The effect of AS101 on the reconstitution of T-cell reactivity following irradiation or cyclophosphamide treatment.

AS101 (ammonium trichloro[dioxyethylene-O-O']tellurate) is a new synthetic compound previously described by us as having immunomodulating properties and minimal toxicity. Phase II clinical trials are currently in progress with AS101 on cancer patients. AS101 has been recently found to have both radioprotective and chemoprotective effects on hemopoiesis of irradiated mice or mice treated with cyclophosphamide (CYP). In this study the effect of AS101 on the recovery of the immune system from sublethal irradiation or CYP treatment was assessed. Mice were injected once with AS101 24 h before being irradiated with 450 cGy or treated with 250 mg/kg body weight CYP. At various time points after treatment the functional capacity of the immune system was determined. It was found that AS101 could significantly reduce the decrease in the number of spleen cells and thymocytes, the decrease in the proliferation rate of these cells to the T-cell mitogen concanavalin A, and the decrease of interleukin 2 secretion by spleen cells. AS101 could initially protect these functions because they were increased over control levels immediately 24 h after treatment. AS101 was also shown to normalize the distribution of T-cell subsets that was impaired following both treatments. These results suggest an immunoregulatory role for AS101 in counteracting chemotherapy and radiation-induced immunological suppression as well as its usefulness as an adjunct treatment of cancer when used in combination with CYP or irradiation.