Prevention of chronic rejection in mouse aortic allografts by combined treatment with CTLA4-Ig and anti-CD40 ligand monoclonal antibody

Background. In this study, using a murine model of aortic allotransplantation, the role of blockade of signaling through CD28/B7 and CD40/CD40 ligand costimulatory pathways in the evolvement of posttransplant vasculopathy was examined. Methods. Aortic allografts were transplanted across C57BL/10J (H2b)→C3H (H2(k)) strain combinations. Transient or more stable blockade of second signaling was achieved by either a single injection or multiple injections of CTLA4-Ig fusion protein (200 μg/dose i.p.) and/or anti-CD40 ligand (CD40L) monoclonal antibody (250 μg i.m.). At day 30 after transplantation, the grafts were harvested for histopathological and immunohistochemical examination. Results. Similar to allografts of untreated animals, aortic allografts obtained from recipients treated with either CTLA4-Ig or anti-CD40L monoclonal antibody alone exhibited marked narrowing of the lumen primarily due to concentric intimal thickening caused by proliferation of α-smooth muscle actin-positive cells. Contemporaneous treatment, however, with either a single injection or multiple injections of CTLA4-Ig and anti-CD40L monoclonal antibody resulted in marked diminution of intimal thickening. Interestingly, concurrent prolonged inhibition of CD28/B7 and CD40/ CD40L pathways resulted in complete abrogation of the development of posttransplant arteriopathy. Conclusion. These data suggest that a more stable disruption of signaling through costimulatory pathways may be required to obviate the development of posttransplant vasculopathy

Abrogation of chronic rejection in a murine model of aortic allotransplantation by prior induction of donor-specific tolerance

Aortic allotransplantation in mice has been well established as a model of choice to study the evolvement of chronic rejection, the etiopathology of which is believed to be that of immune origin. This has prompted the postulation that prior induction of donor-specific tolerance would attenuate or abrogate the underlying events that culminate in posttransplant arteriosclerosis. To study the effects of donor-specific tolerance on chronic rejection, we performed orthotopic liver transplantation without immunosuppression in mice 30 days before aortic allotransplantation across C57Bl/10J (H2b)→C3H (H2(k)) strain combinations (group III). Aortic allografting in syngeneic (group I; C3H→C3H) and allogeneic (group II, C57Bl/10J→C3H) animals served as controls. No morphological changes were evidenced in the transplanted aortas in group I animals. Contrarily, aortic allografts in group H animals underwent a self-limiting acute cellular rejection, which resolved completely and was succeeded by day 30 after transplantation by histopathological changes pathognomonic of chronic rejection. There was evidence for diffuse myointimal thickening, progressive concentric luminal narrowing, and patchy destruction of internal elastic membranes resulting in massive vascular obliteration by day 120 after transplantation. It was of interest that no arteriosclerotic changes were observed for the duration of follow-up (up to 120 days after transplantation) in transplanted aortas (liver donor-type) harvested from animals in group III. However, vasculopathy was prominent in third-party aortic grafts transplanted into tolerant recipients. Taken together, these data suggest that prior induction of tolerance abrogates the development of chronic rejection; this protection seems to be donor specific

Evidence for the presence of multilineage chimerism and progenitors of donor dendritic cells in the peripheral blood of bone marrow-augmented organ transplant recipients

We have postulated that the donor leukocyte microchimerism plays a seminal role in the acceptance of allografts by inducing and perpetuating variable degree of donor-specific nonreactivity in long-surviving organ recipients. Limited information is available, however, concerning the phenotype and function of these chimeric cells in humans. The unequivocal presence of donor dendritic cells (DCs), a prominent lineage in the microchimerism observed in rodents and clinical organ recipients, was difficult to demonstrate in bone marrow (BM)-augmented organ transplant recipients. This enigma was resolved by the recent description of a method for propagating circulating human DCs from their progenitors by culture in a medium enriched with granulocyte-macrophage colony-stimulating factor and interleukin 4, a condition known to inhibit outgrowth of monocytes, thus providing a selective growth advantage to committed progenitors of the myeloid lineage. Cells from BM-augmented organ recipients and normal control subjects harvested from 12- to 14-day cultures exhibited dendritic morphology and potent allostimulatory capacity. Using appropriate primers, the presence of donor DNA was verified by polymerase chain reaction within the lineage(null)/class II(bright) sorted DC. Phenotypic analysis of cultured DCs from BM-augmented patients, unlike that of controls, exhibited a marked down- regulation of B7-1 (CD80) while retaining normal levels of expression of B7- 2 (CD86) cell surface molecules. The presence of donor DNA was also confirmed by polymerase chain reaction in individually sorted lineage+ (T, B, and NK) cells and macrophages, suggesting that the chimerism in BM-augmented patients is multilineage. The presence of progenitors of donor DCs in the peripheral blood of BM-augmented patients further substantiates the already convincing evidence of stem cell engraftment

Kidney/Bone Marrow Transplantation.

Within the past few years, a new conceptual view of transplantation has emerged, based on the observation that renal transplant recipients with extremely long (27-29 years) graft survival all have had evidence of donor cells in their peripheral blood, skin, and lymph nodes. They were thus chimeric. This led to the theory that chimerism is necessary for successful long-term engraftment. It also led to the next logical step of attempting to augment chimerism by transplanting donor bone marrow at the time of organ transplantation. Early reports of combined organ/bone marrow transplantation have suggested that it is safe and is associated with reasonable outcomes. In this paper, we discuss the outcome in the first 30 patients undergoing combined kidney/bone marrow transplantation

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

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. 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. 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. 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

A clinically relevant CTLA4-Ig-based regimen induces chimerism and tolerance to heart grafts

Background. We determined whether a nontoxic CTLA4-Ig-based conditioning regimen effected mixed chimerism and donor-specific tolerance when heart and bone marrow were transplanted simultaneously. Methods. Fully mismatched rat strain combinations were used. Recipients received total-body irradiation (300 centigrays), bone marrow (10 8 cells), and cardiac transplants from the donor on day 0. Subsequently, recipient animals received CTLA4-Ig (2 mg/kg, every other day, × 5 doses), tacrolimus (1 mg/kg/day; days 0 to 9), and one dose (10 mg) of antilymphocyte serum on day 10. Results. All bone marrow recipients (n = 7) developed mixed chimerism (mean = 25% ± 9% at 1 year) and accepted cardiac allografts permanently (> 375 ± 32 days). Recipients that received conditioning regimen but no bone marrow (n = 5) rejected donor hearts within 51 ± 13 days ( p 180 days) donor-specific skin grafts, but rapidly rejected (< 10 days) third-party skin grafts. Conclusions. A nontoxic CTLA4-Ig-based conditioning regimen effects mixed chimerism and donor-specific tolerance when heart and bone marrow are transplanted simultaneously. This regimen may have clinical application

Combined host-conditioning with CTLA4-Ig, tacrolimus, anti-lymphocyte serum, and low-dose radiation leads to stable mixed hematopoietic chimerism

The toxic dose of irradiation required to achieve stable mixed hematopoietic chimerism is the major limitation to its clinical application in transplantation and other nonmalignant conditions such as hemoglobinopathies. This study examines the additive effect of costimulatory blockage, to our previously described tacrolimus-based conditioning regimen, in further reducing the dose of total-body irradiation to achieve stable mixed chimerism in rats. Fully mismatched, 4- to 6-week-old ACI and Wistar Furth rats were used as donors and recipients, respectively. Recipients were administered CTLA4-Ig 2mg/kg/day (alternate days) in combination with tacrolimus 1 mg/kg/day (daily) from day 0 through day +10, anti-lymphocyte serum 10 mg at day +10 (single dose), and total-body irradiation ranging from 100–600 cGy, prior to bone marrow transplantation (day 0) with 100 × 10 6 of T-cell-depleted bone marrow cells. Levels of donor chimerism were determined over a period of 12 months. The short course of CTLA4-Ig, tacrolimus, and ALS led to dramatic engraftments at reduced doses of irradiation: 100% (5/5) and 93% (13/14) of the animals developed mixed chimerism at 400 cGy and 300 cGy, respectively. At 300 cGy, recipients exhibited durable, multilineage mixed chimerism at 365 days with donor cells ranging from 19–42% (mean 23.4%) with no evidence of graft-vs-host disease. These mixed chimeras exhibited in vitro (mixed lymphocyte reaction) and in vivo (skin grafts) donor-specific tolerance. This study suggests that addition of costimulatory blockade to a tacrolimus-based conditioning regimen reduces the dose of irradiation required to achieve stable multilineage chimerism in rats

An internal ribosome entry site mediates the initiation of soluble guanylyl cyclase beta 2 mRNA translation

The soluble guanylyl cyclases (sGC), the receptor for nitric oxide, are heterodimers consisting of an alpha - and beta -subunit. This study aimed to investigate the translational mechanism of the sGC beta 2-subunit. Two mRNA species for sGC beta 2 were isolated from human kidney. These transcripts had dissimilar 5'-untranslated regions (5'-UTRs). The most abundant sGC beta 2 mRNA showed numerous upstream open reading frames (ORFs) and stable secondary structures that inhibited invivo and invitro translation. To evaluate whether these 5'-UTRs harbored an internal ribosome entry site (IRES) that allows translation by an alternative mechanism, we inserted these regions between the two luciferase genes of a bicistronic vector. Transfection of those genetic constructs into HeLa cells demonstrated that both sGC beta 2 leaders had IRES activity in a cell-type dependent manner. Finally, the secondary structural model of the sGC beta 2 5'-UTR predicts a Y-type pseudoknot that characterizes the IRES of cellular mRNAs. In conclusion, our findings suggest that sGC beta 2 5'-UTRs have IRES activity that may permit sGC beta 2 expression under conditions that are not optimal for scanning-dependent translation