BK Polyoma Virus: A Mini Tutorial Joel C Reynolds, MD Walter Reed Army Medical Center Nephrology Service

What We Know: BKV seroprevalence is almost ubiquitous with over 90% of all people seropositive by age BKV nephropathy is a significant cause of renal allograft loss. 2 Urine shedding of BKV is more prevalent than viremia. 1,2 Primary infection with seroconversion has been documented. 1 To date all studies have shown 100% urine PCR positivity when viremia is present by PCR. 1,2

What We Know: BKV nephropathy can resemble acute rejection on biopsy, usually unresponsive to steroids when treated as rejection. 3 Allograft biopsy is currently considered the “gold standard” for diagnosis, but has questionable sensitivity. 3 BKV infected renal tubular epithelial (decoy) cells appear to deteriorate quickly (within minutes), which may limit urine microscopy as a screening tool. 4

What We Know: Urine BKV DNA load is usually at least 10 5 x higher than serum viral DNA load and may be present without viremia. 5 No studies to date have identified clear risk factors which would help predict those at risk for BKV nephropathy, to include tacrolimus, mycophenolate, or steroids. 2

What We Suspect: Overall immunosuppression levels are too high. Prevalence is much higher than previously suspected. Antiviral drugs (cidofovir) may be effective treatment. 6 Failure to detect BKV early leads to irreversible nephropathy. 4 Allograft biopsy sensitivity for BKV is suspect due to the spotty nature of early infection and apparent predeliction of the virus for medullary renal tissue. 3

What We Don’t Know: Is there a reservoir for BKV other than urinary tract? What are the risk factors for developing BKVN? Risk factors for reactivation of harbored BKV? Does serology of donor/recipient change risk? What level of serum BKV DNA denotes those at increased risk of progression to BKVN? How does cidofovir (known to inhibit viral DNA polymerase) inhibit BKV replication (which has no DNA polymerase)?

What We Don’t Know: What is the most cost effective/sensitive test to help predict those at increased risk for developing BKVN? –Serum PCR, very sensitive (4 copies/ml), expensive (~$200), significance of levels? –Urine PCR, very sensitive, expensive, not specific, signficance of levels? –Urine decoy cell microscopy, inexpensive, operator/time dependent, significance of positive finding?

What Is Needed? Large, prospective trials including transplant recipients not on calcineurin inhibitors, and on steroid free protocols, to adequately assess for risk factors which would predispose to infection by BKV. Likely would require multi-center cooperation to achieve power to detect factors with significance (similar to the studies of CMV status of donor/recipient performed in the ‘70s).

References: 1.Hirsch HH, et.al. Prospective study of polyomavirus type BK replication and nephropathy in renal-transplant recipients. N Engl J Med Aug 15;347(7): Ramos E, et.al. Clinical course of polyoma virus nephropathy in 67 renal transplant patients. J Am Soc Nephrol Aug;13(8): Drachenberg RC, et.al. Morphological spectrum of polyoma virus disease in renal allografts: diagnostic accuracy of urine cytology. Am J Transplant 2001 Nov;1(4): Personal observations in our clinic (Walter Reed AMC). 5.Brennan DC, unpublished data, Washington Univ School of Medicine, St. Louis, MO. 6.Vats A, et.al. Quantitative viral load monitoring and cidofovir therapy for the management of BK virus-associated nephropathy in children and adults.Transplantation Jan 15;75(1): Nickeleit V, et.al. BK virus infection after kidney transplantation. Graft Dec; S18 (5): S46-57.

A Pictorial Tutorial Unstained Freshly-Voided Urine with Decoy Cells: (Renal Tubular Epithelial cells with BKV- Associated Intranuclear Inclusions) Digital photographs courtesy of Mr. David Oliver and Mrs. Luana Kiandoli, Nephrology Laboratory, WRAMC

Type I: An amorphous ground-glass variant “Ground-glass” appearance of nucleus 400x (Olympus BH2 microscope) Reference 7

Type II: granular variant surrounded by a “halo” 400x (Olympus BH2 microscope) Reference 7

Type III: a finely granular variant without halo 400x (Olympus BH2 microscope), Enlarged 1.6x in processing image. Reference 7

Type II/III hybrid: 400x (Olympus BH2 microscope), Enlarged 2x in processing image. Intranuclear vesicles Reference 7

Type IV: a vesicular variant with clumped, irregular chromatin 400x (Olympus BH2 microscope), Enlarged 2x in processing image. Reference 7