Strategies for enhancing adoptive T-cell immunotherapy against solid tumors using engineered cytokine signaling and other modalities

Introduction: Cancer therapy has been transformed by the demonstration that tumor-specific T-cells can eliminate tumor cells in a clinical setting with minimal long-term toxicity. However, significant success in the treatment of leukemia and lymphoma with T-cells using native receptors or redirected with chimeric antigen receptors (CARs) has not been recapitulated in the treatment of solid tumors. This lack of success is likely related to the paucity of costimulatory and cytokine signaling available in solid tumors, in addition to a range of inhibitory mechanisms.Areas covered: We summarize the latest developments in engineered T-cell immunotherapy, describe the limitations of these approaches in treating solid tumors, and finally highlight several strategies that may be useful in mediating solid tumor responses in the future, while also ensuring safety of engineered cells.Expert opinion: CAR-T therapies require further engineering to achieve their potential against solid tumors. Facilitating cytokine signaling in CAR T-cells appears to be essential in achieving better responses. However, the engineering of T-cells with potentially unchecked proliferation and potency raises the question of whether the simultaneous combination of enhancements will prove safe, necessitating continued advancements in regulating CAR-T activity at the tumor site and methods to safely switch off these engineered cells.