Tumor cells and macrophages express prostaglandin E2 (PGE2), a soluble factor derived from arachidonic acid and produced by inducible cyclo-oxygenase 2 enzyme (8, 36) that exerts its immunosuppressive effect through subversion of CD8 differentiation, suppression of T cell proliferation, and inhibition of CD4 T cell helper functions (97). The gene discussed is CD4; the disease is neoplasm.