Conditioning of cyclophosphamide-induced leukopenia in humans

This study evaluated whether decrements in peripheral leukocyte counts induced by cyclophosphamide can be conditioned in humans. Ten subjects being treated for multiple sclerosis received four intravenous treatments with cyclophosphamide (unconditioned stimulus) paired with a conditioned stimulus. Subjects received conditioned stimulus plus 10 mg of cyclophosphamide during one of the next two treatments in a double-blind manner. Eight of 10 subjects (P = 0.044) displayed decreased peripheral leukocyte counts following conditioned stimulus. This change may have resulted from classical conditioning processes.