-Author name in bold denotes the presenting author
-Asterisk * with author name denotes a Non-ASH member
Clinically Relevant Abstract denotes an abstract that is clinically relevant.

PhD Trainee denotes that this is a recommended PHD Trainee Session.

Ticketed Session denotes that this is a ticketed session.

1778 JAK2V617F Impairs Lymphoid Differentiation in Myeloproliferative Neoplasms

Program: Oral and Poster Abstracts
Session: 631. Myeloproliferative Syndromes and Chronic Myeloid Leukemia: Basic and Translational: Poster I
Hematology Disease Topics & Pathways:
Fundamental Science, Research, adult, MPN, Chronic Myeloid Malignancies, hematopoiesis, Diseases, Biological Processes, Myeloid Malignancies, Human, Study Population
Saturday, December 9, 2023, 5:30 PM-7:30 PM

Daniel C Choi, MD1, Ghaith Abu-Zeinah, MD1, Pouneh Kermani, PhD2*, Nassima Messali, PhD2, Maria Mia Yabut, MS2*, Katie Erdos1* and Joseph M. Scandura, MD, PhD, MS1

1Richard T. Silver, MD Myeloproliferative Neoplasms Center, Weill Cornell Medicine, New York, NY
2Weill Cornell Medicine, New York, NY

Myeloproliferative neoplasms (MPNs) arise from the clonal acquisition of a driver mutation in a hematopoietic stem cell (HSC), often decades before the emergence of clinical disease. A defining characteristic of an HSC is its potential to give rise to both myeloid and lymphoid hematopoietic lineages. Yet the most common MPN driver mutation, JAK2V617F, has only rarely been observed in lymphocytes. We conducted this study to determine why the JAK2V617F clone does not contribute to mature lymphocytes.

We directly measured myeloid and lymphoid lineage contribution of normal and MPN HSCs in 133 patients with JAK2V617F MPN. Peripheral blood subpopulations were fractionated via fluorescence-activated cell sorting (FACS) and JAK2V617F mutation allele frequency (MAF) was measured in each subpopulation by droplet digital PCR. JAK2V617F was enriched in neutrophils and maintained in erythroid progenitors (EPs) relative to HSCs. In contrast, JAK2V617F alleles were largely absent in T and B cells relative to HSCs.

Lymphopoiesis declines with age, potentially explaining the absence of JAK2V617F in lymphocytes from older patients with MPN even if JAK2V617F has no effect on lymphopoiesis. This “JAK2V617F neutral” hypothesis predicts that patients who acquired the mutation at a younger age, and those who harbor the mutation for a longer duration, have a higher likelihood of accumulating JAK2 mutated lymphocytes. However, we found that JAK2V617F MAF in T and B cells across our cohort does not correlate with either patient age at diagnosis or duration of clinical disease. Thus, predictions of the “JAK2V617F neutral” hypothesis are not supported by patient data.

The alternative explanation is that JAK2V617F impairs lymphocyte differentiation from mutated progenitors. We tested this “JAK2V617F adverse” hypothesis by tracking JAK2V617F during various stages of lymphopoiesis. To assess the relative bias of JAK2V617F HSCs during the early stages of lymphoid and myeloid commitment, we measured JAK2V617F MAF in common lymphoid progenitors (CLPs), common myeloid progenitors (CMPs) and HSCs isolated by FACS from the peripheral blood of 79 patients with JAK2V617F MPN. We found that while myeloid commitment from HSC to CMP was associated with an increase in mean JAK2V617F MAF, there was no statistically significant change in mean MAF between CLPs and the parent HSCs across the cohort. Therefore, JAK2V617F HSCs are not completely excluded from the earliest stages of lymphoid differentiation.

To further define the extent to which JAK2V617F affects lymphopoiesis, we used FACS to isolate CLPs and CMPs from 17 patients with JAK2V617F polycythemia vera (PV) and differentiated each subpopulation in vitro into T cell progenitors (pro- and pre-T cells) and erythroblasts (EBs), respectively. We found that all CLP samples could be differentiated into T cell progenitors. However, we observed a marked depletion of JAK2V617F alleles in progressively mature T cell progenitors (Figure 1). In contrast, JAK2V617F alleles were further enriched in progressively mature erythroblasts. The in vitro differentiation potential of MPN progenitors thus supports the “JAK2V617F adverse” hypothesis.

To determine the effect of JAK2V617F on lymphopoiesis in vivo, we performed competitive transplantations of lethally irradiated CD45.1 mice with congenic CD45.2 donor whole bone marrow (WBM) cells harboring JAK2V617F or wild type JAK2 (JAK2WT). Measuring CD45.2 chimerism by FACS in lymphocytes and neutrophils from engrafted mice revealed that only CD45.2 cells harboring JAK2V617F were preferentially depleted in lymphocytes (Figure 2). Therefore, JAK2V617F HSCs displayed a competitive disadvantage relative to their JAK2WT counterparts during lymphopoiesis in vivo.

Myeloid proliferation in MPN driven by JAK2V617F is well recognized but does not fully explain certain MPN complications such as increased risk of infections and second malignancies. Our findings demonstrate impaired lymphoid differentiation from JAK2V617F stem and progenitor cells that may also contribute to clinical MPN phenotypes. Further study is ongoing to define actionable mechanisms through which JAK2V617F interferes with T cell differentiation.

Disclosures: No relevant conflicts of interest to declare.

*signifies non-member of ASH