Human natural regulatory CD4⁺ T cells comprise 5–10% of peripheral CD4⁺T cells. They constitutively express the IL-2Rα−chain (CD25) and the nuclear transcription Foxp3. These cells are heterogeneous and contain discrete subsets with distinct phenotypes and functions. Studies in mice report that LAG-3 has a complex role in T cell homeostasis and is expressed in CD4⁺CD25⁺ T regulatory cells. In this study, we explored the expression of LAG-3 in human CD4⁺ T cells and found that LAG-3 identifies a discrete subset of CD4⁺CD25^highFoxp3⁺ T cells. This CD4⁺CD25^highFoxp3⁺LAG-3⁺ population is preferentially expanded in the PBMCs of patients with cancer, in lymphocytes of tumor-invaded lymph nodes and in lymphocytes infiltrating visceral metastasis. Ex vivo analysis showed that CD4⁺CD25^highFoxp3⁺LAG-3⁺ T cells are functionally active cells that release the immunosuppressive cytokines IL-10 and TGF-β1, but not IL-2. An in vitro suppression assay using CD4⁺CD25^highLAG-3⁺ T cells sorted from in vitro expanded CD4⁺CD25^high regulatory T cells showed that this subset of cells is endowed with potent suppressor activity that requires cell-to-cell contact. Our data show that LAG-3 defines an active CD4⁺CD25^highFoxp3⁺ regulatory T cell subset whose frequency is enhanced in the PBMCs of patients with cancer and is expanded at tumor sites.

The adjuvant activities of the human lymphocyte activation gene-3 (LAG-3) molecule have been evaluated in a human setting by investigating the ability of a soluble recombinant human LAG-3 protein (hLAG-3Ig) to enhance the in vitro induction of viral- and tumor-specific CTLs. We found that soluble human LAG-3 significantly sustained the generation and expansion of influenza matrix protein Melan-A/MART-1 and survivin-specific CD8⁺ T lymphocytes in peripheral blood mononuclear cells (PBMC) of both cancer patients and healthy donors, showing its ability to boost CD8⁺ T-cell memory response or to prime naive T cells in vitro. The peptide-specific T cells generated in the presence of hLAG-3Ig were endowed with cytotoxic activity and enhanced release of type 1 cytotoxic T (Tc1) cytokines and were able to recognize tumor cells expressing their nominal antigen. Phenotype and cytokine/chemokines produced by antigen-presenting cells (APC) of PBMCs exposed in vitro for 2 days to peptide and hLAG-3Ig indicate that the LAG-3–mediated adjuvant effect may depend on a direct activation of circulating APCs. Our data revealed the activity of hLAG-3Ig in inducing tumor-associated, antigen-specific CD8⁺ T-cell responses in a human setting and strongly support the conclusion that this recombinant protein is a potential candidate adjuvant for cancer vaccines. (Cancer Res 2006; 66(8): 4450-60)

Purpose: The progressive immune dysfunctions that occur in patients with advanced melanoma make them unlikely to efficiently respond to cancer vaccines. A multicenter randomized phase II trial was conducted to test whether immunization with modified HLA class I tumor peptides in the context of adjuvant therapy results in better immunologic responses and improved clinical outcomes in patients with early melanoma (stages IIB/C-III).Experimental Design: Forty-three patients were enrolled to undergo vaccination (n = 22) or observation (n = 21). The vaccine included four HLA-A*0201–restricted modified peptides (Melan-A/MART-1[27L], gp100[210M], NY-ESO-1[165V], and Survivin[97M]) emulsified in Montanide ISA51 and injected subcutaneously in combination with cyclophosphamide (300 mg/m2) and low-dose IL-2 (3 × 106 IU). The immune responses were monitored using ex vivo IFN-γ–ELISpot, HLA/multimer staining, and in vitro short-term peptide sensitization assays.Results: Vaccination induced a rapid and persistent increase in specific effector memory CD8+ T cells in 75% of the patients. However, this immunization was not associated with any significant increase in disease-free or overall survival as compared with the observation group. An extensive immunologic analysis revealed a significantly reduced cross-recognition of the corresponding native peptides and, most importantly, a limited ability to react to melanoma cells.Conclusions: Adjuvant setting is an appealing approach for testing cancer vaccines because specific CD8+ T cells can be efficiently induced in most vaccinated patients. However, the marginal antitumor activity of the T cells induced by modified peptides in this study largely accounts for the observed lack of benefit of vaccination. These findings suggest reconsidering this immunization strategy, particularly in early disease. Clin Cancer Res; 18(23); 6485–96. ©2012 AACR.

The prognostic value of Toll-like receptor 3 (TLR3) is debated in cancer, differing between tumor types, methods, and cell types. We recently showed for the first time that TLR3 expression on early stage non-small-cell lung cancer (NSCLC) results associated with a good prognosis. Here, we provide experimental evidences explaining the molecular reason behind TLR3’s favorable prognostic role. We demonstrated that TLR3 activation in vitro induces apoptosis in lung cancer cell lines and, accordingly, that TLR3 expression is associated with caspase-3 activation in adenocarcinoma NSCLC specimens, both evaluated by immunohistochemistry. Moreover, we showed that TLR3 expression on cancer cells contributes to activate the CD103+ lung dendritic cell subset, that is specifically associated with processing of antigens derived from apoptotic cells and their presentation to CD8+ T lymphocytes. These findings point to the relevant role of TLR3 expression on lung cancer cells and support the use of TLR3 agonists in NSCLC patients to re-activate local innate immune response.

Checkpoint inhibitors (CI) instigate anticancer immunity in many neoplastic diseases, albeit only in a fraction of patients. The clinical success of cyclophosphamide (C)-based haploidentical stem-cell transplants indicates that this drug may re-orchestrate the immune system. Using models of triple-negative breast cancer (TNBC) with different intratumoral immune contexture, we demonstrate that a combinatorial therapy of intermittent C, CI, and vinorelbine activates antigen-presenting cells (APC), and abrogates local and metastatic tumor growth by a T-cell–related effect. Single-cell transcriptome analysis of >50,000 intratumoral immune cells after therapy treatment showed a gene signature suggestive of a change resulting from exposure to a mitogen, ligand, or antigen for which it is specific, as well as APC-to-T-cell adhesion. This transcriptional program also increased intratumoral Tcf1+ stem-like CD8+ T cells and altered the balance between terminally and progenitor-exhausted T cells favoring the latter. Overall, our data support the clinical investigation of this therapy in TNBC. Significance: A combinatorial therapy in mouse models of breast cancer increases checkpoint inhibition by activating antigen-presenting cells, enhancing intratumoral Tcf1+ stem-like CD8+ T cells, and increasing progenitor exhausted CD8+ T cells.