The specificity of recognition of pMHC complexes by T lymphocytes is determined by the V regions of the TCR α- and β-chains. Recent experimental evidence has suggested that Ag-specific TCR repertoires may exhibit a more Vα- than Vβ-restricted usage. Whether Vα usage is narrowed during immune responses to Ag or if, on the contrary, restricted Vα usage is already defined at the early stages of TCR repertoire selection, however, has remained unexplored. Here, we analyzed V and CDR3 TCR regions of single circulating naive T cells specifically detected ex vivo and isolated with HLA-A2/melan-A peptide multimers. Similarly to what was previously observed for melan-A-specific Ag-experienced T cells, we found a relatively wide Vβ usage, but a preferential Vα 2.1 usage. Restricted Vα 2.1 usage was also found among single CD8+ A2/melan-A multimer+ thymocytes, indicating that Vα-restricted selection takes place in the thymus. Vα 2.1 usage, however, was independent from functional avidity of Ag recognition. Thus, interaction of the pMHC complex with selected Vα-chains contributes to set the broad Ag specificity, as underlined by preferential binding of A2/melan-A multimers to Vα 2.1-bearing TCRs, whereas functional outcomes result from the sum of these with other interactions between pMHC complex and TCR.

From cancerous and non-cancerous patients, we derived stable clones of CD4 1 Treg, defined as clones that expressed high CD25 at rest, were anergic in vitro, and suppressed the proliferation of co-cultured CD4 1 cells. A conserved region of FOXP3 intron 1 was demethylated in all Treg clones, whereas it was methylated in non-regulatory Th and CTL clones. In our panel of human clones, this stable epigenetic mark correlated better with suppressive activity than did FOXP3 mRNA or protein expression. We used expression microarrays to compare Treg and Th clones after activation, which is required for suppressive function. The transcriptional profile that is specific of activated Treg clones includes a TGF-b signature. Both activated Treg and Th clones produced the latent form of TGF-b. However, SMAD2 phosphorylation was observed after activation in the Treg but not in the Th clones, indicating that only activated Treg clones produced the bioactive form of TGF-b. A TGF-b signature was also displayed by a Th clone ''suppressed'' by a Treg clone. In conclusion, the hallmark of our panel of activated human Treg clones is to produce bioactive TGF-b which has autocrine actions on Tregs and can have paracrine actions on other T cells.

We have analyzed the T cell responses of HLA-A1 metastatic melanoma patients with detectable disease, following vaccination with a recombinant ALVAC virus, which bears short MAGE-1 and MAGE-3 sequences coding for antigenic peptides presented by HLA-A1. To evaluate the anti-MAGE CTL responses, we resorted to antigenic stimulation of blood lymphocytes under limiting dilution conditions, followed by tetramer analysis and cloning of the tetramer-positive cells. The clones were tested for their specific lytic ability and their TCR sequences were obtained. Four patients who showed tumor regression were analyzed, and an anti-MAGE-3.A1 CTL response was observed in three of these patients. Postvaccination frequencies of anti-MAGE-3.A1 CTL were 3 × 10−6, 3 × 10−3, and 3 × 10−7 of the blood CD8 T cells, respectively. These three responses were monoclonal. No anti-MAGE-1.A1 CTL response was observed. These results indicate that, like peptide immunization, ALVAC immunization produces monoclonal responses. They also suggest that low-level antivaccine CTL responses can initiate a tumor regression process. Taken together, our analysis of anti-MAGE-3.A1 T cell responses following peptide or ALVAC vaccination shows a degree of correlation between CTL response and tumor regression, but firm conclusions will require larger numbers.

The cancer-germline gene MAGE-3 codes for tumor-specific antigens recognized on many tumors by T lymphocytes. A MAGE-3 antigen presented by HLA-A1 has been used in several vaccination trials on metastatic melanoma patients. Only a small minority of patients have shown evidence of tumor regression. Attempts to correlate the tumor rejections with the cytotoxic T lymphocyte (CTL) response against the vaccine have been hampered by the low level of these responses. In noncancerous individuals, the frequency of the T cell precursors against antigen MAGE-3.A1 is Ϸ4 ؋ 10 ؊7 CD8 T cells. The diversity of the T cell receptor repertoire of these anti-MAGE-3.A1 precursors was analyzed in one individual. The results indicate that it is very likely that the repertoire comprises >100 clonotypes. On this basis, it is possible to use not only the frequency of CTL precursors in the blood but also the presence of dominant clonotypes to ascertain in patients the existence of anti-MAGE-3.A1 responses as low as 10 ؊6 of CD8. With this approach, we observed a correlation between tumor regression and anti-MAGE-3.A1 CTL responses in patients vaccinated with a recombinant virus encoding the antigen and also in patients vaccinated with peptide-pulsed dendritic cells. In contrast, for patients showing tumor regression after vaccination with peptide alone, CTL responses were almost never observed. It is possible that even those CTL responses that are below our present detection level can trigger a sequence of events that leads to tumor regression. S hared tumor-specific antigens encoded by cancer-germline genes such as those of the MAGE family have been used for therapeutic vaccination of cancer patients. A number of small clinical trials on metastatic melanoma patients have been performed with the MAGE-3 168-176 antigen EVDPIGHLY, which is presented by HLA-A1 (1, 2). Evidence of tumor regression was observed in Ϸ20% of the patients, but clinical benefit was limited to Ϸ10% of the patients.Our initial work suggested that in most vaccinated patients, even in those who displayed tumor regression, it was difficult to ascertain the existence of an antivaccine T cell response. We nevertheless felt that it was crucial to know whether low-level responses had occurred and whether such cytotoxic T lymphocyte (CTL) responses showed a correlation with tumor regression to understand why most patients failed to show any evidence of regression. We therefore developed a sensitive approach based on in vitro restimulation of blood lymphocytes with the antigenic peptide over 2 weeks, followed by labeling with tetramers. To evaluate precursor frequencies, these mixed lymphocyte-peptide cultures were conducted under limiting dilution conditions. Cells that were labeled with the tetramer were cloned, the lytic specificity of the clones was verified, and their diversity was analyzed by T cell receptor (TCR) sequencing (3).As the interpretation of these analyses was based on both the frequency and the diversity of the anti-MAGE-3.A1 CTL clones, it was necessary t...

'Cancer-germline' genes such as the MAGE gene family are expressed in many tumors and in male germline cells but not in normal tissues. They encode shared tumor-specific antigens, which have been used in therapeutic vaccination trials of metastatic melanoma patients. To establish whether there is a correlation between tumoral regressions and T-cell responses against the vaccine antigen, we evaluated the responses of patients vaccinated with a MAGE-3 antigenic peptide or a recombinant virus coding for the peptide. Blood lymphocytes were stimulated with antigenic peptide followed by detection with tetramer, T-cell cloning, and TCR analysis. In 4/9 regressor patients and in 1/14 progressors we found a low level, usually monoclonal cytolytic T lymphocyte response against the MAGE-3 peptide.