Allogeneic memory T cell response.

Recent data have revealed marked differences in alloresponses mediated by memory T cells during GVH and host-versus-graft (HVG) reactions (summarized in Table 1). Even though the mechanisms are not completely understood, it is clear that all memory T cells including nonallospecific, crossreactive, and allospecific memory T cells have decreased ability to induce GVHD. Selection of memory T cells or removal of naïve T cells will not only prevent GVHD, but could also enhance immune reconstitution, facilitate engraftment, and have the potential to enhance antitumor effects. A clinical trial has been planned. Successful translation of this approach in the clinic will improve the safety, enhance the effectiveness, and broaden the scope of allogeneic hematopoietic stem cell transplantation.