Purpose: The inhibition of tumor growth by anti-CD20 antibody (Ab) treatment is mediated by Ab- and complement-dependent cytotoxicity in xenograft tumor models. In addition, anti-CD20 therapy for B-cell lymphoma can result in intrinsic and extrinsic tumor resistance to further Ab treatment. However, adaptive immune response–related resistance has not been well studied in anti-CD20–mediated tumor control, and adaptive immunity has long been underestimated. The purpose of this study was to explore whether T cells are involved in mediating the effects of anti-CD20 therapy and what factors contribute to adaptive immune response–related resistance.

Experimental Design: Using a syngeneic mouse B-cell lymphoma model, we investigated the role of CD8⁺ T cells in anti-CD20–mediated tumor regression. Furthermore, we revealed how the tumor-specific T-cell response was initiated by anti-CD20. Finally, we studied adaptive immune response–related resistance in advanced B-cell lymphoma.

Results: CD8⁺ T cells played an essential role in anti-CD20–mediated tumor regression. Mechanistically, anti-CD20 therapy promoted dendritic cell (DC)-mediated cross-presentation. Importantly, macrophages were also necessary for the increase in the tumor-specific CTL response after anti-CD20 treatment, via the production of type I IFN to activate DC function. Furthermore, adaptive resistance is gradually developed through the CTLA-4 pathway in Treg cells in larger lymphomas. Further blockade of CTLA-4 can synergize with anti-CD20 treatment in antitumor activities.

Conclusions: The therapeutic function of anti-CD20 depends on tumor-specific CD8⁺ T-cell responses initiated by anti-CD20 through macrophages and DCs. CTLA-4 blockade can synergize with anti-CD20 to overcome adaptive immune response–related resistance in advanced B-cell lymphoma. Clin Cancer Res; 23(1); 193–203. ©2016 AACR.