Adoptive immune cell therapy represents one of the most promising fields of investigation in allogeneic haematopoietic stem cell transplantation (allo-HSCT). Preliminary studies indicate that adoptive immune cell therapy can be used to restore the immunocompetence of allo-HSCT recipients towards widespread pathogens in the early post-transplant period. These strategies can be of fundamental importance in patients given a T-cell-depleted allograft, a type of transplant that has been performed increasingly over the last few years. A few seminal studies have recently documented that prevention/treatment of Epstein-Barr-virus-related lymphoproliferative disorders, human cytomegalovirus disease and invasive aspergillosis can be obtained through infusion of pathogen-specific T-cell lines or clones. Several efforts are also being directed towards the identification of strategies capable of selecting and/or strengthening specific graft-vs-leukaemia responses. In this regard, strategies of ex-vivo generation and expansion of clones or cell lines, specifically or preferentially leukaemia reactive, have been developed.