Another strategy to make non-myeloablative regimens more effective would be to combine the donor graft with infusions of allogeneic donor lymphocytes or subsets of lymphocytes in the form of 'engineered grafts', for example CD4 lymphocytes, which may have a graft vs myeloma effect without increasing GVHD. 29 It may also be possible to exploit killer-Ig-like mismatching between donor and recipient, which has been shown to result in improved PFS due to a reduced rate of relapse. 30, 31 Maintenance strategies, which have been shown to delay disease progression after auto-SCT may also be effective after allo-SCT. 32, 33 Finally, it may be worthwhile to exploit monoclonal antibodies targeting myeloma cells such as the CD40 Ag or CS-1 Ag, in order to increase the ability of donor allogeneic cells to eliminate residual host disease. 34 In any case, due to the substantial morbidity and mortality associated with allografting as well as the uncertain benefits, future approaches to allografting for myeloma should only be performed within well-designed clinical trials.