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We had previously demonstrated the role of CD103 integrin on lung tumor-infiltrating lymphocyte (TIL) clones in promoting specific TCR-mediated epithelial tumor cell cytotoxicity. However, the contribution of CD103 on intratumoral T cell distribution and functions and the prognosis significance of TIL subpopulations in non–small cell lung carcinoma (NSCLC) have thus far not been systematically addressed. In this study, we show that an enhanced CD103+ TIL subset correlates with improved early stage NSCLC patient survival and increased intraepithelial lymphocyte infiltration. Moreover, our results indicate that CD8+CD103+ TIL, freshly isolated from NSCLC specimens, display transcriptomic and phenotypic signatures characteristic of tissue-resident memory T cells and frequently express PD-1 and Tim-3 checkpoint receptors. This TIL subset also displays increased activation-induced cell death and mediates specific cytolytic activity toward autologous tumor cells upon blockade of the PD-1–PD-L1 interaction. These findings emphasize the role of CD8+CD103+ tissue-resident memory T cells in promoting intratumoral CTL responses and support the rationale for using anti–PD-1 blocking Ab to reverse tumor-induced T cell exhaustion in NSCLC patients.

The observation that depletion or inhibition of regulatory T cells (Tregs) unleashes efficient antitumor effector immune responses that can lead to tumor eradication in mice has opened new perspectives for the development of cancer immunotherapy. The quality and overall efficiency of the effector immune responses induced in the absence of Tregs seem to depend on multiple factors that determine the result of a battle involving effector T cells (Teffs), Tregs and tumor cells. In this study, we investigated the quality of tumor-associated antigens (TAAs) as one such factor. We show that the presence of a strong dominant antigen is required for the induction of effector responses capable of tumor eradication in the absence of Tregs. The sole addition of a dominant antigen on tumor cells does not change tumor growth in unmanipulated mice, but improves tumor eradication rate from a few to almost 100% in the absence of Tregs. This eradication can be shown to result from the recruitment and activation of specific Teffs recognizing this antigen. We also show that the presence of such dominant antigens has the side effect of restricting the breadth of the immune response to other TAAs, which could favor the generation of escape mutant by tumor editing. Taken together, our results highlight the potential, and some requirements for cancer immunotherapy based on Treg depletion. They also show that, ultimately, tumor fate depends on multiple factors that should all be taken into consideration for the design of more efficient immunotherapy.

We identified that the antigen preprocalcitonin (ppCT) is recognized on a human lung carcinoma by a cytotoxic T lymphocyte clone derived from autologous tumor-infiltrating lymphocytes. The antigenic peptide ppCT(16-25) is encoded by the gene calcitonin-related polypeptide alpha (CALCA), which codes for CT and is overexpressed in several lung carcinomas compared with normal tissues. The ppCT peptide is derived from the C-terminal region of the signal peptide and is processed independently of proteasomes and the transporter associated with antigen processing (TAP)1/TAP2 heterodimeric complexes. Instead, processing occurs within the endoplasmic reticulum by a novel mechanism involving signal pepsidase (SP) and signal peptide peptidase (SPP). Although lung cancer cells bearing the ppCT(16-25) epitope displayed low levels of TAP, restoration of TAP expression by interferon (IFN)-γ treatment or by TAP1/TAP2 gene transfer inhibited ppCT antigen presentation. Thus, the ppCT(16-25) human tumor epitope requires low TAP expression for efficient presentation. These results indicate that emerging SP-generated peptides represent alternative T cell targets that permit cytotoxic T lymphocytes to destroy TAP-impaired tumors, a process that helps to overcome tumor escape from CD8(+) T cell immunity. Additionally, our data suggest that ppCT is a promising candidate for cancer immunotherapy.

Decreased antigenicity of cancer cells is a major problem in tumor immunology. This is often acquired by an expression defect in the TAP. However, it has been reported that certain murine Ags appear on the target cell surface upon impairment of TAP expression. In this study, we identified a human CTL epitope belonging to this Ag category. This epitope is derived from preprocalcitonin (ppCT) signal peptide and is generated within the endoplasmic reticulum by signal peptidase and signal peptide peptidase. Lung cancer cells bearing this antigenic peptide displayed low levels of TAP, but restoration of their expression by IFN-γ treatment or TAP1 and TAP2 gene transfer abrogated ppCT Ag presentation. In contrast, TAP upregulation in the same tumor cells increased their recognition by proteasome/TAP-dependent peptide-specific CTLs. Thus, to our knowledge, ppCT16–25 is the first human tumor epitope whose surface expression requires loss or downregulation of TAP. Lung tumors frequently display low levels of TAP molecules and might thus be ignored by the immune system. Our results suggest that emerging signal peptidase-generated peptides represent alternative T cell targets, which permit CTLs to destroy TAP-impaired tumors and thus overcome tumor escape from CD8+ T cell immunity.

International audience; Early responses of Tregs and effector T cells (Teffs) to their first encounter with tumor cells have been poorly characterized. Here we have shown, in both implanted and in situ-induced mouse tumor models, that the appearance of tumor cells is immediately sensed by CD44hi memory Tregs that are specific for self antigens. The rapid response of these Tregs preceded and prevented activation of naive antitumor Teffs. The relative speed of the Treg versus the Teff response within the first 2-4 days determined the outcome of the antitumor immune response: tolerance or rejection. If antitumor memory Teffs were present at the time of tumor emergence, both Tregs and Teffs were recruited and activated with memory kinetics; however, the Tregs were unable to control the Teffs, which eradicated the tumor cells. This balance between effector and regulatory responses did not depend on the number of Tregs and Teffs, but rather on their memory status. Thus, in the natural setting, dominant tolerogenic immunosurveillance by self-specific memory Tregs protects tumors, just as it protects normal tissues. More generally, our results reveal that the timing of Treg and Teff engagement, determined by their memory status, is an important mode of regulation of immune responses.