Influence of whole-body PUVA treatments on human peripheral blood NK cell activity

Recent animal studies have demonstrated the importance of cancer surveillance in determining susceptibility to UV-induced cancers. On the other hand, even subcarcinogenic UV doses have been shown to suppress cancer surveillance immune mechanisms in experimental animals. To find out if photochemotherapy may compromise human cancer surveillance mechanisms, natural killer (NK) cell activity was monitored during PUVA treatment for up to 38 irradiations in dermatological patients. A significant depression of basal NK activity was seen during the first 4 to 24 irradiations in psoriatic patients. Thereafter, an increase toward starting values was seen in assays performed at high effector to target (E:T) ratios, but not at low ones. The maximal (interferon-boosted) NK activity, however, remained unchanged during the therapy, due to an increased sensitivity to IFN augmentation. The results are interpreted as a redistribution in the proportions of immature and mature NK cells. Thus, no serious effects of PUVA treatment on human natural resistance against cancer could be demonstrated, but longer follow up studies are recommended.