Characterization of Novel P-Selectin Targeted Complement Inhibitors in Murine Models of Hindlimb Injury and Transplantation

The complement system has long been recognized as a potential druggable target for a variety of inflammatory conditions. Very few complement inhibitors have been approved for clinical use, but a great number are in clinical development, nearly all of which systemically inhibit complement. There are benefits of targeting complement inhibition to sites of activation/disease in terms of efficacy and safety, and here we describe P-selectin targeted complement inhibitors, with and without a dual function of directly blocking P-selectin-mediated cell-adhesion. The constructs are characterized in vitro and in murine models of hindlimb ischemia/reperfusion injury and hindlimb transplantation. Both constructs specifically targeted to reperfused hindlimb and provided protection in the hindlimb ischemia/reperfusion injury model. The P-selectin blocking construct was the more efficacious, which correlated with less myeloid cell infiltration, but with similarly reduced levels of complement deposition. The blocking construct also improved tissue perfusion and, unlike the nonblocking construct, inhibited coagulation, raising the possibility of differential application of each construct, such as in thrombotic vs. hemorrhagic conditions. Similar outcomes were obtained with the blocking construct following vascularized composite graft transplantation, and treatment also significantly increased graft survival. This is outcome may be particularly pertinent in the context of vascularized composite allograft transplantation, since reduced ischemia reperfusion injury is linked to a less rigorous alloimmune response that may translate to the requirement of a less aggressive immunosuppressive regime for this normally nonlife-threatening procedure. In summary, we describe a new generation of targeted complement inhibitor with multi-functionality that includes targeting to vascular injury, P-selectin blockade, complement inhibition and anti-thrombotic activity. The constructs described also bound to both mouse and human P-selectin which may facilitate potential translation.

Combination of a CD26 Inhibitor, G-CSF, and Short-term Immunosuppressants Modulates Allotransplant Survival and Immunoregulation in a Rodent Hindlimb Allotransplant Model

BACKGROUND

Recent studies have demonstrated that inhibition of CD26 potentiates stromal cell-derived factor-1α (SDF-1α), promotes tissue regeneration, and suppresses the rejection of organ transplants. This study investigated whether the combination of a CD26 inhibitor (CD26i) with granulocyte colony-stimulating factor (G-CSF) and short-term immunosuppressants modulates vascularized composite tissue allotransplant survival in a rodent orthotopic hindlimb allotransplant model.

METHODS

The hindlimb allotransplantation from Brown-Norway to Lewis rats was divided into 4 groups. Group 1 (controls) did not receive any treatment. Group 2 was treated with short-term antilymphocyte serum (ALS) and cyclosporine-A (CsA). Group 3 was administrated CD26i and G-CSF. Group 4 received a combination of CD26i/G-CSF/ALS/CsA. Each subgroup comprised 10 rats. Peripheral blood and sampling of transplanted tissues were collected for immunological and histological analysis.

RESULTS

The results revealed that allotransplant survival was found to be significantly prolonged in group 4 with CD26i/G-CSF/ALS/CsA treatment compared with those in the other groups. The interleukin-10 and transforming growth factor-βl levels, the percentage of CD4+/CD25+/FoxP3+ T cells, as well as the levels of SDF-1α expressions were significantly increased in group 4 compared with those in the other groups. Group 4 revealed a statistical increase in the percentage of donor cells (RT1n) expression in the recipient peripheral blood, and the mixed lymphocyte reaction showed hyporesponsiveness of the T cells to donor alloantigens.

CONCLUSION

The combination of CD26i/G-CSF and short-term immunosuppressants prolongs allotransplant survival by inducing immunoregulatory effects and enhancing the percentage of SDF-1α expression. This immunomodulatory approach has great potential as a strategy to increase vascularized composite allotransplantation survival.

A Skin Rejection Grading System for Vascularized Composite Allotransplantation in a Preclinical Large Animal Model

BACKGROUND

The Banff Criteria have been accepted as a system for grading histological rejection in graft skin in human vascularized composite allotransplantation (VCA). Preclinical swine hindlimb transplantation models have an important role in translational studies in VCA. However, unified grading criteria for rejection in swine skin have not yet been established.

METHODS

Two hundred fourteen swine skin biopsy specimens were reviewed, including 88 native skin biopsies and 126 specimens from the skin component of heterotopic swine hindlimb transplants. Thorough review was performed in a blinded fashion by an expert veterinary pathologist with attention paid to the applicability of the Banff criteria as well as specific histologic characteristics and trends. Clinical and histopathologic rejection scores were then directly compared.

RESULTS

Two hundred fourteen specimens reviewed showed significant similarities between swine and human skin, as previously published. Notable swine-specific characteristics, including paucicellular infiltration with rare epidermal cell infiltration or necrosis, were accounted for in a proposed grading system that parallels the Banff Criteria.

CONCLUSIONS

This comprehensive grading system, based on the Banff Classification for skin rejection in VCA, provides a standardized system for more accurate comparison of rejection in preclinical swine VCA models.

Fate of a Chimeric Joint Construct in an Ectopic Site in SCID Mice

This study examines the use of a devitalized biological knee as a scaffold for repopulation with chondrocytes and tests the hypothesis that the devitalized scaffold would become repopulated with the foreign chondrocytes when placed in a suitable environment. Chimeric knee constructs were engineered in vitro and their ectopic in vivo fate was examined in SCID mice. The constructs were made by applying porous collagen sponges that contained viable bovine articular chondrocytes to shaved articular surfaces of devitalized embryonic chick knees. The chimeric joints were cultured for 1 week and were subsequently transplanted into dorsal subcutaneous pouches of 5-week-old mice. Specimens were prepared for histological analysis at 1, 3, 6, or 8 weeks after transplantation. Controls included empty collagen sponges, collagen sponges seeded with viable bovine chondrocytes, and devitalized chick knees without collagen sponge inserts. One week after in vitro incubation of the constructs, the porous collagen sponges with viable bovine chondrocytes were adherent to the shaved articular surfaces of the devitalized chick joints. There was abundant metachromatic neomatrix around the chondrocytes in the collagen sponges. During maintenance of the constructs in vivo, the chimeric joints exhibited dramatic changes. Bovine chondrocytes proliferated in the collagen sponges and formed abundant new matrix. Bovine chondrocytes migrated into preexisting chick cartilage canals at 1 week. Subsequently, bovine chondrocytes invaded the matrix of the devitalized chick knees. Bovine neocartilage obliterated the interface between the collagen sponge and the devitalized chick cartilage. With time in vivo, the bovine neocartilage expanded and replaced the chick matrix. The devitalized cartilage appears to provide a framework for supporting chondrogenesis in a chimeric joint.

Orthotopic Hind Limb Transplantation in the Mouse

In vivo animal model systems, and in particular mouse models, have evolved into powerful and versatile scientific tools indispensable to basic and translational research in the field of transplantation medicine. A vast array of reagents is available exclusively in this setting, including mono- and polyclonal antibodies for both diagnostic and interventional applications. In addition, a vast number of genotyped, inbred, transgenic, and knock out strains allow detailed investigation of the individual contributions of humoral and cellular components to the complex interplay of an immune response and make the mouse the gold standard for immunological research. Vascularized Composite Allotransplantation (VCA) delineates a novel field of transplantation using allografts to replace "like with like" in patients suffering traumatic or congenital tissue loss. This surgical methodological protocol shows the use of a non-suture cuff technique for super-microvascular anastomosis in an orthotopic mouse hind limb transplantation model. The model specifically allows for comparison between established paradigms in solid organ transplantation with a novel form of transplants consisting of various different tissue components. Uniquely, this model allows for the transplantation of a viable vascularized bone marrow compartment and niche that have the potential to exert a beneficial effect on the balance of immune acceptance and rejection. This technique provides a tool to investigate alloantigen recognition and allograft rejection and acceptance, as well as enables the pursuit of functional nerve regeneration studies to further advance this novel field of transplantation.

The effect of chondroitinase on nerve regeneration following composite tissue allotransplantation

PURPOSE

To improve the degree of functional return and sensibility provided by composite tissue allotransplantation, enhanced nerve regeneration is essential. Chondroitin sulfate proteoglycans are found in the extracellular matrix of nerves and inhibit regenerating axons after injury. Treatment with chondroitinase to remove chondroitin sulfate proteoglycans has been shown to improve nerve regeneration in isolated nerve graft and transection-and-repair models. This study assesses the efficacy of chondroitinase as a neurotherapeutic agent in the setting of composite tissue allotransplantation.

METHODS

Adult Lewis rats received either orthotopic hind limb transplants from Brown Norway rat donors (n = 12) or sciatic nerve transection and repair (n = 6). Following approximation of the sciatic nerve, half the animals received intraneural injections of chondroitinase in saline and the other half received intraneural injections of saline alone. Five weeks after transplantation, we killed the animals and analyzed nerves with nonbiased quantitative nerve histomorphometry. One day after transection and repair, we killed animals and harvested sciatic nerves for immunohistochemical staining of cleaved chondroitin sulfate proteoglycans epitope and laminin. We used unpaired t-tests for statistical analysis.

RESULTS

Distal to the suture line, chondroitinase-treated animals demonstrated statistically greater total number of fibers and nerve density compared with controls. There were no statistically significant differences in fiber number or nerve density proximal to the suture line or in fiber widths. We observed staining of cleaved chondroitin sulfate proteoglycan epitopes only in treated animals, with no differences observed in the degree of laminin staining.

CONCLUSIONS

Intraneural injection of chondroitinase cleaved inhibitory chondroitin sulfate proteoglycans without disrupting proregenerative laminin and resulted in enhanced nerve regeneration after composite tissue allotransplantation. Studies at later time points are needed to assess whether this enhanced nerve regeneration will produce improved functional return.

Immunotolerance reaction for allograft-limb in rats induced by gene-modified cell transfusion

The therapeutic value of the transforming growth factor beta 1 (TGF-b) in transplantation has been reported; However, cell-mediated gene therapy using TGF-b is not applied to the organ transplantation widely. This study was to evaluate whether TGF-b-modified donor spleen cell specific transfusion in rat heterotopic allo-limb transplantation could induce tolerance tolerogenicity and prolong allograft's survival time. The Splenic T-cell in Wistar rats responsing to donor spleen cells which received TGF-b-transduced were severely impaired.The Survival time of Sprague-Dawley Allograft-limb in Wistar rats given TGF-b-modified donor spleen cells (5¥106 cells/well, administration of donor TGF-b-transduced donor spleen cells 7 days before transplantation) was extended modestly but significantly.

[Adenovirus-mediated CTLA4 immunoglobulin based conditioning for non-myeloablative allogeneic hematopoietic cell transplantation to induce tolerance to hind limb allografts in rats]

OBJECTIVE

To investigate a non-toxic AdCTLA4-Ig-based protocol for non-myeloablative allogeneic hematopoietic cell transplantation to induce donor-specific tolerance to hind limb allografts in rats.

METHODS

Fully mismatched, 4 to 8 week old Brown Norway (RT1(n)) and Lewis (RT1(1)) rats were used as cell/organ donors and recipients, respectively. Recipients were treated with AdCTLA4-Ig (5 x 10(9) PFU, day -30, 0, 30), standard immunosuppressive therapy (MP: 10 mg x kg(-1) x d(-1), MMF: 20 mg x kg(-1) x d(-1), RAPA: 0.2 mg x kg(-1) x d(-1);day -33 - 100), soon after total body irradiation (3 Gy, day -30) and donor bone marrow (100 x 10(6), day -30) transplantation (BMT). Thirty days after BMT, chimeric animals received hind limb transplantations. And 100 days after hind limb transplantations, immunosuppressive therapy was changed for low-dosed CsA (8 mg x kg(-1) x d(-1), day 100-), until the allografts were rejected.

RESULTS

In Group C, hematopoietic chimerism was (38.8 +/- 10.6)% at day 0, and was stable (29.3 +/- 11.9)% at 330 days post-BMT. There was no graft versus host disease in both Group C and Group D. When the standard immunosuppressive therapy was stopped and changed for low-dosed CsA, chimeric recipients (Lewis, RT1(1)) permanently accepted (> 200 days) donor specific (Brown Norway, RT1(n)) hind limb allografts in Group C, yet rapidly rejected in Group A (8 +/- 2) d, Group B (18 +/- 3) d and in Group C (20 +/- 2) d. Lymphocytes of graft tolerant animals' demonstrated hyporesponsiveness in mixed lymphocyte cultures in a donor-specific manner in Group C. Tolerant graft histology showed no obliterative arteriopathy or chronic rejection.

CONCLUSION

The AdCTLA4-Ig based conditioning regimen with donor BMT produce stable mixed chimerism and induce donor-specific tolerance to hind limb allografts.

Rapamycin, mycophenolate mofetil, methylprednisolone, and cytotoxic T-lymphocyte-associated antigen 4 immunoglobulin-based conditioning regimen to induce partial tolerance to hind limb allografts without cytoreductive conditioning

BACKGROUND

Composite tissue allograft transplantation may represent the next frontier in the field of reconstructive surgery. However, the main obstacles precluding the routine use of composite tissue allotransplants are rejection and toxicity associated with life-long immunosuppressive therapy. In this study, we investigated a nontoxic immunosuppressant and cytotoxic T-lymphocyte-associated antigen 4 immunoglobulin (CTLA4-Ig)-based protocol to induce donor-specific tolerance to hind limb allografts in rats.

METHODS

Fully mismatched, 4- to 10-week-old Brown Norway (BN, RT1n) and Lewis (RT1) rats were used as cell/organ donors and recipients, respectively. Recipients were treated with CTLA4-Ig (2 mg/kg/d) on days -30, -28, -26, -24, and -22, rapamycin, mycophenolate mofetil, and methylprednisolone (RAPA/MMF/MP) combined therapy (from days -30 to day 100), a single dose of anti-lymphocyte serum (10 mg, on day -30), and donor bone marrow (10 x 10(7) T-cell-depleted cells) transplantation (BMT, on day -30). Thirty days after BMT, chimeric animals received hind limb allotransplantations (on day 0). The RAPA/MMF/MP combined therapy was changed to Cyclosporine (CsA, 8 mg/kg/d) on day 100 and maintained thereafter at this level.

RESULTS

Hematopoietic chimerism of 17.6 +/- 9.5% at day 0, was stable (15.2 +/- 5.6%) at 230 days post-BMT; there was no sign of graft-versus-host disease. Chimeric recipients (Lewis) permanently accepted (>200 days) donor (BN)-specific (RT11, n = 6) hind limbs, yet rapidly rejected (20 +/- 2 days) third-party hind limbs (Wistar Furth [WF]). Lymphocytes of graft-tolerant animals demonstrated hyporesponsiveness in mixed lymphocyte cultures in a donor-specific manner. Tolerant graft histology showed no signs of acute and chronic rejection.

CONCLUSIONS

The immunosuppressant and CTLA4-Ig-based conditioning regimen with donor BMT produced mixed chimerism and induced partial donor-specific tolerance to hind limb allografts.

A modified model of hindlimb osteomyocutaneous flap for the study of tolerance to composite tissue allografts

Composite tissue allotransplantation (CTA) is the new frontier in transplantation. More than 25 hand allograft transplants have been performed worldwide, and the feasibility has been well established. The classical experimental model of CTA involves rat orthotopic hindlimb transplantation, a time-consuming procedure associated with high mortality and morbidity. We describe a rat heterotopic osteomyocutaneous flap that serves as a nonfunctional CTA, allowing the study of tolerance induction to a highly antigenic vascularized allograft of bone, muscle, and skin while minimizing the morbidity and mortality of full hind limb transplantation. In the present studies, we explored whether establishing chimerism by nonmyeloablative conditioning would induce tolerance to CTA. When compared with the classic hind limb transplantation model, these results demonstrate that our heterotopic hind limb flap is less morbid and as an effective experimental model for the study of CTA tolerance.

Automatic assessment of dynamic contrast-enhanced MRI in an ischemic rat hindlimb model: an exploratory study of transplanted multipotent progenitor cells

This study presents computerized automatic image analysis for quantitatively evaluating dynamic contrast-enhanced MRI in an ischemic rat hindlimb model. MRI at 7 T was performed on animals in a blinded placebo-controlled experiment comparing multipotent adult progenitor cell-derived progenitor cell (MDPC)-treated, phosphate buffered saline (PBS)-injected, and sham-operated rats. Ischemic and non-ischemic limb regions of interest were automatically segmented from time-series images for detecting changes in perfusion and late enhancement. In correlation analysis of the time-signal intensity histograms, the MDPC-treated limbs correlated well with their corresponding non-ischemic limbs. However, the correlation coefficient of the PBS control group was significantly lower than that of the MDPC-treated and sham-operated groups. In semi-quantitative parametric maps of contrast enhancement, there was no significant difference in hypo-enhanced area between the MDPC and PBS groups at early perfusion-dependent time frames. However, the late-enhancement area was significantly larger in the PBS than the MDPC group. The results of this exploratory study show that MDPC-treated rats could be objectively distinguished from PBS controls. The differences were primarily determined by late contrast enhancement of PBS-treated limbs. These computerized methods appear promising for assessing perfusion and late enhancement in dynamic contrast-enhanced MRI.

Current status of composite tissue allotransplantation

Composite tissue allotransplantation (CTA) is emerging as a potential treatment for complex tissue defects. A major drawback for CTA remains the requirement of lifelong immunosuppression. Up to date numerous experimental CTA models have been introduced to the transplantation literature. After the first hand transplantation in 1998, the clinical applicability of CTA has attracted a lot of attention. This article will outline the historical background of CTA and our experience in different CTA models.

Simultaneous vascularized bone marrow transplantation to promote acceptance of hind limb allografts and its effects on central and peripheral chimerism

Administration of donor bone marrow (BM) cells can improve the outcome of transplantation. The ability of donor vascularized bone marrow transplantation (VBM) to provide an ongoing source of donor cells and improve survival in a rigorous rat model of hind limb transplantation (HLTX) was investigated. HLTX were performed between Brown Norway (BN) donors and Lewis recipients in three groups: HLTX; HLTX plus intravenous donor BM cells and HLTX plus simultaneous VBM transplantation. Animals received 12 weeks triple immunosuppression. Survival was compared at 4 months and donor chimerism was evaluated. Simultaneous VBM transplantation led to slight but nonsignificant prolongation of survival (P=0.056). Donor cells in the VBM were eventually replaced by recipient and there was no long-term increase in chimerism. Few donor cells were observed in thymus. Simultaneous VBM transplantation showed a trend for improved survival of HLTX however the VBM failed to provide a sustained increase in chimerism.

Immunosuppressive Effect of Tryptophan Metabolites in Composite Tissue Allotransplantation

BACKGROUND

Hand transplantations have intensified immunological research into composite tissue allotransplantation to induce tolerance. Pregnancy is a successful, natural model of immunological tolerance. The enzyme indoleamine 2,3-deoxygenase plays an important role by catabolizing the amino acid tryptophan. The resulting metabolites have been shown to be immunosuppressive. The effect of tryptophan metabolites has not been investigated in vascularized organ transplantation before. In this study, the authors applied to composite tissue allotransplantation what nature has developed for pregnancy, and examined the immunosuppressive effect of tryptophan metabolites in a model of hind limb transplantation.

METHODS

Thirty-three allogeneic hind limb transplantations in the rat (Lewis --> Brown-Norway) were performed in three groups. Group A (n = 12) received no immunosuppression, group B (n = 13) received tryptophan metabolites (kynurenine and 3-hydroxyanthranilic acid) locally and systemically, and group C (n = 8) served as a control group receiving FK506. The timing of rejection was assessed by clinical observation.

RESULTS

Rejection of the allogeneic hind limb occurred on average 6.58 days after transplantation in group A (no immunosuppression) and after 8.15 days in group B (tryptophan metabolites). Rejection was significantly delayed (log-rank test, p < 0.01). No rejection was seen with application of FK506 during the follow-up period of 21 days.

CONCLUSIONS

For the first time, tryptophan metabolites have been applied in vascularized composite tissue allotransplantation and showed a significant immunosuppressive effect. These promising first results need further dose-effect and toxicological studies to increase the still limited immunosuppressive effect and define the clinical role these metabolites may play in the future.

Treadmill training for hindlimb transplanted rats

Functional improvement is an important concern for a composite allograft with motor function. As the procedure of rat composite limb transplantation is a well-established model, we focused on the effects of rehabilitation using this model. We performed the rat hindlimb transplantation in syngenic combination using a modified method confirming the processes of vessel anastomosis step-by-step that maintains good vascular patency. We studied the impact of treadmill training on hindlimb transplantated rats using Rodent Robot 3000 (Robomedica). Functional recovery was evaluated electro-physiologically after training. All transplants were conducted successfully. The "drop foot" condition improved in rats that were subjected to a training program. However, there were no significant differences in muscle atrophy improvement or denervation potential as determined by electromyography. This study is the first to detail the effects of rehabilitation on rat limb transplantation. This model is useful for the study of functional improvement for limb transplantation.

Neuroregeneration in Composite Tissue Allografts: Effect of Low-Dose FK506 and Mycophenolate Mofetil Immunotherapy

BACKGROUND

The immunosuppressant FK506 has been reported to increase the rate of peripheral nerve regeneration in nerve crush injury and nerve allograft models. The purpose of this study was to determine whether low doses of FK506 and mycophenolate mofetil had a neuroregenerative effect in revascularized peripheral nerve allografts in a rat hind limb transplantation model.

METHODS

Wistar Furth rat recipients received limbs from syngeneic Wistar Furth donors (group 1, n = 4) or from allogeneic August X Copenhagen Irish rat donors (group 2, n = 6). Wistar Furth recipients received limbs from August X Copenhagen Irish donors and were treated with FK506/mycophenolate mofetil for 5 months (group 3, n = 7). At the end of the follow-up period, histomorphometric analysis of sciatic and tibial nerves from transplanted and intact hind limbs was conducted. Sciatic and tibial nerves were examined at the level of coaptation and near the neuromuscular junction, respectively.

RESULTS

Transplanted limbs in groups 1 and 3 completed the study without rejection, while the limbs in group 2 were rejected within a few days. Sciatic and tibial nerve analysis in groups 1 and 3 limbs showed myelinated axons of various diameters but in significantly fewer numbers than in nontransplanted contralateral nerves. The number and size of myelinated axons of transplanted nerves at corresponding levels were not significantly different between syngeneic and allogeneic (FK506/mycophenolate mofetil-treated) transplants.

CONCLUSIONS

The authors conclude that long-term neuroregeneration of revascularized peripheral nerves using low-dose FK506/mycophenolate mofetil was similar to that of syngeneic transplants. The occurrence of acute rejection episodes with low-dose FK506/mycophenolate mofetil did not appear to benefit nor impair neuroregeneration.

Induction of heat shock proteins in a rat composite tissue allotransplantation model of acute rejection

BACKGROUND

Clinical cases of composite tissue allotransplantation have been reported, but the exact mechanisms of allograft rejection remain unclear. The current study examined the possible involvement of heat shock proteins in major histocompatibility complex-compatible minor-mismatch composite tissue allotransplantation rejection.

METHODS

Allotransplantation (Fisher 344 to Lewis) and isotransplantation (Lewis to Lewis) of rat lower extremities were performed. Temporal profiles of 70-kDa and 60-kDa heat shock proteins (heat shock protein 70 and heat shock protein 60) were conducted by quantitative Western blot analysis and immunohistochemistry. Analyses were performed immediately after reperfusion (day 0) and on postoperative days 1, 3, 7, and 12 (n = 5 for quantitative Western blot analysis and n = 5 for immunohistochemistry).

RESULTS

The expression levels of the inducible forms of heat shock protein 70 and heat shock protein 60 were uniformly and significantly augmented until postoperative day 7 in the allografts, compared with the isografts (p < 0.001 for each protein). Immunoreactivities to heat shock protein 70 and heat shock protein 60 in keratinocytes, hair follicular cells, and endothelial cells of the subdermal vascular plexus were enhanced in the allografts early on postoperative day 1. Positive staining of hair follicles extended to deeper parts of the hair follicles and hair bulbs in the allografts on postoperative day 3. Although dendritic cells were positive for both heat shock protein 70 and heat shock protein 60, infiltrating lymphocytes were positive only for heat shock protein 60.

CONCLUSIONS

These results suggest the possible involvement of heat shock proteins in the process of major histocompatibility complex-compatible minor-mismatch composite tissue allotransplantation rejection. Thus, modulation of the function of heat shock proteins might be an important therapeutic option for improving the outcome of minor-mismatch allografts.

Chimerism after Vascularized Limb Versus Bone Marrow Transplantation

This study used quantitative PCR in the murine model to compare the ability of a limb allograft vs. a comparable dose of marrow suspension to induce chimerism. Female C57Bl/6 mice received a vascularized hindlimb allograft, a comparable dose of 5 x 10 (6) donor bone marrow cells, or a standard dose (20 x 10 (6)) of marrow suspension from male Balb/c donors. All recipients were treated with a regimen based on CD40 costimulation blockade and T cell depletion. Y chromosome-specific quantitative PCR was used to measure chimerism. Most recipients of limb allografts demonstrated low levels of chimerism after 1 week (3/4) and 1 month (3/4). Most recipients of 5 x 10 (6) marrow cells had low levels of chimerism at 1 week (4/6) and only 1/5 after 1 month. All recipients of 20 x 10 (6) cells except one demonstrated either low or high levels of chimerism after 1 week (5/5) and 1 month (5/6). The marrow component of a limb allograft is thus more effective at inducing microchimerism compared to a comparable dose of bone marrow suspension.

Role of thymus in operational tolerance induction in limb allograft transplant model

BACKGROUND

In this study, we evaluated the role of host thymus in tolerance induction in composite tissue allografts (CTA) across major histocompatibility complex (MHC) barrier during a 7-day alphabeta- T-cell receptor (TCR)/ cyclosporine A (CsA) protocol.

MATERIALS AND METHODS

A total of 62 limb allograft transplants were studied. Euthymic (group A) and thymectomized (group B) Lewis recipients (LEW, RT1(1)) received vascularized hind-limb allografts from hybrid Lewis x Brown-Norway (F1), (LBN, RT1(1+n)) donors. Mixed lymphocyte reaction (MLR) and skin grafting assessed donor-specific tolerance in vitro and in vivo, respectively. Flow cytometry determined the efficacy of immunosuppressive protocols and the presence of donor-specific chimerism. Immunocytochemistry revealed the presence of donor-specific cells in the lymphoid organs of recipients.

RESULTS

Isograft transplants survived indefinitely. For thymectomized rats, the median survival time (MST) of limb allograft in non-treated recipients was 7 days; monotherapy with alphabeta-TCR extended MST to 16 days, and CsA therapy extended it to 30 days. Using the alphabeta-TCR/CsA protocol, the MST of allografts was 51 days. For euthymic rats, the MST of limb allograft in non-treated recipients was 7 days; monotherapy with alphabeta-TCR or CsA extended MST to 13 or 22 days, respectively. Treatment with alphabeta-TCR/CsA resulted in indefinite allografts survival (MST=370 days). MLR and skin grafting confirmed donor-specific tolerance in euthymic recipients. Flow cytometry showed stable chimerism in the euthymic rats and transient chimerism in thymectomized limb recipients. Immunoperoxidase staining revealed the persistence of donor-derived cells in the lymphoid tissues of euthymic recipients.

CONCLUSION

We found that the presence of thymus was imperative for the induction of donor-specific tolerance in rat hind-limb composite tissue allografts using a alphabeta-TCR/CsA protocol.

The Effect of A2A Adenosine Receptor Agonist on Composite Tissue Allotransplant Survival: An In Vivo Preliminary Study

BACKGROUND

In vitro experimental studies showed that A2a receptor agonists reduce allostimulatory functions of the dendritic cells through modulation of surface expression of the costimulatory molecules and down-regulation of cytokines. Similar suppressive effects on dendritic cells have also been observed with Cyclosporine A (CsA). In this study we sought to explore if combined use of these two drugs in vivo could prolong the survival of composite tissue allografts across MHC barriers.

MATERIALS AND METHODS

A total of 24 hindlimb transplantations were performed across a major MHC barrier from Brown Norway rats (BN; RT1n) to Lewis rats (Lew; RT1l) In the control group, either isografts (group 1, n = 2) or allografts (group 2, n = 3) were performed and no treatment was given. In the experimental group three kinds of treatment protocols were used: (1) A2a adenosine receptor agonist alone (group 3, n = 6); (2) CsA alone (group 4, n = 7); and (3) A2a adenosine receptor agonist + CsA combined treatment (group 5, n = 6). Mean survival times of each group as well as cytokine levels including IL-2, IL-4, IL-10, INF-gamma, and TNF-alpha were analyzed by ELISA.

RESULTS

Isografts survived indefinitely. The mean survival times for allograft groups (group 2 to 5) were 9.8 +/- 1.3, 10.5 +/- 1.0, 29.8 +/- 1.7, and 22 +/- 1.4 days, respectively. Statistically, there was no difference between the allograft control group and the A2a adenosine receptor agonist treated group (P = 0.35). However, survival of the allografts in the CsA-treated group was significantly higher than the A2a adenosine receptor agonist treated (P < 00001) and combined CsA + A2a adenosine receptor agonist treated group (P < 0.0001). In vivo A2a adenosine receptor agonist treatment alone increased the levels of IL-2, INF-gamma, and TNF-alpha, which are important cytokines for induction of allotransplant rejection. However A2a adenosine receptor agonist in combination with CsA significantly reduced the levels of suppressor cytokines IL-4 and IL-10.

CONCLUSION

As opposed to the previous in vitro studies, the results from this in vivo study showed that A2a adenosine receptor agonist treatment does not prolong composite tissue allograft survival. Compared to CsA treatment alone, the allotransplant survival was even shorter with the combined treatment. Treatment with A2a adenosine receptor agonist possibly promotes the differentiation of alloreactive CD4 cells predominantly into T-helper 1 phenotype. As a result, the levels of stimulatory cytokines contributing to allograft rejection are increased and suppressor cytokines are reduced, leading to accelerated allograft rejection.

From experimental rat hindlimb to clinical face composite tissue allotransplantation: Historical background and current status

The purpose of this article is to review the historical background and clinical status of composite tissue allotransplantation and to discuss the scientific evolution of clinical face transplantation. Composite tissue allotransplantation (CTA) rapidly progressed in the 1980s with the discovery of cyclosporine. Although the most success has been achieved with hand transplantation, others have made progress with allografts of trachea, peripheral nerve, flexor tendon apparatus, vascularized knee, larynx, abdominal wall, and most recently, partial face. The world's first partial face allotransplantation occurred in November 2005 in France. In April of 2006, there was a second performed in China. As of today, there are now multiple institutions with plans to attempt the world's first full facial/scalp transplant. Complete facial/scalp allotransplantation offers a viable alternative for unfortunate individuals suffering severe facial disfigurement and is a product of many decades of experimental research, beginning with rat hindlimb allografts.

Induction of tolerance to composite tissue allograft in a rat model

The goal of this study was to establish a rat model that can be used to determine the variables in influencing induction of tolerance to composite tissue allografts. An anti T-cell depleting agent (R73) and 15-deoxyspergualin were given in different doses and schedule to four groups of Lewis rats receiving a limb transplant from Brown-Norway donors. Graft survival prolongation was maximal combining a single dose of R73 and a 20-day administration of 15-deoxyspergualin. Long-term survivors accepted a skin graft from Brown-Norway donors at 80 days, but rejected grafts from an unrelated donor. Skin grafting did not influence survival of the transplanted limb. Mixed allogeneic chimerism was not detectable in peripheral blood by flow cytometry, but immunohistochemistry identified donor-derived cells in the thymus of tolerant recipients at 100 days. These results suggest a state of donor-specific, dynamic tolerance, with potential for future application in human composite tissue allotransplantation.

Heterotopic hindlimb allotransplantation in rats: an alternative model for immunological research in composite-tissue allotransplantation

A nonfunctional heterotopic hindlimb allotransplantation model is presented, and a study was performed between this model and standard orthotopic hindlimb transplantation to compare operation and ischemia time, overall morbidity, and mortality rates. In this model, the skin component of the hindlimb was stripped away to the ankle level, and the remaining part along with the vascularized epigastric skin was transplanted heterotopically to the inguinal space of the recipient. No osteotomy and intramedullary fixation were performed. Thirty heterotopic and orthotopic hindlimb transplantations were performed in two groups. Each group involved 15 transplantations from inbred, male Brown Norway (BN; RT1n) weighing 150-200 g to Lewis rats (LEW; RT1(1)) weighing 250-300 g. The animals were followed up for 2 weeks under immunosuppression with cyclosporine A (16 mg/kg/day). Mean operation times for heterotopic and orthotopic hindlimb transplantations were 60 and 105 min, with ischemia times of 35 and 85 min, respectively. No animal deaths or major complications were encountered in heterotopic hindlimb transplantation during the follow-up period. Seroma formation was observed in one animal as the only minor complication. The mortality rate for orthotopic hindlimb transplantation was 26.7%, and there were minor complications in 35%, including infection, ulceration, and loss of rigid fixation. This model circumvents the disadvantages of osteotomy and intramedullary fixation, which may increase the risk of blood loss, embolus, and infection in immunosuppressed animals. It also helps avoid tension or kinking on the anastomosis due to inadequate judgment of the osteotomy level, distortion associated with loss of rigid fixation, and weight mismatch between donor and recipient. From the immunological point of view, insult to bone marrow is avoided, and a relatively constant amount of bone marrow is introduced to be used in chimerism-based tolerance studies. We recommend this model for composite-tissue allotransplantation studies when functional recovery is not of primary importance.

Donor Leukocytes Combined With Delayed Immunosupressive Drug Therapy Prolong Limb Allograft Survival

Donor leukocytes administered at the time of transplantation may prolong organ allograft survival. Delayed administration of calcineurin inhibitors, such as FK506 or cyclosporine, may enhance their efficacy. Herein the effectiveness of this strategy to promote limb transplant survival was investigated in the strong histocompatibility barrier of Brown-Norway donor to Lewis recipients. Donor leukocytes (6 x 10(7) intravenously) were injected on the day of transplantation followed on day 1 to 14 with mycophenolate mofetil (MMF; 15 mg/kg/d) and prednisone, (0.5 mg/kg/d) which were then tapered by 20% each week and stopped at week 7. Administration of of FK506 (2 mg/kg/d) was started on day 4 and continued for 8 weeks, then tapered for 4 weeks to a maintenance dose of 0.8 mg/kg/d, which was continued for 12 weeks (group A; n = 8). A control group (n = 8) underwent identical treatment save for donor leukocyte injection but rather commencement of FK506 on day 1. Rejection was common during FK506 tapering in both groups. However group A showed a significantly later onset, a shorter period for reversal of the first rejection, and a significantly lower dosage of FK506 at the time of rejection. After the completion of immunosuppression, rejection occurred significantly later in group A than the control group with one animal surviving without immunosuppression on day 344. This is the first trial of a donor leukocyte injection combined with delayed FK506 administration in limb transplantation, which suggested that it could produce a modest but significant improvement in outcome.

Recipient immature dendritic cells do not prolong allograft survival

Experimental studies on allogeneic transplantation have shown that recipient dendritic cells (DC) play a role in peripheral tolerance as well as in rejection of allografts. It is not known whether DCs exert their tolerogenic function in the graft or in recipient lymphoid tissue. To answer this question we created a chimeric heart model deprived of its own DCs and repopulated with recipient DCs. The rationale for this model was to observe whether recipient mature and immature DCs located in the graft attenuate recruitment and stimulation of recipient lymphocytes, subsequently prolonging graft survival. Vascularized bone marrow transplants from the prospective recipient to the lethally irradiated heart donor, which function for a period of 14 days, were used to replace donor DCs with prospective recipient either mature or immature DCs. Replacement of the donor heart with either of these cells did not prolong graft survival. The intragraft microchimerism did not mitigate the allogeneic rejection reaction.

Functional Recovery of Rat Hind-Limb Allografts

Few papers have assessed the long-term functional recovery of animal limb allografts. In this study, the functional recovery of rat limb allografts was serially and quantitatively investigated for a period of 1 year. The donor's hind limb was orthotopically transplanted into the recipient. Fifteen recipients with allografts were treated with FK506. Functional recovery of the grafted limb was assessed serially by cutaneous reaction test, walking track analysis, and electrophysiologic evaluation. Sensibility improved to a similar extent in both isografts and allografts, and the recovery rate at 1 year was 68 percent, compared to the normal side. Sciatic function index significantly improved to - 70 points after 1 year. The amplitude recorded from the gastrocnemius muscle significantly improved, and the ratio compared to the normal side was 43 percent. Limb isografts and allografts treated with FK506 showed no significant differences in functional recovery. The data can be used as a reference standard for future investigations.

Donor leukocytes combine with immunosuppressive drug therapy to prolong limb allograft survival

Donor leukocytes administered at the time of transplantation may prolong organ allograft survival. This study examined the effectiveness of donor leukocyte injection combined with immunosuppression for limb transplantation across the strong histocompatibility barrier of a Brown Norway donor to a Lewis recipient. Eight animals received 6 x 10(7) donor leukocytes injected on the day of transplantation. From day 1, FK506 (2 mg/kg/d), mycophenolate mofetil (MMF) (15 mg/kg/d), and prednisone (0.5 mg/kg/d) were administered for 2 weeks. After week 2, prednisone and MMF were both tapered by 20% of the initial dosage per week. After week 7, the animals received only FK506 (2 mg/kg/d). From week 8, FK506 was tapered to the maintenance dose of 0.8 mg/kg/d at week 10 and was stopped on week 24. A control group of 8 animals underwent identical treatment except that the leukocyte injection was omitted. Rejection was observed in both groups during FK506 monotherapy; however, the onset of early rejection episodes was significantly later, the period for reversal of the first rejection was significantly shorter, and the dosage of FK506 at the time of rejection was significantly lower among leukocyte-treated recipients. After completion of immunosuppression, survival was modestly prolonged in the leukocyte-treated group. One animal is surviving without immunosuppression on day 234. This trial of donor leukocyte injection combined with immunosuppression in limb transplantation showed a modest, but significant, improvement in outcome.

Prolonged limb allograft survival with CD40 costimulation blockade, T-cell depletion, and megadose donor bone-marrow transfusion

The purpose of this study was to determine the efficacy of a treatment regimen consisting of CD 40 costimulation blockade, T-cell depletion, and megadose donor bone marrow transfusion in the limb allograft model. C57Bl/6 mice underwent limb transplantation from Balb/c mice and received MR1 (anti-CD 40 ligand monoclonal antibody), and CD4(+) and CD8(+) T cell-depleting antibodies with and without 120 x 10(6) donor bone-marrow transfusion. Recipients treated only with antibodies showed rejection at 51.4+/-17 (mean+/-SEM) days, while those who also received donor bone marrow had allograft survival of 67+/-16.4 days, with a range up to 91 days. Treated specimens with rejection had less lymphocytic infiltration than untreated controls. Recipients of donor bone marrow also demonstrated early mixed chimerism, which disappeared after 1 month. While allograft survival was prolonged, tolerance was not achieved, and the mechanism of rejection was more consistent with a chronic process.

Gradual graft-cell repopulation with recipient cells following vasularized bone and limb allotransplantation

Little is known about the fate of graft cells following vascularized bone allografting. This study was conducted to define the process of graft-cell repopulation with recipient cells. Sixty-five vascularized tibial bone and 50 limb allotransplantations were performed in rat sex-mismatched pairs. FK 506 was used for immunosuppression. The ratio of donor and recipient cells in the graft was evaluated by semiquantitative polymerase chain reaction, using the Y-chromosome primers. Allografted bones had no rejection episodes. In the vascularized bone allograft model, donor-derived cells were gradually replaced by cells of recipient origin, such that by 24 weeks, they comprised only 10% of total cells. In the limb allograft model, male recipient cells were detected in female grafts not at 1 week but at 48 weeks posttransplantation. The ratio of recipient cells was more than 10% in the femur and tibia. Recipient-derived cells gradually migrated into the grafted bone cells with the passage of time.

Cell traffic between donor and recipient following rat limb allograft

Although cell traffic from the graft into the recipient and from the recipient into the graft had been noticed in allogeneic organ transplantation, little is known following whole-limb allografting. This study was conducted to define cell migration between donor and recipient. Sixty-seven vascularized hind limb allotransplantations were performed in rat sex-mismatched pairs and the recipient animals were treated with FK506 immunosuppression. The ratio of donor and recipient cells was evaluated by semi-quantitative PCR using the specific primers of the Y-chromosome. Allografted limbs had no rejection episode until the final assessment. The male recipient cells were detected in female limb grafts not at 1 week but at 48 weeks after transplantation. The male donor cells were detected in the humerus and tibia in the female recipient but not in the gastrocnemius muscle and leg skin. Our results demonstrated that recipient-derived cells gradually migrated into the grafted bone, muscle and skin cells with the duration of time. Donor-derived cells migrated into the healthy bones but not into the healthy muscle and skin. Because active regeneration occurs in the grafted limb to compensate graft damage secondary to ischemia and operative intervention, recipient-derived cells may mediate a muscular and dermo-epidermal renewal.

Prolonged survival of rat hindlimb allografts following short-course FK506 and mycophenolate mofetil combination therapy

The immunosuppressive effect of combined therapy using FK506 and mycophenolate mofetil (MMF) was studied in rat limb allotransplantation. Dark Agouti rat donor hindlimbs were orthotopically transplanted into Lewis rat recipients. In total, 38 models of transplantation were performed and divided into 8 groups that were treated individually or in combination with FK506 + MMF therapy. Animals were immunosuppressed for 28 days and then observed for up to 140 days. Graft rejection was evaluated both macroscopically and histologically. Survival times for rat limb allotransplants receiving combination FK506 + MMF therapy were significantly longer than with FK506 or MMF monotherapy, and this was achieved without serious side effects. A histopathological study demonstrated a significantly lower level of rejection with FK506 + MMF combination treatment compared to groups receiving FK506 or MMF monotherapy. Combined FK506 + MMF treatment can prolong the survival of rat limb allografts.

Reduction of Skeletal Muscle Injury in Composite Tissue Allotransplantation by Heat Stress Preconditioning

Ischemia-reperfusion injury is a dominant factor limiting tissue survival in any microsurgical tissue transplantation, a fact that also applies to allogeneic hand transplantation. The clinical experience of the 12 human hand transplantations indicates that shorter ischemia times result in reduced tissue damage and, ultimately, in better hand function. Heat stress preconditioning and the accompanying up-regulation of the heat shock protein 72 have been shown to reduce the ischemia-reperfusion injury following ischemia of various organs, including organ transplantation. The aim of this study was to reduce the ischemia-reperfusion injury in a model of composite tissue allotransplantation. Allogeneic hind limb transplantations were performed from Lewis (donor) to Brown-Norway rats. Donor rats in group A (n = 10) received a prior heat shock whereas rats in group B (n = 10) did not receive any prior heat shock. Group C served as a control group without transplantation. The transplantations were performed 24 hours after the heat shock, at which time the heat shock protein 72 was shown to be up-regulated. The outcome was evaluated 24 hours after transplantation by nitroblue tetrazolium staining and wet-to-dry weight ratio of muscle slices (anterior tibial muscle). The nitroblue tetrazolium staining showed a significant reduction of necrotic muscle in group A (prior heat shock) (p = 0.005). The wet-to-dry ratio was significantly reduced in group A (prior heat shock), indicating less muscle edema and less tissue damage (p = 0.05). Heat shock preconditioning 24 hours before an ischemic event leads to an up-regulation of heat shock protein 72 in muscle and to a tissue protection reducing ischemia-reperfusion injury in composite tissue transplantation.

Lymphadenectomy prior to rat hind limb allotransplantation prevents graft-versus-host disease in chimeric hosts

In previous rat studies, the use of mixed allogeneic chimerism (MAC) to induce host tolerance to hind limb allografts has resulted in severe graft-versus-host disease (GVHD). The purpose of this study was to determine if immunocompetent cells in bone marrow (BM) and/or lymph nodes (LNs) of transplanted limbs were responsible for inducing GVHD in mixed chimeric hosts. [ACI-->Wistar Furth] chimeric rats received ACI hind limbs that were non-irradiated, irradiated (1050 cGy) or lymphadenectomized. Rejection, GVHD and donor chimerism was assessed. Chimeric hosts rejected none of their limbs. However, hosts of non-irradiated hind limbs succumbed to GVHD 22.4+/-0.8 days after transplantation. In contrast, chimeras that received irradiated or lymphadenectomized ACI hind limbs showed no clinical or histological signs of GVHD at 5 months. We conclude that mixed chimeric hosts are susceptible to GVHD due to the immunocompetent cell load provided by the LNs, not the BM, of hind limb allografts.

Experimental limb transplantation, part ii: excellent return of function and indefinite survival after withdrawal of immunosuppression

In this study the three components of an immunosuppressive combination therapy were gradually withdrawn in a rat limb transplantation model to evaluate the effects on long-term survival of the grafted limbs, rejection rate, and functional recovery. The procedure was performed in 16 rats across a strong Brown Norway to Fischer 344 histocompatibility barrier. Eight animals served as a control group that was not given any antirejection therapy and rejected their limb within a few days. The remaining eight animals were administered a 2-week course of immunosuppressive therapy including tacrolimus (TRL; 2 mg/kg/d), mycophenolate mofetil (MMF; 15 mg/kg/d), and prednisolone (Pred; 0.5 mg/kg/d). At 2 weeks, Pred and MMF were simultaneously tapered by 20% of the dosage every week; by week 7 the animals were on TRL only. TRL was then tapered at the same rate (20% every week) to a maintenance dose of 0.6 mg/kg/d at week 12. After 6 months the immunosuppression was stopped. Four of 8 animals did not reject throughout the study up, to the 1-year endpoint. At this stage they show excellent functional outcomes, evaluated by clinical tests and walking tract analysis. The remaining four rats developed a rejection at an average of 267 days postoperatively (range 224 to 302 days), corresponding to an average of 87 days (range 44 to 122 days) without any immunosuppression. They were sacrificed as soon as rejection was confirmed for histological examination of the various tissues. This study showed that a triple combination therapy provides excellent long-term functional outcomes of the transplanted limbs, with no rejection episodes, no side effects, or complications, even 6 months after withdrawal of all immunosuppressive components, suggesting the possible emergence of tolerance.

Comparison of Six Methods for the Assessment of Ischemia-Reperfusion Injury in Skeletal Muscle following Composite Tissue Allotransplantation

Ischemia/reperfusion (I/R) injury is one of the factors determining tissue survival in replantation and transplantation surgery. However, more than 20 methods have been used to evaluate I/R injury in muscle. The aim of this study was to examine I/R injury in muscle tissue in a model of composite tissue allotransplantation (rat hindlimb transplantation), based on the analyses of six parameters: nitroblue tetrazolium staining (NBT); histology of the anterior tibial and extensor digitorum muscle; wet-to-dry weight ratio; serum potassium; and serum creatine kinase (CK)), in order to identify the most practicable and reliable outcome parameter. Results demonstrated that NBT staining and the wet/dry weight ratio are reliable tools for outcome measurement. The wet/dry weight ratio is the easiest to perform and the authors consider it to be useful for screening purposes. Histologic assessment shows areas of necrosis, but is not a reliable method for semi-quantitative evaluation. Serum potassium and CK levels were higher following transplantation, but they cannot be recommended for assessment purposes, as no significant correlation with other parameters was seen. These findings help further researchers in their selection of reliable outcome parameters to measure I/R injury in skeletal muscle.

Tolerance to composite tissue allografts across a major histocompatibility barrier in miniature swine1

BACKGROUND

Tolerance to composite tissue allografts might allow the widespread clinical use of reconstructive allotransplantation if protocols to achieve this could be rendered sufficiently nontoxic. The authors investigated whether tolerance could be generated in miniature swine to composite tissue allografts across a major histocompatibility (MHC) barrier. A clinically relevant tolerance protocol involving hematopoietic cell transplantation without the need for irradiation or myelosuppressive drugs was tested.

METHODS

Seven recipient animals were transiently T-cell depleted and a short course of cyclosporine was initiated. Twenty-four hours later, a donor hematopoietic cell transplant consisting of cytokine-mobilized peripheral blood mononuclear cells or bone marrow cells and a heterotopic limb transplant were performed. In vitro anti-donor responsiveness was assessed by mixed-lymphocyte reaction and cell-mediated lympholysis assays. Acceptance of the limb allografts was determined by gross and histologic appearance. Chimerism in the peripheral blood and lymphohematopoietic organs was assessed by flow cytometry.

RESULTS

All seven experimental animals accepted the musculoskeletal elements but rejected the skin of the allografts. All but one of the animals displayed donor-specific unresponsiveness in vitro. The animals that received cytokine mobilized-peripheral blood mononuclear cells showed chimerism but had clinical evidence of graft-versus-host disease (GVHD). None of the animals that received bone marrow cells showed stable chimerism and none developed GVHD.

CONCLUSIONS

This protocol can achieve tolerance to the musculoskeletal elements of composite tissue allografts across an MHC barrier in miniature swine. Stable chimerism does not appear to be necessary for tolerance and may not be desirable because of the risk of GVHD.

Heterotopic limb allotransplantation model to study skin rejection in the rat

Current rodent models for investigation of limb allotransplantation typically utilize orthotopic whole-limb transplantation, a morbid and time-consuming procedure. Our objective was to design a less morbid rat model to explore the immunological obstacles of limb transplantation, and particularly skin. Twenty lower hindlimbs from 10 donors were transplanted into a heterotopic subcutaneous position into 20 animals (10 isogeneic and 10 allogeneic). Each group was further subdivided to include animals with (n = 5) and without (n = 5) a skin paddle for observation of cutaneous signs of rejection. All grafts in the isogeneic group survived for 100 days, i.e., the endpoint of the study. Allogeneic transplants rejected their allografts at a mean of 12.8 days (with skin) and 20.6 days (without). Our heterotopic limb transplantation model takes less time and is less stressful to the animals, while allowing for early observation of graft skin rejection, when compared to orthotopic whole-limb transplantation.

Donor-specific tolerance in fully major histocompatibility major histocompatibility complexmismatched limb allograft transplants under an anti-αβ T-cell receptor monoclonal antibody and cyclosporine A protocol

BACKGROUND

Recent studies have demonstrated that treatment with alphabeta-T-cell receptor (TCR) monoclonal antibody and cyclosporine A (CsA) can extend survival in composite tissue allografts (CTA). The purpose of this study was to induce tolerance in fully major histocompatibility complex (MHC)-mismatched rat limb allografts under 7 days of a combined alphabeta-TCR-CsA protocol.

METHODS

The authors performed 30 hind-limb allotransplantations across the MHC barrier between Brown Norway donors (BN; RT1n) and Lewis recipients (LEW; RT1l). Isograft and allograft controls received no treatment. The experimental groups received monotherapy of alphabeta-TCR and CsA or a combination of alphabeta-TCR and CsA for 7 days only. Donor-specific tolerance and immunocompetence were determined by standard skin grafting in vivo and mixed lymphocyte reaction (MLR) in vitro. The efficacy of immunosuppressive therapy and the level of donor-specific chimerism were determined by flow cytometry.

RESULTS

Long-term survival (>350 days) was achieved in allograft recipients (n=6) under the 7-day protocol of combined alphabeta-TCR-CsA. Donor-specific tolerance and immunocompetence of long-term chimeras were confirmed by acceptance of skin grafts from the donors and rejection of the third-party alloantigens (AxC Irish). At day 120, MLR demonstrated unresponsiveness to the host and donor antigens but strong reactivity against third-party alloantigens. Flow cytometry confirmed the high efficacy of immunosuppressive treatment and the development of donor-specific chimerism (7.6% of CD4+-RT1n+ cells, 1.3% of CD8+-RT1n+ cells, and 16.5% of CD45RA+-RT1n+ cells) in the periphery of tolerated recipients.

CONCLUSIONS

Combined therapy of alphabeta-TCR-CsA for 7 days resulted in tolerance induction in fully MHC-mismatched rat hind-limb allografts. Tolerance was directly associated with stable, donor-specific chimerism.

Successful allogeneic leg transplantation in rats in conjunction with intra-bone marrow injection of donor bone marrow cells1

BACKGROUND

We have recently established a new method for bone marrow transplantation (BMT) in mice: bone marrow cells are directly injected into the intra-bone marrow (IBM) cavity. IBM-BMT induces persistent donor-specific tolerance and enhances the rapid recovery or reconstitution of the hematolymphoid system of donor origin without any signs of graft-versus-host disease (GVHD) or graft failure. Furthermore, the prior injection of fludarabine can reduce the irradiation dose to the sublethal level (4.5 Gy x 2). Therefore, we hypothesize that IBM-BMT plus fludarabine is applicable to allogeneic leg transplantation in rats.

METHODS

Brown Norway (BN; RT1An) rats were injected intravenously with 50 mg/kg of fludarabine phosphate, followed by sublethal fractionated irradiation (4.5 Gy x 2) 1 day before IBM-BMT. The hind limbs from Fischer 344 (F344; RT1Al) rats were transplanted on day 0, and bone marrow cells (3 x 10(7) cells/50 microL) obtained from the donor F344 rats were injected into the bone marrow cavity of the left tibias of the recipient BN rats.

RESULTS

The hematolymphoid cells in the recipient BN rats were completely reconstituted by the cells of the donor F344 rats. The limbs transplanted from the donor F344 rats were accepted for >1 year without any clinical signs of rejection (10 of 10). The lymphocytes of the BN rats showed tolerance to both donor-type and recipient-type major histocompatibility complex determinants in mixed lymphocyte reaction, but showed a significant response to the third-party major histocompatibility complex determinants.

CONCLUSIONS

Using a combination of the injection of fludarabine, low-dose irradiation, and IBM-BMT, we have succeeded in allogeneic limb transplantation without using any immunosuppressants after the operation. This strategy would be applicable to the transplantation of other vascularized organs in humans.

Composite tissue allotransplantation in chimeric hosts part II. A clinically relevant protocol to induce tolerance in a rat model

BACKGROUND

We and others have shown that mixed allogeneic chimerism induces donor-specific tolerance to composite tissue allografts across major histocompatibility complex barriers without the need for immunosuppression. However, a delay period between bone marrow transplantation and limb allotransplantation is required, making such protocols impractical for clinical application. This study eliminates this delay period in a rat hind limb allotransplantation model by performing mixed allogeneic chimerism induction and transplantation "simultaneously."

METHODS

Group 1 included controls in which naïve Wistar Furth (WF) hosts received ACI hind limbs. Group 2 included (ACI-->WF) chimeras that received limbs from third-party donors (Fisher), and group 3 included chimeras that received irradiated (1,050 cGy) ACI limbs. In group 4, WF hosts conditioned with 950 cGy received irradiated (1,050 cGy) ACI limbs followed by infusion of 100 x 10(6) ACI T-cell-depleted bone marrow cells and immunotherapy (tacrolimus and mycophenolate mofetil) for 28 days. Group 5 animals received the same treatment as group 4 animals without immunotherapy.

RESULTS

The rats in groups 1 and 2 rejected their limbs within 10 days. Only one rat in group 4 survived to the end of the study. Groups 3 and 5 demonstrated long-term limb survival without rejection or graft-versus-host disease. High levels of donor chimerism (>80%) were achieved and maintained throughout the study. Mixed lymphocyte reaction assays in both groups revealed donor-specific hyporesponsiveness with vigorous third-party reactivity.

CONCLUSIONS

This study demonstrated that infusion of donor bone marrow cells into conditioned hosts immediately after limb transplantation results in stable mixed chimerism, robust tolerance, and reliable limb allograft survival.

Low-dose immunosuppression in a rat hind-limb transplantation model

Composite tissue allografts (CTAs) offer an alternative to conventional reconstructive methods. However, the toxicity of the drugs that are required to prevent rejection has prevented its widespread clinical application. The purpose of this study was to determine whether a low-dose, corticosteroid-free combination regimen of tacrolimus and mycophenolate mofetil (MMF) would prevent rejection in a rat hind-limb model, with minimal toxic side effects. Three groups were used in this study. In group I, Wistar Furth (WF) rats received a syngeneic WF hind-limb. In groups II and III, WF rats received an ACI hind-limb. The latter were treated with tacrolimus-MMF. Assessment for rejection, flow cytometry, and mixed lymphocyte reactions was performed. Biopsies were taken regularly and at the time of killing. Combination therapy with low-dose tacrolimus-MMF effectively prolonged CTA survival indefinitely, with minimal side effects. Toxicity associated with immunosuppressive drugs can be avoided in a low-dose combination corticosteroid-free regimen.

A novel gene therapy to the graft organ by a rapid injection of naked DNA I: long-lasting gene expression in a rat model of limb transplantation

BACKGROUND

It is important to develop a nontoxic gene transfer method for immunosuppressed patients. In this study, the authors applied a nonviral gene transfer method using rapid injection of naked DNA into the graft limb in rats.

METHODS

Naked DNA (beta-galactosidase, luciferase, or green fluorescent protein expressing plasmid) was used to test an intravascular gene transfer approach in various conditions on the Lewis rat limb. Then, in a rat limb transplantation model, these marker genes were administered preoperatively (day -2) or perioperatively (day 0) to the graft limb by the authors' "venous protocol." The expression level of luciferase was observed over a long period using a noninvasive living image acquisition IVIS system.

RESULTS

Effective intravascular delivery of gene to the rat limb was achieved by a rapid bolus injection of naked DNA through the femoral caudal epigastric vein. Using this procedure, the limb graft with the marker gene perioperatively in place was safely transplanted. After limb transplantation, sustained marker gene expression was observed for more than 2 months.

CONCLUSIONS

This is the first report showing that the method of rapid injection of naked DNA into the limb can be applied to gene modification for organ transplantation.

Biological Aspects of Limb Transplantation: I. Migration of Transplanted Bone Marrow Cells into Recipient

The transplanted limb contains bone marrow tissue. The hematopoietic cells contained in the bone of the graft normally differentiate after transplantation and can be released to the recipient. The cells migrate to the recipient bone marrow cavities and lymphoid organs. This causes the immune reaction between the donor and the recipient, which develops not only in the graft itself but also in the recipient immune organs where donor bone marrow cells home. The purpose of this study was to investigate the process of migration of the hematopoietic cells from the donor limb to the recipient bone marrow cavities and lymphoid tissues. The questions the authors asked were: what is the rate of release of bone marrow cells from the transplanted bone, where do the released bone marrow cells home in the recipient, how fast are donor bone marrow cells rejected by the recipient, and can some bone marrow cells homing in the recipient tissues survive and create a state of microchimerism. Experiments were performed on Brown Norway and Lewis inbred rat strains (n = 30). Limb donors received intravenous chromium-51-labeled bone marrow cells. Twenty-four hours later, the limb with homing labeled bone marrow cells was transplanted to an allogeneic or syngeneic recipient. The rate of radioactivity of bone marrow cells released from the graft and homing in recipient tissues was measured after another 24 hours. To eliminate factors adversely affecting homing such as the "crowding effect" and allogeneic elimination of bone marrow cells by natural killer cells, total body irradiation and antiasialo-GM1 antiserum were applied to recipients before limb transplantation. In rats surviving with the limb grafts for 7 and 30 days, homing of donor bone marrow cells was studied by specific labeling of donor cells and flow cytometry as well as by detecting donor male Y chromosome. The authors found that transplantation of the limb with bone marrow in its natural spatial relationship with stromal cells and blood perfusion brings about immediate but low-rate release of bone marrow cells and their migration to recipient bone marrow and lymphoid tissues. Large portions of allogeneic bone marrow cells are rapidly destroyed in the mechanism of allogeneic elimination by radioresistant but antiasialo-GM1-sensitive natural killer cells. Some transplanted bone marrow cells remain in the recipient's tissues and create a state of cellular and DNA microchimerism. A low number of physiologically released donor bone marrow cells do not seem to adversely affect the clinical outcome of limb grafting. Quite the opposite, a slight prolongation of the graft survival time was observed.

Long-term acceptance of composite tissue allografts through mixed chimerism and CD28 blockade

BACKGROUND

Clinical composite-tissue (hand) transplantation between genetically disparate individuals currently requires potent, nonspecific immunosuppressive agents that are neither completely successful in preventing acute episodes of rejection nor free from complications. The reliance on long-term immunosuppression has prompted this study to achieve donor-specific transplantation tolerance in adult recipients using a nontoxic, nonmyeloablative protocol.

METHODS

Fully mismatched, 4- to 6-week-old ACI (RT1Aa) and Wistar Furth (WF) rats were used as donors and recipients, respectively. Recipients were administered CTLA4-Ig at 2 mg/kg per day (alternate days) in combination with tacrolimus at 1 mg/kg per day (daily) from day 0 through day +10, antilymphocyte serum at 10 mg at day +10 (single dose), and total-body irradiation t 300 cGy (day 0) before bone-marrow transplantation (BMT) (day 0) with 100 x 10(6) T-cell-depleted bone marrow cells. Hindlimb transplants were performed 4 weeks postBMT. Multilineage donor hematopoiesis was determined pre- and posttransplant using flow cytometry. In vitro T-cell responses were evaluated by mixed lymphocyte reactivity assays.

RESULTS

CD28 blockade in a transplant model of mixed chimerism effectively aborts T-cell clonal expansion in vitro and in vivo, inhibits the development of acute and chronic rejection of vascularized hindlimb allografts in rats (ACI limbs to ACI-->WF chimeras, n=5; WF limbs to ACI-->WF chimeras, n=4), and subsequently leads to long-term survival of allogeneic skin grafts (n=9). Third-party (F344, n=4) transplants were uniformly rejected within 14 days posttransplant. Multilineage donor hematopoiesis was demonstrated pre- and posttransplant. Donor chimerism, present postBMT, increased throughout the study (pretransplant range 2-28%, mean 17%; posttransplant range 5-49%, mean 34%). Transplant recipients maintained full reactivity to respond to third-party antigens without harmful manifestations of graft-versus-host disease.

CONCLUSIONS

Although efforts have been made to induce tolerance to composite tissue allografts in adult recipients, thus far, none have succeeded without toxic, myeloablative host preconditioning. Our demonstration that tolerance can be achieved with minimal preconditioning provides a rationale for application to large animals and humans and suggests that although composite tissue allografts may have a significant skin component (and are therefore felt to be highly antigenic), protocols used to induce tolerance to organ transplants may be equally applicable to composite-tissue allotransplantation.

Mechanisms of alloimmune tolerance associated with mixed chimerism induced by vascularized bone marrow transplants

Rat limb allograft recipients represent surgically induced, immediately vascularized bone marrow transplant (VBMT) chimeras. The majority of these chimeras undergo tolerance while a minority develop graft versus host disease (GVHD). T-cell chimerism and associated mechanisms of cellular immune nonresponsiveness were investigated in tolerant VBMT chimeras. A strong correlation (p < 0.01) was observed between the clinical onset of GVHD and levels of donor T-cell chimerism approximating or greater than 50%. However, stable mixed chimerism was associated with tolerance. In conclusion, three major sequential mechanisms of immune nonresponsiveness were elucidated in tolerant VBMT chimeras over time and included development of nonspecific suppressor cells (which potentially represent natural suppressor cells), maturation of antigen-specific suppressor cell circuits, and eventually putative clonal inactivation.

Extension of composite tissue allograft survival across major histocompatibility barrier under short course of anti-lymphocyte serum and cyclosporine a therapy

In this study, the authors investigated the effects of combined use of cyclosporine A (CsA) and anti-lymphocyte serum (ALS) on the survival of rat hindlimb allografts across a fully allogeneic major histocompatibility complex (MHC) barrier between Brown-Norway rats (BN, RT1 n) and Lewis rats (LEW, RT1 l). Thirty transplantations were performed in five groups of six rats each: Group 1 was the isograft control; Group 2 was the allograft control; Group 3 received ALS, Group 4 received CsA, and Group 5 received CsA and ALS. Treatment was started 2 hr before surgery and was then given for 21 days. Donor-derived chimerism was monitored by FACS analysis. Survival time was calculated as the number of post-transplant days until the first signs of rejection. The allografts in Group 2, Group 3, and Group 4 survived a mean of 5, 6, and 33 days, respectively. The longest mean survival time-51 days-was noted in Group 5 (p<0.05). Donor- derived chimerism peaked at 17 percent and fell to 0 percent at the time of rejection. A combined protocol of ALS/CsA extended survival of rat hindlimb allografts across a fully allogeneic MHC barrier.

Composite tissue allotransplantation in chimeric hosts: part I. Prevention of graft-versus-host disease

BACKGROUND

Mixed allogeneic chimerism (MAC) has been shown to induce tolerance to composite tissue allografts (CTA). However, transplantation of unmanipulated donor-specific limbs results in severe graft-versus-host disease (GVHD). This suggests that nontolerant mature donor-derived cells in the CTA may affect the stability of chimerism, potentially resulting in GVHD. The aim of this study was to develop an approach to study and prevent GVHD in a mixed chimeric-rat hind-limb transplantation model.

METHODS

[ACI-->WF] chimeras received a limb from Wistar Furth (WF) (syngeneic), Fisher (third-party), or ACI (irradiated [1,050 cGy] or nonirradiated) rats. In vitro tolerance was assessed using mixed lymphocyte reactivity (MLR) assays at the time the animals were killed.

RESULTS

[ACI-->WF] chimeras with greater than 85% chimerism exhibited rejection-free survival of donor-specific hind limbs. However, 100% of these animals developed lethal GVHD 22.4+/-2.8 days after limb transplantation. [ACI-->WF] chimeras that underwent transplantation with irradiated ACI or syngeneic WF limbs showed no signs of rejection or GVHD at 5 months. Nonchimeric and third-party controls rejected limbs within 10 days.

CONCLUSIONS

Conditioning of the host WF rats with 950 cGy of irradiation (sublethal, myeloablative) led to high levels of MAC without GVHD. The mature T-cell content of nonirradiated donor (ACI) limbs was sufficient to induce lethal GVHD in 100% of tolerant mixed chimeric [ACI-->WF] hosts. Irradiation of donor limbs before transplantation resulted in long-term donor-specific tolerance and prevented GVHD. These data demonstrate that (1) established chimeras could be susceptible to GVHD caused by immunocompetent donor cells transferred with the hind limb, and (2) inactivating these cells with irradiation prevents GVHD and destabilization of chimerism, and permits rejection-free graft acceptance.