Depletion of NK1.1+ cells by repeated i.p. injections of PK136 antibody significantly enhanced growth of MHC class I+ tumours in syngeneic mice. Depletion starting before tumour transplantation or on the day of transplantation substantially accelerated tumour growth; depletion starting on day 7 or 14 after tumour transplantation was without any effect. These results indicate that the NK1.1+ cells play an important inhibitory role during the early phase of the growth of some MHC class I+ tumours. Since the relevant target for NK cells is a "missing self" signal, absence of the MHC class I molecules, the NK cells cannot be expected to directly inhibit the growth of the MHC class I+ tumours. The results indicate that the effects of non-NK cells or indirect effects mediated by NK cell interactions and release of cytokines were responsible for the results.

Institute of Molecular Genetics Academy of Sciences of the Czech Republic Prague Czech Republic

Immunotherapy augments the effect of 5-azacytidine on HPV16-associated tumours with different MHC class I-expression status