T-Cell Immunotherapy with a Chimeric Receptor Against CD38 Is Effective in Eliminating Myeloma Cells
Authors: Mihara Keichiro , Bhattacharyya Joyeeta , Kitanaka Akira , Ihara Akihiro , Sakai Akira , Kuroda Yoshiaki , Asaoku Hideki , Takihara Yoshihiro , Kimura Akiro 
Published: October 2019

Abstract
Abstract 885
Myeloma cells themselves are not merely less sensitive to chemotherapy due to their dormancy but prone to becoming drug-resistant. Thus, new therapeutic options are needed for patients with myeloma, especially those over 60 years old. Myeloma cells show the strong expression of CD38. Thus, we investigated whether the retroviral vector-mediated transduction of an anti-CD38-chimeric antigen receptor (CAR) gene contributed to the abrogation of myeloma cells. We had previously designed the retroviral vector carrying anti-CD38-CAR and GFP. T-cells obtained from healthy donors were transduced with retroviral supernatant containing the anti-CD38-CAR vector. The anti-CD38-CAR was expressed with high efficiency. The median percentage of transduced cells was 65.89% (range, 48.98%–89.98%). We confirmed the expression of the anti-CD38-CAR by flow cytometry using a goat-anti-mouse polyclonal antibody conjugated to biotin followed by streptavidin-PerCP, which reacts with the extracellular antibody-derived single-chain variable domain (scFv) of the anti-CD38-CAR. To assess their cytotoxicity, the T-cells transduced with the anti-CD38-CAR were incubated with the KMM1 and RPMI8226 myeloma cell lines for 3 days at a variety of effector (E): target (T) ratios. The transduced cells exerted a highly cytotoxic effect on RPMI8226 cells in a time-dependent manner. The chimeric receptor-mediated cytotoxicity was dose-dependent. The specific cytotoxicity of T-cells with the anti-CD38-CAR to myeloma cell lines at an E: T ratio of 0.5:1. By contrast, there was no detectable cytotoxicity in experiments with the U266-A4 cells, lacking CD38 expression (0.05%). These results demonstrated that CD38-specific T-cells from donors effectively exerted a cytotoxic effect on myeloma cell lines in a dose- and time-dependent fashion. We next evaluated the effect of the anti-CD38-specific T-cells on myeloma cells from the patients. Myeloma cells freshly isolated from the five patients accounted for over 80% of the cells in bone marrow. After myeloma cells were co-cultured with T-cells bearing the anti-CD38-CAR for 3 days, cytotoxic activity was assessed as described above. Intriguingly, mean specific cytotoxicity observed at an E: T ratio of 0.5: 1 for 3 days was >90% in individual patients. Moreover, we obtained the similar results in the autologous settings as well. These results showed that T-cells harboring the anti-CD38-CAR definitively eliminated myeloma cells from the patients as well as myeloma cell lines. Anti-CD38 antibodies or antibody variants have been shown to provide therapeutics for the treatment of CD38-positive hematological malignancies. Introduction of the antibody against CD38 may, however, raise concerns of side effects such as an infusion reaction and pharmacological phenomena associated with the long half-life of the antibody. Although antibodies against CD38 have been administered to patients with myeloma or B-cell lymphoma, there has been no report of adverse effects. Indeed, daratumumab, a novel therapeutic human CD38 antibody and humanized monoclonal CD38 antibody, is currently in clinical trials. In this study, we demonstrated that human T-cells with the anti-CD38-CAR were highly cytotoxic against myeloma cells strongly expressing CD38. Improvements to immunotherapy using autologous T-cells transduced with the anti-CD38-CAR might shed further light on the treatment of myeloma patients with a poor prognosis.

Disclosures:
No relevant conflicts of interest to declare.