Bispecific T-cell engagers for the recruitment of T cells in solid tumors: a literature review

In the past decade, T-cell-based immunotherapies have grown to become some of the most promising treatments for cancer. Following the success of immune checkpoint inhibitors, other T-cell-based therapies emerged including CAR-T cells and bispecific T-cell engagers (BiTEs). BiTEs have the unique ability to crosslink T cells and tumor cells independently of major histocompatibility complex (MHC) restriction. They do not rely on TCR specificity or the CD4+/CD8+ costimulatory molecules, overcoming tumor MHC downregulation and low-affinity TCR binding. However, like many other immunotherapies, BiTEs have shown limited success beyond the treatment of hematological malignancies. BiTEs for the treatment of solid tumors still face challenges. Studies in gastrointestinal tumors have revealed Fc toxicity, short half-lives, and immunotoxicity, leading to Fc-silenced half-life extended BiTEs with humanized single-chain variable fragments. Studies in prostate tumors, lung tumors, and malignant gliomas have identified promising targets in PSMA, DLL3, and EGFRvIII, respectively, but also highlighted the problems of on-target off-tumor and BiTE-specific toxicities and inaccessible or immunosuppressive tumor microenvironments. Ongoing research to overcome these limitations remains an interesting field to follow, as BiTEs have the potential to be a powerful tool, especially when used in combination with other immunotherapies.