Infiltration, accumulation, and survival of chimeric antigen receptor T (CAR-T) cells in solid tumors is crucial for tumor clearance. We engineered CAR-T cells to express interleukin (IL)-7 and CCL19 (7 × 19 CAR-T cells), as these factors are essential for the maintenance of T-cell zones in lymphoid organs. In mice, 7 × 19 CAR-T cells achieved complete regression of pre-established solid tumors and prolonged mouse survival, with superior anti-tumor activity compared to conventional CAR-T cells. Histopathological analyses showed increased infiltration of dendritic cells (DC) and T cells into tumor tissues following 7 × 19 CAR-T cell therapy. Depletion of recipient T cells before 7 × 19 CAR-T cell administration dampened the therapeutic effects of 7 × 19 CAR-T cell treatment, suggesting that CAR-T cells and recipient immune cells collaborated to exert anti-tumor activity. Following treatment of mice with 7 × 19 CAR-T cells, both recipient conventional T cells and administered CAR-T cells generated memory responses against tumors.

Therapeutic cancer vaccines are designed to treat cancer by boosting the endogenous immune system to fight against the cancer. In the development of clinically effective cancer vaccines, one of the most practical objectives is to identify adjuvants that are capable of optimizing the vaccine effects. In this study, we explored the potential of polyinosinic–polycytidylic acid (poly(I:C)) and LAG‐3‐Ig (soluble recombinant protein of lymphocyte activation gene‐3 [LAG‐3] extracellular domain fused with human IgG Fc region) as adjuvants for P1A tumor antigen peptide vaccine in a pre‐established P815 mouse tumor model with a transfer of tumor‐specific T cells. Whereas the use of poly(I:C) or LAG‐3‐Ig as a signal adjuvant induced a slight enhancement of P1A vaccine effects compared to incomplete Freund's adjuvant, combined treatment with poly(I:C) plus LAG‐3‐Ig remarkably potentiated antitumor effects, leading to complete rejection of pre‐established tumor and long‐term survival of mice. The potent adjuvant effects of poly(I:C) plus LAG‐3‐Ig were associated with an enhanced infiltration of T cells in the tumor tissues, and an increased proliferation and Th1‐type cytokine production of tumor‐reactive T cells. Importantly, the combined adjuvant of poly(I:C) plus LAG‐3‐Ig downregulated expressions of PD‐1, LAG‐3, and TIGIT on P1A‐specific T cells, indicating prevention of T cell exhaustion. Taken together, the results of the current study show that the combined adjuvants of poly(I:C) plus LAG‐3‐Ig with tumor peptide vaccine induce profound antitumor effects by activating tumor‐specific T cells.