Use of T cell cloning to detect in vivo mutations induced by cyclophosphamide

By cloning T cells, mutations at the hypoxanthine-guanine phosphoribosyltransferase locus were quantified in peripheral blood lymphocytes of 12 patients with connective tissue diseases receiving long-term cyclophosphamide. Frequency of mutation was higher than in control subjects and was related to the duration of therapy; therefore, some cells with mutations are long-lived, and these cells accumulate in the peripheral circulation. Mutation frequency was also independently related to age. The results indicate that even low doses of cyclophosphamide are mutagenic and may explain, in part, why these patients are at risk of drug-induced malignancy.