Lymphoid irradiation results in long‐term increases in natural killer cells in patients treated for Hodgkin's disease

Therapeutic lymphoid irradiation has been shown to produce profound long‐term alterations in lymphocyte subpopulations and immunologic responsiveness. Dual immunofluorescence flow cytometry and functional cytolytic assays were used to investigate the effects of lymphoid irradiation either alone or in combination with chemotherapy on T‐cell and natural killer (NK) cell populations in the blood of patients treated for Hodgkin's disease. Patients treated with mantle and paraaortic lymphoid irradiation show significant increases in the proportion of cells bearing the NK cell phenotypic marker Leu‐11 (CD16). These patients also display proportionately increased cytotoxicity againat K.562 tumor targets in vitro. A sizable number of these NK cells label dimly with Leu‐2 (CD8) although they lack the pan‐T‐cell marker Leu‐4 (CD3). The emergence, after lymphoid irradiation of this population of Leu‐11⁺2⁺ NK cells may lead to an apparent decrease in the ratio of helper to suppressor T‐cells, although the actual ratio of these T‐cell subsets generally is normal. These changes persist for years after the completion of radiation therapy. It was concluded that lymphoid irradiation may produce profound changes in NK cell populations in patients treated for Hodgkin's disease; the clinical significance of these changes is unclear.