Immunological monitoring of renal transplant recipients to predict acute allograft rejection following the discontinuation of tacrolimus

CD4+CD25+ T regulatory cells in renal transplantation

The immune response to an allograft activates lymphocytes with the capacity to cause rejection. Activation of CD4+CD25+Foxp3+T regulatory cells (Treg) can down-regulate allograft rejection and can induce immune tolerance to the allograft. Treg represent <10% of peripheral CD4+T cells and do not markedly increase in tolerant hosts. CD4+CD25+Foxp3+T cells include both resting and activated Treg that can be distinguished by several markers, many of which are also expressed by effector T cells. More detailed characterization of Treg to identify increased activated antigen-specific Treg may allow reduction of non-specific immunosuppression. Natural thymus derived resting Treg (tTreg) are CD4+CD25+Foxp3+T cells and only partially inhibit alloantigen presenting cell activation of effector cells. Cytokines produced by activated effector cells activate these tTreg to more potent alloantigen-activated Treg that may promote a state of operational tolerance. Activated Treg can be distinguished by several molecules they are induced to express, or whose expression they have suppressed. These include CD45RA/RO, cytokine receptors, chemokine receptors that alter pathways of migration and transcription factors, cytokines and suppression mediating molecules. As the total Treg population does not increase in operational tolerance, it is the activated Treg which may be the most informative to monitor. Here we review the methods used to monitor peripheral Treg, the effect of immunosuppressive regimens on Treg, and correlations with clinical outcomes such as graft survival and rejection. Experimental therapies involving ex vivo Treg expansion and administration in renal transplantation are not reviewed.

Donor-derived regulatory dendritic cell infusion results in host cell cross-dressing and T cell subset changes in prospective living donor liver transplant recipients

Regulatory dendritic cells (DCreg) promote transplant tolerance following their adoptive transfer in experimental animals. We investigated the feasibility, safety, fate, and impact on host T cells of donor monocyte-derived DCreg infused into prospective, living donor liver transplant patients, 7 days before transplantation. The DCreg expressed a tolerogenic gene transcriptional profile, high cell surface programed death ligand-1 (PD-L1):CD86 ratios, high IL-10/no IL-12 productivity and poor ability to stimulate allogeneic T cell proliferation. Target DCreg doses (range 2.5-10 × 10⁶ cells/kg) were achieved in all but 1 of 15 recipients, with no infusion reactions. Following DCreg infusion, transiently elevated levels of donor HLA and immunoregulatory PD-L1, CD39, and CD73 were detected in circulating small extracellular vesicles. At the same time, flow and advanced image stream analysis revealed intact DCreg and "cross-dressing" of host DCs in blood and lymph nodes. PD-L1 co-localization with donor HLA was observed at higher levels than with recipient HLA. Between DCreg infusion and transplantation, T-bet^hi Eomes^hi memory CD8⁺ T cells decreased, whereas regulatory (CD25^hi CD127^- Foxp3⁺ ): T-bet^hi Eomes^hi CD8⁺ T cell ratios increased. Thus, donor-derived DCreg infusion may induce systemic changes in host antigen-presenting cells and T cells potentially conducive to modulated anti-donor immune reactivity at the time of transplant.

T-cell Subset Profile in Kidney Recipients of Extended or Standard Donors

INTRODUCTION

The usage of extended-criteria donors (ECD) became a routinely accepted manner in the last decade. ECD is a potential risk factor for antibody-mediated rejection. Analysis of lymphocyte subsets might be a complementary diagnostic toolkit because there is limited knowledge about this term.

METHOD

Between May 12, 2016, and September 4, 2019, a total of 130 patients who had undergone kidney transplant were investigated. Patients were divided in ECD and standard criteria donor (SCD) groups. Blood samples were collected before the operation, then in the first week and after 30, 60, 180, and 365 days. Besides routine laboratory tests, multicolor flow cytometry was performed for lymphocyte subsets.

RESULTS

ECD grafts were transplanted to older recipients. The number of CD4+ cells increased in the SCDs from the first week to until the end of first month, and then decreased. The number of CD4+ cells decreased from the beginning of the study until the end of first year to 66% of its original value in ECDs. At the first month, the number of CD19+ cells was higher in SCD compared with ECD cases; the number then decreased in both groups. T-regulatory cells had a drop at the first week that lasted until the first month. A bigger increase in SCD and a moderate increase in ECD group were then observed. The kinetics of CD19+ and CD19+ naive cells are similar in the ECD and SCD groups. In the SCD group, cell count decreased in both CD19+ (13%) and CD19+ naive (12%) between third and sixth month. The count of CD19+ cells decreased by 9%, but the count of CD19+ naive cells increased by 11% between the sixth month and first year.

DISCUSSION

The prolonged postoperative uremic state caused by the poorer initial function, together with an aging immune system, explains the weaker immune response in ECD patients, which may be the cause of the decreased number of memory and regulatory T cells. Older patients with an ECD graft need a tailored, personalized, and less aggressive immunosuppressive treatment.

Evaluation of alloreactive T cells based on the degree of MHC incompatibility using flow cytometric mixed lymphocyte reaction assay in dogs

It has become anticipated that regenerative medicine will extend into the field of veterinary medicine as new treatments for various disorders. Although the use of allogeneic stem cells for tissue regeneration is more attractive than that of autologous cells in emergencies, the therapeutic potential of allogeneic transplantation is often limited by allo-immune responses inducing graft rejection. Therefore, a methodology for quantifying and monitoring alloreactive T cells is necessary for evaluating allo-immune responses. The mixed lymphocyte reaction (MLR) is widely used to evaluate T cell alloreactivity. In human, flow cytometric MLR with carboxyfluorescein diacetate succinimidyl ester has been established and used as a more useful assay than conventional MLR with radioisotope labeling. However, the available information about alloreactivity based on the differences of dog major histocompatibility complex (MHC) (dog leukocyte antigen, DLA) is quite limited in dog. In this paper, we describe our established flow cytometric MLR method that can quantify the T cell alloreactivity while distinguishing cell phenotypes in dog, and T cell alloreactivity among DLA-type matched pairs was significantly lower than DLA-mismatched pairs, suggesting that our developed flow cytometric MLR method is useful for quantifying T cell alloreactivity. In addition, we demonstrated the advantage of DLA homozygous cells as a donor (stimulator) for allogeneic transplantation. We also elucidated that the frequency of alloreactive T cell precursors was almost the same as that of mouse and human (1-10%). To our knowledge, this is the first report to focus on the degree of allo-immune responses in dog based on the differences of DLA polymorphisms.

Blood biomarkers of kidney transplant rejection, an endless search?

INTRODUCTION

The tailoring of immunosuppressive treatment is recognized as a promising strategy to improve long-term kidney graft outcome. To guide the standard care of transplant recipients, physicians need objective biomarkers that can identify an ongoing pathology with the graft or low intensity signals that will be later evolved to accelerated transplant rejection. The early identification of 'high-risk /low-risk' patients enables the adjustment of standard of caring, including managing the frequency of clinical visits and the immunosuppression dosing. Given their ease of availability and the compatibility with a large technical array, blood-based biomarkers have been widely scrutinized for use as potential predictive and diagnostic biomarkers. Areas covered: Here, the authors report on non-invasive biomarkers, such as modification of immune cell subsets and mRNA and miRNA profiles, identified in the blood of kidney transplant recipients collected before or after transplantation. Expert commentary: Combined with functional tests, the identification of biomarkers will improve our understanding of pathological processes and will contribute to a global improvement in clinical management.

Donor-specific alloreactive T cells can be quantified from whole blood, and may predict cellular rejection after renal transplantation

Preformed cellular alloreactivity can exist prior to transplantation and may contribute to rejection. Here, we used a rapid flow-cytometric whole-blood assay to characterize the extent of alloreactive T cells among 1491 stimulatory reactions from 61 renal transplant candidates and 75 controls. The role of preformed donor-specific alloreactive T cells in cellular rejection was prospectively analyzed in 21 renal transplant recipients. Alloreactive CD8⁺ T cells were more frequent than respective CD4⁺ T cells, and these levels were stable over time. CD8⁺ T cells were effector-memory T cells largely negative for expression of CD27, CD62L, and CCR7, and were susceptible to steroid and calcineurin inhibitor inhibition. Alloreactivity was more frequent in samples with higher number of HLA mismatches. Moreover, the percentage of individuals with alloreactive T cells was higher in transplant candidates than in controls. Among transplant candidates, 5/61 exhibited alloreactive CD8⁺ T cells against most stimulators, 23/61 toward a limited number of stimulators, and 33/61 did not show any alloreactivity. Among 21 renal transplant recipients followed prospectively, one had donor-specific preformed T-cell alloreactivity. She was the only patient who developed cellular rejection posttransplantation. In conclusion, donor-specific alloreactive T cells may be rapidly quantified from whole blood, and may predict cellular rejection after transplantation.

Monitoring alloimmune response in kidney transplantation

Currently, immunosuppressive therapy in kidney transplant recipients is generally performed by protocols and adjusted according to functional or histological evaluation of the allograft and/or signs of drug toxicity or infection. As a result, a large fraction of patients are likely to receive too much or too little immunosuppression, exposing them to higher rates of infection, malignancy and drug toxicity, or increased risk of acute and chronic graft injury from rejection, respectively. Developing reliable biomarkers is crucial for individualizing therapy aimed at extending allograft survival. Emerging data indicate that many assays, likely used in panels rather than single assays, have potential to be diagnostic and predictive of short and also long-term outcome. While numerous cross-sectional studies have found associations between the results of these assays and the presence of clinically relevant post-transplantation outcomes, data from prospective studies are still scanty, thereby preventing widespread implementation in the clinic. Of note, some prospective, randomized, multicenter biomarker-driven studies are currently on-going aiming at confirming such preliminary data. These works as well as other future studies are highly warranted to test the hypothesis that tailoring immunosuppression on the basis of results offered by these biomarkers leads to better outcomes than current standard clinical practice.

Biomarkers to assess donor-reactive T-cell responses in kidney transplant patients

Different to antibody-mediated rejection (ABMR), T-cell mediated rejection (TCMR) still unpredictably occurs after kidney transplantation in a great part because of a poor immunologic evaluation of the cellular allogeneic immune response. However, in the last years, important efforts have focused on the development of novel and more sensitive assays to monitor T-cell alloimmune responses at different biological levels that may improve the understanding of the functional status of the cellular immune compartment in patients undergoing organ transplantation. In this direction, immune assays evaluating T-cell proliferation, intracellular ATP release, multiparameter flow cytometry, profiling T-cell receptor repertoires and measurements of frequencies of cytokine-producing T-cells using an IFN-γ enzyme-linked immunospot assay (IFN-γ ELISPOT) have been reported showing interesting associations between the cellular alloimmune response and kidney transplant outcomes. In summary, an important progress has been made in the assessment of alloreactive T-cell responses in the context of organ transplantation using novel immune assays at different biological levels. However, there is an urgent need for prospective, randomized clinical studies to validate these encouraging preliminary data to ultimately introduce them in current clinical practice for refining current immune-risk stratification in kidney transplantation.

Clinically-relevant cyclosporin and rapamycin concentrations enhance regulatory T cell function to a similar extent but with different mechanisms: an in-vitro study in healthy humans

Evidence indicates that regulatory T cells (Tregs) are profoundly involved in promoting allograft tolerance after organ transplantation. Since a successful transplantation currently still requires a long-term immunosuppressive treatment, clarifying the specific impact of these drugs on Tregs may be of high clinical relevance. Conflicting results arise from the literature, particularly as concerns cyclosporine (CsA). The specific aim of this work was to evaluate in-vitro the direct effects of clinically-relevant drug concentrations of three widely used immunosuppressive drugs, i.e. CsA, rapamycin (RAPA) and mycophenolic acid (MPA), on Treg activity, number and forkhead/winged helix transcription factor (FoxP3) expression in humans. Tregs (CD4(+)CD25(+)) isolated from healthy donors were cultured in the presence of different concentrations of CsA, RAPA or MPA. The suppressive activity of Tregs was evaluated in mixed lymphocyte reactions with CD4(+)CD25(-) T cells. Phenotype analysis and FoxP3 expression were assessed by flow cytometry. Clinically-relevant CsA and RAPA concentrations significantly enhanced to a similar extent the suppressive activity of Tregs. Although this effect was associated with an increase in Treg number as well as in FoxP3 expression with both drugs, the driving mechanism seemed to be primarily quantitative (i.e. increase of the cell number) for RAPA, whereas mainly qualitative (i.e. increase in FoxP3 levels) for CsA, respectively. Conversely, MPA did not show any effect on Treg function and number. These findings suggest that both RAPA and CsA may be beneficial in promoting Treg-dependent allograft tolerance after organ transplantation.

Longitudinal analysis of T and B cell phenotype and function in renal transplant recipients with or without rituximab induction therapy

Background

Prevention of rejection after renal transplantation requires treatment with immunosuppressive drugs. Data on their in vivo effects on T- and B-cell phenotype and function are limited.

Methods

In a randomized double-blind placebo-controlled study to prevent renal allograft rejection, patients were treated with tacrolimus, mycophenolate mofetil (MMF), steroids, and a single dose of rituximab or placebo during transplant surgery. In a subset of patients, we analyzed the number and phenotype of peripheral T and B cells by multiparameter flow cytometry before transplantation, and at 3, 6, 12, and 24 months after transplantation.

Results

In patients treated with tacrolimus/MMF/steroids the proportion of central memory CD4⁺ and CD8⁺ T cells was higher at 3 months post-transplant compared to pre-transplant levels. In addition, the ratio between the percentage of central memory CD4⁺ and CD4⁺ regulatory T cells was significantly higher up to 24 months post-transplant compared to pre-transplant levels. Interestingly, treatment with tacrolimus/MMF/steroids resulted in a shift toward a more memory-like B-cell phenotype post-transplant. Addition of a single dose of rituximab resulted in a long-lasting B-cell depletion. At 12 months post-transplant, the small fraction of repopulated B cells consisted of a high percentage of transitional B cells. Rituximab treatment had no effect on the T-cell phenotype and function post-transplant.

Conclusions

Renal transplant recipients treated with tacrolimus/MMF/steroids show an altered memory T and B-cell compartment post-transplant. Additional B-cell depletion by rituximab leads to a relative increase of transitional and memory-like B cells, without affecting T-cell phenotype and function.

Trial Registration

ClinicalTrials.gov NCT00565331

Monitoring T cell alloreactivity

Currently, immunosuppressive therapy in kidney transplant recipients is center-specific, protocol-driven, and adjusted according to functional or histological evaluation of the allograft and/or signs of drug toxicity or infection. As a result, a large fraction of patients receive too much or too little immunosuppression, exposing them to higher rates of infection, malignancy and drug toxicity, or increased risk of acute and chronic graft injury from rejection, respectively. The individualization of immunosuppression requires the development of assays able to reliably quantify and/or predict the magnitude of the recipient's immune response toward the allograft. As alloreactive T cells are central mediators of allograft rejection, monitoring T cell alloreactivity has become a priority for the transplant community. Among available assays, flow cytometry based phenotyping, T cell proliferation, T cell cytokine secretion, and ATP release (ImmuKnow), have been the most thoroughly tested. While numerous cross-sectional studies have found associations between the results of these assays and the presence of clinically relevant post-transplantation outcomes, data from prospective studies are still scanty, thereby preventing widespread implementation in the clinic. Future studies are required to test the hypothesis that tailoring immunosuppression on the basis of results offered by these biomarkers leads to better outcomes than current standard clinical practice.

Soluble CD30 does not predict late acute rejection or safe tapering of immunosuppression in renal transplantation

BACKGROUND

Previous reports revealed the potential value of the soluble CD30 level (sCD30) as biomarker for the risk of acute rejection and graft failure after renal transplantation, here we examined its use for the prediction of safe tapering of calcineurin inhibitors as well as late acute rejection.

METHODS

In a cohort of renal transplant patients receiving triple immunosuppressive therapy we examined whether sCD30 can be used as a marker for safe (rejection-free) discontinuation of tacrolimus at six months after transplantation (TDS cohort: 24 rejectors and 44 non-rejecting controls). Also, in a second cohort of patients (n=22, rejectors n=11 and non-rejectors n=11), participating in a clinical trial of rituximab as induction therapy after renal transplantation (RITS cohort), we examined whether sCD30 could predict the occurrence of late (>3months post-transplant) acute rejection episodes. sCD30 was measured by ELISA in serum taken before and at several time points after transplantation.

RESULTS

Overall, in the TDS cohort sCD30 decreased after transplantation. No difference in sCD30 was observed between rejectors and non-rejecting controls at any of the time points measured. In addition, in the RITS cohort, sCD30 measured at three months after transplantation were not indicative for the occurrence of late acute rejection.

CONCLUSION

In two prospectively followed cohorts of renal transplant patients we found no association between sCD30 and the occurrence of either late acute rejection or acute rejection after reduction of immunosuppression.

Imbalance of different types of CD4(+)Foxp3(+) T cells in renal transplant recipients

AIMS

To determine the number of CD4(+)CD25(-)Foxp3(+), CD4(+)CD25(+)Foxp3(+) and CD4(+)CXCR5(+)Foxp3(+) T cells in renal transplant recipients that are transplanted stable (TS), or experiencing accelerated rejection (ALR), or acute rejection (AR).

METHODS

Renal transplantation was conducted in 28 patients with end-stage renal failure (ESRF). The number of peripheral CD4(+)CD25(-)Foxp3(+), CD4(+)CD25(+)Foxp3(+), or CD4(+)CXCR5(+)Foxp3(+) T cells and the serum levels of interleukin-10 (IL-10) were measured in pre- and post-transplant patients and these results were compared to 10 healthy controls (HC). Correlation between CD4(+)CD25(+)Foxp3(+) and estimated glomerular filtration rate (eGFR), CD4(+)CD25(-)Foxp3(+) and serum creatinine (Cr) levels, or Cr and IL-10 levels in TS patients was also determined.

RESULTS

The number of CD4(+)CD25(-)Foxp3(+) T cells was significantly increased in patients with ESRF, as compared to HC. Stratification analysis demonstrated that TS patients contained greater numbers of CD4(+)CD25(+)Foxp3(+) and CD4(+)CXCR5(+)Foxp3(+) T cells, higher levels of serum IL-10, and fewer numbers of CD4(+)CD25(-)Foxp3(+) T cells than ESRF patients. In contrast, ALR and AR patients contained fewer numbers of CD4(+)CD25(+)Foxp3(+) and CD4(+)CXCR5(+)Foxp3(+) T cells, greater numbers of CD4(+)CD25(-)Foxp3(+) T cells, and lower levels of serum IL-10 than ESRF patients. In TS patients, the numbers of CD4(+)CD25(+)Foxp3(+) and CD4(+)CD25(-)Foxp3(+) T cells were positively correlated with eGFR and serum Cr levels, respectively.

CONCLUSION

An imbalance of different types of CD4(+)Foxp3(+) T cells might be involved in renal transplant rejection.

MHC universal cells survive in an allogeneic environment after incompatible transplantation

Cell, tissue, and organ transplants are commonly performed for the treatment of different diseases. However, major histocompatibility complex (MHC) diversity often prevents complete donor-recipient matching, resulting in graft rejection. This study evaluates in a preclinical model the capacity of MHC class I-silenced cells to engraft and grow upon allogeneic transplantation. Short hairpin RNA targeting β2-microglobulin (RN_shβ2m) was delivered into fibroblasts derived from LEW/Ztm (RT1^l) (RT1-A^l) rats using a lentiviral-based vector. MHC class I (RT1-A-) expressing and -silenced cells were injected subcutaneously in LEW rats (RT1^l) and MHC-congenic LEW.1W rats (RT1^u), respectively. Cell engraftment and the status of the immune response were monitored for eight weeks after transplantation. In contrast to RT1-A-expressing cells, RT1-A-silenced fibroblasts became engrafted and were still detectable eight weeks after allogeneic transplantation. Plasma levels of proinflammatory cytokines IL-1α, IL-1β, IL-6, TNF-α, and IFN-γ were significantly higher in animals transplanted with RT1-A-expressing cells than in those receiving RT1-A-silenced cells. Furthermore, alloantigen-specific T-cell proliferation rates derived from rats receiving RT1-A-expressing cells were higher than those in rats transplanted with RT1-A-silenced cells. These data suggest that silencing MHC class I expression might overcome the histocompatibility barrier, potentially opening up new avenues in the field of cell transplantation and regenerative medicine.

Cross-validation of IFN-γ Elispot assay for measuring alloreactive memory/effector T cell responses in renal transplant recipients

Assessment of donor-specific alloreactive memory/effector T cell responses using an IFN-γ Elispot assay has been suggested to be a novel immune-monitoring tool for evaluating the cellular immune risk in renal transplantation. Here, we report the cross-validation data of the IFN-γ Elispot assay performed within different European laboratories taking part of the EU RISET consortium. For this purpose, development of a standard operating procedure (SOP), comparisons of lectures of IFN-γ plates assessing intra- and interlaboratory assay variability of allogeneic or peptide stimuli in both healthy and kidney transplant individuals have been the main objectives. We show that the use of a same SOP and count-settings of the Elispot bioreader allow low coefficient variation between laboratories. Frozen and shipped samples display slightly lower detectable IFN-γ frequencies than fresh samples. Importantly, a close correlation between different laboratories is obtained when measuring high frequencies of antigen-specific primed/memory T cell alloresponses. Interestingly, significant high donor-specific alloreactive T cell responses can be similarly detected among different laboratories in kidney transplant patients displaying histological patterns of acute T cell mediated rejection. In conclusion, assessment of circulating alloreactive memory/effector T cells using an INF-γ Elispot assay can be accurately achieved using the same SOP, Elispot bioreader and experienced technicians in kidney transplantation.

Differing effects of rapamycin or calcineurin inhibitor on T-regulatory cells in pediatric liver and kidney transplant recipients

In a cross-sectional study, we assessed effects of calcineurin inhibitor (CNI) or rapamycin on T-regulatory (Treg) cells from children with stable liver (n = 53) or kidney (n = 9) allografts several years posttransplant. We analyzed Treg number, phenotype, suppressive function, and methylation at the Treg-specific demethylation region (TSDR) using Tregs and peripheral blood mononuclear cells. Forty-eight patients received CNI (39 as monotherapy) and 12 patients received rapamycin (9 as monotherapy). Treg numbers diminished over time on either regimen, but reached significance only with CNI (r =-0.424, p = 0.017). CNI levels inversely correlated with Treg number (r =-0.371, p = 0.026), and positively correlated with CD127+ expression by Tregs (r = 0.437, p = 0.023). Patients with CNI levels >3.6 ng/mL had weaker Treg function than those with levels <3.6 ng/mL, whereas rapamycin therapy positively correlated with Treg numbers (r = 0.628, p = 0.029) and their expression of CTLA4 (r = 0.726, p = 0.041). Overall, CTLA4 expression, TSDR demethylation and an absence of CD127 were important for Treg suppressive function. We conclude that rapamycin has beneficial effects on Treg biology, whereas long-term and high dose CNI use may impair Treg number, function and phenotype, potentially acting as a barrier to attaining host hyporesponsiveness to an allograft.

CD4(+)CD25(+)Foxp3(+)IFNγ(+) Treg are immunosuppressive in vitro and increase with intensity of the alloresponse in pretransplant MLC

IFNγ-producing CD3(+)CD4(+)CD25(+)Foxp3(+) induced Treg are more frequently detectable in patients with good than in patients with impaired long-term kidney graft function. We investigated the in-vitro function of separated CD3(+)CD4(+)CD25(+)Foxp3(+)IFNγ(+) PBL that were induced by phorbol-12-myristate-13-acetate(PMA)/Ionomycin or alloantigenic stimulation. Additionally, we studied iTreg induction and cell proliferation in MLC with pretransplant obtained PBL. CD4(+)CD25(+)IFNγ(+) PBL separated from PMA/Ionomycin-stimulated PBL of healthy controls inhibited secondary cell cultures of autologous PBL. Furthermore, CD4(+)CD25(+)IFNγ(+) PBL separated from primary MLC and added to secondary MLC suppressed allogeneic T-cell activation in secondary MLC unspecifically, irrespective of the stimulator cell. However, the strongest suppression was observed in specific MLC. Patients with poor long-term graft outcome were able to form IFNγ(+) iTreg in pretransplant MLC. Eight patients with a serum creatinine level ranging from 0.9 to 14 mg/dl 18-29 years posttransplant were studied. In MLC with pretransplant obtained recipient and donor cells, strong IFNγ(+) iTreg (p=0.007) and strong blast induction (p=0.047) were associated with impaired long-term graft outcome. Long-term graft outcome was not associated with cell proliferation and iTreg induction in unspecific MLC with third-party cells as stimulator. The data indicate that patients with impaired long-term graft outcome are able to form high numbers of IFNγ(+) iTreg in specific pretransplant MLC. Quantity of induced IFNγ(+) iTreg depends on the strength of the alloresponse and both parameters are inversely associated with long-term graft outcome.

Foxp3+ T cells in peripheral blood of renal transplant recipients and clinical correlations

AIM

Immunophenotype peripheral blood T cells from renal transplant recipients (RTR) using cellular markers of regulatory T cells (Tregs) and flow cytometry, including Foxp3, and correlate these findings with clinical parameters.

METHODS

Expression of phenotypic markers of Tregs was assessed by flow cytometric analysis of peripheral blood lymphocytes (PBL) from (i) RTR (n = 95); (ii) patients with end-stage renal failure (ESRF) awaiting transplantation (n = 17); and (iii) normal healthy controls (n = 18).

RESULTS

The percentage of CD4(+) CD25(+) Foxp3(+) cells within the CD4(+) cell population did not significantly alter at different time points post-transplant. However, the percentage of CD4(+) CD25(+) Foxp3(+) cells within the CD4(+) population was significantly lower in RTR compared with patients with ESRF. In contrast, RTR and ESRF had a similar percentage of CD4(+) CD25(+) cells expressing Foxp3. Multivariate analysis of PBL and clinical parameters demonstrated (i) a positive linear relationship between the percentage CD4(+) CD25(+) cells expressing Foxp3 and estimated glomerular filtration rate and (ii) a higher percentage of CD4(+) CD25(+) cells in the CD4(+) cell population in patients with malignancy (the majority were skin cancers). Malignancy also correlated strongly with time post-transplant and age of the RTR.

CONCLUSION

Immune monitoring of the PBL phenotype in RTR using CD4, CD25 and Foxp3 may stratify RTR and predict graft outcome and function, and risk of complications from immunosuppression. Longitudinal and functional studies of Tregs are essential to extend the findings of the present study.

Long-term effects of alemtuzumab on regulatory and memory T-cell subsets in kidney transplantation

BACKGROUND

Induction with lymphocyte-depleting antibodies is routinely used to prevent rejection but often skews T cells toward memory. It is not fully understood which memory and regulatory T-cell subsets are most affected and how they relate to clinical outcomes.

METHODS

We analyzed T cells from 57 living-donor renal transplant recipients (12 reactive and 45 quiescent) 2.8±1.4 years after alemtuzumab induction. Thirty-four healthy subjects and nine patients with acute cellular rejection (ACR) were also studied.

RESULTS

We found that alemtuzumab caused protracted CD4 more than CD8 T-lymphocyte deficiency, increased proportion of CD4 memory T cells, and decreased proportion of CD4 regulatory T cells. Reactive patients exhibited higher proportions of CD4 effector memory T cells (TEM) and CD8 terminally differentiated TEM (TEMRA), with greater CD4 TEM and CD8 TEMRA to regulatory T cell ratios, than quiescent patients or healthy controls. Patients with ongoing ACR had profound reduction in circulating CD8 TEMRA. Mixed lymphocyte assays showed significantly lower T-cell proliferation to donor than third-party antigens in the quiescent group, while reactive and ACR patients exhibited increased effector molecules in CD8 T cells.

CONCLUSIONS

Our findings provide evidence that T-cell skewing toward TEM may be associated with antigraft reactivity long after lymphodepletion. Further testing of TEM and TEMRA subsets as rejection predictors is warranted.

DR(high+)CD45RA(-)-Tregs potentially affect the suppressive activity of the total Treg pool in renal transplant patients

Recent studies show that regulatory T cells (Tregs) play an essential role in tolerance induction after organ transplantation. In order to examine whether there are differences in the composition of the total CD4⁺CD127^low+/−FoxP3⁺- Treg cell pool between stable transplant patients and patients with biopsy proven rejection (BPR), we compared the percentages and the functional activity of the different Treg cell subsets (DR^high+CD45RA⁻-Tregs, DR^low+CD45RA⁻-Tregs, DR⁻CD45RA⁻-Tregs, DR⁻CD45RA⁺-Tregs). All parameters were determined during the three different periods of time after transplantation (0–30 days, 31–1,000 days, >1,000 days). Among 156 transplant patients, 37 patients suffered from BPR. The most prominent differences between rejecting and non-rejecting patients were observed regarding the DR^high+CD45RA⁻-Treg cell subset. Our data demonstrate that the suppressive activity of the total Treg pool strongly depends on the presence of these Treg cells. Their percentage within the total Treg pool strongly decreased after transplantation and remained relatively low during the first year after transplantation in all patients. Subsequently, the proportion of this Treg subset increased again in patients who accepted the transplant and reached a value of healthy non-transplanted subjects. By contrast, in patients with acute kidney rejection, the DR^high+CD45RA⁻-Treg subset disappeared excessively, causing a reduction in the suppressive activity of the total Treg pool. Therefore, both the monitoring of its percentage within the total Treg pool and the monitoring of the HLA-DR MFI of the DR⁺CD45RA⁻-Treg subset may be useful tools for the prediction of graft rejection.

Quantitative in situ analysis of FoxP3+ T regulatory cells on transplant tissue using laser scanning cytometry

There is abundant evidence that immune cells infiltrating into a transplanted organ play a critical role for destructive inflammatory or regulatory immune reactions. Quantitative in situ analysis (i.e., in tissue sections) of immune cells remains challenging due to a lack of objective methodology. Laser scanning cytometry (LSC) is an imaging-based methodology that performs quantitative measurements on fluorescently and/ or chromatically stained tissue or cellular specimens at a single-cell level. In this study, we have developed a novel objective method for analysis of immune cells, including Foxp3(+) T regulatory cells (Tregs), on formalin-fixed /paraffin-embedded (FFPE) transplant biopsy sections using iCys® Research Imaging Cytometer. The development of multiple immunofluorescent staining was established using FFPE human tonsil sample. The CD4/CD8 ratio and the population of Tregs among CD4(+) cells were analyzed using iCys and compared with the results from conventional flow cytometry analysis (FCM). Our multiple immunofluorescent staining techniques allow obtaining clear staining on FFPE sections. The CD4/CD8 ratio analyzed by iCys was concordant with those obtained by FCM. This method was also applicable for liver, small intestine, kidney, pancreas, and heart transplant biopsy sections and provide an objective quantification of Tregs within the grafts.

Do CD4+ Foxp3+ Treg cells correlate with transplant outcomes: a systematic review on recipients of solid organ transplantation

Regulatory T cells (Tregs) are considered to be critical for the induction of transplant tolerance. Tregs counts were measured in blood, biopsy and urine sample after transplantation in many studies. Although not unanimous, some studies have suggested that Tregs is associated with better outcome and can also serve as an immune marker to predict the individual risk of rejection and identify tolerant patients. In this study, we systematically reviewed the correlation between Tregs and transplant outcomes, identifying if Tregs can predict transplant rejection and tolerance. A total of 22 articles were included and assessed, the results showed that Tregs in recipients are helpful to maintain a stable graft function, reduce acute/chronic rejection rate. And the Tregs in graft and urine, rather than in PBL, may have a better diagnostic value for transplant outcomes. However, since the low quality of included studies, results may be influenced by bias. More high quality studies with bigger sample size are still needed in future.

Increased CD64 expression on polymorphonuclear neutrophils indicates infectious complications following solid organ transplantation

The aim of this study was to evaluate the diagnostic value of monitoring CD64 antigen upregulation on polymorphonuclear neutrophils (PMN) for the identification of infectious complications in the postoperative course of solid organ transplanted patients. Twenty-five kidney, 13 liver, and four pancreas-kidney transplanted patients were included. Beginning with preoperative values up to postoperative values after 3 months for each patient, the PMN CD64 Index, HLA-DR on monocytes, NKp44+ NK and NK/T cells, CXCR3+ NK cells, CXCR3+ T helper cells, CXCR3+ NK/T cells, and CD4/CD8 ratio were measured by flow cytometry. Subsequently they were correlated with confirmed postoperative complications. Measuring the PMN CD64 Index reached a sensitivity of 89% and a specificity of 65% in the detection of infectious complications. Concerning this matter, it was a significantly better marker than all other included parameters except CXCR3+ NK/T cells. In contrast, according to our results the PMN CD64 Index has no diagnostic relevance in detection of rejections. The combination of included parameters showed no improved diagnostic value. Due to its high sensitivity and specificity for infectious complications CD64 on PMN could be proven a very good indicator in evaluating suspected infectious complications in the postoperative course of transplanted patients.

Immune reconstitution following rabbit antithymocyte globulin

Depletional induction therapies are routinely used to prevent acute rejection and improve transplant outcome. The effects of depleting agents on T-cell subsets and subsequent T-cell reconstitution are incompletely defined. We used flow cytometry to examine the effects of rabbit antithymocyte globulin (rATG) on the peripheral T-cell repertoire of pediatric and adult renal transplant recipients. We found that while rATG effectively depleted CD45RA+CD27+ naïve and CD45RO+CD27+ central memory CD4+ T cells, it had little effect on CD45RO+CD27- CD4+ effector memory or CD45RA+CD31-, CD45RO+CD27+ and CD45RO+CD27- CD8+ T cell subsets. When we performed a kinetic analysis of CD31+ recent thymic emigrants and CD45RA+/RO+ T cells, we found evidence for both thymopoiesis and homeostatic proliferation contributing to immune reconstitution. We additionally examined the impact of rATG on peripheral CD4+Foxp3+ T cells. We found that in adults, administration of rATG-induced peripheral expansion and new thymic emigration of T cells with a Treg phenotype, while CD4+Foxp3+ T cells of thymic origin predominated in children, providing the first evidence that rATG induces Treg in vivo. Collectively our data indicate that rATG alters the balance of regulatory to memory effector T cells posttransplant, providing an explanation for how it positively impacts transplant outcome.

Detecting adaptive immunity: applications in transplantation monitoring

In recent decades, continuous improvements in immunosuppressive therapy have led to a significant increase in kidney allograft survival. Despite innovative developments and improvements in immunosuppression, chronic allograft injury and late graft loss still remain major causes of morbidity and mortality. In clinical practice, long-term immunosuppression is adapted and fine-tuned according to drug levels, kidney function, and biopsy results. As an invasive procedure, indication biopsy still represents an indispensible diagnostic gold standard. However, in an effort to further improve outcomes on the basis of individualized treatment, there is an urgent need for noninvasive assays, as well as biomarkers, to more accurately monitor allogeneic responses and predict the risk of acute and chronic allograft rejection. This article discusses strategies for immune monitoring of T-cell responsiveness and humoral alloreactivity. Furthermore, new microarray and gene profiling data are highlighted, which may identify hyporesponsive transplant recipients who could benefit from a reduction or even withdrawal of immunosuppression. Finally, supplementary transplant risk assessment markers, such as soluble CD30 and urinary effector molecule analysis, are discussed as promising new tools. Recent developments and improvements in test principles to monitor and predict allograft immunity are encouraging and may herald the transition of present empiric immunosuppression to individualized immunosuppressive treatment. Nonetheless, before implementation of immune monitoring in routine clinical practice, there is still a need for prospective trials designed to clarify the actual diagnostic potential of individual test systems in a therapeutic context.

T cells in ANCA-associated vasculitis: what can we learn from lesional versus circulating T cells?

Anti-neutrophil cytoplasmic antibody (ANCA) - associated vasculitis (AAV) is a life-threatening autoimmune disease characterized by an antibody-mediated glomerulonephritis and necrotizing vasculitis. Apart from antibodies, T cells are also involved in disease pathogenesis. This review stresses the hallmarks of T cell-mediated pathology in AAV and highlights the characteristics of lesional and circulating T cells in the immune response in AAV. Circulating effector T-cell populations are expanded and are in a persistent state of activation. Circulating regulatory T-cell subsets are less well characterized but seem to be impaired in function. Lesional effector T cells are present in granulomas, vasculitic lesions, and nephritis. Lesional T cells usually show pro-inflammatory properties and promote granuloma formation. Apart from T cells, dendritic cells are abundantly present at the sites of inflammation and locally orchestrate the immune response. Targeting the above-mentioned T cell-mediated disease mechanisms will potentially provide powerful therapeutic tools for AAV.

Two-year follow-up of a prospective study of circulating regulatory T cells in renal transplant patients

CD4(+)CD25(high)FOXP3(+) regulatory T cells (Tregs) are involved in alloreactivity and may be associated with protection from rejection. Their quantification in peripheral blood could guide clinicians in the management of renal transplant patients. Thus, we prospectively monitored the levels and in vitro suppression of circulating Tregs in 33 renal transplant patients from deceased donors within the first two yr of transplantation. Patients received maintenance immunosuppression with tacrolimus, mofetil mycophenolate and prednisolone. Results showed that peripheral blood Tregs were significantly lower six months after transplantation and recovered to almost basal levels at first post-transplant year. The number of circulating Tregs increased significantly over basal levels afterwards. The decrease in circulating Tregs at six months may be explained by the high load of tacrolimus, as demonstrated by the inverse correlation between the blood concentration of Tregs and tacrolimus. Likewise, nine patients treated with anti-CD25 antibodies showed higher numbers of Tregs at six months than those that did not, although differences were not observed later. In conclusion, circulating Tregs decrease in the first six months but recover thereafter up to two yr after kidney transplantation. Such a decrease is favored by high levels of tacrolimus but not by induction protocols with anti-CD25.

Contribution of naïve and memory T-cell populations to the human alloimmune response

T-cell alloimmunity plays a dominant role in allograft rejection. The precise contribution of naïve and memory T cells to this response however remains unclear. To address this question, we established an ex vivo flow-cytometric assay that simultaneously measures proliferation, precursor frequency and effector molecule (IFNgamma, granzyme B/perforin) production of alloreactive T cells. By applying this assay to peripheral blood mononuclear cells from healthy volunteers, we demonstrate that the CD4+ and CD8+ populations mount similar proliferative responses and contain comparable frequencies of alloreactive precursors. Effector molecule expression, however, was significantly higher among CD8+ T cells. Analysis of sorted naïve and memory T cells showed that alloreactive precursors were equally present in both populations. The CD8+ effector and terminally differentiated effector memory subsets contained the highest proportion of granzyme B/perforin after allostimulation, suggesting that these cells present a significant threat to transplanted organs. Finally, we demonstrate that virus-specific lymphocytes contribute significantly to the alloresponse in certain responder-stimulator HLA combinations, underscoring the importance of T-cell cross-reactivity in alloimmunity. These results provide a quantitative assessment of the roles of naïve and memory T-cell subsets in the normal human alloimmune response and establish a platform for measuring T-cell alloreactivity pre- and posttransplantation.