European perspective on human polyomavirus infection, replication and disease in solid organ transplantation.

Human polyomaviruses (HPyVs) are a growing challenge in immunocompromised patients in view of the increasing number of now 12 HPyV species and their diverse disease potential. Currently, histological evidence of disease is available for BKPyV causing nephropathy and haemorrhagic cystitis, JCPyV causing progressive multifocal leukoencephalopathy and occasionally nephropathy, MCPyV causing Merkel cell carcinoma and TSPyV causing trichodysplasia spinulosa, the last two being proliferative skin diseases. Here, the current role of HPyV in solid organ transplantation (SOT) was reviewed and recommendations regarding screening, monitoring and intervention were made. Pre-transplant screening of SOT donor or recipient for serostatus or active replication is currently not recommended for any HPyV. Post-transplant, however, regular clinical search for skin lesions, including those associated with MCPyV or TSPyV, is recommended in all SOT recipients. Also, regular screening for BKPyV replication (e.g. by plasma viral load) is recommended in kidney transplant recipients. For SOT patients with probable or proven HPyV disease, reducing immunosuppression should be considered to permit regaining of immune control. Antivirals would be desirable for treating proven HPyV disease, but are solely considered as adjunct local treatment of trichodysplasia spinulosa, whereas surgical resection and chemotherapy are key in Merkel cell carcinoma. Overall, the quality of the clinical evidence and the strength of most recommendations are presently limited, but are expected to improve in the coming years.

Cidofovir inhibits polyomavirus BK replication in human renal tubular cells downstream of viral early gene expression.

The human polyomavirus BK (BKV) causes nephropathy and hemorrhagic cystitis in kidney and bone marrow transplant patients, respectively. The anti-viral cidofovir (CDV) has been used in small case series but the effects on BKV replication are unclear, since polyomaviruses do not encode viral DNA polymerases. We investigated the effects of CDV on BKV(Dunlop) replication in primary human renal proximal tubule epithelial cells (RPTECs). CDV inhibited the generation of viral progeny in a dose-dependent manner yielding a 90% reduction at 40 microg/mL. Early steps such as receptor binding and entry seemed unaffected. Initial large T-antigen transcription and expression were also unaffected, but subsequent intra-cellular BKV DNA replication was reduced by >90%. Late viral mRNA and corresponding protein levels were also 90% reduced. In uninfected RPTECs, CDV 40 microg/mL reduced cellular DNA replication and metabolic activity by 7% and 11% in BrdU and WST-1 assays, respectively. BKV infection increased DNA replication to 142% and metabolic activity to 116%, respectively, which were reduced by CDV 40 microg/mL to levels of uninfected untreated RPTECs. Our results show that CDV inhibits BKV DNA replication downstream of large T-antigen expression and involves significant host cell toxicity. This should be considered in current treatment and drug development.

Human umbilical vein endothelial cells lack expression of the estrogen receptor.

Estrogens may influence the expression of various cytokines, adhesion molecules, von Willebrand factor and prostacyclin produced by endothelial cells. However, reports concerning expression of the estrogen receptor in endothelial cells are controversial. Primary human umbilical vein endothelial cells (HUV-EC), the non continuous human umbilical vein endothelial cell line HUV-EC-C (ATCC CRL 1730) and endothelial cells from 10 frozen umbilical cords were analyzed for the expression of the estrogen receptor. Immunological studies using estrogen receptor specific antibodies failed to detect the expression of the receptor in all human umbilical vein endothelial cells tested. No estrogen receptor transcripts were found in primary HUV-EC or HUV-EC-C by reverse transcriptase-polymerase chain reaction. Weak hybridization signals were detected when the PCR amplicons were hybridized with estrogen receptor cDNA sequences as a probe. In vitro protein-DNA interaction studies revealed no complexes between a fully consensus estrogen response element and HUV-EC-C extracts. Finally, transient transfection studies in HUV-EC-C could not demonstrate 17beta-estradiol-induced transcription of the beta-galactosidase reporter gene linked to a consensus estrogen response element. These observations suggest that human umbilical vein endothelial cells lack the estrogen receptor.

The agnogene of the human polyomavirus BK is expressed.

Primate polyomavirus genomes all contain an open reading frame at the 5' end of the late coding region called the agnogene. A simian virus 40 agnoprotein with unknown functions has previously been demonstrated. We now show that a BK virus agnoprotein appears in the perinuclear area and cytoplasm late in the infectious cycle. It is phosphorylated in vivo and coimmunoprecipitates with a subset of host cell proteins.