Red Blood Cell Contribution to Thrombosis in Polycythemia Vera and Essential Thrombocythemia

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Julien Grenier, Wassim El Nemer, and Maria De Grandis

Abstract

Polycythemia vera (PV) and essential thrombocythemia (ET) are myeloproliferative neoplasms (MPN) characterized by clonal erythrocytosis and thrombocytosis, respectively. The main goal of therapy in PV and ET is to prevent thrombohemorrhagic complications. Despite a debated notion that red blood cells (RBCs) play a passive and minor role in thrombosis, there has been increasing evidence over the past decades that RBCs may play a biological and clinical role in PV and ET pathophysiology. This review summarizes the main mechanisms that suggest the involvement of PV and ET RBCs in thrombosis, including quantitative and qualitative RBC abnormalities reported in these pathologies. Among these abnormalities, we discuss increased RBC counts and hematocrit, that modulate blood rheology by increasing viscosity, as well as qualitative changes, such as deformability, aggregation, expression of adhesion proteins and phosphatidylserine and release of extracellular microvesicles. While the direct relationship between a high red cell count and thrombosis is well-known, the intrinsic defects of RBCs from PV and ET patients are new contributors that need to be investigated in depth in order to elucidate their role and pave the way for new therapeutical strategies.

SOHO State of the Art Updates and Next Questions | Diagnosis, Outcomes, and Management of Prefibrotic Myelofibrosis

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Pankit Vacchani, Sanam Lohgavi, Prithviraj Bose

Abstract

Prefibrotic primary myelofibrosis (prefibrotic PMF) is a myeloproliferative neoplasm with distinct characteristics comprising histopathological and clinico-biological parameters. It is classified as a subtype of primary myelofibrosis. In clinical practice, it is essential to correctly distinguish prefibrotic PMF from essential thrombocythemia especially but also overt PMF besides other myeloid neoplasms. Risk stratification and survival outcomes for prefibrotic PMF are worse than that of ET but better than that of overt PMF. Rates of progression to overt PMF and blast phase disease are also higher for prefibrotic PMF than ET. In this review we first discuss the historical context to the evolution of prefibrotic PMF as an entity, its presenting features and diagnostic criteria. We emphasize the differences between prefibrotic PMF, ET, and overt PMF with regards to presenting features and disease outcomes including thrombohemorrhagic events and progression to fibrotic and blast phase disease. Next, we discuss the risk stratification models and contextualize these in the setting of clinical management. We share our view of personalizing treatment to address unique patient needs in the context of currently available management options. Lastly, we discuss areas of critical need in clinical research and speculate on the possibility of future disease course modifying therapies in prefibrotic PMF.

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Prediction models for essential thrombocythemia from two longitudinal studies involving 2000 patients

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January 23, 2024

Tiziano Barbui and Alessandra Carobbio

Over the past two decades, significant progress has been made in several areas of Philadelphia chromosome-negative myeloproliferative neoplasms (Ph-neg MPNs), namely polycythemia vera (PV), essential thrombocythemia (ET), and myelofibrosis (MF). The driver mutations in the JAK2-V617, MPL, calreticulin opened new diagnostic and prognostic possibilities and provided new targets for therapy [1].

ET is currently diagnosed according to the World Health Organization (WHO) [2] and International Consensus Criteria (ICC) [3] criteria, involving a comprehensive evaluation of clinical, laboratory and molecular features, and is defined by clonal thrombocytosis with characteristic bone marrow megakaryocyte morphology, which allows a differentiation from PV and prefibrotic myelofibrosis (pre-PMF); the latter is a distinct entity with a clinical picture often characterized by isolated thrombocytosis mimicking ET. In a multicenter series of 1104 patients previously classified as having ET, the diagnosis was re-evaluated following strict application of the 2008 WHO classification, which includes well-defined histopathological criteria. The diagnosis of ET was confirmed in 891 patients (81%) and revised to pre-PMF in 180 (16%) [4]. A subset of ET patients has a triple-negative (TN) genotype due to the absence of detectable mutations in driver genes and is observed in ~10% of ET cases [1].

Current information on risk factors of the major critical events (thrombosis, evolution to MF, blast phase (BP), and survival) derives from registry and multicenter observational studies while single-center reports conducted at tertiary referral institutions are very limited [5]. Each study design has its strengths and limitations. Observational multicenter studies and registries can capture a large number of cases but may face challenges related to data quality and consistency. Ensuring the accuracy and uniformity of data across multiple centers becomes a critical consideration.

Studies conducted in tertiary centers, exemplified by those presented in this Blood Cancer Journal issue from Florence [6] and Mayo Clinic [7] hospitals, are more robust in nature as they can provide a solid description of natural history of this myeloproliferative neoplasm. These are conducted by specialized teams comprising clinician hematologists, pathologists, geneticists, and other experts with proficiency in MPNs and are equipped with up-to-date technologies including molecular analyses, which are essential in the case of ET where genetic mutations play a significant role in diagnosis and prognosis. Nevertheless, despite providing comprehensive insights into a well-defined cohort of patients, these centers may have a patient referral bias and limited generalizability to the broader population. This may suggest that description of disease presentation and results on prognostic factors may not be universally reproducible, and caution should be exercised when extrapolating the results to consecutive patient groups.

The Mayo and Florence reports each included 1000 ET patients; all 2000 cases met ICC 2022 and WHO diagnostic criteria and were fully annotated for driver mutations; diagnosis required hematopathology review to minimize unintended inclusion of patients with masked PV or pre-PMF. This revision is critical for patients diagnosed with ET prior to the WHO recognition of masked PV and pre-PMF, as the incidence of complications such as thrombosis, myelofibrosis, blast phase, and overall survival differs between these entities compared to “true ET”. All patients in the two studies were annotated for driver mutations, which were found in approximately 90% of cases, with similar proportions in the two series for JAK2 V617F, CALR including CALR type 1/1-like and CALR type 2/2-like, MPL and TN. Interestingly, female sex clustered preferentially with TN and JAK2 vs. CALR/MPL mutations (p < 0.01), and extreme thrombocytosis clustered with CALR (type 2 more than type 1), TN, and MPL, whereas leukocytosis clustered with JAK2 mutation (p < 0.001). It is noteworthy that the two patients’ series from Mayo and Florence showed remarkably similar presentations over the extensive recruitment period of more than 40 years.

In these retrospective cohorts, 20% of patients had a history of vascular complications at diagnosis and a similar percentage of driver mutations clustered in a similar manner. Importantly, these findings are consistent with data observed in other real-world routine clinical practice of recent reviews on ET [8, 9]. This convergence of information on disease presentation between Mayo and Florence highlights that the characteristics of these two retrospective cohorts are unlikely to have been influenced by potential reference bias. Thus, the consistency of these patterns across different settings adds value to the findings of these two studies, reinforcing the reliability of the observed trends and minimizing the impact of referral bias.

Therefore, the Mayo and Florence longitudinal studies offer the unique advantage of capturing the dynamic evolution of ET disease in real-world clinical practice over an extended period of median 8.5 years (range, 0.01–52.7) and 8 years (range, 0.03–42.9), respectively, providing robust estimates of disease-specific outcomes, i.e., arterial and venous thrombosis, progression to overt MF, BP, and survival. This makes the results on risk factors for each of these critical events highly reliable and generalizable. In this context, the confirmation of the prognostic role of increased neutrophil granulocytes and decreased lymphocytes as independent risk factors for survival in 1164 ET patients should be highlighted. This new knowledge opens new avenues for future clinical trials on the role of inflammation in MPN and the associated new targets for therapy [10, 11]. In addition, the large number of cases annotated for driver mutations allowed the identification of risk scores for progression to myelofibrosis and blast phase and confirmed the predictive power of the International Prognostic Score of Thrombosis (IPSET-thrombosis) score. We agree with the authors that these results, obtained in a large series of patients with ET, mutually validated, can constitute a reference standard against which other series of cases fully annotated for driver mutations and followed up for a long time can be compared.

Inspired by the extensive ET series of these two Blood Cancer Journal papers, we reviewed our data on 891 WHO-diagnosed ET patients enrolled from multi-center institutions, in whom we investigated the effect of post-diagnosis intermediate events (thrombosis, MF, and BP) on mortality using multistate models [12]. Using these models, which increase the precision of estimation by correcting for competing risk factors, we found that patients with incident thrombosis had a progressively increased risk of death compared with patients without this event. As expected, the highest risk of death was associated with the occurrence of MF and BP (Fig. 1). Notably, in the time-dependent multivariate analysis, arterial but not venous thrombosis occurrence during follow-up was independently associated with death, together with evolution into MF and BP (Table 1). Therefore, in future analysis of longitudinal studies, we suggest that the conventional baseline prognostic evaluation in MPN should be revised by considering the intermediate events that might integrate the risk of the final outcome of interest in the single patient.

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A Rare Coexistence of Smoldering Multiple Myeloma and JAK2-Positive Myeloproliferative Neoplasm: A Case of Dual Synchronous Hematological Malignancy

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January 20, 2024

Abstract

This article explores the rare case of an 82-year-old man diagnosed concurrently with essential thrombocythemia and smoldering multiple myeloma (SMM). The limited existing literature on individuals harboring both myeloproliferative neoplasm (MPN) and monoclonal gammopathy (MG) is of significant interest due to the distinct origins of these malignancies. The etiology of MG in MPN patients remains elusive, leading to speculation about a potential relationship or interplay between the two conditions. This unique case prompts a deeper exploration of the mechanisms underlying the coexistence of JAK2-positive MPN and SMM. It underscores the importance of tailored therapeutic strategies that carefully consider the inherent risks and potential adverse outcomes associated with these specific malignancies, thereby warranting further clinical research.

Introduction

While existing literature acknowledges the coexistence of dual malignancies within the same patient [1], there is relatively limited documentation regarding the simultaneous occurrence of dual hematological malignancies (DHMs) [2,3], encompassing both myeloid and lymphoid hemopathies. A noteworthy aspect is the distinctive origin of these two malignancies from separate lineages within the hematopoietic ancestral tree [4]. DHMs can be classified as synchronous, manifesting within six months of the initial malignancy diagnosis, or asynchronous if they arise later [5].

Since its inclusion in the classification of monoclonal gammopathy (MG), smoldering multiple myeloma (SMM) has emerged as a significant aspect of MG [6], attracting attention in various clinical investigations.

Currently, no established strategies exist for treating or monitoring patients with myeloproliferative neoplasms (MPNs) and concurrent SMM. Additionally, the precise source of SMM in patients with MPN is not well understood, and there is uncertainty regarding whether an aberrant plasma cell condition arises from the identical hematopoietic clone as the MPN.

Numerous case reports have highlighted the occurrence of monoclonal gammopathy of undetermined significance (MGUS) or multiple myeloma (MM) in patients with MPN, with details from only a limited number of patient cohorts published [7]. Remarkably, to date, there have been no reported instances of the concurrent diagnosis of essential thrombocythemia (ET) and SMM. In this report, we present a case of synchronous concurrent SMM and ET and provide a comprehensive review of the existing literature.

Case Presentation

An 82-year-old man with a history of hypertension and diabetes was referred to our department for the management of thrombocytosis. Physical examination revealed no remarkable findings, and there was no evidence of lymphadenopathy or hepatosplenomegaly. Laboratory results indicated a platelet count of 946 g/L, hemoglobin of 12.5 g/dL, and a white blood cell count of 6.4 g/L. The patient had no systemic symptoms.

Thrombocytosis workup was initiated, initially excluding infections and iron deficiency. The platelet count was notably elevated, suggesting uncommonly high levels for secondary causes of thrombocytosis.

The patient’s chemistry panel results are shown in Table 1. Monoclonal protein was measured at 36.6 g/L. Serum immunofixation electrophoresis revealed IgG lambda gammopathy. Free light chain lambda was elevated, and kappa was normal.

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Dr Vincelette on MYC Expression in Myelofibrosis

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Nicole D. Vincelette, PhD

Nicole D. Vincelette, PhD, postdoctoral fellow, Moffitt Cancer Center, discusses findings from a study investigating the role of MYC expression and S100A9-mediated inflammation in a subgroup of triple-negative myeloproliferative neoplasms (MPNs).

To determine how MYC expression drives MPNs, such as polycythemia vera, essential thrombocythemia, and primary myelofibrosis, Vincelette and colleagues conducted a study in which they generated a mouse model that overexpresses MYC in the stem cell compartment. This analysis demonstrated that MYC overexpression was associated with the mice developing a myelofibrosis-like phenotype, which included anemia, atypical megakaryocytes, splenomegaly, bone marrow fibrosis, liver fibrosis, spleen fibrosis. The mice also experienced adverse clinical outcomes, such as reduced overall survival (OS), compared with wild-type mice, Vincelette says.

Since the MYC-overexpressed mice developed myelofibrosis, the next step of this research was to investigate how MYC drives myelofibrosis, Vincelette explains. Investigators performed single-cell RNA sequencing to compare the bone marrow cells from MYC-overexpressed and wild-type mice. MYC overexpression correlated with upregulation of the S100A9 protein, which contributes to inflammation and innate immunity, according to Vincelette. Therefore, MYC drives the development of myelofibrosis through S100A9-mediated chronic inflammation. To validate the role of S100A9 downstream of MYC in myelofibrosis, investigators created a mouse model with S100A9 knockout in the presence of MYC overexpression, Vincelette notes. The S100A9 knockout protected against the development of myelofibrosis phenotype in that mouse model, Vincelette emphasizes.

By generating a mouse model that overexpresses S100A9, investigators also determined that S100A9 overexpression alone contributes to the development of myelofibrosis phenotypes, Vincelette says. When investigators treated the MYC-overexpressing mice with the S100A9 inhibitor tasquinimod (ABR-215050), the agent only partially abrogated the myelofibrosis phenotype, meaning the mice had reduced atypical megakaryocytes and splenomegaly. Additionally, the mice developed anemia and no OS difference occurred between tasquinimod and vehicle treatment, potentially because of off-target drug effects, Vincelette concludes.

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The role of inherited genetic variants in rare blood cancer

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January 17, 2024

Researchers from the University of Cambridge, Wellcome Sanger Institute, and collaborators have shown how inherited genetic variants can influence the risk of developing a rare blood cancer.

Large-scale genetic analysis has helped researchers uncover the relationship between cancer-driving genetic mutations and inherited genetic variants in a rare type of blood cancer.

The team combined datasets to understand the impact of cancer-driving spontaneous mutations and inherited genetic variation on the risk of developing myeloproliferative neoplasms (MPN).

Published in Nature Genetics, the study describes how inherited genetic variants can influence whether a spontaneous mutation in a particular gene increases the risk of developing this rare blood cancer.

The analysis will have an impact on current clinical predictions of disease development in individuals.

More research is needed to understand the mechanisms behind how the inherited genetic variants influence the probability of developing rare blood cancer.

In the future, the work could aid drug development interventions that reduce the risk of disease.

Myeloproliferative neoplasms

MPNs are a group of rare and chronic blood cancers, with around 4,000 cases in the UK each year. These occur when the bone marrow overproduces blood cells, resulting in blood clots and bleeding.

MPNs can also progress into other forms of blood cancer.

Genetic risk score

There is a large amount of natural variation between individuals’ blood cells which can affect the amount of blood cells a person has and their traits. This is because different genes can influence blood cell features in an individual.

Researchers take known information about these genes during routine blood tests and analyse the variation to give a genetic risk score. This is how likely that individual is to develop a disease over their lifetime.

MPNs have been linked to random somatic mutations in a gene called JAK2; however, mutated JAK2 is commonly found in the global population. The vast majority of these individuals do not have or go on to develop MPN.

Previous studies identified over a dozen associated inherited genetic variants that increase the risk of MPN. However, these studies do not explain why most individuals do not go on to develop MPN.

Inherited genetic variants can influence risk

The new study combined information on the known somatic driver mutations in MPN inherited genetic variants, and genetic risk scores from individuals with MPN.

They found that the inherited genetic variants that cause natural blood cell variation in the population also impact whether a JAK2 somatic mutation will cause MPN. The team also discovered that individuals with an inherited risk of having a higher blood cell count could display MPN features in the absence of cancer-driving mutations, mimicking disease.

Dr Jing Guo, from the University of Cambridge and the Wellcome Sanger Institute and first author of the study, said: “Our large-scale statistical study has helped fill the knowledge gaps in how variants in DNA, both inherited and somatic, interact to influence complex disease risk.

“By combining these three different types of datasets we were able to get a more complete picture of how these variants combine to cause blood disorders.”

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Fedratinib Improves Myelofibrosis Management Compared With Ruxolitinib

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By Patrick Daly – Last Updated: January 17, 2024

Treatment with fedratinib, a Janus kinase inhibitor (JAKi), induced superior spleen volume reduction (SVR) and symptom response rates compared with best available therapy in patients with myelofibrosis (MF) who previously received ruxolitinib, according to data from the open-label phase III FREEDOM2 study, presented at the 65th American Society of Hematology Annual Meeting & Exposition.

“Most patients on best available therapy received ruxolitinib, highlighting a need for an alternative JAKi,” stated lead author of the study, Claire Harrison, MD, FRCP, from Guy’s and St. Thomas’ NHS Foundation Trust in London, England.

The FREEDOM2 trial enrolled patients aged 18 years or older with primary, post-polycythemia vera, or post-essential thrombocythemia MF with splenomegaly who were intolerant or refractory to, or relapsed after ruxolitinib. The primary endpoint was SVR ≥35% (SVR35) at the end of the sixth 28-day cycle.

Fedratinib for Myelofibrosis Treatment Superior to Ruxolitinib

In total, 201 patients were randomized to fedratinib (n=134) or best available therapy (n=67). The cohort had a median age of 70 (interquartile range, 64-74), 52.2% were male, 54.7% had primary MF, and 76.1% had a Dynamic International Prognostic Scoring System risk score of intermediate-2.

Overall, 70.1% of patients in the best available therapy arm received ruxolitinib, 10.4% received hydroxyurea, and 7.5% received ruxolitinib plus hydroxyurea. Additionally, 46 (68.7%) patients in the best available therapy arm crossed over to fedratinib after either disease progression or the sixth cycle response assessment.

With a median follow-up of 15 months at the data cutoff, researchers reported the fedratinib group had a significantly higher SVR35 rate of 35.8% at the end of cycle six compared with best available therapy at 6.0% (P<.0001). Fedratinib also yielded superior SVR ≥25% at the cycle six assessment and superior SVR35 at any point during treatment. The rate of symptom response at the end of cycle six was 34.1% with fedratinib versus 16.9% with best available therapy (P=.0033).

In short, “fedratinib demonstrated superior SVR and symptom response rates compared with [best available therapy]” in patients with MF and prior ruxolitinib treatment, concluded Dr. Harrison and colleagues.

Reference

Harrison CN, Mesa RA, Talpaz M, et al. Efficacy and safety of fedratinib in patients with myelofibrosis previously treated with ruxolitinib: results from the phase 3 randomized FREEDOM2 study. Abstract #3204. Presented at the 65th ASH Annual Meeting & Exposition; December 9-12, 2023; San Diego, California.

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CALR-Mutated Essential Thrombocythemia Associated With Higher Progression to Myelofibrosis Risk

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CALR mutations in essential thrombocythemia are associated with lower thrombosis risk and higher risk of progression to myelofibrosis (MF) compared with other driver mutations, according to a recent study.

The study was led by Katie Erdos, a Research Program Assistant at Weill Cornell Medicine’s Richard T. Silver, MD Myeloproliferative Neoplasms Center, and presented at the 65th American Society of Hematology Annual Meeting & Exposition.

Erdos and colleagues conducted the study to evaluate the impact of driver mutations on the risks of thromboembolic events, disease progression, and patient mortality.

Of 338 total patients, 216 (64%) were positive for JAK2V617F, 85 (25%) were positive for CALR, 19 (6%) were positive for MPL, and 18 were (5%) triple-negative (TN). Red cell parameters were slightly higher in patients with JAK2V617F mutations (P<0.001), white blood cell count was highest in TN patients (P=0.012), and platelet count did not significantly vary across mutation groups (P=0.064).

The 20-year thrombosis-free survival was 71% for JAK2V617F, 100% for CALR, 90% for MPL, and 83% for TN (P=0.0027). The 20-year MF-free survival was 87% for JAK2V617F, 48% for CALR, 65% for MPL, and 94% for TN (P=0.00053). Meanwhile, the 20-year overall survival was 76% for JAK2V617F, 86% for CALR, 89% for MPL, and 90% for TN (P=0.66).

“Our findings reinforce the need for long-term data to guide therapy for ET based not only on the near-term thrombotic risk, but also on the long-term risk of progression,” wrote Erdos and colleagues.

Reference

Erdos K, Lee N, Lebbe A, et al. Low thrombosis risk CALR mutations confer higher risk of essential thrombocythemia progression. Abstract #1819. Presented at the 65th ASH Annual Meeting & Exposition; December 9-12, 2023; San Diego, California.

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Inherited polygenic effects on common hematological traits influence clonal selection on JAK2V617F and the development of myeloproliferative neoplasms

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Jing Guo, Klaudia Walter, Pedro M. Quiros, Muxin Gu, E. Joanna Baxter, John Danesh, Emanuele Di Angelantonio, David Roberts, Paola Guglielmelli, Claire N. Harrison, Anna L. Godfrey, Anthony R. Green, George S. Vassiliou, Dragana Vuckovic, Jyoti Nangalia & Nicole Soranzo

Nature Genetics (2024)

Abstract

Myeloproliferative neoplasms (MPNs) are chronic cancers characterized by overproduction of mature blood cells. Their causative somatic mutations, for example, JAK2V617F, are common in the population, yet only a minority of carriers develop MPN. Here we show that the inherited polygenic loci that underlie common hematological traits influence JAK2V617F clonal expansion. We identify polygenic risk scores (PGSs) for monocyte count and plateletcrit as new risk factors for JAK2V617F positivity. PGSs for several hematological traits influenced the risk of different MPN subtypes, with low PGSs for two platelet traits also showing protective effects in JAK2V617F carriers, making them two to three times less likely to have essential thrombocythemia than carriers with high PGSs. We observed that extreme hematological PGSs may contribute to an MPN diagnosis in the absence of somatic driver mutations. Our study showcases how polygenic backgrounds underlying common hematological traits influence both clonal selection on somatic mutations and the subsequent phenotype of cancer.

Main

Myeloproliferative neoplasms (MPNs) are rare chronic hematological cancers characterized by the overproduction of mature blood cells leading to elevated blood cell parameters. They are typically driven by somatically mutated JAK2-mediated, calreticulin (CALR)-mediated or MPL-mediated clonal expansion1. JAK2 mutations are found in both polycythemia vera (PV) and essential thrombocythemia (ET), which are distinct but overlapping MPNs characterized by increased numbers of red blood cells and platelets, respectively. Mutant JAK2 is commonly detectable in 0.1–3% of the healthy population as clonal hematopoiesis (CH)2,3,4,5,6,7, with the vast majority of carriers not meeting or going on to develop disease-defining characteristics of MPN. Little is understood about why only a minority of individuals with mutated JAK2 develop more severe hematological manifestations of MPN and the factors that influence blood count heterogeneity in MPNs.

The 46/1 haplotype near JAK2 is a known germline risk factor for MPNs in the population8. Genome-wide association studies (GWAS) have identified additional disease-associated germline risk loci, estimating the liability-scale heritability of MPNs based on common single-nucleotide polymorphisms (SNPs) to be ~6.5% (refs. 9,10,11). However, these germline risk loci insufficiently explain the phenotypic heterogeneity observed within MPNs and in JAK2-mutated healthy carriers.

Blood cell traits vary widely in the healthy population. The genetic architecture underlying these traits is highly polygenic, with more than 11,000 independently associated genetic variants discovered so far12,13,14. These genome-wide associated variants, when combined in polygenic scores (PGSs), explain a large proportion of phenotypic variance among healthy individuals (from 2.5% for basophil count to 27.3% for mean platelet volume) and are associated with multiple common diseases and rare hematological disorders14. We hypothesized that a genetic burden of germline variants associated with extreme hematological traits could influence phenotypic heterogeneity in association with mutated JAK2, by influencing the clonal dynamics of mutant JAK2 and/or modifying its downstream consequences. In this study, we integrate information on somatic driver mutations, germline genetic variants associated with MPNs, and CH and hematological trait PGSs to study how inherited polygenic variation underlying blood cell traits influences clonal selection on mutated JAK2 and MPN disease phenotypes (Supplementary Fig. 1).

Results

Inherited polygenic contribution to JAK2 V617F positivity

One in 30 healthy individuals reportedly harbors JAK2V617F in their blood, as determined using sensitive assays6. The majority of such individuals have low levels of JAK2V617F and do not meet clinical criteria for MPN due to the absence of elevated blood cell parameters. We wished to understand whether inherited polygenic loci that underlie blood cell traits influence the strength of clonal selection on JAK2V617F.

We studied the germline characteristics of individuals in UK Biobank (UKBB) with and without JAK2V617F. From 162,534 genetically unrelated individuals of European ancestry within the UKBB whole-exome sequencing cohort (‘200k UKBB-WES cohort’; Methods), we identified 540 individuals with one or more mutant reads for JAK2V617F (0.3%, median variant allele frequency (VAF) = 0.056, range = 0.019–1; Supplementary Fig. 2; ‘UKBB-JAK2V617F cohort’). The lower rate of JAK2V617F in the UKBB-WES cohort compared to other population studies6,7 could be explained by its low sequencing coverage (21.5× depth), as also reported previously15 (Supplementary Fig. 3). As expected, there was some overlap among individuals with JAK2V617F and those with a diagnosis of MPN. Of the 423 individuals labeled with a diagnosis of MPN (156 with ET, 161 with PV and 106 with myelofibrosis (MF)), 72 were positive for JAK2V617F (Supplementary Table 1).

We built PGSs for 29 blood cell traits covering a wide range of hematopoietic parameters (Supplementary Table 2). Blood cell trait-specific PGSs were then weighted (by effect size) by the sum of all common (minor allele frequency (MAF) > 0.01) variants that were independently associated with a blood cell trait at genome-wide significance (P < 5 × 10−8) in UKBB (Methods)14. To assess the association between hematological PGSs and small (VAF < 0.1, n = 397) or large (VAF ≥ 0.1, n = 143) JAK2V617F clones, we used multinomial logistic regression including PGSs for each hematological trait (units of s.d.), together with previously reported germline sites associated with MPN9 and CH16 (PGSMPN and PGSCH) as covariates. To account for the recognized predisposition risk for MPN driven by the JAK2 46/1 haplotype8, we computed two PGSMPN scores, separating rs1327494 (tagging the JAK2 46/1 haplotype; PGSMPN–46/1) from nontagging JAK2 variants (PGSMPN-other). We found a negative association between the PGSs for both mean reticulocyte volume (PGSMRV) and immature reticulocyte fraction (PGSIRF) and small JAK2V617F clones (P = 6.2 × 10−4 and 0.0018, false discovery rate (FDR) < 0.05; Supplementary Table 3). We also found significant positive associations with small JAK2V617F clones for the PGSs of plateletcrit (PGSPCT) and monocyte count (PGSMONO) (P = 9.5 × 10−4 and 0.0036, FDR < 0.05). Germline predisposition to high MONO and PCT values was also positively associated with large JAK2V617F clones at modest significance (P = 0.033 and 0.0022, FDR-adjusted P = 0.31 and 0.064; Fig. 1a). Repeating the analysis above excluding MPN cases still demonstrated a significant association between PGSPCT or PGSMONO and small JAK2V617F clones (P < 0.013, Bonferroni corrected; Supplementary Table 4), suggesting that the inherited effects on JAK2V617F were not driven by the subset of MPN cases. These associations were independent of the known germline risk loci associated with MPN and CH (Supplementary Table 3). Validating these associations in the full UKBB-WES dataset (n = 799 and 326 for small and large clones, respectively, and n = 338,919 for controls), we again replicated the associations between PGSPCT and small JAK2V617F clones and between PGSMONO and large JAK2V617F clones at FDR < 0.05 (PCT: odds ratio (OR) = 1.15 (change in odds per increase of 1 s.d. in PGS), 95% confidence interval (CI) = 1.07–1.24, P = 1.4 × 10−4; MONO: OR = 1.20, 95% CI = 1.07–1.34, P = 0.0014; Supplementary Table 5).

Data are presented as ORs (solid dots) with 95% CIs (error bars). a, PGSs with significant associations with small clone size of JAK2V617F (FDR < 0.05) compared to the CH and MPN PGSs (Supplementary Table 3). OR was defined as the change in odds per increase of 1 s.d. in PGS. b, Causal effects estimated by four MR methods for the exposure traits whose PGSs were found to have significant predisposition risk for JAK2V617F positivity (Supplementary Table 7). OR was defined as the change in odds per increase of 1 s.d. in exposure. The MR results shown were based on GWAS summary statistics for JAK2V617F positivity in the full UKBB (Supplementary Fig. 4). Results based on the main discovery set (200k UKBB-WES cohort) are shown in Supplementary Table 6. The MR result for MRV was not available due to a lack of corresponding GWAS summary data in INTERVAL.

To understand the causal relationship among these associations, we undertook Mendelian randomization (MR) analyses with GWAS estimates for the exposure (blood traits) and the outcome (JAK2V617F positivity; Supplementary Fig. 4) obtained from two independent sources. We used genetic instruments for hematological traits identified from UKBB, with effect size estimates from INTERVAL17 (n = 30,305), an external independent cohort. MRV was excluded due to a lack of data in INTERVAL. Both PCT and MONO showed significant causality on the presence of a JAK2V617F clone based on inverse variance-weighted (IVW)18 MR and demonstrated consistent effect estimates using two other MR methods (simple median and weighted median), suggesting that higher MONO and higher PCT values cause a detectable JAK2V617F clone (Supplementary Table 6).

Extending this analysis to the full UKBB-WES cohort (JAK2V617F, n = 1,125; controls, n = 338,919) validated these causal associations with greater estimation accuracy (PCT: ORIVW = 1.52, 95% CI = 1.29–1.78, P = 3.0 × 10−7; MONO: ORIVW = 1.3, 95% CI = 1.15–1.49, P = 4.6 × 10−5; Fig. 1b and Supplementary Table 7). The IVW method of MR (Methods) assumes that the germline loci that drive MONO and PCT have no direct causal effect on driving a JAK2V617F clone (that is, there are no direct causal effects of the genetic instruments on the outcome). We found no evidence of pleiotropy using the MR-Egger19 test; the estimated intercept was not significantly different from zero with P = 0.84 and P = 0.90 for PCT and MONO, respectively. The causal relationship was also significant for PCT and MONO (P < 0.05; Supplementary Table 7 and Supplementary Fig. 5). Additionally, the estimates were not biased by any potential pleiotropic outlier variants and were highly consistent with outlier-corrected causal estimates (Supplementary Table 7 and Methods). Lastly, to ensure the results were not confounded by the possibility that the genetic loci used as instruments for MR directly promoted the outcome (that is, JAK2V617F positivity), we repeated the analysis excluding genetic instruments associated with JAK2V617F positivity (Passociation < 10−6), as well as those that correlated with JAK2V617F variants (that is, those variants and JAK2V617F variants are in linkage disequilibrium (LD) r2 > 0.01) or were in proximity to JAK2V617F variants (in the 10-Mb region centered on each variant), and found no major changes (Supplementary Table 8). Importantly, any reverse causal effect we detected for MONO and PCT was subtle and with pleiotropic effects (PEgger > 0.05 and PEgger-intercept < 0.05; Supplementary Table 9 and Supplementary Fig. 6).

Overall, the association results combined with MR suggest that higher PCT and MONO are causal for the presence of a JAK2V617F clone. This would also explain why individuals with germline predisposition to high PCT and MONO are also more likely to harbor a JAK2V617F clone. Given that acquisition of somatic mutations in blood is largely stochastic in healthy populations20, our data suggest that genetically predicted PCT and MONO influence clonal selection on nascent JAK2V617F cells to promote mutation acquisition.

Germline contribution to blood cell count variation in MPNs

Having shown that polygenic germline loci can predispose to JAK2 clone positivity through their influence on blood cell trait levels, we next studied the contribution of these inherited sites to clinical phenotypes of MPN. We first considered the four blood cell traits that are used to define MPN subcategories clinically21 as follows: hemoglobin concentration (HGB) (g dl–1 divided by 10), hematocrit (HCT) (%), platelet count (PLT) (×109 divided by 1,000) and white blood cell count (WBC) (×109 divided by 100). We used SNP arrays to measure genome-wide polymorphism in an MPN cohort of 761 patients (PV, n = 112; ET, n = 581; MF, n = 68), in whom diagnostic blood cell counts were available and mutation status for a panel of cancer-associated genes (Fig. 2a) had previously been characterized22.

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GB2064 Displays Preliminary Efficacy, Tolerability in Myelofibrosis

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January 16, 2024

Kyle Doherty

The potential first-in-class, oral, lysyl oxidase-like 2 (LOXL2) inhibitor GB2064 displayed efficacy with a generally acceptable tolerability profile in the treatment of patients with myelofibrosis, according to topline findings from the phase 2a MYLOX-1 trial (NCT04679870).1

Among evaluable patients with myelofibrosis who were treated with GB2064 monotherapy for a minimum of 6 months (n = 10), 6 experienced a reduction in collagen fibrosis of the bone marrow of at least 1 grade. All patients who achieved this reduction in bone marrow fibrosis displayed stable hematological parameters, including hemoglobin, white blood cell count, and platelet count. This indicates the agent’s potential impact on disease progression and disease-modifying capabilities. At 6 months of treatment, 1 patient experienced a reduction in spleen volume of at least 35%, 2 reduced their Total Symptom Score (TSS) by over 50%, and another patient experienced an anemia response.

“It is exciting and encouraging to see that the data from the MYLOX-1 trial affirms the safety and effectiveness of LOXL-2 inhibition in the challenging landscape of myelofibrosis,” Claire Harrison, MD, FRCP, FRCPath, chair of the Safety Review Committee for the MYLOX-1 trial, a professor of myeloproliferative neoplasms, and the clinical director of Guy’s and St Thomas’ NHS Foundation Trust in London, England, said in a press release. “I am especially intrigued by the unique observed improvements in bone marrow collagen fibrosis, showcasing the targeted impact on a crucial aspect of this relentless disease.”

MYLOX-1 was an open-label, single-arm study that enrolled adult patients with primary or secondary myelofibrosis who were ineligible, refractory, or intolerant to treatment with a JAK inhibitor. Patients had intermediate-2 or high-risk disease by the Dynamic International Prognostic Scoring System-plus, or low-risk disease with symptomatic splenomegaly. Eligible patients were also required to have an ECOG performance status of 2 or less, not be receiving JAK inhibitor therapy, display required baseline laboratory counts, and have a documented history of transfusion records in the preceding 12 weeks to day 1 of study treatment.2

All patients on the study treatment received 1000 mg of oral GB2064 twice daily for 9 months. Patients underwent bone marrow biopsies at the beginning of the trial and again at 3, 6 and 9 months. The primary end point was the safety and tolerability of GB2064; key secondary end points included evaluating hematological parameters and the direct anti-fibrotic activity of GB2064 by blocking LOXL2 in an indication that allows for repeated tissue biopsies.1,2

The study dosed a total of 18 patients with myelofibrosis. Most patients (61%) had previously received the JAK inhibitor ruxolitinib (Jakafi); 8 of these patients were refractory to JAK inhibitor therapy and 3 were intolerant.1

Additional assessment of bone marrow biopsies in MYLOX-1 revealed that GB2064 penetrated the bone marrow and could exert its anti-fibrotic effect directly in the disease compartment. Additionally, the agent displayed systemic target engagement by binding to LOXL2 in plasma. Four patients who experienced clinical benefit with GB2046, as determined by the treating physician, have entered the extension phase of MYLOX-1. Notably, 1 of these patients has received treatment for over 30 months.

GB2064 displayed a tolerable safety profile, with 8 of the 18 dosed patients completing treatment in the core phase of MYLOX-1. The remaining 10 patients discontinued treatment due to adverse effects or progressive disease. The most common any-grade treatment-related adverse effects were manageable with standard therapy and gastrointestinal in nature. The lone treatment-related serious adverse effect was a case of fall, which was determined to be possibly related to GB2064 treatment.

“We believe that the topline results from the MYLOX-1 trial reaffirm the anti-fibrotic activity observed in the intermediate assessment of the trial announced in September 2022,” Hans T. Schambye, MD, PhD, the president and chief executive officer of Galecto, said in the press release. “We are very excited with the proof of principle achieved with GB2064, showcasing its strong anti-fibrotic impact in a very challenging patient population. The encouraging topline results from the MYLOX-1 trial reinforce our confidence in GB2064’s potential as a transformative therapy for various cancers and a range of fibrotic diseases, but we will not make any decisions relating to funding additional trials with GB2064 until we complete our previously announced strategic alternative process.”

In September 2023, Galecto announced that it completed a review of its business and would conduct a comprehensive exploration of strategic alternatives focused on maximizing shareholder value. Galecto did not set a timetable for completion of the evaluation and said it did not intend to disclose further developments or guidance on the status of its programs unless it determined that further disclosure is appropriate or necessary.3

References

  1. Topline results from MYLOX-1 trial demonstrate reduction in fibrosis of the bone marrow in patients with myelofibrosis. News release. Galecto, Inc. December 21, 2023. Accessed January 16, 2024. https://www.biospace.com/article/releases/topline-results-from-mylox-1-trial-demonstrate-reduction-in-fibrosis-of-the-bone-marrow-in-patients-with-myelofibrosis/
  2. A study to evaluate the safety, tolerability, pharmacokinetics and pharmacodynamics of oral GB2064 in participants with myelofibrosis. ClinicalTrials.gov. Updated May 6, 2023. Accessed January 16, 2024. https://clinicaltrials.gov/study/NCT04679870
  3. Galecto announces plans to explore strategic alternatives. News release. Galecto, Inc. September 26, 2023. Accessed January 16, 2024. https://ir.galecto.com/news-releases/news-release-details/galecto-announces-plans-explore-strategic-alternatives

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