Leveraging T cell co-stimulation for enhanced therapeutic efficacy of trispecific antibodies targeting prostate cancer

Background Clinical trials have demonstrated the efficacy of bispecific antibodies in eliciting potent antitumor responses by redirecting T cells to target cancer cells, particularly for the treatment of hematologic malignancies. However, their efficacy against solid tumors is limited by intratumoral T-cell dysfunction and inadequate persistence. The co-stimulatory domains of 4-1BB, OX40, and CD28 are most widely used in engineering chimeric antigen receptor T-cells to augment T-cell responses. Methods In this study, we designed three co-stimulatory trispecific T cell-engaging antibodies (TriTCEs) that target Prostate-specific membrane antigen, CD3, and an additional co-stimulatory receptor(OX40, 4-1BB, or CD28). We conducted comparative profiling of the attributes of distinct co-stimulatory signals to T-cell functions in prostate cancer models. Results Co-stimulatory trispecific T-cell engagers enhance T-cell activation, proliferation, and display tumor cell-killing activity in vitro. These trispecific antibodies further boosted antitumor activity in humanized mouse xenograft models and increased the infiltration of CD45 + immune cells into solid tumors. Specifically, TriTCE-4-1BB and TriTCE-CD28 selectively promoted the expansion of effector memory T cells and increased the presence of CD4 + T cells more than TriTCE-OX40. T cells stimulated with TriTCE-4-1BB exhibited reduced exhaustion. Furthermore, T cells treated with co-stimulatory trispecific antibodies demonstrated enhanced metabolic activity characterized by increased oxidative phosphorylation and elevated glycolysis. Conclusions Collectively, incorporating co-stimulatory receptor targeting domains represents a potentially effective strategy to unlock the full therapeutic potential of T-cell-engaging antibodies for the treatment of solid tumors.