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Sixty-one patients with leukemia and no immunity to chickenpox were given dialyzable transfer factor or placebo and followed for 12 to 30 months in a double-blind trial designed to examine the clinical efficacy of transfer factor. Sixteen patients in the transfer-factor group and 15 in the placebo group were exposed to varicella zoster, and most of them had a rise in antibody titer. Chickenpox developed in 13 of 15 exposed patients in the placebo group but in only one of 16 in the transfer-factor group (P = 1.3 x 10(-5)). In the patients treated with transfer factor and exposed to varicella without acquiring chickenpox the titer of antibody to varicella zoster was equal to that in the patients given placebo who became infected with chickenpox. Transfer factor converted negative results on skin tests for varicella zoster to positive in approximately half the recipients. Passive immunization with dialyzable transfer factor appears useful in nonimmune persons.

New knowledge of the relationship between the varicella-zoster virus and its host suggests a heretofore unappreciated dynamic pattern. Molecular finger-printing has demonstrated a degree of heterogeneity between different strains of virus. It is probable that exogenous reinfection with different strains and endogenous reactivation are commonplace events, although usually asymptomatic. The lability of the endogenous interaction inversely parallels the responsiveness of the cell-mediated immune system--a major factor in viral containment by the human host. Thus, the therapeutic use of immunosuppressive or cytotoxic substances increases the morbidity and mortality associated with varicella-zoster. Promising new approaches to the prevention and treatment of the virus should alter the balance in favor of the host.