Abstract B061: CD81: A new target for therapy of B cell lymphoma

Abstract

Abstract CD81 belongs to an evolutionary conserved family of proteins named tetraspanins and it was originally described as a B cell target. Tetraspanins associate in multi-molecular complexes in tetraspanin-enriched microdomains (TEMS). Indeed, in B cells CD81 associates with CD19 and CD21, and together function as co-receptor to lower the cell activation threshold initiated by the BCR. Recently, we have demonstrated the importance of CD81 in tumor growth and metastasis of solid tumors1. However, the role of CD81 in B cell malignancies has not been explored. Previously, we have shown that anti-CD81 antibodies had anti-proliferative effects on human B cell lymphoma cell lines in vitro2. Here we tested the therapeutic effect of a mouse anti-human CD81 antibody in vivo against Raji and SUP-B8 B cell lymphomas using a xenograft model in SCID mice. Our studies demonstrated that our anti-CD81 antibody had therapeutic effect comparable to rituximab. Moreover, we found ADCC as one of the mechanism of action. Furthermore, to enhance the anti-CD81-mediated ADCC we engineered chimeric antibodies containing human IgG1ADCC-HIGH and human IgG4 ADCC-LOW Fc constant regions. Indeed, the chimeric human IgG1 anti-CD81 mAb showed a remarkable increase in NK cell-mediated ADCC compared to Rituximab in vitro. These results suggest that CD81 can be a potential therapeutic target on B cell lymphomas by virtue of both its direct cytotoxic effect and as a mediator of ADCC. The Human IgG1 version is being developed as a therapeutic candidate. 1. Vences-Catalan, F., et al. Cancer Res 75, 4517-4526 (2015). 2. Oren, R., Takahashi, S., Doss, C., Levy, R. & Levy, S. Mol Cell Biol 10, 4007-4015 (1990). Citation Format: Felipe Vences-Catalán, Chiung-Chi Kuo, Ranjani Rajapaksa, Ronald Levy, Shoshana Levy. CD81: A new target for therapy of B cell lymphoma [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B061.