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 ≤ 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. © 1996 Wiley‐Liss, Inc.