Using knockout and bone marrow chimera mouse models, Oba, Hoki, and Yamauchi et al. showed that CD40 and CD70, but not CD80/86, signaling on Batf3-dependent host cDC1s was essential for the expansion and antitumor efficacy of adoptively transferred gp100-specific CD8+ T cells (ACT) in mice bearing B16 tumors and treated with a vaccine (hgp100 peptide, TLR7 agonist, agonistic (ag) anti-CD40 Ab) and systemic IL-2. Administration of Flt3L prior to ACT with TLR3/agCD40-based vaccination induced and activated host cDC1s and enhanced the expansion of transferred T cells, which could be useful in a clinical setting.
Contributed by Lauren Hitchings
ABSTRACT: In vivo expansion of adoptively transferred CD8(+) T cells is a critical determinant of successful adoptive T cell therapy. Emerging evidence indicates Batf3-dependent conventional type 1 dendritic cells (cDC1s) rarely found within the tumor myeloid compartment are crucial for effector T cell recruitment to the tumor microenvironment. However, the role of cDC1s in expansion of tumor-specific CD8(+) T cells remains unclear. In this article, we addressed the role of cDC1s and their costimulatory molecules, CD40, CD70, and CD80/CD86, in expansion and antitumor efficacy of adoptively transferred in vitro-primed CD8(+) T cells recognizing nonmutated tumor-associated self-antigens. We found that TLR/CD40-mediated expansion and antitumor efficacy of adoptively transferred tumor-specific CD8(+) T cells were abrogated in Batf3(-/-) mice. Further mechanistic studies using mixed bone marrow chimeric mice identified that CD40 and CD70 but not CD80/CD86 signaling in cDC1s played a critical role in expansion and antitumor efficacy of adoptively transferred CD8(+) T cells. Moreover, induction and activation of cDC1s by administration of FMS-like tyrosine kinase 3 ligand (Flt3L) and TLR/CD40 agonists augmented expansion of adoptively transferred CD8(+) T cells, delayed tumor growth, and improved survival. These findings reveal a key role for CD40 and CD70 signaling in cDC1s and have major implications for the design of new vaccination strategies with adoptive T cell therapy.