Donor bone marrow, chimerism, histocompatibility and renal allograft rejection

Donor and recipient pretransplant conditioning with nonlethal radiation and antilymphocyte serum improves the graft survival in a rat small bowel transplant model

BACKGROUND

Lymphoid tissue within the intestinal graft require immunomodulatory strategies to prevent graft versus host disease (GVHD) after transplant. Herein, we evaluate the potential advantage of donor-specific bone marrow infusions in donor and or recipient preconditioned with total body irradiation and or antilymphocyte serum (ALS) on the incidence of GVHD and rejection after small bowel transplantation.

METHODS

Heterotopic SBTx was performed from DA to Lewis rats and distributed in nine groups: control group G0 (n=4) and G1 (n=6) without irradiation; recipients in G2 (n=4) were given 400 rd although in groups 3 (n=5), G4 (n=6), G6 (n=5), G7 (n=5), and G8 (n=6) with 250 rd. Donors in G5 (n=4) and G6 were given 250 rd of total body irradiation 2 hours before intestinal retrieval. Donors and recipients in G7 and donors in G8 additionally received ALS (day -5). G1, 2, 3, 5, 6, 7, and 8 were infused with UDBM and G4 with the same amount of TCDBM. Animals received tacrolimus for 15 days and accessed for rejection, GVHD and for chimerism analysis.

RESULTS

High mortality due to GVHD was observed in G2, 3, and 4, and correlated with high levels of donor T cells in recipients blood. G0 and G1 showed early acute rejection with progression toward chronic rejection, in contrast to the preconditioned groups. High and low doses of total body irradiation resulted in allogeneic and in a mixed chimerism, respectively. Decrease in donor chimeric cells after 11 weeks in preconditioned groups was correlated with severe allograft rejection.

CONCLUSION

Donor preconditioning with 250 rd and or ALS combined with recipient preconditioning and donor-specific bone marrow infusions prevented GVHD and resulted in a transient mixed chimerism with inhibition of allograft rejection after small bowel transplantation.

Current treatment practice in immunosuppression

New drugs have recently been added that may eventually replace the two-decade dominance of cyclosporin in solid organ transplantation. This cornerstone of immunosuppression was introduced by Borel [1] and Calne [2] in the mid-70s. In 1989, Starzl et al., after 2 years of preclinical experimentation, introduced tacrolimus (originally designated as FK506 by the Fujisawa Pharmaceutical Company of Japan) as a potent immunosuppressant for liver transplants [3]. Also, in recent years, a variety of novel purine and pyrimidine biosynthesis inhibitors have been tested for transplantation therapy. The leading agent which appears to be replacing the 35-year position occupied by azathioprine is the semi-synthetic morpholinoethyl ester of mycophenolic acid (MPA), mycophenolate mofetil (MMF), introduced by Allison [4] and Sollinger [5], and developed by the Syntex Corporation (now Roche Pharmaceuticals). Others, affecting different intra- or intercellular messages amplifying immunity, are in the pipeline.