CD20 is a molecular target for scFvFc:zeta receptor redirected T cells: Implications for cellular immunotherapy of CD20+ malignancy

The CD20 molecule was evaluated as a B-cell lymphoma target epitope for T cells expressing a CD20-specific single-chain FvFc-zeta (scFvFc:zeta) chimeric receptor. A cDNA construct consisting of a murine kappa leader sequence, CD20-specific scFv, human immunoglobulin (Ig) G1 hinge-C(H)2-C(H)3, the human CD4 transmembrane, and the intracellular signaling domain of the human CD3 complex's zeta chain was synthesized by polymerase chain reaction splice-overlap extension. The human CD4+ Jurkat cell line was electroporated with the CD20-specific scFvFc:zeta construct cloned into the mammalian expression vector pcDNAneo. Western blot analysis of transfectant whole cell lysate with an anti-zeta antibody demonstrated the expression of both endogenous zeta and the chimeric receptor protein, with a mobility consistent with the expected molecular weight of 66 kD under reducing conditions; nonreduced lysate revealed a chimeric receptor complex of approximately 132 kD. The scFvFc:zeta receptor was present on the cell surface as detected by flow cytometry of T-cell transfectants stained with an anti-mouse Fab-specific antibody and anti-human Fc gamma-specific monoclonal antibody. Coculture of Jurkat transfectants with CD20+ lymphoma cells resulted in the accumulation of interleukin (IL)-2 in culture supernatants as detected by ELISA. IL-2 production was triggered by the specific interaction between the CD20 molecule and the scFvFc:zeta as IL-2 was not detected in cultures with mock transfected Jurkat cells or CD20- stimulator cells. Furthermore, IL-2 production was inhibited by the addition of a soluble anti-CD20 monoclonal antibody to cocultured Jurkat transfectants and CD20+ stimulator cells. The capacity of CD20 to trigger the lytic machinery of scFvFc:zeta-expressing cytotoxic T lymphocytes (CTLs) was assessed using the murine allo-specific CD8+ CTL clone 2c. CD20-specific redirected cytolytic activity against human lymphoma targets was observed with 2c transfectants in a 4-hour chromium release assay. These results demonstrate that CD20 can serve as a target epitope for scFvFc:zeta receptor-expressing T cells.