Regulatory cells and transplantation tolerance

Therapeutic Potential of HLA-I Polyreactive mAbs Mimicking the HLA-I Polyreactivity and Immunoregulatory Functions of IVIg

HLA class-I (HLA-I) polyreactive monoclonal antibodies (mAbs) reacting to all HLA-I alleles were developed by immunizing mice with HLA-E monomeric, α-heavy chain (αHC) open conformers (OCs). Two mAbs (TFL-006 and TFL-007) were bound to the αHC's coated on a solid matrix. The binding was inhibited by the peptide 117AYDGKDY123, present in all alleles of the six HLA-I isoforms but masked by β2-microglobulin (β2-m) in intact HLA-I trimers (closed conformers, CCs). IVIg preparations administered to lower anti-HLA Abs in pre-and post-transplant patients have also shown HLA-I polyreactivity. We hypothesized that the mAbs that mimic IVIg HLA-I polyreactivity might also possess the immunomodulatory capabilities of IVIg. We tested the relative binding affinities of the mAbs and IVIg for both OCs and CCs and compared their effects on (a) the phytohemagglutinin (PHA)-activation T-cells; (b) the production of anti-HLA-II antibody (Ab) by B-memory cells and anti-HLA-I Ab by immortalized B-cells; and (c) the upregulation of CD4+, CD25+, and Fox P3+ T-regs. The mAbs bound only to OC, whereas IVIg bound to both CC and OC. The mAbs suppressed blastogenesis and proliferation of PHA-activated T-cells and anti-HLA Ab production by B-cells and expanded T-regs better than IVIg. We conclude that a humanized version of the TFL-mAbs could be an ideal, therapeutic IVIg-mimetic.

Down-regulation of CCR7 via AKT pathway and GATA2 inactivation suppressed trophoblast migration and invasion in recurrent spontaneous abortion†

The underlying mechanism of the chemokine-C receptor 7 (CCR7) that leads to aberrant trophoblast migration and invasion in recurrent spontaneous abortion (RSA) remains unknown. CCR7 is considered crucial for migration and invasion and has been associated with the risk of miscarriage. However, the functional role of CCR7 in RSA is not fully understood. Our study found that CCR7 mRNA and protein abundance were significantly decreased in the villous from RSA patients compared with healthy controls. Knockdown of CCR7 caused a significant reduction of migration and invasion in JAR and JEG-3 cells. Meanwhile, CCR7 functioned as a positive upstream factor of the AKT pathway contributing to the expression of GATA2, promoting trophoblast migration, and invasion via MMP2. Notably, a decreased abundance of CCR7 was positively correlated with the phosphorylation of AKT and with an abundance of GATA2 and MMP2 in human villous specimens of RSA compared with the control group. CCL19, a ligand of CCR7, could promote trophoblast migration and invasion by activating the deregulation of the CCR7-mediated pathway in RSA. We are convinced that CCR7 and its downstream factors may be possible mechanisms for the pathogenesis of RSA.

Regulatory T cells promote alloengraftment in a model of late-gestation in utero hematopoietic cell transplantation

In utero hematopoietic cell transplantation (IUHCT) has the potential to cure congenital hematologic disorders including sickle cell disease. However, the window of opportunity for IUHCT closes with the acquisition of T-cell immunity, beginning at approximately 14 weeks gestation, posing significant technical challenges and excluding from treatment fetuses evaluated after the first trimester. Here we report that regulatory T cells can promote alloengraftment and preserve allograft tolerance after the acquisition of T-cell immunity in a mouse model of late-gestation IUHCT. We show that allografts enriched with regulatory T cells harvested from either IUHCT-tolerant or naive mice engraft at 20 days post coitum (DPC) with equal frequency to unenriched allografts transplanted at 14 DPC. Long-term, multilineage donor cell chimerism was achieved in the absence of graft-versus-host disease or mortality. Decreased alloreactivity among recipient T cells was observed consistent with donor-specific tolerance. These findings suggest that donor graft enrichment with regulatory T cells could be used to successfully perform IUHCT later in gestation.

Blockade of OX40/OX40L pathway combined with ethylene-carbodiimide-fixed donor splenocytes induces donor-specific allograft tolerance in presensitized recipients

Background

Memory T cells (Tms) are the major barrier preventing long-term allograft survival in presensitized transplant recipients. The OX40/OX40L pathway is important in the induction and maintenance of Tms.

Methods

In this study, we added anti-OX40L mAb to ethylene-carbodiimide-fixed donor splenocytes (ECDI-SPs)-a method which is effective in inducing allograft tolerance in non-presensitized mouse heart transplant model. Recipient mice received heart transplantation after 6 weeks of donor skin presensitization and were treated with anti-OX40L mAb, ECDI-SPs or anti-OX40L mAb + ECDI-SPs, respectively.

Results

Our data showed that the combination of ECDI-SPs and anti-OX40L mAb induced donor-specific tolerance in skin-presensitized heart transplant recipients, with the mechanism for this being associated with suppression of Tms and upregulation of CD4⁺CD25⁺Foxp3⁺ T regulatory cells (Tregs). Importantly, CD25⁺ T-cell depletion in the combined therapy-treated recipients broke the establishment of allograft tolerance, whereas adoptive transfer of presensitization-derived T cells into tolerant recipients suppressed Tregs expansion and abolished established tolerance.

Conclusions

Blockade of OX40/OX40L pathway in combination with ECDI-SPs appears to modulate the Tms/Tregs imbalance so as to create a protective milieu and induce graft tolerance in presensitized recipients.

Signal Transduction Via Co-stimulatory and Co-inhibitory Receptors

T-cell receptor (TCR)-mediated antigen-specific stimulation is essential for initiating T-cell activation. However, signaling through the TCR alone is not sufficient for inducing an effective response. In addition to TCR-mediated signaling, signaling through antigen-independent co-stimulatory or co-inhibitory receptors is critically important not only for the full activation and functional differentiation of T cells but also for the termination and suppression of T-cell responses. Many studies have investigated the signaling pathways underlying the function of each molecular component. Co-stimulatory and co-inhibitory receptors have no kinase activity, but their cytoplasmic region contains unique functional motifs and potential phosphorylation sites. Engagement of co-stimulatory receptors leads to recruitment of specific binding partners, such as adaptor molecules, kinases, and phosphatases, via recognition of a specific motif. Consequently, each co-stimulatory receptor transduces a unique pattern of signaling pathways. This review focuses on our current understanding of the intracellular signaling pathways provided by co-stimulatory and co-inhibitory molecules, including B7:CD28 family members, immunoglobulin, and members of the tumor necrosis factor receptor superfamily.

Ratio of CD147high/CD147low in CD4+CD25+ T cells: A potential biomarker for early diagnosis and prediction of response to therapy for autoimmune diseases

Regulatory T cell (Treg cell) is an important immunosuppressive T cell subset and plays a dominant role in maintaining the immune balance in vivo. The function defects in Treg cells have been involved in the pathogenesis of many autoimmune diseases. The detection of Treg cell suppressive function is important for early diagnosis and prediction of response to treatment for autoimmune diseases. The traditional detection of Treg cell suppressive function needs at least 20 mL peripheral blood sample of patients and the results would be got in sixth day, therefore, it could not be widely applied in clinical. However, to find fast and simple detection method is very important. CD147 is a transmembrane protein and its expression is related to Treg cell suppressive function. Recent research has shown that the Treg cells with high CD147 expression have stronger suppressive function than which with low CD147 expression. In this work, we detected the ratio of CD147^high/CD147^low in CD4⁺CD25⁺ T cells in patients with active AS using fluorescence-activated cell sorter (FACS). The results show the ratio of CD147^high/CD147^low decreased obviously in patients with active AS compared with healthy controls, which reflects the suppressive function deficit of Treg cell. In the same time, the detection of the ratio of CD147^high/CD147^low needs only 150 μL peripheral blood sample and the result would be got in 4 h. We therefore hypothesize that the ratio of CD147^high/CD147^low is a good indicator for the Treg cell function, and it is especially suitable for early diagnosis and prediction of response to therapy targeted recovering Treg cell function in autoimmune diseases.

An investigation of the relationship between recurrent spontaneous abortion and memory T follicular helper cells

PROBLEM

Immune tolerance with respect to a semi-allogeneic fetus plays a key role in the establishment of a pregnancy. Memory T follicular helper (Tfh) cells have a central role in the regulation of the adaptive immune response. Much of our knowledge of memory Tfh cells' function comes from immune-related diseases. However, the true physiological characteristics of memory Tfh cells and their mode of action in pregnancy remain unclear.

METHODS OF STUDY

Deciduas and blood were obtained from 25 recurrent spontaneous abortion (RSA) patients undergoing surgical abortion and 19 normal women in early pregnancy undergoing elective termination. RSA patients were grouped into antibody-positive patients and antibody-negative patients, respectively. The memory Tfh cells with the CD4⁺ CXCR5⁺ PD1⁺ CCR7^- and CD4⁺ CXCR5⁺ PD-1⁺ ICOS⁺ phenotypes were assessed by flow cytometry. The B cells were evaluated by flow cytometry. A correlation analysis of the subsets of memory Tfh cells and B cells in antibody-positive RSA patients was made by the Pearson test.

RESULTS

Memory Tfh cells with the CD4⁺ CXCR5⁺ PD1⁺ CCR7^- and CD4⁺ CXCR5⁺ PD-1⁺ ICOS⁺ phenotypes showed a significant increase in RSA patients compared to women with a normal pregnancy who had chosen termination. When RSA patients were grouped according positive or negative antibodies, it was surprising to find that decidual CD4⁺ CXCR5⁺ PD-1⁺ ICOS⁺ memory Tfh cells significantly increased in RSA patients with positive antibody compared to RSA patients with negative antibody. However, the percentages of CD4⁺ CXCR5⁺ PD1⁺ CCR7^- memory Tfh cells did not change in the deciduas of the two groups. Circulating and decidual B cells significantly increased in antibody-positive RSA patients compared with antibody-negative RSA patients. Correlation analysis indicated a strong association between the decidual CD4⁺ CXCR5⁺ PD-1⁺ ICOS⁺ memory Tfh cells and B cells in antibody-positive RSA patients.

CONCLUSION

These new findings provide unique insights into memory Tfh cells in mediating feto-maternal immune tolerance.

Splenocyte Infusion and Whole-Body Irradiation for Induction of Peripheral Tolerance in Porcine Lung Transplantation: Modifications of the Preconditioning Regime for Improved Clinical Feasibility

BACKGROUND

Preoperative low-dose whole-body irradiation (IRR) with 1.5 and 7 Gy thymic IRR of the recipient, combined with a perioperative donor splenocyte infusion lead to reliable donor specific peripheral tolerance in our allogeneic porcine lung transplantation model. To reduce the toxicity of this preconditioning regime, modifications of the IRR protocol and their impact on allograft survival were assessed.

METHODS

Left-sided single lung transplantation from major histocompatibility complex and sex mismatched donors was performed in 14 adult female minipigs. Recipient animals were exposed to 3 different protocols of nonmyeloablative IRR within 12 hours before transplantation. All animals were administered a donor splenocyte infusion on the day of lung transplantation. Intravenous pharmacologic immunosuppression was withdrawn after 28 postoperative days. Allograft survival was monitored by chest radiographs and bronchoscopy.

RESULTS

IRR prolonged transplant survival in a dose- and field-dependent manner. Shielding of the bone marrow from IRR (total lymphoid IRR at 1.5 and 7 Gy thymic IRR) significantly reduced protocol toxicity defined as thrombocytopenia and consecutive increased bleeding propensity, but had a less effective impact on graft survival. Whole-body IRR at 0.5 and 7 Gy thymic IRR proved to be ineffective for reliable tolerance induction. Eventually, high levels of circulating CD4⁺CD25^high regulatory T cells were present in long-term survivors.

CONCLUSIONS

These data show that the infusion of donor-specific alloantigen in combination with IRR is efficient once a threshold dose is exceeded.

HLA Class Ia and Ib Polyreactive Anti-HLA-E IgG2a Monoclonal Antibodies (TFL-006 and TFL-007) Suppress Anti-HLA IgG Production by CD19+ B Cells and Proliferation of CD4+ T Cells While Upregulating Tregs

The anti-HLA-E IgG2a mAbs, TFL-006 and TFL-007, reacted with all HLA-I antigens, similar to the therapeutic preparations of IVIg. Indeed, IVIg lost its HLA reactivity, when its HLA-E reactivity was adsorbed out. US-FDA approved IVIg to reduce antibodies in autoimmune diseases. But the mechanism underlying IVIg-mediated antibody reduction could not be ascertained due to the presence of other polyclonal antibodies. In spite of it, the cost prohibitive high or low IVIg is administered to patients waiting for donor organ and for allograft recipients for lowering antiallograft antibodies. A mAb that could mimic IVIg in lowering Abs, with defined mechanism of action, would be highly beneficial for patients. Demonstrably, the anti-HLA-E mAbs mimicked several functions of IVIg relevant to suppressing the antiallograft Abs. The mAbs suppressed activated T cells and anti-HLA antibody production by activated B cells, which were dose-wise superior to IVIg. The anti-HLA-E mAb expanded CD4+, CD25+, and Foxp3+ Tregs, which are known to suppress T and B cells involved in antibody production. These defined functions of the anti-HLA-E IgG2a mAbs at a level superior to IVIg encourage developing their humanized version to lower antibodies in allograft recipients, to promote graft survival, and to control autoimmune diseases.

The Induction and Maintenance of Transplant Tolerance Engages Both Regulatory and Anergic CD4+ T cells

Therapeutic tolerance to self-antigens or foreign antigens is thought to depend on constant vigilance by Foxp3⁺ regulatory T cells (Tregs). Previous work using a pancreatic islet allograft model and a short pulse of CD3 antibody therapy has shown that CD8⁺ T cells become anergic and use TGFβ and coinhibitory signaling as their contribution to the tolerance process. Here, we examine the role of CD4⁺ T cells in tolerization by CD3 antibodies. We show that both Foxp3⁺ Tregs and CD4⁺ T cell anergy play a role in the induction of tolerance and its maintenance. Foxp3⁺ Tregs resisted CD3 antibody-mediated depletion, unlike intragraft Th1 CD4⁺ lymphocytes coexpressing granzyme B and Tbx21, which were selectively eliminated. Tregs were mandatory for induction of tolerance as their depletion at the time of CD3 antibody therapy or for a short time thereafter, by an antibody to CD25 (PC61), led to graft rejection. Early treatment with CTLA-4 antibody gave the same outcome. In contrast, neither PC61 nor anti-CTLA-4 given late, at day 100 posttransplant, reversed tolerance once established. Ablation of Foxp3 T cells after diphtheria toxin injection in tolerant Foxp3^DTR recipient mice provided the same outcome. Alloreactive T cells had been rendered intrinsically unresponsive as total CD4⁺ or Treg-deprived CD4⁺ T cells from tolerant recipients were unable to mount donor-specific IFN-γ responses. In addition, intragraft Treg-deprived CD4⁺ T cells lacked proliferative capacities, expressed high levels of the inhibitory receptor PD-1, and exhibited a CD73^hiFR4^hi phenotype, thus reflecting a state of T cell anergy. We conclude that Tregs play a substantive and critical role in guiding the immune system toward tolerance of the allograft, when induced by CD3 antibody, but are less important for maintenance of the tolerant state, where T cell anergy appears sufficient.

A Novel Model on DST-Induced Transplantation Tolerance by the Transfer of Self-Specific Donor tTregs to a Haplotype-Matched Organ Recipient

Donor-specific blood transfusion (DST) can lead to significant prolongation of allograft survival in experimental animal models and sometimes human recipients of solid organs. The mechanisms responsible for the beneficial effect on graft survival have been a topic of research and debate for decades and are not yet fully elucidated. Once we discover how the details of the mechanisms involved are linked, we could be within reach of a procedure making it possible to establish donor-specific tolerance with minimal or no immunosuppressive medication. Today, it is well established that CD4+Foxp3+ regulatory T cells (Tregs) are indispensable for maintaining immunological self-tolerance. A large number of animal studies have also shown that Tregs are essential for establishing and maintaining transplantation tolerance. In this paper, we present a hypothesis of one H2-haplotype-matched DST-induced transplantation tolerance (in mice). The formulated hypothesis is based on a re-interpretation of data from an immunogenetic experiment published by Niimi and colleagues in 2000. It is of importance that the naïve recipient mice in this study were never immunosuppressed and were therefore fully immune competent during the course of tolerance induction. Based on the immunological status of the recipients, we suggest that one H2-haplotype-matched self-specific Tregs derived from the transfusion blood can be activated and multiply in the host by binding to antigen-presenting cells presenting allopeptides in their major histocompatibility complex (MHC) class II (MHC-II). We also suggest that the endothelial and epithelial cells within the solid organ allograft upregulate the expression of MHC-II and attract the expanded Treg population to suppress inflammation within the graft. We further suggest that this biological process, here termed MHC-II recruitment, is a vital survival mechanism for organs (or the organism in general) when attacked by an immune system.

Barcelona Consensus on Biomarker-Based Immunosuppressive Drugs Management in Solid Organ Transplantation

With current treatment regimens, a relatively high proportion of transplant recipients experience underimmunosuppression or overimmunosuppression. Recently, several promising biomarkers have been identified for determining patient alloreactivity, which help in assessing the risk of rejection and personal response to the drug; others correlate with graft dysfunction and clinical outcome, offering a realistic opportunity for personalized immunosuppression. This consensus document aims to help tailor immunosuppression to the needs of the individual patient. It examines current knowledge on biomarkers associated with patient risk stratification and immunosuppression requirements that have been generally accepted as promising. It is based on a comprehensive review of the literature and the expert opinion of the Biomarker Working Group of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology. The quality of evidence was systematically weighted, and the strength of recommendations was rated according to the GRADE system. Three types of biomarkers are discussed: (1) those associated with the risk of rejection (alloreactivity/tolerance), (2) those reflecting individual response to immunosuppressants, and (3) those associated with graft dysfunction. Analytical aspects of biomarker measurement and novel pharmacokinetic-pharmacodynamic models accessible to the transplant community are also addressed. Conventional pharmacokinetic biomarkers may be used in combination with those discussed in this article to achieve better outcomes and improve long-term graft survival. Our group of experts has made recommendations for the most appropriate analysis of a proposed panel of preliminary biomarkers, most of which are currently under clinical evaluation in ongoing multicentre clinical trials. A section of Next Steps was also included, in which the Expert Committee is committed to sharing this knowledge with the Transplant Community in the form of triennial updates.

Impact of Immune-Modulatory Drugs on Regulatory T Cell

Immunosuppression strategies that selectively inhibit effector T cells while preserving and even enhancing CD4FOXP3 regulatory T cells (Treg) permit immune self-regulation and may allow minimization of immunosuppression and associated toxicities. Many immunosuppressive drugs were developed before the identity and function of Treg were appreciated. A good understanding of the interactions between Treg and immunosuppressive agents will be valuable to the effective design of more tolerable immunosuppression regimens. This review will discuss preclinical and clinical evidence regarding the influence of current and emerging immunosuppressive drugs on Treg homeostasis, stability, and function as a guideline for the selection and development of Treg-friendly immunosuppressive regimens.

Novel technologies to engineer graft for tolerance induction

PURPOSE OF REVIEW

Conquering allograft rejection remains an elusive goal in spite of recent breakthroughs in the field of immunosuppression. Much of the problem lies in the toxicity and side-effects of long-term use of systemic immunosuppressant drugs, which are sometimes ineffective in controlling rejection, but also hinder establishment of transplant tolerance. In this review, we discuss novel technologies that use grafts engineered with immunomodulatory molecules as a means of inducing tolerance.

RECENT FINDINGS

Several recent studies have demonstrated the feasibility of engineering cells, tissues, or solid organ grafts with immunoregulatory biologics to achieve long termgraft survival without the use of chronic immunosuppression. This approach was shown to primarily change the ratio of T effector versus CD4+CD25+FoxP3+ T regulatory cells within the graft microenvironment in favor of attaining localized tolerance induction and maintenance.

SUMMARY

Localized immunomodulation using biologic-engineered allografts represent a new paradigm for achieving long-term graft survival in the absence of chronic use of immunosuppression. The manipulation of the graft, rather than the recipient, not only ensures short- and long-term safety by minimizing the adverse effects of immunosuppression, but also allows retention of immune competency critical for the ability of the recipient to fight infections and cancer.

Ubiquitous LEA29Y Expression Blocks T Cell Co-Stimulation but Permits Sexual Reproduction in Genetically Modified Pigs

We have successfully established and characterized a genetically modified pig line with ubiquitous expression of LEA29Y, a human CTLA4-Ig derivate. LEA29Y binds human B7.1/CD80 and B7.2/CD86 with high affinity and is thus a potent inhibitor of T cell co-stimulation via this pathway. We have characterized the expression pattern and the biological function of the transgene as well as its impact on the porcine immune system and have evaluated the potential of these transgenic pigs to propagate via assisted breeding methods. The analysis of LEA29Y expression in serum and multiple organs of CAG-LEA transgenic pigs revealed that these animals produce a biologically active transgenic product at a considerable level. They present with an immune system affected by transgene expression, but can be maintained until sexual maturity and propagated by assisted reproduction techniques. Based on previous experience with pancreatic islets expressing LEA29Y, tissues from CAG-LEA29Y transgenic pigs should be protected against rejection by human T cells. Furthermore, their immune-compromised phenotype makes CAG-LEA29Y transgenic pigs an interesting large animal model for testing human cell therapies and will provide an important tool for further clarifying the LEA29Y mode of action.

Generation of Tolerogenic Dendritic Cells and Their Therapeutic Applications

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that bridge innate and adaptive immune responses, thereby leading to immune activation. DCs have been known to recognize pathogen-associated molecular patterns such as lipopolysaccharides (LPS) and nucleic acids via their pattern recognition receptors, which trigger signaling of their maturation and effector functions. Furthermore, DCs take up and process antigens as a form of peptide loaded on the major histocompatibility complex (MHC) and present them to T cells, which are responsible for the adaptive immune response. Conversely, DCs can also play a role in inducing immune suppression under specific circumstances. From this perspective, the role of DCs is related to tolerance rather than immunity. Immunologists refer to these special DCs as tolerogenic DCs (tolDCs). However, the definition of tolDCs is controversial, and there is limited information on their development and characteristics. In this review, we discuss the current concept of tolDCs, cutting-edge methods for generating tolDCs in vitro, and future applications of tolDCs, including clinical use.

Regulatory T Cells in Autoimmune Diabetes: Mechanisms of Action and Translational Potential

Since the discovery of specialized T cells with regulatory function, harnessing the power of these cells to ameliorate autoimmunity has been a major goal. Here we collate the evidence that regulatory T cells (Treg) can inhibit Type 1 diabetes in animal models and humans. We discuss the anatomical sites and molecular mechanisms of Treg suppressive function in the Type 1 diabetes setting, citing evidence that Treg can function in both the pancreatic lymph nodes and within the pancreatic lesion. Involvement of the CTLA-4 pathway, as well as TGF-β and IL-2 deprivation will be considered. Finally, we summarize current efforts to manipulate Treg therapeutically in individuals with Type 1 diabetes. The translation of this research area from bench to bedside is still in its infancy, but the remarkable therapeutic potential of successfully manipulating Treg populations is clear to see.

Hyperlipidemia Alters Regulatory T Cell Function and Promotes Resistance to Tolerance Induction Through Costimulatory Molecule Blockade

Recent work from our laboratory has shown that hyperlipidemia promotes accelerated rejection of vascularized cardiac allografts in mice by inducing anti-donor Th17 reactivity and production of IL-17. Here, we show that hyperlipidemia also affects FoxP3(+) regulatory T cells (Tregs). Hyperlipidemia promotes the development of Tregs that express low levels of CD25. Hyperlipidemia also promotes a decrease in central Tregs and an increase in effector Tregs that appears to account for the increase in the frequency of CD25(low) Tregs. Alterations in Treg subsets also appear to lead to alterations in Treg function. The ability of FoxP3(+) , CD25(high) , CD4(+) Tregs from hyperlipidemic mice to inhibit proliferation of effector T cells stimulated with anti-CD3 and CD28 was reduced when compared with Tregs from control mice. Regulatory T cells isolated from hyperlipidemic recipients exhibit increased activation of Akt, and a reduction in Bim levels that permits the expansion of FoxP3(+) CD25(low) CD4(+) T cells. Hyperlipidemic mice were also resistant to tolerance induction using costimulatory molecule blockade consisting of anti-CD154 and CTLA4Ig, a strategy that requires Tregs. Together, our data suggest that hyperlipidemia profoundly affects Treg subsets and function as well as the ability to induce tolerance.

Regulatory T Cells: Serious Contenders in the Promise for Immunological Tolerance in Transplantation

Regulatory T cells (Tregs) play an important role in immunoregulation and have been shown in animal models to promote transplantation tolerance and curb autoimmunity following their adoptive transfer. The safety and potential therapeutic efficacy of these cells has already been reported in Phase I trials of bone-marrow transplantation and type I diabetes, the success of which has motivated the broadened application of these cells in solid-organ transplantation. Despite major advances in the clinical translation of these cells, there are still key questions to be addressed to ensure that Tregs attest their reputation as ideal candidates for tolerance induction. In this review, we will discuss the unique traits of Tregs that have attracted such fame in the arena of tolerance induction. We will outline the protocols used for their ex vivo expansion and discuss the future directions of Treg cell therapy. In this regard, we will review the concept of Treg heterogeneity, the desire to isolate and expand a functionally superior Treg population and report on the effect of differing culture conditions. The relevance of Treg migratory capacity will also be discussed together with methods of in vivo visualization of the infused cells. Moreover, we will highlight key advances in the identification and expansion of antigen-specific Tregs and discuss their significance for cell therapy application. We will also summarize the clinical parameters that are of importance, alongside cell manufacture, from the choice of immunosuppression regimens to the number of injections in order to direct the success of future efficacy trials of Treg cell therapy. Years of research in the field of tolerance have seen an accumulation of knowledge and expertise in the field of Treg biology. This perpetual progression has been the driving force behind the many successes to date and has put us now within touching distance of our ultimate success, immunological tolerance.

Deltex1 antagonizes HIF-1α and sustains the stability of regulatory T cells in vivo

Application of regulatory T cells (Tregs) in transplantation, autoimmunity and allergy has been extensively explored, but how Foxp3 and Treg stability is regulated in vivo is incompletely understood. Here, we identify a requirement for Deltex1 (DTX1), a contributor to T-cell anergy and Foxp3 protein level maintenance in vivo. Dtx1(-/-) Tregs are as effective as WT Tregs in the inhibition of CD4(+)CD25(-) T-cell activation in vitro. However, the suppressive ability of Dtx1(-/-) Tregs is greatly impaired in vivo. We find that Foxp3 expression is diminished when Dtx1(-/-) Tregs are co-transferred with effector T cells in vivo. DTX1 promotes the degradation of HIF-1α. Knockout of HIF-1α restores the Foxp3 stability and rescues the defective suppressive activity in Dtx1(-/-) Treg cells in vivo. Our results suggest that DTX1 exerts another level of control on Treg stability in vivo by sustaining the expression of Foxp3 protein in Tregs.

Anti-OX40L monoclonal antibody prolongs secondary heart allograft survival based on CD40/CD40L and LFA-1/ICAM-1 blockade

BACKGROUND

Memory T cells (Tms) form a barrier against long-term allograft survival; however, CD4(+)Foxp3(+) regulatory T cells (Tregs) can suppress allograft rejection. The OX40/OX40L pathway is critical to the generation of Tms and turns off Treg suppressor function.

METHODS

B6 mice that rejected BALB/c skin grafts after 4 weeks were used as the secondary heart transplant recipients. The skin recipient mice, termed S0, S2 and S3, were treated with the isotype antibodies, anti-CD40L/LFA-1 or anti-OX40L combined with anti-CD40L/LFA-1 mAbs, respectively. The secondary heart recipients, termed H0 and H2, received anti-CD40L/LFA-1 mAbs or not, respectively (Fig. 1).

RESULTS

Four weeks after primary skin transplantation, the Tms in the S3 group that received anti-OX40L with anti-CD40L/LFA-1 mAbs were reduced compared to those in the S2 group (CD4(+) Tm: 32.61 ± 2.20% in S2 vs. 25.36 ± 1.16% in S3; CD8(+) Tm: 27.76 ± 1.96% in S2 vs. 20.95 ± 1.30% in S3; P < 0.01). Meanwhile, the proportions of Tregs in S3 increased compared to those in S2 (P < 0.05). The anti-OX40L with anti-CD40L/LFA-1 mAbs group (S3H2) prolonged the mean survival time (MST) following secondary heart transplantation from 9.5 days to 21 days (P < 0.001). Furthermore, allogeneic proliferation of recipient splenic T cells and graft-infiltrating lymphocytes were significantly inhibited in the S3H2 group. Additionally, a higher level of IL-10 was detected in sera and allografts.

CONCLUSIONS

Anti-OX40L mAb could prolong secondary heart allograft survival based on CD40/CD40L and LFA-1/ICAM-1 blockade. The mechanism of protecting allografts using anti-OX40L mAb involved impairing the generation of Tm and up-regulating IL-10 producing Tregs, inhibiting the function of T cells.

Transplantation tolerance: from theory to clinic

Tolerance induction and alloreactivity can be applied to the clinic for the transplantation of solid organs and in the treatment of human cancers respectively. Hematopoietic chimerism, the stable coexistence of host and donor blood cells, guarantees that a solid organ from the same donor will be tolerated without a requirement for maintenance immunosuppression, and it also serves as a platform for the adoptive immunotherapy of hematologic malignancies using donor lymphocyte infusions. This review focuses on clinically relevant methods for inducing hematopoietic chimerism and transplantation tolerance, with a special emphasis on reduced intensity transplantation conditioning and high dose, post-transplantation cyclophosphamide to prevent graft rejection and graft-versus-host disease (GVHD). Reduced intensity transplantation regimens permit a transient cooperation between donor and host immune systems to eradicate malignancy without producing GVHD. Their favorable toxicity profile also enables the application of allogeneic stem cell transplantation to treat non-malignant disorders of hematopoiesis and to induce tolerance for solid organ transplantation.

Tolerance--is it worth it?

We are entering an exciting time in the study of immunologic tolerance. Several cellular and molecular strategies have been developed that show promise in nonhuman transplant models and these approaches are just now appearing in clinical trials. Tolerance strategies that prevent immune rejection and obviate the need for immunosuppressive medications (with inherent risk of cancer, infection, and organ toxicity) would improve both graft and patient survival. Each tolerance protocol brings its own set of associated risks. As the results of these trials become available, we must continue to evaluate their successes and failures. The balance of these outcomes will help us answer the question: "Tolerance-Is it worth it?"

A transendocytosis perspective on the CD28/CTLA-4 pathway

T cell activation is a key event in the adaptive immune response and vital to the generation of both cellular and humoral immunity. Activation is required not only for effective CD4 T cell responses but also to provide help for B cells and the generation of cytotoxic T cell responses. Unsurprisingly, impaired T cell activation results in infectious pathology, whereas dysregulated activation can result in autoimmunity. The decision to activate is therefore tightly regulated and the CD28/CTLA-4 pathway represents this apical decision point at the molecular level. In particular, CTLA-4 (CD152) is an essential checkpoint control for autoimmunity; however, the molecular mechanism(s) by which CTLA-4 achieves its regulatory function are not well understood, especially how it functionally intersects with the CD28 pathway. In this chapter, we review the established molecular and cellular concepts relating to CD28 and CTLA-4 biology, and attempt to integrate these by discussing the transendocytosis of ligands as a new model of CTLA-4 function.