BIOTECHNOLOGICAL AND GENE THERAPEUTIC STRATEGIES IN CANCER-TREATMENT

New anti-cancer agents are being developed which incorporate cancer-ce ll-specific recognition functions and are thus able to distinguish bet ween normal and tumor cells. Recognition is dependent on the enhanced expression of antigenic determinants on the surface of tumor cells. Th e ErbB-2 receptor (ErbB-2R) is overproduced in a high percentage of ad enocarcinomas arising in the breast, ovary, lung and stomach, when com pared to normal cells. The tumor-enriched expression and extracellular accessibility make this receptor a suitable target for directed tumor therapy. A gene expressing the single-chain antibody molecule (scFv), specific for the extracellular domain of the ErbB-2R, was constructed by joining cDNAs encoding the light- and heavy-chain variable domains of the monoclonal antibody (mAb) FRP5. This scFv-encoding gene has be en used as a targeting domain for two effecters: (i) A recombinant imm unotoxin-encoding gene was constructed by adding sequences encoding a modified Pseudomonas aeroginosa exotoxin A (ETA) to the scFv-encoding DNA. (ii) Cytotoxic T-lymphocytes (CTL) with specificity for ErbB-2R-p roducing tumor cells were generated by retroviral transfer of a chimer ic gene which encodes the scFv(FRP5), a hinge region and the zeta-chai n of the T-cell. receptor (TCR) complex. The bacterially produced reco mbinant immunotoxin scFv(FRP5)-ETA binds specifically to the ErbB-2R a nd displays both in vitro and in vivo cytotoxic effects selective for tumor cells producing high levels of the ErbB-2R. Target cells express ing the ErbB-2R gene were lysed in vitro with high specificity by the scFv::hinge::zeta-expressing T-cells. The growth of ErbB-2R transforme d cells in athymic nude mice was retarded by adoptively transferred sc Fv::hinge::zeta-expressing CTL. Our results suggest that cytotoxic eff ector functions targeted to tumor cells via tumor selective-binding do mains may become useful therapeutic reagents. The selective tumor cell lysis by CTL grafted in vitro with a novel, MHC-independent recogniti on specificity could become a gene therapy approach to cancer treatmen t.