Enhanced immunogenicity of xenogenized tumor cells in rats pretreated with cyclophosphamide.

Immunization with xenogenized tumor cells, tumor cells infected with murine leukemia viruses, produced strong antitumor immunity. In this study, the immunogenicity of xenogenized tumor cells was compared in cyclophosphamide-treated and non-treated rats. CY treatment 3 days before immunization with xenogenized tumor cells enhanced antitumor cell-mediated immunity and antibody responses. However, CY treatment after immunization had no effect. Transfer of thymus cells form normal rats before the tumor challenge abolished the CY-induced augmenting effect. From these results, it is suggested that the elimination of precursors of suppressor T-cells by CY treatment results in enhanced immunogenicity of xenogenized tumor cells.