Thromboembolic complication is common in severe coronavirus disease 2019 (COVID-19), leading to an investigation into the presence of prothrombotic antibodies akin to those found in heparin-induced thrombocytopenia (HIT). In a study of samples from 130 hospitalized patients, collected 3.6 days after COVID-19 diagnosis, 80% had immunoglobulin G (IgG) antibodies recognizing complexes of heparin and platelet factor 4 (PF4; PF4/H), and 41% had antibodies inducing PF4-dependent P-selectin expression in CpG oligodeoxynucleotide-treated normal platelets. Unlike HIT, both PF4/H-reactive and platelet-activating antibodies were found in patients with COVID-19 regardless of recent heparin exposure. Notably, PF4/H-reactive IgG antibodies correlated with those targeting the receptor-binding domain (RBD) of the severe acute respiratory syndrome coronavirus 2 spike protein. Moreover, introducing exogenous RBD to or removing RBD-reactive IgG from COVID-19 plasma or IgG purified from COVID-19 plasma significantly reduced their ability to activate platelets. RBD-specific antibodies capable of platelet activation were cloned from peripheral blood B cells of patients with COVID-19. These antibodies possessed sequence motifs in the heavy-chain complementarity-determining region 3 (HCDR3), resembling those identified in pathogenic HIT antibodies. Furthermore, IgG+ B cells having these HCDR3 signatures were markedly expanded in patients with severe COVID-19. Importantly, platelet-activating antibodies present in patients with COVID-19 were associated with a specific elevation of platelet α-granule proteins in the plasma and showed a positive correlation with markers for inflammation and tissue damage, suggesting a functionality of these antibodies in patients. The demonstration of functional and structural similarities between certain RBD-specific antibodies in patients with COVID-19 and pathogenic antibodies typical of HIT suggests a novel mechanism by which RBD-specific antibodies might contribute to thrombosis in COVID-19.

Haploidentical hematopoietic cell transplantation (haplo-HCT) is an increasingly used treatment for hematologic malignancies. Although posttransplant cyclophosphamide (PtCy) has improved graft-versus-host disease (GVHD) prophylaxis in haplo-HCT, patients continue to experience life-threatening complications. Interferon gamma and interleukin-6 are central in the pathophysiology of GVHD and cytokine release syndrome (CRS), and both cytokines signal through Janus kinase 1 (JAK-1). We tested the effect of adding the JAK-1 selective inhibitor, itacitinib, to PtCy-haplo-HCT to mitigate these complications and improve overall survival (OS). This open-label, single-arm study evaluated the safety and efficacy of itacitinib combined with standard GVHD prophylaxis after haplo-HCT. A total of 42 patients were treated with itacitinib 200 mg daily from day -3 through +100 or +180, followed by a taper. Itacitinib resulted in low CRS grades, all patients had grade 0 (22%) or grade 1 (78%) CRS and there were no cases of grade 2 to 5 CRS. There were no cases of primary graft failure. No patients developed grade 3 to 4 acute GVHD (aGVHD) through day +180. The cumulative incidence of grade 2 aGVHD at day +100 was 21.9%. The 1-year cumulative incidence of moderate or severe chronic GVHD was 5%. The cumulative incidence of relapse at 2 years was 14%. OS at 1 year was 80%. The cumulative incidence of nonrelapse mortality (NRM) at day 180 was 8%. Itacitinib, when added to standard GVHD prophylaxis, was well tolerated and resulted in low rates of CRS, acute and chronic GVHD, and NRM, and encouraging rates of GVHD-free relapse-free survival and OS after haplo-HCT. This trial was registered at www.ClinicalTrials.gov as #NCT03755414.

The level of frailty, according to the International Myeloma Working Group frailty index, is highly dynamic during antimyeloma treatment. Dynamic frailty assessment improved the prediction of survival and early mortality compared with the prognostic value of static frailty level at baseline.

Myeloid differentiation primary response protein 88 (MYD88) is a key adaptor molecule in the signaling pathways of toll-like receptor and interleukin-1 receptor. A somatic mutation resulting in a leucine-to-proline change at position 265 of the MYD88 protein (MYD88 L265P) is one of the most prevalent oncogenic mutations found in patients with hematological malignancies. In this study, we used high-throughput screening to identify lasalocid A as a potent small molecule that selectively inhibited the viability of lymphoma cells expressing MYD88 L265P and the associated activation of NF-κB. Further investigations using CRISPR-CRISPR-associated protein 9 genetic screening, proteomics, and biochemical assays revealed that lasalocid A directly binds to the MYD88 L265P protein, enhancing its interaction with the ubiquitin ligase RNF5. This interaction promotes MYD88 degradation through the ubiquitin-dependent proteasomal pathway, specifically in lymphomas with the MYD88 L265P mutation. Lasalocid A exhibited strong antitumor efficacy in xenograft mouse models, induced disease remission in ibrutinib-resistant lymphomas, and showed synergistic activity with the B-cell lymphoma 2 inhibitor venetoclax. This study highlights the potential of inducing MYD88 L265P degradation using small molecules, offering promising strategies for treating lymphomas that harbor the MYD88 L265P mutation.

Macrophages execute core functions in maintaining tissue homeostasis, in which their extensive plasticity permits a spectrum of functions from tissue remodeling to immune defense. However, perturbations to tissue-resident macrophages during disease, and the subsequent emergence of monocyte-derived macrophages, can hinder tissue recovery and promote further damage through inflammatory and fibrotic programs. Gaining a fundamental understanding of the critical pathways defining pathogenic macrophage populations enables the development of targeted therapeutic approaches to improve disease outcomes. In the setting of chronic graft-versus-host disease (cGVHD), which remains the major complication of allogeneic hematopoietic stem cell transplantation, colony-stimulating factor 1 (CSF1)-dependent donor-derived macrophages have been identified as key pathogenic mediators of fibrotic skin and lung disease. Antibody blockade of the CSF1 receptor (CSF1R) to induce macrophage depletion showed remarkable capacity to prevent fibrosis in preclinical models and has subsequently demonstrated impressive efficacy for improving cGVHD in ongoing clinical trials. Similarly, macrophage depletion approaches are currently under investigation for their potential to augment responses to immune checkpoint inhibition. Moreover, both monocyte and tissue-resident macrophage populations have recently been implicated as mediators of the numerous toxicities associated with chimeric antigen receptor T-cell therapy, further highlighting potential avenues of macrophage-based interventions to improve clinical outcomes. Herein, we examine the current literature on basic macrophage biology and contextualize this in the setting of cellular and immunotherapy. Additionally, we highlight mechanisms by which macrophages can be targeted, largely by interfering with the CSF1/CSF1R signaling axis, for therapeutic benefit in the context of both cellular and immunotherapy.

Inflammatory form of Waldenström macroglobulinemia (iWM) predicts outcomes after immuno-chemotherapy and Bruton tyrosine kinase inhibitors, but its origin is unknown. Here, we unravel increased clonal hematopoiesis in patients with iWM (61% vs 23% in noninflammatory WM), suggesting a contribution of environmental cells to iWM.

Nearly half of patients with multiple myeloma (MM) have hyperdiploidy (HMM) at diagnosis. Although HMM occurs early, the mutational processes before and after hyperdiploidy are still unclear. Here, we used 72 whole-genome sequencing samples from patients with HMM and identified pre- and post-HMM mutations to define the chronology of the development of hyperdiploidy. An MM cell accumulated a median of 0.56 mutations per megabase before HMM, and for every clonal pre-HMM mutation, 1.21 mutations per megabase accumulated after HMM. This analysis using mutations before and after hyperdiploidy shows that hyperdiploidy happens after somatic hypermutation. Prehyperdiploidy mutations are activation-induced cytidine deaminase and age/clock-like signature driven, whereas posthyperdiploidy mutations are from DNA damage and APOBEC. Interestingly, the first hyperdiploidy event occurred within the first 3 decades of life and took a decade to complete. Copy number changes affecting chromosomes 15 and 19 occurred first. Finally, mutations before initiating event affected chromosomes at different rates, whereas post-initiating event mutational processes affect each chromosome equally.

CD70 has emerged as a promising target in acute myeloid leukemia (AML), and we have previously demonstrated the potency of an optimized CD70-targeted ligand-based chimeric antigen receptor (CAR). However, here, we identify in vivo CD70 antigen escape as a limitation of single-antigen targeting. Combination targeting of CD70 and CD33 may overcome AML antigen heterogeneity. We hypothesized that modifying our CD70 CAR platform to secrete a bispecific T-cell engaging antibody molecule (TEAM) targeting CD33 (7033) would create a therapeutic window whereby AML heterogeneity could be addressed without increasing tissue toxicity. We found that CD33 TEAMs mediated specific cytotoxicity across AML cell lines, including CD33 or CD70 single-antigen knockout tumors. 7033 CAR T cells eradicated tumor in an in vivo mixed tumor model of CD70 antigen escape and outperformed the previously optimized CD70 CAR in a patient-derived xenograft. In vivo gene expression profiling of CAR T cells revealed enhanced 7033 CAR T-cell pathway scoring for persistence, activation, and T-cell receptor signaling. Additionally, CD33 TEAMs successfully redirected T cells isolated from patients with AML to activate, secrete cytokines, and kill tumor targets despite exposure to substantial prior cytotoxic therapies. In summary, our findings demonstrate the feasibility of our 7033 CAR to overcome AML heterogeneity and leverage the bystander T cells of patients; this approach warrants further study in patients with this dire clinical need.

Detection of light chain (LC) monoclonal gammopathies (MGs) traditionally relies on serum free LC (FLC) κ, λ, and their ratio (κ/λ) reference ranges based on a mostly White population. We investigated FLC values in a racially diverse population by screening 10 035 individuals for heavy chain MG, identifying 9028 negative cases whose FLC were measured. Participants included 4149 from the PROMISE study (United States, n = 2383; South Africa, n = 1766) and 4879 from the Mass General Brigham Biobank, with 44% self-identifying as Black. Using standard FLC reference ranges, 1074 of 10 035 individuals (10.7%) were diagnosed with LC monoclonal gammopathy of undetermined significance (MGUS), with 99% being κ-restricted. In the United States, 14.8% of Black and 4% of White individuals were diagnosed (P < .01). Among US participants of African (AFR) and European (EUR) genetic ancestry, 14.4% AFR and 2.9% EUR were diagnosed (P < .01). Among South Africans (100% Black), 27.8% were diagnosed using standard ranges. To avoid overdiagnosis, we propose a new κ/λ ratio reference range (0.686 to 2.10) for populations of AFR descent with normal renal function, with standard values for κ and λ being 7.97 to 77.50 mg/L and 6.20 to 49.20 mg/L, respectively. This reduces LC-MGUS overdiagnosis by 91% (10.7% vs 0.97%). Using the new reference, LC-MGUS accounts for 8.8% of MGUS cases, with 74% being κ-restricted, consistent with LC myeloma rates. These findings highlight the importance of basing disease definitions, such as MGUS, on diverse populations. Adopting our proposed FLC reference values would reduce MGUS overdiagnosis among Black individuals, avoiding unnecessary financial, psychological, and medical consequences. This study includes data from NCT03689595.

We have developed a cost-effective DNA methylation sequencing assay to improve monitoring of clonal hematopoiesis. By inferring cell-type proportions, this method enhances interpretation of clonal trajectories compared with interpretation based on variant allele fraction only.