H-2 restriction and non-restriction of T-cell-mediated cytotoxicity against mouse mammary tumour targets

CELL-MEDIATED CYTOTOXICITY (CMC) against C3H/Umc (C3H) syngeneic mammary tumours measured in vitro, after in vivo immunisation, is mediated by cytotoxic T lymphocytes (CTL) and is directed mostly against cross-reacting antigens related to the mouse mammary tumour virus (MTV)1–3. The long-term CMC assay required for detecting this response against adherent target cells has complex kinetics and at least two superimposing components: (1) an initial early peak of cytotoxicity, detectable at approximately 6 h and accounting for 20–30% of the CMC, and (2) a later peak, detectable after 18–20 h and representing an additional 40–50% of the cytotoxic effect3. Both peaks are mediated by CTL with the Ly23 phenotype (that is, Ly1−Ly2,3+); however, non-cytotoxic T cells of Ly1 and probably Ly123 phenotype (that is, Ly1+Ly2,3− and Ly1+Ly2,3+, see refs 3 and 4 for nomenclature and functional characteristics of these T-cell subsets) are required for the expression of the second cytotoxic peak3. On the other hand, the short-term assays of CTL-mediated CMC show single-hit kinetics5, perhaps comparable to part of the early CMC peak in our system. During our studies of immunity to syngeneic mammary tumours, we observed that when C3H or C3Hf immune CTL were tested against allogeneic MTV-induced mammary tumour targets, a relative degree of H–2 restriction of CMC was observed2, although not of the magnitude detected in other systems using mostly short-term CMC assays6–11. The experiments reported here show that when the kinetics of the CMC response against adherent syngeneic and allogeneic mammary tumour targets were compared, some differences became apparent: whereas the early CMC peak showed absolute H–2 restriction, no restriction was observed in the late CMC peak, although both events were mediated by Ly23 CTL (ref. 3).