The role of cyclophosphamide and granulocyte colony-stimulation factor in achieving high-level chimerism in allotransplanted limbs

Adipose-derived stromal cell therapy combined with a short course nonmyeloablative conditioning promotes long-term graft tolerance in vascularized composite allotransplantation

The risks of chronic immunosuppression limit the utility of vascularized composite allotransplantation (VCA) as a reconstructive option in complex tissue defects. We evaluated a novel, clinically translatable, radiation-free conditioning protocol that combines anti-lymphocyte serum (ALS), tacrolimus, and cytotoxic T-lymphocyte-associated protein 4 immunoglobulin (CTLA4-Ig) with adipose-derived stromal cells (ASCs) to allow VCA survival without long-term systemic immunosuppression. Full-mismatched rat hind-limb-transplant recipients received tacrolimus (0.5 mg/kg) for 14 days and were assigned to 4 groups: controls (CTRL) received no conditioning; ASC-group received CTLA4-Ig (10 mg/kg body weight i.p. postoperative day [POD] 2, 4, 7) and donor ASCs (1 × 10⁶ iv, POD 2, 4, 7, 15, 28); the ASC-cyclophosphamide (CYP)-group received CTLA4-Ig, ASC plus cyclophosphamide (50 mg/kg ip, POD 3); the ASC-ALS-group received CTLA4-Ig, ASCs plus ALS (500 µL ip, POD 1, 5). Banff grade III or 120 days were endpoints. ASCs suppressed alloresponse in vitro. Median rejection-free VCA survival was 28 days in CTRL (n = 7), 34 in ASC (n = 6), and 27.5 in ASC-CYP (n = 4). In contrast, ASC-ALS achieved significantly longer, rejection-free VCA survival in 6/7 animals (86%), with persistent mixed donor-cell chimerism, and elevated systemic and allograft skin T_regs , with no signs of acute cellular rejection. Taken together, a regimen comprised of short-course tacrolimus, repeated CTLA4-Ig and ASC administration, combined with ALS, promotes long-term VCA survival without chronic immunosuppression.

Immunomodulatory effects of pre-irradiated extremity allograft in the rodent model

Allogeneic human hand transplantation requires combination immunotherapy to maintain viability. Immunosuppression will be lifelong, with doses as high or higher than those required for solid organ allotransplantation. The risks associated with lifelong immunosuppression are unacceptable, particularly for younger transplant patients. It therefore becomes imperative to explore ways to reduce or eliminate the requirement for immunosuppression. Reconstructive surgery should consider, to a large extent, graft pre-treatment as a strategy for the transplantation of vascularised limb tissue allografts with reduced requirement for immunosuppression. In the clinical setting of composite tissue allograft (CTA), the graft is always procured from a cadaveric donor. Therefore, only a short time is available between harvesting the graft from the donor and transplanting into the recipient. This period provides the only opportunity to manipulate the CTA. Quite a few studies, however, have so far investigated donor pre-treatment and pre-transplant modification of the extremity allograft. Work from our group and others has demonstrated that removal of allogeneic bone marrow in the limb graft by irradiation and its rapid reconstitution with recipient marrow cells can significantly prolong the survival of limb allografts in the absence of immunosuppression. In the current work, we review these studies and discuss the immunomodulatory effects on the extremity allograft.

Myeloablative irradiation, granulocyte-colony stimulating factor, and FK506 can induce macrochimerism and prolong the survival of experimental extremity allografts

BACKGROUND

A key component of composite tissue allografts is the vascularized limb/bone marrow because of its capacity to reconstitute the marrow cavity of the recipient. The efficacy of a new protocol that uses total body irradiation (TBI), granulocyte colony-stimulation factor (G-CSF), and FK506 to induce high level bone marrow chimerism was evaluated with particular reference to the dose requirement and toxicity of TBI.

MATERIALS AND METHODS

In total, 82 whole-limb allotransplants from LacZ transgenic rats to LEW rats were performed. TBI was administered just prior to transplantation with various doses ranging from 100 to 1500 R (almost equal to 1-15 Gy). G-CSF was given for 4 d, while FK506 was used for 28 d. The level of chimerism was evaluated by semiquantitative polymerase chain reaction (PCR).

RESULTS

The survival of limb allografts in recipients that were pretreated with a myeloablative TBI dose of >1000 R was prolonged to more than 1 y. Recipients pretreated with <500 R showed no prolongation of limb graft survival. A majority of long-term survivors showed chronic, nonlethal graft-versus-host disease (GVHD). PCR analysis revealed a high level of intra-bone marrow chimerism in the recipient, thus demonstrating successful induction of macrochimerism.

CONCLUSION

Vascularized limb/bone marrow graft is a proven method for supplying donor cells to the bone marrow of irradiated recipients. A new protocol involving pretransplant myeloablative TBI with >1000 R followed by treatment with G-CSF and FK506 was found to induce a high level of chimerism and significantly prolong the survival of limb allografts without causing lethal GVHD.

Prolonged survival of experimental extremity allografts: a new protocol with total body irradiation, granulocyte-colony stimulation factor, and FK506

The induction of a high-level of chimerism (macrochimerism) may be the most reliable strategy for achieving donor-specific tolerance. The purpose of this study was to evaluate the efficacy of a new protocol using total-body irradiation (TBI) and granulocyte-colony stimulation factor (G-CSF) to induce high-level chimerism following rat whole-limb allotransplantation. In this study, we investigated whether the timing of TBI influenced the period of graft survival. In total, 50 whole-limb allotransplants from LacZ transgenic rats to LEW rats were performed. TBI was performed at days 0 and 14, and G-CSF was given for 4 days after TBI. FK506 was given for 28 days after transplant. Nontreated limb allografts were rejected after 4.2 days. The survival time was prolonged to 64 days in the FK506 monotherapy group. In the group receiving TBI at day 14, limb allograft survival was significantly prolonged to 81 days. In the group receiving TBI at day 0, 26% of recipients died but in the surviving recipients the grafts survived for longer than 1 year without lethal graft-versus-host disease (GVHD). Polymerase chain reaction (PCR) analysis revealed a high level of intrabone marrow chimerism in the recipient, thus demonstrating successful induction of macrochimerism. A new protocol of pretransplant TBI followed by treatment with G-CSF and FK506 was found to induce a high level of chimerism and to significantly prolong the survival of limb allografts in recipients without lethal GVHD.

Intragraft chimerism following composite tissue allograft

Until now, more than 35 hand transplants have been performed in humans and have generated much public interest. Cell traffic from the recipient into the graft, so-called intragraft chimerism, appears to play a major role in graft acceptance and graft rejection. Little is known about cell migration following extremity allografts. In this review, recent experimental studies are presented for intragraft chimerism of the extremity allograft. Technical tools for detecting recipient cells in the graft were: (1) immunohistochemistry, (2) karyotyping, (3) fluorescent in situ hybridization, (4) polymerase chain reaction, and (5) transgenic animals. This study demonstrates that recipient-derived cells gradually repopulate into grafted skin, bone tissues, bone marrow, and endothelial cells, but muscle, periosteum, and cartilage tissues retain donor cell origin.

NLR proteins: integral members of innate immunity and mediators of inflammatory diseases

The innate immune system is the first line of defense against microorganisms and is conserved in plants and animals. The nucleotide-binding domain, leucine rich containing (NLR) protein family is a recent addition to the members of innate immunity effector molecules. These proteins are characterized by a central oligomerization domain, termed nucleotide-binding domain (NBD) and a protein interaction domain, leucine-rich repeats (LRRs) at the C terminus. It has been shown that NLR proteins are localized to the cytoplasm and recognize microbial products. To date, it is known that Nod1 and Nod2 detect bacterial cell wall components, whereas Ipaf and Naip detect bacterial flagellin, and NACHT/LRR/Pyrin 1 has been shown to detect anthrax lethal toxin. NLR proteins comprise a diverse protein family (over 20 in humans), indicating that NLRs have evolved to acquire specificity to various pathogenic microorganisms, thereby controlling host-pathogen interactions. Activation of NLR proteins results in inflammatory responses mediated by NF-kappaB, MAPK, or Caspase-1 activation, accompanied by subsequent secretion of proinflammatory cytokines. Mutations in several members of the NLR protein family have been linked to inflammatory diseases, suggesting these molecules play important roles in maintaining host-pathogen interactions and inflammatory responses. Therefore, understanding NLR signaling is important for the therapeutic intervention of various infectious and inflammatory diseases.