Critical Role of Tripartite Fusion and LBD Truncation in Certain RARA- and all RARG-Related Atypical APL.

Atypical acute promyelocytic leukemia (aAPL) presents a complex landscape of retinoic acid receptor (RAR) fusion genes beyond the well-known PML::RARA fusion. Among these, 31 individually rare RARA and RARG fusion genes have been documented, often reported in the canonical X::RAR bipartite fusion form. Intriguingly, some artificially mimicked bipartite X::RAR fusions respond well to all-trans retinoic acid (ATRA) in vitro, contrasting with the ATRA resistance observed in patients. To unravel the underlying mechanisms, we conducted a comprehensive molecular investigation into the fusion transcripts in 27 RARA fusion gene-positive aAPL (RARA-aAPL) and 21 RARG-aAPL cases. Our analysis revealed an unexpected novel form of X::RAR::X or X::RAR::Y-type tripartite fusions in certain RARA- and all RARG-aAPL cases, with shared features and notable differences between these two disease subgroups. In RARA-aAPL cases, the occurrence of RARA 3' splices was associated with their 5' fusion partner genes, mapping across the coding region of helix 11_12 (H11_12) within the ligand-binding domain (LBD), resulting in LBD-H12 or H11_12 truncation. In RARG-aAPL cases, RARG 3' splices were consistently localized to the terminus of exon 9, leading to LBD-H11_12 truncation. Significant differences were also observed between RARA and RARG 5' splice patterns. Our analysis also revealed extensive involvement of transposable elements in constructing RARA and RARG 3' fusions, suggesting transposition mechanisms for fusion gene ontogeny. Both protein structural analysis and experimental results highlighted the pivotal role of LBD-H11_12/H12 truncation in driving ATRA unresponsiveness and leukemogenesis in tripartite fusion-positive aAPL, through a protein allosteric dysfunction mechanism.

Allogeneic CAR-T cells with of HLA-A/B and TRAC disruption exhibit promising antitumor capacity against B cell malignancies.

BACKGROUND: Although chimeric antigen receptor T (CAR-T) cells have been proven to be an effective way of treating B cell malignancies, a lot of patients could not benefit from it because of failure in CAR-T cell manufacturing, disease progression, and unaffordable price. The study aimed to explore universal CAR-T cell products to extend the clinical accessibility. METHODS: The antitumor activity of CRISPR/Cas9-edited allogeneic anti-CD19 CAR-T (CAR-T19) cells was assessed in vitro, in animal models, and in patients with relapsed/refractory (R/R) acute B cell lymphoblastic leukemia (B-ALL) or diffuse large B cell lymphoma. RESULTS: B2M-/TRAC- universal CAR-T19 (U-CAR-T19) cells exhibited powerful anti-leukemia abilities both in vitro and in animal models, as did primary CD19+ leukemia cells from leukemia patients. However, expansion, antitumor efficacy, or graft-versus-host-disease (GvHD) was not observed in six patients with R/R B cell malignancies after U-CAR-T19 cell infusion. Accordingly, significant activation of natural killer (NK) cells by U-CAR-T19 cells was proven both clinically and in vitro. HLA-A-/B-/TRAC- novel CAR-T19 (nU-CAR-T19) cells were constructed with similar tumoricidal capacity but resistance to NK cells in vitro. Surprisingly, robust expansion of nU-CAR-T19 cells, along with rapid eradication of CD19+ abnormal B cells, was observed in the peripheral blood and bone marrow of another three patients with R/R B-ALL. The patients achieved complete remission with no detectable minimal residual disease 14 days after the infusion of nU-CAR-T19 cells. Two of the three patients had grade 2 cytokine release syndrome, which were managed using an IL-6 receptor blocker. Most importantly, GvHD was not observed in any patient, suggesting the safety of TRAC-disrupted CAR-T cells generated using the CRISPR/Cas9 method for clinical application. CONCLUSIONS: The nU-CAR-T19 cells showed a strong response in R/R B-ALL. nU-CAR-T19 cells have the potential to be a promising new approach for treating R/R B cell malignancies.

Bispecific antibodies in immunotherapy for adult acute leukemia: latest updates from the 65th American Society of Hematology 2023 Annual Meeting.

Introduction Bispecific antibodies (BsAbs) represent a novel and potentially effective approach in cancer immunotherapy. These antibodies feature two unique binding domains, enabling them to simultaneously attach to two antigens or two epitopes of a single antigen. Recently, a variety of BsAbs targeting distinct B-cell antigens and myeloid lineage-specific surface markers-such as CD19xCD3, CD38xCD3, and CD123xCD3-have demonstrated promising results in heavily pretreated relapsed/refractory acute lymphoblastic leukemia (R/R ALL) and relapsed/refractory acute myeloid leukemia (R/R AML) patients. Areas covered New trail results were reported by different research groups at the 65th annual meeting of the American Society of Hematology (ASH). We provide a summary of the latest progress in BsAbs for immunotherapy in adult acute leukemia. Expert opinion B-ALL is the most favored leukemia for treatment with BsAbs, unlike T-ALL and AML, which are limited in constructs and results. The clinical application of blinatumomab in the first-line setting, combined with other therapies, has clearly benefited these B-ALL patients, especially older adults, due to its lower toxicity. In the B-ALL relapsed/refractory setting, new combinations with blinatumomab are under investigation, such as PD-1 or CTLA-4 inhibitors. We believe that with more clinical trial results, it is possible that blinatumomab will be used in new clinical indications soon. No novel BsAbs developed for B-ALL have yielded better results.

The novel HLA-DPA1*02:117 allele, identified by Sanger dideoxy nucleotide sequencing in a Chinese individual.

HLA-DPA1*02:117 differs from HLA-DPA1*02:02:02:01 by one nucleotide in exon 2.

Bispecific antibodies targeting CD20xCD3 in immunotherapy for adult B-cell lymphoma: insights from the 65th American Society of Hematology 2023 annual meeting.

INTRODUCTION: At the 65th American Society of Hematology (ASH) 2023 Annual Meeting, the latest advancements in CD20×CD3 BsAbs for B-cell lymphoma (BCL) were highlighted, particularly in relapsed/refractory (R/R) follicular lymphoma (FL) and R/R diffuse large B-cell lymphoma (DLBCL). AREAS COVERED: This summary highlights some of the major studies on CD20×CD3 BsAbs for BCL. EXPERT OPINION/COMMENTARY: CD20×CD3 is the most widely studied BsAb, with promising results in patients with R/R DLBCL and R/R FL ≥ two prior lines of systemic therapy. Trials with the first line of B-cell lymphoma also revealed promising results. Hopefully, BsAb monotherapy or BsAb-containing regimens may become the standard therapy in patients with FL and DLBCL.