Cellular stimuli for rejection of sarcoma I tumor allografts by BALB/c recipient mice

We have evaluated the role of passenger leukocytes in Sarcoma I (SaI) tumor allograft rejection by BALB/c recipient mice. SaI tumor cells grown in tissue culture expressed low levels of class I MHC antigens as determined by flow cytometry. Ascites-derived tumor cells contained additional cell populations of A/J host origin which expressed high levels of class I and class II alloantigens. Tissue culture-derived SaI grafts grew progressively or were rejected in delayed fashion by some BALB/c hosts. In contrast, ascites-derived tumor allografts were rejected rapidly by 100% of recipient mice. Passenger cells appear to be responsible for these striking differences in immunogenicity because the addition of allogeneic A/J splenocytes to the tissue culture form of SaI caused rapid rejection. When tissue culture- and ascites-derived tumors simultaneously were grafted on opposite shoulders of recipient mice, both tumors were rejected. These data indicate that passenger cells provide the primary stimulus for SaI tumor allograft rejection by BALB/c mice. The mechanism of SaI enhancement by anti-Ia antibodies may be analogous to the prolonged survival of endocrine grafts after depletion of Ia+ passenger leukocytes.