The Primate EAE Model Points at EBV-Infected B Cells as a Preferential Therapy Target in Multiple Sclerosis

The remarkable clinical efficacy of anti-CD20 monoclonal antibodies (mAb) in relapsing-remitting multiple sclerosis points at the critical involvement of B cells in the disease. However, the exact pathogenic contribution of B cells is poorly understood. In this publication we review new data on the role of CD20+ B cells in a unique experimental autoimmune encephalomyelitis (EAE) model in common marmosets (Callithrix jacchus), a small-bodied neotropical primate. We will also discuss the relevance of these data for MS. Different from rodent EAE models, but similar to MS, disease progression in marmosets can develop independent of autoantibodies. Progressive disease is mediated by MHC class Ib (Caja-E) restricted cytotoxic T cells, which are activated by γ-herpesvirus-infected B cells and cause widespread demyelination of cortical gray matter. B-cell directed monoclonal antibody therapies (anti-CD20 versus anti-BLyS and anti-APRIL) have a variable effect on EAE progression, which we found associated with variable depletion of the Epstein Barr virus (EBV)-like γ-herpesvirus CalHV3 from lymphoid organs. These findings support an important pathogenic role of CD20+ B cell in MS, especially of the subset infected with EBV.

Comparative analysis of inflammatory infiltrates in collagen-induced arthritis, kidney graft rejection and delayed-type hypersensitivity in non-human primates

OBJECTIVES

Non-human primates are immunologically closely related to humans providing relevant models of inflammatory disorders often used to evaluate new immunomodulating therapies. The aim of the study was to compare inflammatory infiltrates of acute graft rejection (AR) and collagen-induced arthritis (CIA) to delayed-type hypersensitivity (DTH) reactions as the latter model may serve as a less invasive animal model.

MATERIALS AND METHODS

Tissue samples of AR, CIA and DTH were obtained from rhesus monkeys used in several pre-clinical studies. The infiltrate composition was determined by immunohistochemical analysis.

RESULTS

The infiltrates in AR consisted of T cells, macrophages and B cells. The presence of lymphoid structures in AR suggested ongoing intragraft immune activation. The synovia of CIA contained predominantly macrophages and few T cells. The DTH infiltrates were dominated by T cells when the challenged was ovalbumin (OVA) and by macrophages when the challenge was tetanus toxoid (TT).

CONCLUSIONS

The histology of AR resembles aspects of DTH to OVA while that of CIA showed similarities of the DTH to TT. The DTH reaction could serve as a model to study immunomodulating drugs for acute rejection and the acute inflammatory phase of autoimmunity.

The autoimmune response to vimentin after renal transplantation in nonhuman primates is immunosuppression dependent

BACKGROUND

Chronic allograft nephropathy (CAN) is a common late complication of kidney transplantation. Antibodies to both human leukocyte antigen and nonhuman leukocyte antigen antigens have been implicated in the development of this condition. Here we investigated the presence of antivimentin antibodies in nonhuman primate recipients of kidney allografts as a possible predictor of CAN and the effects of immunosuppression.

METHODS

Thirty seven rhesus monkeys received a kidney allograft to study the potency of several different immunosuppressive regimens (conventional immunosuppression, n=19, vs. costimulatory blockade, n=18). Monkeys were tested for antivimentin antibody by enzyme-linked immunosorbent assay and for anti-donor antibody by staining donor spleen cells with recipient serum. The appearance of antibodies was correlated with the graft pathology in biopsy and necropsy material.

RESULTS

Antivimentin antibodies were found in 31 of 37 animals, whereas only 15 of 32 animals made anti-donor antibodies. Conventional immunosuppression did not prevent antivimentin antibody formation. Costimulation blockade, in particular blocking CD40 and CD86, significantly delayed or prevented antivimentin antibody formation, but did not prevent CAN. Antivimentin antibodies were not significantly associated with development of CAN.

CONCLUSIONS

We postulate that vimentin acts as an autoantigen after renal transplantation; it elicits an autoimmune response that is not regulated by cyclosporine. This autoimmune response may be part of the complex immunologic events occurring posttransplantation and may contribute to the development of CAN, but cannot be considered as a major cause of CAN because this condition also develops without antivimentin antibodies.

Inhibition of costimulation allows for repeated systemic administration of adenoviral vector in rhesus monkeys

Immunogenicity of recombinant adenoviral (Ad) vectors severely hampers the clinical development of gene therapy protocols using repeated vector administrations. Inhibition of costimulation by APCs was explored as a strategy to circumvent the immune response against Ad particles. This strategy was tested in rhesus monkeys, treated transiently with chimeric anti-human CD40 and anti-human CD86 antagonist monoclonal antibodies (MAbs) at the time of systemic administration of a recombinant Ad vector. After Ad vector administration in the absence of immunosuppressive treatment, transgene expression in the serum lasted about 3-4 weeks. All control animals developed a strong neutralizing antibody (NAb) response to the Ad particles, which totally prevented efficient administration of a second vector, as shown by the lack of transgene expression. Treatment with anti-CD40 and anti-CD86 chimeric MAbs delayed or blocked the development of a humoral response against Ad and the infiltration of CD8(+) lymphocytes into the liver. This resulted in (i) increased persistence of Ad-transduced cells after injection of a first vector encoding a nonimmunogenic transgene, and (ii) the possibility of readministering a second Ad vector with significant efficacy. In both respects, the combined blockade of CD40 and CD86 was more efficient than treatment with anti-CD40 alone. This study shows for the first time in non-human primates that blocking CD40 and CD86 costimulatory molecules represents a promising strategy to inhibit immune responses against an Ad vector injected systemically.

Mobilization of primitive and committed hematopoietic progenitors in nonhuman primates treated with defibrotide and recombinant human granulocyte colony-stimulating factor

OBJECTIVE

The aim of this study was to evaluate the capacity of defibrotide in enhancing cytokine-induced hematopoietic mobilization in rhesus monkeys.

MATERIALS AND METHODS

Animals received recombinant human granulocyte colony-stimulating factor (rhG-CSF, 100 microg/kg/day SC for 5 days) and, after a 4- to 6-week washout period, were remobilized with defibrotide (15 mg/kg/hour continuous intravenous for 5 days) plus rhG-CSF. Hematopoietic mobilization was evaluated by complete blood counts, differential counts, as well as frequency and absolute numbers of colony-forming cells (CFCs), high-proliferative potential CFCs (HPP-CFCs), and long-term culture-initiating cells (LTC-ICs).

RESULTS

Compared to baseline values, rhG-CSF increased circulating CFCs, HPP-CFCs, and LTC-ICs by 158-, 125-, and 67-fold, respectively; the same figures for defibrotide/rhG-CSF were 299-, 1452-, and 295-fold, respectively. Defibrotide/rhG-CSF treatment compared to rhG-CSF alone increased CFCs, HPP-CFCs, and LTC-ICs by 1.4- (35,089 vs 25,825, p< or =0.02), 6- (4358 vs 748, p< or =0.02), and 5-fold (884 vs 168, p< or =0.04), respectively. We then evaluated the effects of a 2-day defibrotide treatment associated with a 5-day rhG-CSF treatment. Compared to rhG-CSF, defibrotide/rhG-CSF increased the mobilization of CFCs, HPP-CFCs, and LTC-ICs by 2- (31,128 vs 15,527, p< or =0.05), 8- (5361 vs 660, p< or =0.01), and 8-fold (954 vs 119, p< or =0.01), respectively.

CONCLUSION

Our data demonstrate that in nonhuman primates: 1) defibrotide enhances rhG-CSF-elicited mobilization of primitive and committed progenitors; and 2) a 2-day defibrotide injection is as effective as a 5-day injection.

Induction of allograft tolerance through costimulatory blockade: first selection of drugs in vitro

The development of an in vitro assay predicting the chances of graft survival after treatment with immunoregulatory agents is a major topic in transplantation. Antibodies (Abs) interfering in the costimulatory pathway are promising candidates for the induction of tolerance. To evaluate these antibodies for clinical use studies non-human primates are the only feasible option due to species specificity of the antibodies. Peripheral blood mononuclear cells, isolated from a large panel of rhesus monkeys, were used in a unidirectional mixed lymphocyte reaction to evaluate the ability of antibodies blocking the costimulatory pathway, to affect both primary and secondary proliferative and cytolytic allospecific immune responses in vitro. These blocking antibodies were also used in protocols prolonging allograft survival in a life-supporting kidney allotransplant model in rhesus macaques. The ultimate aim is to establish a correlation between parameters obtained in vitro and the success of transplantation in vivo. The combination of anti-CD80 and anti-CD86 resulted in a complete abrogation of the primary alloresponse as measured in a proliferation assay. Adding anti-CD40 significantly reduced this inhibitory effect although the in vivo effects of this antibody have been shown to be beneficial. The secondary response was most prominently inhibited by the combination of anti-CD80/86. Paradoxically, anti-CD40 alone markedly inhibited the secondary proliferative response, but did not add to the inhibitory effect of the combination of anti-CD80/86. The cytolytic response was inhibited maximally only when CsA was added to the combination of anti-CD80/86. Treatment with monoclonal antibodies alone without immunosuppressive drugs was sufficient to maintain graft survival during the time of treatment in most animals. However, rejection was initiated as soon as the treatment ceased and no tolerance, resulting in long-term graft and patient survival, was established. The complete inhibition of primary alloresponses and the partial inhibition of secondary proliferative alloresponses correlate with prolonged graft survival during treatment, but have no predictive value for the success of tolerance induction for kidney allografts in rhesus monkeys.

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.