Development and manufacture of novel locally produced anti-BCMA CAR T cells for the treatment of relapsed/refractory multiple myeloma: results from a phase I clinical trial.

Anti-B-cell maturation antigen (BCMA) chimeric antigen receptor T-cell (CAR T) therapy shows remarkable efficacy in patients with relapsed and/or refractory (R/R) multiple myeloma (MM). HBI0101, a novel second generation optimized anti- BCMA CAR T-cell therapy, was developed in an academic setting. We conducted a phase I dose-escalation study of HBI0101 (cohort 1: 150x106 CAR T cells, n=6; cohort 2: 450x106 CAR T cells, n=7; cohort 3: 800x106 CAR T cells, n=7) in 20 heavily pre-treated R/R MM patients. Grade 1-2 cytokine release syndrome (CRS) was reported in 18 patients (90%). Neither grade 3-4 CRS nor neurotoxicity of any grade were observed. No dose-limiting toxicities were observed in any cohort. The overall response rate (ORR), (stringent) complete response (CR/sCR), and very good partial response rates were 75%, 50%, and 25%, respectively. Response rates were dose-dependent with 85% ORR, 71% CR, and 57% minimal residual disease negativity in the high-dose cohort 3. Across all cohorts, the median overall survival (OS) was 308 days (range 25-466+), with an estimated OS of 55% as of June 27th (data cut-off). The median progression-free survival was 160 days, with 6 subjects remaining progression free at the time of data cut-off. Our findings demonstrate the manageable safety profile and efficacy of HBI0101. These encouraging data support the decentralization of CAR T production in an academic setting, ensuring sufficient CAR T supply to satisfy the increasing local demand. Clinicaltrials.gov NCT04720313.

Risk factors and outcomes of COVID-19 in adult patients with hematological malignancies: A single-center study showing lower than expected rates of hospitalization and mortality.

BACKGROUND: Studies addressing coronavirus disease 2019 (COVID-19) in patients with hematological malignancies have reported mortality rates of up to 40%; however, included predominantly hospitalized patients. METHODS: During the first year of the pandemic, we followed adult patients with hematological malignancies treated at a tertiary center in Jerusalem, Israel, who contracted COVID-19, with the aim of studying risk factors for adverse COVID-19-related outcomes. We used remote communication to track patients managed at home-isolation, and patient questioning to assess the source of COVID-19 infection, community versus nosocomial. RESULTS: Our series included 183 patients, median age was 62.5 years, 72% had at least one comorbidity and 39% were receiving active antineoplastic treatment. Hospitalization, critical COVID-19, and mortality rates were 32%, 12.6%, and 9.8%, respectively, remarkably lower than previously reported. Age, multiple comorbidities, and active antineoplastic treatment were significantly associated with hospitalization due to COVID-19. Treatment with monoclonal antibodies was strongly associated with both hospitalization and critical COVID-19. In older (≥60) patients not receiving active antineoplastic treatment, mortality, and severe COVID-19 rates were comparable to those of the general Israeli population. We did not detect patients that contracted COVID-19 within the Hematology Division. CONCLUSION: These findings are relevant for the future management of patients with hematological malignancies in COVID-19-affected regions.

High rate of adenovirus detection in gastrointestinal biopsies of symptomatic stem cell transplant recipients.

OBJECTIVES: The gastrointestinal (GI) tract is a major human adenovirus (HAdV) replication site in patients undergoing hematopoietic stem cell transplantation (HSCT), yet the prevalence and correlates of HAdV GI infection in this setting have remained poorly recognized, especially among adult HSCT recipients. DESIGN OR METHODS: We retrospectively studied the prevalence and risk factors of HAdV GI-tissue infection in HSCT recipients (73 adults and 15 children) with GI symptoms who underwent GI-tissue biopsy between January-2012 and December-2017. The presence of HAdV in the GI tissues was determined by real-time PCR. RESULTS: HAdV GI-tissue infection was detected in 21 (23.9%) patients, with similar infection rates identified in adults and children. GI-tissue detection was more common at late (>100 days) compared to early times post-transplantation (50% vs. 12.9%, p < .001). The presence of bloody diarrhea, Arab ethnicity (p = .014) and concurrent cytomegalovirus GI-tissue detection (p = .025) were significantly correlated with HAdV GI-tissue infection, while chronic graft versus host disease was of borderline association (p = .055). CONCLUSIONS: Our findings reveal a high rate and new clinical-demographic correlates of HAdV GI-tissue infection in adult and pediatric HSCT recipients with GI symptoms. The findings highlight the need for future prospective studies to assess the relatedness of HAdV infection to the GI symptoms, and the prevalence, impact, and treatment of HAdV GI infection in HSCT recipients.

Mesenchymal stroma/stem cells: Haematologists' friend or foe?

Mesenchymal stromal cells (MSCs) are non-haematopoietic cells found in fetal and adult organs, that play important roles in tissue repair, inflammation and immune modulation. MSCs residing in the bone marrow interact closely with haematopoietic cells and comprise an important component of the microenvironment supporting haematopoiesis, in both health and disease states. Since their identification in 1970, basic scientific and preclinical research efforts have shed light on the role of MSCs in the regulation of haematopoiesis and evoked interest in their clinical application in haematopoietic stem cell transplantation (HSCT) and malignant haematology. Over the last two decades, these research efforts have led to numerous clinical trials, which have established the safety of MSC therapy; however, the optimal mode of administration and the benefit remain inconclusive. In this paper, we will review the clinical experience with use of MSCs in HSCT for enhancement of engraftment, prevention and treatment of graft-versus-host disease and haemorrhagic cystitis. Then, we will discuss the contradictory evidence regarding tumour-promoting versus tumour-suppressing effects of MSCs in haematological malignancies, which may have relevance for future clinical applications.

Endothelial Activation and Stress Index Score as a Prognostic Factor of Cytokine Release Syndrome in CAR-T Patients - A Retrospective Analysis of Multiple Myeloma and Large B-Cell Lymphoma Cohorts.

Endothelial Activation and Stress Index (EASIX) has been proposed as a prognostic factor of adverse events or survival in hematological malignancies. Endothelial dysfunction has been associated with complications following stem cell transplantation and chimeric antigen receptor (CAR)-T therapy. This retrospective cohort study evaluated the utility of the EASIX score as a prognostic factor of cytokine release syndrome (CRS) in multiple myeloma/light-chain amyloidosis (MM/AL amyloidosis; N = 69) and large B-cell lymphoma (LBCL) cohorts (N = 65). Occurrence of CRS grade ≥3 was the primary endpoint. For both cohorts, the EASIX and simplified EASIX (s-EASIX) scores were calculated at four different time points before CAR-T infusion to assess its prognostic value. In the MM/AL amyloidosis cohort, neither EASIX nor s-EASIX scores calculated at any time point were associated with the occurrence of CRS grade ≥3. In the LBCL cohort, EASIX and s-EASIX scores measured before lymphodepletion (EASIX-pre and s-EASIX-pre) showed a significant relationship with CRS grade ≥3 (odds ratio [OR] = 1.06 and OR = 1.05, respectively). The cutoff value of 1.835 for EASIX-pre was associated with 4.59-fold increased OR of CRS grade ≥3 (95% confidence interval [CI]: 1.13-21.84), whereas s-EASIX-pre cutoff equaled 2.134 and was associated with 4.13-fold increased OR of CRS grade ≥3 (95% CI: 1.01-17.93). However, after internal validation with bootstrapping, the significance was lost both for the EASIX-pre and s-EASIX-pre cutoff. The presented findings indicate that the EASIX scores fail to predict CRS in MM/amyloidosis CAR-T patients, whereas they can be implemented as CRS grade ≥3 predictors in LBCL CAR-T patients.

Clinical evaluation and determinants of response to HBI0101 (BCMA CART) therapy in relapsed/refractory multiple myeloma.

ABSTRACT: HBI0101 is an academic chimeric antigen receptor T-cell (CART)-targeted to B-cell maturation antigen (BCMA) for the treatment of relapsed and refractory multiple myeloma (R/RMM) and light chain amyloidosis. Herein, we present the phase 1b/2 results of 50 heavily pretreated patients with R/RMM dosed with 800 × 106 CART cells. Inclusion criteria were relatively permissive (i.e., performance status and baseline organ function) and consequently, approximately half of the enrolled patients would have been ineligible for pivotal clinical trials. The median time elapsed from patient enrollment until CART delivery was 25 days (range, 14-65). HBI0101-related toxicities included grade 1 to 3 cytokine release syndrome, grade 3 to 4 hematologic toxicities, and grade 1 to 2 immune effector cell-associated neurotoxicity syndrome. Responses were achieved in 90% of the patients, 56% achieved stringent and complete response, and 70% reached a minimal residual disease negativity. Within a median follow-up of 12.3 months, the median progression-free survival (PFS) was 11.0 months (95% confidence interval [CI], 6.2-14.6), and the overall survival was not reached (95% CI, 13.3 to not reached). Multivariable analysis on patient/disease and CART-related characteristics revealed that high-risk cytogenetic, extramedullary disease, and increased number of effector-memory T cells in CART products were independently associated with inferior PFS. In conclusion, comprehensive analyses of the parameters affecting the response to CART therapy are essential for improving patients' outcome. This trial was registered at www.ClinicalTrials.gov as #NCT04720313.

Long-Term Results with Thiotepa-Containing Conditioning Regimens for Autologous Stem Cell Transplantation.

Autologous stem cell transplantation (ASCT) remains a cornerstone in the treatment of both Hodgkin lymphoma (HL) and various non-Hodgkin lymphoma (NHL) subtypes. BEAM (carmustine, etoposide, cytarabine, and melphalan) is the most frequently used conditioning regimen; however, owing due to limited availability and toxicity of carmustine, thiotepa-containing regimens have been suggested. We previously reported encouraging results in ASCT with a TECAM (thiotepa, etoposide, cyclophosphamide, cytarabine, and melphalan) conditioning regimen from 2000 to 2013. We aimed to update our experience with the TECAM regimen by adding our experience from 2013 to 2020 to the previously reported cohort. Moreover, we aimed to use the detailed data for the 2 transplant cohorts to identify improvements in ASCT outcomes in the recent era. We retrospectively analyzed all lymphoma patients who underwent ASCT at our center between January 2000 and December 2020. A total of 353 lymphoma patients were included (142 in the newer cohort added to 211 previously reported patients), all of whom were treated with our standard TECAM conditioning regimen. The cohort included 127 patients with HL, 107 with DLBCL, and 119 with other NHL subtypes. The newer cohort was characterized by significantly poorer Eastern Cooperative Oncology Group Performance Status (ECOG-PS) prior to ASCT (45.7% versus 19.3% with ECOG-PS ≥1; P < .01), whereas a higher proportion of patients entered transplantation in complete response (CR) (71.9% versus 47.8%; P < .01). The median follow-up after ASCT was 136.4 months (95% confidence interval [CI], 91.4 to 181.4 months). The 3-year progression-free survival (PFS) and overall survival (OS) rates post-ASCT for the entire cohort were 59.8% and 79.3%, respectively. Evaluating the 303 of 353 patients (86.4%) who entered ASCT with a responsive disease-a population that represents today's approach to the selection of patients for ASCT-the 3-year PFS and OS rates were 61.5% and 81.9%, respectively. In this population, the 3-year PFS rate was 62.2% for HL, 62.6% for DLBCL, 64.3% for primary central nervous system lymphoma (PCNSL), and the 3-year OS rate were 90.1%, 75.2%, and 78.6%, respectively. OS was significantly better in the newer cohort (P < .01), but not when evaluating only patients who entered ASCT with responsive disease. Dose reductions, poor disease status, and poor ECOG-PS at ASCT entry were associated with worse outcomes across all lymphoma subtypes. In accordance with our previous report, patients entering transplantation for DLBCL with a partial response achieved similar outcomes as those with a CR. Eighteen patients died within the first 100 days, 8 due to disease progression and 10 due to transplantation-related complications (2.8%). There were no cases of interstitial pneumonitis syndrome. Twenty-two cases (6.2%) of secondary malignancies were documented. Our results confirm that TECAM is an effective and safe conditioning regimen for ASCT in patients with HL and various NHLs, including favorable results in PCNSL. Despite a higher proportion of frail patients, the newer cohort's outcomes were favorable, driven by better lymphoma control pretransplantation. In the DLBCL cohort, ECOG-PS had more prognostic value than achieving a CR pre-ASCT, a finding relevant to the optimal allocation of patients to different treatment options in the era of chimeric antigen receptor T cell availability.

Clonal Myeloid Dysplasia Following CAR T-Cell Therapy: Chicken or the Egg?

Multiple myeloma (MM) is characterized by recurrent relapses. Consequently, patients receive multiple therapy lines, including alkylating agents and immune modulators, which have been associated with secondary malignancies such as myelodysplastic syndrome (MDS). Anti-B-cell maturation antigen (BCMA) chimeric antigen receptor T cell (CART) therapy is efficacious in patients with relapsed/refractory (R/R) MM. However, the long-term complications, particularly MDS, are not well understood. Whether CART therapy causes or promotes MDS has not been thoroughly investigated. In this study, we explored the causal relationship between MDS and CART therapy. We retrospectively examined the prevalence of MDS-related morphological and mutational changes before and after administration of CART therapy in five patients. Among them, four developed MDS after CART therapy, while one had pre-existing MDS prior to CART. None of the four patients who developed post-CART MDS showed morphological MDS changes prior to CART therapy. However, all four patients exhibited molecular alterations associated with MDS in their pre-CART as well as post-CART therapy bone marrow. No new mutations were observed. Our findings provide initial evidence suggesting that anti-BCMA CART therapy in MM may promote expansion of pre-existing MDS clones rather than causing development of new clones.

A simplified scoring tool for prediction of readmission in elderly patients hospitalized in internal medicine departments.

BACKGROUND: Frequent readmissions significantly contribute to health care costs as well as work load in internal medicine wards. OBJECTIVE: To develop a simple scoring method that includes basic demographic and medical characteristics of elderly patients in internal medicine wards that would allow prediction of readmission within 3 months of discharge. METHODS: We conducted a retrospective observational study of 496 hospitalized patients using data collected from discharge letters in the computerized archives. Univariate and multivariate logistic regression analyses were performed and factors that were significantly associated with readmission were selected to construct a scoring tool. Validity was assessed in a cohort of 200 patients. RESULTS: During a 2 year follow-up 292 patients were readmitted at least once within 3 months of discharge. Age 80 or older, any degree of impaired cognition, nursing home residence, congestive heart failure, and creatinine level > 1.5 mg/dl were found to be strong predictors of readmission. The presence of each variable was scored as 1. A score of 3 or higher in the derivation and validation cohorts corresponded with a positive predictive value of 80% and 67%, respectively, when evaluating the risk of rehospitalization. CONCLUSIONS: We propose a practical, readily available five-item scoring tool that allows prediction of most unplanned readmissions within 3 months. The strength of this scoring tool, as compared with previously published scores, is its simplicity and straightforwardness.

Neutrophil decline rate following autologous transplant for lymphoma is a predictor of patients' outcome.

Neutropenia postchemotherapy is associated with favorable outcomes, which was attributed to optimal dosing. However, little is known about the neutrophil decline rate as a predictor of cancer outcomes, which may reflect a dynamic marker of chemosensitivity. We assessed the association between the neutrophil decline rate and disease outcomes in a known cohort of 212 lymphoma patients, treated with thiotepa, etoposide, cyclophosphamide, cytarabine, and melphalan (TECAM) conditioning followed by autologous transplant in our center between 2000 and 2013. Slower neutrophil decline rate was correlated with worse overall survival, mediated not by shorter time to progression (TTP), but rather by worse survival post-progression, possibly pointing to chemosensitivity at each line of therapy as the responsible mechanism. The effect was seen across histologies and was independent of stronger predictors of outcome like performance status (PS) and response before transplant. Prospective research is needed to confirm our results and expand their validity to other clinical scenarios.

Feasibility of a Novel Academic BCMA-CART (HBI0101) for the Treatment of Relapsed and Refractory AL Amyloidosis.

PURPOSE: AL amyloidosis (AL) treatments are generally based on those employed for multiple myeloma. Anti-B-cell maturation antigen (BCMA) chimeric antigen receptor T (CART)-cell therapy, already approved for multiple myeloma, might be too toxic for patients with AL. EXPERIMENTAL DESIGN: Here we describe the ex vivo applicability of a novel in-house, academic anti-BCMA CAR construct on AL primary cells, as well as the safety and efficacy in 4 patients with relapsed/refractory (RR) primary AL, treated in a phase I clinical trial (NCT04720313). RESULTS: Three had MAYO stage IIIa cardiac involvement at enrollment. The treatment proved relatively safe, with a short and manageable grade 3 cytokine release syndrome evident in 2 patients and no neurotoxicity in any. Cardiac decompensations, observed in 2 patients, were also short and manageable. The overall hematologic response and complete response rates were observed in all patients with an organ response evident in all four. Within a median follow-up period of 5.2 (2.5-9.5) months, all 4 patients maintained their responses. CONCLUSIONS: BCMA-CART cells provide a first proof-of-concept that this therapy is safe enough and highly efficacious for the treatment of patients with advanced, RR AL.

Re-induction versus salvage for D14-resiudal acute myeloid leukemia: A retrospective multi-center study.

Remission assessment in acute myeloid leukemia has evolved over the recent years with the advent of molecular and flow-based minimal residual disease determination. Nonetheless, early time point such as day 5 and day 14 (D14), still have prognostic and therapeutic implications. D14 refractory disease is regarded as a poor prognostic factor, however the therapeutic intervention is still under debate, with evidence suggesting a successful re-induction might offer similar long-term outcome as D14 aplasia. Others advocate the use of more intensive salvage protocols as a mean to overcome the negative prognostic effect. In the current study, we compare outcome of D14 refractory AML patients treated with either re-induction or salvage protocol. More importantly, we identify response characteristics that might suggest which patients will benefit from re-induction approach. Accurate identification of chemotherapy refractory patients might allow the early incorporation of non-chemotherapy based protocols in the future.

Rituximab, methotrexate, procarbazine and lomustine (R-MPL) for the treatment of primary Central nervous system lymphoma.

The optimal high-dose methotrexate (HDMTX)-based combination therapy for primary central nervous system lymphoma is unknown. We report our experience with rituximab, HDMTX, procarbazine and lomustine (R-MPL) given as first-line treatment in our center. Fifty-two patients between 2006 and 2019 were included. Eighteen patients proceeded to autologous transplant or two cycles of intermediate-dose cytarabine. The median age was 62 y (range 28-94) and the Eastern Cooperative Oncology Group performance status (ECOG-PS) was ≥2 in 62% (32/52). The overall/complete response rates were 79% (41/52) and 52% (27/52), respectively. The median progression-free/overall survival was 19 m/84m, respectively. Grade 3-4 adverse events included infections (17%) and kidney injury (13%). Ten patients (19%) discontinued therapy for toxicity. There were no treatment-related deaths. In summary, in a cohort enriched in frail patients, R-MPL achieved good responses and OS and was safe for all ages. The PFS was sub-optimal, possibly explained by a low proportion of consolidation. This regimen should be evaluated prospectively.

Ex vivo expansion of hematopoietic stem cells: Finally transitioning from the lab to the clinic.

Hematopoietic stem cells (HSCs) have been used for therapeutic purposes for decades in the form of autologous and allogeneic transplantation and are currently emerging as an attractive target for gene therapy. A low stem cell dose is a major barrier to the application of HSC therapy in several situations, primarily umbilical cord blood transplantation and gene modification. Strategies that promote ex vivo expansion of the numbers of functional HSCs could overcome this barrier, hence have been the subject of intense and prolonged research. Several ex vivo expansion strategies have advanced to evaluation clinical trials, which are showing favorable outcomes along with convincing safety signals. Preclinical studies have recently confirmed beneficial incorporation of ex vivo expansion into HSC gene modification protocols. Collectively, ex vivo HSC expansion holds promise for significantly broadening the availability of cord blood units for transplantation, and for optimizing gene therapy protocols to enable their clinical application.

COVID-19 among patients with hematological malignancies: a national Israeli retrospective analysis with special emphasis on treatment and outcome.

This national Israeli multicenter retrospective study aimed to characterize the clinical course of COVID-19 infection among patients with hematological malignancies, with special emphasis on treatment efficacy and outcome. Clinical and laboratory data from haemato-oncological patients diagnosed with COVID-19 from 16 medical centers were centrally reported. Multivariate regression analyses were used to determine variables associated with severe disease, hospitalization, and mortality. In total, 313 patients were included: 103 (35.7%) developed severe/critical respiratory infection, 178 (61.4%) were hospitalized, and 60 (20.0%) died. Age > 70 years was associated with severe/critical disease (p = 0.036) and mortality (p = 0.023), hypertension with severe/critical disease (p = 0.046) and hospitalization (p = 0.001), active haemato-oncological treatment with hospitalization (p = 0.009), and remdesivir treatment was associated with decreased mortality (p = 0.021). Convalescent plasma, enoxaparin, and corticosteroids resulted in no clinical benefit. In conclusion, COVID-19 infection seems particularly severe in patients with hematological malignancies, and of all examined therapies, remdesivir appears to be the most effective.

Expansion and preservation of the functional activity of adult hematopoietic stem cells cultured ex vivo with a histone deacetylase inhibitor.

Attempts to expand ex vivo the numbers of human hematopoietic stem cells (HSCs) without compromising their marrow repopulating capacity and their ability to establish multilineage hematopoiesis has been the subject of intense investigation. Although most such efforts have focused on cord blood HSCs, few have been applied to adult HSCs, a more clinically relevant HSC source for gene modification. To date, the strategies that have been used to expand adult HSCs have resulted in modest effects or HSCs with lineage bias and a limited ability to generate T cells in vivo. We previously reported that culturing umbilical cord blood CD34+ cells in serum-free media supplemented with valproic acid (VPA), a histone deacetylase inhibitor, and a combination of cytokines led to the expansion of the numbers of fully functional HSCs. In the present study, we used this same approach to expand the numbers of adult human CD34+ cells isolated from mobilized peripheral blood and bone marrow. This approach resulted in a significant increase in the numbers of phenotypically defined HSCs (CD34+CD45RA-CD90+D49f+). Cells incubated with VPA also exhibited increased aldehyde dehydrogenase activity and decreased mitochondrial membrane potential, each functional markers of HSCs. Grafts harvested from VPA-treated cultures were able to engraft in immune-deficient mice and, importantly, to generate cellular progeny belonging to each hematopoietic lineage in similar proportion to that observed with unmanipulated CD34+ cells. These data support the utility of VPA-mediated ex vivo HSC expansion for gene modification of adult HSCs.

Current approaches to challenging scenarios in myeloproliferative neoplasms.

INTRODUCTION: The Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs) including polycythemia vera, essential thrombocythemia and primary myelofibrosis are clonal hematological malignancies that originate at the level of the hematopoietic stem cell, and are characterized by excessive proliferation of cells belonging to one or more of the myeloid lineages. Central to the pathogenesis of the MPNs is constitutive activation of the JAK/STAT signaling pathway due to a family of driver mutations affecting JAK2, CALR or MPL. These disorders share common clinical and laboratory features, a significant burden of systemic symptoms, increased risk of developing arterial and venous thrombotic events, and the potential to progress to myelofibrosis and acute leukemia. Areas covered: We identified four clinical situations which represent challenging management dilemmas for patients with MPNs. Our conclusions and recommendations are based on a literature search using MEDLINE and recent meeting abstracts using the keywords, focusing on publications directly addressing these scenarios and on recent contributions to the field. Expert commentary: Multi-center efforts to study large cohorts of MPN patients have led to more uniform and evidence-based approaches to key aspects in MPN management. However, treatment strategies to deal with specific clinical scenarios are lacking.

Dysregulated iron metabolism in polycythemia vera: etiology and consequences.

Polycythemia vera (PV) is a chronic myeloproliferative neoplasm. Virtually all PV patients are iron deficient at presentation and/or during the course of their disease. The co-existence of iron deficiency and polycythemia presents a physiological disconnect. Hepcidin, the master regulator of iron metabolism, is regulated by circulating iron levels, erythroblast secretion of erythroferrone, and inflammation. Both decreased circulating iron and increased erythroferrone levels, which occur as a consequence of erythroid hyperplasia in PV, are anticipated to suppress hepcidin and enable recovery from iron deficiency. Inflammation which accompanies PV is likely to counteract hepcidin suppression, but the relatively low serum ferritin levels observed suggest that inflammation is not a major contributor to the dysregulated iron metabolism. Furthermore, potential defects in iron absorption, aberrant hypoxia sensing and signaling, and frequency of bleeding to account for iron deficiency in PV patients have not been fully elucidated. Insufficiently suppressed hepcidin given the degree of iron deficiency in PV patients strongly suggests that disordered iron metabolism is an important component of the pathobiology of PV. Normalization of hematocrit levels using therapeutic phlebotomy is the most common approach for reducing the incidence of thrombotic complications, a therapy which exacerbates iron deficiency, contributing to a variety of non-hematological symptoms. The use of cytoreductive therapy in high-risk PV patients frequently works more effectively to reverse PV-associated symptoms in iron-deficient relative to iron-replete patients. Lastly, differences in iron-related parameters between PV patients and mice with JAK2 V617F and JAK2 exon 12 mutations suggest that specific regions in JAK2 may influence iron metabolism by nuanced changes of erythropoietin receptor signaling. In this review, we comprehensively discuss the clinical consequences of iron deficiency in PV, provide a framework for understanding the potential dysregulation of iron metabolism, and present a rationale for additional therapeutic options for iron-deficient PV patients.