Clinical Operational Tolerance After Kidney Transplantation: A Short Literature Review

Clinical Operational Tolerance and Immunosuppression Minimization in Kidney Transplantation: Where Do We Stand?

BACKGROUND

The 20th century represents a breakthrough in the transplantation era, since the first kidney transplantation between identical twins was performed. This was the first case of tolerance, since the recipient did not need immunosuppression. However, as transplantation became possible, an immunosuppression-free status became the ultimate goal, since the first tolerance case was a clear exception from the hard reality nowadays represented by rejection.

METHODS

A plethora of studies was described over the past decades to understand the molecular mechanisms responsible for rejection. This review focuses on the most relevant studies found in the literature where renal tolerance cases are claimed. Contrasting, and at the same time, encouraging outcomes are herein discussed and a glimpse on the main renal biomarkers analyzed in this field is provided.

RESULTS

The activation of the immune system has been shown to play a central role in organ failure, but also it seems to induce a tolerance status when an allograft is performed, despite tolerance is still rare to register. Although there are still overwhelming challenges to overcome and various immune pathways remain arcane; the immunosuppression minimization might be more attainable than previously believed.

CONCLUSION

. Multiple biomarkers and tolerance mechanisms suspected to be involved in renal transplantation have been investigated to understand their real role, with still no clear answers on the topic. Thus, the actual knowledge provided necessarily leads to more in-depth investigations, although many questions in the past have been answered, there are still many issues on renal tolerance that need to be addressed.

Steroid withdrawal in kidney allograft recipients

This review highlights the aggregate of knowledge obtained from the temporal trend of kidney transplant immune suppression. We will discuss the burden of steroid side effects and their impact on quality of life in kidney allograft recipients, which have led to minimizing steroid exposure. Issues arising since the inception of the concept of steroid withdrawal will be discussed, along with how they have continually led to a shift in research focus on this subject matter. The usefulness of surveillance biopsies and how further elucidation of the pathophysiology of interstitial fibrosis and tubular atrophy could contribute to improving long-term allograft outcomes will also be discussed. We will elaborate on the role of calcineurin inhibitor minimization alongside steroid withdrawal in improving long-term graft survival. Future expectations of subsequent studies with a view to improving overall kidney allograft outcomes by eliminating attendant problems associated with steroids will also be covered.

Allorecognition in the Tasmanian devil (Sarcophilus harrisii), an endangered marsupial species with limited genetic diversity

Tasmanian devils (Sarcophilus harrisii) are on the verge of extinction due to a transmissible cancer, devil facial tumour disease (DFTD). This tumour is an allograft that is transmitted between individuals without immune recognition of the tumour cells. The mechanism to explain this lack of immune recognition and acceptance is not well understood. It has been hypothesized that lack of genetic diversity at the Major Histocompatibility Complex (MHC) allowed the tumour cells to grow in genetically similar hosts without evoking an immune response to alloantigens. We conducted mixed lymphocyte reactions and skin grafts to measure functional MHC diversity in the Tasmanian devil population. The limited MHC diversity was sufficient to produce measurable mixed lymphocyte reactions. There was a wide range of responses, from low or no reaction to relatively strong responses. The highest responses occurred when lymphocytes from devils from the east of Tasmania were mixed with lymphocytes from devils from the west of Tasmania. All of the five successful skin allografts were rejected within 14 days after surgery, even though little or no MHC I and II mismatches were found. Extensive T-cell infiltration characterised the immune rejection. We conclude that Tasmanian devils are capable of allogeneic rejection. Consequently, a lack of functional allorecognition mechanisms in the devil population does not explain the transmission of a contagious cancer.

Differential monocyte STAT6 activation and CD4(+)CD25(+)Foxp3(+) T cells in kidney operational tolerance transplanted individuals

In organ transplantation, the immunosuppression withdrawal leads, in most cases, to rejection. Nonetheless, a special group of patients maintain stable graft function after complete withdrawal of immunosuppression, achieving a state called "operational tolerance." The study of such patients may be important to understand the mechanisms involved in human transplantation tolerance. We compared the profile of CD4(+)CD25(+)Foxp3(+) T cells and the signaling pathways IL-6/STAT3 (signal transducers and activators of transcription) and IL-4/STAT6 in peripheral blood mononuclear cells of four kidney transplant groups: (i) operational tolerance (OT), (ii) chronic allograft nephropathy (CR), (iii) stable graft function under standard immunosuppression (Sta), (iv) stable graft function under low immunosuppression, and (v) healthy individuals. Both CR and Sta displayed lower numbers and percentages of CD4(+)CD25(+)Foxp3(+) T cells compared with all other groups (p < 0.05). The OT patients displayed a reduced activation of the IL-4/STAT6 pathway in monocytes, compared with all other groups (p < 0.05). The lower numbers of CD4(+)CD25(+)Foxp3(+) T cells observed in CR individuals may be a feature of chronic allograft nephropathy. The differential OT signaling profile, with reduced phosphorylation of STAT6, in monocytes' region, suggests that some altered function of STAT6 signaling may be important for the operational tolerance state.