During attempts to transplant tumors induced in newborn inbred LSH hamsters by virus-free, clonally derived lines of UV-inactivated, Ad2-transformed LSH hamster embryo cells to 3- to 4-week-old weanling animals, most of the tumors

Adenovirus 2 (Ad2) inactivated by UV was used to transform LSH hamster embryo cells. Evaluation of transformed cell lines produced by Ad2 (prototype strain adenoid 6) or isolates of Ad2 obtained from children in Washington, D. C., or West Bengal, India, showed that 13 of 15 lines induced tumors when injected into newborn inbred LSH or randomly bred NIH ham sters [1o@cells/hamster with a median tumor incidence in syngeneic newborns of 65% (range, 8 to 100%)J. Six of these cell lines did not induce tumors when 1O@cells were injected s.c. into weanling animals over 21 days old. In contrast to the Ad2-transformed lines, similarly derived cell lines transformed by adenovirus 12 or SV4O uniformly produced tumors in wean lings following s.c. inoculation of 1O@cells. Transplantation of tumors from animals treated as newborns with Ad2-trans formed cell lines to other newborns was readily accomplished in 639 of 640 (99.8%) inoculated newborns. However, only 53 of 467 (11.3%) weanling hamsters challenged with these tumor lines developed neoplasms. Each of these Ad2-transformed lines contained Ad2 T-antigen detectable by complement-fix ation or immunofluorescence. None of six lines yielded Ad2 by Sendai fusion with human embryonic kidney cells or other contaminating agents by a variety of assays. The difference in oncogenicity in weanling hamsters of Ad2-transformed cells and Ad2 newborn tumor lines compared to adenovirus 12 and SV4O-transformed cells was not related to the dose of tumor injected or to differences in in vitro growth properties of the cell lines (e.g. , doubling times, saturation densities, growth in spinner medium, or colony formation in soft agar). With the two tumor lines tested, weanling rejection of transplants of tumors from newborn hamsters could not be overcome by inocula containing 25 times the usual dose of tumor suspension. These same two newborn tumor lines produced progressively enlarg ing neoplasms in 17 to 77% of syngeneic weanling hamsters which had been thymectomized as newborns. These results suggest that the production of virus-transformed cells which are not oncogenic in immunocompetent syngeneic hamsters is a general property of Ad2 and that the Ad2-transformed ham ster cell system may be a useful model for studying the inter action of the viral genome, the transformed cell, and developing host immunity in virus-induced carcinogenesis.