Changes in T-cell subsets, preexisting cytopenias and hyperferritinaemia correlate with cytopenias after BCMA targeted CAR T-cell therapy in relapsed/refractory multiple myeloma: Results from a prospective comprehensive biomarker study.

Biomarkers for cytopenias following CAR T-cell treatment in relapsed/refractory (RR) multiple myeloma (MM) are not completely defined. We prospectively analysed 275 sequential peripheral blood (PB) samples from 58 RRMM patients treated with BCMA-targeted CAR T cells, and then divided them into three groups: (i) baseline (before leukapheresis), (ii) ≤day+30, and (iii) >day+30 after CAR T-cell therapy. We evaluated laboratory data and performed flow cytometry to determine the (CAR) T-cell subsets. Baseline hyperferritinaemia was a risk factor for long-lasting grade ≥3 anaemia (r = 0.47, p < 0.001) and thrombocytopenia (r = 0.44, p = 0.002) after CAR T-cell therapy. Low baseline haemoglobin (Hb) and PLT were associated with long-lasting grade ≥3 anaemia (r = -0.56, p < 0.001) and thrombocytopenia (r = -0.44, p = 0.002) respectively. We observed dynamics of CAR-negative T-cell subsets following CAR T-cell infusion. In the late phase after CAR T-cell therapy (>day+30), CD4Tn frequency correlated with anaemia (r = 0.41, p = 0.0014) and lymphocytopenia was related to frequencies of CD8+ T cells (r = 0.72, p < 0.001) and CD8Teff (r = 0.64, p < 0.001). CD4Tcm frequency was correlated with leucocytopenia (r = -0.49, p < 0.001). In summary, preexisting cytopenias and hyperferritinaemia indicated long duration of grade ≥3 post-CAR T-cell cytopenias. Prolonged cytopenia may be related to immune remodelling with a shift in the CAR-negative T-cell subsets following CAR T-cell therapy.

Soluble B-cell maturation antigen in lacrimal fluid as a potential biomarker and mediator of keratopathy in multiple myeloma.

Belantamab mafodotin (belantamab) is a first-in-class anti-BCMA antibody-drug conjugate approved for the treatment of triple-class refractory multiple myeloma. It provides a unique therapeutic option for patients ineligible for CAR-T and bispecific antibody therapy, and/or patients progressing on anti-CD38 treatment where CAR-T and bispecifics might be kept in reserve. Wider use of the drug can be challenged by its distinct ocular side effect profile, including corneal microcysts and keratopathy. While dose reduction has been the most effective way to reduce these toxicities, the underlying mechanism of this BCMA off-target effect remains to be characterized. In this study, we provide the first evidence for soluble BCMA (sBCMA) in lacrimal fluid and report on its correlation with tumor burden in myeloma patients. We confirm that corneal cells do not express BCMA, and show that sBCMA-belantamab complexes may rather be internalized by corneal epithelial cells through receptor-ligand independent pinocytosis. Using an hTcEpi corneal cell-line model, we show that the pinocytosis inhibitor EIPA significantly reduces belantamab-specific cell killing. As a proof of concept, we provide detailed patient profiles demonstrating that, after belantamab-induced cell killing, sBCMA is released into circulation, followed by a delayed increase of sBCMA in the tear fluid and subsequent onset of keratopathy. Based on the proposed mechanism, pinocytosis-induced keratopathy can be prevented by lowering the entry of sBCMA into the lacrimal fluid. Future therapeutic concepts may therefore consist of belantamab-free debulking therapy prior to belantamab consolidation and/or concomitant use of gamma-secretase inhibition as currently evaluated for belantamab and nirogacestat in ongoing studies.

Clonal competition assays identify fitness signatures in cancer progression and resistance in multiple myeloma.

Multiple myeloma (MM) is a genetically heterogeneous disease and the management of relapses is one of the biggest clinical challenges. TP53 alterations are established high-risk markers and are included in the current disease staging criteria. KRAS is the most frequently mutated gene affecting around 20% of MM patients. Applying Clonal Competition Assays (CCA) by co-culturing color-labeled genetically modified cell models, we recently showed that mono- and biallelic alterations in TP53 transmit a fitness advantage to the cells. Here, we report a similar dynamic for two mutations in KRAS (G12A and A146T), providing a biological rationale for the high frequency of KRAS and TP53 alterations at MM relapse. Resistance mutations, on the other hand, did not endow MM cells with a general fitness advantage but rather presented a disadvantage compared to the wild-type. CUL4B KO and IKZF1 A152T transmit resistance against immunomodulatory agents, PSMB5 A20T to proteasome inhibition. However, MM cells harboring such lesions only outcompete the culture in the presence of the respective drug. To better prevent the selection of clones with the potential of inducing relapse, these results argue in favor of treatment-free breaks or a switch of the drug class given as maintenance therapy. In summary, the fitness benefit of TP53 and KRAS mutations was not treatment-related, unlike patient-derived drug resistance alterations that may only induce an advantage under treatment. CCAs are suitable models for the study of clonal evolution and competitive (dis)advantages conveyed by a specific genetic lesion of interest, and their dependence on external factors such as the treatment.

Impaired FADD/BID signaling mediates cross-resistance to immunotherapy in Multiple Myeloma.

The treatment landscape in multiple myeloma (MM) is shifting from genotoxic drugs to immunotherapies. Monoclonal antibodies, immunoconjugates, T-cell engaging antibodies and CART cells have been incorporated into routine treatment algorithms, resulting in improved response rates. Nevertheless, patients continue to relapse and the underlying mechanisms of resistance remain poorly understood. While Impaired death receptor signaling has been reported to mediate resistance to CART in acute lymphoblastic leukemia, this mechanism yet remains to be elucidated in context of novel immunotherapies for MM. Here, we describe impaired death receptor signaling as a novel mechanism of resistance to T-cell mediated immunotherapies in MM. This resistance seems exclusive to novel immunotherapies while sensitivity to conventional anti-tumor therapies being preserved in vitro. As a proof of concept, we present a confirmatory clinical case indicating that the FADD/BID axis is required for meaningful responses to novel immunotherapies thus we report impaired death receptor signaling as a novel resistance mechanism to T-cell mediated immunotherapy in MM.