Abstract
Renal transplantation remains the ideal renal replacement therapy. The first cadaveric renal transplant in Singapore was performed in July 1970. For cadaveric transplants the graft survival at 1 year is 89%, 5 years is 85% and 10 years is 77%. For living-related donor transplants, the graft survival is 98% at 1 year, 92% at 5 years and 82% at 10 years. Living-related donor transplants have been performed since 1976. We have seen more than four decades of renal transplants in Singapore. From 1970 to 1985, the immunosuppressive regimen consisted of azathioprine and prednisolone. Since 1985, we have introduced cyclosporine A, initially as part of dual therapy with prednisolone and, over the past 20 years, as part of triple therapy which includes prednisolone and low-dose azathioprine (50 mg per day).1,2
Cyclosporine A (CyA) has ameliorated many of the immunological risk factors in renal transplantation. It causes temporary immune paralysis by arresting intracellular activation signals. CyA inhibits the processing and presentation of antigen. It passes through the cell membrane to bind to a unique cytosolic protein, cyclophilin. By altering membrane characteristics and intracellular biochemical events, CyA down-regulates the antigen signal and selectively impedes transcription of the lymphokine genes, inhibiting the release of interleukin-2 (IL-2), interferon-gamma (IFN-γ) and other immune transmitter molecules. In the absence of these growth factors, lymphokine proliferation and differentiation are arrested, and cellular and humoral immune response attenuated.
However, with the use of CyA, preformed cytotoxic antibodies are still important in causing rejection. Living-related donor transplants with full-house human leukocyte antigen (HLA) match on azathioprine and prednisolone fared better than those with one haplotype match, 96% versus 70% graft survival at 5 years. With CyA-based immunosuppression and prednisolone, this difference was not apparent at 5 years (96.6%). With regards to cadaver transplantation on CyA, HLA matching and blood transfusion no longer exerted any difference in graft survival. Overall, for both living-related and cadaver transplants, rejection still remains the leading cause of graft loss, even with CyA. But there are fewer deaths because of decreased usage of pulse therapy with methylprednisolone in treatment of rejection, smaller dosage of prednisolone used in combination with CyA compared to the azathioprine-based immunosuppression and earlier use of monoclonal antibodies like OKT3 and anti-thymocyte globulin (ATG) in acute rejection. 3
With the earlier azathioprine-based immunosuppressive regimen, using a combination of azathioprine and prednisolone, and the later CyA-based regimen, either in combination with prednisolone or with prednisolone and a small dose of azathioprine as triple therapy, only septicaemia and vascular necrosis of the bones, among the various complications, showed a marked decreased incidence. There are fewer patients with diabetes mellitus but this difference has not been significant.
The future of renal transplantation has the greatest potential among the 3 options of end stage renal failure therapy. For the past two decades we have been employing the newer immunosuppressants like FK506, mycophenolic acid (MMF) and sirolimus (rapamycin) and allowing the individual patient variation in transplant regimes best suited to enhance the half-life of the allograft and avoid toxicity of immunosuppressants. Some regimes are already phasing out the use of cyclosporine A and prednisolone. 4
Novel immunosuppressive agents
We have had more than 40 years of experience in the field of renal transplantation. Some 15 years ago, when we analysed the transplant data of the prednisolone/azathioprine Era, we had noted that despite the use of CyA, the long term survival data of patients treated with CyA whether as part of dual immunosuppression therapy using prednisolone and azathioprine or as part of triple therapy, using prednisolone/CyA/azathioprine, the results of long term graft survival were no better than what we achieved in the old days using only prednisolone and azathioprine. For the small group of patients who cannot tolerate azathioprine on prednisolone/azathioprine after about 10 years or so, when they develop thrombocytopenia and necessitate a change from azathioprine to CyA, we have observed that these patients begin to lose their graft after a few years, and many after about 5 years or so had to return to life on dialysis again. Also, for those on Prednisolone/Azathioprine, even when they do develop chronic allograft failure after 15–20 years post transplant, their grafts can still last another 10 years or so before they reach a serum creatinine of about 400–500 μmol, which signals the time to think about restarting dialysis.
We are not alone with this conviction. Whilst some patients may experience a reduction of acute rejection episodes in the first year post transplant, in the longer term this does not translate into longer term graft survival. In the USA, after a mean post-transplant period of 7 years, many grafts start to fail. We believe that many of these graft failures are the result of CNI nephrotoxicity induced by CyA and this believe is also held by others. 5
We should therefore explore the possibilities of newer immunosuppressive agents with less calcineurin-induced (CNI) nephrotoxicity and which offer a promise for long term preservation of renal allograft function. Some of the newer drugs for the future which are now undergoing clinical trials may include voclosporin, sotrastaurin, belatacept, everolimus, alefacept and efaluzimab. 5
Genomics
In this genomic era, it is appropriate to end on a genomic note. In an editorial of Kidney International (KI) entitled “Should kidney donors be genotyped for APOL 1 risk alleles?” by Freedman and Julian, 6 it was reported that kidneys in African-American patients respond differently to hyperglycaemia and systemic hypertension compared to kidneys in European American patients. Kidneys donated by African Americans have shorter survival after transplant, whether transplanted into African-American or non-African-American recipients. African-American recipients have higher likelihoods of prolonged allograft survival when receiving non-African-American deceased donor kidneys. Human and animal studies have shown that hypertension and salt sensitivity travel with transplanted kidneys and impact these phenotypes in recipients. 6
Genovase et al. have reported identification of impressive genetic association between two coding variants in the apolipoprotein L1 gene (APOL1) and a spectrum of nondiabetic nephropathies in individuals with recent African ancestry. 7 This finding is a striking example where a variation in a single gene is associated with pronounced risk for a complex disease. The two nephropathy-risk genes include G1, a non-synonymous coding variant, and G2, a 6 base pair deletion. Possession of two APOL1 nephropathy risk variants (G1/G1, G1/G2 or G2/G2) is markedly associated with increased risk for progressive chronic kidney disease due to focal segmental glomerulosclerosis (FSGS)
Individuals of European, Asian and Hispanic origin descent virtually lack APOL1 G1 and G2 nephropathy risk alleles. It has been suggested in this editorial that rapid genotyping of deceased African-American kidney donors is coming of age. In an era of precision medicine, rapidly performed PCR for viral infections (hepatitis B, hepatitis C and HIV) is now standard for deceased organ donors. The authors suggest that PCR based genotyping for APOL1 G1 and G2 risk variants in deceased donors with African ancestry should be implemented. 7
Graft tolerance
In a recent issue of KI, Baron et al. reported a common gene signature across multiple studies which relate biomarkers and functional regulation of tolerance in renal allografts. 8 As practicing nephrologists we all have patients with kidney transplants who for various reasons have stopped taking their transplant immunosuppressive (IS) medication. Many would end up with graft rejection but in a few, surprisingly, despite stopping the IS, their renal function remained stable.
It is presumed that patients who have developed renal graft tolerance would share specific blood cell transcriptional pattern, but five different studies on tolerance had produced transcriptional pattern that were inconsistent. 8 So the authors for this article decided to perform a meta-analysis on these five studies, 8 in an attempt to identify a common gene signature which could characterise graft tolerance.
The meta-analyses of these five studies identified a robust gene signature involving proliferation of B and CD4 T cells and inhibition of CD 14 monocyte related functions among 96 tolerant samples. The top 20 genes involved which were differentially expressed in tolerant (TOL) patients in the whole meta-analyses were identified.
They compared these with markers from patients with chronic rejection and found that these patients had a markedly different profile from the TOL patients.
Finally, to validate the gene signature they performed a full cross validation procedure. This analysis yielded good predictions and enabled the validation of B cell related markers. In the next step, these 20 markers were revalidated in an independent cohort of new TOL samples. The analysis yielded good prediction performances (91.7%). Hence the authors concluded that these 20 biomarkers could be used reliably to detect tolerance and stratify kidney recipients in clinics.
Footnotes
Conflict of interest
The authors declare that there are no conflicts of interest.
Funding
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.