Harnessing regulatory T cells for transplant tolerance in the clinic through mTOR inhibition: myth or reality?

Different Patterns of Foxp3 Gene Expression in Pre-and Post-Transplantation Kidney Biopsies and the Effect of Use Mammalian Target of Rapamycin Inhibitors

BACKGROUND

Trafficking of regulatory T cells (Tregs) modulates the inflammatory response after kidney transplantation (KTx). There is scarce information on whether circulating and intragraft Tregs are similarly affected by immunosuppressive drugs and the type of deceased kidney donor.

METHODS

FOXP3 gene expression was measured in the pretransplant kidney biopsies (PIBx) from donors who met extended (ECD) and standard (SCD) criteria donors. In the third month after KTx, the patients were divided according to tacrolimus (Tac) or everolimus (Eve) and the type of kidney they had received. FOXP3 gene expression in the peripheral blood (PB) and kidney biopsies (Bx) was analyzed using real-time polymerase chain reaction.

RESULTS

FOXP3 gene expression in the PIBx was higher in ECD kidneys. FOXP3 gene expression in the PB and Bx was greater in Eve- than in Tac-treated patients. However, SCD recipients treated with Eve (SCD/Eve) had higher FOXP3 expression than ECD/Eve.

CONCLUSION

Pretransplant kidney biopsies from ECD kidneys had higher FOXP3 gene expression than SCD, and the use of Eve may affect the expression of the FOXP3 gene only in SCD kidneys.

The number of FoxP3 regulatory T cells in the circulation may be a predictive biomarker for kidney transplant recipients: A multistage systematic review

BACKGROUND

The kinetics of the FoxP3 regulatory T-cell (Treg) population in kidney transplant recipients (KTR) are related to the clinical effect of immunosuppression based on mammalian Target Of Rapamycin inhibitors (mTORi) with/without belatacept (predictive biomarker).

METHODS

A multistage systematic review of published and unpublished literature is presented [registration IDs in the International Prospective Register of Systematic Reviews (PROSPERO): CRD42017057570, CRD42018085019, CRD42018084941, CRD42018085186]. A multidisciplinary supervision mechanism for contextualizing of search findings was required. The peripheral blood immune cell phenotypes encompassing all regulatory cells in KTRs were assessed in order to suggest new markers of acute rejection-associated acute allograft dysfunction (AR/AAD) events in KTRs treated with mTORi alone or combined to belatacept. Quantitative estimates and evaluation of the body of evidence are provided.

RESULTS

An increase in Tregs and other regulatory cell types in the circulation in KTRs under mTORi with/without belatacept were observed. Patients with increased Tregs presented a low frequency of AR/AAD events compared to those in which the number of Tregs remained unchanged or even diminished [Odds Ratio (OR)/95% confidence interval (95% CI)/I²/number of studies (n): 0.31/0.10-0.93/0%/6]. Nevertheless, there are too few trials to consider Tregs in the circulation as a predictive biomarker. Inadequate reporting prevents appreciating clinical relevance in such studies.

CONCLUSIONS

Despite advances, clinical qualification of potential predictive biomarkers continues to be difficult. Clinical evidence on Tregs in KTRs needs to be enlarged. Biomarkers should be able to evaluate the effect of medicines targeted to specific patient populations.

Mechanisms of Mixed Chimerism-Based Transplant Tolerance

Immune responses to allografts represent a major barrier in organ transplantation. Immune tolerance to avoid chronic immunosuppression is a critical goal in the field, recently achieved in the clinic by combining bone marrow transplantation (BMT) with kidney transplantation following non-myeloablative conditioning. At high levels of chimerism such protocols can permit central deletional tolerance, but with a significant risk of graft-versus-host (GVH) disease (GVHD). By contrast, transient chimerism-based tolerance is devoid of GVHD risk and appears to initially depend on regulatory T cells (Tregs) followed by gradual, presumably peripheral, clonal deletion of donor-reactive T cells. Here we review recent mechanistic insights into tolerance and the development of more robust and safer protocols for tolerance induction that will be guided by innovative immune monitoring tools.

Mammalian-target of rapamycin inhibition with temsirolimus in myelodysplastic syndromes (MDS) patients is associated with considerable toxicity: results of the temsirolimus pilot trial by the German MDS Study Group (D-MDS)

The mammalian-target of rapamycin (also termed mechanistic target of rapamycin, mTOR) pathway integrates various pro-proliferative and anti-apoptotic stimuli and is involved in regulatory T-cell (TREG) development. As these processes contribute to the pathogenesis of myelodysplastic syndromes (MDS), we hypothesized that mTOR modulation with temsirolimus (TEM) might show activity in MDS. This prospective multicentre trial enrolled lower and higher risk MDS patients, provided that they were transfusion-dependent/neutropenic or relapsed/refractory to 5-azacitidine, respectively. All patients received TEM at a weekly dose of 25 mg. Of the 9 lower- and 11 higher-risk patients included, only 4 (20%) reached the response assessment after 4 months of treatment and showed stable disease without haematological improvement. The remaining patients discontinued TEM prematurely due to adverse events. Median overall survival (OS) was not reached in the lower-risk group and 296 days in the higher-risk group. We observed a significant decline of bone marrow (BM) vascularisation (P = 0·006) but were unable to demonstrate a significant impact of TEM on the balance between TREG and pro-inflammatory T-helper-cell subsets within the peripheral blood or BM. We conclude that mTOR-modulation with TEM at a dose of 25 mg per week is accompanied by considerable toxicity and has no beneficial effects in elderly MDS patients.

Expression of Treg subsets on intestinal T cell immunity and endotoxin translocation in porcine sepsis after severe burns

In the present study, the changes of the regulatory T cells (Treg) expression, endotoxin translocation, and the relationships in intestinal lymph nodes were investigated in porcine sepsis induced by severe burns. Flow cytometry, western blot, and Tachypleus amebocyte lysate were applied to study after the burn injury model was built. We found that the upregulated Treg expression was negatively related to the CD3(+)CD4(+)/CD3(+)CD8(+) ratio (r = -0.832, P < 0.05) after burn injury-induced sepsis. While Treg expression and portal venous plasma endotoxin translocation levels were positively correlated (r = 0.876, P < 0.05) when compared with the control group. Moreover, we detected a transforming of T cell subsets from T helper 1 cells to T helper 2 cells. Therefore, intestinal Treg cells expression exerts immunosuppressive effects on other intestinal T lymphocytes and was closely related to endotoxin translocation in porcine sepsis after severe burns injuries. Above all, the intestinal Treg cells may play an important role in the intestinal immune barrier system after severe burns injuries.

T-cell energy metabolism as a controller of cell fate in transplantation

PURPOSE OF REVIEW

To highlight some of the recent developments in the novel field of immunometabolism and the therapeutic potential of the many regulatory components of this immunometabolic network for transplantation.

RECENT FINDINGS

In response to cytokines, changes in nutrients, and other alterations in the local milieu, immune cells are capable of changing their internal metabolic pathways to meet their energy demands. Recent studies demonstrate that activated T effectors (Th1 and Th17) are supported by aerobic glycolysis, whereas regulatory T cells and CD8 memory T cells favor fatty acid oxidation and lipid biosynthesis through mitochondrial oxidative phosphorylation. These bioenergetic processes are dependent upon the activation of metabolic sensors such as mammalian target of rapamycin and AMP-activated protein kinase, respectively, indicating that the cross-talk between immunity and metabolism can shape the fate and function of immune cells. Finally, exciting new studies suggest that differences in the bioenergetic mechanisms within the various immune subsets may selectively be exploited for regulating the immune responses.

SUMMARY

In this review, we will discuss the metabolic signatures adopted by various immune cells during tolerance versus immunity and the promising avenues that can be modulated by targeting metabolic pathways with either nutrition or pharmacological intervention for establishing long-term transplantation tolerance.

Prognostic significance of graft Foxp3 expression in renal transplant recipients: a critical review and attempt to reconcile discrepancies

A large body of evidence has been accumulated from experimental models in the past decade to support the critical role of Foxp3-expressing regulatory T cells (Tregs) in the suppression of alloimmune responses. This has prompted transplant clinicians to investigate whether Foxp3 analysis might be used as an immunodiagnostic tool for better assessment of the significance of graft infiltrate and to predict its impact on graft outcome. However, conflicting results have emerged from these studies and may have generated more confusion than clarification. Foxp3 expression has been antagonistically correlated with either good or poor prognosis. We discuss here how methodological issues and specific clinical settings may have accounted for the discrepancies between the results of these studies. Depending on many factors, including the techniques used, the method of sampling normalization, the extent of intra-graft inflammation, the immunosuppressive regimen and the depletion or repletion of T lymphocyte compartment, the significance of Foxp3 expression may vary. We propose here the conditions to be fulfilled in order to use Foxp3 analysis as a relevant biomarker for graft outcome assessment. Far from challenging the key role of Tregs in dampening alloimmune responses, this review highlights the need for technical harmonization and standards.

Does the PI3K pathway promote or antagonize regulatory T cell development and function?

Regulatory T cells (Tregs) prevent autoimmunity and inflammation by suppressing the activation of other T cells and antigen presenting cells. The role of phosphoinositide 3-kinase (PI3K) signaling in Treg is controversial. Some studies suggest that inhibition of the PI3K pathway is essential for the development of Tregs whereas other studies have shown reduced Treg numbers and function when PI3K activity is suppressed. Here we attempt to reconcile the different studies that have explored PI3K and the downstream effectors Akt, Foxo, and mTOR in regulatory T cell development and function and discuss the implications for health and therapeutic intervention.

The Role of the PI3K Signaling Pathway in CD4(+) T Cell Differentiation and Function

The relative activity of regulatory versus conventional CD4(+) T cells ultimately maintains the delicate balance between immune tolerance and inflammation. At the molecular level, the activity of phosphatidylinositol 3-kinase (PI3K) and its downstream positive and negative regulators has a major role in controlling the balance between immune regulation and activation of different subsets of effector CD4(+) T cells. In contrast to effector T cells which require activation of the PI3K to differentiate and mediate their effector function, regulatory T cells rely on minimal activation of this pathway to develop and maintain their characteristic phenotype, function, and metabolic state. In this review, we discuss the role of the PI3K signaling pathway in CD4(+) T cell differentiation and function, and focus on how modulation of this pathway in T cells can alter the outcome of an immune response, ultimately tipping the balance between tolerance and inflammation.

Immunity and tolerance to fungi in hematopoietic transplantation: principles and perspectives

Resistance and tolerance are two complementary host defense mechanisms that increase fitness in response to low-virulence fungi. Resistance is meant to reduce pathogen burden during infection through innate and adaptive immune mechanisms, whereas tolerance mitigates the substantial cost of resistance to host fitness through a multitude of anti-inflammatory mechanisms, including immunological tolerance. In experimental fungal infections, both defense mechanisms are activated through the delicate equilibrium between Th1/Th17 cells, which provide antifungal resistance, and regulatory T cells limiting the consequences of the ensuing inflammatory pathology. Indoleamine 2,3-dioxygenase (IDO), a rate-limiting enzyme in the tryptophan catabolism, plays a key role in induction of tolerance against fungi. Both hematopoietic and non-hematopoietic compartments contribute to the resistance/tolerance balance against Aspergillus fumigatus via the involvement of selected innate receptors converging on IDO. Several genetic polymorphisms in pattern recognition receptors influence resistance and tolerance to fungal infections in human hematopoietic transplantation. Thus, tolerance mechanisms may be exploited for novel diagnostics and therapeutics against fungal infections and diseases.