CD25+CD4+ Regulatory T Cells Develop in Mice Not Only During Spontaneous Acceptance of Liver Allografts but Also After Acute Allograft Rejection

Transplant Tolerance, Not Only Clonal Deletion

The quest to understand how allogeneic transplanted tissue is not rejected and how tolerance is induced led to fundamental concepts in immunology. First, we review the research that led to the Clonal Deletion theory in the late 1950s that has since dominated the field of immunology and transplantation. At that time many basic mechanisms of immune response were unknown, including the role of lymphocytes and T cells in rejection. These original observations are reassessed by considering T regulatory cells that are produced by thymus of neonates to prevent autoimmunity. Second, we review "operational tolerance" induced in adult rodents and larger animals such as pigs. This can occur spontaneously especially with liver allografts, but also can develop after short courses of a variety of rejection inhibiting therapies. Over time these animals develop alloantigen specific tolerance to the graft but retain the capacity to reject third-party grafts. These animals have a "split tolerance" as peripheral lymphocytes from these animals respond to donor alloantigen in graft versus host assays and in mixed lymphocyte cultures, indicating there is no clonal deletion. Investigation of this phenomenon excludes many mechanisms, including anti-donor antibody blocking rejection as well as anti-idiotypic responses mediated by antibody or T cells. This split tolerance is transferred to a second immune-depleted host by T cells that retain the capacity to effect rejection of third-party grafts by the same host. Third, we review research on alloantigen specific inhibitory T cells that led to the first identification of the CD4+CD25+T regulatory cell. The key role of T cell derived cytokines, other than IL-2, in promoting survival and expansion of antigen specific T regulatory cells that mediate transplant tolerance is reviewed. The precise methods for inducing and diagnosing operational tolerance remain to be defined, but antigen specific T regulatory cells are key mediators.

Regulatory T Cell Therapy Following Liver Transplantation

Liver transplantation (LT) is considered the gold standard of curative treatment for patients with end-stage liver disease or nonresectable hepatic malignant tumors. Rejection after LT is the main nontechnical factor affecting the prognosis of recipients. Medical and surgical advances, combined with improved immunosuppression with drugs such as calcineurin inhibitors (CNIs), have contributed to an increase in 1-year graft survival to around 80%. However, medium- and long-term improvements in LT outcomes have lagged behind. Importantly, CNIs and other classical immunosuppressive drugs are associated with significant adverse effects, including malignancies, cardiovascular disease, and severe renal dysfunction. Immunomodulation using regulatory T cells (Tregs) is emerging as a promising alternative to classical immunosuppression. Since their discovery, the immunomodulatory effects of Tregs have been demonstrated in a range of diseases. This has rejuvenated the interest in using Tregs as a therapeutic strategy to induce immune tolerance after LT. In this review, we first summarize the discovery and development of Tregs. We then review the preclinical data supporting their production, mechanism of action, and therapeutic efficacy followed by a summary of relevant clinical trials. Finally, we discuss the outstanding challenges of Treg therapy and its future prospects for routine use in LT.

Role of regulatory T cells in CD47/donor-specific transfusion-induced immune tolerance in skin-heart transplantation mice

OBJECTIVES

To explore the role of regulatory T (T_reg ) cells in the establishment of immune tolerance induced by donor-specific transfusion (DST) in mice with skin-heart transplantation.

METHODS

C57BL/6 mice received DST of splenocytes from CD47^+/+ or CD47^-/- H-2^bm1 mice or no DST 7 days before skin-heart transplantation from major histocompatibility complex class I-mismatched H-2^bm1 donors. The number and proportion of T_reg cells in graft and lymphoid organs were measured by flow cytometry (FACS) and immunohistochemistry (IHC). The inhibitory function of T_reg cells and anti-donor T-cell responses were assessed by mixed lymphocyte reaction.

RESULTS

We observed that mean survival time (MST) of skin or heart graft was significantly longer in C57BL/6 mice which received DST from CD47^+/+ H-2^bm1 mice than from CD47^-/- H-2^bm1 mice. By FACS, we found that the number of T_reg cells in spleen was increased significantly in mice which received CD47^-/- DST compared to mice which received CD47^+/+ DST. However, the percentages of T_reg cells in total splenocytes and lymph node cells were significantly higher in mice that received CD47^+/+ DST than mice which received CD47^-/- DST. Immunohistochemistry showed an increased heart grafts infiltration of T_reg cells in the recipients with CD47^-/- DST, but not CD47^+/+ DST. Supporting this, we found that donor T-cell proliferation was significantly suppressed in mice which received CD47^+/+ DST compared to mice which received CD47^-/- DST. There was no difference of inhibitory function of T_reg cells between these two groups.

CONCLUSION

Our results indicated that CD47 expression on DST cells plays an important role in the induction of immune tolerance in mice with skin-heart transplantation. Increased percentage of T_reg cells may contribute to immune tolerance induced by CD47^+/+ DST.

Inducción de tolerancia inmunológica: alotrasplantes compuestos vascularizados y trasplantes de órgano sólido

Introducción. La inducción de tolerancia inmunológica solucionaría los problemas asociados con la inmunosupresión de por vida, necesaria para evitar el rechazo de aloinjertos.Objetivos. Revisar aspectos inmunológicos, modelos clínicos utilizados y resultados obtenidos en la tolerancia y comparar los resultados obtenidos con trasplante de órgano sólido y alotrasplante compuesto vascularizado.Materiales y métodos. Se realizó una búsqueda en la base de datos PubMed que arrojó 299 resultados; se revisaron las bibliografías de los artículos y se consultaron las referencias pertinentes. Al final se seleccionaron 83 artículos.Resultados. Existen mecanismos centrales y periféricos para mantener la tolerancia a antígenos propios; en la práctica clínica, la tolerancia central ha sido más utilizada, esto se ha hecho mediante estrategias que utilizan trasplante conjunto de medula ósea. Varios ensayos clínicos, la mayoría en pacientes con trasplante renal, han mostrado resultados prometedores pero inconsistentes.Conclusiones. En trasplantes renales fue posible suspender de forma exitosa la inmunosupresión, mientras que en trasplantes de mano se logró disminuirla considerablemente. El quimerismo inmunológico parece ser indispensable para el desarrollo de tolerancia a aloinjertos, por lo que es necesario desarrollar protocolos para inducir quimerismo mixto persistente.

Significant association between FOXP3 gene polymorphism and steroid-resistant acute rejection in living donor liver transplantation

Previous studies have found that preferential accumulation of regulatory T (Treg) cells in liver allografts during acute cellular rejection (ACR) is associated with less severe rejection, suggesting a role of Treg cells in preventing excessive progress of ACR. We investigated the impact of single nucleotide polymorphisms (SNPs) in the Forkhead box P3 (FOXP3) gene, a master regulator gene of Treg cells, on ACR severity in liver transplant (LT) recipients. In total, 102 living donor LT patients were enrolled in this study and categorized into no rejection (n = 86), steroid-sensitive acute rejection (SSAR; n = 11), and steroid-resistant acute rejection (SRAR; n = 5). FOXP3 SNPs -3499 A/G (rs3761547), -3279 A/C (rs3761548), and -924 A/G (rs2232365) were genotyped using the polymerase chain reaction restriction fragment length polymorphism technique. T-cell responses to allostimulation were evaluated by the mixed lymphocyte reaction assay. We found no statistical association between the FOXP3 SNP genotype frequencies and ACR incidence. However, significantly higher incidence of SRAR was observed in LT patients with the FOXP3 rs3761548 A/C+A/A genotype than in those with the C/C genotype (A/C+A/A versus C/C; no rejection, SSAR, SRAR, 85.71%, 0%, 14.29% versus 83.58%, 16.42%, 0%, respectively; P =  0.0005). The mixed lymphocyte reaction assay performed at the time of ACR diagnosis showed higher anti-donor CD4+ T-cell responses in patients carrying rs3761548 A/C+A/A than in those with the C/C genotype (P =  0.019). No significant association was observed between the incidence of SRAR and either rs3761547A/G or rs2232365 A/G. Infectious complications and overall survival were not related to FOXP3 SNPs. Conclusion: Our findings indicate that FOXP3 SNP rs3761548 A/C might be a predisposing factor for SRAR after liver transplantation. (Hepatology Communications 2017;1:406-420).

From immunosuppression to tolerance

The past three decades have seen liver transplantation becoming a major therapeutic approach in the management of end-stage liver diseases. This is due to the dramatic improvement in survival after liver transplantation as a consequence of the improvement of surgical and anaesthetic techniques, of post-transplant medico-surgical management and of prevention of disease recurrence and other post-transplant complications. Improved use of post-transplant immunosuppression to prevent acute and chronic rejection is a major factor in these improved results. The liver has been shown to be more tolerogenic than other organs, and matching of donor and recipients is mainly limited to ABO blood group compatibility. However, long-term immunosuppression is required to avoid severe acute and chronic rejection and graft loss. With the current immunosuppression protocols, the risk of acute rejection requiring additional therapy is 10-40% and the risk of chronic rejection is below 5%. However, the development of histological lesions in the graft in long-term survivors suggest atypical forms of graft rejection may develop as a consequence of under-immunosuppression. The backbone of immunosuppression remains calcineurin inhibitors (CNI) mostly in association with steroids in the short-term and mycophenolate mofetil or mTOR inhibitors (everolimus). The occurrence of post-transplant complications related to the immunosuppressive therapy has led to the development of new protocols aimed at protecting renal function and preventing the development of de novo cancer and of dysmetabolic syndrome. However, there is no new class of immunosuppressive drugs in the pipeline able to replace current protocols in the near future. The aim of a full immune tolerance of the graft is rarely achieved since only 20% of selected patients can be weaned successfully off immunosuppression. In the future, immunosuppression will probably be more case oriented aiming to protect the graft from rejection and at reducing the risk of disease recurrence and complications related to immunosuppressive therapy. Such approaches will include strategies aiming to promote stable long-term immunological tolerance of the liver graft.

MiR-152 may silence translation of CaMK II and induce spontaneous immune tolerance in mouse liver transplantation

Spontaneous immune tolerance in mouse liver transplantation has always been a hotspot in transplantation-immune research. Recent studies revealed that regulatory T cells (Tregs), hepatic satellite cells and Kupffer cells play a potential role in spontaneous immune tolerance, however the precise mechanism of spontaneous immune tolerance is still undefined. By using Microarray Chips, we investigated different immune regulatory factors to decipher critical mechanisms of spontaneous tolerance after mouse liver transplantation. Allogeneic (C57BL/6-C3H) and syngeneic (C3H-C3H) liver transplantation were performed by 6-8 weeks old male C57BL/6 and C3H mice. Graft samples (N = 4 each group) were collected from 8 weeks post-operation mice. 11 differentially expressed miRNAs in allogeneic grafts (Allografts) vs. syngeneic grafts (Syngrafts) were identified using Agilent Mouse miRNA Chips. It was revealed that 185 genes were modified by the 11 miRNAs, furthermore, within the 185 target genes, 11 of them were tightly correlated with immune regulation after Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis and Genbank data cross-comparison. Verified by real-time PCR and western blot, our results indicated that mRNA expression levels of IL-6 and TAB2 were respectively down regulated following miR-142-3p and miR-155 augment. In addition, increased miR-152 just silenced mRNA of CaMK II and down-regulated translation of CaMK II in tolerated liver grafts, which may play a critical role in immune regulation and spontaneous tolerance induction of mouse liver transplantation.

Magnetic cell sorting and flow cytometry sorting methods for the isolation and function analysis of mouse CD4+ CD25+ Treg cells

OBJECTIVE

In this paper we compared the two methods of cell sorting (magnetic cell sorting and flow cytometry sorting) for the isolation and function analysis of mouse CD4(+) CD25(+) regulatory T (Treg) cells, in order to inform further studies in Treg cell function.

METHODS

We separately used magnetic cell sorting and flow cytometry sorting to identify CD4(+) CD25(+) Treg cells. After magnetic cell separation, we further used flow cytometry to analyze the purity of CD4(+) CD25(+) Treg cells, trypan blue staining to detect cell viability, and propidium iodide (PI) staining to assess the cell viability. We detected the immune inhibition of CD4(+) CD25(+) Treg cells in the in vitro proliferation experiments.

RESULTS

The results showed that compared to flow cytometry sorting, magnetic cell sorting took more time and effort, but fewer live cells were obtained than with flow cytometry sorting. The CD4(+) CD25(+) Treg cells, however, obtained with both methods have similar immunosuppressive capacities.

CONCLUSION

The result suggests that both methods can be used in isolating CD4(+) CD25(+) Treg cells, and one can select the best method according to specific needs and availability of the methodologies.

Heterosexual and homosexual partners practising unprotected sex may develop allogeneic immunity and to a lesser extent tolerance

BACKGROUND

Epidemiological studies suggest that allogeneic immunity may inhibit HIV-1 transmission from mother to baby and is less frequent in multiparous than uniparous women. Alloimmune responses may also be elicited during unprotected heterosexual intercourse, which is associated ex vivo with resistance to HIV infection.

METHODOLOGY/PRINCIPAL FINDINGS

The investigation was carried out in well-defined heterosexual and homosexual monogamous partners, practising unprotected sex and a heterosexual cohort practising protected sex. Allogeneic CD4(+) and CD8(+) T cell proliferative responses were elicited by stimulating PBMC with the partners' irradiated monocytes and compared with 3(rd) party unrelated monocytes, using the CFSE method. Significant increase in allogeneic proliferative responses was found in the CD4(+) and CD8(+) T cells to the partners' irradiated monocytes, as compared with 3(rd) party unrelated monocytes (p<or=0.001). However, a significant decrease in proliferative responses, especially of CD8(+) T cells to the partners' compared with 3(rd) party monocytes was consistent with tolerization, in both the heterosexual and homosexual partners (p<0.01). Examination of CD4(+)CD25(+)FoxP3(+) regulatory T cells by flow cytometry revealed a significantly greater proportion of these cells in the homosexual than heterosexual partners practising unprotected sex (p<0.05). Ex vivo studies of infectivity of PBMC with HIV-1 showed significantly greater inhibition of infectivity of PBMC from heterosexual subjects practising unprotected compared with those practising protected sex (p = 0.02).

CONCLUSIONS/SIGNIFICANCE

Both heterosexual and homosexual monogamous partners practising unprotected sex develop allogeneic CD4(+) and CD8(+) T cell proliferative responses to the partners' unmatched cells and a minority may be tolerized. However, a greater proportion of homosexual rather than heterosexual partners developed CD4(+)CD25FoxP3(+) regulatory T cells. These results, in addition to finding greater inhibition of HIV-1 infectivity in PBMC ex vivo in heterosexual partners practising unprotected, compared with those practising protected sex, suggest that allogeneic immunity may play a significant role in the immuno-pathogenesis of HIV-1 infection.

Donor reactive regulatory T cells

PURPOSE OF REVIEW

Donor reactive regulatory T cells (Treg) play an important role in tolerance induction and maintenance in experimental transplant models. In this review we focus on the formation of the donor reactive Treg pool and explore the potential of these cells for therapeutic application in clinical transplantation.

RECENT FINDINGS

Donor reactive Treg can arise by both conversion of alloreactive nonregulatory cells and expansion of naturally occurring Treg (nTreg) cross-reactive with donor alloantigen but the quantitative contribution of each of these pathways is at present unclear. However, the fact that donor reactive Treg can be driven both in vivo and ex vivo by alloantigen challenge of nonregulatory precursors is encouraging as it demonstrates that the functional potential of these cells for use in clinical transplantation will not be limited by fortuitous cross-reactivity between nTreg and donor alloantigens. Treg can be generated in vivo by transplantation or alloantigen challenge in combination with Treg-permissive immunosuppression, or ex vivo by phenotypic selection or by polyclonal or antigen-specific stimulation. A number of ex-vivo protocols exist for the enrichment of Treg in the laboratory and in many cases these cells have demonstrable function both in vitro and in relevant graft-versus-host disease (GVHD) or organ transplant models. The challenge now is to understand the clinical opportunities and limitations that these populations present.

SUMMARY

Combined with appropriate immunosuppression, Treg generated/expanded in vivo or ex vivo may hold the final key to operational tolerance in clinical setting.

Short-term anti-CD25 monoclonal antibody administration down-regulated CD25 expression without eliminating the neogenetic functional regulatory T cells in kidney transplantation

CD4(+)CD25(+) forkhead box P3 (FoxP3)(+)regulatory T (T(reg)) cells are generated and play a key role in the induction and maintenance of transplant tolerance in organ recipients. It has been proposed that interleukin (IL)-2/IL-2 receptor (IL-2R) signalling was essential for the development and proliferation of antigen-activated T cells that included both effector T cells and T(reg) cells. Basiliximab (Simulect), a chimeric monoclonal antibody directed against the alpha-chain of the IL-2R (CD25), can be expected to not only affect alloreactive effector T cells, but also reduce the number and function of T(reg) cells. We therefore examined the effect of basiliximab induction therapy on the number and function of the T(reg) cells in renal recipients. Basiliximab decreased the percentage of CD4(+)CD25(+)T cells, but failed to influence the percentage of CD4(+)FoxP3(+) T(reg) cells. The cellular CD25 expression was decreased significantly by basiliximab injection, but CD4(+)CD25(+) T cells was not depleted from the circulating pool through monoclonal antibody activation-associated apoptosis. Functional analysis revealed that inhibitory function of T(reg) cells from recipients with basiliximab injection was not significantly different from recipients without injection. These data indicate that the functional T(reg) population may not be influenced by short-term basiliximab treatment.

The effects of immunosuppression on regulatory CD4(+)CD25(+) T cells: impact on immunosuppression selection in transplantation

During immune response and T-cell activation, both effector T cells and regulatory T(T(reg)) cells are activated and regulated simultaneously by both positive and negative pathways. CD4(+)CD25(+) T(reg) cells play a critical role in immune tolerance to self antigens as well as to allografts in some transplant settings. Effective immunosuppressive regimens significantly reduced the incidence of acute allograft rejection in patients following organ transplantation. However, the impact of immunosuppressive treatment on the potential induction of transplant tolerance has not been well determined. In this review we summarize the effects of immunosuppressive reagents on CD4(+)CD25(+) T(reg) cells in order to bring attention to this issue, which may affect the choice of immunosuppressive regimen in the clinical setting.

Dendritic cells, the liver, and transplantation

Interstitial liver dendritic cells (DCs) exhibit phenotypic diversity and functional plasticity. They play important roles in both innate and adaptive immunity. Their comparatively low inherent T cell stimulatory ability and the outcome of their interactions with CD4(+) and CD8(+) T cells, as well as with natural killer (NK) T cells and NK cells within the liver, may contribute to regulation of hepatic inflammatory responses and liver allograft outcome. Liver DCs migrate in the steady state and after liver transplantation to secondary lymphoid tissues, where the outcome of their interaction with antigen-specific T cells determines the balance between tolerance and immunity. Systemic and local environmental factors that are modulated by ischemia-reperfusion injury, liver regeneration, microbial infection, and malignancy influence hepatic DC migration, maturation, and function. Current research in DC biology is providing new insights into the role of these important antigen-presenting cells in the complex events that affect liver transplant outcome.

Intragraft FOXP3 mRNA Expression Reflects Antidonor Immune Reactivity in Cardiac Allograft Patients

BACKGROUND

Regulatory FOXP3+ T cells control immune responses of effector T cells. However, whether these cells regulate antidonor responses in the graft of cardiac allograft patients is unknown. Therefore, we analyzed the gene expression profiles of regulatory and effector T-cell markers during immunological quiescence and acute rejection.

METHODS

Quantitative real-time polymerase chain reaction was used to analyze mRNA expression levels in time-zero specimens (n=24) and endomyocardial biopsies (EMB; n=72) of cardiac allograft patients who remained free from rejection (nonrejectors; n=12) and patients with at least one histologically proven acute rejection episode (rejectors; International Society for Heart and Lung Transplantation [ISHLT] rejection grade>2; n=12).

RESULTS

For all analyzed regulatory and effector T-cell markers, mRNA expression levels were increased in biopsies taken after heart transplantation compared with those in time-zero specimens. Posttransplantation, the FOXP3 mRNA levels were higher in EMB assigned to a higher ISHLT rejection grade than the biopsies with grade 0: the highest mRNA levels were detected in the rejection biopsies (rejection grade>2; P=0.003). In addition, the mRNA levels of CD25, glucocorticoid-induced TNF receptor family-related gene, cytotoxic T lymphocyte-associated antigen 4, interleukin-2, and granzyme B were also significantly higher in rejecting EMB than in nonrejecting EMB (rejection grade<or=2). This increase in expression levels in relation to the histological rejection grade was only observed in patients who developed an acute rejection episode; the mRNA levels of nonrejectors remained stable irrespective of ISHLT rejection grade.

CONCLUSIONS

These observations suggest that, after clinical heart transplantation, FOXP3+ T cells do not prevent acute rejection, but rather are a response to antidonor effector T-cell activity.

Allogeneic stimulation of naturally occurring CD4+CD25+ T cells induces strong regulatory capacity with increased donor-reactivity

Current therapies in transplantation require continuous immunosuppression and do not result in transplantation tolerance. It is increasingly appreciated that CD4(+)CD25(+) regulatory T-cell (T(REG)) activation is pivotal for the induction and maintenance of peripheral tolerance. To optimally exploit T(REG) in allograft tolerance, we investigated how to further harness their function. In vitro, CD4(+)CD25(+)T cells were expanded by allogeneic bone-marrow derived DC or polyclonal stimulation and were compared in suppressive capacity and phenotype. In vivo, naive allogeneic CD4(+)CD25(+)T cells were analyzed in wild type hosts for proliferative capacity and suppressive capacity upon priming by alloantigen. DC of donor origin were found to potently stimulate alloreactive T(REG)in vitro. This was accompanied by a substantial enhancement of the suppressive capacity of the T(REG) population as a whole, likely due to a proportional rise of alloreactive T(REG) as indicated by CFSE analysis. In vivo analysis of infused naturally occurring allogeneic T(REG) revealed a robust proliferative capacity for T(REG) upon stimulation. Moreover, allogeneic skin transplantation resulted in enhanced capacity of the T(REG) population to suppress the response towards donor antigens. Combining, activation of alloreactive T(REG) is an intrinsic part of the regular alloimmune response and this feature can be exploited for therapeutic purposes. We propose that selectively favoring the effects of alloreactive T(REG) is a pivotal element in inducing graft acceptance.