Cellular and personalized therapies in multiple myeloma with special emphasis on retargeted natural killer cells

Abstract

Multiple myeloma (MM) is a clonal plasma cell malignancy accounting for approximately 10% of all hematological cancer cases. Despite considerable advances in MM management, which led to exceptional response and survival rates, patients still experience relapse and cure remains elusive. Personalized, antibody-based and cellbased immunotherapies have given new hope to patients with relapsed or refractory disease. The aim of this thesis was to investigate the potential of novel targeted treatments for MM, specifically those based on Natural Killer (NK) cells and patient stratification.

Studies I and II focus on retargeting applications of Natural Killer (NK) cells. NK cells have emerged as a promising alternative to current T cell-based therapies, due to their potent effector functions, safer profile and possibility for use as off-the-shelf treatments. However, the immunosuppressive microenvironment of MM drives NK cell dysfunctionality which impacts the efficacy of adoptive NK cell therapy. To address this issue we have relied on chimeric receptors; a strategy that is proven to enhance the targeting potential of NK cells while improving the exertion of cytotoxicity.

The first study centers around CD38; a protein that is highly expressed on the surface of myeloma cells. CD38-targeting with monoclonal antibodies, such as Daratumumab and Isatuximab, has revolutionized MM treatment, inducing durable responses in a fraction of patients. Targeting CD38 using Chimeric Antigen Receptor (CAR)-expressing NK has also been attempted. It is, however, met with feasibility challenges, such as the intrinsic CD38 expression on NK cells which may lead CAR-NK cells to perform fratricide. Here, we demonstrate an alternative approach by harnessing the CD38dim phenotype occurring during long-term cytokine stimulation of primary NK cells. Our findings show that the combination of a functional, affinity-optimized αCD38-CAR construct with a suitable NK cell expansion and activation protocol results in a promising immunotherapeutic strategy for MM.

The second study aims to improve outcomes of adoptive NK cell therapy by converting the inhibitory signals, that NK cells receive from the PD1/ PD-L1 axis, to stimulating signals. For this purpose, we designed novel PD1-based chimeric switch receptors (PD1-CSRs) by fusing the PD1 ectodomain to the activating signaling domains of NKp46, DAP10, DAP12, and CD3ζ. The results show that PD1-CSR+ NK cells exert potent anti-tumor activity against PD-L1+ cancer cell lines and primary MM cells in vitro, laying the foundation for improved treatment of PD-L1+ tumors.

The third study investigates the use of the BCL2 inhibitor Venetoclax in MM and ALamyloidosis patients harboring the t(11;14) genetic mutation. This clinical study concludes that treatment with a daily low-dose of Venetoclax is adequately safe and has promising efficacy. The study also identifies resistance mechanisms associated with t(11;14), such as the downregulation of IRF5 targeted genes, which can be further exploited by therapeutic interventions. Overall, the present doctoral thesis investigates novel approaches of NK cell-based immunotherapy and stratified chemotherapy for MM. The findings of these studies provide foundation for future research in the field and contribute to the expansion of current therapeutic options.