Relative susceptibilities of T cell subsets involved in delayed-type hypersensitivity to sheep red blood cells to the in vitro action of 4-hydroperoxycyclophosphamide.

4-Hydroperoxycyclophosphamide, a derivative of cyclophosphamide, in aqueous solution yields 4-hydroxycyclophosphamide, which acts on lymphocytes in vitro. This compound was employed to determine the relative susceptibilities of T cell subsets involved in delayed-type hypersensitivity to sheep red blood cells in vitro. The following ranking order could be established: precursors of suppressor T cells > antigen-activated suppressor T cells > T cells mediating DTH. These data provide direct in vitro evidence that the enhancement of the cellular immune response to sheep red blood cells by cyclophosphamide is due to selective inactivation of suppressor T cells or their precursors, respectively.