Polyoma virus nephropathy with simian virus 40 antigen–containing tubular basement membrane immune complex deposition

BK Polyomavirus Nephropathy in Kidney Transplantation: Balancing Rejection and Infection

BK polyomavirus nephropathy (BKVN) and allograft rejection are two closely-associated diseases on opposite ends of the immune scale in kidney transplant recipients. The principle of balancing the immune system remains the mainstay of therapeutic strategy. While patient outcomes can be improved through screening, risk factors identification, and rapid reduction of immunosuppressants, a lack of standard curative therapy is the primary concern during clinical practice. Additionally, difficulty in pathological differential diagnosis and clinicopathology’s dissociation pose problems for a definite diagnosis. This article discusses the delicate evaluation needed to optimize immunosuppression and reviews recent advances in molecular diagnosis and immunological therapy for BKVN patients. New biomarkers for BKVN diagnosis are under development. For example, measurement of virus-specific T cell level may play a role in steering immunosuppressants. The development of cellular therapy may provide prevention, even a cure, for BKVN, a complex post-transplant complication.

BK polyomavirus in solid organ transplantation-Guidelines from the American Society of Transplantation Infectious Diseases Community of Practice

The present AST-IDCOP guidelines update information on BK polyomavirus (BKPyV) infection, replication, and disease, which impact kidney transplantation (KT), but rarely non-kidney solid organ transplantation (SOT). As pretransplant risk factors in KT donors and recipients presently do not translate into clinically validated measures regarding organ allocation, antiviral prophylaxis, or screening, all KT recipients should be screened for BKPyV-DNAemia monthly until month 9, and then every 3 months until 2 years posttransplant. Extended screening after 2 years may be considered in pediatric KT. Stepwise immunosuppression reduction is recommended for KT patients with plasma BKPyV-DNAemia of >1000 copies/mL sustained for 3 weeks or increasing to >10 000 copies/mL reflecting probable and presumptive BKPyV-associated nephropathy, respectively. Reducing immunosuppression is also the primary intervention for biopsy-proven BKPyV-associated nephropathy. Hence, allograft biopsy is not required for treating BKPyV-DNAemic patients with baseline renal function. Despite virological rationales, proper randomized clinical trials are lacking to generally recommend treatment by switching from tacrolimus to cyclosporine-A, from mycophenolate to mTOR inhibitors or leflunomide or by the adjunct use of intravenous immunoglobulins, leflunomide, or cidofovir. Fluoroquinolones are not recommended for prophylaxis or therapy. Retransplantation after allograft loss due to BKPyV nephropathy can be successful if BKPyV-DNAemia is definitively cleared, independent of failed allograft nephrectomy.

Immune Complex Tubulointerstitial Nephritis Due to Autoantibodies to the Proximal Tubule Brush Border

Immune complex tubulointerstitial nephritis due to antibodies to brush border antigens of the proximal tubule has been demonstrated experimentally and rarely in humans. Our patient developed ESRD and early recurrence after transplantation. IgG and C3 deposits were conspicuous in the tubular basement membrane of proximal tubules, corresponding to deposits observed by electron microscopy. Rare subepithelial deposits were found in the glomeruli. The patient had no evidence of SLE and had normal complement levels. Serum samples from the patient reacted with the brush border of normal human kidney, in contrast with the negative results with 20 control serum samples. Preliminary characterization of the brush border target antigen excluded megalin, CD10, and maltase. We postulate that antibodies to brush border antigens cause direct epithelial injury, accumulate in the tubular basement membrane, and elicit an interstitial inflammatory response.

Diagnosis in Pediatric Transplant Biopsies

Infant recipients have better survival after solid organ transplantation than older children and adults possibly due to immune tolerance. Over the past two decades, postsurgical complications have markedly decreased, and multidrug immunosuppressive regimens have become effective in preventing and treating rejection. Immunocompromised for life, these patients are susceptible to both the usual bacterial as well as opportunistic infections that often involve the lung. Post-transplant lymphoproliferative disease seems to be decreasing even further in frequency. This article focuses on the findings seen on biopsy, usually of the transplanted organ, and also of other sites affected by post-transplant complications.

The significance of renal C4d staining in patients with BK viruria, viremia, and nephropathy

Peritubular capillary C4d staining in allograft kidney is an important criterion for antibody-mediated rejection. Whether BK virus infection can result in complement activation is not known. We studied 113 renal allograft biopsies from 52 recipients with a history of BK virus activation. The samples were classified into four groups according to the concurrent detection of BK virus DNA in urine, plasma, and/or biopsy: BK-negative (n=37), viruria (n=53), viremia (n=7), and nephropathy (n=16) groups. The histological semiquantitative peritubular capillary C4d scores in the viremia (0.3+/-0.8) and BK nephropathy (0.6+/-0.9) groups were lower than those in the BK-negative group (1.2+/-1.1, P=0.05 and P=0.06, respectively) and the viruria group (1.2+/-1.1, P=0.04 and P=0.06, respectively). Diffuse or focal peritubular capillary C4d staining was present in 9/76 (12%) and 14/76 (19%) of all samples with concurrent BK virus reactivation (viruria, viremia, and nephropathy). The diagnosis of antibody-mediated rejection could be established in 7/9 (78%) and 5/14 (36%) of these samples, respectively. Diffuse tubular basement membrane C4d staining was restricted to BK nephropathy cases (4/16, 25%). Semiquantitative tubular basement membrane C4d scores were higher in BK nephropathy (1.2+/-1.3) compared with BK-negative (0.05+/-0.3, P=0.017) and viruria (0.0+/-0.0, P=0.008) groups. Bowman's capsule C4d staining was more frequent in BK nephropathy (5/16) compared with the aforementioned groups (2/36 (P=0.023) and 4/51 (P=0.03), respectively). Within the BK nephropathy group, samples with tubular basement membrane stain had more infected tubular epithelial cells (12.1+/-7.6% vs 4.4+/-5.0%, P=0.03) and a trend toward higher interstitial inflammation scores. In conclusion, peritubular capillary C4d staining remains a valid marker for the diagnosis of antibody-mediated rejection in the presence of concurrent BK virus infection. A subset of biopsies with BK nephropathy shows tubular basement membrane C4d staining, which correlates with marked viral cytopathic effect.

Clinical significance of the distribution of C4d deposits in different anatomic compartments of the allograft kidney

Diffuse C4d deposition in peritubular capillaries is a well-recognized marker of antibody-mediated rejection. The significance of staining patterns that are focal or affect non-peritubular capillary compartments is less well defined. Paired frozen section and paraffin-embedded tissue stains were performed in 52 kidney allograft biopsies, and correlated with clinicopathologic parameters. Diffuse peritubular capillary C4d deposits were more often seen in frozen sections (22/52, 43% frozen tissue vs 10/52, 19% paraffin-embedded tissue), whereas focal staining was observed more frequently within paraffin sections (13/52, 25% paraffin-embedded tissue vs 7/52, 14% frozen tissue). In biopsies taken from patients with a history of donor-specific antibodies, diffuse, focal and negative peritubular capillary C4d staining patterns were seen in 11/14 (79%), 1/14 (7%) and 2/14 (14%) of frozen biopsies vs 5/14 (36%), 6/14 (43%) and 3/14 (21%) of paraffin-embedded biopsies. Transplant glomerulopathy score in paraffin-embedded biopsies was higher in specimens with vs without glomerular basement membrane C4d staining (1.5+/-0.8 vs 1.0+/-0.6, P=0.03). Tubular basement membrane staining was present in 4% paraffin-embedded and 48% frozen specimens independent of tubular atrophy. Arteriolar hyalinosis score in paraffin-embedded specimens was higher in biopsies with vs those without arteriolar C4d deposits (1.3+/-0.9 vs 0.9+/-0.8, P=0.04). Arterial staining was unrelated to the degree of intimal thickening. In conclusion, peritubular capillary deposits correlate well with circulating donor-specific antibody. For paraffin-embedded tissue, combining the results of focal and diffuse staining allows a diagnostic sensitivity comparable to diffuse staining in frozen tissue. Finally, C4d deposits preferentially in lesions of chronic transplant glomerulopathy and arteriolar hyalinosis.