CD28 and neoplasm: PKM2 on the other hand is upregulated in activated immune cells such as LPS-activated macrophages and CD3/CD28 activated T cells.136 A switch from PKM1 to PKM2 expression occurs in some tumor types, but more importantly, PKM2 expression is upregulated in all cancer types investigated.137,138 In addition, replacing PKM2 with PKM1 has been found to inhibit tumor proliferation and aerobic glycolysis.138