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

Chapter 8: Current techniques and concepts in peripheral nerve repair

Despite the progress in understanding the pathophysiology of peripheral nervous system injury and regeneration, as well as advancements in microsurgical techniques, peripheral nerve injuries are still a major challenge for reconstructive surgeons. Thorough knowledge of anatomy, pathophysiology, and surgical reconstruction is a prerequisite of proper peripheral nerve injury management. This chapter reviews the currently available surgical treatment options for different types of nerve injuries in clinical conditions. In overview of direct nerve repair, various end-to-end coaptation techniques and the role of end-to-side repair for proximal nerve injuries is described. When primary repair cannot be performed without undue tension, nerve grafting or tubulization techniques are required. Current gold standard for bridging nerve gaps is nerve autografting. However, disadvantages of this approach, such as donor site morbidity and limited length of available graft material encouraged the search for alternative means of nerve gap reconstruction. Nerve allografting was introduced for repair of extensive nerve injuries. Tubulization techniques with natural or artificial conduits are applicable as an alternative for bridging short nerve defects without the morbidities associated with harvesting of autologous nerve grafts. Achieving better outcomes depends both on the advancements in microsurgical techniques and introduction of molecular biology discoveries into clinical practice. The field of peripheral nerve research is dynamically developing and concentrates on more sophisticated approaches tested at the basic science level. Future directions in peripheral nerve reconstruction including, tolerance induction and minimal immunosuppression for nerve allografting, cell based supportive therapies and bioengineering of nerve conduits are also reviewed in this chapter.

CD8+ T-Cell depletion and rapamycin synergize with combined coreceptor/stimulation blockade to induce robust limb allograft tolerance in mice

The growing development of composite tissue allografts (CTA) highlights the need for tolerance induction protocols. Herein, we developed a mouse model of heterotopic limb allograft in a stringent strain combination in which potentially tolerogenic strategies were tested taking advantage of donor stem cells in the grafted limb. BALB/c allografts were transplanted into C57BL/6 mice treated with anti-CD154 mAb, nondepleting anti-CD4 combined to either depleting or nondepleting anti-CD8 mAbs. Some groups received additional rapamycin. Both depleting and nondepleting mAb combinations without rapamycin only delayed limb allograft rejection, whereas the addition of rapamycin induced long-term allograft survival in both combinations. Nevertheless, robust donor-specific tolerance, defined by the acceptance of a fresh donor-type skin allograft and simultaneous rejection of third-party grafts, required initial CD8(+) T-cell depletion. Mixed donor-recipient chimerism was observed in lymphoid organs and recipient bone marrow of tolerant but not rejecting animals. Tolerance specificity was confirmed by the inability to produce IL-2, IFN-gamma and TNF-alpha in MLC with donor antigen while significant alloreactivity persisted against third- party alloantigens. Collectively, these results show that robust CTA tolerance and mixed donor-recipient chimerism can be achieved in response to the synergizing combination of rapamycin, transient CD8(+) T-cell depletion and costimulation/coreceptor blockade.

Alloantigen-pulsed host dendritic cells induce T-cell regulation and prolong allograft survival in a rat model of hindlimb allotransplantation

BACKGROUND

Composite tissue allotransplantation is restricted due to the risks presented by long-term therapeutic immunosuppression. This study is conducted to investigate whether treatment with recipient immature dendritic cells (DCs) pulsed with donor alloantigens can prolong allograft survival and induce T-cell regulation in a rodent model.

MATERIALS AND METHODS

Orthotopic hindlimb transplants from Brown-Norway (RT1(n)) to Lewis (RT1(1)) rats were performed (day 0). DCs were propagated from the recipient bone marrow and pulsed with the donor alloantigen lysate. Group 1 (control group) did not receive any treatment. Groups 2 and 3 received cyclosporine A (CsA) at a concentration of 10 and 16 mg.kg(-1).day(-1), respectively, on days 0-20 following composite tissue allotransplantation. Group 4 received antilymphocyte serum (i.p. administered 4 d before and 1 d after transplantation) therapy. Group 5 received combined treatment with CsA (10 mg.kg(-1).day(-1), days 0-20) and donor alloantigen-pulsed recipient DCs (i.v. administered on days 7, 14, and 21). Group 6 received combined treatment with CsA (10 mg.kg(-1).day(-1) on days 0-20), antilymphocyte serum (administered i.p. 4 d before and 1 d after transplantation), and DCs (administered i.v. on days 7, 14, and 21). Graft rejection was defined as epidermolysis/desquamation of the donor skin. The mixed lymphocyte reaction was performed to determine the donor T-cell reactivity. Tissue samples were biopsied to analyze the histological changes, and flow cytometry was performed to quantify the donor T-cells.

RESULTS

Allograft survival was significantly prolonged (>200 d) in Group 6 when compared with the other groups (P < 0.001). The mixed lymphocyte reaction performed for Group 6 revealed hyporesponsiveness of the T-cells to donor alloantigens. Flow cytometric analysis in Group 6 revealed a significant increase in the percentage of CD4(+)/CD25(+) and CD4(+)/foxP3(+) T-cells expression, and significant increase in the percentage of donor cells (RT1(n)) in the recipient peripheral blood. Immunohistochemical staining of allo-skin revealed a significant increase in the proportion of CD25(+) cells in the subcutaneous and dermis layers in Group 6, as compared to other groups.

CONCLUSION

Treatment with donor alloantigen-pulsed recipient immature DCs in combination with transient immunosuppression prolongs allograft survival and induced tolerance by inducing T-cell hyporesponsiveness to donor alloantigens and increasing the CD4(+)/CD25(+) T-cell population.

Hematopoietic stem cell engraftment and seeding permits multi-lymphoid chimerism in vascularized bone marrow transplants

Vascularized bone marrow transplantation (VBMT) across a MHC barrier under a 7-day alphabeta-TCR mAb and CsA protocol facilitated multiple hematolymphoid chimerism via trafficking of the immature (CD90) bone marrow cells (BMC) between donor and recipient compartments. Early engraftment of donor BMC [BN(RT1(n))] into the recipient BM compartment [LEW(RT1(l))] was achieved at 1 week posttransplant and this was associated with active hematopoiesis within allografted bone and correlated with high chimerism in the hematolymphoid organs. Two-way trafficking between donor and recipient BM compartments was confirmed by the presence of recipient MHC class I cells (RT1(l)) within the allografted bone up to 3 weeks posttransplant. At 10 weeks posttransplant, decline of BMC viability in allografted bone corresponded with bone fibrosis and lack of hematopoiesis. In contrast, active hematopoiesis was present in the recipient bone as evidenced by the presence of donor-specific immature (CD90/RT1(n)) cells, which correlated with chimerism maintenance. Clonogenic activity of donor-origin cells (RT1(n)) engrafted into the host BM compartment was confirmed by colony-forming units (CFU) assay. These results confirm that hematolymphoid chimerism is developed early post-VBMT by T-cell lineage and despite allografted bone fibrosis chimerism maintenance is supported by B-cell linage and active hematopoiesis of donor-origin cells in the host BM compartment.

Chimerism and bone marrow based therapies in transplantation

Composite tissue allotransplantation holds a great potential for providing increased knowledge of anatomy and microsurgical experience for life-enhancing reconstructions. Many transplant cases around the world have made this a clinical reality at the present time. Composite tissue allotransplants contain multiple tissue types, including bone, muscle, vessels, nerves, skin, and immune cells and bear a huge antigenic load. Although immunosuppressive drugs are applied successfully to prevent allograft rejection, their side effects pose a barrier to worldwide use. Bone marrow therapy in many tolerance induction protocols, therefore, provides a guide to reaching the target of permanent immunotolerance. Multiple studies suggest that bone marrow is immunomodulatory and may facilitate allograft acceptance. In this review, bone marrow based therapy protocols of clinical and experimental models are presented in two major categories: solid organ and composite tissue transplantation.

Skin tolerance: in search of the Holy Grail

In 1943, Gibson and Medawar opened the modern era of transplantation research with a paper on the problem of skin allograft rejection. Ten years later Billingham, Brent and Medawar demonstrated that it was possible to induce selective immune acceptance of skin grafts in mice, a state of tolerance. After over six decades, however, the precise mechanism of skin allograft rejection remains still ill-defined. Furthermore, it has not been possible to achieve reliably clinical tolerance allowing the widespread application of skin allotransplantation techniques. The first successful applications of skin allotransplantation have included the hand and face. However, complications from the chronic immunosuppression regimens limit the application of these techniques. Induction of tolerance to skin (and the other tissues in the allograft) would be the most effective way to overcome all these difficulties, but this is yet to be achieved reliably, stimulating some to look for other ways to surmount the current limitations. This paper summarizes alternatives to enlarge the scope of skin allotransplantation techniques, current understanding of mechanisms of skin rejection, and the utility and limitations of animal models used to study skin rejection and tolerance induction. Finally, manipulation strategies to achieve skin tolerance are outlined.

Immunologic approaches to composite tissue allograft

This article discusses the immunologic principles and the most promising immunologic approaches for composite tissue allograft tolerance. We have previously reviewed some of the pharmacologic approaches for composite tissue allo-transplantation. In this review, we will summarize the range of options that may address the challenge of transplantation in reconstructive surgery.

Donor–origin cell engraftment after intraosseous or intravenous bone marrow transplantation in a rat model

We compared the effects of intraosseous BMT with those of standard i.v. BMT on the efficacy on donor-cell engraftment into the BM and lymphoid organs across an MHC barrier in rats. Twenty-four intraosseous and 24 i.v. BMTs were performed from 48 ACI (RT1(a)) donors to 48 Lewis (RT1(l)) recipients. Each transplant group received either intraosseous or i.v. BMT. Groups I and II served as controls without immunosuppression (n=16); groups III and IV received cyclosporine monotherapy (n=16); and V and VI received alphabeta-TCR monoclonal antibody and cyclosporine A (alphabeta-TCR/CsA) for 7 days (n=16). In each group, four rats received 35 x 10(6) transplanted bone marrow cells (BMCs) and four received 70 x 10(6) cells. All animals survived without GVHD. Mean (+/-s.d.) donor-cell engraftment into BM of recipients after intraosseous BMT was 7.9% (+/-1.3%) in recipients receiving alphabeta-TCR-CsA and 70 x 10(6) BMCs, and 4.2% (+/-1.4%) in recipients after i.v. transplantation. The seeding efficacy of donor cells into lymphoid tissue was greater after intraosseous BMT and alphabeta-TCR-CsA than after standard i.v. transplantation. In our model, intraosseous BMT facilitated donor-cell engraftment under short-term immunodepletive alphabeta-TCR/CsA protocol, which resulted in a temporary state of immune unresponsiveness.

Donor T-cell development in host thymus after heterotopic limb transplantation in mice

We developed a mouse model of heterotopic limb transplantation in which we took advantage of Thy1.1 and Thy1.2 congenic strains to track and characterize donor T cells, to determine the role of recipient's thymus in mixed T-cell chimerism induction as well as transplant immunocompetence. The vascularized Thy1.1 limb graft composed of femur, muscle, and skin (VBT) survived long-term in more than 87.5% of Thy1.2 recipients. Percentages of donor-type Thy1.1 T cells increased from day 30 to 90 in thymus and spleen of recipients. Most peripheral donor T cells displayed a naïve phenotype and a few others were regulatory T cells. Thymectomy prevented peripheral T-cell chimerism. Congenic VBT in immunodeficient RAG mice restored their ability to reject skin allografts. These observations suggest that donor T cells differentiated in host thymus might contribute to maintenance of mixed chimerism after transplantation of tissue composite grafts that include vascularized bone.

Tissue Transplantation in Plastic Surgery

The functional and aesthetic outcome following application of conventional reconstructive procedures or prosthetic materials is not satisfactory, especially in patients who have severe deformities and disabilities. Since the first successful hand transplantation in France in 1998, composite tissue allograft transplantation has gained a great deal of interest in the field of plastic surgery. It is obvious that composite tissue allograft transplantation will improve patients' life quality, but this might be at the expense of decreasing life expectancy. Currently, the main obstacle for composite tissue allograft transplantation is the use of life-long immunosuppression therapy because of their well-known side effects. In addition, the ethical, social, and psychologic issues are raised when discussing face transplantation. The long-term results of the recently performed partial face transplantations will be critical to judge the future applications of partial or total face transplantation.

Applications of bilateral vascularized femoral bone marrow transplantation for chimerism induction across the major histocompatibility (MHC) barrier: part II

Bilateral vascularized bone marrow transplant (VBMT) model was designed to induce chimerism across the major histocompatibility (MHC) barrier under combined alphabeta T-cell receptor monoclonal antibody and cyclosporine A (alphabeta-TCRmAb/CsA) protocol. Seventeen transplants were performed between BN(RT1) donors and Lewis(RTI) recipients. Group I, isograft controls; Group II, allografts rejection controls; Group III, allografts under 7-day protocol of alphabeta-TCRmAb/CsA. Donor bilateral femoral bones were bilaterally anastomosed to the abdominal aorta and inferior vena cava of recipient. At day 7 posttransplantation, all bone flaps were viable. Groups I and III survived without signs of rejection. In Group III, peak level of chimerism in peripheral blood was evaluated at day 21 (24.2%), at day 63 declined to 1.5%, and was maintained at this level thereafter. Donor-derived cells were present in the bone marrow of recipients at 28.2% at day 21 posttransplant. Histology confirmed viability of bone marrow cells in isograft during the entire follow-up and up to 35 days in treatment Group III. Bilateral VBMT induced donor-specific chimerism across the MHC barrier under the immunomodulatory protocol of alphabeta-TCRmAb/CsA.

Chimerism induction in vascularized bone marrow transplants augmented with bone marrow cells

Composite tissue allografts (CTAs) are currently accepted in the clinic; however, long-term immunosuppression is still needed for allograft survival. The presence of donor-specific chimerism may induce tolerance. Thirty-six vascularized bone marrow transplantation (VBMT) allotransplantation were performed across MHC barrier under short-term protocol of 7-day alphabeta-TCRmAb and Cyclosporin A therapy to determine the efficacy of VBMT alone and VBMT augmented with donor bone marrow transplantation (BMT) in chimerism induction. Flow cytometry analysis revealed that VBMT supported with donor BMT directly into the bone resulted in chimerism augmentation and maintenance compared to VBMT. In vivo and in vitro tolerance testing showed prolonged survival of donor skin graft up to 35 days and moderate reactivity in MLR assay that suggests only tolerance induction. Transplantation of vascularized bone without chronic immunosuppression provides a substantial source of bone marrow cells, leading to the development of stable donor-specific chimerism.

Face Transplantation: A Review of the Technical, Immunological, Psychological and Clinical Issues with Recommendations for Good Practice

Three years ago, the Working Party on Facial Transplantation concluded that until there was more information available about risks any potential patient would be exposed to, it would be unwise to proceed with transplantation of the human face. Over the last three years, there has been a deepening understanding of the potential psychological problems of facial transplantation as well as a very considerable debate on the ethical aspects of the procedure. Further data on experimental work in animal models of facial transplantation as well as medium-term follow-up data from 24 hand and forearm transplants in 18 patients has now become available. Furthermore, a partial facial transplantation has been performed in France and a second one in China. In this second edition of the report, the technical, immunological, psychological, and ethical issues are discussed again in the light of this developing knowledge. In particular, there has been a major expansion of the sections on the psychological and societal issues, as well as the ethical and legal problems of facial transplantation. The working party still has considerable reservations about facial transplantation. Although it accepts that on balance the risks cannot be precisely quantified, they remain substantial. Therefore, if patients are allowed to make an informed choice to proceed, they must be very carefully selected and protected in the process, along with the families of both the donors and the recipients. To achieve this, the working party insists that 15 minimum requirements, described at the end of this report, must be fulfilled before it would be appropriate for a research ethics committee/institutional review board to approve of a proposal to undertake facial transplantation.

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.

Trafficking of Donor-Derived Bone Marrow Correlates With Chimerism and Extension of Composite Allograft Survival Across MHC Barrier

We proposed to evaluate differences between recipient's immune response to vascularized skin and combined vascularized skin/bone allografts, under a 7-day alphabeta-TCR plus cyclosporine (CsA) treatment protocol. Thirty-six transplantations were performed in six groups: group I (isograft control-vascularized skin graft; n=6); group II (isograft control-combined vascularized skin/bone graft; n=6); group III (allograft rejection control group-vascularized skin graft; n=6); group IV (allograft rejection control-combined vascularized skin/bone graft; n=6); group V (allograft treatment-vascularized skin graft; n=6); and group VI (allograft treatment-combined vascularized skin/bone graft; n=6). Isograft transplantations were performed between Lewis rats and allografts were transplanted across the MHC barrier from Brown Norway to Lewis rats. In the allograft treatment group, a combined alphabeta-TCR+CsA protocol was applied for 7 days. All groups were compared clinically, immunologically and histologically. Statistical significance was determined with two-tailed Student's t test. Indefinite graft survival was achieved in the isograft control group (>300 days). Allograft rejection controls rejected within 5 to 9 days posttransplant; chimerism levels were undetectable (<.5%). Allografts under the alphabeta-TCR+CsA protocol had significantly extended survival when skin was combined with bone (61-125 days) compared to vascularized skin allografts (43-61 days). Lymphoid macrochimerism was significantly higher in group VI than group V. Histology confirmed skin and bone viability. Combined vascularized skin/bone allografts had higher and sustained levels of donor-specific chimerism and extended allograft survival.

Bilateral Vascularized Femoral Bone Transplant

We present a new model of vascularized bone marrow transplantation-bilateral vascularized femoral bone (BVFB) isograft transplant based on abdominal aorta and inferior vena cava. A total of 7 BVFB isograft transplants were performed between Lewis (RT1) rats. In the donor, both femoral bones were harvested based on the abdominal aorta and inferior vena cava. In the recipient, the harvested isograft transplants were transferred into the inguinal region (in 3 animals) and into the abdominal cavity (in 4 animals). The mean operation time was 3 hours and 35 minutes. The mean warm ischemic time was 35 minutes. The vascular pedicles of the transplants that were transferred into the inguinal region were thrombosed at day 7 posttransplantation. The vascular pedicles of transplants into the abdominal cavity were patent and the bones were viable during the follow-up period of 63 days posttransplant. We have confirmed the feasibility of BVFB transplantation based on abdominal aorta and inferior vena cava.

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.

Development and Maintenance of Donor-Specific Chimerism in Semi-Allogenic and Fully Major Histocompatibility Complex Mismatched Facial Allograft Transplants

BACKGROUND

The clinical application of composite tissue allograft transplants opened the discussion on the restoration of facial deformities by allotransplantation. We introduce a hemifacial allograft transplant model to investigate the rationale for the development of operational tolerance across a major histocompatibility complex (MHC) barrier.

MATERIAL AND METHODS

Thirty rats were studied in five groups of six animals each. The composite hemiface isograft transplantations were performed in group 1. Allograft rejection controls included semi-allogenic transplantations from LBN (RT1(1+n) donors (group 2) and fully allogenic transplantations from ACI (RT1a) donors (group 3) to LEW (RT1(1)) recipients. In the allograft treatment groups, recipients of LBN (group 4) and ACI donors (group 5) were treated with cyclosporine A monotherapy (16 mg/kg/day, tapered to 2 mg/kg/day). Face allografts were evaluated clinically and histologically. Donor-specific chimerism for MHC class I RT1n and RT1a antigens was assessed by flow cytometry. Mixed lymphocyte reaction for donor-specific tolerance in vitro was tested at day 160 posttransplant.

RESULTS

Isograft controls survived indefinitely. All nontreated allografts rejected within 5 to 8 days posttransplant. Long-term survival was achieved in 100% of LBN (up to 400 days) and ACI (up to 330 days) recipients. At day 160, posttransplant donor-specific chimerism was present in recipients of LBN (10.14% CD4/RT1n, 6.38% CD8/RT1n, 10.02% CD45RA/RT1n) and ACI (17.54% CD4/RT1a, 9.28% CD8/RT1a) transplants, and mixed lymphocyte reaction confirmed tolerance in recipients of LBN transplants and moderate reactivity in recipients of ACI allografts.

CONCLUSION

Operational tolerance was induced in hemiface allograft transplants across an MHC barrier under cyclosporine A monotherapy protocol. It was associated directly with the presence of multilineage donor-specific chimerism.

Direct Revascularization is Superior for Rat Parathyroid Allotransplantation with Fk506

Parathyroid gland allotransplantation has been a challenging goal for decades. Our objective was to optimize a parathyroid allotransplantation model for analysis of short-term or low-dose immunosuppressive regimens. Rats that had undergone parathyroidectomy received parathyroid allografts either by direct microvascular anastomoses as part of a composite laryngotracheal graft or by direct implantation into hind limb muscle. All rats were maintained on daily low-dose FK506 (tacrolimus). Intact serum parathyroid hormone (PTH) levels for both groups were recorded over a period of at least 45 days and compared with a repeated-measures mixed model. We found that microvascular anastomosis was superior to implantation for parathyroid gland survival, as all revascularized grafts immediately produced normal levels of PTH, whereas implanted grafts had a significantly slower recovery of function (p < .001). Four of the 11 implanted grafts (36%) never produced detectable PTH levels. Using this model, we are developing innovative strategies that will lead to successful parathyroid allotransplantation without the need for chronic immunosuppression.

Different routes of donor-derived hematopoietic stem cell transplantation for donor-specific chimerism induction across MHC barrier

Transplantation of donor-derived stem cells can improve organ allograft survival in animal models. This study was designed to investigate the effect of different routes of bone marrow cell (BMC) transplantation on donor-specific tolerance induction across MHC barrier under short-term CsA monotherapy and alphabetaTCR/CsA treatment protocols. Forty-eight BMC transplantations were performed between BN(RT1(n)) donors and LEW(RT1(1)) recipients. Intraosseous and intravenous BMC transplantation was studied in six groups of eight animals each receiving 35 x 10(6) (n = 4) and 70 x 10(6) (n = 4) bone marrow cells. Groups I and II (controls) received BMC transplantation but no treatment, groups III and IV CsA monotherapy, and groups V, VI alphabetaTCR/CsA protocol for 7 days. Flow cytometry monitored immunodepletion and donor-specific chimerism for MHC class I RT1(n)/CD4, RT1(n)/CD8 and RT1(n)/CD45RA antigens. All animals survived without graft-versus-host disease. At day 63 under CsA monotherapy a low level of chimerism for RT1(n)/CD4 was induced after intraosseous (1.9%) and intravenous (0.8%) transplantation of (70 x 10(6)) BMC. Under alphabetaTCR/CsA protocol chimerism for RT1(n)/CD4 revealed 6.5% and 0.9% in intraosseous and intravenous (70 x 10(6)) BMC transplantation, respectively. The total number of chimerism in intraosseous and intravenous (70 x 10(6)) BMC transplantation groups was 9.9% and 3.4%, respectively. Following intraosseous BMC transplantation under alphabetaTCR/CsA protocol chimerism was 50% higher in a group receiving 70 x 10(6) (9.9%) vs 35 x 10(6) (4.9%) BMC. Intraosseous transplantation of donor BMC under alphabetaTCR/CsA protocol was 75% more efficient in induction of donor-specific chimerism compared to intravenous transplantation.

Strategies to develop chimerism in vascularized skin allografts across MHC barrier

In this study, we investigated the effects of 7-day-protocols of alphabeta-T-cell receptor monoclonal antibody (alphabeta-TCRmAb), cyclosporine A (CsA), and tacrolimus (FK-506) immunosuppressive monotherapies, and their combinations on the survival of vascularized skin allografts (VSA). Forty-two transplantations of VSA across a strong MHC barrier were performed between ACI (RT1a) donors and Lewis (RT1(l)) recipients in seven groups. Isograft and allograft rejection controls received no treatment. Treatment groups received a 7-day protocol of alphabeta-TCRmAb, CsA, or FK-506 monotherapy, or a combination of alphabeta-TCRmAb/CsA and alphabeta-TCRmAb/FK-506. VSA transplants were evaluated on a daily basis. Donor-specific chimerism was determined by flow cytometry (FC). The combined protocols of alphabeta-TCRmAb/FK-506 and alphabeta-TCRmAb/CsA significantly prolonged VSA survivals compared to monotherapy groups ( P < 0.005). FC analysis revealed 15.82% of donor-specific chimerism on day 7 under the alphabeta-TCRmAb/CsA protocol and a gradual chimerism decline on day 63 posttransplant. The significant extension of VSA survival achieved under 7-day protocols of combined therapies was directly associated with the presence of donor-specific chimerism.

Experimental limb transplantation, part III: Induction of tolerance in the rigorous strain combination of Brown Norway donor to Lewis recipient

The complete withdrawal of immunosuppressive therapy after hind-limb transplantation across a strong histocompatibility barrier (Brown-Norway to Lewis) included a low-dose combination of FK506, mycophenolate mofetil (MMF), and prednisone. MMF and prednisone were tapered and withdrawn between weeks 2 and 7. From weeks 8 to 24, Group 1 animals (n=23) had FK506 tapered; for those in Group 2 (n=11) the dose of FK506 was not changed. At week 24, FK506 was stopped. The six limb grafts in Group 1 (26%) that achieved the 1-year end-point uneventfully showed chimerism by bone marrow and skin grafting supporting the presence of donor-specific tolerance. Rejection, which was common during tapering of FK506, was reversed by salvage therapy. All limbs were rejected postwithdrawal in Group 2. This study showed that tapering of FK506 combined with salvage therapy may allow long-term survival of some transplanted limbs after complete withdrawal of immunosuppressive therapy despite a complete MHC barrier.