Purpose: Adoptive cellular immunotherapy is a promising approach to eradicate established tumors. However, a significant hurdle in the success of cellular immunotherapy involves recently identified mechanisms of immune suppression on cytotoxic T cells at the effector phase. Transforming growth factor-beta (TGF-beta) is one of the most important of these immunosuppressive factors because it affects both T-cell and macrophage functions. We thus hypothesized that systemic blockade of TGF-beta signaling combined with adoptive T-cell transfer would enhance the effectiveness of the therapy.
Experimental design: Flank tumors were generated in mice using the chicken ovalbumin-expressing thymoma cell line, EG7. Splenocytes from transgenic OT-1 mice (whose CD8 T cells recognize an immunodominant peptide in chicken ovalbumin) were activated in vitro and adoptively transferred into mice bearing large tumors in the presence or absence of an orally available TGF-beta receptor-I kinase blocker (SM16).
Results: We observed markedly smaller tumors in the group receiving the combination of SM16 chow and adoptive transfer. Additional investigation revealed that TGF-beta receptor blockade increased the persistence of adoptively transferred T cells in the spleen and lymph nodes, increased numbers of adoptively transferred T cells within tumors, increased activation of these infiltrating T cells, and altered the tumor microenvironment with a significant increase in tumor necrosis factor-alpha and decrease in arginase mRNA expression.
Conclusions: We found that systemic blockade of TGF-beta receptor activity augmented the antitumor activity of adoptively transferred T cells and may thus be a useful adjunct in future clinical trials.