Immunotherapy as a means to induce transplantation tolerance

Human papillomavirus detected in viral warts of renal transplant recipients

OBJECTIVES

Few studies have been conducted in South America regarding the detection and genotyping of human papillomavirus (HPV) in viral warts of renal transplant recipients (RTRs). The characterization of the population most susceptible to the development of warts and the knowledge of the main HPV types in this environment prompted this study, which focuses on the detection and typing of HPV in RTRs in Brazil.

METHODS

Fifty-eight patients with viral warts from the Hospital São Paulo/Federal University of São Paulo were included in this study. HPV was detected by polymerase chain reaction (PCR) using combinations of the following primers: PGMY 09/11, RK 91, CP 65/70, and CP 66/69. Restriction fragment length polymorphism and automated sequencing techniques were used for HPV typing.

RESULTS

HPV was detected by PCR in 89.7% of viral wart samples. The most frequently detected HPV types included 57, 27, 1a, 2a, and 20. Other types of HPV-epidermodysplasia verruciformis were also detected, including 14, 15, 19, 20, 21, 23, 36, and 38. Rare HPV types were also detected in our environment, including RTR X1, RTR X7, and 100. The time after transplant was correlated with an increased number of lesions and beta papillomavirus genus infection.

CONCLUSIONS

The HPV types detected in the RTR population were similar to those described in immunocompetent populations. However, the diversity of the HPV types identified and the number of lesions were increased in the RTR population.

Transplantation of CD6-depleted peripheral blood stem cells after DLA-haploidentical bone marrow transplantation contributes to engraftment and tolerance in a preclinical model of stem cell transplantation

Human leukocyte antigen (HLA)-haploidentical stem cell transplantation is an opportunity for nearly all patients lacking an HLA matched stem cell donor. However, graft rejection and graft-versus-host disease (GvHD) as well as infectious complications still result in high treatment-related mortality. Here, we used the dog as a preclinical model for the study of tolerance induction with the aim to optimize and to improve a clinical protocol of haploidentical stem cell transplantation. For this purpose CD6-depleted peripheral blood stem cells (PBSCs) were transfused 6d after transplantation of unmodified bone marrow from dog leukocyte antigen (DLA)-haploidentical littermate donors in order to induce immune tolerance. Besides hematopoietic stem cells CD6-depleted PBSC contain, NK cells and a minority of suppressive CD8-positive cells that may suppress activated T lymphocytes. Recipients were conditioned with, cyclophosphamide and antithymocyte globulin (ATG) preceded by a transfusion of donor buffy coat and either 1, 2 or 3 × 3.3 Gy total body irradiation (TBI). Postgrafting immunosuppression was limited to 30 d of cyclosporine and methotrexate. The additional administration of CD6-depleted PBSCs after unmodified marrow could not prevent GvHD, but it may improve engraftment and chimerism after conditioning with 2 × 3.3 Gy TBI. Reasons for incomplete suppression and possible improvements for clinical applications are discussed.

Should microchimerism turn into rejection prophylactics?

Non-self cells can circulate in the body of an individual after any sort of contact with an allogeneic source of cells, thus creating a situation of chimerism that can be transient or prolonged over time. This situation may appear after stem cell transplantation, pregnancy, transfusion or transplantation. Concerning transplantation, many hypotheses have been formulated regarding the existence, persistence and role of these circulating cells in the host. We will review the principal hypotheses that have been formulated for years since the first description of non-self circulating cells in mammals to the utilization of artificially induced chimerism protocols for the achievement of tolerance.

CD28/CD154 blockade prevents autoimmune diabetes by inducing nondeletional tolerance after effector t-cell inhibition and regulatory T-cell expansion

OBJECTIVE

Blocking T-cell signaling is an effective means to prevent autoimmunity and allograft rejection in many animal models, yet the clinical translation of many of these approaches has not resulted in the success witnessed in experimental systems. Improved understanding of these approaches may assist in developing safe and effective means to treat disorders such as autoimmune diabetes.

RESEARCH DESIGN AND METHODS

We studied the effect of anti-CD154 and CTLA4-Ig on diabetes development, and the requirements to induce tolerance in nod.scid mice after transfer of transgenic beta-cell reactive BDC2.5.NOD T-cells.

RESULTS

Nod.scid recipients of diabetogenic BDC2.5.NOD cells were protected indefinitely from diabetes by a short course of combined costimulation blockade, despite the continued diabetogenic potential of their T-cells. The presence of pathogenic T-cells in the absence of disease indicates peripheral immune tolerance. T-cell maturation occurred in protected recipients, yet costimulation blockade temporarily blunted early T-cell proliferation in draining pancreatic nodes. Tolerance required preexisting regulatory T-cells (Tregs), and protected recipients had greater numbers of Tregs than diabetic recipients. Diabetes protection was successful in the presence of homeostatic expansion and high T-cell precursor frequency, both obstacles to tolerance induction in other models of antigen-specific immunity.

CONCLUSIONS

Immunotherapies that selectively suppress effector T-cells while permitting the development of natural regulatory mechanisms may have a unique role in establishing targeted long-standing immune protection and peripheral tolerance. Understanding the mechanism of these approaches may assist in the design and use of therapies for human conditions, such as type 1 diabetes.

Transient depletion of dividing T lymphocytes in mice induces the emergence of regulatory T cells and dominant tolerance to islet allografts

We previously showed that transient depletion of dividing T cells at the time of an allogeneic transplantation induces long-term tolerance to the allograft. Here we investigated the role of homeostatic perturbation and regulatory T cells (Treg) in such tolerance. Transient depletion of dividing T cells was induced at the time of an allogeneic pancreatic islets graft, by administration of ganciclovir for 14 days, into diabetic transgenic mice expressing a thymidine kinase (TK) conditional suicide gene in T cells. Allograft tolerance was obtained in 63% of treated mice. It was not due to global immunosuppression, permanent deletion or anergy of donor-alloantigens specific T cells but to a dominant tolerance process since lymphocytes from tolerant mice could transfer tolerance to naïve allografted recipients. The transient depletion of dividing T cells induces a 2- to 3-fold increase in the proportion of CD4(+)CD25(+)Foxp3(+) Treg, within 3 weeks that persisted only in allograft-bearing mice but not in nongrafted mice. Tolerance with similar increased proportion of Treg cells was also obtained after a cytostatic hydroxyurea treatment in normal mice. Thus, the transient depletion of dividing T cells represents a novel means of immuno-intervention based on disturbance of T-cell homeostasis and subsequent increase in Treg proportion.

The use of CD3-specific antibodies in autoimmune diabetes: a step toward the induction of immune tolerance in the clinic

CD3-specific monoclonal antibodies were the first rodent monoclonals introduced in clinical practice in the mid 1980s as approved immunosuppressants to prevent and treat organ allograft rejection. Since then compelling evidence has been accumulated to suggest that in addition to their immunosuppressive properties, CD3-specific antibodies can also afford inducing immune tolerance especially in the context of ongoing immune responses. Thus, they are highly effective at restoring self-tolerance in overt autoimmunity, a capacity first demonstrated in the experimental setting, which was recently transferred to the clinic with success.

Hematopoietic chimerism induces renal and skin allograft tolerance in DLA-identical dogs

OBJECTIVE

Hematopoietic chimerism, a state where donor and recipient bone marrow cells coexist, is associated with donor-specific tolerance. Nonmyeloablative bone marrow transplantation (BMT) has been shown to induce stable mixed hematopoietic chimerism in dog leukocyte antigen (DLA)-matched dogs. The potential for inducing renal and skin allograft tolerance with nonmyeloablative BMT was investigated in DLA-identical and DLA-haploidentical dogs in this study.

MATERIALS AND METHODS

Renal allografts were performed in 8 DLA-identical and 4 DLA-haploidentical dogs with nonmyeloablative conditioning (200 cGy TBI) and transient immunosuppression with cyclosporine (CSP) and mycophenolate mofetil (MMF) with (n = 8) and without (n = 4) simultaneous BMT. Skin allografts were performed in 2 DLA-identical and 4 DLA-haploidentical dogs after stopping CSP and MMF. Two DLA-identical control dogs received renal allografts without TBI, BMT, or immunosuppression with CSP and MMF. Molecular chimerism was determined with a PCR-based DNA microsatellite assay. Serum creatinine (Cr) concentration, urine specific gravity, and sequential renal biopsies were monitored to assess renal allograft function.

RESULTS

Donor-type blood cells were first detected 4 weeks posttransplantation in both the myeloid and lymphoid lineages. Donor chimerism was present for at least 76 weeks in the DLA-identical dogs. Mixed chimerism was not observed in the DLA-haploidentical dogs or DLA-identical dogs that did not undergo BMT. The renal allografts were acutely rejected within 14 days in the 2 DLA-identical control dogs. There was long-term (> 5 yrs) renal allograft survival as evidenced by a normal (< 2.0 mg/dL) serum Cr concentration in both the DLA-identical and DLA-haploidentical dogs that underwent 200 cGy TBI and transient immunosuppression with CSP and MMF either with or without simultaneous BMT. Renal allograft inflammation was severe in the control dogs, mild to moderate in the DLA-haploidentical dogs, and minimal in the DLA-identical dogs. Donor-specific skin grafts were accepted in the DLA-identical dogs but rejected in the DLA-haploidentical dogs. Nonmyeloablative conditioning (200 cGy TBI) and transient immunosuppression with CSP and MMF induce renal and skin allograft tolerance in DLA-identical and permit long-term renal allograft survival in DLA-haploidentical dogs. These findings suggest it may possible to obtain long-term allograft survival in DLA-identical and -haploidentical dogs without the need for chronic immunosuppressive therapy.

Transforming growth factor-beta and T-cell-mediated immunoregulation in the control of autoimmune diabetes

It is now well-established that CD4+ regulatory T cells are instrumental in controlling immune responses both to self-antigens and to non-self-antigens. However, the precise modalities involved in their differentiation and survival, their mode of action and their antigen specificity are only partially understood. We have been particularly interested in the study of regulatory T cells controlling autoimmune insulin-dependent diabetes. Here, we provide evidence to support the phenotypic and functional diversity of regulatory T cells mediating transferable 'active' or 'dominant' peripheral tolerance in the non-obese diabetic mouse model (NOD). They include natural and adaptive regulatory T cells that are operational both in unmanipulated NOD mice and in animals undergoing treatments aimed at inducing/restoring tolerance to self-beta-cell antigens. At least in our hands, the differential cytokine-dependency appears as a major distinctive feature of regulatory T cells subsets. Among immunoregulatory cytokines, transforming growth factor-beta(TGF-beta) appeared to play a key role. Herein we discuss these results and the working hypothesis they evoke in the context of the present literature, where the role of TGF-beta-dependent T-cell-mediated immunoregulation is still debated.

CD3-specific antibodies as promising tools to aim at immune tolerance in the clinic

Currently, therapies applied in transplantation and autoimmunity are essentially based on the use of immunosuppressants. These agents depress all immune responses and expose individuals to the recurrence of the pathogenic immune process once they are withdrawn, thus necessitating a chronic administration leading to the risk of recurrent infections and increased frequency of tumors. At variance, CD3 monoclonal antibodies appear unique in their capacity to induce immunological tolerance that is an antigen-specific unresponsiveness in the absence of chronic immunosuppression. This has been well-established in experimental models, and recent data show successful clinical translation using humanized anti-CD3 antibodies. The aim of this brief review is to discuss the main characteristics of these very promising tools and to present the experimental and clinical results arguing for their unique tolerogenic ability.

Design of a Peptibody Consisting of the Antimicrobial Peptide dhvar5 and a llama Variable Heavy-chain Antibody Fragment

Immunoconjugates have been widely studied as potential therapeutics for infectious diseases to direct unspecific antimicrobials to pathogens. In this study, the recombinant approach was used for expression of the immunoconjugate composed of the variable domain of a llama heavy-chain antibody (VHH) against Streptococcus mutans and dhvar5, a synthetic antimicrobial peptide. Before cloning, the impact of the elongation of the peptide termini on its biological activity was evaluated by chemical synthesis of the N- or C-termini extended dhvar5 peptides. As the elongation of the C-terminus had a greater influence on decline of the antimicrobial activity, the N-terminal fusion was designed. To promote in vivo release of the active peptide, a factor Xa cleavage site was inserted between VHH and dhvar5. Propagation of transformed Escherichia coli with the constructed plasmid was only possible in the absence of isopropyl beta-D-thiogalactoside (IPTG). Although these data demonstrate that the diminished antimicrobial activity of dhvar5 by the N-terminal fusion to VHH was not sufficient for the protection of the bacterial host cells against the peptide lethal effect, an insight into propeptides biological activities may be beneficial not only for new and more successful rearrangement of the VHH-dhvar5 immunoconjugate construct, but also design of the other recombinant molecules composed of peptides toxic to host cells.

Thymocyte/Splenocyte-Derived CD4+CD25+Treg Stimulated by Anti-CD200R2 Derived Dendritic Cells Suppress Mixed Leukocyte Cultures and Skin Graft Rejection

BACKGROUND

CD200 delivers immunoregulatory signals following engagement of its receptor, CD200R. A family of CD200Rs (CD200R1-4) has been described. Spleen expresses cell surface CD200R1, while bone marrow shows predominantly expression of cell surface CD200R2/R3. We showed that dendritic cell precursors (DCp) cultured with anti-CD200R2/3 develop the capacity to induce CD4(+)CD25(+) regulatory T cells (Treg) from peripheral lymphocytes. We now characterize DCs involved in induction of antigen-specific Treg from thymocytes or peripheral T cells, and the properties of Treg cells maintained in long-term culture.

METHODS

Bone marrow DCp (C3H or BL/6 origin) were cultured for 8 days with GMCSF, IL-4 and anti-CD200R2, or with CD200Fc and a previously described peptide inhibitor of CD200R1 to allow preferential engagement of non-CD200R1 receptors by CD200. Mixed leukocyte cultures (MLCs) were initiated with allogeneic responder lymphocytes/thymocytes (BL/6 or C3H) and mitomycin-c treated DCs to induce Treg. Treg cells were maintained by reculture with DCs derived in the same manner and IL-2, cloned at limiting dilution, and tested for their ability to suppress MLCs and skin graft rejection in vivo.

RESULTS

Foxp3(+) CD4(+)CD25(+) Treg were derived from 60-hr thymocyte and splenocyte T cell cultures using both DC populations. Cloned C3H Treg (Foxp3(+)) suppressed both C3H anti-BL/6 reactivity in a fresh MLC and rejection of BL/6 skin allografts in C3H recipients; the converse was true for BL/6 Treg.

CONCLUSIONS

We conclude that CD200 triggering of bone-marrow DCs in the absence of CD200R1 engagement induces CD4(+)CD25(+) Treg, and these cloned antigen-specific Treg may have clinical utility.

Intravenous apoptotic spleen cell infusion induces a TGF-beta-dependent regulatory T-cell expansion

Apoptotic leukocytes are endowed with immunomodulatory properties that can be used to enhance hematopoietic engraftment and prevent graft-versus-host disease (GvHD). This apoptotic cell-induced tolerogenic effect is mediated by host macrophages and not recipient dendritic cells or donor phagocytes present in the bone marrow graft as evidenced by selective cell depletion and trafficking experiments. Furthermore, apoptotic cell infusion is associated with TGF-beta-dependent donor CD4+CD25+ T-cell expansion. Such cells have a regulatory phenotype (CD62L(high) and intracellular CTLA-4+), express high levels of forkhead-box transcription factor p3 (Foxp3) mRNA and exert ex vivo suppressive activity through a cell-to-cell contact mechanism. In vivo CD25 depletion after apoptotic cell infusion prevents the apoptotic cell-induced beneficial effects on engraftment and GvHD occurrence. This highlights the role of regulatory T cells in the tolerogenic effect of apoptotic cell infusion. This novel association between apoptosis and regulatory T-cell expansion may also contribute to preventing deleterious autoimmune responses during normal turnover.

Renal Allograft Tolerance in DLA-Identical and Haploidentical Dogs After Nonmyeloablative Conditioning and Transient Immunosuppression With Cyclosporine and Mycophenolate Mofetil

BACKGROUND

Canine models of bone marrow and renal transplantation have provided important preclinical data relevant to developing novel therapeutic protocols for hematopoietic and solid organ transplantation in human beings. Nonmyeloablative transplantation has been shown to induce stable mixed hematopoietic chimerism in normal dogs and correct the phenotype of canine pyruvate kinase deficiency and Glanzman's thrombasthenia. In this study, we investigated the potential for inducing renal allograft tolerance using a nonmyeloablative bone marrow transplantation strategy that induces mixed chimerism in DLA-identical dogs.

METHODS

Reciprocal renal allografts were performed in 4 DLA-identical and 4 DLA-haploidentical dogs with nonmyeloablative conditioning (200 cGy total body irradiation [TBI]) and transient immunosuppression with cyclosporine (CSP) and mycophenolate mofetil (MMF) with and without simultaneous bone marrow transplantation. Two DLA-identical control dogs received reciprocal renal allografts without TBI or immunosuppression with CSP and MMF. Serum creatinine (Cr) concentration was monitored to assess renal allograft function.

RESULTS

The renal allografts were acutely rejected in the 2 DLA-identical dogs without TBI or immunosuppression. There was long-term (>1 year) renal allograft survival as evidenced by a normal (<2.0 mg/dL) serum Cr concentration in both the DLA-identical and DLA-haploidentical dogs that underwent 200 cGy TBI and transient immunosuppression with CSP and MMF either with or without simultaneous bone marrow transplantation.

CONCLUSIONS

Nonmyeloablative conditioning (200 cGy TBI) and transient immunosuppression with CSP and MMF induce renal allograft tolerance in DLA-identical and DLA-haploidentical dogs without donor/host mixed hematopoietic chimerism. These findings suggest it may be possible to induce tolerance to solid organ transplants without the need for chronic immunosuppressive therapy or stable hematopoietic chimerism in the setting of both DLA-matched and haploidentical transplants.

CD3-specific antibodies restore self-tolerance: mechanisms and clinical applications

The treatment of autoimmune diseases using conventional chemical immunosuppressants has short-term effects, imposing the need for chronic treatment with its risks of over-immunosuppression. CD3-specific monoclonal antibodies can restore self-tolerance in a durable fashion after a single short-term treatment, as demonstrated in several experimental models and clinically in recent-onset insulin-dependent diabetes. Disease remission involves first an immediate 'freezing' of the autoimmune response, which is linked to CD3-specific antibody-induced antigenic modulation of CD3-TCR complex at the T lymphocyte surface, followed by 'resetting' of TGF-beta-dependent T-cell mediated immunoregulation. Tolerance induction is demonstrated by persisting disease protection in spite of recovery of full immunocompetence to unrelated antigens.

Cyclosporine Preserves the Anergic State of Human T Cells Induced by Costimulation Blockade In Vitro

BACKGROUND

Costimulation blockade based tolerance-inducing therapies might be disrupted by adjunct conventional immunosuppressive drug use. In the current study, we evaluated the compatibility of various immunosuppressive agents on costimulation blockade-based immunosuppression and T-cell anergy induction of human alloreactive T-cells in vitro. T-cell anergy is crucial in transplantation tolerance.

METHODS

T cell anergy was induced in human mixed lymphocyte cultures in vitro, by monoclonal antibodies directed against the costimulatory ligands CD40 and CD86. The effect of coadministration of conventional immunosuppressive drugs (CsA, rapamycin or FK506) on the inhibitory potential of costimulation blockade and the induction and maintenance of T cell anergy was analyzed.

RESULTS

We found that monoclonal antibodies against CD40 and CD86 and the simultaneous use of conventional immunosuppressive drugs resulted in strong immunosuppression of proliferation and cytokine production. Rapamycin, in contrast to FK506 and CsA, facilitated T-cell apoptosis. However, drug cotreatment prevented costimulation blockade induced T-cell anergy. Induction of human T-cell anergy in vitro required approximately 5 days of culture. Coadministration of drugs at day 5 after the start of mAb treatment, when anergy was established, did not increase the immunosuppressive effect of mAb treatment. But interestingly, in the majority of experiments, in contrast to rapamycin and FK506, CsA did not affect the anergic state when given after T-cell anergy induction. Moreover, the cell death facilitating potential of rapamycin vanished when used later after T-cell activation.

CONCLUSIONS

Timing and choice of conventional drug are crucial in the success of costimulation blockade-based tolerance induction therapies.

CD4 expression decrease by antisense oligonucleotides: inhibition of rat T CD4+ cell reactivity

In previous studies, we have demonstrated the inhibition of CD4 expression in rat lymphocytes treated with phorbol myristate acetate (PMA) by antisense oligonucleotides (AS-ODNs) directed against the AUG start region of the cd4 gene. The aim of the present study was to inhibit CD4 expression in lymphocytes without promoting CD4 synthesis and to determine the effect of this inhibition on CD4+ T cell function. Four 21-mer ODNs against the rat cd4 gene (AS-CD4-1 to AS-CD4-4) were used. Surface CD4 expression was measured by immunofluorescence staining and flow cytometry, and mRNA CD4 expression was measured by RT-PCR. T CD4+ cell function was determined by specific and unspecific proliferative response of rat-primed lymphocytes. After 24 hours of incubation, AS-CD4-2 and AS-CD4-4 reduced lymphocyte surface CD4 expression by 40%. This effect remained for 72 hours and was not observed on other surface molecules, such as CD3, CD5, or CD8. CD4 mRNA expression was reduced up to 40% at 24 hours with AS-CD4-2 and AS-CD4-4. After 48 hours treatment, CD4 mRNA decreased up to 27% and 29% for AS-CD4-2 and AS-CD4-4, respectively. AS-CD4-2 and AS-CD4-4 inhibited T CD4+ cell proliferative response upon antigen-specific and unspecific stimuli. Therefore, AS-ODNs against CD4 molecules inhibited surface and mRNA CD4 expression, under physiologic turnover and, consequently, modulate T CD4+ cell reactivity.

IDEC-131 (anti-CD154), sirolimus and donor-specific transfusion facilitate operational tolerance in non-human primates

CD154-specific antibody therapy prevents allograft rejection in many experimental transplant models. However, initial clinical transplant trials with anti-CD154 have been disappointing suggesting the need for as of yet undetermined adjuvant therapy. In rodents, donor antigen (e.g., a donor blood transfusion), or mTOR inhibition (e.g., sirolimus), enhances anti-CD154's efficacy. We performed renal transplants in major histocompatibility complex-(MHC) mismatched rhesus monkeys and treated recipients with combinations of the CD154-specific antibody IDEC-131, and/or sirolimus, and/or a pre-transplant donor-specific transfusion (DST). Therapy was withdrawn after 3 months. Triple therapy prevented rejection during therapy in all animals and led to operational tolerance in three of five animals including donor-specific skin graft acceptance in the two animals tested. IDEC-131, sirolimus and DST are highly effective in preventing renal allograft rejection in primates. This apparently clinically applicable regimen is promising for human renal transplant trials.

T-cell tolerance and autoimmunity to systemic and tissue-restricted self-antigens

We have used transgenic mouse models to examine the mechanisms of tolerance in CD4(+) T lymphocytes to soluble, systemic and cell-associated, tissue-restricted self-antigens. Anergy to an islet antigen, as a model of a tissue antigen, is dependent on the inhibitory receptor cytotoxic T-lymphocyte antigen-4 (CTLA-4), and tissue-restricted autoimmunity is inhibited by regulatory T lymphocytes. Anergy to a circulating systemic antigen can occur independently of CTLA-4 signals, and it is induced primarily by a block in proximal receptor-initiated signals. CD4(+)CD25(+) regulatory T cells are generated in response to both forms of self-antigens, but the induction is much more efficient with the tissue antigen. Receptor desensitization can be induced by the systemic antigen even in the absence of regulatory T cells, but tolerance can be broken by immunization much more easily if these cells are absent. Deletion of mature T cells is striking with the systemic antigen; there is little evidence to support peripheral deletion as a mechanism of tolerance to the tissue antigen. Thus, both distinct and overlapping mechanisms account for unresponsiveness to different forms of self-antigens. These results establish a foundation for searching for genetic influences and pathogenic mechanisms in organ-specific and systemic autoimmune diseases.

Immune properties of recombinant vaccinia virus encoding CD154 (CD40L) are determined by expression of virally encoded CD40L and the presence of CD40L protein in viral particles

Expression of costimulatory molecules by recombinant poxviruses is a promising strategy for enhancing therapeutic vaccines. CD40-CD40L interactions are critical for conditioning dendritic cells (DC) and priming T- and B-cell immunity. We constructed a vaccinia virus expressing murine CD40L (rV-CD40L) and studied its immunomodulatory properties in vitro. Direct DC infection with control vaccinia or psoralen/UV-inactivated rV-CD40L stimulated high levels of interleukin 12 (IL-12) release. However, replication-competent rV-CD40L did not stimulate IL-12 under similar conditions. We observed a high level of CD40L protein on purified viral particles and demonstrated that induction of IL-12 by nonreplicating rV-CD40L was blocked by anti-CD40 antibodies suggesting that functional CD40L on viral particles contributed to alterations in IL-12 synthesis. Since cross-presentation of tumor-associated antigens by DC is augmented by viral infection of tumor cells, we infected MC38 murine colon carcinoma cells with rV-CD40L. Infected cells stimulated IL-12 secretion by DC and proliferation of B cells and DX5(+) (NK/NKT) cells through direct CD40-CD40L interaction. A subpopulation of NKT cells expressing CD40 (NK1.1(+), CD3(lo)) appeared to be a major effector population responding to MC38/rV-CD40L. These results highlight the complex immune regulatory effects of rV-CD40L defined by the cumulative effects of CD40L expression, presence of CD40L protein in viral particles, and the replication potential of the virus.

Development of a Chimeric Anti-CD40 Monoclonal Antibody That Synergizes with LEA29Y to Prolong Islet Allograft Survival

In recent years, reagents have been developed that specifically target signals critical for effective T cell activation and function. Manipulation of the CD28/CD80/86 and CD40/CD154 pathways has exhibited extraordinary efficacy, particularly when the pathways are blocked simultaneously. Despite the reported efficacy of anti-CD154 in rodents and higher models, its future clinical use is uncertain due to reported thromboembolic events in clinical trials. To circumvent this potential complication, we developed and evaluated a chimeric Ab targeting CD40 (Chi220, BMS-224819) as an alternative to CD154. Although Chi220 blocks CD154 binding, it also possesses partial agonist properties and weak stimulatory potential. The anti-CD40 was tested alone and in combination with a rationally designed, high affinity variant of CTLA4-Ig, LEA29Y (belatacept), in a nonhuman primate model of islet transplantation. Although either agent alone only modestly prolonged islet survival (Chi220 alone: 14, 16, and 84 days; LEA29Y alone: 58 and 60 days), their combination (LEA29Y and Chi220) dramatically facilitated long term survival (237, 237, 220, >185, and 172 days). We found that the effects of Chi220 treatment were not mediated solely through deletion of CD20-bearing cells and that the combined therapy did not significantly impair established antiviral immunity.

Role of B7 in T cell tolerance

The induction of effective immune responses requires costimulation by B7 molecules, and Ag recognition without B7 is thought to result in no response or tolerance. We compared T cell responses in vivo to the same Ag presented either by mature dendritic cells (DCs) or as self, in the presence or absence of B7. We show that Ag presentation by mature B7-1/2-deficient DCs fails to elicit an effector T cell response but does not induce tolerance. In contrast, using a newly developed adoptive transfer system, we show that naive OVA-specific DO11 CD4+ T cells become anergic upon encounter with a soluble form of OVA, in the presence or absence of B7. However, tolerance in DO11 cells transferred into soluble OVA transgenic recipients can be broken by immunization with Ag-pulsed DCs only in B7-deficient mice and not in wild-type mice, suggesting a role of B7 in maintaining tolerance in the presence of strong immunogenic signals. Comparing two double-transgenic models--expressing either a soluble or a tissue Ag--we further show that B7 is not only essential for the active induction of regulatory T cells in the thymus, but also for their maintenance in the periphery. Thus, the obligatory role of B7 molecules paradoxically is to promote effective T cell priming and contain effector responses when self-Ags are presented as foreign.

PROLONGED SURVIVAL OF NEONATAL PORCINE ISLET XENOGRAFTS IN MICE TREATED WITH A DONOR-SPECIFIC TRANSFUSION AND ANTI-CD154 ANTIBODY1

BACKGROUND

Combined treatment with a single donor-specific transfusion (DST) and a brief course of anti-mouse CD154 monoclonal antibody (mAb) to induce co-stimulation blockade leads to long-term murine islet allograft survival. The authors hypothesized that this protocol could also induce long-term survival of neonatal porcine islet cell clusters (NPCC) in chemically diabetic immunocompetent mice and allow their differentiation into functional insulin-producing cells.

METHODS

Pancreata from 1- to 3-day-old pigs were collagenase digested and cultured for 8 days. NPCC were recovered and transplanted into the renal subcapsular space. Recipients included chemically diabetic nonobese diabetic (NOD)-scid and C57BL/6 mice that were otherwise untreated, treated with anti-CD154 mAb alone, or treated with DST plus anti-CD154 mAb. Plasma glucose concentration and body weight were measured, and xenografts were examined histologically.

RESULTS

NPCC fully differentiated and restored normoglycemia in four of five diabetic NOD-scid recipients but were uniformly rejected by diabetic C57BL/6 recipients. Anti-CD154 mAb monotherapy restored normoglycemia in 4 of 10 (40%) NPCC-engrafted, chemically diabetic C57BL/6 mice, but combined treatment with DST and anti-CD154 mAb restored normoglycemia in 12 of 13 (92%) recipients. Reversal of diabetes required 5 to 12 weeks. Surviving grafts were essentially free of inflammatory infiltrates 15 weeks after transplantation.

CONCLUSIONS

Combination therapy with a single DST and a brief course of anti-mouse CD154 mAb without maintenance immunosuppression permits survival and differentiation of NPCC in diabetic C57BL/6 mice. Successful grafts were associated with durable restoration of normoglycemia and the absence of graft inflammation.

IL-15 and cognate antigen successfully expand de novo-induced human antigen-specific regulatory CD4+ T cells that require antigen-specific activation for suppression

An important prerequisite in using regulatory T cells for immunotherapy is their ex vivo expansion without loss of suppressor function. Human anergic regulatory T cells are expandable by Ag-specific stimulation in the presence of IL-2. IL-15, like IL-2, is a T cell growth factor that, in contrast to IL-2, stimulates survival of T cells. In this study, we examined whether IL-15 could be exploited as a superior growth factor of human CD4(+) anergic regulatory T cells that were generated by costimulation blockade. Next, IL-15, as compared with IL-2, was investigated with respect to expansion and function of these regulatory T cells. Optimal expansion required cognate allogeneic stimulation in the presence of exogenous IL-15. IL-15 resulted in enhanced survival that was paralleled by an increased number of Bcl-2-expressing cells. Moreover, IL-15 induced a distinct type of anergy characterized by hyperreactivity to IL-15, resulting in improved expansion. This is likely attributed to increased propensity of these cells to up-regulate both alpha- and gamma-chains of the IL-2 and IL-15 receptor. Notably, IL-15-expanded regulatory CD4(+) T cells suppressed both naive and memory T cells in a superior way. Immunosuppression required alloantigen-specific stimulation and appeared gamma-irradiation resistant and independent of IL-10, TGFbeta, or CTLA-4 interactions. These regulatory T cells were stable suppressors, mediating bystander suppression upon TCR stimulation, but leaving recall responses unaffected in the absence of cognate Ag. Finally, human naturally occurring regulatory CD4(+)CD25(+) T cells appeared important in generating regulatory T cells by costimulation blockade. In conclusion, IL-15-expanded, de novo-induced human anergic regulatory CD4(+) T cells are of interest in Ag-specific immunotherapy.

Development of donor-specific chimerism and tolerance in composite tissue allografts under ??-T-cell receptor monoclonal antibody and cyclosporine a treatment protocols

Recently, we induced donor-specific tolerance to rat hindlimb allografts under a 35-day course of alphabeta-T-cell receptor monoclonal antibody (alphabeta-TCR mAb) and cyclosporine A (CsA). In this report, we investigated the role of shorter alphabeta-TCR/CsA protocols on tolerance induction. We performed 52 hindlimb transplantations, between Lewis-Brown-Norway (LBN, F1) donors and Lewis recipients to test the impact of 21-, 7-, and 5-day protocols of combined alphabeta-TCR/CsA treatment on tolerance induction. Donor-specific tolerance and immunocompetence were tested by mixed lymphocyte reaction (MLR) in vitro and by standard skin grafting in vivo. The efficacy of immunosuppressive protocol and donor-specific chimerism was assessed by flow cytometry. All transplants under 5, 7, and 21 days of combined alphabeta-TCR/CsA therapy survived over 350 days. Clinical tolerance and immunocompetence were confirmed by skin grafting in vivo and MLR in vitro. Flow cytometry revealed a high level of donor chimerism in the peripheral blood of long-term survivors. The extension of survival of limb allografts and allo-unresponsiveness were directly associated with the development of stable chimerism in the tolerant recipients.

Donor-specific tolerance in fully major histocompatibility major histocompatibility complexmismatched limb allograft transplants under an anti-αβ T-cell receptor monoclonal antibody and cyclosporine A protocol

BACKGROUND

Recent studies have demonstrated that treatment with alphabeta-T-cell receptor (TCR) monoclonal antibody and cyclosporine A (CsA) can extend survival in composite tissue allografts (CTA). The purpose of this study was to induce tolerance in fully major histocompatibility complex (MHC)-mismatched rat limb allografts under 7 days of a combined alphabeta-TCR-CsA protocol.

METHODS

The authors performed 30 hind-limb allotransplantations across the MHC barrier between Brown Norway donors (BN; RT1n) and Lewis recipients (LEW; RT1l). Isograft and allograft controls received no treatment. The experimental groups received monotherapy of alphabeta-TCR and CsA or a combination of alphabeta-TCR and CsA for 7 days only. Donor-specific tolerance and immunocompetence were determined by standard skin grafting in vivo and mixed lymphocyte reaction (MLR) in vitro. The efficacy of immunosuppressive therapy and the level of donor-specific chimerism were determined by flow cytometry.

RESULTS

Long-term survival (>350 days) was achieved in allograft recipients (n=6) under the 7-day protocol of combined alphabeta-TCR-CsA. Donor-specific tolerance and immunocompetence of long-term chimeras were confirmed by acceptance of skin grafts from the donors and rejection of the third-party alloantigens (AxC Irish). At day 120, MLR demonstrated unresponsiveness to the host and donor antigens but strong reactivity against third-party alloantigens. Flow cytometry confirmed the high efficacy of immunosuppressive treatment and the development of donor-specific chimerism (7.6% of CD4+-RT1n+ cells, 1.3% of CD8+-RT1n+ cells, and 16.5% of CD45RA+-RT1n+ cells) in the periphery of tolerated recipients.

CONCLUSIONS

Combined therapy of alphabeta-TCR-CsA for 7 days resulted in tolerance induction in fully MHC-mismatched rat hind-limb allografts. Tolerance was directly associated with stable, donor-specific chimerism.

Regeneration therapy for diabetes mellitus

Regeneration therapy can be classified into three categories. The first category, in vitro regeneration therapy, makes use of transplanted cultured cells, including embryonic stem (ES) cells, pancreatic precursor cells and beta-cell lines, in conjunction with immunosuppressive therapy or immunoisolation for the treatment of patients with Type 1 diabetes. In the second type of regeneration therapy, ex vivo regeneration therapy, a patient's own cells, such as bone marrow stem cells, are transiently removed and induced to differentiate into beta-cells in vitro. However, at the present time, insulin-producing cells cannot be generated from bone marrow stem cells. In vivo regeneration therapy, the third type of regeneration therapy, enables impaired tissue to regenerate from a patient's own cells in vivo. beta-Cell neogenesis from non-beta-cells, and beta-cell proliferation in vivo have been considered in particular as regeneration therapies for patients with Type 2 diabetes. Regeneration therapy for pancreatic beta-cells can be combined with various other therapeutic strategies, including islet transplantation, cell-based therapy, gene therapy and drug therapy, to promote beta-cell proliferation and neogenesis; it is hoped that these strategies will, in the future, provide a cure for diabetes.

Inhibition of CD4 expression by antisense oligonucleotides in PMA-treated lymphocytes

To decrease CD4 expression on T helper (Th) lymphocyte surface, antisense oligonucleotides (AS-ODNs), delivered by the cationic liposome DOTAP, were assayed in vitro on rat spleen lymphocytes. Four 21-mer ODNs (AS-CD4-1, AS-CD4-2, AS-CD4-3, and AS-CD4-4) directed against the translation start region of the cd4 gene were designed. AS-CD4-1 was phosphorothioate (PS)-modified in each base, and the other three were PS-modified at both ends and in the internal pyrimidine residues. Four ODN controls (fully PS-modified ODN-A and partially modified ODN-B, ODN-C, and ODN-D) were also assayed. CD4 resynthesis was stimulated by treatment with phorbol 12-myristate 13-acetate (PMA) at the same time as the incubations with the ODN. After 24 hours of treatment, CD4 expression was measured by immunofluorescence staining and flow cytometry. CD4 reexpression in rat PMA-treated lymphocytes was counteracted by 40% by means of AS-CD4-2 and AS-CD4-4 treatments. On the other hand, AS-CD4-3 produced only 20% inhibition, similar to that produced by ODN-B, and AS-CD4-1 did not have any significant effect compared with control ODNs. Both AS-CD4-2 and AS-CD4-4 decreased CD4 mRNA, as determined by RT-PCR, and in addition, they did not affect the expression of other surface lymphocyte molecules. Inhibition of surface CD4 expression remained at least 72 hours. The addition of both AS-ODNs did not further increase the effect obtained separately by each AS-ODN. Treatment of rat PMA-lymphocytes with two concentrations of AS-CD4-2 and AS-CD4-4 added 24 hours apart did not further decrease CD4 expression. In summary, AS-CD4-2 and AS-CD4-4 could constitute a good strategy to inhibit CD4 expression on Th lymphocytes and modulate their function.