Antitumor Activity of Immunotoxins with T-Cell Receptor–like Specificity against Human Melanoma Xenografts

In this study, we have explored the use of Fab-toxin proteins (immunotoxin) to target antigen-specific MHC-peptide complexes of in vitro and in vivo cancer cells. A human phage display library was used to screen for T-cell receptor (TCR)–like antibodies that are highly specific for the peptide melanoma-associated antigen MART-1 26-35 presented by HLA-A201. We also used previously selected TCR-like antibodies specific for the peptide melanoma-associated antigen gp100 280-288 presented by HLA-A201. The recombinant immunotoxin constructs were generated by fusing the targeting Fab fragment to a truncated form of Pseudomonas exotoxin, PE38KDEL. These immunotoxins bound with high affinity to the EBV-transformed JY cell line pulsed with the aforementioned peptides and internalized within 30 min. A significant inhibition of protein synthesis, which resulted in cell death, was detected at 24 h. MART-1–specific and gp100-specific immunotoxins bound and killed HLA-A201 melanoma MART-1 + and gp100 + cell lines that were presented at natural levels but do not bind to HLA-A201 − or to HLA-A201 + MART-1 − and gp100 − cell lines. In severe combined immunodeficient mice, MART-1 and gp100 immunotoxins significantly and discriminately inhibited human melanoma growth. These results show that MHC class I/peptide complexes can serve as a specific target for passive immunotherapy of cancer. [Cancer Res 2008;68(15):6360–7]