Title: Author(s): Source: Document Type: DOI: Copyright:

Is urine mRNA analysis a useful tool in the detection of acute rejection? Uwe Heemann Expert Review of Clinical Immunology. 9.11 (Nov. 2013): p1011. Report http://dx.doi.org/10.1586/1744666X.2013.850417 COPYRIGHT 2013 Expert Reviews Ltd. http://www.expert-reviews.com/loi/eci

Full Text: Author(s): Uwe Heemann 1 Keywords : acute rejection; kidney biopsy; kidney transplantation; mRNA; urine analysis Over the last decades, improvements of the immunosuppressive regimen following kidney transplantation were causative for a major drop in the rate of acute rejection and thus graft loss. Nonetheless, even nowadays a substantial number of grafts is lost or at least affected by acute rejection episodes. These rejections primarily occur during the first year after transplantation. From the perspective of a clinician, a timely diagnostic would be advisable which would preferentially be noninvasive. Currently, a rejection is diagnosed based on a rise in creatinine followed by a biopsy, the gold standard of diagnostics. This concept has some limitations. First of all, a rise in creatinine is rather late and also depends on the quality of the donated organ. If the transplanted organ has a very good quality with a lot of glomerular function units, a rise of creatinine will occur only after a substantial damage to the kidney. In a poor quality kidney with few glomerular function units, a rise in creatinine will be observed after a mild damage. The biopsy will thus come after the damage and the timing depends on the initial quality of the kidney as well as on the awareness of the physician. Furthermore, although a lot of energy has been put into the classification of renal biopsies after transplantation, there is still room for interpretation so that the same biopsy may result in different results. Last but not least, any invasive procedure such as a renal biopsy may cause some injuries or side effects which may hamper the kidney. Therefore, a number of noninvasive measures have been undertaken to circumvent the necessity of a renal biopsy and come to the diagnosis of acute rejection earlier than based on creatinine. Various trials have been reported on markers in serum or urine which were able to detect acute rejection early [1-3] . However, almost all were single-center studies which were never repeated or could not be verified in other settings. Furthermore, it is one thing to correlate results of some laboratory testings with the results of renal biopsies retrospectively and another ballpark to predict based on laboratory testings the result of a renal biopsy. Suthanthiran et al . [4] did a wonderful job in performing a multicenter study on the value of mRNA profiling of urine samples after transplantation. They not only distinguished between rejection and no rejection but also between types of rejection and urinary tract infection. Methods & results Suthanthiran et al . prospectively collected 4300 urine specimens from 485 kidney-graft recipients from day 3 through month 12 after transplantation. mRNA levels were measured in urinary cells and correlated with allograft-rejection status with the use of logistic regression. A three-gene signature of 18S ribosomal (rRNA)-normalized measures of CD3ε mRNA and interferon-inducible protein 10 (IP-10) mRNA, and 18S rRNA discriminated between biopsy specimens showing acute cellular rejection and those not showing rejection (area under the curve (AUC): 0.85; 95% CI: 0.78-0.91; p < 0.001 by receiver-operatingcharacteristic curve analysis). The cross-validation estimate of the AUC was 0.83 by bootstrap resampling, and the

Hosmer-Lemeshow test indicated good fit (p = 0.77). In an external-validation data set, the AUC was 0.74 (95% CI: 0.61-0.86; p < 0.001) and did not differ significantly from the AUC in our primary data set (p = 0.13). The signature distinguished acute cellular rejection from acute antibody-mediated rejection and borderline rejection (AUC: 0.78; 95% CI: 0.68-0.89; p < 0.001). It also distinguished patients who received anti-IL-2 receptor antibodies from those who received T-cell-depleting antibodies (p < 0.001) and was diagnostic of acute cellular rejection in both groups. Urinary tract infection did not affect the signature (p = 0.69). The average trajectory of the signature in repeated urine samples remained below the diagnostic threshold for acute cellular rejection in the group of patients with no rejection, but in the group with rejection, there was a sharp rise during the weeks before the biopsy showing rejection (p < 0.001). Discussion The results of Suthanthiran et al . are based on more than 4000 urine samples and the analysis was performed centralized and in a blinded fashion. This was the first study which used mRNA evaluation on a broad scale to investigate acute rejection. A second similar study investigating urinary mRNA in pediatric transplant recipients has just been published which suggests CXCL9 as a risk marker [5] . An important benefit of the urinary mRNA analysis used in the study of Suthathiran et al . is the independence of actual kidney function. Obviously, urine production is based on kidney function and, thus, the concentration of cells, and mRNA, correlates to urine production, but as creatinine is a very late marker mRNA analysis is certainly more reliable. Based on this method, it should be possible to detect acute rejection earlier than based on creatinine alone. However, this assumption has not been tested in the present study and the study has somewhat more limitations. Only a small number of biopsies (n = 50) were obtained on which the statistical analysis was based. Furthermore, the results of the RNA analysis were correlated on the results of the biopsies and the biopsies were not interpreted by an independent central pathologist in a blinded fashion. A central pathologist would have been advisable as a biopsy can be interpreted in different ways. Although the BANFF classification helped a lot to standardize the interpretation, and a biopsy is a gold standard, it is humans who do the analysis. Thus, at present there is still a lot of room for subtle but clinically relevant differences in the analysis of the same sample. Although the authors claim to be able to distinguish between types of rejection and urinary tract infection, this assumption is based on a very limited number of biopsies. Thirteen were diagnosed as antibody-mediated rejection, 27 as borderline and 9 as 'other findings' which includes urinary tract infections. One biopsy was not clearly stated in the manuscript. In a similar fashion, Wilflingseder et al . investigated biopsies with various forms of rejection and correlated urinary mRNA results to these forms [6] . They also observed a striking correlation. However, whether these claims of precise correlation hold true in the real world need at least a higher number of biopsies with urinary tract infections or samples in the presence of such infections. Another surprise is the low number of rejections in the evaluated biopsies. Four hundred and ten biopsies were collected, among them 89 protocol or surveillance biopsies. However, although 321 were performed because of clinical signs of rejection (in most cases a rise in creatinine), 199 revealed no signs of clinical rejection or other pathological signs. This is more than surprising as in most other studies, particularly those of immunosuppressives, the rate of rejection in biopsies if driven by clinical signs of rejection is more than 50% [7-9] . Even in studies of protocol biopsies this rate is usually much lower. In order to prove the validity of the concept, it is needed to test the algorithm suggested in a prospective fashion. In other words, only if the algorithm predicts the biopsy it is safe to assume that the algorithm is worthwhile pursuing. Until this study has been successfully undertaken, this is just another although very intriguing report on post hoc urinary data statistics. Expert commentary

Urine analysis of mRNA or microRNA will certainly be of high importance in the future. However, at present there is a need for prospective large scale trials in order to identify the proper targets. Five-year view Suthathiran et al . used urine testing to predict acute rejection and circumvent the need for a biopsy. At present, this method is very cumbersome as the samples have to be specifically prepared, sent to a certain laboratory and then evaluated. However, it is reasonable to assume that such an analysis can be performed in a laboratory in charge of the evaluation of transplant recipients. It is even thinkable that such a test can be performed by the patient himself. If it would be possible to use such a test as a screening test performed by the patient, the detection of acute rejection would be not only easier but also faster. This would certainly extend graft survival remarkably. At present, the costs of mRNA analysis are rather high making this method a scientific tool rather a standard routine. However, once we know exactly which gene products are important for the prediction of acute rejection, it is very well imaginable to assume that the costs will shrink remarkably, particularly if this method is applied on a large scale. Another option which may be even easier would be the analysis of proteomics in the urine. A recently published pilot study indicated that this approach may also have some merits [10] . In summary, it is more than likely that urinary tests for acute rejection will become available which can be handled by the transplant recipient himself. References 1 Chatterjee P , Mathur SR , Dinda AK et al. Analysis of urine sediment for cytology and antigen expression in acute renal allograft rejection: an alternative to renal biopsy . Am. J. Clin. Pathol . 137 ( 5 ), 816 - 824 ( 2012 ). 2 Kohei J , Ishida H , Kazunari et al. Neutrophil gelatinase-associated lipocalin is a sensitive biomarker for the early diagnosis of acute rejection after living-donor kidney transplantation . Int. Urol. Nephrol . 45 ( 4 ), 1159 - 1167 ( 2013 ). 3 Heyne N , Kemmner S , Schneider C et al. Urinary neutrophil gelatinase-associated lipocalin accurately detects acute allograft rejection among other causes of acute kidney injury in renal allograft recipients . Transplantation 93 ( 12 ), 1252 - 1257 ( 2012 ). 4 Suthanthiran M , Schwartz JE , Ding R et al. Urinary-cell mRNA profile and acute cellular rejection in kidney allografts . N. Engl. J. Med . 369 ( 1 ), 20 - 31 ( 2013). 5 Hricik DE , Nickerson P , Formica RN et al. Multicenter Validation of Urinary CXCL9 as a Risk-Stratifying Biomarker for Kidney Transplant Injury . Am. J. Transplant . 13 ( 10 ), 2634 - 2644 ( 2013 ). 6 Wilflingseder J , Regele H , Perco P et al. miRNA profiling discriminates types of rejection and injury in human renal allografts . Transplantation 95 ( 6 ), 835 - 841 ( 2013 ). 7 Aoun B , Decramer S , Vitkevic R et al. Protocol biopsies in pediatric renal transplant recipients on cyclosporine versus tacrolimus-based immunosuppression . Pediatr. Nephrol . 28 ( 3 ), 493 - 498 ( 2013 ). 8 Flechner SM , Gurkan A , Hartmann A et al. A randomized, open-label study of sirolimus versus cyclosporine in primary de novo renal allograft recipients . Transplantation 95 ( 10 ), 1233 - 1241 ( 2013 ). 9 Gaber AO , Moore LW , Alloway RR et al. Acute rejection characteristics from a prospective, randomized, doubleblind, placebo-controlled multicenter trial of early corticosteroid withdrawal . Transplantation 95 ( 4 ), 573 - 579 ( 2013 ). 10 Loftheim H , Midtvedt K , Hartmann A et al. Urinary proteomic shotgun approach for identification of potential acute rejection biomarkers in renal transplant recipients . Transplant. Res . 1 ( 1 ), 9 ( 2012 ).

Source Citation (MLA 7th Edition) Heemann, Uwe. "Is urine mRNA analysis a useful tool in the detection of acute rejection?" Expert Review of Clinical Immunology 9.11 (2013): 1011+. Expanded Academic ASAP. Web. 16 May 2014.

Uwe Heemann

No writing assistance was utilized in the production of this manuscript.

The author has no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending or royalties.

Financial & competing interests disclosure

[email protected]

Author Note(s):

1 Nephrology Department, Technical University Munich, Munich, Germany

Author Affiliation(s):

Is urine mRNA analysis a useful tool in the detection of acute rejection?

Suthanthiran et al. have correlated the mRNA of more than 4000 urine samples in a blinded fashion with the result of kidney biopsies after transplanta...
95KB Sizes 0 Downloads 0 Views