Cyclophosphamide-induced leukopenia and suppression of limb regeneration in the adult newt, notophthalmus viridescens.

Cyclophosphamide (cytoxan), a clinical immunosuppressant, produced a marked, persistent leukopenia (greater than 40% reduction) in adult newts in contrast to a transient, milder leukopenia accompanying amputations without cytoxan treatments. In addition, cytoxan suppressed the formation of regeneration blastemata initially: however, blastema formation occurred if a second amputation was performed two or more weeks following the cessation of cytoxan treatments. The failure of the leukopenias of these latter cases to be corrected suggests that although a cytoxan-induced leukopenia is correlated with the absence of forelimb regeneration, this leukopenia is not, of itself, a sufficient condition to inhibit regeneration.