Adoptive T cell therapy (ACT) has demonstrated remarkable efficacy in treating hematological cancers. However, its efficacy against solid tumors remains limited and the emergence of cancer cells that lose expression of targeted antigens often promotes resistance to ACT. Importantly, the mechanisms underlying effective and durable ACT-mediated tumor control are incompletely understood. Here, we show that adoptive transfer of TCR-transgenic CD8+ T cells eliminates established murine melanoma tumors, with concomitant accumulation of tumor-infiltrating CD8+ T cells exhibiting both progenitor-exhausted and terminally-differentiated phenotypes. Interestingly, host CD8+ T cells contributed to ACT-mediated elimination of primary tumors and rejected ACT-resistant melanoma cells lacking the targeted antigen. Mechanistically, ACT induced TNF-α- and cross-presenting dendritic cell-dependent tumor accumulation of endogenous CD8+ T cells and effective tumor elimination. Importantly, although lymphodepleting preconditioning enhanced ACT-mediated tumor elimination, it abrogated host antitumor immunity and protection against ACT-resistant melanoma cells. Enrichment of transcriptional signatures associated with TNF-α signaling, cross-presenting dendritic cells and tumor-specific CD8+ T cells in human melanoma tumors correlated with favorable responses to ACT and increased survival. Our findings reveal that long-term efficacy of ACT is determined by the interplay between transferred and endogenous CD8+ T cells and is undermined by lymphodepleting preconditioning, which ultimately favors ACT resistance.### Competing Interest StatementThe authors have declared no competing interest.

Gallbladder cancer (GBC) is commonly diagnosed at late stages when conventional treatments achieve only modest clinical benefit. Therefore, effective treatments for advanced GBC are needed. In this context, the administration of T cells genetically engineered with chimeric antigen receptors (CAR) has shown remarkable results in hematological cancers and is being extensively studied for solid tumors. Interestingly, GBC tumors express canonical tumor-associated antigens, including the carcinoembryonic antigen (CEA). However, the potential of CEA as a relevant antigen in GBC to be targeted by CAR-T cell-based immunotherapy has not been addressed. Here we show that CEA was expressed in 88% of GBC tumors, with higher levels associated with advanced disease stages. CAR-T cells specifically recognized plate-bound CEA as evidenced by up-regulation of 4-1BB, CD69 and PD-1, and production of effector cytokines IFN-γ and TNF-α. In addition, CD8+ CAR-T cells up-regulated the cytotoxic molecules granzyme B and perforin. Interestingly, CAR-T cell activation occurred even in the presence of PD-L1. Consistent with these results, CAR-T cells efficiently recognized GBC cell lines expressing CEA and PD-L1, but not a CEA-negative cell line. Furthermore, CAR-T cells exhibited in vitro cytotoxicity and reduced in vivo tumor growth of GB-d1 cells. In summary, we demonstrate that CEA represents a relevant antigen for GBC that can be targeted by CAR-T cells at the preclinical level. This study warrants further development of the adoptive transfer of CEA-specific CAR-T cells as a potential immunotherapy for GBC.

Dendritic cells (DCs) are antigen-presenting cells controlling T cell activation. In humans, the diversity, ontogeny, and functional capabilities of DC subsets are not fully understood. Here, we identified circulating CD88(-)CD1c(+)CD163(+) DCs (called DC3s) as immediate precursors of inflammatory CD88(-)CD14(+)CD1c(+) CD163(+)Fc epsilon RI+ DCs. DC3s develop via a specific pathway activated by GM-CSF, independent of cDC-restricted (CDP) and monocyte-restricted (cMoP) progenitors. Like classical DCs but unlike monocytes, DC3s drove activation of naive T cells. In vitro, DC3s displayed a distinctive ability to prime CD8(+) T cells expressing a tissue homing signature and the epithelial homing alpha-E integrin (CD103) through transforming growth factor beta (TGF-beta) signaling. In vivo, DC3s infiltrated luminal breast cancer primary tumors, and DC3 infiltration correlated positively with CD8(+)CD103(+)CD69(+) tissue-resident memory T cells. Together, these findings define DC3s as a lineage of inflammatory DCs endowed with a strong potential to regulate tumor immunity.

Memory CD8+ T cell responses have the potential to mediate long-lasting protection against cancers. Resident memory CD8+ T (Trm) cells stably reside in non-lymphoid tissues and mediate superior innate and adaptive immunity against pathogens. Emerging evidence indicates that Trm cells develop in human solid cancers and play a key role in controlling tumor growth. However, the specific contribution of Trm cells to anti-tumor immunity is incompletely understood. Moreover, clinically applicable vaccination strategies that efficiently establish Trm cell responses remain largely unexplored and are expected to strongly protect against tumors. Here we demonstrated that a single intradermal administration of gene- or protein-based vaccines efficiently induces specific Trm cell responses against models of tumor-specific and self-antigens, which accumulated in vaccinated and distant non-vaccinated skin. Vaccination-induced Trm cells were largely resistant to in vivo intravascular staining and antibody-dependent depletion. Intradermal, but not intraperitoneal vaccination, generated memory precursors expressing skin-homing molecules in circulation and Trm cells in skin. Interestingly, vaccination-induced Trm cell responses strongly suppressed the growth of B16F10 melanoma, independently of circulating memory CD8+ T cells, and were able to infiltrate tumors. This work highlights the therapeutic potential of vaccination-induced Trm cell responses to achieve potent protection against skin malignancies.