Coexistence of Th1- and Th2-type cytokine profiles in anti-CD2 monoclonal antibody-induced tolerance

Coexisting Th1 and Th2 cytokines in patients with collagenous gastritis and implications for its pathogenesis

OBJECTIVES

Collagenous gastritis (CG) is a rare cause of refractory dyspepsia and anemia that frequently affects children and young adults and whose histological hallmark is chronic mucosal inflammation with a subepithelial collagen band. The etiology remains obscure, and no established treatments exist. We investigated the pathogenesis of CG by determining the expression profiles of genes related to immunity and inflammation in index biopsies.

METHODS

Gastric biopsies from 10 newly diagnosed patients with CG were evaluated using the NanoString nCounter assay. Gastric biopsies from 14 normal individuals served as controls. The gene expression ratios for CG versus controls were determined in pooled samples and confirmed in individual samples by quantitative reverse transcription polymerase chain reaction. The results were compared with previously reported expression data from a cohort of patients with collagenous colitis, a colonic disorder with similar morphology, including subepithelial collagen band.

RESULTS

CG biopsies featured enhanced expression of key genes encoding both Th1 (IFNγ, TNF-α, IL-2, IL-10, IL-12A, IL-12B, and IL-18) and Th2 cytokines (IL-3, IL-4, IL-5, IL-6, and IL-13). In contrast, biopsies from patients with CC exhibited upregulated Th1 cytokines only.

CONCLUSIONS

We show in this first published gene expression profiling study that CG involves simultaneous upregulation of Th1 and Th2 cytokines. This finding is unique, contrasting with other types of chronic gastritis as well as with collagenous colitis, which shares the presence of a collagen band. Involvement of Th2 immunity in CG would support further investigation of potential dietary, environmental, or allergic factors to guide future therapeutic trials.

Prospects for the application of antibodies in medicine

Prospects for the Application of Antibodies in Medicine.

Boosting regulatory T cell function by CD4 stimulation enters the clinic

Understanding tolerance mechanisms at the cellular and molecular level holds the promise to establish novel immune intervention therapies in patients with allergy or autoimmunity and to prevent transplant rejection. Administration of mAb against the CD4 molecule has been found to be exceptionally well suited for intentional tolerance induction in rodent and non-human primate models as well as in humanized mouse models. Recent evidence demonstrated that regulatory T cells (Treg) are directly activated by non-depleting CD4 ligands and suggests Treg activation as a central mechanism in anti-CD4-mediated tolerance induction. This review summarizes the current knowledge on the role of Treg in peripheral tolerance, addresses the putative mechanisms of Treg-mediated suppression and discusses the clinical potential of harnessing Treg suppressive activity through CD4 stimulation.

Antiproliferative effects of NKH477, a forskolin derivative, on cytokine profile in rat lung allografts

OBJECTIVE

NKH477 was recently identified as a water-soluble forskolin derivative and was reported to prolong survival of murine cardiac allografts. However, the mechanism of the efficacy is not clear in vivo. The aim of this study was to investigate the immunosuppressive effects of NKH477 on acute lung allograft rejection in the rat model and its mechanism of action in vivo.

METHODS

Left lungs were transplanted orthotopically from Brown-Norway donors to Lewis recipients. Recipient rats were untreated or treated daily with different doses of NKH477. Grafts were excised on Day 3 or Day 5 to determine histopathological rejection and expressions of interleukin (IL)-2, IL-4, IL-10, and interferon (IFN)-gamma by enzyme-linked immunosorbent assay. The cytokine expression at Day 3 or Day 5 was also evaluated in recipient spleens by immunohistochemistry. Furthermore, mesenteric lymph node cells from recipients at Day 5 were cultured alone or stimulated with donor antigens for 72 hours to determine cell proliferation by means of thymidine incorporation.

RESULTS

NKH477 significantly extended allograft survival time in a dose-dependent manner and reduced histopathological rejection. Treatment with NKH477 inhibited IFN-gamma and IL-10 expression, whereas expression of these cytokines were markedly upregulated in the untreated allografts. Expression of IL-2 and IL-10 also increased in the spleen of untreated allorecipients. NKH477 suppressed expression of both cytokines in the spleen. In addition, lymphocyte proliferation was inhibited in NKH477-treated recipients as compared with untreated recipients.

CONCLUSION

These results suggest that NKH477 exerts an antiproliferative effect on lymphocytes in vivo with an altered cytokine profile in rat recipients of lung allografts.

A Role for CD2 Antibodies (BTI-322 and its Humanized Form) in the in vivo Elimination of Human T Lymphocytes Infiltrating an Allogeneic Human Skin Graft in SCID Mice: An Fcγ Receptor-Related Mechanism Involving Co-Injected Human NK Cells

BACKGROUND

Pilot clinical studies have shown that the rat anti-human-CD2 monoclonal antibody, LoCD2a/BTI-322, can efficiently prevent and treat acute kidney rejection. However, the in vivo mechanism by which it prevents allograft rejection has not been studied. BTI-322 and its humanized form have been shown to mediate in vitro antibody-dependent cell-mediated cytotoxicity (ADCC) against CD2 cells through the activation of monocytes or natural killer (NK) cells.

METHODS

Human fetal skin samples were grafted into severe combined immunodeficient/nonobese diabetic mice. Five weeks later (day 0), the mice were injected with human allogeneic peripheral blood lymphocytes (PBL). Either on day 0 or on day 14, mice were treated with BTI-322, hu-BTI-322, or their F(ab')2 fragments. Peripheral blood mononuclear cells (PBMC) thoroughly devoid of NK cells were also assayed.

RESULTS

After injection of PBL, the human skins became heavily infiltrated with activated human T lymphocytes, resulting in dermal microvascular injuries indicative of graft rejection. Early treatment with BTI-322 and hu-BTI-322 prevented all these events. These CD2 antibodies rapidly eliminated human T lymphocytes that had already infiltrated the grafts, with no evidence of recirculation toward the spleen. Their F(ab')2 fragments were, in contrast, ineffective. Elimination of NK cells from injected PBMC prevented the curative effect exerted by whole CD2 antibodies. It also abrogated their cytotoxicity potential against CD2 cells in ADCC assays.

CONCLUSION

F(ab')2 fragments of the CD2 antibodies could not prevent allograft rejection, whereas whole immunoglobulin G could, and human NK cells were required for the curative effect exerted by these antibodies. The results are consistent with an FcgammaR-dependent ADCC mechanism mediated in vivo by human NK cells.

Reprogramming the immune system

The immune system is organized so as to react to pathogens without risking damage to self. Harnessing those processes that prevent self-reactivity will have enormous potential in clinical medicine. This review outlines the efforts of this laboratory over the last 25 years to exploit tolerance so as to reprogram the immune system for therapeutic purposes.

Evidence of T cell clonality in the infectious tolerance pathway: implications toward identification of regulatory T cells

We have shown that a rare population of regulatory CD4+ T cells plays a key role in the acquisition of infectious tolerance in rat sensitized recipients of cardiac allografts pretreated with nondepleting anti-CD4 mAb. This study was designed to analyze the TCR Vbeta expression patterns in this transplantation model. First, we used Vbeta-specific RT-PCR to show that there was no differential usage of TCR Vbeta genes by T cells mediating rejection or tolerance. Indeed, graft-infiltrating lymphocytes expressed most of the 22 known rat TCR Vbeta genes in both recipient groups, suggesting unrestricted TCR Vbeta repertoire in alloreactive T cells. Then, we applied CDR3 spectrotyping of TCR beta-chain to assess the clonality of T cells at different anatomic sites. CDR3 size restriction, indicative of the presence of T cell clones, was observed in graft-infiltrating lymphocytes but not in draining lymph nodes or spleen of tolerant hosts. Consisent with the clonal expansion, T cells in tolerated grafts exhibited the memory phenotype at a much higher percentage as compared with peripheral lymphoid organs. Moreover, in tolerated graft-infiltrating lymphocytes, the CD3 size restriction occurred in limited Vbeta gene families, with Vbeta8.1 and Vbeta18 most frequently detected. Hence, T cells at the graft site of tolerant recipients contain T cell clones expressing selective Vbeta genes. This phenotypic characteristics of the tolerogenic GILs may potentially be used as a novel marker to identify operational regulatory T cells in organ allograft recipients.

Anti-CD2 monoclonal antibodies prevent the induction of experimental autoimmune myocarditis

We investigated the effect of a monoclonal antibody against CD2 molecules (OX34) in preventing the induction of experimental autoimmune myocarditis (EAM) induced by immunizing Lewis rats with cardiac myosin. Administration of OX34 before immunization, on Days -6, -4, -2 and 0, completely prevented EAM. On the other hand, treatment with OX34 just before the appearance of myocardial lesions, on Days 9, 11, 13 and 15, had only a partial effect in preventing the disease. Flow cytometric analysis of lymph node cells showed that CD3+ T cells were immediately depleted with the administration of OX34 but had largely recovered on Day 21. Lymph node cells in OX34-treated rats had no proliferative responses to cardiac myosin-rod, but the proliferation was restored when recombinant IL-2 was added. Ultimate production of the anti-myosin antibody was not inhibited by the treatment with OX34. These results suggest that the prevention of EAM by administering the anti-CD2 monoclonal antibody OX34 resulted from T cell depletion during the induction phase, and might in addition result from T cell anergy of Th1, but not Th2 cells.

Effects on human and nonhuman primate immune response of a new rat anti-CD2 monoclonal antibody

BACKGROUND

Nonhuman primate models are highly clinically relevant in transplantation. The development of immunosuppressive tools or a tolerogenic regimen for primate models therefore represents an important goal of transplantation immunological research. Hence, we have developed a rat monoclonal antibody (mAb) that recognizes the CD2 molecule (LO-CD2b) on both human and nonhuman primate cells.

METHODS

The LO-CD2b mAb has been characterized by flow cytometry, E-rosetting inhibition, and Western blotting. In vitro inhibition of immune responses by LO-CD2b was assessed after both mitogenic and allogeneic stimulation in mixed lymphocyte reactions (MLR). Several LO-CD2b dose and time responses were tested. In vivo, peripheral and lymph node T-cell depletion was examined both by flow cytometry and immunohistology in 10 baboons that received intravenous injection of LO-CD2b at different doses and time courses. Xenosensitization (anti-rat) was assessed by ELISA. Renal allograft survival was followed in two baboons treated with iterative LO-CD2b injections.

RESULTS

In vitro, LO-CD2b binds a lymphocyte antigenic determinant of 52 kDa that is recognized by other well-characterized anti-CD2 mAbs (T11, Leu5b). LO-CD2b recognized natural killer CD2+ cells. Administration of 200 ng/ml LO-CD2b almost completely inhibited human and baboon mitogenic stimulation. Allogeneic baboon and human MLR were completely inhibited by the addition of LO-CD2b (at 312 ng/ml) on the day of the initiation of culture; when added after 1 or 2 days, LO-CD2b still provided a significant MLR inhibition (>50%). Incubation of LO-CD2b with baboon peripheral blood mononuclear cells produced very low cytokine levels (interferon-y, tumor necrosis factor-alpha, interleukin 2). In secondary MLR, baboon peripheral blood mononuclear cells previously incubated with LO-CD2b were unable to respond to a second allogeneic stimulation but were able to react to mitogens. In vivo, within the first hour after LO-CD2b injection (at 0.15, 0.5, and 2 mg/kg), an 85-90% peripheral depletion of CD2+ cells was observed. A partial T-cell depletion in inguinal lymph nodes was seen after 1 week. The mechanism of peripheral T-cell depletion could have been antibody-dependent cell cytotoxicity or opsonization but was complement independent. Iterative LO-CD2b injections (12 days at 0.35 mg/kg) slightly prolonged the renal allograft survival in two baboons.

CONCLUSION

LO-CD2b is a nonactivating rat anti-CD2 mAb able to strongly inhibit both mitogenic and allogeneic responses in human and nonhuman primates. In vivo, LO-CD2b provides a rapid peripheral T-cell depletion, which is reversible within days after the cessation of injections. This rat mAb represents a very important tool for in vivo experimental investigation in nonhuman primates because it similarly reacts against human T cells in vitro.

Tolerance induced without immunosuppression in a T-lymphocyte suicide-gene therapy cardiac allograft model in mice

BACKGROUND

Life-long immunosuppression is a major cause of mortality and morbidity in transplant recipients. Gene therapy could provide new ways to obtain tolerance and avoid indefinite immunosuppression. EpTK mice are derived from the FVB/N strain (H2q) and express the thymidine kinase gene of herpesvirus in all mature T cells. Thus any mature dividing T cell can be killed in the presence of ganciclovir. We investigated the survival of alloincompatible C57B1/6 (H2b) hearts heterotopically transplanted into EpTK mice given only ganciclovir from day 0 to day 7 or 14.

METHODS

Abdominal cardiac transplantations were performed in 22 control mice (untreated FVB [n = 15], ganciclovir-treated FVB [n = 5], and untreated EpTK mice [n = 2]) and in 28 EpTK mice given ganciclovir from day 0 to day 7 (n = 15) or day 14 (n = 13). Rejection was defined as complete cessation of cardiac beat. Histologic examination of the grafts was performed at rejection, at day 7, or at day 100. Lymphocyte proliferation assays (concanavalin A stimulation or mixed lymphocyte reaction) were performed at day 7 and at day 100.

RESULTS

All control animals rejected transplants in 7 days (range, 5-9 days), whereas indefinite survival (>100 days) was observed in 89% of the ganciclovir-treated EpTK group, irrespective of the duration of ganciclovir treatment. Graft histology showed extensive cellular infiltrates with myocyte necrosis and arteritis in the control animals but only a mild infiltrate without necrosis or arteritis in the ganciclovir-treated EpTK group. The proliferative responses of the tolerant mice at day 100 were identical to those of naive mice, including a preserved proliferation against the donor's lymphocytes in mixed lymphocyte reaction.

CONCLUSION

Functional transplantation tolerance of a fully incompatible heart can be achieved without immunosuppressive drugs in this model of suicide gene therapy.

Plant alkaloid tetrandrine and its analog block CD28-costimulated activities of human peripheral blood T cells: potential immunosuppressants in transplantation immunology

BACKGROUND

T lymphocyte activation mediated by CD28 costimulation plays a critical role in graft rejection. Plant alkaloid tetrandrine, purified from a Chinese antirheumatic herb, is a potent immunosuppressant. Here, we examined its effects on several CD28-costimulated T-cell activities. In addition, such effects were readily compared with the effects of three tetrandrine analogs.

METHODS

T lymphocytes were purified from whole blood by negative selection. The stimuli that mimic CD28 costimulation included both anti-CD3 + anti-CD28 monoclonal antibody and PMA+anti-CD28 monoclonal antibody. The determination of CD28-costimulated cell proliferation was performed by tritium uptake, cytokine production by ELISA, cell surface interleukin 2Ra and CD69 expression by flow cytometry, and mixed leukocyte reaction by tritium uptake. Drug cytotoxicity was determined by trypan blue exclusion, propidium iodide staining, and MTT colorimetric assays.

RESULTS

Tetrandrine inhibited CD28-costimulated T-cell proliferation and cytokine production through a mechanism different from that of cyclosporine. In addition, tetrandrine down-regulated both T helper 1 and T helper 2 cytokine production in CD4+ and CD8+ T-cell subpopulations. By examining cytokine production and T-cell activation marker expression, we further demonstrated that, among tetrandrine and its analogs tested, dauricine was the most potent suppressor of CD28-costimulated T-cell activities. Furthermore, the different immunosuppressive activities of these compounds were not associated with their cytotoxic capacities. Finally, the unparalleled inhibitory potency of dauricine on both mixed leukocyte reaction and CD28-costimulated T-cell proliferation suggests that dauricine preferentially targeted CD28-costimulated T-cell activities.

CONCLUSIONS

This is the first report to show that tetrandrine and its analogs potently inhibited both PMA+CD28-costimulated and CD3 + CD28-costimulated activation of human peripheral blood T cells. Based upon their structural similarity and different immunosuppressive potency, these in vitro data also provide very useful information for further identification and development of more potent and less toxic immunosuppressants to achieve transplantation success.

Expression of gamma-IFN mRNA in bronchoalveolar lavage fluid correlates with early acute allograft rejection in lung transplant recipients

Various cytokines are upregulated in acute allograft rejection (AR). Local production of Th-1 cytokines is suggested to play a pathogenic role in AR, and Th-2 cytokines in the development of allograft tolerance. The purpose of this study was to correlate the expression of Th-1 [interleukin-2 (IL-2) and gamma-interferon (gamma-IFN)], and Th-2 [interleukin-10 (IL-10)] cytokines in bronchoalveolar lavage (BAL) fluid with AR in lung transplant (LT) recipients. The role of Th-1 dominance expressed as IgG2/IgG1 ratio in BAL in AR was also examined. The mRNA expression for IL-2, gamma-IFN and IL-10 was examined in 64 BAL specimens from 23 LT recipients using reverse transcriptase-polymerase chain reaction (RT-PCR). IgG1 and IgG2 levels were measured in 55 BAL specimens by enzyme-linked immunosorbent assay (ELISA). The expression on mRNA for these cytokines, and the ratio of IgG2/IgG1 was correlated with AR (early AR occurring within 3 months of transplant and late AR occurring after 3 months). Ten patients had 17 episodes of biopsy proven AR. Twelve episodes of AR (6 patients) occurred within the first 3 months of transplantation. In 5 patients, AR was diagnosed 4, 5, 6, 9 and 24 months post-transplantation. Detection of gamma-IFN mRNA correlated significantly with early AR (p < 0.001), whereas it lacked correlation with late AR. Expression of IL-2 and IL-10 mRNA did not correlate with AR. IL-10 was present in most samples irrespective of the presence or absence of AR. The ratio of IgG2/IgG1 was similar in patients with or without AR. Our findings suggest that the detection of gamma-IFN mRNA in BAL by RT-PCR is useful for immune monitoring of early AR in LT recipients. Absence of elevated IgG2/IgG1 ratio, and presence of IL-10 in BAL during AR suggests that Th-1 cytokines may not be the sole mediator of rejection in LT recipients.

Human allogeneic vascular rejection after arterial transplantation and peripheral lymphoid reconstitution in severe combined immunodeficient mice

BACKGROUND

Interspecies differences create important shortcomings in existing animal models used to describe in vivo events responsible for allograft rejection. Alloimmune destruction of human dermal microvessels, histologically consistent with rejection, has been demonstrated in human skin-grafted severe combined immunodeficient (SCID) mice receiving allogeneic human peripheral blood mononuclear cells (PBMC). We have now documented human alloimmune injury in a vascularized, SCID-human arterial transplantation model.

METHODS

Fresh human artery was used to replace the CB.17 SCID/beige mouse infrarenal aorta. Seven days later, 3x10(8) human PBMC were administered intraperitoneally, and lymphocyte engraftment was considered successful when circulating human CD3+ cells were later identified in peripheral blood.

RESULTS

Forty-six of 49 (94%) mice undergoing transplantation survived, including 14 controls with arterial grafts receiving no PBMC. Twenty-eight of 32 mice demonstrated circulating human CD3+ cells, 14 days after PBMC administration. Animals were killed at 14, 21, or 28 days after receiving allogeneic PBMC, and arteries were recovered for histology and immunohistology. All 14 control mice had patent transplanted grafts with normal vascular histology and no lymphoid infiltration. Damage to transplanted arteries among lymphocyte-engrafted mice was apparent by 14 and 21 days in some animals, whereas 16 of 22 exhibited moderate to severe intimal, medial, and/or adventitial lymphocytic infiltration with intimal expansion by day 28. The infiltrate consisted of HLA-A, -B, -C+, and -DR+, human CD3+ cells, approximately equally distributed as CD4+ and CD8+ subsets. Some infiltrating lymphocytes were cytolytic cells as demonstrated by perforin staining. The endothelium of transplanted human arteries exhibited endothelialitis, and the endothelial cells stained intensely with anti-HLA-A, -B, -C and anti-HLA-DR antibodies. The expanded intima was predominantly smooth muscle cells, staining positively for smooth muscle alpha-actin, HLA-A, -B, -C and HLA-DR. Medial necrosis was not observed.

CONCLUSION

The results provide evidence of alloimmune-mediated vascular rejection in this human arterial transplantation model.

Predominant expression of T helper 2 cytokines and altered expression of T helper 1 cytokines in long-term allograft survival induced by intrathymic immune modulation with donor class I major histocompatibility complex peptides

BACKGROUND

We have recently demonstrated that three synthetic peptides corresponding to the alpha-helices of the alpha1 and alpha2 domains of the donor class I RT1.Aa molecule served as efficient CD4+ T-cell epitopes for indirect recognition of this molecule during cardiac allograft rejection in the PVG.R8-toPVG.1U rat strain combination. These peptides induce long-term graft survival when injected into the thymus 7 days before transplantation under the cover of transient immunosuppression with anti-rat lymphocyte serum. In this study, we analyzed intragraft cytokine gene expression to test whether immune deviation to the T helper (Th) 2 response is associated with long-term allograft survival in this model.

METHODS

Intragraft cytokine gene expression was analyzed using a competitive reverse transcription polymerase chain reaction method we developed for this study. Cytokine gene expression was quantified in control allografts (n=5) with acute rejection and allografts from intrathymically manipulated recipients with acute rejection (n=5), delayed rejection (n=7), or no rejection (n=8).

RESULTS

Long-surviving allografts expressed high levels of interleukin (IL)-4, IL-10, transforming growth factor (TGF)-beta, interferon (IFN)-gamma, and undetectable levels of IL-2. Allografts that were rejected in a delayed fashion expressed mostly IL-2, IFN-gamma, and TGF-beta with low or undetectable levels of IL-4 and IL-10. Acutely rejected allografts from unmanipulated controls or peptide-manipulated recipients expressed high levels of IL-2, IFN-gamma, TGF-beta and undetectable levels of IL-4 or IL-10. All allografts also expressed T-cell receptor Cbeta gene, providing evidence for the presence of T-cell infiltrates in the grafts.

CONCLUSIONS

These observations demonstrate that acute graft rejection in this model is associated with the expression of Th1 cytokines, IL-2, and IFN-gamma, whereas long-term survival is associated with predominant expression of Th2 cytokines, IL-4, and IL-10. The expression of IFN-gamma in long-surviving allografts in the absence of IL-2 provides evidence for altered activation of the Th1 response in this intrathymic immune modulation model.

Effects of the anti-CD2 mAb OX34 on in vivo proliferation

In vitro studies indicate that CD2 plays an important role in the intestinal immune system with regard to T cell proliferation and T helper 2 differentiation. We asked whether anti-CD2 mAb induces T-cell proliferation in vivo. Rats received anti-CD2 mAb OX34 or control mAb over 3 days. Before exsanguination BrdU was injected. Lymphatic organs were processed for two-color immunohistology. OX34 depleted CD4+ but not CD8+ T cells in all organs. Remaining CD4+ T cells proliferated in the periarteriolar lymphocyte sheets. Surprisingly, OX34 led to strong proliferation of splenocytes in the red pulp. These cells were negative for markers of T cells, B cells, NK cells, macrophages, and myeloid cells. Taken together, the anti-CD2 mAb OX34 leads to proliferation of an as-yet-unidentified cell type in the red pulp of the spleen but not to proliferation of T cells.

Analysis of primate renal allografts after T-cell depletion with anti-CD3-CRM9

BACKGROUND

FN18-CRM9 is a CD3-specific immunotoxin that is capable of depleting CD3+ T cells. Pretreatment of rhesus monkeys with this agent before transplantation can induce donor-specific tolerance and "split tolerance" to renal allografts.

METHODS

Heterotopic renal transplants were performed on monkeys that received posttransplant FN18-CRM9. Histological and immunohistological staining, as well as analysis of the intragraft cytokine profile by reverse transcriptase polymerase chain reaction, was performed on percutaneous allograft biopsies.

RESULTS

Experimental monkeys had significant prolongation of allograft survival. Although an interstitial, mononuclear cell infiltrate was seen in all of the renal transplants, there was minimal evidence of acute cellular rejection. Histological evidence of alloantibody-mediated damage was detected 3 to 5 months after transplantation in the monkeys treated with FN18-CRM9. Immunohistology demonstrated the reappearance of CD3+ and CD4+ T cells, as well as CD20+ B cells, in the grafts. Cytokine analysis demonstrated expression of interferon-gamma. An intact anti-donor IgG response was seen.

CONCLUSION

Treatment of monkeys with FN18-CRM9 immediately after transplantation significantly prolongs renal allograft survival. Allograft biopsies demonstrate a lack of acute cellular rejection; however, alloantibody-mediated graft damage and rejection occur, with an intact anti-donor IgG response. The intragraft expression of the interferon-gamma may reflect this ongoing humoral rejection. These data suggest that even a brief period of T-cell allosensitization may lead to humorally mediated allograft damage. Efforts to achieve tolerance with posttransplant FN18-CRM9 will require modification of the protocol to deplete T cells before allosensitization exposure or to supplement the posttransplant immunomodification strategy.

How do monoclonal antibodies induce tolerance? A role for infectious tolerance?

One of the major goals in therapeutic immunosuppression has been to achieve long-term benefit from short-term therapy. The discovery in the mild-1980s that CD4 antibodies can induce immunological tolerance without depleting CD4+ T cells has reawakened interest in the use of nondepleting monoclonal antibodies for reprogramming the immune system in autoimmunity and in transplantation. Since that time, antibodies to CD11a, CD4OL, CD25, CD3, and CTLA4-Ig have all been shown capable of facilitating tolerance. In order to apply to principle of reprogramming in the clinic, we have sought to understand the mechanisms that are involved in its induction and its maintenance. In a number of allogeneic transplant models (heart, skin, bone marrow) anti-CD4 (+/- CD8) antibodies can be shown to block the rejection process while selectively promoting the development of CD4+ regulatory T cells responsible for a dominant tolerance that is reflected in findings of linked suppression and infectious tolerance. In these models, T cells that have never been exposed to CD4 antibodies become tolerant to grafted antigens by experiencing antigen in the microenvironment of regulatory T cells. Dominant tolerance is not the only mechanism that can be facilitated by CD4 Mab therapy. If allogeneic marrow is given at high cell doses under the umbrella of CD4 and CD8 antibodies, then tolerance can be achieved through clonal deletion. The mechanism by which regulatory CD4+ T cell suppress is not yet defined but could be active or passive. We have proposed the "civil service model" to explain how tolerant T cells might interfere with the responses of competent T cells in such a way as to render them tolerant.

Potent Apoptotic Signaling and Subsequent Unresponsiveness Induced by a Single CD2 mAb (BTI-322) in Activated Human Peripheral T Cells

Manipulation of CD2 molecules with CD2 mAb pairs has been shown to deliver apoptotic signals to activated mature T cells. We show that BTI-322, a CD2 mAb directed at a peculiar epitope of CD2, can trigger on its own the apoptotic death of IL-2-activated peripheral T cells and of OKT3-stimulated T cells, contrasting in this respect with a series of other mouse or rat CD2 mAb. F(ab′)2 fragments were as potent as the whole Ab. BTI-322-induced apoptosis proceeded in a few hours and was independent of the Fas/Fas ligand system. Less than 5 ng/ml of BTI-322, added at the begining of culture, were able to eliminate within 4 days most CD3+ cells from OKT3- and IL-2-stimulated lymphocytes, the only cells remaining being CD16+CD2− NK cells. T cell proliferative responses induced by a mitogenic CD2 mAb pair or by PHA-P (which mainly binds to CD2) were not inhibited by BTI-322. In this case, the apoptotic effect was successfully counteracted by simultaneous enhancement of T cell divisions. Thus, the killing effect of BTI-322 was most effective when T cells were exclusively stimulated through the CD3/TCR complex. Apoptosis of the responding T cells may explain why T cells recovered from a primary MLC performed in the presence of BTI-322 responded to third party cells but not to the primary stimulatory cells. These data constitute the rational basis for the use of BTI-322 for inducing tolerance in human allotransplantation.

Induction of tolerance with nondepleting anti-CD4 monoclonal antibodies is associated with down-regulation of TH2 cytokines

BACKGROUND

Induction of tolerance with anti-CD4 has mainly focused on monoclonal antibodies (mAbs) that deplete CD4+ T cells. In this study, the mechanisms by which nondepleting anti-CD4 mAbs induce tolerance in the Dark Agouti to PVG rat heart graft model were examined.

METHODS

Five anti-CD4 mAbs were tested. Immunohistology and cytokine mRNA profiles were analyzed within grafts. Effects of combining anti-CD4 therapy with alloantibody (alloAb), interleukin (IL)-4, and anti-IL-4 mAb were also examined.

RESULTS

All mAbs tested induced indefinite graft survival (>150 days), with blocking of alloAb production. Exogenous alloAb did not restore rejection. Similar T cell receptor alphabeta+, CD8+, IL-2 receptor+ T cell, macrophage, and natural killer cell infiltration and comparable MHC II and intercellular adhesion molecule-1 levels were seen in rejecting and tolerant grafts. mRNA for IL-2, interferon-gamma, lymphotoxin, tumor necrosis factor-alpha, transforming growth factor-beta, cytolysin, and granzyme-A/B was comparable, although inducible nitric oxide synthase was slightly reduced in tolerant grafts. IL-4 and IL-5 were significantly reduced in tolerant grafts, although IL-6, IL-10, and IL-13 levels were similar; this was consistent with partial T helper (Th)2 response inhibition, which was also manifested by inhibited alloAb. The combination of alloAb, IL-4, or anti-IL-4 mAb with anti-CD4 did not prevent tolerance induction.

CONCLUSIONS

This study demonstrated that anti-CD4 mAb therapy did not inhibit activation and infiltration of Th1 and CD8+ effector T cells. Preferential induction of Th2 responses, especially IL-4, was not essential for the induction of tolerance. Our studies also found no evidence to support induction of anergy or transforming growth factor-beta as mechanisms of tolerance induction. These results question whether IL-4 is required for induction of transplantation tolerance.