Differences in the Rejection of an Allogeneic Tumor Graft in two Strains of Inbred Mice and Their F₁ Hybrids¹

Abstract

The rejection of a Sarcoma tumor (Sal) was compared in two histoin-compatible strains of mice (C57BL/6, CBA) and in their F₁ hybrids. Based on the tumor growth curves, allograft rejection appeared much stronger in C57BL/6 than in CBA mice, the former rejecting the tumor graft rapidly, the latter showing delayed regression with occasional tumor enhancement. Differences in the response to the tumor allograft between male and female recipients were more pronounced in CBA than in C57BL/6 mice. Male and female C57BL/6 recipients exhibited the same rate of rejection, whereas the mortality in male CBA mice was higher than in females. This difference was even more striking for the (C57BL/6 x CBA) F₁ hybrids: the female hybrids rejected tumor grafts as rapidly as C57BL./6 recipients, whereas the male hybrids failed to reject the tumor allograft in most of the cases (80%) and died from progressive tumor growth. The humoral and cellular immune responses tested in vitro were much weaker and somewhat delayed in CBA mice as compared to those of C57BL/6 recipients. These findings would suggest that the immunogenicity of the different H-2 specificities is not identical in these two strains for the different immune responses and that histoincompatibility at the H-2 locus is not necessarily the major factor responsible for allograft rejection.