Ly-6C+ natural T (NT) cells mediate immune surveillance against NK-sensitive and NK-resistant transplantable tumours in certain strains of mice.

We have previously shown that anti-Ly-6C monoclonal antibody (MAb) 2B6-F2 identifies a subset of (CBA +/- C57BL/6)F1 splenic NK-1.1+ natural T (NT) cells which kill the NK-sensitive YAC-1 target in vitro. Furthermore, these Ly-6C+ cells are responsible for 40-50% of in vitro YAC-1 killing in all mouse strains tested. In BALB/c and DBA/2 mice, these cells killed not only YAC-1 but also the NK-resistant WEHI-164 M1/16 target via a receptor that recognises a shared determinant on these targets in vitro. In the present study, the anti-tumour role of Ly-6C+ cells against the NK-sensitive B16 melanoma and NK-resistant tumours WEHI-7 T lymphoma and WEHI-164/1C fibrosarcoma was studied in vitro and in vivo. In vitro, B16, WEHI-7 and WEHI-164/1C tumour cell lines were highly sensitive to Ly-6C+ cell killing. In vivo, these same tumours showed significantly increased growth when transplanted s.c. into syngeneic mice treated with 2B6-F2 (0.05 < or = p < 0.0005), and this was most marked in the first 15 days following tumour appearance, when tumours were <15 mm in diameter. Our results show that Ly-6C+ cells play a role in controlling the growth of transplantable NK-sensitive B16 melanoma, and in BALB/c mice, at least, the repertoire of susceptible tumours is extended to include NK-resistant WEHI-7 and WEHI-164/1C. We conclude that Ly-6C+ NT cells play a role in immunosurveillance against NK-sensitive as well as NK-resistant tumours in certain strains of mice.