Modulation of delayed-type hypersensitivity and cellular immunity to microbial vaccines: effects of cyclophosphamide on the immune response to tularemia vaccine.

Treatment of guinea pigs with cyclophosphamide before immunization with killed tularemia vaccine in Freund incomplete adjuvant produced a prolongation and intensification of delayed-type hypersensitivity and in vitro lymphocyte transformation reactions to tularemia antigen. Such reactions resemble those ordinarily associated with the administration of live tularemia vaccine, killed vaccine in Freund complete adjuvant, or recovery from natural infection. The immunopotentiation lasted longer than that seen previously in other antigenic systems with this drug and was dependent on the dose of vaccine used. More intense delayed skin reactivity could be transferred into normal controls by cells from immunized donors pretreated with cyclophosphamide than by cells from immunized donors that were not pretreated.