Polyomavirus Infection in Renal Transplant Recipients

Abstract

Polyomavirus-associated nephropathy (PyVAN) occurs in recipients of kidney transplantation. The development of PyVAN can cause a decrease or complete loss of the function of the kidney. Two of the human polyomaviruses BKPyV, JCPyV are known to be involved in the pathogenesis of PyVAN, and a further virus HPyV9 has been found in renal transplant recipients. A multiplex quantitative polymerase chain reaction (qPCR) for BKPyV, JCPyV, and HPyV9 DNA, together with an internal control molecule, was used to investigate polyomavirus infection in the late transplant period. Results for BKPyV, JCPyV were reported in IU/mL. The dynamic range, linearity and reproducibility of the assay was good (intra- and inter-assay variation for each viral target of <1% or less, with a wide range of target concentrations). In a cohort of 466 renal transplant recipients investigated late after transplant, blood samples from 27 were positive for BKPyV with a viral load of between log 2.97 IU/ml to log 8.48 IU/mL; 15 were positive for JCPyV with generally lower viral loads (log 3.55 and 6.56 IU/mL); 4 were HPyV9 positive but with only very low viral load (log 0.42 to log 1.25 copies/mL). The age range, sex, and ethnicity of positive patients were similar to those of the population from which the samples were drawn. BKPyV was detected most frequently (in 27 of the 466 patients; 5.8%), the BKPyV positive samples tended to be collected earlier after transplantation, with a median of 2.33 years (maximal follow up post-transplant was 34 years). Fewer patients were JCPyV positive even though the JCPyV positive blood samples tended to be even earlier after transplant (median collection time of 0.38 years). The low rate of detection and low viral load detected in HPyV9 positive samples does not support the role of HPyV9 in disease causation both early and late after transplant. The VP1 proteins of BKPyV, JCPyV and HPyV9 were produced in insect cells using a baculovirus protein expression system using pOET8.VE2 transfer vector with flashBAC™ expression system and purified using nickel chelate purification of Histidine tagged proteins. Preliminary analysis of the protein was made in ELISA, but additional optimisation of expression and purification of the antigens will be required for use in the serological investigation of polyomavirus infection.