Acalabrutinib is a Bruton tyrosine kinase inhibitor approved for treatment of chronic lymphocytic leukemia. We present results from ELEVATE-TN (NCT02475681) after median follow-up of 74.5 months. Overall, 535 patients were randomized (acalabrutinib-obinutuzumab, n = 179; acalabrutinib, n = 179; chlorambucil-obinutuzumab, n = 177). Median age was 70 years, 63.0% had unmutated IGHV (uIGHV), 13.6% had del(17p) and/or mutated TP53, and 17% had complex karyotype (CK; ≥3 chromosomal abnormalities). Median progression-free survival (PFS) was not reached (NR) for acalabrutinib-obinutuzumab and acalabrutinib vs 27.8 months for chlorambucil-obinutuzumab (both P < .0001); estimated 72-month overall PFS rates were 78.0%, 61.5%, and 17.2%, respectively. Acalabrutinib-obinutuzumab resulted in improved PFS vs acalabrutinib monotherapy (hazard ratio [HR]: 0.58, P = .0229). Patients with uIGHV, del(17p) and/or mutated TP53, or CK had significantly improved PFS with acalabrutinib ± obinutuzumab vs chlorambucil-obinutuzumab (P < .0001, P ≤ .0009, and P < .0001 for both acalabrutinib-containing arms, respectively). Median overall survival (OS) was NR for all treatments, with significantly longer OS for acalabrutinib-obinutuzumab vs chlorambucil-obinutuzumab (HR: 0.62, P = .0349). Estimated 72-month OS rates were 83.9%, 75.5%, and 74.7% for acalabrutinib-obinutuzumab, acalabrutinib, and chlorambucil-obinutuzumab, respectively. Adverse events (AEs) occurring after >4 years were mostly grade 1-2. Rates of AEs, serious AEs, and events of clinical interest were similar between acalabrutinib-containing arms and consistent with the known safety profiles of acalabrutinib and obinutuzumab. Efficacy and safety of acalabrutinib-containing arms were maintained, with longer PFS in both acalabrutinib arms vs chlorambucil-obinutuzumab including in patients with high-risk features.

FCARH143, an autologous BCMA-targeted CAR-T therapy which incorporates a fully human BCMA-specific scFv and 4-1BB costimulatory domain, was evaluated in a phase 1 trial (NCT03338972) for relapsed/refractory multiple myeloma (RRMM). Patients were stratified by bone marrow (BM) plasma cell involvement (10-30% or >30%) and received lymphodepleting chemotherapy followed by escalating CAR-T cell doses (50×106 to 450×106). The primary endpoint was safety; secondary endpoints were overall response rate (ORR), duration of response (DOR), and progression-free survival (PFS). Among 28 enrolled patients, all underwent leukapheresis and successful CAR-T manufacturing, though three (11%) did not proceed to infusion. The 25 treated patients (median age 64 years) had a median of eight prior therapies, 80% were triple-class refractory, and 44% had extramedullary disease (EMD). Cytokine release syndrome (CRS) occurred in 84% (8% grade 3-4, no grade 5), and neurotoxicity in 24% (12% grade 3, no grade 4-5). No treatment-related deaths occurred. At a median follow-up of 67.3 months, treated patients had an ORR of 100%, including a stringent complete response in 64%. Median PFS and overall survival (OS) were 15.5 and 32.1 months, respectively. In an intention-to-treat analysis (median follow-up 69.6 months), the ORR was 89.3%, and OS was 30.2 months. FCARH143 demonstrated potent anti-myeloma activity with a 100% response rate and manageable toxicity, independent of disease burden or cytogenetic risk. Further evaluation in high-risk RRMM is warranted.

Lineage switch (LS), defined as the immunophenotypic transformation of acute leukemia, has emerged as a mechanism of relapse following antigen-targeted immunotherapy which is associated with dismal outcomes. Through an international collaborative effort, we identified cases of LS following a host of antigen-targeted therapies (e.g., CD19, CD22, CD38 and CD7), described how LS was diagnosed, reviewed treatment approaches, and analyzed overall outcomes for this form of post-immunotherapy relapse. Collectively, 75 cases of LS were evaluated, including 53 (70.7%) cases of B-ALL to AML, 17 (22.7%) cases of B-ALL to mixed phenotypic acute leukemia (MPAL)/acute leukemias of ambiguous lineage (ALAL), and 5 (6.7%) cases of rare LS presentation (i.e., T-cell ALL to AML). An additional 10 cases with incomplete changes in immunophenotype, referred to as "lineage drift" were also described. With a primary focus on the 70 cases of LS from B-ALL to AML or MPAL/ALAL, LS emerged at a median of 1.5 months (range, 0-36.5 months) post-immunotherapy, with 81.4% presenting with LS within the first 6 months from the most proximal immunotherapy. While the majority involved KMT2A rearrangements (n=45, 64.3%), other rare cytogenetic and/or molecular alterations were uniquely observed. Treatment outcomes were generally poor with < 40% remission rates. The median overall survival following LS diagnosis was 4.8 months. Outcomes were similarly poor for those with rare immunophenotypes of LS or "lineage drift." This global initiative robustly categorizes lineage changes post-immunotherapy and, through enhanced understanding, establishes a foundation for improving outcomes of LS.

The therapeutic success of first line quadruplet (QUAD) induction therapy and autologous stem cell transplantation (ASCT) has reinvigorated an interest in fixed-duration therapy, yet optimal short-term efficacy endpoint for treatment cessation is unknown. Using data from a phase II clinical trial and a prospective institutional database, we tested the predictive performance of 5 short-term efficacy endpoints among 221 patients who received QUAD+ASCT followed by treatment cessation if minimal residual disease (MRD by next generation sequencing) negative for two consecutive timepoints. Efficacy endpoints tested were IMWG-defined stringent complete response (sCR), MRD<10-5 (single datapoint), MRD<10-6, sustained MRD (S-MRD, two consecutive assessments at least 1 year apart) <10-5and S-MRD<10-6. We built five parallel Cox regression models for each efficacy endpoint with progression free survival (PFS) as the outcome. Best fitting models were determined using Akaike's information criterion (AIC) and Heagerty & Zheng C-index. The best fitting model (AIC 417.2, C-stat 0.757) was based on S-MRD<10-5 (HR=0.23, 95% C.I. 0.11-0.47). Similar results were seen for predicting risk of progression/MRD resurgence among 121 patients undergoing MRD-guided treatment cessation. S-MRD<10-5 is the best predictor of PFS and yields best predictive models for risk of MRD resurgence or progression in the setting of fixed duration therapy. NCT03224507.

Inflammation is increasingly recognized as a critical factor in acute myeloid leukemia (AML) pathogenesis. We performed blood-based proteomic profiling of 251 inflammatory proteins in 543 patients with newly diagnosed AML. Using a machine learning model, we derived an 8-protein prognostic score termed the leukemia inflammatory risk score (LIRS). Individual proteins were evaluated in multivariable Cox models, and model performance was assessed by cumulative concordance index. Findings were validated in internal and external cohorts across 2 institutions. Blood-based LIRS significantly outperformed the European LeukemiaNet 2022 risk model and was independently prognostic of overall survival after accounting for known clinical and molecular prognostic factors. Oncostatin M receptor was uniquely identified as the strongest independent predictor of survival, early mortality, and induction chemotherapy response, and further validated in an independent assay. These blood-based biomarkers could have significant clinical implications for risk stratification and prognostication in patients with newly diagnosed AML.

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 MAPK activation in hematopoietic cells. Historically, LCH has been staged according to involvement of "risk organs" (ROpos; bone marrow, liver, spleen), based on risk of death. With improvements in supportive care and efficacy of MAPK pathway inhibitors, LCH patients now rarely die. However, most LCH patients with multi-system 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 pre-therapy peripheral blood mononuclear cells (PBMC) and bone marrow on systemic and CNS outcomes in a cohort of 385 pediatric LCH patients and 115 adults, followed for a median of 4 years (0.02-18). Five year event-free survival was 50.7% for pediatric patients and 32.7% for adult LCH patients. In the pediatric cohort, presence of BRAFV600E PBMC was strongly associated with front-line treatment failure (hazard ratio 7.7). Remarkably, BRAFV600E PBMC at diagnosis also identified patients at the highest risk of developing LCH-ND (hazard ratio 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 (e.g. 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 employed single-cell RNA sequencing (scRNA-seq) of peripheral blood mononuclear cells (PBMCs) from a cohort of 15 patients with iMCD and four 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 (IL-6R) 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 NK/NKT cells through enhanced type II interferon (IFN-II) signaling, while 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 was 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 of 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 anti-tumor 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 newly-diagnosed MM (NDMM) patients for evidence of T cell activation and exhaustion. We applied single-cell multi-omic sequencing and mass cytometry to longitudinal BM and peripheral blood (PB) samples taken from timepoints spanning from diagnosis through induction therapy, autologous stem cell transplant (ASCT), and maintenance therapy. We identified an exhausted-like population that lacked several canonical exhaustion markers, was not significantly enriched in NDMM patients, and consisted of small, nonpersistent clonotypes. We also observed an activated population with increased frequency in the PB of NDMM patients 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 NDMM patients 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 NDMM patients at any timepoint.

Polypeptide blood group antigens, many of which are created by single exofacial amino acid (AA) substitutions, have varying immunogenicities. Why some AA substitutions are more immunogenic than others is little understood. Using AlphaFold2, an artificial intelligence system that predicts three-dimensional protein structure along with multiple other structure analysis programs, we investigated protein structure at sites of AA substitutions that create nine clinically-significant blood group antigens. Based on structure predictions, the AA substitutions that create the four most immunogenic of the nine antigens (K, Jka, Lua, 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 five less immunogenic antigens (c, M, Fya, C, S; 0.13 versus 0.81; P=.003), and higher mean AlphaFold2 confidence score (92.5 versus 48.3; P=.001; scores <50 predict protein disorder). Substitutions creating the five least immunogenic antigens (c, Fya, M, C, S) were all predicted to be in flexible regions with high accessibility, either in surface-accessible loops (C, c) or disordered coils (Fya, M, 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 structure at AA 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 don't significantly extend survival beyond 12 months. BCL-xL has been found to be overexpressed in leucocytes from MPN patients, 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 (PROTAC), in preclinical models of post-MPN AML. We found that BCL2L1, the gene encoding BCL-xL, is expressed at higher levels in post-MPN AML patients compared to those with de novo AML. Single-cell multi-omics analysis revealed that leukemia cells harboring both MPN-driver and TP53 mutations exhibited higher BCL2L1 expression, 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 (iPSC-HPCs), 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 post-MPN AML patients. 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 (MDS) 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 (iPSC)-based models of SRSF2-mutant MDS and primary MDS patient cells, 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 suppression of clonogenic ability by IFNs. Treatment with the proteasome inhibitor bortezomib increased STAT1 protein levels and restored 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.