OBJECTIVETo investigate the effect of immature dendritic cells (inDC) genetically modified to express sTNFR I on acute graft-versus-host disease (aGVHD) and the graft-versus-leukemia (GVL) effect ofter allogeneic bone marrow transplantation (allo-BMT) in leukemic mice and its mechanism.

METHODSAn EL4 leukemia allo-BMT model was established with the BALB/c (H-2d) donor mice (DM)and C57BL/6 (H-2b) recipient mice (RM). The RM received DM bone marrow (BM) cells at a 1:1 ratio with spleen cells intravenously via tail vein at 4 h after TBI. Fifty DM were separated randomly into five groups: (1) Group A: total body irradiation (TBI) group, (2) Group B: lymphoma cell leukemia group, (3) Group C: allo-BMT group, (4) Group D: pXZ9-DC group, (5) Group E: sTNFR I-DC group. Acute GVHD scores, incidence of leukemic cell infiltration, histopathological analysis, survival rate, and survival rate of the recipients were estimated after allo-BMT. Enzyme-linked immunosorbent assay (ELISA) method was used to detect cytokines (INF-gamma and IL-4 ) production. Flow cytometry (FCM) analysis was used to detect allogeneic chimerism.

RESULTS(1) The mice in group A and group B all died of the BM failure and lymphoma cell leukemia, respectively. The mice in group C developed typical clinical signs of a GVHD after BMT with an average survival time(AST) of (11.50 +/- 3.50) d. The signs of aGVHD were less evident in the group D and E, and their AST (21.70 +/- 5.80 and 25.80 +/- 5.20 days, respectively) were all longer than that in group C (P < 0.05). AST of group E was the longest (P < 0.05). The mice in group B all died of leukemia within 18 days after engraftment of EL4 cells. There was was no significant difference in groups C, D and E in the incidence of leukemia (P > 0.05). (2) Serum IFN-gamma level reached peak value. At + 12 d, then decreased gradually in group C, D, and E, and then reached the nadir at +18 d post-BMT, with the lowest in group E (P < 0.05), and the level was significantly lower in group D than in group C (P < 0.05). After BMT, serum IL-4 level slightly decreased in group C, but gradually elevated in group D and E and reached their peak at +12 d, and even more significantly increased in group E (P < 0.05). There was no statistical significance in the pair wise comparison among three group (P < 0.05). (3) The average proportion of H-2d positive cells in RM was 95%-100% on day 30 post-BMT, with complete donor-type implantation.

CONCLUSIONImmature DC can induce immuno tolerance. Immature DC genetically modified to express sTNFR I has been shown to prevent acute GVHD in lethally irradiated mice reconstituted with allogeneic bone marrow grafts while maintaining the GVL response.