Alternation in malignancy of rat spontaneous tumour cells after in vitro supertransformation by ASV.

Neoplastic cells from a spontaneous mammary carcinosarcoma (SAM-LEW) of LEW/CUB rats and spontaneously in vitro transformed Lewis rat embryo fibroblasts (LW13K2) were infected in vitro and transformed with avian sarcoma virus B77. Clones of B77 super-transformants (SAMB774, K2B773) were isolated and tested in vitro and in vivo for the rescue of infections B77 virus with positive results. These virogenic B77 supertransformants were then tested in the immunogenetic test of malignancy established in the LEW rat congenic system. The supertransformants exhibited restricted growth on RT1-different congenic recipients without killing them. It was in sharp contrast to parental tumours of spontaneous origin which were able to kill about one half of the RT1-different congenic recipients. This indicated a decrease in malignancy from grade IV (spontaneous parental) to grade III (ASV supertransformants) as expressed in the ITM.