Nonpeptide antigens, presentation mechanisms, and immunological memory of human Vγ2Vδ2 T cells:: discriminating friend from foe through the recognition of prenyl pyrophosphate antigens

Human V gamma 2V delta 2 T cells play important roles in mediating immunity against microbial pathogens and have potent anti-tumor activity. V gamma 2V delta 2 T cells recognize the pyrophosphorylated isoprenoid intermediates (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP), an intermediate in the foreign 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway, and isopentenyl pyrophosphate (IPP), an intermediate in the self-mevalonate pathway. Infection with bacteria and protozoa using the MEP pathway leads to the rapid expansion of V gamma 2V delta 2 T cells to very high numbers through preferential recognition of HMBPP. Activated V gamma 2V delta 2 T cells produce proinflammatory cytokines and chemokines, kill infected cells, secrete growth factors for epithelial cells, and present antigens to alpha beta T cells. V gamma 2V delta 2 T cells can also recognize high levels of IPP in certain tumors and in cells treated with pharmacological agents, such as bisphosphonates and alkylamines, that block farnesyl pyrophosphate synthase. Activated V gamma 2V delta 2 T cells are able to kill most tumor cells because of recognition by T-cell receptor and natural killer receptors. The ubiquitous nature of the antigens converts essentially all V gamma 2V delta 2 T cells to memory cells at an early age. Thus, primary infections with HMBPP-producing bacteria are perceived by V gamma 2V delta 2 T cells as a repeat infection. Extensive efforts are underway to harness these cells to treat a variety of cancers and to provide microbial immunity.