TCR's genetically linked to CD28 and CD3e do not mispair with endogous TCR chains and mediate enhanced T cell persistance and anti-melanoma activity

Adoptive transfer of T cells that are gene engineered to express a defined TCR represents a feasible and promising therapy for patients with tumors. However, TCR gene therapy is hindered by the transient presence and effectiveness of transferred T cells, which are anticipated to be improved by adequate T cell costimulation. In this article, we report the identification and characterization of a novel two-chain TCR linked to CD28 and CD3e (i.e., TCR:28e). This modified TCR demonstrates enhanced binding of peptide–MHC and mediates enhanced T cell function following stimulation with peptide compared with wild-type TCR. Surface expression of TCR:28e depends on the transmembrane domain of CD28, whereas T cell functions depend on the intracellular domains of both CD28 and CD3e, with IL-2 production showing dependency on CD28:LCK binding. TCR:28e, but not wild-type TCR, induces detectable immune synapses in primary human T cells, and such immune synapses show significantly enhanced accumulation of TCR transgenes and markers of early TCR signaling, such as phosphorylated LCK and ERK. Importantly, TCR:28e does not show signs of off-target recognition, as evidenced by lack of TCR mispairing, as well as preserved specificity. Notably, when testing TCR:28e in immune-competent mice, we observed a drastic increase in T cell survival, which was accompanied by regression of large melanomas with limited recurrence. Our data argue that TCR transgenes that contain CD28, and, thereby, may provide T cell costimulation in an immune-suppressive environment, represent candidate receptors to treat patients with tumors.