A partial conditioning approach to achieve mixed chimerism in the rat: depletion of host natural killer cells significantly reduces the amount of total body irradiation required for engraftment

The importance of MHC class II in allogeneic bone marrow transplantation and chimerism-based solid organ tolerance in a rat model

Mixed hematopoietic chimerism enables donor-specific tolerance for solid organ grafts. This study evaluated the influence of different serological major histocompatibility complex disparities on chimerism development, graft-versus-host disease incidence and subsequently on solid organ tolerance in a rat model. For bone marrow transplantation conditioning total body irradiation was titrated using 10, 8 or 6 Gray. Bone marrow transplantation was performed across following major histocompatibility complex mismatched barriers: complete disparity, MHC class II, MHC class I or non-MHC mismatch. Recipients were clinically monitored for graft-versus-host disease and analyzed for chimerism using flow cytometry. After a reconstitution of 100 days, composition of peripheral leukocytes was determined. Mixed chimeras were challenged with heart grafts from allogeneic donor strains to define the impact of donor MHC class disparities on solid organ tolerance on the basis of stable chimerism. After myeloablation with 10 Gray of total body irradiation, chimerism after bone marrow transplantation was induced independent of MHC disparity. MHC class II disparity increased the incidence of graft-versus-host disease and reduced induction of stable chimerism upon myelosuppressive total body irradiation with 8 and 6 Gray, respectively. Stable mixed chimeras showed tolerance towards heart grafts from donors with MHC matched to either bone marrow donors or recipients. Isolated matching of MHC class II with bone marrow donors likewise led to stable tolerance as opposed to matching of MHC class I. In summary, MHC class II disparity was critically associated with the onset of graft-versus host disease and was identified as obstacle for successful development of chimerism after bone marrow transplantation and subsequent donor-specific solid organ tolerance.

A Depleting Anti-CD45 Monoclonal Antibody as Isolated Conditioning for Bone Marrow Transplantation in the Rat

Objective

A monoclonal antibody (mAb) against the leukocyte common antigen CD45 (RT7 in rats) could facilitate bone marrow transplantation (BMT). This study in rats evaluates a depletive rat anti-RT7^a mAb as isolated tool for BMT conditioning without using irradiation or any chemotherapeutic / immunosuppressive agent.

Methods

The model used a CD45 di-allelic polymorphism (RT7^a/RT7^b). The anti-RT7^a mAb was intravenously administered to LEW.1W rats (RT1^uRT7^a) at 5, 10 and 15 mg/kg. 1x10⁸ BM cells of MHC syngeneic (RT1^u), MHC disparate (RT1^l) or MHC haploidentical (RT1^u/l) donors were transplanted. All BM donor strains carried the RT7^b allele so that their CD45⁺ cells were not affected by the anti-RT7^a mAb. Recipients were monitored for reconstitution and donor-chimerism in blood leukocytes.

Results

mAb dosages of 5 or 10 mg/kg were myelosuppressive, whereas 15 mg/kg was myeloablative. Multi-lineage donor-chimerism at day 100 indicated engraftment of MHC syngeneic BM after any used mAb dosage (5 mg/kg: 46+/-7%; 10 mg/kg: 62+/-5%; 15 mg/kg: 80+/-4%). MHC disparate BM resulted in autologous reconstitution after conditioning by 10 mg/kg of the mAb and caused transient chimerism ending up in death associated with aplasia after conditioning by 15 mg/kg of the mAb. MHC haploidentical BM (F1 to parental) engrafted only after conditioning by 15 mg/kg (chimerism at day 100: 78+/-7%). Abandonment of α/β TCR⁺ cell depletion from BM grafts impaired the engraftment process after conditioning using 15 mg/kg of the mAb in the MHC syngeneic setting (2 of 6 recipients failed to engraft) and the MHC haploidentical setting (3 of 6 recipients failed).

Conclusion

This depletive anti-RT7^a mAb is myelosuppressive and conditions for engraftment of MHC syngeneic BM. The mAb also facilitates engraftment of MHC haploidentical BM, if a myeloablative dose is used. RT7^b expressing, BM-seeded α/β TCR⁺ cells seem to impair the engraftment process after myeloablative mAb conditioning.

Immune tolerance in orthotopic liver transplantation induced by allogenic bone marrow transplantation in rats

AIM: To establish the allogeneic animal bone marrow and orthotopic liver transplantation model in rats, and to investigate the feasibility and possible mechanism of immune tolerance induced by allogeneic animal bone marrow tansplantation.

METHODS: SD rats (donor, ♂) and Wistar rats (recipient, ♀) were randomly and averagely divided into three groups and conditioned by three methods. Group II Wistar rats (recipient, ♀) were induced with sublethal total body irradiation (TBI, 11 Gy) and group III with TBI (7 Gy), followed by infusion of SD (donor, ♂) rat bone marrow cells (8×10⁷) within 4 h, then rats in group III were administered intraperitoneally with cytoxan (CTX, 50 mg/kg) 2 days later. Then three groups were performed orthotopic liver transplantations using modified Kamada's two-cuff technique in rats 28 days later. According to the GenBank, the specific primer of rat SRY gene was designed. Recipient rats were detected for donor origin cells in the peripheral blood lymphocyte on day 10, 20 using polymerase chain reaction (PCR). PCR product was analyzed by electrophoresis. Delayed type hypersensitivity (DTH), survival time and the histopathologic changes in liver after liver transplantation in rats were compared.

RESULTS: Chimera of SD rats was found in the peripheral blood lymphocytes of the Wistar rats in Group II and III. DTH results showed that Wistar rats were specifically tolerant to the SD rats. The DTH in group II or III is obviously lower than that in group I (0.22 ± 0.028 mm, 0.23 ± 0.032 mm vs 0.71 ± 0.026 mm, P < 0.01). The rats in Group I died 4-5 days later. The survival rate in Group II or III were significantly higher than that in group I (8.14 ± 2.53 d, 8.33 ± 2.11 d vs 3.79 ±0.83 d, P < 0.01). According the Banff scores, the rats in group II and III showed lighter pathological changes than in group I.

CONCLUSION: Treatment of 7 Gy TBI and the injection of CTX (50 mg/kg) plus donor bone marrow transplantation (BMT) establishes a rat chimera model successfully and enhance the survival time of liver transplantation model in rats. Infusion of the bone marrow cells might be an effective method for maintaining the tolerant state and for prolonging survival time of liver transplantation model in rats.

Influence of killer immunoglobulin-like receptor/HLA ligand matching on achievement of T-cell complete donor chimerism in related donor nonmyeloablative allogeneic hematopoietic stem cell transplantation

Achievement of complete donor chimerism (CDC) after allogeneic nonmyeloablative hematopoietic stem cell transplantation (NMHSCT) is important for preventing graft rejection and for generating a graft-vs-malignancy effect. The alloreactivity of NK cells and some T-cell subsets is mediated through the interaction of their killer immunoglobulin-like receptors (KIRs) with target cell HLA/KIR ligands. The influence of KIR matching on the achievement of T-cell CDC after NMHSCT has not been previously described. We analyzed 31 patients undergoing T-cell replete related donor NMHSCT following fludarabine and 200 cGy TBI. Recipient inhibitory KIR genotype and donor HLA/KIR ligand matches were used to generate an inhibitory KIR score from 1 to 4 based upon the potential number of recipient inhibitory KIRs that could be engaged with donor HLA/KIR ligands. Patients with a score of 1 were less likely to achieve T-cell CDC (P=0.016) and more likely to develop graft rejection (P=0.011) than those with scores greater than 1. Thus, patients with lower inhibitory KIR scores may have more active anti-donor immune effector cells that may reduce donor chimerism. Conversely, patients with greater inhibitory KIR scores may have less active NK cell and T-cell populations, which may make them more likely to achieve CDC.

Immune tolerance: mechanisms and application in clinical transplantation

The achievement of immune tolerance, a state of specific unresponsiveness to the donor graft, has the potential to overcome the current major limitations to progress in organ transplantation, namely late graft loss, organ shortage and the toxicities of chronic nonspecific immumnosuppressive therapy. Advances in our understanding of immunological processes, mechanisms of rejection and tolerance have led to encouraging developments in animal models, which are just beginning to be translated into clinical pilot studies. These advances are reviewed here and the appropriate timing for clinical trials is discussed.

NK cells rapidly reject allogeneic bone marrow in the spleen through a perforin- and Ly49D-dependent, but NKG2D-independent mechanism

We have used a sensitive and specific in vivo killing assay to monitor the kinetics, anatomic location and mechanisms controlling NK-mediated rejection of Balb/c bone marrow by C57BL/6 natural killer (NK) cells. We find that NK killing of fully allogeneic bone marrow is a rapid, highly efficient process, leading to substantial rejection of transplanted marrow within 6 h of transplant and elimination of 85% of the transplanted cells within 2 days. NK-mediated rejection occurred predominantly in the spleen, with sparing of rejection in the bone marrow and lymph nodes. Rejection was dependent on Perforin gene function, but was independent of interferon-gamma. Finally, rejection of Balb/c bone marrow by B6 NK cells required signaling through the Ly49D receptor, but occurred despite blockade of NKG2D, which distinguishes these results from previous studies using semiallogeneic transplant pairs. These results identify NK cells as highly active mediators of bone marrow rejection, and suggest that inhibiting NK function early during transplantation may increase the efficiency of engraftment and allow successful engraftment of limiting doses of donor bone marrow.

Efficacy and Limitations of Natural Killer Cell Depletion in Cyclophosphamide-Induced Tolerance

PURPOSE

We previously developed a cyclophosphamide (CP)-induced tolerance protocol, consisting of an intravenous injection of 1 x 10(8) donor spleen cells (SC) given on day 0 and an intraperitoneal injection of 200 mg/kg CP given on day 2. In the present study, we modified this protocol with natural killer cell (NK) depletion in recipient mice, and evaluated the efficacy of tolerance induction.

METHODS

We used B10.D2 (H-2d; IE+) and B10 (H-2b; IE-) mice as both donors and recipients. The recipient mice were treated with donor SC, CP, and donor bone marrow cells (BMCs) with or without NK depletion.

RESULTS

A higher level of mixed chimerism was achieved in the NK-depleted recipients. Survival of both the skin and heart donor grafts was significantly prolonged in the NK-depleted recipients. Donor reactive Vbeta11+ T cells were found at the same level as in untreated control mice. Pretreatment with recipient NK cell depletion was effective in inducing higher levels of donor mixed chimerism; however, permanent engraftment of donor bone marrow was not achieved.

CONCLUSION

Survival of donor grafts was remarkably prolonged in the NK cell-depleted group, but transplantation tolerance could not be induced. Our results suggest that NK cell depletion in CP-induced tolerance conditioning has some effect on the induction of donor-specific tolerance.

Anti-NK cell treatment induces stable mixed chimerism in MHC-mismatched, T cell-depleted, nonmyeloablative bone marrow transplantation

OBJECTIVE

To clarify natural killer (NK) cell-mediated resistance under cytoreductive conditioning and T cell-depleted bone marrow transplantation, we investigated the effects of host NK cell depletion on engraftment and induction of stable mixed chimerism.

METHODS

BALB/c mice (H-2kd) were injected intraperitoneally with anti-asialoGM1 antibody (anti-NK Ab) on day -1. On day 0, they received total body irradiation (TBI) at a dose of 500 cGy, followed by intravenous infusion of 2 x 10(7) T cell-depleted (TCD) bone marrow cells from C57BL/6 mice (H-2kb). Early engraftment and chimerism were determined by the relative ratio of peripheral blood (PB) lymphocytes expressing either H-2kd or H-2kb on day +21. Long-term engraftment and chimerism were evaluated on PB and spleen by multicolor flow cytometry.

RESULTS

Although no recipients treated with TBI alone showed engraftment, all the recipients conditioned with anti-NK Ab and TBI showed successful engraftment as well as a donor-dominant pattern of mixed chimerism in both PB and spleen. Spleen cells from recipients with mixed chimerism showed specific tolerance to both host and donor strains, but not to a third party (C3H/He). None of the reconstituted mice showed signs of graft vs host disease, and all survived up to day +330.

CONCLUSION

These observations indicate that host NK cell depletion may be used to reduce the intensity of conditioning regimens for engraftment of TCD grafts, and can contribute to establishment of stable mixed chimerism in major histocompatibility complex-mismatched nonmyeloablative transplantation.

Preconditioning of NOD mice with anti-CD8 mAb and costimulatory blockade enhances chimerism and tolerance and prevents diabetes, while depletion of alpha beta-TCR+ and CD4+ cells negates the effect

Bone marrow transplantation blocks diabetes pathogenesis and reverses autoimmunity in nonobese diabetic (NOD) mice. However, there is a greater barrier to engraftment in the context of autoimmunity. In the present study, we characterized which recipient cells influence engraftment in prediabetic NOD mice, with the goal to replace myelotoxic conditioning with antigen-specific deletion of reactive host cells. Preconditioning of NOD mice with anti-CD8 and anti-CD154 monoclonal antibodies (mAbs) synergistically enhanced engraftment and significantly reduced the minimum total body irradiation (TBI) dose for engraftment. Strikingly, preconditioning with anti-CD4 mAb significantly impaired engraftment, negating the beneficial effect of anti-CD8, and resulted in a requirement for more TBI-based conditioning compared with controls conditioned with TBI alone. Similarly, more TBI was required when anti-T-cell receptor beta (TCRbeta) mAb was administered as preconditioning. The addition of anti-CD152 to CD154 preconditioning abrogated the engraftment-enhancing effect of anti-CD154. Taken together, these data indicate a role for CD4+ regulatory T cells in vivo which require signaling via CD152 in the induction of chimerism and tolerance in NOD recipients. Notably, disease prevention and reversal of autoimmunity was absolutely correlated with the establishment of chimerism. These studies have important implications for the design of novel clinical approaches to treat type 1 diabetes.

Nonhuman Primate Models for Islet Transplantation in Type 1 Diabetes Research

Insulin-dependent diabetes mellitus is an autoimmune disease that causes a progressive destruction of the pancreatic beta cells. As a result, the patient requires exogenous insulin to maintain normal blood glucose levels. Both the pancreas and the islets of Langerhans have been transplanted successfully in humans and in animal models, resulting in full normalization of glucose homeostasis. However, insulin independence, transient or persistent, was documented in only a small fraction of cases until recently. The chronic immunosuppression required to avoid immunological rejection appears to be toxic to the islets and adds the risk of lymphoproliferative disease reported earlier. For islet transplantation to become the method of choice, it is essential first to identify islet-friendly immunosuppressive regimens and/or to develop methods that induce donor-specific tolerance and improve islet isolation and transplantation protocols. Indeed, researchers have already successfully allografted islets in the presence of nonsteroidal immunosuppression in a process known as the Edmonton protocol. An alternative method, gene therapy, could replace these other methods and better meet the insulin requirement of an individual without requiring pancreatic or islet transplantation. This alternative, however, requires animal models to develop and test clinical protocols and to demonstrate the feasibility of preclinical trials. Nonhuman primates are ideally suited to achieve these goals. The efforts toward developing a nonhuman primate diabetic model with demonstrable insulin dependence are discussed and include pancreatic and islet transplant trials to reverse the diabetic state and achieve insulin independence. Also described are the various protocols that have been tested in primates to circumvent immunosuppression by using tolerance induction strategies in lieu of immunosuppression, thus exploring the field of donor-specific tolerance that extends beyond islet transplantation.

The immunobiology of natural killer cells and bone marrow allograft rejection

Natural killer (NK) cells mediate the acute rejection of bone marrow cell (BMC) allografts, but not solid tissue grafts, in lethally irradiated mice. However, the mechanisms underlying this capability for rejecting BMC remain unclear. NK cells express (1) inhibitory receptors specific for major histocompatibility complex (MHC) class I molecules and (2) activating receptors with diverse specificities. Inhibitory NK receptors confer to NK cells the ability to discriminate between MHC class I-positive and -negative target cells and are therefore involved in the control of NK cell tolerance to self, as well as in the elimination of cells that have downregulation of MHC class I molecules. Preclinical studies in mice have provided good evidence that subsets of NK cells that bear different combinations of both inhibitory and activating Ly49 receptors can interact with each other and target specific BMC rejection, as well as NK cell responses toward tumor cells. Recent clinical studies have also shown that the use of killer cell immunoglobulin-like receptor ligand incompatibility in patients with leukemia who received hematopoietic stem cell transplants correlated not only with the elimination of graft rejection, but also with eradication of tumor and prevention of graft-versus-host disease; this offers a significant advantage for survival. In this review, we attempt to bring together literature regarding the biology of NK cells and discuss the current issues in bone marrow transplantation and the potential clinical role of NK cell alloreactivity in the efficacy of this procedure for immunotherapy of cancer and infectious states.

Lineage-specific chimaerism after stem cell transplantation in children following reduced intensity conditioning: potential predictive value of NK cell chimaerism for late graft rejection

Chimaerism of FACS-sorted leucocyte subsets (CD14+, CD15+, CD3-/56+, CD3+/4+, CD3+/8+, CD19+) was monitored prospectively between days +14 and +100 in 39 children undergoing allogeneic stem cell transplantation with reduced intensity-conditioning regimens. Cell subsets exceeding 1% of nucleated cells were subject to cell sorting. Chimaerism was analysed by dual-colour FISH and/or by short tandem repeat-polymerase chain reaction. The chimaerism pattern on day +28 was evaluated with regard to its correlation with graft rejection. Of 39 patients, nine patients had donor chimaerism (DC) in all subsets. Mixed/recipient chimaerism (MC/RC) was detectable within T cells in 62%, within NK cells in 39% and within monocytes and granulocytes in 38% of the patients. The correlation of secondary graft rejection with the chimaerism pattern on day +28 revealed the strongest association between RC in NK-cells (P<0.0001), followed by T cells (P=0.001), and granulocytes and monocytes (P=0.034). Notably, patients with RC in T cells rejected their graft only if MC or RC was also present in the NK-cell subset. By contrast, none of the children with DC in NK cells experienced a graft rejection. These observations suggest that, in the presence of recipient T-cell chimaerism, the chimaerism status in NK-cells on day +28 might be able to identify patients at high risk for late graft rejection.

Immunotherapy of cancer by active vaccination: does allogeneic bone marrow transplantation after non-myeloablative conditioning provide a new option?

The critical role of antigen-specific T cells in cancer immunotherapy has been amply demonstrated in many model systems. Though success of clinical trials still remains far behind expectation, the continuous improvement in our understanding of the biology of the immune response will provide the basis of optimized cancer vaccines and allow for new modalities of cancer treatment. This review focuses on the current status of active therapeutic vaccination and future prospects. The latter will mainly be concerned with allogeneic bone marrow cell transplantation after non-myeloablative conditioning, because it is my belief that this approach could provide a major breakthrough in cancer immunotherapy. Concerning active vaccination protocols the following aspects will be addressed: i) the targets of immunotherapeutic approaches; ii) the response elements needed for raising a therapeutically successful immune reaction; iii) ways to achieve an optimal confrontation of the immune system with the tumor and iv) supportive regimen of immunomodulation. Hazards which one is most frequently confronted with in trials to attack tumors with the inherent weapon of immune defense will only be briefly mentioned. Many question remain to be answered in the field of allogeneic bone marrow transplantation after non-myeloablative conditioning to optimize the therapeutic setting for this likely very powerful tool of cancer therapy. Current considerations to improve engraftment and to reduce graft versus host disease while strengthening graft versus tumor reactivity will be briefly reviewed. Finally, I will discuss whether tumor-reactive T cells can be "naturally" maintained during the process of T cell maturation in the allogeneic host. Provided this hypothesis can be substantiated, a T cell vaccine will meet a pool of virgin T cells in the allogeneically reconstituted host, which are tolerant towards the host, but not anergised towards tumor antigens presented by MHC molecules of the host.

Donor-derived hematopoietic cells in organ transplantation: a major step toward allograft tolerance?

Infusion of donor-derived cells can improve organ allograft survival in animal models. Under certain conditions, it can even induce tolerance (i.e., unlimited organ survival without any maintenance immunosuppressive therapy). Use of nonmyeloablative regimens allows engraftment of donor-derived bone marrow cells, induction of mixed chimerism, and tolerance in rodents. High doses of bone marrow cells together with anti-T-cell antibodies can even result in mixed chimerism without cytoablative host conditioning. Cultured donor-derived CD34+ cells or donor-derived immature (or even mature) dendritic cells associated with monoclonal antibodies directed against co-stimulatory molecules might also induce tolerance. Among the numerous experimental protocols leading to tolerance of solid organs in animal models, how can we find our bearings in human transplantation? Numerous problems have yet to be solved: the type and amount of donor-derived cells (including stromal cells) to be used, the timing for infusion of donor cells in keeping with organ transplantation, the route of infusion (should it be intravenous, into the portal vein?), and the conditioning regimen. The first clinical trials would appear to indicate that tolerance induction in humans using donor-derived cells is a relatively safe solution that is both promising and realistic.

Optical imaging of PKH-labeled hematopoietic cells in recipient bone marrow in vivo

This work describes an optical technique for characterization of the early stages of hematopoietic stem cell (HSC) engraftment under physiological conditions and in real time. Bone marrow cells (BMCs) labeled with PKH membrane linkers were injected into conditioned recipients (B10-->B10.BR mice) preoperated for placement of optical windows over femoral epiphyses. Labeled cells were tracked in vivo by fluorescence microscopy. Cellular adhesion to the BM stroma was tested with laser tweezers, and viability was assayed by the propidium iodide (PI) exclusion test, as determined from energy-transfer measurements of the pair PKH67-PI in freshly excised femurs in situ. At optimal concentrations for in vivo tracking, 1-4 micro M PKH dyes neither impaired the viability of BMCs nor the capacity of allogeneic HSCs to reconstitute hematopoiesis in myeloablated recipients. The optical window allowed in vivo visualization of 23%-26% of the PKH-labeled BMCs in the femur. The homing efficiencies at 16 hours posttransplantation were quantified as 1.77% +/- 0.15% and 0.21% +/- 0.02% for syngeneic and allogeneic BMCs, respectively. In femurs excised 16 hours after transplantation, 70% +/- 9% of the cells were adherent to the BM stroma, and two-thirds of the cells were PI negative (viable). In vivo tracking and in situ assessment of labeled HSCs in recipient BM provide important quantitative and qualitative insights into the early stages of engraftment. Correlation of early events and the efficiency of durable engraftment serve as the basis for a systematic approach toward optimization of the conditions for transplantation.

Dog leukocyte antigen-haploidentical stem cell allografts after anti-CD44 therapy and reduced-intensity conditioning in a preclinical canine model

OBJECTIVE

We previously described a nonmyeloablative hematopoietic stem cell transplantation regimen in dog leukocyte antigen (DLA)-identical littermate recipients consisting of low-dose total body irradiation (TBI) before and mycophenolate mofetil (MMF)/cyclosporine (CSP) given after transplant to control both graft-vs-host and residual host-vs-graft reactions. In this study, we sought to develop a reduced-intensity regimen to achieve engraftment across major histocompatibility complex barriers in DLA-haploidentical littermate recipients.

MATERIALS AND METHODS

We tested a regimen of 450-cGy TBI with or without postgrafting MMF/CSP for 28 and 35 days, respectively, and with the administration of monoclonal antibody (mAb) S5 (anti-CD44), at a dose of 0.2 mg/kg/day from days -7 through -2, prior to receiving TBI.

RESULTS

One of six dogs conditioned with 450-cGy TBI alone achieved engraftment of granulocyte colony-stimulating factor-mobilized peripheral blood stem cells. Three of six dogs achieved sustained donor cell engraftment using 450-cGy TBI and posttransplantation MMF/CSP. None of three dogs given mAb S5 followed by 450-cGy TBI showed signs of donor cell engraftment. However, when S5 mAb pretreatment was added to 450-cGy TBI and postgrafting MMF/CSP, 10 of 12 dogs achieved sustained engraftment (p = 0.008 or 0.007 vs 450-cGy alone or to S5 + 450-cGy TBI without MMF/CSP, respectively), with only three dogs developing severe graft-vs-host disease on this short regimen of immunosuppression.

CONCLUSION

These results show that engraftment across a DLA haplotype-mismatched barrier can be achieved after reduced-intensity conditioning when mAb S5 directed at CD44 is added to this regimen.

Induction of donor-specific tolerance in rat hind-limb allografts under antilymphocyte serum and cyclosporine A protocol

Composite tissue allograft (CTA) transplantation became a clinical reality despite major side effects associated with the administration of chronic immunosuppression. Development of new treatment modalities eliminating life-long immunosuppression is essential for the future of CTA transplantation. In this study, combined use of cyclosporine A (CsA) and antilymphocyte serum (ALS) was tested for the potential to induce tolerance in the rat hind-limb allograft recipients across a major histocompatibility (MHC) barrier (Lewis-Brown-Norway [LBN, RT1(l+n)] to Lewis [LEW, RT1(l)] rats). Thirty transplantations were performed in 5 experimental groups. Animals received CsA and ALS 12 hours before surgery for 21 days thereafter. Although the allograft controls rejected their limbs at day 7 combined treatment of CsA and ALS resulted in indefinite survival (over 420 d) in all allograft recipients. Long-term survivors showed 35% to 42% of donor-specific chimerism in the peripheral blood. Clinical tolerance was confirmed by acceptance of the donor-specific skin grafts and immunocompetence was confirmed by rejection of the third-party grafts. Mixed lymphocyte reaction revealed suppressed response against donor-type antigens and increased response to third-party antigens. Donor-specific tolerance across MHC barrier was induced in CTA allografts under 21 days protocol of ALS/CsA.

Rantes production during development of cardiac allograft vasculopathy

BACKGROUND

RANTES (regulated on activation, normal T cell expressed and secreted) production has been shown to correlate with mononuclear cell recruitment and precede intimal thickening in cardiac allograft vasculopathy (CAV). However, the cells that produce RANTES in CAV are undefined. Therefore, in an MHC II-mismatched murine model of CAV, we sought to (1) define the cellular sources of RANTES and (2) determine the role of CD4+ lymphocytes in RANTES production during CAV development.

METHODS

B6.CH-2bm12 strain donor hearts were transplanted heterotopically into wild-type (WT) or CD4 knockout (CD4KO) C57BL/6 mice (MHC II mismatch). No immunosuppression was used. Recipients were sacrificed at 7, 14, and 24 days. Intragraft RANTES gene expression and protein levels were determined with ribonuclease protection assay and ELISA, respectively. At days 7 and 24, RANTES production by graft-infiltrating cells was defined with intracellular RANTES staining and multicolor FACS analysis. Intimal thickening was quantitated morphometrically. In murine hearts and in six explanted human hearts with advanced CAV, RANTES was also localized immunohistochemically.

RESULTS

NK, NKT, and gammadelta+ cells, in addition to CD4+, CD8+ lymphocytes, and CD11b+ macrophages, produced RANTES in early and late stages of CAV. RANTES-producing NK, NKT, and gammadelta+ cells tripled in number during CAV development; by day 24, NK and gammadelta+ cells each outnumbered CD4+ lymphocytes and CD11b+ macrophages. The presence of CD4+ lymphocytes was required for sustained RANTES production in allografts, which correlated with mononuclear cell recruitment and preceded intimal thickening. In murine and explanted human hearts with advanced CAV, RANTES immunolocalized with graft-infiltrating mononuclear cells and vessel wall cells.

CONCLUSIONS

We present evidence that other cell types in addition to CD4+, CD8+ T lymphocytes, and CD11b+ macrophages contribute significantly to RANTES production in CAV. In this MHC II-mismatched murine model of CAV, sustained RANTES production requires CD4+ lymphocytes, correlates with mononuclear cell recruitment, and precedes intimal thickening. In experimental and human CAV, vessel wall cells may also produce RANTES. Interventions aimed at inhibiting RANTES production in CAV may need to target several types of cells, and neutralization of RANTES bioactivity may reduce mononuclear cell recruitment and CAV development.