The difficulty of eliminating donor leukocyte microchimerism in rat recipients bearing established organ allografts

The Positive Impact of Donor Bone Marrow Cells Transplantation into Immunoprivileged Compartments on the Survival of Vascularized Skin Allografts

Using the vascularized skin allograft (VSA) model, we compared the tolerogenic effects of different allogeneic bone marrow transplantation (BMT) delivery routes into immunoprivileged compartments under a 7-day protocol immunosuppressive therapy. Twenty-eight fully MHC mismatched VSA transplants were performed between ACI (RT1^a) donors and Lewis (RT1¹) recipients in four groups of seven animals each, under a 7-day protocol of alfa/beta TCRmAb/CsA (alpha/beta-TCR monoclonal antibodies/Cyclosporine A therapy). Donor bone marrow cells (BMC) (100 × 106 cells) were injected into three different immunoprivileged compartments: Group 1: Control, without cellular supportive therapy, Group 2: Intracapsular BMT, Group 3: Intragonadal BMT, Group 4: Intrathecal BMT. In Group 2, BMC were transplanted under the kidney capsule. In Group 3, BMC were transplanted into the right testis between tunica albuginea and seminiferous tubules, and in Group 4, cells were injected intrathecally. The assessment included: skin evaluation for signs and grade of rejection and immunohistochemistry for donor cells engraftment into host lymphoid compartments. Donor-specific chimerism for MHC class I (RT1^a) antigens and the presence of CD4⁺/CD25⁺ T cells were assessed in the peripheral blood of recipients. The most extended allograft survival, 50–78 days, was observed in Group 4 after intrathecal BMT. The T cells CD4⁺/CD25⁺ in the peripheral blood were higher after intrathecal BMC injection than other experimental groups at each post-transplant time point. Transplantation of BMC into immunoprivileged compartments delayed rejection of fully mismatched VSA and induction of robust, donor-specific chimerism.

Donor-derived bone marrow transfusion produces mixed chimerism and promotes a Th2 shift in Th1/Th2 balance in rat heterotopic small bowel transplantation

BACKGROUND AND AIM

In this study, we investigated immunomodulatory effects of donor-derived bone marrow transfusion in rat heterotopic small bowel transplantation.

METHODS

Rat heterotopic segmental small bowel transplantation models (male Brown Norway to female Lewis) were established. The recipients were randomly divided into control group (pute small bowel transplantation), tacrolimus group (small bowel transplantation plus oral tacrolimus) and small bowel transplantation plus oral tacrolimus and intraportal infusion of donor-derived bone marrow cells group. We investigated the survival time, graft pathologic injuries and rejection grade by haematoxylin-eosin staining, serum IL-2 and IL-10 detection by enzyme labelled immunosorbent assay after small bowel transplantation. The recipients mixed chimerism were observed by detecting sex-determining region of Y chromosome gene in blood, liver, spleen and intestine by using real-time polymerase chain reaction and fluorescence in situ hybridization.

RESULTS

Bone marrow cells group showed a superior survival than the other groups, accompanied by milder pathologic injuries and lower rejection grade, decreasing serum IL-2 and increasing serum IL-10. The recipient chimerism rate in blood, liver, spleen and intestine in bone marrow cells group was significantly higher than the other groups.

CONCLUSION

Transfusion of donor-derived bone marrow cells via portal vein induces mixed chimerism in rats after small bowel transplantation, which may promote a Th2 shift in Th1/Th2 balance and facilitate the induction of immune tolerance.

Should microchimerism turn into rejection prophylactics?

Non-self cells can circulate in the body of an individual after any sort of contact with an allogeneic source of cells, thus creating a situation of chimerism that can be transient or prolonged over time. This situation may appear after stem cell transplantation, pregnancy, transfusion or transplantation. Concerning transplantation, many hypotheses have been formulated regarding the existence, persistence and role of these circulating cells in the host. We will review the principal hypotheses that have been formulated for years since the first description of non-self circulating cells in mammals to the utilization of artificially induced chimerism protocols for the achievement of tolerance.

Acquired immunologic tolerance: with particular reference to transplantation

The first unequivocally successful bone marrow cell transplantation in humans was recorded in 1968 by the University of Minnesota team of Robert A. Good (Gatti et al. Lancet 2: 1366-1369, 1968). This achievement was a direct extension of mouse models of acquired immunologic tolerance that were established 15 years earlier. In contrast, organ (i.e. kidney) transplantation was accomplished precociously in humans (in 1959) before demonstrating its feasibility in any experimental model and in the absence of a defensible immunologic rationale. Due to the striking differences between the outcomes with the two kinds of procedure, the mechanisms of organ engraftment were long thought to differ from the leukocyte chimerism-associated ones of bone marrow transplantation. This and other concepts of alloengraftment and acquired tolerance have changed over time. Current concepts and their clinical implications can be understood and discussed best from the perspective provided by the life and times of Bob Good.

Simultaneous bone marrow and intestine transplantation promotes marrow-derived hematopoietic stem cell engraftment and chimerism

Organ allografts have been shown to provide a syngeneic microenvironment for organ-based donor hematopoietic stem cells to maintain long-lasting chimerism after transplantation. We hypothesized that organ allografts would also support engraftment and hematopoiesis of adjunctively infused donor marrow stem cells, syngeneic to organ grafts, in nonmyeloablated recipients. In BN-to-LEW and GFP-to-ACI rat combinations, donor bone marrow (BM) infusion together with small intestine transplantation (SITx) under short-course tacrolimus immunosuppression resulted in persistent macrochimerism (more than 5%) for 150 days. In contrast, after BM infusion or SITx alone, chimerism was temporary and disappeared by day 100. Y-chromosome polymerase chain reaction (PCR) in sex-mismatched male BM plus female intestine or female BM plus male intestine transplantation into female recipients suggested that persistent macrochimerism was derived from infused BM. BM infusion together with lymphoid-depleted intestine grafts also supported macrochimerism development; however, third-party intestine grafts did not. After GFP-positive BM plus wild-type (WT) SITx into ACI, large numbers of GFP-positive leukocytes were found in WT intestine grafts. Isolated cells from WT intestine grafts developed GFP-positive CFU-Cs and propagated multilineage GFP-positive leukocytes when adoptively transferred into lethally irradiated WT recipients. These findings suggest that intestine allograft supports simultaneously infused donor (syngeneic to organ grafts) marrow stem cell engraftment, differentiation, and persistence of chimerism.