Renal Pathology

Acute Renal Allograft Rejection

Michael Mengel, University of Alberta, Edmonton, Canada


Case History
A 32-years old male patient received in November 1998 his first renal transplant from a diseased donor (35 years, female). Failure of his own kidneys was accounted to IgA nephropathy but never confirmed by biopsy. Prior to transplantation T cell PRA peaked at 17% and B cell PRA at 42%, but at transplantation the patient was PRA and cross match negative. The allograft showed slow initial graft function with a reduction of the serum creatinine between day 0 and day 11 from 800 to 185 µmol/L. Initial immunosuppression comprised Cyclosporine, Steroids, and Sirolimus, no antibody induction therapy was done.


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Clinical Data at Time of Biopsy (Dec 2004, ˜ 6 Years Post Transplant)
Indication for the biopsy was an acute deterioration of renal graft function two weeks before biopsy. The serum creatinine increased from 175 µmol/L to 212 µmol/L. However, the patient was unable to come for biopsy at this time. The serum creatinine dropped without anti-rejection therapy from 212 µmol/L to 163 µmol/L at the day of biopsy. PRAs were negative and no BK in urine was detectable at the day of biopsy. Maintenance immunosuppression comprised Tacrolimus (Tac level: 8.5), Steroids, and MMF (2g/d).

Renal Biopsy
Light microscopic examination of the paraffin-embedded sections stained with, H&E and PAS (both of which were provided to you) demonstrated medulla and renal cortex containing up to 12 glomeruli of which 7 are globally sclerosed. The non-sclerotic glomerular show segmentally a moderate increase in mesangial matrix without cell proliferation. Adjacent to globally scarred glomeruli groups of atrophic tubules with perifocal interstitial fibrosis can be observed. In these IFTA areas partly dense nodular and sometimes more scattered mononuclear infiltrates can be seen. No extensive infiltrates in non scarred area and no tubulitis can be observed. Some of the tubular epithelial cells showed evidence of acute tubular injury. Two medium size muscular arteries demonstrated mild to moderate intimal sclerosis. One partially present large arcuata artery showed moderate intimal sclerosis and few mononuclear cells in the subendothelial space and in the adjacent sclerotic intima with endothelial cells being activated and swollen, representing mild endothelialitis. Arteriolar segments showed segmental hyalinosis.

Material submitted for immunofluorescence microscopy was negative for C4d deposition in peritubular capillaries.

By electron microscopy peritubular capillaries showed a maximum of four layers of their basal membranes but no active capillaritis. No deposits in the glomeruli were observed.

Interpretation and Morphologic Diagnosis

Renal biopsy with acute cellular, vascular rejection (Banff grade IIa).

Banff scores: g0 cg0, i0, ci1, t0, ct1,v1, cv2, ah2, mm2, ptc0, PTCML4, C4d0

Microarray Analysis of the Allograft Biopsy
At the University of Alberta for almost every kidney allograft biopsy for cause a second biopsy core is analyzed by cDNA microarrays as part of a prospective Genome Canada funded study at the Alberta Transplant Applied Genomics Centre (ATAGC). Whole genome expression results are organized as so called Pathogenesis based transcripts sets (PBTs). Pathogenesis Based Transcript sets summarize large groups of related molecules [1, 2, 3, 4, 5, 6, 7]. These gene sets were derived from experimental models and represent a priori defined major biological processes in renal allografts. They include cytotoxic T-cell associated (CATs) [1, 2], interferon-γ (Ifng) induced (GRITs) [4], and injury and repair induced transcripts (IRITs) (5), loss of epithelial transcripts (KTs) [3], and infiltration by B cells (BATs) or plasma cells associated transcripts (IGTs) [8]. Cytotoxic T-cell and interferon-γ associated transcripts correlate with interstitial inflammatory cell scores in human renal allograft biopsies [6], whereas the interstitial inflammatory T cell burden can be assessed by a refined set of quantitative Cytotoxic T-cell Associated Transcripts (QCATs [9] ). By the PBT approach large scale and cumbersome microarray gene expression results can be collapsed into single PBT scores representing a measurement of the respective biological/pathological process in the tissue. Vice versa the PBT annotation of a probeset acts as a rapid way of understanding the biological process represented by changes in that probeset.

Microarray results from this biopsy were within the range of 'non-rejecting' biopsies, i.e. other biopsies showing histologically no signs of acute cellular or humoral rejection.

Follow-up
Since the creatinine came down already at the time point of the biopsy no anti-rejection treatment was initiated. However, due the diagnosis of 'vascular rejection' by pathology the patient was followed closer and the creatinine started to increase again after a relatively short period. A follow-up biopsy was performed 35 days after the initial biopsy. The biopsy showed no further evidence of endothelialitis or signs of tubulo-interstitial or antibody-mediated rejection. In addition to the previous biopsy now few small mesangial IgA deposits were found and thus the diagnosis of recurrent glomerulonephritis was made. Clinically the decision was to continue with the maintenance immunosuppression base don MMF, tacrolimus, and steroids. After the two biopsies the allograft function showed an oscillating course but returned to baseline in the long-term:

BDI Bx crea course

Discussion
Endothelialitis/intimal arteritis was identified as a histological hallmark of allograft rejection right from the beginning [10]. And since then it evolved into a more or less pathogonomic lesion for the diagnosis of acute rejection. According to the current Banff classification a single inflammatory cell under the endothelium of an artery is enough to make the diagnosis of acute rejection, despite the lack of any other histological lesion [11, 12]. Thus without any question the present case fulfills the criteria for acute vascular cellular rejection. However, our cases showed no severe abnormalities on a molecular level and a favorable long-term course without specific treatment.

Analysis of series in the nineties showed that cases with vascular involvement have a worse prognosis compared to those with pure tubule-interstitial rejection [13, 14]. Especially those cases with v3/severe arteritis showing transmural inflammation and/or fibrinoid necrosis are associated with a dismal prognosis [13, 14, 15]. However, these studies were done before C4d staining and thorough testing for antibodies in the patient's serum were part of the diagnostic spectrum. Especially the v3 cases were always suspicious to be antibody associated and thus representing a different entity than the milder Banff v1 and v2 cases. Comparing v1 to v2 cases revealed differences in terms of response to treatment and thus prognosis with v2 having a worse prognosis than the v1 cases [16]. Furthermore, responds to treatment was better when a v1 case showed no or only mild tubulitis than moderate or severe tubulitis. However, cases with mild interstitial infiltrate in addition to arteritis had a worse prognosis that those with moderate interstitial infiltrate. In our own series of 168 biopsies for cause we were able to identify 9 cases with Banff v>0 but i/t<2 and being C4d negative. None of these cases failed or showed by microarray analysis major molecular abnormalities compared to other allograft biopsies with histological signs of tubulo-interstitial rejection. And some of these cases were not even specifically treated (as the presented) at the clinicians discretion. Overall these and other incomplete data suggest that cases with 'isolated' v-lesions, i.e. those with mild to moderate arteritis (Banff grade IIa and IIb) and no or only mild (<i2t2) tubulo-interstitial rejection lesions have a better prognosis than those with combined tubulo-interstitial and vascular rejection.

These observations were discussed at the last Banff meeting in 2007 and a multicentre trial was suggested to investigate isolated v-cases in more detail [12]. Such a study could answer the question whether intimal arteritis observed in renal allografts represents a heterogeneous spectrum of entities lumped together as acute vascular rejection in the current Banff classification.

Reference List
  1. Einecke G, Melk A, Ramassar V, Zhu LF, Bleackley RC, Famulski KS et al. Expression of CTL associated transcripts precedes the development of tubulitis in T-cell mediated kidney graft rejection. Am J Transplant 2005; 5(8):1827-1836.

  2. Einecke G, Mueller T.F., Famulski KS, Ramassar V, Sis B, Halloran PF. Cytotoxic T cells, Interferon gamma and the renal response: Pathogenesis-based transcript sets have high diagnostic value in human kidney allograft rejection. Am J Transplant 2006; 6(s2):65-472.

  3. Einecke G, Broderick G, Sis B, Halloran PF. Early loss of renal transcripts in kidney allografts: relationship to the development of histologic lesions and alloimmune effector mechanisms. Am J Transplant 2007; 7(5):1121-1130.

  4. Famulski KS, Einecke G, Reeve J, Ramassar V, Allanach K, Mueller T et al. Changes in the transcriptome in allograft rejection: IFN-g induced transcripts in mouse kidney allografts. Am J Transplant 2006; 6(6):1342-1354.

  5. Famulski KS, Broderick G, Hay K, Cruz J, Sis B, Mengel M et al. Transcriptome analysis reveals heterogeneity in the injury response of kidney transplants. Am J Transplant 2007; 7(11):2483-2495.

  6. Mueller TF, Einecke G, Reeve J, Sis B, Mengel M, Jhangri.G. et al. Microarray analysis of rejection in human kidney transplants using pathogenesis-based transcript sets. Am J Transplant 2007; 7(12):2712-2722.

  7. Hidalgo LG, Einecke G, Allanach K, Mengel M, Sis B, Mueller TF et al. The transcriptome of human cytotoxic T cells: measuring the burden of CTL-associated transcripts in human kidney transplants. Am J Transplant 2008; 8(3):637-646.

  8. Einecke G, Reeve J, Mengel M, Sis B, Bunnag S, Mueller TF et al. Expression of B cell and immunoglobulin transcripts is a feature of inflammation in late allografts. Am J Transplant 2008; 8(7):1434-1443.

  9. Hidalgo LG, Einecke G, Allanach K, Mengel M, Sis B, Mueller TF et al. The transcriptome of human cytotoxic T cells: measuring the burden of CTL-associated transcripts in human kidney transplants. Am J Transplant 2008; 8(3):637-646.

  10. Dammin GJ. The kidney as a homograft and its host. Med Bull (Ann Arbor) 1960; 26:278-283.

  11. Racusen LC, Solez K, Colvin RB, Bonsib SM, Castro MC, Cavallo T et al. The Banff 97 working classification of renal allograft pathology. Kidney Int 1999; 55(2):713-723.

  12. Solez K, Colvin RB, Racusen LC, Haas M, Sis B, Mengel M et al. Banff 07 classification of renal allograft pathology: updates and future directions. Am J Transplant 2008; 8(4):753-760.

  13. Nickeleit V, Vamvakas EC, Pascual M, Poletti BJ, Colvin RB. The prognostic significance of specific arterial lesions in acute renal allograft rejection. J Am Soc Nephrol 1998; 9(7):1301-1308.

  14. Schroeder TJ, Weiss MA, Smith RD, Stephens GW, First MR. The efficacy of OKT3 in vascular rejection. Transplant 1991; 51:312-315.

  15. Minervini MI, Torbenson M, Scantlebury V, Vivas C, Jordan M, Shapiro R et al. Acute renal allograft rejection with severe tubulitis (Banff 1997 grade IB). Am J Surg Pathol 2000; 24(4):553-558.

  16. Haas M, Kraus ES, Samaniego-Picota M, Racusen LC, Ni W, Eustace JA. Acute renal allograft rejection with intimal arteritis: histologic predictors of response to therapy and graft survival. Kidney Int 2002; 61(4):1516-1526.