Diagnostic Value of Regulatory T Cells: A New Facet of a Much Studied Cell Population

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.

Regulatory T-cell subset analysis and profile of interleukin (IL)-10, IL-17 and interferon-gamma cytokine-producing cells in kidney allograft recipients with donor cells infusion

BACKGROUND

This pilot study aimed to assess whether the perioperative infusion of donor bone marrow cells (DBMC) in renal allograft recipients can affect the appearance of peripheral regulatory T-cell subsets and the profile of cytokine-producing cells [interferon-gamma (IFN-γ), interleukin (IL)-17 and IL-10] 2 years after transplantation.

METHODS

Fresh blood samples were collected from 14 kidney recipients who received infusion and from 13 kidney recipients without infusion who served as controls at the end of the second post-transplantation year. Initially the percentages of CD4(+)CD25(+)FoxP3(+) T cells and CD3(+)CD8(+)CD28(-) T cells were quantified using flowcytometry. Thereafter, the frequencies of IL-10-, IL-17- and IFN-γ-producing cells were determined separately using the ELISPOT technique with peptides corresponding to mismatched donor HLA-DR molecules and phytohemagglutinin (PHA).

RESULTS

The mean numbers of IFN-γ- and IL-17-producing cells in response to PHA were lower in infused patients than in controls (P = 0.02 and P = 0.18, respectively); however, an increased frequency of IL-10-producing cells was observed compared to controls (P = 0.07). Furthermore, the ratio of IL-10/IFN-γ-producing cells was significantly higher in the DBMC-infused group versus controls (P = 0.01). There was a negative correlation between the percentage of CD3(+)CD8(+)CD28(-)T cells and IL-17-producing cells in the infused group (r = -0.539, P = 0.04). The mean levels and the frequency of microchimerism within the first post-transplantation year were also significantly higher in infused patients than in controls (P = 0.007 and P = 0.001, respectively).

CONCLUSION

Our findings suggest that DBMC infusion could partially stimulate the regulatory mechanisms against alloimmune responses in kidney allograft recipients

Different regulatory and cytotoxic CD4+ T lymphocyte profiles in renal transplants with antibody-mediated chronic rejection or long-term good graft function

Comparative analysis of the different subsets of CD4(+) T-lymphocytes may provide hints on the immunologic mechanisms operating in the long-term fate of a kidney transplant. We analyzed peripheral regulatory CD4(+) T cells (Tregs) and CD4(+) cytotoxic T lymphocytes (CTLs) in antibody-mediated chronic rejection (AMCR), in middle-term kidney transplants (2-4 years, MTKT) with good graft function and rejection-free history, in long-term kidney transplants (>15 years, LTKT) and in normal healthy subjects (NHS). Transplant groups with good prognosis (MTKT and LTKT) displayed a significant lower amount of CD4(+)CD25(high) T lymphocytes than NHS, with a trend of a higher percentage in AMCR than in MTKT and LTKT. However, CD4(+)CD25(high) Foxp3(+) cells were significantly higher in LTKT and MTKT than AMCR. Characterization of CD4(+)CD25(high) T cells showed a marked increase of intracellular CTLA-4 in the AMCR group in respect to the other transplant groups, while the expression of the surface molecule seemed to follow a reverse trend. In addition, CD27, a costimulatory receptor involved in long-term T cell survival and prevention of immune tolerance, is significantly reduced in CD4(+)CD25(high) and CD4(+)Foxp3(+) T cells in the LTKT in respect to the other transplant groups. CD4(+)CD25(high)CD45RO(+) and CD4(+)Foxp3(+)CD45RO(+) regulatory T cells with memory function were increased in LTKT compared to NHS and for the latter also in AMCR group. Finally, CD4(+)CTLs that were quantified on the basis of granzyme A expression, were more represented in AMCR patients in comparison to the other groups. Strikingly, CD27 in the CD4(+)CTLs was suppressed in LTKT and MTKT and markedly expressed in AMCR group. No significant differences in the expression of CD28 were observed among different groups. In conclusion, different profiles of Tregs and CD4(+)CTL populations correlate with different long-term conditions of kidney-transplanted patients, suggesting their role in the development of immunologic events in kidney transplantation.

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.

Dendritic cell generation and CD4+ CD25high FOXP3+ regulatory t cells in human head and neck carcinoma during radio-chemotherapy

Background

Regulatory T cells (Treg) and dendritic cells (DC) play an important role in tumor immunity and immune escape. However, their interplay and the effects of anti-cancer therapy on the human immune system are largely unknown.

Methods

For DC generation, CD14⁺ monocytes were enriched by immunomagnetic selection from peripheral blood of advanced head and neck squamous cell carcinoma (HNSCC) patients and differentiated into immature DC using GM-SCF and IL-4. DC maturation was induced by addition of TNFα. The frequency of CD4⁺CD25^highF0XP3⁺ Treg in HNSCC patients was analyzed before and after radio-chemotherapy (RCT) by four-color flow cytometry.

Results

In HNSCC patients, the frequency of Treg (0.33 ± 0.06%) was significantly (p = 0.001) increased compared to healthy controls (0.11 ± 0.02%), whereas RCT had variable effects on the Treg frequency inducing its increase in some patients and decrease in others. After six days in culture, monocytes of all patients had differentiated into immature DC. However, DC maturation indicated by CD83 up-regulation (70.7 ± 5.5%) was successful only in a subgroup of patients and correlated well with lower frequencies of peripheral blood Treg in those patients.

Conclusion

The frequency of regulatory T cells is elevated in HNSCC patients and may be modulated by RCT. Monocyte-derived DC in HNSCC patients show a maturation deficiency ex vivo. Those preliminary data may have an impact on multimodality clinical trials integrating cellular immune modulation in patients with advanced HNSCC.

CD4+CD25+CD127dimFoxp3+ T cells are cytotoxic for human neurons

MS lesions are characterized by destruction of myelin and significant neuronal and axonal loss. Preliminary studies with the use of T(regs) in the mouse model of MS have been extremely encouraging. However, recent studies with human cells have shown the presence of different subpopulations of T cells within the CD4(+)CD25(+)Foxp3(+) T cell phenotype, some of which do not have regulatory functions. These findings suggest a potential difference between mouse and human in the regulatory phenotype. Here, we show that human activated CD4(+)CD25(+)Foxp3(+) T cells are neurotoxic in vitro. These cells expressed high levels of the cytotoxic molecule GrB and had no suppressive effect. On the contrary, they produced IFN-γ and low IL-17, suggesting a shift toward a T(H)1 phenotype. Thus, our data confirm the presence of a nonregulatory cytotoxic subpopulation within the human CD4(+)CD25(+)Foxp3(+) T cells and suggest further studies on the human regulatory phenotype prior to any potential therapeutic application.

Decreased percentage of CD4+FoxP3+ cells in bronchoalveolar lavage from lung transplant recipients correlates with development of bronchiolitis obliterans syndrome

BACKGROUND

Lung transplantation, in patients with end-stage lung disease, is limited by chronic rejection, which occurs with an incidence and severity exceeding most other transplanted organs. Alloimmune responses play an important role in progression to chronic rejection that manifests as bronchiolitis obliterans syndrome (BOS), but no biomarker can currently predict the progression to BOS. Studies in animal models suggest that intragraft T regulatory cells (Tregs) are important in maintaining transplantation tolerance, and FoxP3 is the protoypic Treg marker.

METHODS

Leukocytes in blood and bronchoalveolar lavage (BAL) fluid were compared for expression of FoxP3 by flow cytometry in 14 stable lung transplant recipients and 6 lung transplant recipients who eventually developed BOS.

RESULTS

Stable patients, compared with patients who subsequently developed BOS, consistently had a significantly increased percentage of FoxP3 cells among CD4 cells in BAL and greater levels of the Treg-attracting chemokine CCL22. These differences were observed in limited sequential analyses, before, at the time of acute rejection, and postacute rejection. In this pilot study, a threshold of 3.2% CD4/FoxP3 cells in the BAL distinguished stable recipients from those subsequently developing BOS within the first 2 years posttransplantation.

CONCLUSION

The proportion of FoxP3 cells among CD4 cells in BAL may help to predict lung allograft outcome and guide therapeutic immunosuppression in lung transplant recipients.

Potential T regulatory cell therapy in transplantation: how far have we come and how far can we go?

Summary Graft survival has been lately improved by the introduction of efficient immunosuppressive drugs. However, late graft loss caused by chronic rejection and the side effects of long-term immunosuppression remain major obstacles for successful transplantation. Operational tolerance, which is defined by the lack of acute and chronic rejection and indefinite graft survival with normal graft function in the absence of continuous immunosuppression, represents an attractive alternative. Nevertheless, tolerance after allogeneic transplantation is commonly considered the 'mission impossible' for both immunologists and clinicians. One of the mechanisms involved in tolerance is the suppression of graft-specific alloreactive T cells, which largely mediate graft rejection, by regulatory T cells (Tregs) or by soluble factors produced by Treg cells. With this review, I will make an effort to collect and describe the significant studies performed in transplanted patients, and not in animal models or in in vitro systems, with the attempt to: (i) understand how tolerance is achieved, (ii) define whether and how Treg cells influence transplant tolerance, (iii) describe the first clinical trials with Treg cells in humans (i.e. how far have we come) and (iv) predict the future of Treg cell-based therapy in humans (i.e. how far can we go).

Regulatory T cells in alloreactivity after clinical heart transplantation

PURPOSE OF REVIEW

As the knowledge of CD4+CD25bright+FoxP3+ regulatory T cells in experimental transplant models grows, we need to understand how and to what extent these suppressor cells regulate donor-directed immune events in the transplantation clinic. This review focuses on the function of regulatory T cells in the peripheral blood and the transplanted organ of patients after heart transplantation during immunological quiescence and rejection.

RECENT FINDINGS

Here, we present data that peripheral CD4+CD25bright+FoxP3+ T cells of heart transplant patients who experience acute rejection have inadequate immune regulatory function in vitro compared with those of nonrejecting patients. During rejection, potent donor-specific T-cell suppressors are present in the transplanted organ.

SUMMARY

The studies in transplant patients' show that the function of CD4+CD25bright+FoxP3+ regulatory T cells in alloimmunity is to inhibit the activation of effector T cells, to prevent rejection, and to control the antidonor response at the graft itself at later stages of immune reactivity.

Regulatory T cells in kidney allograft infiltrates correlate with initial inflammation and graft function

BACKGROUND

The relevance of borderline change (BL) and subclinical cellular rejection (SCR) observed in renal transplantation remains to be determined. Several studies have shown in BL and SCR the presence of a Th1 immune response, qualitatively similar to but quantitatively reduced in comparison with infiltrates typical of acute cellular rejection (ACR).

METHODS

To elucidate the role of regulatory T cells (Tregs) in the local control of the allogenic response, we studied their presence by immunohistochemistry in 24 biopsies with graft dysfunction (12 ACR and 12 BL) and in 16 protocol biopsies at 1 year (eight SCR and eight subclinical BL).

RESULTS

The proportion of Tregs in CD4 T infiltrates was higher in BL and SCR when compared with ACR. Moreover, their presence was correlated with the intensity of interstitial inflammation (r=-0.35, P=0.027, n=40) and with graft function at the time of the biopsy (r=-0.37, P=0.018, n=40).

CONCLUSION

These data suggest Treg recruitment at the acute phase of the allogenic response, where they could act to diminish the interstitial inflammation and its associated lesions.

Rituximab treatment of patients with severe, corticosteroid-resistant thyroid-associated ophthalmopathy

PURPOSE

To study the effectiveness of anti-CD20 (rituximab [RTX]; Rituxan; Genentech, Inc., South San Francisco, CA) therapy in patients with severe, corticosteroid (CS)-resistant thyroid-associated ophthalmopathy (TAO).

DESIGN

Retrospective, interventional case series.

PARTICIPANTS

Six consecutive subjects with severe, progressive TAO unresponsive to CS.

METHODS

Electronic medical record review of consecutive patients receiving RTX during the previous 18 months. Responses to therapy were graded using standard clinical assessment and flow cytometric analysis of peripheral lymphocytes.

MAIN OUTCOME MEASURES

Clinical activity score (CAS), proptosis, strabismus, treatment side effects, and quantification of regulatory T cells.

RESULTS

Six patients were studied. Systemic CS failed to alter clinical activity in all patients (mean CAS+/-standard deviation, 5.3+/-1.0 before vs. 5.5+/-0.8 during therapy for 7.5+/-6.4 months; P = 1.0). However, after RTX treatment, CAS improved from 5.5+/-0.8 to 1.3+/-0.5 at 2 months after treatment (P<0.03) and remained quiescent in all patients (CAS, 0.7+/-0.8; P<0.0001) at a mean follow-up of 6.2+/-4.5 months. Vision improved bilaterally in all 4 patients with dysthyroid optic neuropathy (DON). None of the 6 patients experienced disease relapse after RTX infusion, and proptosis remained stable (Hertel measurement, 24+/-3.7 mm before therapy and 23.6+/-3.7 mm after therapy; P = 0.17). The abundance of T regulatory cells, assessed in 1 patient, increased within 1 week of RTX and remained elevated at 18 months of follow-up.

CONCLUSIONS

In progressive, CS-resistant TAO, rapid and sustained resolution of orbital inflammation and DON followed treatment with RTX.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.