Abstract
NK cell activity was studied in childhood acute leukemia by 51Cr-release assay using K562 target cells.
NK cell activity of ALL in the remission phase was 23.5±9.2% specific lysis (n=25), being depressed as compared with the normal value of 47.2±5.7% (p<0.01). The decrease of NK cell activity became predominant at the time of onset or relapse: % specific lysis was 9.0±4.9% (n=20). The majority of off-therapy ALL patients still exhibited lower NK cell activity than normal subjects. In vitro studies demonstrated that, among the conventional anti-leukemic agents, prednisolone, arabinosylcytosine and daunorubicine depressed NK cell activity. The anti-leukemic agents appear to contribute to the impaired NK cell activity in ALL. The continuous decrease of NK cell activity even after the cessation of antileukemic therapy, however, cannot be explained by their effect alone, suggesting that the NK cell impairment is one of the characteristic features of ALL.
Serial assays of NK cell activity in five patients demonstrated that a significant decrease of NK cell activity occured 4 to 8 weeks before the relapse when there were no apparent changes of the peripheral blood cell counts and bone marrow pictures. In frank relapse, the NK cell activity was further depressed. These results demonstrated that the assay of the NK cell activity is a useful tool to predict and detect relapse of ALL at an earlier time. The in vitro responsiveness of NK cells to IFN or poly I: C varied according to the stage of the disease.
In remission phase, NK cells responded to both IFN and poly I: C and their activated activity reached the normal endogenous level. NK cells treated with antileukemic agents were also augmented in their activity in response to IFN.
