Anti-Tumor activity of cytotoxic t lymphocytes elicited with recombinant and synthetic forms of a model tumor-associated antigen

The recent cloning of tumor-associated antigens (TAAs) recognized by CD8⁺T lymphocytes (TCD8⁺) has made it possible to use recombinant and synthetic forms of TAAs to generate TCD8⁺with anti-tumor activity. To explore new therapeutic strategies in a mouse model, we retrovirally transduced the experimental murine tumor CT26 (H-2^d), with the lacZ gene encoding our model TAA, β-galactosidase (β-gal). The transduced cell line, CT26.CL25, grew as rapidly and as lethally as the parental cell line in normal, immunocompetent animals. In an attempt to elicit TCD8⁺directed against our model TAA by using purely recombinant and synthetic forms of our model TAA, we synthesized a nine-amino-acid long immunodominant peptide of β-gal (TPHPARIGL), corresponding to amino acid residues 876–884, which was known to be presented by the L^dmajor histocompatibility complex (MHC) class I molecule, and a recombinant vaccinia virus encoding the full-length β-gal protein (VJS6). Splenocytes obtained from naïve mice and co-cultured with β-gal peptide could not be expanded in primary ex vivo cultures. However, mice immunized with VJS6, but not with a control recombinant vaccinia virus, yielded splenocytes that were capable of specifically lysing CT26.CL25 in vitro after co-culture with β-gal peptide. Most significantly, adoptive transfer of these cells could effectively treat mice bearing 3-day-old established pulmonary metastases. These observations show that therapeutic TCD8⁺directed against a model TAA could be generated by using purely recombinant and synthetic forms of this antigen. These findings point the way to a potentially useful immunotherapeutic strategy, which has been made possible by the recent cloning of immunogenic TAAs that are expressed by human malignancies.