TCR-T immunotherapy and cancer therapy

Cell therapy is a kind of medicine aiming to cure disease or alleviate disease symptoms via direct infusion or transplantation of cells, which can be autologous or allogeneic. With several decades’ development and optimization, immuno-oncology cells (such as T cells, nature killer cells, etc.), stem cells (embryonic stem cells, induced pluripotent stem cells, progenitor cells, etc.) or other genetic re-engineered cells have been widely applied for cell therapy. Numerous cell types have been translated into clinical trials and promising cell therapy outcomes have been achieved from Phase I, Phase II and Phase III trials for a great number of diseases.

T-cell receptor (TCR)–engineered T-cell therapy (TCR-T) is one potentially powerful treatment that utilizes genetically modified natural T cells to specifically target tumors and destroy tumors with greater potentials [37]. Unlike CARs, TCRs rely on their interactions with peptide-major histocompatibility complex (pMHC), formed by peptide [38,39], generated from intracellular antigen proteolysis, bound with MHC (Fig. 3) [40]. Besides TCR, additional costimulatory or co-inhibitory signals are also required for TCR-T function. For example, CD4 on the surface of helper T cells, which binds to class II MHC complex, and CD8 on the surface of cytotoxic T cells, which binds to class I MHC complex, activates the TCR-T mediated cell destruction [41], while cytotoxic T-lymphocyte antigen 4 (CTLA-4) and programmed cell death protein 1 (PD-1) are responsible for T cell signaling extinguisher [42]. Given that only ~28% antigens are expressed on the cell surface, it is difficult for most of the antigens to be recognized by CAR [43]. Therefore, compared to CAR-T, TCR-T cell therapy shows remarkable advantages over the destruction of tumor cells with intracellular antigens [44]. To date, TCR-T mediated cell therapy has achieved many promising curative potency in both solid tumors and hematological cancers, and some of them have been applied in clinic trials (Table 2).