The success of targeted therapies for hematological malignancies has heralded their potential as both salvage treatment and early treatment lines, reducing the need for high-dose, intensive, and often toxic chemotherapeutic regimens. For young patients with classic Hodgkin lymphoma (cHL), immunotherapies provide the possibility to lessen long-term, treatment-related toxicities. However, suitable therapeutic targets are lacking. By integrating single-cell dissection of the tumor landscape and an in-depth, single-cell-based off-tumor antigen prediction, we identify CD86 as a promising therapeutic target in cHL. CD86 is highly expressed on Hodgkin and Reed-Sternberg cancer cells and cHL-specific tumor-associated macrophages. We reveal CD86-CTLA-4 as a key suppressive pathway in cHL, driving T-cell exhaustion. Cellular therapies targeting CD86 had extraordinary efficacy in vitro and in vivo and were safe in immunocompetent mouse models without compromising bacterial host defense in sepsis models. Our results prove the potential value of anti-CD86 immunotherapies for treating cHL.

Langerhans cell histiocytosis (LCH) is a myeloid neoplastic disorder driven by mitogen-activated protein kinase (MAPK) activation in hematopoietic cells. Historically, LCH has been staged according to involvement of "risk organs" (bone marrow, liver, and spleen), based on risk of death. With improvements in supportive care and efficacy of MAPK pathway inhibitors, patients with LCH now rarely die. However, most patients with LCH with multisystem disease are not cured with current front-line chemotherapy, and treatment failure is associated with long-term morbidity, including LCH-associated neurodegeneration (LCH-ND). In this study, we evaluated the impact of extent of LCH at presentation, tumor genotype, and BRAFV600E in pretherapy peripheral blood mononuclear cells (PBMCs) and bone marrow on systemic and central nervous system outcomes in a cohort of 385 pediatric patients with LCH and 115 adults with LCH, followed up for a median of 4 years (range, 0.02-18 years). Five-year event-free survival was 50.7% for pediatric patients and 32.7% for adult patients with LCH. In the pediatric cohort, presence of BRAFV600E PBMC was strongly associated with front-line treatment failure (hazard ratio [HR], 7.7). Remarkably, BRAFV600E PBMC at diagnosis also identified patients at the highest risk of developing LCH-ND (HR, 23.1). These findings support an updated model of pediatric LCH pathogenesis in which persistence of disease reservoir and cell of origin determine extent of disease and clinical risks. We, therefore, propose a major revision of pediatric LCH diagnostic staging, shifting from focus on historical risk of death to risks of systemic treatment failure and LCH-ND based on lesion location, lesion genotype, and peripheral LCH reservoir (eg, BRAFV600E PBMC).

A deeper understanding of the immune landscape in patients with idiopathic multicentric Castleman disease (iMCD) is essential to establish early prognostic stratification and uncover novel therapeutic targets. We used single-cell RNA sequencing of peripheral blood mononuclear cells (PBMCs) from a cohort of 15 patients with iMCD and 4 healthy controls. To explore the sources of interleukin-6 (IL-6), we included lymph node and bone marrow samples for comparison with PBMCs. Our results indicate that IL-6 primarily originates from the lymph nodes, particularly from activated B cells. Similarly, in peripheral blood, activated B cells are also the main source of IL-6. IL-6 receptor is primarily expressed in monocytes in PBMCs, with CCL monocytes showing the strongest activation of the IL-6 signaling pathway. This suggests that CCL monocytes in iMCD may play an important role in driving peripheral inflammatory storms. CellChat analysis reveals that during disease flares, CCL monocytes interact with specific natural killer (NK)/NKT cells through enhanced type II interferon (IFN-II) signaling, whereas this interaction significantly diminishes during remission, indicating a significant role for IFN-II in the pathogenesis of iMCD. Notably, serum IFN-γ levels positively correlate with both disease severity and treatment resistance, a finding validated by a large independent iMCD cohort. Our findings confirm that the IL-6 pathway remains central to iMCD pathogenesis and highlight a significant role for IFN-II pathway activation in amplifying inflammatory storms. Our findings provide valuable biomarkers for assessing disease severity and identify new therapeutic targets for iMCD.

Dysregulation of the bone marrow (BM) niche in multiple myeloma (MM) alters the composition and state of resident immune cells, potentially impeding antitumor immunity. One common mechanism of immune inhibition in solid tumors is the induction of exhaustion in tumor-specific T cells. However, the extent of T-cell exhaustion is not well characterized in MM. As the specific mechanisms of immune evasion are critical for devising effective therapeutic strategies, we deeply profiled the CD8+ T-cell compartment of patients with newly diagnosed MM (NDMM) for evidence of T-cell activation and exhaustion. We applied single-cell multiomic sequencing and mass cytometry to longitudinal BM and peripheral blood (PB) samples taken from time points spanning from diagnosis to induction therapy, autologous stem cell transplant, and maintenance therapy. We identified an exhausted-like population that lacked several canonical exhaustion markers, was not significantly enriched in patients with NDMM, and consisted of small, nonpersistent clonotypes. We also observed an activated population with increased frequency in the PB of patients with NDMM exhibiting phenotypic and clonal features consistent with homeostatic, cytokine-driven activation. As an orthogonal measurement of T-cell exhaustion, we performed intracellular cytokine staining and found that patients with NDMM lacked functionally exhausted T cells. In summary, there was no evidence of "tumor-experienced" T cells displaying hallmarks of terminal exhaustion and/or antigen-driven activation/expansion in patients with NDMM at any time point.

Polypeptide blood group antigens, many of which are created by single exofacial amino acid substitutions, have varying immunogenicities. Why some amino acid substitutions are more immunogenic than others is little understood. Using AlphaFold2, an artificial intelligence system that predicts 3-dimensional protein structure, along with multiple other structure analysis programs, we investigated protein structure at sites of amino acid substitutions that create 9 clinically significant blood group antigens. Based on structure predictions, the amino acid substitutions that create the 4 most immunogenic of the 9 antigens (K, Jka, Lua, and E) were typically buried or partially buried in rigid, ordered protein regions, usually helices and β-strands. This was reflected by their lower mean relative solvent accessibility (RSA) than the 5 less immunogenic antigens (c, M, Fya, C, and S; 0.13 vs 0.81; P = .003) and higher mean AlphaFold2 confidence score (92.5 vs 48.3; P = .001; scores <50 predict protein disorder). Substitutions creating the 5 least immunogenic antigens (c, Fya, M, C, and S) were all predicted to be in flexible regions with high accessibility, either in surface-accessible loops (C, c) or disordered coils (Fya, M, and S). Scatter plots revealed a positive linear correlation of immunogenicity with confidence score (R2 = 0.826; P = .0007) and percent helix/β-strand in 15-mers centered around the substitution sites (R2 = 0.763; P = .0021) and a negative linear correlation with RSA (R2 = 0.688; P = .0057). Therefore, based on an informatics analysis, the protein secondary and tertiary structures at amino acid substitution sites that create blood group antigens are significant correlates and potential determinants of immunogenicity.

Acute myeloid leukemia (AML) that evolves from myeloproliferative neoplasm (MPN) is known as post-MPN AML. Current treatments do not significantly extend survival beyond 12 months. B-cell lymphoma-extra large (BCL-xL) has been found to be overexpressed in leucocytes from patients with MPN, making it a potential therapeutic target. We investigated the role of BCL-xL in post-MPN AML and tested the efficacy of DT2216, a platelet-sparing BCL-xL proteolysis-targeting chimera, in preclinical models of post-MPN AML. We found that BCL2L1, the gene encoding BCL-xL, is expressed at higher levels in patients with post-MPN AML than in those with de novo AML. Single-cell multiomics analysis revealed that leukemia cells harboring both MPN-driver and TP53 mutations exhibited higher BCL2L1 expression and elevated scores for leukemia stem cell, megakaryocyte development, and erythroid progenitor than wild-type cells. BH3 profiling confirmed a strong dependence on BCL-xL in post-MPN AML cells. DT2216 alone, or in combination with standard AML/MPN therapies, effectively degraded BCL-xL, reduced the apoptotic threshold, and induced apoptosis in post-MPN AML cells. DT2216 effectively eliminated viable cells in JAK2-mutant AML cell lines, induced pluripotent stem cell-derived hematopoietic progenitor cells, primary samples, and reduced tumor burden in cell line-derived xenograft model in vivo by degrading BCL-xL. DT2216, either as a single agent or in combination with azacytidine, effectively inhibited the clonogenic potential of CD34+ leukemia cells from patients with post-MPN AML. In summary, our data indicate that the survival of post-MPN AML is BCL-xL dependent, and DT2216 may offer therapeutic advantage in this high-risk leukemia subset with limited treatment options.

Myelodysplastic syndromes (MDSs) are myeloid malignancies often driven by mutations in genes encoding splicing factors (SFs). How these mutations drive the clonal expansion of MDS stem/progenitor cells to outcompete normal hematopoietic stem/progenitor cells (HSPCs) remains unexplained. Although a role for inflammatory processes in promoting clonal expansion of mutant HSPCs and MDS pathogenesis has been proposed, the specific mechanisms implicated remain incompletely understood. In this study, using human isogenic induced pluripotent stem cell-based models of SRSF2-mutant MDS and primary cells from patients with MDS, we show that the SRSF2 P95L mutation downregulates basal STAT1 expression. STAT1 downregulation dampens interferon (IFN) signaling in MDS stem/progenitor cells, which, unlike normal HSPCs, show resistance to the suppression of clonogenic ability by IFNs. Treatment with the proteasome inhibitor bortezomib increased STAT1 protein levels and restored the sensitivity of SRSF2-mutant cells to inflammatory stimuli. These results indicate that rewiring of STAT1 signaling by SRSF2 mutations blunts responsiveness to IFNs, conferring clonal fitness to SRSF2-mutant HSPCs against normal HSPCs in the presence of inflammatory stimuli. Our study provides a novel mechanistic link between SF mutations and inflammatory dysregulation and suggests proteasome inhibition as a potential strategy to treat MDS with SRSF2 mutations.

HFE-related hemochromatosis induces systemic iron overload. Although extensive studies indicate a pivotal role for iron homeostasis in αβ T-cell immunity, its effect on γδ T cells is unknown. Here, we found a reversal of the Vδ2+/Vδ2- ratio in the γδ T-cell compartment as a feature of hemochromatosis, which is associated with a Vδ2+ population that cannot be enriched by zoledronic acid (ZOL) stimulation, despite evidence of T-cell receptor (TCR)-ligand formation and strong proliferative behavior. In vivo, reactive oxygen species (ROS) production and exhaustion marker expression are significantly increased on Vδ2+ T cells in hemochromatosis compared with healthy individuals. Ex vivo, hemochromatosis donor-derived Vδ2+ cells are hyporesponsive to TCR stimulation in terms of ROS production but significantly increase their paramount expression of exhaustion markers. Fas-Fas ligand coexpression indicates their high susceptibility to activation-induced cell death. Consistent therewith, FeSO4 alone induces Vδ2+ subset-specific proliferation in healthy peripheral blood mononuclear cells comparable to stimulation by ZOL, and blocking experiments identify FeSO4-induced proliferation as BTN3A1/TCR mediated. Pyrophosphate is key for Vδ2+-TCR ligand formation. Iron, by suppressing pyrophosphatase alkaline phosphatase, promotes their stability. Therefore, our data suggest that the transcriptional repression of pyrophosphatases, as under the conditions of iron overload in hemochromatosis in vivo, leads to the constitutive availability of stress-signaling Vδ2+-TCR ligand and permanent TCR triggering in Vδ2+ T cells even under homeostatic conditions, which ultimately results in their subset-specific, activation-induced cell death. A similar phenotype was observed in patients with iron overload due to inborn hemoglobinopathies, suggesting an inverted Vδ2+/Vδ2- ratio in the γδ T-cell compartment as a hallmark of iron overload.

Potentially fatal non-immune effector cell-associated neurotoxicity syndrome neurotoxicities (NINTs) after B-cell maturation antigen-targeted chimeric antigen receptor (CAR) T-cell therapy have been linked to high CAR T-cell expansion. Cyclophosphamide to ablate CAR T cells is an effective strategy to mitigate steroid-refractory NINTs.