Lack of evidence for natural cytotoxicity deficiency against human ex vivo tumour cells in allograft recipients

Background. Allograft recipients, who have a high risk of developing malignancies, are deficient in natural killer cells which mediate natural cytotoxicity against tumour cells. We evaluated the relevance of NK deficiency in transplant patients with regard to the natural lysis of human tumour cells. Methods. Target cells were ex vivo tumour cells, obtained from solid tumours from kidney transplant patients and non-immunocompromised patients. Peripheral blood was extracted from kidney recipients and from normal controls. mononuclear cells were separated after anti-CD3 and anti-TCR immunostaining to obtain NK and T cell subsets. LAK cells were obtained by in vitro IL2-activation. For each tumour, natural cytotoxicity assays were performed to compare effector cells from a kidney recipient with those from a normal control. Twenty-seven solid rumours, either allogenic or syngenic, were analysed, mainly consisting of renal, colon, and skin carcinomas. Results. Natural cytotoxicity assays on K562 targets confirmed the expected NK deficiency in the kidney recipients. However, the NK and LAK cells from the kidney recipients did not kill a smaller number of tumour target cells than the controls, whatever the tumour type, under both the syngenic and allogenic conditions. Conclusions. We conclude that natural cytotoxicity against human tumour cells cannot be extrapolated from the cytotoxicity assays with established cell lines, and that natural lysis of ex vivo human tumour cells is not impaired in transplant patients.