VACCINATION WITH IL-12 GENE-MODIFIED AUTOLOGOUS MELANOMA-CELLS - PRECLINICAL RESULTS AND A FIRST CLINICAL-PHASE-I STUDY

Cytokine gene transfer into tumor cells has been shown to mediate tumo r regression and antimetastatic effects in several animal models via i mmunomodulation. Therefore, clinical protocols have been developed to treat cancer patients with cytokine gene-modified tumor cells, We inse rted the genes coding for the p35 and p40 chain of interleukin-12 (IL- 12) in two independent eukaryotic expression vectors and transduced me lanoma cells of 15 different primary tumor cultures with both plasmids by a ballistic gene transfer approach. Secreted IL-12 demonstrated st rong bioactivity by inducing interferon-gamma release from peripheral blood lymphocytes upon coculture with cell culture supernatants after IL-12 gene transfer which could at least partly be blocked by IL-12-sp ecific antisera. Further enrichment of transduced tumor cells by magne tic separation directly after gene transfer increased cytokine secreti on from a mean of 119 pg in the unsorted to 507 pg IL-12 (24 h/10(6) c ells) in the magnetically enriched cell fraction. Irradiation of these cells led to a further elevation of secreted IL-12 (mean 987 pg). Ele vated IL-12 levels were detected over 7 days after irradiation in vitr o. In a subsequent first clinical phase I study six patients with meta static melanoma were vaccinated with autologous, interleukin-12 gene-m odified tumor cells. Melanoma cells were expanded in vitro from surgic ally removed metastases, transduced by ballistic gene transfer, irradi ated and were then injected subcutaneously (s.c.) at weekly intervals. Clinically, there was no major toxicity except for mild fever. All pa tients completed more than four s.c. vaccinations over 6 weeks and wer e eligible for immunological evaluation. Post-vaccination, peripheral mononuclear cells were found to contain an increased number of tumor-r eactive proliferative as well as cytolytic cells as determined by a li miting dilution analysis in two patients. Two patients developed DTH r eactivity against autologous melanoma cells and one had a minor clinic al response. Biopsies taken from that patient's metastases revealed a heavy infiltration of CD4(+) and CD8(-) T lymphocytes. In conclusion, vaccination induced immunological changes even in a group or advanced, terminally ill patients. These changes can be interpreted as an incre ased antitumor immune response.