Sequential Bone Marrow Research Articles

Localized blastic plasmacytoid dendritic cell neoplasm associated with progressive clonal hematopoiesis and myelodysplastic syndrome.

Clonal hematopoiesis is highly prevalent in elderly patients with blastic plasmacytoid dendritic cell neoplasm (BPDCN), and around 20% of BPDCN patients have an associated myeloid malignancy. We present a patient with localized BPDCN and concomitant myelodysplastic syndrome (MDS), previously followed for several years due to clonal cytopenia of unknown significance. Compared targeted next-generation sequencing (NGS) of the skin tumor and sequential bone marrow samples showed shared variants in ASXL1 and TET2 with a de novo NRAS variant in both BPDCN and MDS compared to preceding bone marrow samples. These findings illustrate a shared clonal origin of BPDCN and MDS resulting from progressive clonal hematopoiesis.

Acute Promyelocytic Leukemia With Torque Teno Mini Virus::RARA Fusion: An Approach to Screening and Diagnosis

Acute promyelocytic leukemia (APL) with variant RARA translocation is linked to over 15 partner genes. Recent publications encompassing 6 cases have expanded the spectrum of RARA partners to torque teno mini virus (TTMV). This entity is likely underrecognized due to the lack of clinician and pathologist familiarity, inability to detect the fusion using routine testing modalities, and informatic challenges in its recognition within next-generation sequencing (NGS) data. We describe a clinicopathologic approach and provide the necessary tools to screen and diagnose APL with TTMV::RARA using existing clinical DNA- or RNA-based NGS assays, which led to the identification of 4 cases, all without other known cytogenetic/molecular drivers. One was identified prospectively and 3 retrospectively, including 2 from custom automated screening of multiple data sets (50,257 cases of hematopoietic malignancy, including 4809 acute myeloid leukemia/myeloid sarcoma/APL cases). Two cases presented as myeloid sarcoma, including 1 with multiple relapses after acute myeloid leukemia-type chemotherapy and hematopoietic stem cell transplant. Two cases presented as leukemia, had a poor response to induction chemotherapy, but achieved remission upon reinduction (including all-trans retinoic acid in 1 case) and subsequent hematopoietic stem cell transplant. Neoplastic cells demonstrated features of APL including frequent azurophilic granules and dim/absent CD34 and HLA-DR expression. RARA rearrangement was not detected by karyotype or fluorescent in situ hybridization. Custom analysis of NGS fusion panel data identified TTMV::RARA rearrangements and, in the prospectively identified case, facilitated monitoring in sequential bone marrow samples. APL with TTMV::RARA is a rare leukemia with a high rate of treatment failure in described cases. The diagnosis should be considered in leukemias with features of APL that lack detectable RARA fusions and other drivers, and may be confirmed by appropriate NGS tests with custom informatics. Incorporation of all-trans retinoic acid may have a role in treatment but requires accurate recognition of the fusion for appropriate classification as APL.

Early Detection of Molecular Residual Disease and Risk Stratification for Children with Acute Myeloid Leukemia via Circulating Tumor DNA.

Patient-tailored minimal residual disease (MRD) monitoring based on circulating tumor DNA (ctDNA) sequencing of leukemia-specific mutations enables early detection of relapse for pre-emptive treatment, but its utilization in pediatric acute myelogenous leukemia (AML) is scarce. Thus, we aim to examine the role of ctDNA as a prognostic biomarker in monitoring response to the treatment of pediatric AML. A prospective longitudinal study with 50 children with AML was launched, and sequential bone marrow (BM) and matched plasma samples were collected. The concordance of mutations by next-generation sequencing-based BM-DNA and ctDNA was evaluated. In addition, progression-free survival (PFS) and overall survival (OS) were estimated. In 195 sample pairs from 50 patients, the concordance of leukemia-specific mutations between ctDNA and BM-DNA was 92.8%. Patients with undetectable ctDNA were linked to improved OS and PFS versus detectable ctDNA in the last sampling (both P < 0.001). Patients who cleared their ctDNA post three cycles of treatment had similar PFS compared with persistently negative ctDNA (P = 0.728). In addition, patients with >3 log reduction but without clearance in ctDNA were associated with an improved PFS as were patients with ctDNA clearance (P = 0.564). Thus, ctDNA-based MRD monitoring appears to be a promising option to complement the overall assessment of pediatric patients with AML, wherein patients with continuous ctDNA negativity have the option for treatment de-escalation in subsequent therapy. Importantly, patients with >3 log reduction but without clearance in ctDNA may not require an aggressive treatment plan due to improved survival, but this needs further study to delineate.

Targeted NGS on sequential bone marrow biopsies aids in the evaluation of cytopenias and monocytosis and documents clonal evolution—a proof of principle study

Differential diagnosis of clonal versus reactive cytopenia and monocytosis, respectively, frequently presents a diagnostic challenge. With the two recent classifications of myeloid disorders, mutational analysis has gained importance as a diagnostic tool. However, reports on its utility on trephine bone marrow biopsies (BMB) are sparse. The aim of our proof of principle study was to determine the suitability of targeted sequencing for the longitudinal evaluation of cytopenia and monocytosis and demonstration of clonal evolution on sequential BMB. Seventy-seven EDTA-decalcified BMB of 33 patients with peripheral cytopenia and/or monocytosis, including at least one follow-up biopsy/patient, were included. Initial morphological diagnoses were idiopathic cytopenia of undetermined significance (ICUS, 8 cases), MDS (without blast increase, 7 cases), MDS with increased blasts/excess blasts (MDS-IB/EB) (11 cases), and CMML (7 cases). Thirty-one genes relevant for myeloid disorders were examined using two custom AmpliSeq NGS panels. Mutations were found in the initial BMB of 5/8 cases of ICUS, thus changing the diagnosis to clonal cytopenia of unknown significance (CCUS), 5/7 MDS, 10/11 MDS-IB/EB, and 7/7 CMML. Clonal evolution was observed in 14/33 (42%) cases, mostly associated with disease progression. None of the wild-type patients acquired mutations during follow-up. NGS-based mutation profiling is a robust diagnostic tool for BMB and provides valuable additional information, especially for cases with no/minimal dysplasia, and for better risk stratification of MDS. Tracking variant allele frequency and appearance of mutations over time allows for observing clonal evolution or relapse.

Abstract 3269: Reappraisal of immunologic mechanisms of hypomethylating agents in treatment of high-risk myelodysplastic syndrome and acute myeloid leukemia

Abstract Hypomethylating agents (HMA) have been used for the treatment of high-risk myelodysplastic syndrome (HR-MDS) and acute myeloid leukemia (AML) of the elderly. In addition to direct cytotoxic effect of HMA on MDS/AML, HMA upregulates effector T-cell function by demethylating T-cell exhaustion-associated genes (Hazem, Cell 2017) and promoting effector T-cells trafficking to tumor microenvironment by Th1-type chemokines reactivation (Peng, Nature 2019). To elucidate dynamic changes of immune cells profile and gene expression after HMA treatment in MDS/AML, we conducted single cell RNA sequencing of three sequential bone marrow (BM) samples from one HR-MDS patient treated with azacitidine. In BM samples at diagnosis (‘diagnosis’), after 2 cycles of azacitidine (BM blasts increased from 6 to 11%; ‘progression’), and after 3 additional cycles of azacitidine (BM blasts decreased to 3.5% with trilineage hematopoiesis; ‘response’), cell clusters were identified according to immune cell types. The relative proportion of the NK-cell cluster showed the most significant increase up to response (1.3% at ‘diagnosis’, 4.3% at ‘progression’, and 11.8% at ‘response’). By contrast, the CD8 T-cells cluster showed modest increase of proportion at the 3 timepoints (2.7%, 3.9%, and 7%, respectively). Differentially Expressed Gene (DEG) analysis showed CXCR4 was overexpressed in the BM NK-cell cluster at the ‘response’ time point. To determine whether the NK cells can be trafficked to BM by HMA treatment in mouse MDS/AML models, mouse myeloid leukemia cells (C1498 cells) were transplanted into the tail vein of 6-to-8-week aged syngeneic C57/BL6 mice. C1498 bearing mice were intraperitoneally treated with HMA (decitabine) or vehicle for 5 consecutive days. While HMA inhibited in vivo AML proliferation, the quantity of NK cells (NK1.1+) was significantly increased in BM of HMA-treated mice than vehicle controls. In addition, CXCR4 expression in NK1.1+ cells from BM of HMA-treated mice were significantly up-regulated, compared with vehicle controls. The NK depletion in HMA-treated AML mice decreased anti-leukemic effect, suggesting that NK cells may be one of immune cell subsets responsible for HMA induced anti-leukemia effect. Taken together, recruitment of NK cells into MDS/AML BM through CXCR4 overexpression and anti-leukemic cytotoxicity exerted by NK cells can be one of the important immunologic mechanisms of HMA in MDS/AML. Treatment strategy of recruiting more NK cells BM by HMA and maximizing cytotoxicity of NK cells should be further investigated. Citation Format: Junshik Hong, Suji Min, Jihyun Park, Carly M. Fielder, Qianni Hu, Sung-Soo Yoon, Tae Kon Kim. Reappraisal of immunologic mechanisms of hypomethylating agents in treatment of high-risk myelodysplastic syndrome and acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3269.

Graft Versus Leukaemia (GvL): Identification & Characterisation of Alloreactive Antigens and Cognate T Cell Responses in Acute Myeloid Leukemia

Allogeneic stem cell transplantation (allo-SCT) is the most established, curative T cell cancer immunotherapy. The curative effect of allo-SCT relies on a graft-versus-leukemia (GvL) effect; but this can be difficult to dissociate from graft-versus-host disease (GvHD). For decades, the key unsolved challenge has been to identify common alloreactive peptide-human leukocyte antigen (HLA) complexes targeted by T cells that mediate GvL but not GvHD. We developed a workflow for unbiased identification of alloreactive antigens and analysis of cognate donor alloreactive T cells and their T cell receptors (TCRs; Fig 1). We studied sequential bone marrow and peripheral blood samples, collected over 15 years, from 12 high-risk AML patients who remain in continuous complete remission following allo-SCT (all >2 years). All patients had relapsed at least once pre-allo-SCT and/or were AML flow cytometry minimal residual disease (MRD)+ pre-allo-SCT. 7 had received donor lymphocyte infusions. No patients developed >1 grade GvHD. We performed whole exome sequencing of DNA from isolated patient T cells (patient germline), AML blasts and donor DNA to identify: (i) AML-specific coding variants; and (ii) germline coding single nucleotide polymorphisms (SNPs), mismatched between patient and donor. 98.7% of the mismatched variants were germline. More variants were identified in unrelated compared with sibling donors (mean: 5744 vs 3253 variants). To narrow the list of variants taken forward for functional studies, we applied two sequential filtering steps: (i) we restricted analysis to variants expressed in the patients' AML cells (determined by RNA-Seq). 28.7% of all mismatched coding variants were expressed in AML cells; and (ii) we used in silico prediction of HLA-binding affinities of peptides spanning variant amino acids to patient-specific HLA-I and -II using NetMHCpan 4.0 and NetMHCIIpan 3.0. To functionally identify alloreactive antigens, we then screened ~200-900 peptides per patient-donor pair (total 5300 peptides) for recognition by T cells present in patient peripheral blood collected 2-7 years after allo-SCT. This enriches for the identification of long-lived anti-AML responses at a time when patients were both infection- and GvHD- free. Response screening, using IFNγ ELISPOT assays, identified T cell responses to 24 germline, mismatched epitopes. In all cases, responses were only observed when the amino acid encoded by the patient SNP, but not the donor allele, was present in the peptide. The phenotype of the epitope-specific T cells was established by intracellular cytokine staining (ICS) and flow cytometry analysis, and the HLA restriction of each T cell response was determined using HLA-I, -DR, -DP and -DQ blocking antibodies. Of the 24 alloreactive peptides,19 elicited CD4+ HLA class II restricted responses and 3 were targeted by CD8+ class I restricted T cells. Two remain to be characterised (Fig 2). The population allele frequency of the germline variant SNPs targeted varies from 0.5% to 72% in the Caucasian population. Likewise, some of the restricting HLA alleles are very common (e.g. a HLA-DP allele presenting 3 epitope peptides is present in ~66% of the Caucasian population). ICS showed that epitope-specific CD4+ T cells produce Th1 cytokines (IFNg, TNFa) and degranulate (express CD107a) in response to peptide stimulation (Fig 2). Next, we performed single cell 5'RNA-seq with TCR-seq of epitope-restricted T cells (isolated via IFN-g catch assay) for all CD4+ epitope-specific T cells. Alloreactive CD4+ T cells have cytokine-producing and cytotoxic effector potential, expressing MIP1a and b, IFNg, granzyme B and FasL (Fig 2). Finally, lentiviral-based gene transfer of one of the candidate alloreactive epitope-specific TCRs into third party primary T cells confers the capacity to generate IFNg and TNFa in response to peptide stimulation, and to recognise primary AML cell-derived antigen in the presence of monocyte-derived dendritic cells (Fig 2). In vitro and in vivo killing assays are in progress. The high proportion of CD4+ T Cell responses identified by our pipeline is concordant with downregulation of HLA II expression on AML blasts at relapse post-allo-SCT, which is a common mechanism of immune evasion, found in one-third of patients. Our approach dissects the biology of alloreactive anti-AML GvL and GvHD responses and to manipulate them for therapeutic purposes. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Characteristics of Germline CHEK2 Mutated Patients in a Large Cohort of 2322 Myeloid Malignancies

Background Checkpoint kinase 2 (CHEK2) is a critical mediator of the DNA damage response and plays a role in DNA double strand break-induced apoptosis and cell cycle arrest (Bartek, 2003). Deleterious germline CHEK2 variants (CHEK2germ) have been associated with an increased risk for breast, colon, prostate, thyroid and kidney cancers (Cybulski, 2004). Early studies suggested that germline CHEK2 variants also predispose to myeloid malignancies, including myelodysplastic syndromes (MDS) (Janiszewska, 2018). Recently, CHEK2 was identified as the most frequent germline mutated gene in a cohort of 391 adult patients with AML (Yang, 2022). However, more data is warranted to clarify the role of germline CHEK2 mutations in the development of myeloid malignancies. Here we analyzed the prevalence of germline CHEK2 variants in a large series of unselected patients diagnosed with myeloid malignancies and describe their clinical features. Methods Between February 2018 and June 2022, 2322 consecutive adult patients diagnosed at Saint-Louis hospital, Paris with a myeloid malignancy were included in the study. DNA obtained from bone marrow or peripheral blood cells was subjected to capture-based next-generation sequencing of genes recurrently mutated in myeloid malignancies, including CHEK2. In selected patients, germline mutation testing was performed using Sanger sequencing of DNA obtained from skin fibroblasts or sorted CD3-positive cells from peripheral blood. Results We identified a CHEK2 variant in 38 out of 2322 (1.6%) unrelated patients. We focused on the 24 patients with a variant allele frequency (VAF) equal or higher than 40%, highly suggestive of a germline origin, which was subsequently confirmed in all patients with available germline DNA. Of these, 16 variants (Fig1 A) were considered as pathogenic/likely pathogenic (P/LP) according to the American College of Medical Genetics as well as 3 missense variants which were semi-functional in an in-vivo, yeast-based, functional assay (Delimitsou, 2019). The 5 remaining variants were considered of unknown significance (VUS). Finally, 19 CHEK2germ variants were considered causal for the myeloid malignancy representing a frequency of 0.8% (19/2322). Noteworthy, two out of them (10.5%) had a second somatic hit in CHEK2. (Fig1 B) The median age of the 19 CHEK2germ patients was 75 years (42-87) at diagnosis of the hematological disease. According to the revised WHO classification, there were 7 (37%) MDS-MLD, 2 (11% ) MDS-RS, 4 (21%) MDS-EB, 3 (16%) MPN, 2 (11%) AML, and 1 (5%) ICUS. Karyotype was normal in 7 patients (39%), 8 patients had an isolated abnormality, 3 patients had a complex karyotype and one had cytogenetic failure. Additional driver mutations (Fig 1 B) were identified in most patients (18/19, 95%), however no particular association was noticed. Seven patients (37%) had a personal history of cancer (prostate n=4, breast n=1, thyroid n=1, colon n=1). Five patients (26%) had a family history of hematologic disorders (MPN, n=2, multiple myeloma n=2, ICUS n=1) and 7 patients (37%) of non-hematological cancer (breast n=2, brain n=2, lung n=1, ovary n=1, intestinal n=1). Eleven patients were classified as low-risk MDS according to the IPSS classification with a median survival of 5.6 years. They mainly received ESA (N=2) or lenalidomide (N=2). Among the 3 high-risk MDS patients 2 received hypomethylating agent with a survival of 5 and 1.7 years, the remaining one is still alive after sequential bone marrow transplant. One AML patient is still receiving hypomethylating agent with BCL2-inhibitor in complete remission with a follow up of 1.1 year, while the other AML patient died of relapse after 2 sequential bone marrow transplants. Regarding the 3 MPN patients, 1 is still alive after 1.3 year and the 2 others died 11.5 and 3.8 years after diagnosis. Conclusion This is the largest study addressing the frequency (0.8%) and characteristics of carriers of germline CHEK2 pathogenic variants within patients with myeloid disorders. Their presentation is rather heterogenous with a majority of low-risk MDS. They did not appear to have a more complex karyotype or a poorer prognosis and seems to be less frequent than previously suggested. Compared to more frequent genetic predisposition to myeloid malignancies like DDX41, CHEK2germ hematological malignancies did not seem to represent a specific entity, in line with recent debate on CHEK2germ solid cancer. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

In vivo generation of bone marrow from embryonic stem cells in interspecies chimeras.

Generation of bone marrow (BM) from embryonic stem cells (ESCs) promises to accelerate the development of future cell therapies for life-threatening disorders. However, such approach is limited by technical challenges to produce a mixture of functional BM progenitor cells able to replace all hematopoietic cell lineages. Herein, we used blastocyst complementation to simultaneously produce BM cell lineages from mouse ESCs in a rat. Based on fluorescence-activated cell sorting analysis and single-cell RNA sequencing, mouse ESCs differentiated into multiple hematopoietic and stromal cell types that were indistinguishable from normal mouse BM cells based on gene expression signatures and cell surface markers. Receptor-ligand interactions identified Cxcl12-Cxcr4, Lama2-Itga6, App-Itga6, Comp-Cd47, Col1a1-Cd44, and App-Il18rap as major signaling pathways between hematopoietic progenitors and stromal cells. Multiple hematopoietic progenitors, including hematopoietic stem cells (HSCs) in mouse-rat chimeras derived more efficiently from mouse ESCs, whereas chondrocytes predominantly derived from rat cells. In the dorsal aorta and fetal liver of mouse-rat chimeras, mouse HSCs emerged and expanded faster compared to endogenous rat cells. Sequential BM transplantation of ESC-derived cells from mouse-rat chimeras rescued lethally irradiated syngeneic mice and demonstrated long-term reconstitution potential of donor HSCs. Altogether, a fully functional BM was generated from mouse ESCs using rat embryos as 'bioreactors'.

PiggyBac Transposon-Mediated CD19 Chimeric Antigen Receptor-T Cells Derived From CD45RA-Positive Peripheral Blood Mononuclear Cells Possess Potent and Sustained Antileukemic Function.

The quality of chimeric antigen receptor (CAR)-T cell products, namely, memory and exhaustion markers, affects the long-term functionality of CAR-T cells. We previously reported that piggyBac (PB) transposon-mediated CD19 CAR-T cells exhibit a memory-rich phenotype that is characterized by the high proportion of CD45RA+/C-C chemokine receptor type 7 (CCR7)+ T-cell fraction. To further investigate the favorable phenotype of PB-CD19 CAR-T cells, we generated PB-CD19 CAR-T cells from CD45RA+ and CD45RA− peripheral blood mononuclear cells (PBMCs) (RA+ CAR and RA− CAR, respectively), and compared their phenotypes and antitumor activity. RA+ CAR-T cells showed better transient gene transfer efficiency 24 h after transduction and superior expansion capacity after 14 days of culture than those shown by RA− CAR-T cells. RA+ CAR-T cells exhibited dominant CD8 expression, decreased expression of the exhaustion marker programmed cell death protein-1 (PD-1) and T-cell senescence marker CD57, and enriched naïve/stem cell memory fraction, which are associated with the longevity of CAR-T cells. Transcriptome analysis showed that canonical exhaustion markers were downregulated in RA+ CAR-T, even after antigen stimulation. Although antigen stimulation could increase CAR expression, leading to tonic CAR signaling and exhaustion, the expression of CAR molecules on cell surface after antigen stimulation in RA+ CAR-T cells was controlled at a relatively lower level than that in RA− CAR-T cells. In the in vivo stress test, RA+ CAR-T cells achieved prolonged tumor control with expansion of CAR-T cells compared with RA− CAR-T cells. CAR-T cells were not detected in the control or RA− CAR-T cells but RA+ CAR-T cells were expanded even after 50 days of treatment, as confirmed by sequential bone marrow aspiration. Our results suggest that PB-mediated RA+ CAR-T cells exhibit a memory-rich phenotype and superior antitumor function, thus CD45RA+ PBMCs might be considered an efficient starting material for PB-CAR-T cell manufacturing. This novel approach will be beneficial for effective treatment of B cell malignancies.

Flow cytometry of bone marrow aspirates from neuroblastoma patients is a highly sensitive technique for quantification of low-level neuroblastoma

Background: Bone marrow involvement is an important aspect of determining staging of disease and treatment for childhood neuroblastoma. Current standard of care relies on microscopic examination of bone marrow trephine biopsies and aspirates respectively, to define involvement. Flow cytometric analysis of disaggregated tumour cells, when using a panel of neuroblastoma specific markers, allows for potentially less subjective determination of the presence of tumour cells. Methods: A retrospective review of sequential bone marrow trephine biopsies and aspirates, performed at Great Ormond Street Hospital, London, between the years 2015 and 2018, was performed to assess whether the addition of flow cytometric analysis to these standard of care methods provided concordant or additional information. Results: There was good concurrence between all three methods for negative results 216/302 (72%). Positive results had a concordance of 52/86 (61%), comparing samples positive by flow cytometry and positive by either or both cytology and histology. Of the remaining samples, 20/86 (23%) were positive by either or both cytology and histology, but negative by flow cytometry. Whereas 14/86 (16%) of samples were positive only by flow cytometry. Conclusions: Our review highlights the ongoing importance of expert cytological and histological assessment of bone marrow results. Flow cytometry is an objective, quantitative method to assess the level of bone marrow disease in aspirates. In this study, flow cytometry identified low-level residual disease that was not detected by cytology or histology. The clinical significance of this low-level disease warrants further investigation.

Flow cytometry of bone marrow aspirates from neuroblastoma patients is a highly sensitive technique for quantification of low-level neuroblastoma

Background: Bone marrow involvement is an important aspect of determining staging of disease and treatment for childhood neuroblastoma. Current standard of care relies on microscopic examination of bone marrow trephine biopsies and aspirates respectively, to define involvement. Flow cytometric analysis of disaggregated tumour cells, when using a panel of neuroblastoma specific markers, allows for potentially less subjective determination of the presence of tumour cells. Methods: A retrospective review of sequential bone marrow trephine biopsies and aspirates, performed at Great Ormond Street Hospital, London, between the years 2015 and 2018, was performed to assess whether the addition of flow cytometric analysis to these standard of care methods provided concordant or additional information. Results: There was good concurrence between all three methods for negative results 216/302 (72%). Positive results had a concordance of 52/86 (61%), comparing samples positive by flow cytometry and positive by either or both cytology and histology. Of the remaining samples, 20/86 (23%) were positive by either or both cytology and histology, but negative by flow cytometry. Whereas 14/86 (16%) of samples were positive only by flow cytometry. Conclusions: Our review highlights the ongoing importance of expert cytological and histological assessment of bone marrow results. Flow cytometry is an objective, quantitative method to assess the level of bone marrow disease in aspirates. In this study, flow cytometry identified low-level residual disease that was not detected by cytology or histology. The clinical significance of this low-level disease warrants further investigation.

Molecular Progression of Myeloproliferative and Myelodysplastic/Myeloproliferative Neoplasms: A Study on Sequential Bone Marrow Biopsies.

Simple SummaryMyeloid neoplasms (MN) are malignant hematopoietic stem cell disorders, which can progress into aggressive forms of blood cancer, likely due to the acquisition of additional genetic alterations. We investigated bone marrow biopsies of MN patients who underwent progression and compared them to a cohort with stable disease course. We identified certain mutations that promote an unfavorable outcome and found that patients with a known progress harbor more genetic alterations in their MN than those who do not deteriorate. Furthermore, we underpinned the hypothesis that not only the sum of genetic alterations but also the order in which they appear matters in disease evolution. Our findings emphasize the importance of genetic testing in MN patients in order to assess their risk of progression into aggressive blood cancer.Myeloproliferative neoplasms (MPN) and myelodysplastic/myeloproliferative neoplasms (MDS/MPN) both harbor the potential to undergo myelodysplastic progression or acceleration and can transform into blast-phase MPN or MDS/MPN, a form of secondary acute myeloid leukemia (AML). Although the initiating transforming events are yet to be determined, current concepts suggest a stepwise acquisition of (additional) somatic mutations—apart from the initial driver mutations—that trigger disease evolution. In this study we molecularly analyzed paired bone marrow samples of MPN and MDS/MPN patients with known progression and compared them to a control cohort of patients with stable disease course. Cases with progression displayed from the very beginning a higher number of mutations compared to stable ones, of which mutations in five (ASXL1, DNMT3A, NRAS, SRSF2 and TP53) strongly correlated with progression and/or transformation, even if only one of these genes was mutated, and this particularly applied to MPN. TET2 mutations were found to have a higher allelic frequency than the putative driver mutation in three progressing cases (“TET2-first”), whereas two stable cases displayed a TET2-positive subclone (“TET2-second”), supporting the hypothesis that not only the sum of mutations but also their order of appearance matters in the course of disease. Our data emphasize the importance of genetic testing in MPN and MDS/MPN patients in terms of risk stratification and identification of imminent disease progression.

Piggybac Transposon Mediated CD19 CAR-T Cells Derived from CD45RA-Positive PBMCs Possess Potent and Sustained Antileukemic Function

Background: The quality of chimeric antigen receptor (CAR)-T cell products, including the expression of memory and exhaustion markers, has been shown to influence their long-term functionality. We previously demonstrated that piggyBac (PB) transposon-mediated CD19 CAR-T cells exhibit memory-rich phenotype that is characterized by a high proportion of CD45RA+/CCR7+ T cell fraction. To further investigate the favorable phenotype of PB-CD19 CAR-T cells, we generated PB-CD19 CAR-T cells from CD45RA+ and CD45RA− peripheral blood mononuclear cells (PBMCs) (RA+ CAR and RA− CAR, respectively), and compared their phenotype and antitumor function.Methods: CD45RA+ and CD45RA− PBMCs were isolated by magnetic selection from whole PBMCs, then the CD19-CAR transgene was transduced into these cells using the PB transposon system, as described previously. Transduction efficiency of CD19 CAR transgene was determined 24 hours by flow cytometry after transduction. The phenotype of CD19 CAR-T was evaluated by flow cytometry on day 14. High throughput RNA sequencing was performed to see the T cell activation/exhaustion profile upon antigen stimulation. Sequential killing assays were performed by adding fresh tumor cells into CAR-T cells co-cultured with tumor cells every three days by restoring an effector target ratio of 1:1. To see the durable antitumor efficacy in vivo, we performed in vivo stress test, in which CAR T-cells dosage was lowered to the functional limits, so that these CAR-T cells should be maintained and expanded in vivo, to achieve the antitumor efficacy. We injected 5 x 10 5 of firefly luciferase-labeled CD19+ tumor cells (REH) into NSG mice via tail vein, then these mice were treated with 1 x 10 5 of CD19 RA+ CAR-T, RA− CAR-T, or control CAR-T cells, respectively, at day 6 after the tumor injection.Results: RA+ CAR T cells demonstrated better transient transduction efficiency 24 h after transduction (RA+ CAR-T: 77.5 ± 9.8% vs RA− CAR-T: 39.7 ± 3.8%), and superior expansion capacity after 14 days of culture than RA− CAR-T cells (RA+ CAR-T: 32.5 ± 9.3-fold vs RA− CAR-T: 11.1 ± 5.4-fold). RA+ CAR-T cells exhibited dominant CD8 expression (RA+ CAR-T: 84.0 ± 3.4% vs RA− CAR-T: 34.1 ± 10.6%), less expression of exhaustion marker PD-1 (RA+ CAR-T: 3.1 ± 2.5% vs RA− CAR-T: 19.2 ± 6.4%) and T cell senescence marker CD57 (RA+ CAR-T: 6.8 ± 3.6% vs RA− CAR-T: 20.2 ± 6.9%), and enrichment of naïve/stem cell memory fraction (CAR+/CD45RA+CCR7+ fraction; RA+ CAR-T: 71.9 ± 9.7% vs RA− CAR-T: 8.0 ± 5.3%), which were associated with longevity of CAR-T cells. Transcriptome analysis revealed that RA+ CAR-T cells exhibited the enrichment of naïve/memory phenotype and less expression of canonical exhaustion markers, and these exhaustion profiles even maintained after the antigen stimulation. RA+ CAR-T cells demonstrated sustained killing activity even after multiple tumor rechallenges in vitro, without inducing exhaustion marker expression of PD-1. Although antigen stimulation could increase CAR expression, leading to tonic CAR signaling and exhaustion, in our study, the expression of CAR molecule on the cell surface following antigen stimulation in RA+ CAR was controlled at a relatively lower level that in RA− CAR-T cells. RA+ CAR-T cells achieved prolonged tumor control with expansion of CAR-T cells than RA− CAR-T cells in in vivo stress test (Fig.1A-C). On day15, bone marrow studies in RA+ CAR group exhibited abundant human CD3 positive T cells with less expression of PD-1, and relatively smaller amount of REH cells than RA− CAR group (Fig.1D). Furthermore, in two of long-lived mice in RA+ CAR group, human CD3 positive T cells were expanded even day 50 after treatment as confirmed by sequential bone marrow studies (Fig.1E), which indicated the antigen-induced proliferation and long-term functionality of RA+ CAR-T cells in vivo.Conclusion: Our results suggest that PB-mediated RA+ CAR-T cells exhibit memory-rich phenotype and superior antitumor function, thereby indicating the usefulness of CD45RA+ PBMC as a starting material of PB-CAR-T cells. [Display omitted] DisclosuresYagyu: AGC Inc.: Research Funding. Nagao: AGC Inc.: Current Employment. Kubota: AGC Inc.: Current Employment. Shimizu: AGC Inc.: Current Employment. Nakazawa: AGC Inc.: Research Funding; Toshiba Corporation: Research Funding.

Flow cytometry of bone marrow aspirates from neuroblastoma patients is a highly sensitive technique for quantification of low-level neuroblastoma.

Background: Bone marrow involvement is an important aspect of determining staging of disease and treatment for childhood neuroblastoma. Current standard of care relies on microscopic examination of bone marrow trephine biopsies and aspirates respectively, to define involvement. Flow cytometric analysis of disaggregated tumour cells, when using a panel of neuroblastoma specific markers, allows for potentially less subjective determination of the presence of tumour cells. Methods: A retrospective review of sequential bone marrow trephine biopsies and aspirates, performed at Great Ormond Street Hospital, London, between the years 2015 and 2018, was performed to assess whether the addition of flow cytometric analysis to these standard of care methods provided concordant or additional information. Results: There was good concurrence between all three methods for negative results 216/302 (72%). Positive results had a concordance of 52/86 (61%), comparing samples positive by flow cytometry and positive by either or both cytology and histology. Of the remaining samples, 20/86 (23%) were positive by either or both cytology and histology, but negative by flow cytometry. Whereas 14/86 (16%) of samples were positive only by flow cytometry. Conclusions: Our review highlights the ongoing importance of expert cytological and histological assessment of bone marrow results. Flow cytometry is an objective, quantitative method to assess the level of bone marrow disease in aspirates. In this study, flow cytometry identified low-level residual disease that was not detected by cytology or histology. The clinical significance of this low-level disease warrants further investigation.

Precision Chemotherapy for Patients with Acute Myeloid Leukemia Using the πiChemo Prediction and Optimization Tool

Acute Myeloid Leukemia (AML) has poor treatment outcomes in older patients, due to poor performance status and biological heterogeneity of the disease derived from antecedent hematological disorders. Current treatments for AML take into consideration a small number of patient-specific and leukemia-specific parameters, with choice of chemotherapy regimen often dependent on the treating physician's experience. Patient-specific mutation profiling has now created the potential for personalized treatments, yet it is unclear how such treatments are best used. We have developed a novel dynamic mathematical model (πiChemo) that uses patient- and leukaemia-specific data to predict treatment outcomes, which could be used for precision optimization of drug selection, schedule and choice of treatment regimen for patients with AML.The πiChemo tool predicts normal and leukemic population dynamics in bone marrow (BM) of patients with AML, and consists of five population balance models (PBMs) for each population, normal and leukemic (L), describing cell cycle fractions in the following compartments: (1) long-term stems cells (LT-HSC and LT-LSC), (2) short-term stem cells (ST-HSC and ST-LSC), (3) multi-potent progenitors (MPP and L-MPP), (4) common myeloid progenitors (CMP and L-CMP) and, (5) common lymphoid progenitors (CLP and L-CLP). The model also predicts the absolute number of leukemic blasts, red blood cells (RBC), white blood cells (WBC) and neutrophils in peripheral blood (PB), critical in evaluating recovery from chemotherapy-induced hypoplasia. The PBMs determine number of cells in G1 and S phase of cell cycle, which are vulnerable to drug effect, as calculated by the pharmacokinetic and pharmacodynamic (PK/PD) module of the model which used treatment-specific parameters. The integrated PBM & PK/PD model, enables prediction of cell death due to drug and enumerates normal and leukemic cells in BM and PB over time. The PBMs have 3086 variables, 428 differential equations, 2609 algebraic equations and 49 parameters.The model development framework consists of 4 stages: (1) development of the high fidelity model, described above, (2) model analysis using global sensitivity analysis (GSA) to identify significant model parameters; (3) patient-specific parameter estimation of the significant model parameters identified by GSA to obtain the most accurate predictions of treatment outcome; (4) model validation whereby the model was implemented to predict treatment outcome.The model predicted normal and leukemic population dynamics in BM for 6 patients treated with low-dose Ara-C. Clinical and biological patient-specific features used in the model were: height (1.55-1.77 m), weight (49-74.6 Kg), age (71-80 years old), gender (2 males), cellularity factor (1=hypocellular, 2=normocellular and 3=hypercellular), and initial percentage of leukemic blasts (range 23-74%). Treatment-specific parameters were: dose (20 mg), administration route (subcutaneous bolus injection), treatment schedule (bid for 10 days) and number of cycles (2, 3 and 4). The model only required an initial BM sample (cell count and assessment of mutations), and daily PB cell count to monitor model-fit to ensure accurate predictions of treatment outcome. These patient datasets enabled predictions of the absolute number of normal and leukemic populations, and the leukemic blast percentage over time for the 6 patients as determined by BM restaging assessments; three patients achieved complete morphologic remission (after 4 cycles), one patient entered partial remission (after 3 cycles) and two patients relapsed (after 2 and 4 cycles), as per the documented patient outcomes.We have presented a novel tool for prediction of treatment outcomes for patients with AML undergoing chemotherapy. The innovative πiChemo platform is rendered patient- and leukaemia-specific by using BM and PB results and datasets usually acquired during AML diagnosis and treatment during routine clinical care. These datasets enabled model-monitoring and reduced the interval for model-fit testing compared with sequential BM sampling, increasing the PBM & PK/PD model accuracy for the design of a precision chemotherapy regimen. The πiChemo tool has the potential to personalize leukemia treatment in real-time, and could represent a step-change in the approach to the use of both standard chemotherapy and novel targeted treatments. DisclosuresNo relevant conflicts of interest to declare.

Immune Senescence and Exhaustion Correlate with Response to Flotetuzumab, an Investigational CD123×CD3 Bispecific Dart® Molecule, in Acute Myeloid Leukemia

Immune Senescence and Exhaustion Correlate with Response to Flotetuzumab, an Investigational CD123×CD3 Bispecific Dart® Molecule, in Acute Myeloid Leukemia

Investigating macrophage function as a mechanism of resistance to daratumumab in relapsed refractory multiple myeloma patients.

e20547 Background: Daratumumab (Dara), an anti-CD38 antibody, has a variety of Fc-dependent immune effector mechanisms of action including macrophage-mediated antibody-dependent cellular phagocytosis (ADCP). However, it remains unclear which mechanism, when disrupted, drives in vivo resistance. Given widespread use of this agent for treatment of multiple myeloma, identifying how to overcome Dara resistance has become an urgent clinical need. We hypothesized that inhibiting macrophage activity, via increased plasma cell surface expression of the CD47 “don’t eat me” signal, could be a mechanism of acquired Dara resistance. Methods: We retrospectively identified 11 patients with relapsed refractory multiple myeloma who progressed on Dara and had sequential bone marrow core biopsies before and after Dara with both samples containing &gt; 20% plasma cells. Nine patients had sufficient material for analysis. Core biopsy slides were stained and analyzed for expression of CD47 (H-scoring for total intensity on plasma cells, as well as annotation of membrane vs. cytosolic localization), CD68 (cell counts of macrophages), and CD4/CD8/FOXP3 triple stain (cell counts of CD4 and CD8 effector and regulatory T-cells). Results: Median age was 57 years. Median R-ISS stage was 2. Two patients had high-risk cytogenetics at diagnosis. Median time from diagnosis to progression on Dara was 56.3 months (95% CI 37.43 – 88.92). Median overall survival was 69.5 months (95% CI: 46.5 – 97.1). Plasma cells in all samples expressed CD47 (H-score median = 96, range 43 - 290). However, in contrast to our hypothesis, there was no significant change in CD47 H-score at progression on Dara (H-score median = 100, range 29 – 140). Furthermore, we observed no significant change in CD68+ macrophage counts nor CD68+ localization at Dara progression. We did note a trend toward CD47 expression shifting from membrane to cytosol at Dara resistance ( p = 0.14). Consistent with prior studies, in our cohort we observed no influx in Tregs but a markedly increased CD8/CD4 ratio at resistance ( p = 0.01). Conclusions: In vitro and murine studies have proposed ADCP as an important mechanism of Dara efficacy. However, we did not observe signatures of resistance in patients being driven by this pathway. Our work suggests that anti-CD47 therapy, leading to activation of macrophages to eliminate tumor cells, will potentially be efficacious for both the Dara-naïve and Dara-refractory settings.

Mass Spectrometry–Based Method Targeting Ig Variable Regions for Assessment of Minimal Residual Disease in Multiple Myeloma

Multiple myeloma is a systemic malignancy of monoclonal plasma cells that accounts for 10% of hematologic cancers. With development of highly effective therapies for multiple myeloma, minimal residual disease (MRD) assessment has emerged as an important end point for management decisions. Currently, serologic assays lack the sensitivity for MRD assessment, and invasive bone marrow sampling with flow cytometry or molecular methods has emerged as the gold standard. We report a sensitive and robust targeted mass spectrometry proteomics method to detect MRD in serum, without the need of invasive, sequential bone marrow aspirates. The method detects Ig-derived clonotypic tryptic peptides predicted by sequencing the clonal plasma cell Ig genes. A heavy isotope-labeled Ig internal standard is added to patient serum at a known concentration, the Ig is enriched in a light chain type specific manner, and proteins are digested and analyzed by targeted mass spectrometry. Peptides from the constant regions of the λ or κ light chains, Ig heavy chains, and clonotypic peptides unique to thepatient monoclonal Igs are targeted. This technique is highly sensitive and specific for the patient-specific monoclonal Igs, even in samples negative by multiparametric flow cytometry. Our method can accurately and precisely detect monoclonal protein in serum of patients treated for myeloma and has broad implications for management of hematologic patients.

Monocytic Myeloid-Derived Suppress Cells Restore Adipogenic Bone Marrow Microenvironment in Aplastic Anemia By Inhibiting Intra-BM CD8+ T Cells Proliferation

Aplastic anemia (AA) is a hematopoietic disorder resulted from immune-related hypocellular hematopoiesis in bone marrow (BM). It has been clearly addressed that the activated T cells contribute to the exhaustion of hematopoietic progenitors and hypo-hematopoiesis. The adipogenic BM is one of the characteristics to make AA diagnosis. However, little is known about the relationship of intra-BM immune imbalance and hematopoietic microenvironment abnormity in this disease entity. Functional hematopoiesis relies on not only abundant hematopoietic stem cells (HSCs) but also the balanced supportive hematopoietic niche. Intra-BM immune balance, at either cellular or cytokine level, is one of the key footstones to maintain hematopoietic microenvironment. Various intra-BM immune cellular components play both sides of one coin. Among them, myeloid-derived suppressive cells (MDSCs) are heterogeneous myeloid progenitor cells characterized by the negative immune response in cancers and other inflammatory diseases. In BM aspiration and biopsy samples from the patients who were diagnosed as AA in our study, massive activated lymphocytes infiltration and adipocytes accumulation were observed. Interestingly, the absolute numbers of immune modulatory MDSCs either in AA patients' PB or in BM of immune-related AA mice were reduced, indicating a potential link between polarized BM adipo-osteogenic microenvironment and immune disorder under AA circumstance. We thus adopted AA mice model to look into the embedded details both in vivo and in vitro. We clarified that BM components were more vulnerable to the attack of CD8+ T cells than that of CD4+ T cells. Taking into the fact that BM adipocytes are more abundant either in AA patients or in AA mice models, we differentiated mesenchymal stromal cells (MSCs), the major BM stroma cells, into osteoblastic or adipogenic lineages to mimic the osteo-adipogenic differentiation in BM microenvironment. Interestingly, CD8+ T cells and interferon-γ(IFN-γ) exerted dramatically adipocytic stimulation on BM-MSCs either in vitro or in vivo, by determination of increasing expression of adipogenetic genes including Ap2, Perilipin, Pparg and Cebpα, as well as staining of Oil Red O and perilipin. To dissect intra-BM cellular immune balance, MDSCs were isolated as representative immune regulating population to investigate their function on osteo-adipogenic balance. Interestingly, not CD11b+Ly6G+Ly6C-granulocytic-MDSCs (gMDSCs) but CD11b+Ly6G-Ly6C+monocytic-MDSCs (mMDSCs) inhibited both T cell proliferation and IFN-γ production. Addition of L-NMMA, the antagonist of iNOS pathway in mMDSCs-containing system restored T cell proliferative curve and cell numbers, whereas Nor-NOHA, the antagonist of Arg-1 pathway didn't abrogate mMDSCs' immune-regulation properties, indicating that mMDSCs inhibited T cell proliferation via iNOS pathway. We then performed single dose or multi-dose injection of mMDSCs in AA mice to see whether mMDSCs are able to reconstitute the impacted hematopoiesis. Single injection of mMDSCs was able to prevent from CTL infiltration in a very short term. However, multi-injection of mMDSCs showed significant benefit in overall survival rate compared to AA mice. We further detected the function of mMDSCs on polarized BM-MSCs adipo-osteogenic differentiation potential. To detect sequential BM adipogenetic progression in AA microenvironment, we performed in vivo fluorescent microscopy on AP2 (Fabp4)-Cre×mT/mG reporting mice at different transfusion time points of T cells and mMDSCs. GFP-expressing AP2+ adipocytes accumulated adjacently to perivascular niches whose boarders were labelled by Dextran-CY5 in a time-dependent manner after T cell infusion. Monocytic MDSCs transfused AA mice showed decreased GFP+ adipocytes which was coincident with our in vitro findings. In conclusion, intra-BM immune balance is one of the environmental factors seesawing by activating and suppressive ends to support functional hematopoiesis. Adoptive transfusion of mMDSCs, the immune-suppressive population might be a novel immune-regulating strategy to treat AA, relying on not only restoring the intra-BM immune balance but also improving stroma's multi-differentiating microenvironment. Figure Disclosures No relevant conflicts of interest to declare.

Processing and CD3+/CD19+ depletion of cadaveric vertebral bone marrow for primary immunodeficiency patients undergoing sequential bilateral orthotopic lung transplant (BOLT) and bone marrow transplant (BMT)

Background & Aim Patients with primary immune-deficiency (PID) may develop pulmonary complications and at that stage most are ineligible for either lung transplant (LTX) or bone marrow transplant (BMT) alone due to futility. We are conducting a first in human prospective trial, ClinicalTrials.gov: NCT01852370 where PID patients in lung failure -past the opportunity for curative BMT alone- may receive a 2 of 6 HLA antigen-matched cadaveric BOLT and minimum 8 weeks alter cryopreserved BMT from the same deceased UNOS donor. We hypothesized: 1) hematopoietic stem cells prepared from organ donor vertebral bodies (VB) would yield greater CD34+ cell dose compared to iliac crest aspirates-in part due to limited harvest time to avoid delay in the activity of organ recovery teams; 2) cryopreserved CD3/CD19 depleted bone marrow could generate durable hematopoiesis and donor derived immunity. Here we present the first 5 consecutive cases vertebral bone marrow (VBM) processing experience at Children's Hospital of Pittsburgh and subsequent CD3+/CD19+ cell depletion on the CliniMACS® device. With a threshold viability of 70% prior to cryopreservation the CD3/CD19-depleted product must contain 1 × 10E+6/kg CD34+ cells and 1 × 10E+5/kg CD3+ T cells to achieve durable engraftment and reduce the risk of GVHD respectively.® Methods, Results & Conclusion For details of pre/post processing, see Table. Since early 2017 we introduced chest/abdominal cavity wash with 1:1 saline-betadine mix and scrubbing T11-L4VB logs with chlora-prep that has eliminated bacterial contamination for the last 3 products. The first 2 were infused without adverse events following IRB/FDA approved antibiotic prophylaxis. Initially, processing of the VBs was arduous, using a scalpel and wire brush to clean the logs, then dissecting into small pieces with a mallet and osteotome. Since early 2017 a Stryker RemB saw has been used. A physical task that had taken 2 technologists 3 hours to complete has become almost effortless and one tech is freed up. The target pre-cryo CD34+ dose and viabilities have met target at all times, in fact CD34+ recovery has increased >70%, see Table. The entire process (dissection, crushing, filtering, CD3/CD19 depletion and cryopreservation) can be completed in 12 hours with 3 technologists. In summary, we have developed a complex sequence of procedures that even exceeded our target of 2E+06 CD34/kg pre-cryo dose (mean: 4.49E+06) leading to prompt and multilineage engraftment in 3 of the first 4 analyzable patients.