Genetic unresponsiveness to a murine fibrosarcoma determined by the host genetic environment but not by lymphocyte precursor genotype.

(BALB/c X C3Hf) (H-2d X H-2k)F1 hybrid mice but not parental BALB/c or other BALB/c X H-2k F1 hybrids, were unresponsive in transplantation and in neutralization (Winn) assay against a 3-methylcholanthrene-induced BALB/c fibrosarcoma. In BALB/c mice the antitumor activity revealed by Winn assay with antitumor immune lymphoid cells was shown to be tumor specific and mediated by Thy 1+ cells. Mouse chimeras were constructed by injecting fetal liver cells into irradiated recipients. BALB/c----(BALB/c X C3Hf)F1 and control (BALB/c X C3Hf)F1----(BALB/c X C3Hf)F1 chimeras were unable to develop a transplantation immunity against the immunizing tumor, whereas (BALB/c X C3Hf)F1----BALB/c chimeras were able to respond to the immunizing tumor. Thus, unresponsiveness was shown to be due to a defect in the maturation of precursor stem cells both of parental and F1 hybrid origin in the body of the (BALB/c X C3Hf)F1 animals.