Targeted cancer immunotherapy via combination of designer bispecific antibody and novel gene-engineered T cells.

backgroundRedirection of T lymphocytes against tumor antigens can induce dramatic regression of advanced stage malignancy. The use of bispecific antibodies (BsAbs) that bind both the T-cell receptor (TCR) and a target antigen is one promising approach to T-cell redirection. However, BsAbs indiscriminately bind all CD3+ T-cells and trigger TCR activation in the absence of parallel costimulatory signals required to overcome T-cell unresponsiveness or anergy.

methodsTo address these limitations, a combination platform was designed wherein a unique BsAb referred to as frBsAb exclusively engages T-cells engineered to express a novel chimeric receptor comprised of extracellular folate receptor fused to intracellular TCR and CD28 costimulatory signaling domains in tandem; a BsAb-binding immune receptor (BsAb-IR). As a surrogate TCR, the BsAb-IR allows for concomitant TCR and costimulatory signaling exclusively in transduced T-cells upon engagement with specific frBsAbs, and can therefore redirect T-cells on command to desired antigen. Human primary T-cells were transduced with lentiviral vector and expanded for 14-18 days. BsAb-IRs were harvested and armed with frBsAbs to test for redirected cytotoxicity against CD20 positive cancer cell lines.

resultsUsing frBsAbs specific for CD20 or HER2, the lytic activity of primary human T-cells expressing the BsAb-IR was specifically redirected against CD20+ leukemic cells or HER2+ epithelial cancer cells, respectively, while non-engineered T-cells were not activated. Notably, elimination of the CD28 costimulatory domain from the BsAb-IR construct significantly reduced frBsAb-redirected antitumor responses, confirming that frBsAbs are capable of delivering simultaneous TCR activation and costimulatory signals to BsAb-IR T-cells.

conclusionIn summary, our results establish the proof of concept that the combination of BsAbs with optimized gene-engineered T-cells provides the opportunity to specify and augment tumor antigen-specific T-cell activation and may improve upon the early success of conventional BsAbs in cancer immunotherapy.