Complete withdrawal of immunosuppression in allograft recipients. A study in rhesus monkeys

Characterization of naturally occurring CD4+CD25+ regulatory T cells in rhesus monkeys

BACKGROUND

Translational research in a relevant preclinical model is recommended before Treg-inducing protocols can be implemented in humans. We have characterized rhesus monkey CD25 cells phenotypically and functionally.

METHODS

The phenotype of CD4(+)CD25(high) cells was determined by FACS, focusing on established markers of mouse and human Treg cells. Percentages of cells positive for CD45RA, CD62L, and intracellular CTLA-4 and FOXP3 were compared between CD4(+)CD25(high) and CD4(+)CD25(-) cells. CD25 cells stimulated with anti-CD3, ConA, and/or allogeneic peripheral blood mononuclear cells were mixed with freshly isolated CD25 cells. The suppressive activity of the CD25 cells in vitro was assessed using several experimental conditions.

RESULTS

Rhesus monkey CD4(+)CD25(high) cells expressed high intracellular levels of CTLA-4 and FOXP3, whereas expression was negligible in CD4(+)CD25(-) cells. The CD25(high) population was mostly CD45RA(-), indicative of a memory phenotype. The CD25(+) cells were anergic, because they showed low proliferative responses, no interleukin-2 production, and some interferon-gamma and interleukin-10 production. Proliferation of CD4(+)CD25(-) cells stimulated by anti-CD3 or allogeneic cells was decreased when CD4(+)CD25(-) cells were added at a 1:1 ratio. In addition, we found that CD25 cells inhibited the interleukin-2 and interferon-gamma production by anti-CD3-stimulated CD25 cells in a dose-dependent fashion, through a cell-cell contact-dependent mechanism.

CONCLUSIONS

Rhesus monkey CD4(+)CD25(+) cells have similar phenotypic and functional characteristics as natural Tregs in humans. These findings allow testing of Treg expansion and induction protocols in a relevant preclinical model, the rhesus monkey.

Combination Treatment with Donor-Specific Transfusions and Cyclosporine A Induces Long-Term Survival of Cardiac Allografts in Miniature Swine

BACKGROUND

To evaluate whether pretransplant donor-specific transfusions (DST) can induce tolerance to cardiac allografts in large animals, heterotopic cardiac transplants were performed across a class I MHC barrier in inbred miniature swine.

METHODS

Experimental animals received two DSTs, each containing 1.4x10 viable peripheral blood mononuclear cells, 14 and 7 days prior to transplantation together with a 12-day course of cyclosporine (CyA) (13 mg/kg IV) starting on postoperative day (POD) 0.

RESULTS

Untreated (n=2) and DST-only (n=2) treated control animals rejected between POD 6 and 8. Animals treated with CyA alone (n=3) exhibited graft survival to 53, 52 and 59 days. In contrast, the combination of DST and CyA (n=3) led to stable graft function for >200 days. Long-term survivors maintained peripheral CML response against donor antigen. Following DSTs, the donor-specific proliferative response of CD8+ recipient T cells was significantly increased (P=0.011), and a significant number of CD8+ T cells underwent apoptosis (10.1% on POD 0; 5.2% on POD -14; P=0.04). None of the DST-treated animals developed donor-specific antibodies.

CONCLUSIONS

These results are the first to demonstrate the ability of DST to induce operational tolerance to cardiac allografts in large animals, and they suggest that peripheral mechanisms of tolerance mediate this effect.

Metastable tolerance to rhesus monkey renal transplants is correlated with allograft TGF-beta 1+CD4+ T regulatory cell infiltrates

Approaches that prevent acute rejection of renal transplants in a rhesus monkey model were studied to determine a common mechanism of acceptance. After withdrawal of immunosuppression, all 14 monkeys retained normal allograft function for >6 mo. Of these, nine rejected their renal allograft during the study, and five maintained normal function throughout the study period. The appearance of TGF-beta 1(+) interstitial mononuclear cells in the graft coincided with a nonrejection histology, whereas the absence/disappearance of these cells was observed with the onset of rejection. Analysis with a variety of TGF-beta 1-reactive Abs indicated that the tolerance-associated infiltrates expressed the large latent complex form of TGF-beta 1. Peripheral leukocytes from rejecting monkeys lacking TGF-beta 1(+) allograft infiltrates responded strongly to donor Ags in delayed-type hypersensitivity trans-vivo assays. In contrast, allograft acceptors with TGF-beta 1(+) infiltrates demonstrated a much weaker peripheral delayed-type hypersensitivity response to donor alloantigens (p < 0.01 vs rejectors), which could be restored by Abs that either neutralized active TGF-beta 1 or blocked its conversion from latent to active form. Anti-IL-10 Abs had no restorative effect. Accepted allografts had CD8(+) and CD4(+) interstitial T cell infiltrates, but only the CD4(+) subset included cells costaining for TGF-beta 1. Our data support the hypothesis that the recruitment of CD4(+) T regulatory cells to the allograft interstitium is a final common pathway for metastable renal transplant tolerance in a non-human primate model.

Long-term kidney graft survival by delayed T cell ablative treatment in rhesus monkeys

BACKGROUND

Tolerance to organ allografts in primates including man has been elusive, although in rodents and pigs tolerance can be achieved to organ allografts with relatively short courses of immunosuppressive treatment. In all varieties of graft acceptance that do not require full-dose maintenance immunosuppression, immunological engagement of donor and recipient and an early unstable period have been observed. On the basis of the hypothesis that elimination of aggressive T cell function should tip the balance in favor of an operationally tolerant state, experiments have been performed in monkeys allowing recipient-donor interaction before T-cell ablation and a short course of immunosuppression.

METHODS

Rhesus monkeys received an allogeneic kidney graft from a MHC-mismatched donor. The animals either received anti-CD3 immunotoxin (FN18-CRM9) alone, started 2 days after transplantation, or in combination with a short course of cyclosporine (CsA) and/or rapamycin (RAPA), started at 5 days after transplantation. Kidney function was followed by monitoring serum creatinine levels and regular biopsies. Humoral and cellular antidonor immunity was tested in vitro before and at several time points after transplantation.

RESULTS

Graft survival of monkeys that received CsA alone (mean survival time (MST)=29.3) was significantly prolonged compared with the controls (MST=6). FN18-CRM9 treatment alone also resulted in prolonged graft survival (MST=29.4). The combined treatment of FN18-CRM9 and CsA and/or RAPA resulted in prolonged graft survival after all immunosuppression was stopped (MST=207.8).

CONCLUSIONS

It seems feasible to postpone immunosuppression posttransplantation and yet prevent allograft rejection without the need of permanent immunosuppression.

Both self and non-inherited maternal HLA antigens influence the immune response

Recent studies suggest that exposure of the fetus and newborn to non-inherited maternal major histocompatibility complex HLA antigens (NIMA) has a life-long effect on allograft recognition that could influence tolerance of organ grafts. NIMA also appear to influence disease susceptibility. Here, Jon van Rood and Frans Claas discuss evidence that three HLA haplotypes, those inherited from the parents plus NIMA, shape the immune response.

Complete withdrawal of immunosuppression in kidney allograft recipients: a prospective study in rhesus monkeys

BACKGROUND

We previously reported the successful withdrawal of immunosuppression in kidney-allografted rhesus monkeys. Recipients had received pretransplant blood transfusions and cyclosporine (CsA) immunosuppression for 6 to 12 months. One animal is still alive at more than 15 years after transplantation. Our hypothesis was that the sharing of a single DR antigen between blood donor and recipient, and the sharing of the same DR antigen with the kidney donor, may be beneficial to allograft survival. We now report on the results from a prospective study.

METHODS

The animals received three pretransplant blood transfusions from a single donor sharing one DR antigen with the recipient. Subsequently, a life-supporting kidney from a donor sharing the same DR antigen was transplanted. CsA was given for at least 6 months after transplantation.

RESULTS

Two animals rejected their graft at 5-8 weeks after cessation of CsA treatment. One animal is still alive at 700 days after transplantation. This animal showed MLR nonreactivity to its kidney donor, similar to the animal at more than 15 years after transplantation.

CONCLUSION

These results demonstrate that withdrawal of immunosuppression may be a realistic option in kidney graft patients under careful immunological monitoring of donor-specific immunity.

Indications of immunological tolerance in kidney transplantation

As a complication to immunosuppressive treatment in allotransplantation, malignant diseases such as post-transplant lymphoproliferative disorder (PTLD) may occur. The patient in the present case is a 21-year-old man transplanted at the age of 11 with a kidney from his mother and at the age of 15 with a kidney from his father. During the immunosuppressive treatment the patient developed PTLD resulting in the withdrawal of the immunosuppressive drugs. At the time of writing, the immunosuppressive drugs have been withdrawn for more than 3 years. We report the findings of a state of donor-specific tolerance occurring after transplantation. Post-transplant cells from the patient show a non-reactive response in mixed lymphocyte cultures (MLCs) to cells from both the mother and the father. We demonstrate a reduction in the mRNA expression of the Thl cytokines IL-2 and IFN-gamma in the very same MLCs. The expression of Th1 cytokine mRNA was measured semi-quantitatively using competitive reverse transcription-polymerase chain reaction (RT-PCR). The reduction in the Th1 cytokine mRNA expression is not seen in the MLCs with patient cells against cells from a paternal HLA-A, B and DR-matched individual, suggesting the influence of other allorecognition factors than HLA-A, B and DR. Detection in vitro of a lowered expression of Th1 cytokine mRNA supports the notion of these mRNAs as indicators of post-transplant tolerance. Further studies will reveal whether the cytokine mRNA measurements on short time stimulated lymphocytes can be used more generally as a monitoring parameter of tolerance in kidney transplantation.

Peritransplant tolerance induction with anti-CD3-immunotoxin: a matter of proinflammatory cytokine control

BACKGROUND

Tolerance is gaining momentum as an approach to reduce lifelong immunosuppressive therapy while improving transplant longevity. Anti-CD3 immunotoxin (IT), FN18-CRM9, has potential to induce tolerance owing to its exceptional ability to deplete sessile lymph node T cells. However, if initiated at the time of transplantation, alpha-CD3-IT alone elicits a proinflammatory cytokine response, precluding establishment of tolerance.

METHODS

Four groups of rhesus monkeys received kidney allografts and immunosuppression. Three groups received alpha-CD3-IT alone or alpha-CD3-IT supplemented with 15-deoxyspergualin (DSG) and/or methylprednisolone (MP). One group received alpha-CD3-monoclonal antibody with DSG and MP. Cytokines were measured by enzyme-linked immunosorbent assay.

RESULTS

Supplementing peritransplant alpha-CD3-IT treatment with a brief course of DSG and MP promoted rejection-free kidney allograft acceptance in 75% of macaques followed for up to 550 days. Among those given alpha-CD3-IT alone or with MP, none were long-term survivors. Tolerance developed after alpha-CD3-IT, DSG, and MP treatment, but not when the unconjugated a-CD3 monoclonal antibody was substituted for IT. Systemic production of proinflammatory cytokines interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha induced after peritransplant alpha-CD3-IT was prevented only in animals given DSG. Despite high levels of interleukin (IL)-12 in the first month after transplant, tolerant recipients exhibited IL-12 resistance, as evidenced by baseline plasma levels of IFN-gamma but elevated IL-4. DSG was shown to inhibit IL-12-driven IFN-gamma production by a mechanism associated with inhibition of nuclear factor kappa-B.

CONCLUSIONS

In this model, peritransplant induction of tolerance is promoted by efficient elimination of sessile lymph node T cells and control of the proinflammatory IFN-gamma response by a mechanism that appears to involve resistance to IL-12.

Preclinical studies of allograft tolerance in rhesus monkeys: a novel anti-CD3-immunotoxin given peritransplant with donor bone marrow induces operational tolerance to kidney allografts

A major challenge in clinical transplantation today is to design a practical and effective protocol for tolerance induction compatible with cadaver organ transplantation. A preclinical rhesus monkey kidney allograft model using immediate peritransplant anti-CD3 immunotoxin (anti-CD3-IT) and donor bone marrow (DBM) is shown here to induce operational tolerance with prolonged graft survival in the absence of chronic immunosuppressive drugs. Bone marrow harvested from the kidney donor was depleted of mature alloantigen-presenting cells and T cells by removing DR(bright) cells and CD3(bright) cells, respectively. In outbred, major histocompatibility complex-incompatible donor-recipient pairs with high pretransplant mixed lymphocyte response and cytotoxic T lymphocyte precursor activity, four of six allografts survived for periods of 120 days to >1.5 years. Graft acceptance after peritransplant treatment followed robust elimination of both peripheral blood T cells and lymph node T cells. In most recipients given anti-CD3-IT and DBM infusion, anti-donor immunoglobulin G responses were completely inhibited. Microchimerism was observed in all recipients studied, including those not given DBM, but levels of microchimerism did not correlate with graft survival. Anti-CD3-IT induction in combination with modified DBM protocols such as the depletion of mature T cells and DR(bright) antigen-presenting cells may offer new opportunities to improve clinical tolerance protocols beyond those attempted in the clinic to date. Overall, these results with anti-CD3-IT show promise for development of cadaver transplant tolerance induction.