CD4 and severe combined immunodeficiency: Adoptive transfer of either naïve TCR transgenic CD8+ T cells or polyclonal CD4+ T cells to lymphopenic Rag1-/- or nonobese diabetic (NOD) severe combined immunodeficiency (SCID) common-γ chain-deficient (NSG) mice or sublethally irradiated hosts demonstrated that proliferation of CD8+ and CD4+Ptpn22-/- T cells was markedly enhanced in vivo compared to Ptpn22+/+ counterparts.25