Contrasting frequencies of antitumor and anti-vaccine T cells in metastases of a melanoma patient vaccinated with a MAGE tumor antigen

Melanoma patients have high frequencies of T cells directed against antigens of their tumor. The frequency of these antitumor T cells in the blood is usually well above that of the anti-vaccine T cells observed after vaccination with tumor antigens. In a patient vaccinated with a MAGE-3 antigen presented by HLA-A1, we measured the frequencies of anti-vaccine and antitumor T cells in several metastases to evaluate their respective potential contribution to tumor rejection. The frequency of anti–MAGE-3.A1 T cells was 1.5 × 10−5 of CD8 T cells in an invaded lymph node, sixfold higher than in the blood. An antitumor cytotoxic T lymphocyte (CTL) recognizing a MAGE-C2 antigen showed a much higher enrichment with a frequency of ∼10%, 1,000 times higher than its blood frequency. Several other antitumor T clonotypes had frequencies >1%. Similar findings were made on a regressing cutaneous metastasis. Thus, antitumor T cells were ∼10,000 times more frequent than anti-vaccine T cells inside metastases, representing the majority of T cells present there. This suggests that the anti-vaccine CTLs are not the effectors that kill the bulk of the tumor cells, but that their interaction with the tumor generates conditions enabling the stimulation of large numbers of antitumor CTLs that proceed to destroy the tumor cells. Naive T cells appear to be stimulated in the course of this process as new antitumor clonotypes arise after vaccination

High frequency of antitumor T cells in the blood of melanoma patients before and after vaccination with tumor antigens

After vaccination of melanoma patients with MAGE antigens, we observed that even in the few patients showing tumor regression, the frequency of anti-vaccine T cells in the blood was often either undetectable or <10−5 of CD8 T cells. This frequency being arguably too low for these cells to be sole effectors of rejection, we reexamined the contribution of T cells recognizing other tumor antigens. The presence of such antitumor T cells in melanoma patients has been widely reported. To begin assessing their contribution to vaccine-induced rejection, we evaluated their blood frequency in five vaccinated patients. The antitumor cytotoxic T lymphocyte (CTL) precursors ranged from 10−4 to 3 × 10−3, which is 10–10,000 times higher than the anti-vaccine CTL in the same patient. High frequencies were also observed before vaccination. In a patient showing nearly complete regression after vaccination with a MAGE-3 antigen, we observed a remarkably focused antitumoral response. A majority of CTL precursors (CTLp's) recognized antigens encoded by MAGE-C2, another cancer-germline gene. Others recognized gp100 antigens. CTLp's recognizing MAGE-C2 and gp100 antigens were already present before vaccination, but new clonotypes appeared afterwards. These results suggest that a spontaneous antitumor T cell response, which has become ineffective, can be reawakened by vaccination and contribute to tumor rejection. This notion is reinforced by the frequencies of anti-vaccine and antitumor CTLs observed inside metastases, as presented by Lurquin et al. (Lurquin, C., B. Lethé, V. Corbière, I. Théate, N. van Baren, P.G. Coulie, and T. Boon. 2004. J. Exp. Med. 201:249–257)

MAGE-B5, MAGE-B6, MAGE-C2 and MAGE-C3: Four new members of the MAGE family with tumor-specific expression

A number of genes of the MAGE-A, B, and C families have been shown to code for antigens that are recognized on many human tumors by autologous cytolytic T lymphocytes. These antigens ought to be strictly tumor specific because the encoding MAGE genes are not expressed in normal adult cells except for male germline cells, which lack HLA expression. To identify new genes of this type, we performed representational difference analysis on a melanoma cell line by subtraction with a normal skin sample. This led to the identification of MAGE-C2, a new member of the MAGE-C family. A search for nucleotide sequences encoding MAGE-like proteins in public databases led to the identification of three additional MAGE genes, which were named MAGE-B5, MAGE-B6, and MAGE-C3. The four new MAGE genes are not expressed in normal tissues. except for testis, and are expressed in tumors of different histological origins. Therefore, like other MAGE genes expressed specifically in tumors, MAGE-B5, MAGE-B6, MAGE-C2, and MAGE-C3 ought to encode antigens that could be targets for cancer immunotherapy. Int. J. Cancer 87:55-60, 2000. (C) 2000 Wiley-Liss, Inc