Folate-mediated targeting of T cells to tumors

Recently various strategies have been developed to exploit in a clinical setting the well established finding that T cells can specifically recognize and destroy tumor cells. Several independent approaches to the targeting of T cells against cancer have been explored, including the use of bispecific antibodies (anti-T cell/anti-tumor cell) to redirect T cells, vaccines to induce tumor-reactive T cells, and adoptive transfer of ex vivo activated, tumor-reactive T cells. In this review, we focus on studies in which high-affinity folate receptors (FRs) on tumor cells have served as targets for redirecting or enhancing the effectiveness of activated T cells. Bispecific antibody conjugates of folate and antibodies to the T cell receptor (TCR) complex can generate tumor-reactive T cell responses. The development of folate/antibody conjugates specific for the T cell co-stimulatory molecule CD28 could yield activated T cells that recognize endogenous peptide-major histocompatibility complex (MHC) antigens on tumor cells. Finally, we discuss a less investigated area in which high-affinity FRs on macrophages, or other antigen presenting cells (APCs), may provide opportunities in the design of tumor-antigen-specific vaccines.