Preoperative low-dose irradiation promotes long-term allograft acceptance and induces regulatory T cells in a porcine model of pulmonary transplantation.
BACKGROUND
A simplified conditioning protocol including single-dose preoperative thymic and low-dose whole body irradiation with or without subsequent donor bone marrow transplantation (BMTx) can be applied in porcine lung transplantation. We hypothesized that this protocol would prolong allograft survival.


METHODS
Left-sided single lung transplantation from major histocompatibility complex (MHC)-mismatched donors was performed in 27 minipigs. Recipients received whole body (1.5 Gy) and thymic irradiation (7 Gy) before transplantation (IRR group, n=6), intravenous immunosuppression with methylprednisolone, cyclosporine, and azathioprine for 27 postoperative days (IS group, n=5) or both (IRR+IS group, n=10). BMTx group recipients were treated with irradiation, immunosuppression and a donor bone marrow infusion on postoperative day 1. Peripheral blood leukocyte phenotype and donor cell chimerism were monitored by flow cytometry. Purified CD25+ T cells from long-term survivors or rejecting animals were used for in vitro MLR suppression assays.


RESULTS
Median graft survival was: IRR 12 days, IS 55 days, IRR+IS 239 days, and BMTx 80 days (P<0.0001). Early peripheral blood macrochimerism was substantial in both the IRR+IS and the BMTX group but was lost in all groups after day 80. The frequency and suppressive function of CD4+CD25+ T cells were enhanced in IRR+IS group long-term survivors.


CONCLUSIONS
Although donor bone marrow infusion was not beneficial in our model, a substantial proportion of the animals treated with irradiation and a 28-day course of immunosuppression accepted their lung allografts long term. The mechanism involved in maintaining allograft tolerance may be based on peripheral T-cell regulation.
Warnecke
Gregor
G
Division of Thoracic and Cardiovascular Surgery, Hannover Medical School, Hannover, Germany.
Avsar
Murat
M
Morancho
Manuel
M
Peters
Carsten
C
Thissen
Stefanie
S
Kruse
Bianca
B
Baumann
Rolf
R
Ungefroren
Hendrik
H
Simon
André R
AR
Hohlfeld
Jens M
JM
Karstens
Johann H
JH
Haverich
Axel
A
Strüber
Martin
M
D000818:Animals; D016026:Bone Marrow Transplantation; D015704:CD4 Antigens / Q000032:analysis; D006085:Graft Survival / Q000276:immunology / Q000528:radiation effects*; D008168:Lung / Q000276:immunology / Q000473:pathology; D016040:Lung Transplantation / Q000276:immunology*; D007959:Lymphocyte Culture Test, Mixed; D023421:Models, Animal; D015375:Receptors, Interleukin-2 / Q000032:analysis; D013552:Swine; D050378:T-Lymphocytes, Regulatory / Q000276:immunology / Q000528:radiation effects*; D013950:Thymus Gland / Q000166:cytology / Q000528:radiation effects; D014184:Transplantation, Homologous; D014916:Whole-Body Irradiation
D015704:CD4 Antigens; D015375:Receptors, Interleukin-2