Passive immunotherapy of mice bearing Ehrlich ascites tumor expressing human, membrane-bound placental alkaline phosphatase.

The objective of our study was to test if a tumor expressing a transgene coding for a membrane-bound protein is amenable to immunotherapy by antibodies to the same protein. To this end, we have established an Ehrlich ascites tumor (EAT) cell line, EAT-DAP, stably expressing human, membrane-bound placental alkaline phosphatase (PLAP) by infecting EAT cells (EATC) with the retroviral vector DAP and selecting neomycin-resistant cells. EATC and EAT-DAP cells grew at similar rates in vitro, and produced ascites tumor in Swiss-Webster mice with similar efficiency. We have treated mice bearing EAT-DAP ascites tumor with a mouse monoclonal antibody to human PLAP or with a monoclonal antibody to human C proteins of the heterogenous ribonucleoprotein complex (hnRNP). The average survival of mice treated with anti-hnRNP was 16.4 +/- 1.1 days (n = 8). Treatment with anti-PLAP prolonged the survival of mice; in 4 mice average survival was 23.3 +/- 5.7 days. Four animals, however, survived for 60 days when they were killed and had no visible signs of tumor. These data support the notion that passive immunotherapy using antibodies against a membrane protein, expressed in tumor cells transduced by a viral vector coding for that protein, may be effective in controlling tumor growth.