Transplantation in the onco-hematology field: Focus on the manipulation of αβ and γδ T cells

γ/δ T cells represent a subset of T cells expressing a T cell receptor (TCR) variant composed of gamma and delta chains. The γ/δ TCR is expressed by 2-10% of all T cells in human peripheral blood, whereas the majority of T cells express α/β TCRs. γ/δ T cells display a range of innate effector functions including rapid secretion of chemokines and cytokines, as well as target cell lysis. Recent interest has focused on the function of γ/δ T lymphocytes in allogeneic transplantation in the onco-hematology field. Several studies, in vitro and in vivo, suggest that γ/δ T lymphocytes are potential beneficial effector cells in the context of hematopoietic stem cell transplantation (HSCT). In addition, in this review, we discuss the depletion of α/β T lymphocytes in the graft for allogeneic transplantation. In fact, an efficient TCR α/β cell depletion potentially reduces the risk of GvHD. Furthermore, TCR α/β T cell depletion, especially with immunomagnetic negative selection, retains other potential beneficial effector cells in the graft, such as γ/δ T cells, NK cells, and stem cells. These "facilitating" cells might facilitate engraftment, exert GvL effects, and reduce the risk for infections.