Engraftment of DLA-haploidentical marrow with ex vivo expanded, retrovirally transduced cytotoxic T lymphocytes

Genetically modified donor T cells with an inducible "suicide" gene have th e potential to improve the safety and availability of allogeneic hematopoie tic stem cell transplantation by enhancing engraftment and permitting contr ol of graft-versus-host disease (GVHD). However, several clinical studies o f gene-modified T cells have shown limited to no in vivo function of the ex vivo expanded T cells. Using the well-established dog model of allogeneic marrow transplantation, the question was asked if retrovirally transduced, donor derived, ex vivo expanded cytotoxic T lymphocytes (CTLs) that are rec ipient specific could enhance engraftment of dog leukocyte antigen (DLA)-ha ploidentical marrow following a single dose of 9.2 Gy total body irradiatio n and no postgrafting immunosuppression. In this setting, only 4 of 11 cont rol recipients of DLA-haploidentical marrow without added CTLs engrafted. C TLs did not enhance engraftment of CD34(+) selected peripheral blood stem c ells. However, recipient-specific CTLs enhanced engraftment of DLA-haploide ntical marrow in 9 of 11 evaluable recipients (P =.049). All dogs that engr afted developed multiorgan GVHD. To facilitate in vivo tracking, 8 dogs rec eived CTLs transduced with a retroviral vector encoding green fluorescent p rotein (GFP) and neomycin phosphotransferase (neo). Recipients that engraft ed had sharp increases in the numbers of circulating GFP(+) CTLs an days +5 to +6 after transplantation. GFP+ CTLs isolated from blood were capable of recipient-specific lysis. At necropsy, up to 7.1% of CD3(+) cells in tissu es were GFP+ and polymerase chain reaction in situ hybridization for neo sh owed infiltration of transduced CTLs in GVHD-affected organs. These results show that ex. vivo expanded, transduced T cells maintained in vivo functio n and enhanced marrow engraftment. (Blood. 2001;98: 3447-3455) (C) 2001 by The American Society of Hematology.