Multiple myeloma (MM) patients eventually develop multi-drug-resistant disease with poor survival. Hence, the development of novel treatment strategies is of great importance. Recently, different classes of immunotherapeutic agents have shown great promise in heavily pre-treated MM, including T cell-redirecting bispecific antibodies (BsAbs). These BsAbs simultaneously interact with CD3 on effector T cells and a tumor-associated antigen on MM cells, resulting in redirection of T cells to MM cells. This leads to the formation of an immunologic synapse, the release of granzymes/perforins, and subsequent tumor cell lysis. Several ongoing phase 1 studies show substantial activity and a favorable toxicity profile with BCMA-, GPRC5D-, or FcRH5-targeting BsAbs in heavily pre-treated MM patients. Resistance mechanisms against BsAbs include tumor-related features, T cell characteristics, and impact of components of the immunosuppressive tumor microenvironment. Various clinical trials are currently evaluating combination therapy with a BsAb and another agent, such as a CD38-targeting antibody or an immunomodulatory drug (e.g., pomalidomide), to further improve response depth and duration. Additionally, the combination of two BsAbs, simultaneously targeting two different antigens to prevent antigen escape, is being explored in clinical studies. The evaluation of BsAbs in earlier lines of therapy, including newly diagnosed MM, is warranted, based on the efficacy of BsAbs in advanced MM.
Chimeric antigen receptor (CAR) T cells are highly successful in the treatment of hematologic malignancies. We recently generated affinity-optimized CD38CAR T cells, which effectively eliminate multiple myeloma (MM) cells with little or no toxicities against nonmalignant hematopoietic cells. The lack of universal donors and long manufacturing times however limit the broad application of CAR T cell therapies. Natural killer (NK) cells generated from third party individuals may represent a viable source of “off the shelf” CAR-based products, as they are not associated with graft-versus-host disease unlike allogeneic T cells. We therefore explored the preclinical anti-MM efficacy and potential toxicity of the CD38CAR NK concept by expressing affinity-optimized CD38CARs in KHYG-1 cells, an immortal NK cell line with excellent expansion properties. KHYG-1 cells retrovirally transduced with the affinity-optimized CD38CARs expanded vigorously and mediated effective CD38-dependent cytotoxicity towards CD38high MM cell lines as well as primary MM cells ex vivo. Importantly, the intermediate affinity CD38CAR transduced KHYG-1 cells spared CD38neg or CD38int nonmalignant hematopoietic cells, indicating an optimal tumor nontumor discrimination. Irradiated, short living CD38CAR KHYG-1 cells also showed significant anti-MM effects in a xenograft model with a humanized bone marrow-like niche. Finally, CD38CAR KHYG-1 cells effectively eliminated primary MM cells derived from patients who are refractory to CD38 antibody daratumumab. Taken together, the results of this proof-of-principle study demonstrate the potential value of engineering affinity-optimized CD38CARs in NK cells to establish effective anti-MM effects, with an excellent safety profile, even in patients who failed to response to most advanced registered myeloma therapies, such as daratumumab.
Background:Multiple Myeloma (MM), a disease characterized by a clonal expansion of plasma cells, still remains incurable with current treatment options. The genetic engineering of T lymphocytes with chimeric antigen receptors (CAR) has recently emerged as a promising therapeutic approach and BCMA has shown to be a good MM‐specific antigenic target. Despite its specificity, the intensity of BCMA is variable in MM patients and may not be uniform across different subclonal populations which might explain why first clinical trials of BCMA‐CAR‐T cells report lower complete remission rates as well as relapses of BCMA‐low clonal variants. Another MM‐related antigen, CD38, is uniformly highly expressed in all malignant MM cells.Aims:We hypothesized that targeting 2 MM‐related antigens would increase cytotoxic ability of CAR‐T cells and the incorporation of a dual costimulation design would confer increased persistence. Thus, we propose to improve CAR‐T cell therapy for MM by dual targeting of BCMA and CD38 and incorporating full costimulation with 4‐1BB and CD28 signaling by using the combination of a CAR and a chimeric costimulatory receptor (CCR).Methods:To this end, we designed first and second generation CAR constructs targeting BCMA (BCMA‐z and BCMA‐28z), CCR constructs targeting CD38 (CD38‐28BB and CD38‐BB) as well as a CD38‐engager construct lacking intracellular domain (CD38del). We then evaluated in vitro the anti‐MM cytotoxic potential, cytokine production, proliferative capacity and exhaustion of the double‐targeting CAR‐T cells (BCMA‐z/38‐28BB, BCMA‐28z/CD38‐BB or BCMA‐z/CD38del) compared to single‐targeting T cells carrying a conventional CAR (BCMA‐28z, BCMA‐BBz, BCMA‐z), or CCR (38‐28z or 38‐28BB).Results:We found that double‐targeting BCMA‐z/38‐28BB CAR‐T cells showed significantly increased cytotoxic capacity against BCMA+CD38+ MM cell lines and primary MM cells, even in low effector to target ratios, as compared to the single‐targeting BCMA‐CAR‐T cells. This effect was diminished when a BCMA+CD38‐ cell line was used as target, while cells carrying only a CCR had no cytotoxic potential. Interestingly, BCMA‐z/CD38del T cells, where CD38‐engagement does not mediate any costimulation signal, had similar cytotoxic ability as BCMA‐z/38‐28BB cells, therefore the increased killing capacity of double‐targeting CAR‐T cells is due to CD38 engagement and the consecutive increase in avidity. Finally, double‐targeting BCMA‐z/38‐28BB CAR‐T cells showed significantly higher cytokine secretion (IL‐2, IFN‐γ, TNF‐α), proliferative capacity and induction of PD‐1 expression than single‐targeting BCMA‐CAR‐T cells, which was not reproduced by BCMAz/CD38del T cells indicating that this effect is a result of combining both CD28 and 4‐1BB costimulation.Summary/Conclusion:In conclusion, we here show that double targeting MM with a BCMA‐CAR and a CD38‐CCR provides higher effector‐MM avidity and full costimulation. Engagement of the CD38‐CCR enhances the anti‐MM cytotoxicity and persistence and reduces the exhaustion of double‐targeting compared to conventional single‐targeting CAR T cells. Therefore double‐targeting of BCMA and CD38 is a powerful strategy to improve clinical outcomes of BCMA‐CAR T cell therapy.
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