Total Lymphoid Irradiation for Immunosuppression

Abstract

Total lymphoid irradiation (TLI) is a potent means of immunosuppression. The immunosuppressive effects of TLI in patients treated for Hodgkin’s disease were detailed by Fuks et al. (1976) in an analysis of 227 treated and untreated patients with Hodgkin’s disease. They observed a marked depression of the total peripheral blood lymphocyte count during TLI which persisted for about two years, with gradual recovery to normal levels thereafter in most patients. Examination of lymphocyte populations in these patients revealed differential effects of TLI on specific lymphocyte subsets. For example, the majority of patients were noted to have a persistent decrease in the total number and percent of T-cells (T-lymphocytopenia) and in the same patients there was a cornpensatory increase in the total number and percent of B-cells (B-lymphocytosis). Therefore, in long term followup, most patients had normal total peripheral blood lymphocyte counts but had a reversal of the normal T/B cell ratio. Furthermore, when subsets of T-cells were examined in patients treated with TLI, a differential sensitivity of various T-cell subsets was observed (Posner et al. 1983). The T-lymphocytopenia was primarily due to a decrease in the number of helper T-cells with a persistence of normal or nearly normal numbers of suppressor T-cells. This resulted in a reversal of the normal helper: suppressor T-cell ratio to a value less than 1.0 compared to a value greater than 1.0 in normal controls or untreated patients with Hodgkin’s disease.