Prevention of SV40 virus oncogenesis in hamsters. I. Tumor resistance induced by human cells transformed by SV40.

SV40 virus-induced tumors, and cell cultures transformed by this virus, possess new antigens. The one most frequently studied has been the induced complementfixation antigen, ICFA.1-5 Studies which measure parameters other than CF ability would suggest that more than one new antigenic component is present as a result of virus-induced transformation. This especially pertains to studies with the SV40-induced hamster tumors, and cell cultures prepared from such tumors, which are highly effective in preventing the occurrence of tumors in hamsters inoculated with SV40 when newborn.6 Since results of studies with SV40 ICFA suggest that it is located primarily in the cell nucleus, the question arises whether the tumor rejection mechanism is directed against, or mediated by, this antigen. Human cell cultures transformed by SV40 similarly possess ICFA,2-5 and this antigen is retained after the cultures have recovered from "crisis"4 7 and no longer shed infectious virus. It was of interest to determine whether SV40-transformed human cells can also prevent SV40 virus-induced oncogenesis even though the cells are of a species foreign to the experimental host. This report presents evidence indicating that this effect is demonstrable and most probably results from an antigen other than ICFA. For purpose of identification we have indicated this postulated new antigen as SV40 "induced tumor resistance antigen" or ITRA. Materials and Methods.-Virus strain: SV40 virus strain Rh 911, isolated from a culture of primary rhesus monkey kidney, was propagated in cell cultures of grivet monkey (Cercopithecus aethiops) kidney (GMK) as described previously.8 Hamsters: Pregnant hamsters were obtained from Lakeview Hamster Colony, Newfield, N. J. Animal care and observations were as described previously.6 Human cell cultures transformed by SV40 and recovered after crisis were documented previously;7 these were W-18VA2 (adult buccal mucosa), W-98VA1 (adult skin), and WI-26VA4 (embryonic lung). Cell culture medium consisted of 10% calf serum in Eagle's basal medium (BME) supplemented to twice the concentration with amino acids and vitamins. SV40 hamster tumor tissue culture line, F5-1, was propagated serially as described as monolayer cell cultures employing medium 199 with 5% calf serum. The cell cultures were free of infectious SV40 virus but contained SV40 ICFA. Trypsin, 0.25% in BME, was employed for routine subcultivation and for dispersing cells for the immunizing inocula. Preparation of immunizing inocula: Fourto six-day-old cell cultures were trypsinized, and the resultant suspensions were adjusted to contain the desired cell concentration in each 1 ml of BME. When viable whole cells were employed for immunization, no treatment was necessary. Frozen and thawed suspensions were prepared by several cycles of slow freezing (-200C) and thawing (room temperature) of the whole cell preparations. Formalin-treated cells were prepared by the method described by Bismanis.9 Trypsinized cells were sedimented by centrifugation, and a 1-2% suspension was prepared in BME containing 0.5% formalin. These suspensions were aspirated with care, recentrifuged, and the sedimented cells were treated with 0.5% formalinBME for 3 successive cycles. For inoculation, the cells were adjusted to the appropriate concentration in BAIE. Experimental design: Newborn hamsters, less than 24 hr old, were inoculated subcutaneously into the inteiscapular space, each receiving 0.2 ml undiluted SV40 containing 107-108 TCID50.