Marie-Thérèse Duffour

The expression of mouse gene P1A in testis does not prevent safe induction of cytolytic T cells against a P1A‐encoded tumor antigen

Tumor antigen P815AB is recognized by cytolytic T lymphocytes (CTL) on mouse mastocytoma P815. This antigen is encoded by P1A, a gene activated in several tumors but silent in normal tissues except for testis and placenta. Notwithstanding the expression of P1A in testis, we found that male mice mounted P815AB‐specific CTL responses as efficiently as females. The responding males remained fertile and no autoimmune lesions were observed in their testes. By immunohistochemistry with a rabbit antiserum directed against the P1A protein, we identified spermatogonia as the testicular cells expressing P1A. The absence of MHC class‐1 molecules on spermatogonia could be one of the mechanisms of protection against testicular autoimmunity, as the antigenic peptide should not be displayed at the cell surface. Human genes MAGE, BAGE and GAGE, which also code for tumor antigens recognized by autologous CTL, are not expressed in normal tissues other than testis. The results obtained in mice with antigen P815AB suggest that immunization of human males with such antigens will not generate autoimmune side‐effects. Although P1A is strongly expressed in placenta, we also found that gestation did not prevent generation of CTL responses against antigen P815AB, and that such CTL responses did not affect gestation outcome. We identified labyrinthine trophoblasts as the placental cells expressing P1A. Again, the absence of MHC class‐1 molecules on these cells provides a plausible explanation for placental protection, although other mechanisms may also play a role. Int. J. Cancer, 70:349–356, 1997.

Induction of a cytolytic T-cell response in mice with a recombinant adenovirus coding for tumor antigen P815A

We investigated the efficacy of a recombinant adenovirus in inducing a cytolytic T‐lymphocyte (CTL) response in mice against tumor antigen P815A, which is present on mouse mastocytoma P815. The recombinant adenoviral vector (Adeno.PIA) contained the sequence coding for the antigenic nonapeptide which binds to the H‐2.Ld molecule to form antigen P815A. We verified that murine cells infected in vitro with Adeno.PIA were lysed by an anti‐P815A CTL clone. Mice then received a single intradermal injection of Adeno.PIA, and after a few weeks their spleen cells were stimulated in vitro with tumor cells expressing antigen P815A. An anti‐P815A CTL response was observed with the spleen lymphocytes of nearly all the mice, providing the lymphocytes were re‐stimulated in vitro with cells expressing both P815A and co‐stimulatory molecule B7.1. When the stimulatory cells did not express B7.1, a specific CTL response was observed in only 45% of the mice, and it was less intense. The Adeno.PIA viral vector was unable to raise an anti‐P815A response in mice that had been previously infected with a recombinant adenovirus carrying the β‐galactosidase gene or with a defective adenovirus. We conclude that adenoviral vectors may be very useful for the priming of cytolytic T‐cell responses directed against human tumor antigens. Other modes of immunization may be necessary to boost the responses induced with adenoviral vectors.

Inducible Hsp70 as target of anticancer immunotherapy: Identification of HLA-A*0201-restricted epitopes

The design of a broad application tumor vaccine requires the identification of tumor antigens expressed in a majority of tumors of various origins. We questioned whether the major stress‐inducible heat shock protein Hsp70 (also known as Hsp72), a protein frequently overexpressed in human tumors of various histological origins, but not in most physiological normal tissues, constitutes a tumor antigen. We selected the p391 and p393 peptides from the sequence of the human inducible Hsp70 that had a high affinity for HLA‐A*0201. These peptides were able to trigger a CTL response in vivo in HLA‐A*0201‐transgenic HHD mice and in vitro in HLA‐A*0201+ healthy donors. p391‐ and p393‐specific human and murine CTL recognized human tumor cells overexpressing Hsp70 in a HLA‐A*0201‐restricted manner. Tetramer analysis of TILs showed that these Hsp70 epitopes are targets of an immune response in many HLA‐A*0201+ breast cancer patients. Hsp70 is a tumor antigen and the Hsp70‐derived peptides p391 and p393 could be used to raise a cytotoxic response against tumors of various origins.

Strategies for cancer gene therapy using adenoviral vectors.

Modification of tumor cells using gene transfer either to enhance host immunity or to act directly on tumor cells is being intensively studied in animal models. Remarkable results have yielded to approved clinical protocols in the treatment of cancer patients using this approach. Several methods of gene delivery have been developed. This article is particularly devoted to the interest of the use of adenoviral vectors in the different strategies of cancer gene therapy.

Induction of cytolytic T lymphocytes by immunization of mice with an adenovirus containing a mouse homolog of the human MAGE-A genes.

Abstract The genes of the MAGE-A family code for antigens that are strictly tumor-specific and are shared by many human tumors. Melanoma patients have been immunized against these antigens and some tumor regressions have been observed. However, no unequivocal evidence of cytolytic T cell responses has been obtained by analyzing the blood lymphocytes of these patients. Hence it was considered worthwhile to examine in mouse systems whether or not immunization against antigens derived from the mouse Mage homologs can produce cytolytic T cell responses. We have identified an antigenic peptide encoded by mouse gene Mage-a2, and here we show that immunization of DBA/2 mice with a recombinant adenovirus containing either just the sequence encoding this peptide or a large part of the Mage-a2 coding sequence produces strong cytolytic T cell responses. The Mage-a2 system should prove useful for the comparison of vaccination modalities that could be applied to human patients in therapeutic vaccination trials with MAGE antigens.