DNA vaccination against the ovarian carcinoma-associated antigen folate receptor alpha (FR alpha) induces cytotoxic T lymphocyte and antibody responses in mice

Human folate receptor alpha (FR alpha) is a folate-binding protein that is selectively overexpressed in ovarian carcinoma and has been regarded as a s uitable target antigen for immunotherapy purposes. To study the possible us e of this antigen in DNA vaccination, FR alpha cDNA was ligated into the VR 1012 (Vical) expression vector under the transcriptional control of the cyt omegalovirus promoter. A total of 100 mu g of purified plasmid DNA was inje cted intramuscularly in BALB/c mice three times at 14-day intervals. At 10 days after the second injection, the sera of the animals (100%) displayed s ignificant antibody titers (by indirect immunofluorescence and fluorescence -activated cell sorter analysis) against syngeneic C26 cells transduced wit h FR alpha, but not against unmodified C26 cells. Immunoglobulin G2a was th e predominant isotype. In addition, specific cytotoxic T lymphocyte activit y against FR alpha-transduced C26 cells could be detected in splenocytes fr om all immunized animals. Coinjection of a plasmid containing interleukin-2 cDNA increased both antibody titers and cytotoxic T lymphocyte activity. C hallenge by subcutaneous injection with FR alpha-transduced C26 cells (perf ormed 10 days after the third injection) showed a statistically significant delay in tumor growth. Vaccination with the FR alpha and interleukin-2 cDN A mixture, which was performed after an intravenous injection of FR alpha-t ransduced cells, enhanced the mean survival time and reduced the number of lung metastases, thus suggesting that such vaccination is effective even ag ainst preexisting tumor cells.