpyuan@ihcams.ac.cn, shijun@ihcams.ac.cn Fig. 1 Schematic illustration of erythropoiesis regulated by PUS1-mediated pseudouridylation. Under physiological conditions (left), PUS1 regulates mt-tRNA abundance by catalyzing the pseudouridine synthesis of specific mt-tRNAs, thereby regulating mitochondrial translation, and ultimately affecting mitochondrial function and erythroid differentiation. In MLASA disease states (right), PUS1 deficiency causes the loss of pseudouridine modifications of specific tRNAs and thus affects the amount of PUS1 targeted tRNAs and its corresponding mitochondrial protein products, leading to mitochondrial dysfunction. The defects resulted in aberrant activation of the mTOR signaling pathway and accelerated global translation rate, ultimately leading to a blockage in erythroid differentiation, which could be relieved with rapamycin treatment.

JAK2V617F Activates IL-10R Signalling Potentially through Transactivation of JAK1

Classical myeloproliferative neoplasms (MPNs) arise from somatic mutations in haematopoietic stem cells (HSCs) that lead to unregulated proliferation of mature myeloid cells. The most common mutation associated with MPNs is JAK2 V617F, this causes constitutive JAK-STAT signalling leading to excessive production of mature myeloid cells. In humans, for MPN to arise, a JAK2 V617F HSC must have a selective advantage over WT HSC. However, in mouse MPN models Jak2 V617F HSCs do not display an overt selective advantage. This suggests that unique selective pressures may be present among those predisposed to acquire MPN that allow for the emergence of Jak2 V617F clones. We have identified defects in the IL-10R signalling pathway among MPN patients, with evidence that this defect is an intrinsic not acquired abnormality. In mice, we found that the blockade of IL-10R extends the cycling of WT but not Jak2 V617FHSC in response to inflammatory stimuli and hastens proliferation-induced WT HSC exhaustion. We hypothesized that IL-10R blockade may create an environment that affords Jak2 V617F HSC a selective advantage, indeed we found that IL-10R blocking antibody allowed Jak2 V617F cells to outcompete WT cells in mouse transplant experiments. From these mouse data, we hypothesized that Jak2 V617Fenhances IL-10R signalling. To test this hypothesis, we created Ba/F3 cell lines co-expressing IL-10Rα and Jak2 V617F. We found that Jak2 V617F enhances growth at limiting concentrations of IL-10. We also found that cytokine-independent IL-10Rα Jak2 V617F clones (but never IL-10Rα Jak2 WTor IL-10Rα cells) emerge at day 8-10 in culture after withdrawal of cytokines. We performed a limiting dilution assay to pinpoint the proportion of IL-10R Jak2 V617F cells capable of surviving IL-3 withdrawal. One in 126 IL-10Rα Jak2 V617F cells has transforming ability, whereas 1 in 1.4 MPL Jak2 V617F has transforming ability. Together, these data support our hypothesis that Jak2 V617F enhances IL-10R signalling and can activate IL-10Rα, however with weaker transformation potential compared to Jak2V617F's activation of MPL signalling. JAK2 canonically does not participate in the IL-10R pathway. It has been previously shown that JAK1 can transactivate JAK2 when JAK2 V617F cells are under the stress of persistent JAK2 inhibitor exposure, and this is the purported mechanism of JAK inhibitor resistance among MPN patients. We hypothesized that JAK2 V617F can transactivate JAK1, leading to the activation of IL-10R. The same transfected BaF3 cells aforementioned were serum starved for 4 hours and stimulated with mIL-10 for 15 minutes to induce signalling. By way of Western Blot analysis, cytokine-independent Jak2 V617F IL-10Rα Ba/F3 cells showed constitutive activation of phosphorylated JAK1 and JAK2 as well as STAT3 and STAT5, consistent with transactivation. Studies to demonstrate direct interactions between JAK2 V617F and JAK1 are currently ongoing.

CYP26 Activity Maintains the Bone Marrow Niche and Stem Cell Homeostasis

Vitamin A and its active compound, retinoic acid (RA), manifest pleomorphic activities in hematopoiesis. Vitamin A homeostasis is maintained systemically through hepatic CYP26. Emerging data suggests that CYP26 mediated RA metabolism also plays a role in controlling hematopoietic stem and progenitor cells (HSPCs) behavior (Ghiaur G et al. PNAS 2013, Schonberger K et al. Cell Stem Cell 2022). We generated Cyp26a1/ Cyp26b1 inducible knockout (CYP26KO) using ROSA26CreERT Cyp26a1/ Cyp26b1 conditional mice to study the impact on hematopoiesis and the bone marrow microenvironment (BME). Tamoxifen induces complete CYP26KO in these mice and subsequently higher retinoid levels and systemic inflammation (Snyder JM et al. FASEB J 2020). Here, we characterize the hematopoietic, bone and bone marrow (BM) phenotype of these mice. Compared to the CYP26 wild type controls (CTR), we observed leukocytosis and mild anemia as well as signs of extramedullary hematopoiesis in CYP26KO mice (Table). Spleen histology and flow cytometry showed an increased number of all mature elements, including megakaryocytes as well as increased absolute numbers of all hematopoietic progenitor populations (HPCs): LSK, CMP, GMP and MEP (Table). BM analysis showed decreased cellularity and myeloid biased in CYP26KO mice (Table). There was an increased frequency of colony forming unit cell (CFU-C) in the BM of CYP26KO mice but overall preserved absolute numbers when accounted for cellularity (Table). We observed increased frequency of LSK (Table) but decreased numbers of CMP, GMP and MEP in the BM of CYP26KO mice. Both CFU assay and flow cytometry showed myeloid biased HPCs found in the BM of CYP26KO mice (Table). When analyzing the stem cell compartment, short term stem cells and multipotent progenitor cells number were decreased in CYP26KO BM (p<0.01), but the long-term HSCs (LT-HSC) were relatively preserved (0.04 ± 0.01 vs. 0.17 ± 0.04 x10 6/femur, CTR vs CYP26KO, p<0.05). Both flow cytometry and CFU assay confirmed the presence of circulating HPCs in CYP26KO mice (Table). Thus, hematopoiesis of CYP26KO mice migrated away from the BM and into extramedullary tissues. The hematopoietic phenotype was most likely due to the cell extrinsic role of CYP26 since bone marrow transplantation experiments confirmed that a CYP26KO recipient (regardless of the genotype of the hematopoietic cells) and not CYP26 wild type recipient recapitulates the observed hematopoietic findings. This observation, together with necropsy findings of thin, frail bones in CYP26KO mice, prompted a closer look at the BM matrix/microenvironment of these mice. CYP26KO mice had smaller BM cavities, decreased trabecular bone and an increased fat/bone marrow volume ratio (Table). Consistent with these findings, CYP26KO mesenchymal stroma cells (MSC) had no osteoblastic differentiation potential in vitro but showed preserved adipogenic potential. The number of CFU-fibroblasts was decreased in the BM of CYP26KO mice but were found circulating in the PB and were dramatically increased in the spleen of these mice (Table). Single cell RNAseq showed quantitative and qualitative alterations in the BME populations with relative reduction of Cxcl12 abundant MSC2, which explained the qRT-PCR observation of lower levels of Cxcl12 mRNA in MSC isolated from CYP26KO mice. More so, Spp1 mRNA was downregulated in various MSC populations of CYP26KO bone marrow, consistent with their osteopenia and with potential implications for the observed HSPC phenotype. Receptor ligand analysis revealed that various components of the BME have impaired interactions with the extracellular matrix. Thus, the leading hypothesis is that absence of CYP26 leads to a dysregulated BME and to migration of a HSCs-niche unit out of the BM and into secondary hematopoietic organs. Interestingly, scRNAseq experiments uncovered upregulation of S100a8/9 in the CYP26KO neutrophil progenitors, which may be in response to systemic stress. The observed bone alterations (osteopenia and increased BM fat) coupled with noted changes in hematopoiesis (i.e. myeloid bias and inflammatory stress) may represent early signs of aging of the bone and bone marrow and suggest a central role of retinoid homeostasis in this process.

Distinct and Targetable Role of Calcium and Calcium Sensing Receptor in Leukaemia

Calcium, the most abundant mineral in the body, is a key component of bones and is released by bone remodelling. Calcium ions play a role in the localisation, engraftment and the adhesion of normal haematopoietic stem cells (HSC) to extracellular matrix (ECM) proteins in the bone marrow microenvironment (BMM) via the calcium sensing receptor (CaSR), thereby maintaining normal haematopoiesis. However, the role of this heterotrimeric G-protein-coupled receptor and its associated pathways in the local BMM for the development of leukaemia is poorly understood. We hypothesized that calcium ions, subject to a fine balance between osteoblasts and osteoclasts and released from bone, and/or CaSR contribute to development, progression and response to therapy in leukaemia and might be targetable via CaSR. By imaging of a genetically-encoded calcium indicator using intravital microscopy (IVM), we have shown that the local calcium concentration forms a gradient in the BMM with the highest concentrations close to the endosteal area. Furthermore, calcium levels differ between different leukaemias, with the calcium concentration of mice and human patients being highest in acute myeloid leukaemia (AML). Additionally, CaSR was expressed at a higher level on AML compared to chronic myeloid leukaemia (CML) cells. Using genetic deletion or overexpression or pharmacological inhibition of CaSR, we revealed that this receptor influences the localization of CML and AML cells in the BMM. Furthermore, we showed that the secondary messenger intracellular calcium (iCa 2+) can be regulated by CaSR in different leukaemia cell lines which have differential sensitivity to extracellular calcium (eCa 2+). Exposure of the human cell lines K562 (BCR-ABL1 +) and THP1 (MLL-AF9 +) to increasing calcium concentrations revealed that CaSR expression, migration and adhesion to the extracellular matrix (ECM) protein fibronectin were not altered in CML, but significantly increased in AML. Genetic deletion or overexpression of Casr in leukaemia-initiating cells in murine models revealed that CaSR acts as tumour suppressor in BCR-ABL1-driven CML and B-cell acute lymphoblastic leukaemia (B-ALL) and as oncogene in AML. Conversely, overexpression of CaSR in CaSR-deficient AML-initiating cells ‘rescued’ the disease. Limiting dilution transplantation of CaSR-deficient AML-initiating cells to assess leukaemic stem cell number and/or function revealed a 6.5-fold reduction of leukemic stem cells. Treatment of mice with the CaSR agonist cinacalcet and imatinib prolonged survival of mice with CML, while treatment with a CaSR antagonist NPS-2143 significantly reduced tumour burden and prolonged survival of mice with AML in syngeneic and xenogeneic transplantation experiments. In summary, our results suggest that calcium ions, likely originating from the BMM and/or CaSR strongly and differentially influence leukaemia localisation and progression. As an adjunct to existing treatment strategies, targeting of CaSR with specific pharmacologic agonists may be beneficial in CML and B-ALL, while CaSR antagonists may prolong survival of patients with AML.

Hematopoietic Stem Cells Expressing Engineered CD45 Enable a Near Universal Targeted Therapy for Hematologic Diseases

Allogeneic hematopoietic cell transplantation (HCT) is the only curative treatment for a broad range of hematological malignancies. Unfortunately, the current standard of care relies on untargeted toxic conditioning regimens associated with severe morbidity and mortality curtailing HCT's wider use. In the last decade, antigen-specific cell depleting therapies have revolutionized clinical practice in hematology. Although target selection remains complex, the pan-hematopoietic marker CD45, a protein tyrosine phosphatase which is exclusively expressed on all nucleated hematopoietic cells, could enable targeted depletion of the entire hematopoietic system including HSCs. Combined with HSCs engineered to be shielded from a CD45-targeting antibody-drug conjugate (ADC), this approach could create a near-universal strategy to replace a diseased hematopoietic system, irrespective of disease etiology or cell type. We performed alanine (Ala) scanning of the entire extracellular domain of CD45 to identify specific residues forming the epitopes for three different monoclonal antibodies (mAbs). Next, we screened base editors (BE) to generate amino acid substitutions that reduced or abolished the binding of specific mAbs, purified the first two extracellular regions of the most promising protein variants (CD45 D1-D2) and measured their binding to the mAbs by biolayer interferometry (BLI). Two antibodies showed drastically reduced or no binding to some of the CD45 variants. Some variants only reduced the binding of the mAb of the corresponding epitope while others affected the binding of mAbs from multiple epitopes located in more distant regions. These results suggested that several CD45 amino acid exchanges altered the receptor structure in a way that spanned at least two structural domains. This interpretation is supported by a substantial decrease in protein thermal stability, calling for caution when selecting suitable variants. Nevertheless, through a series of experiments and optimizations of the sgRNAs we identified a BE (ABE8e-SpRY + sgRNA49.3) that resulted in biophysically stable protein variants with editing of about 50% of hematopoietic stem and progenitor cells (HSPCs). These base edited HSPCs formed equal numbers of colonies as well as relative numbers of myeloid and erythroid colonies comparable to control HSPCs. Furthermore, they engrafted and supported multi-lineage cell differentiation in NBSGW host mice comparable to non-edited control HSPCs. Secondary transplantation experiments confirmed successful editing of long-term reconstituting HSCs (LT-HSCs). Collectively, these results indicate that the edited HSPCs were functionally intact. We further developed a humanized, Fc silent CD45-ADC designated CIM053-ADC. A single dose of 0.5mg/kg was very well tolerated by NBSGW mice engrafted with hCD34 + HSPCs and effectively depleted human hematopoietic cells including LT-HSCs. Next, we injected luciferase marked MOLM-14 cells, an aggressive myeloid tumor cell line, in mice priorly xenografted with edited or control human HSPCs. CIM053-ADC treatment was initiated 12 days after tumor injection when mice demonstrated clearly detectable, extensive and multilocular disease ( Fig. A). We deliberately assigned the mice with the most advanced disease to the ADC group. Mice then obtained saline or two doses of CIM053-ADC i.v.. Tumors were cleared in all CIM053-ADC treated mice whereas in all the mice that obtained saline the MOLM-14 cells rapidly grew and mice had to be euthanized 21-23 days post tumor injection ( Fig. B). Importantly, CIM053-ADC eliminated unedited hCD45 + non-tumor cells but base edited cells persisted in all tested organs. In summary, we developed a novel, highly potent tumor-selective therapy that spares a shielded hematopoietic system. Since CIM053-ADC targets the pan-hematopoietic marker CD45 this approach may not only be applicable to treat AML but most hematologic malignancies and possibly other diseases requiring HCT.