Preserved Activity of CD20-Specific Chimeric Antigen Receptor–Expressing T Cells in the Presence of Rituximab

• Published in: Cancer immunology research 2016-06, Vol.4 (6), p.509-519, Article 509
• Main Authors: Rufener, Gregory A, Press, Oliver W, Olsen, Philip, Lee, Sang Yun, Jensen, Michael C, Gopal, Ajay K, Pender, Barbara, Budde, Lihua E, Rossow, Jeffrey K, Green, Damian J, Maloney, David G, Riddell, Stanley R, Till, Brian G
• Format: Article
• Language: English
• Subjects: Animals; Antigens, CD20 - drug effects; Antigens, CD20 - immunology; Antigens, CD20 - metabolism; Antineoplastic Agents - administration & dosage; Antineoplastic Agents - pharmacology; Cell Proliferation - drug effects; Combined Modality Therapy; Cytokines - biosynthesis; Cytotoxicity, Immunologic - drug effects; Dose-Response Relationship, Drug; Humans; Immunotherapy, Adoptive - methods; Lymphoma, B-Cell - immunology; Lymphoma, B-Cell - therapy; Mice, Inbred NOD; Mice, SCID; Receptors, Antigen, T-Cell - metabolism; Rituximab - administration & dosage; Rituximab - pharmacology; T-Lymphocyte Subsets - drug effects; T-Lymphocyte Subsets - immunology; T-Lymphocyte Subsets - transplantation; Tumor Cells, Cultured; Xenograft Model Antitumor Assays
• ISSN: 2326-6066; 2326-6074
• DOI: 10.1158/2326-6066.cir-15-0276

CD20 is an attractive immunotherapy target for B-cell non-Hodgkin lymphomas, and adoptive transfer of T cells genetically modified to express a chimeric antigen receptor (CAR) targeting CD20 is a promising strategy. A theoretical limitation is that residual serum rituximab might block CAR binding to CD20 and thereby impede T cell-mediated anti-lymphoma responses. The activity of CD20 CAR-modified T cells in the presence of various concentrations of rituximab was tested in vitro and in vivo CAR-binding sites on CD20(+) tumor cells were blocked by rituximab in a dose-dependent fashion, although at 37°C blockade was incomplete at concentrations up to 200 μg/mL. T cells with CD20 CARs also exhibited modest dose-dependent reductions in cytokine secretion and cytotoxicity, but not proliferation, against lymphoma cell lines. At rituximab concentrations of 100 μg/mL, CAR T cells retained ≥50% of baseline activity against targets with high CD20 expression, but were more strongly inhibited when target cells expressed low CD20. In a murine xenograft model using a rituximab-refractory lymphoma cell line, rituximab did not impair CAR T-cell activity, and tumors were eradicated in >85% of mice. Clinical residual rituximab serum concentrations were measured in 103 lymphoma patients after rituximab therapy, with the median level found to be only 38 μg/mL (interquartile range, 19-72 μg/mL). Thus, despite modest functional impairment in vitro, the in vivo activity of CD20-targeted CAR T cells remains intact at clinically relevant levels of rituximab, making use of these T cells clinically feasible. Cancer Immunol Res; 4(6); 509-19. ©2016 AACR