Induction of anti-tumour immunity by suicide-gene-modified HPV-16-transformed hamster cells

From K3/II, which is a highly oncogenic HPV16-transformed Syrian hamster cell line, thymidine-kinase(TK)-less cells, denoted B 49, were derived. B49 cells were transfected by a plasmid containing the herpes-simplex-virus TK gene (HSV TK) and several sub-lines expressing this gene were isolated from the transfected cultures. The HSV TK+ cells were highly sensitive to ganciclovir (GCV) and other anti-viral substances whose inhibitory effect is based on their phosphorylation by HSV TK. One of the cell lines, denoted KL1/6, exhibited relatively high stability of the HSV TK+ phenotype and was used in subsequent experiments. When KL1/6 cells were co-cultivated in the presence of GCV with various other cell lines of hamster, mouse or monkey origin, the by-stander effect (BE) was observed. GCV treatment of hamsters prevented development of tumours after the administration of KL1/6 cells but not K3/II cells. The treatment of animals with already established KL1/6-induced tumours resulted in tumour regression in all instances, but complete regression was observed only in animals carrying small tumours. The BE of KL1/6 cells on K3/II cells was also seen in vivo. In addition, concomitant immunity was observed in animals simultaneously inoculated with KL1/6 cells and K3/11 cells at 2 separate sites of the body. This effect was evident not only in animals in which KL1/6 tumours developed, but also in those in which tumour outgrowth was prevented by GCV treatment. In other experiments it was demonstrated that one KL1/6 + GCV treatment resulted in partial resistance, 2 such treatments in complete resistance to the challenge with K3/II cells.