Human Polyomaviruses 6 and 7 (HPyV6/7) Are Not Detectable in Merkel Cell Carcinoma.
Eric J Duncavage, John D Pfeifer. University of Utah, Salt Lake City; Washington University, St. Louis, MO
Background: Merkel cell carcinoma (MCC) is a rare cutaneous tumor that shows a high correlation with Merkel Cell Polyomavirus (MCPyV) in up to 80% of cases. However, there appears to be little difference in the morphology and molecular biology between MCPyV positive and negative MCC. An intriguing hypothesis has been that another similar polyomavirus may be associated with MCPyV negative MCC leading to a similar morphologic and molecular phenotype. Recently, two additional human polyomaviruses, Human Polyomaviruses 6 and 7 (HPyV6/7), were identified along with MCPyV in the skin of normal individuals by rolling circle amplification. Both HPyV6 and 7 share a high degree of sequence similarity to MCPyV. We sought to determine if the presence of HPyV6/7 could account for MCPyV negative MCC.
Design: DNA was extracted from formalin-fixed paraffin-embedded tissue blocks of 38 previously characterized MCC cases that included 22 MCPyV positive and 16 negative cases. A 110bp PCR product targeting the beta globin gene was used as an amplification control. Primers were designed to produce ∼140bp products by targeting HPyV6 and 7 large T antigens and were aligned against all polyomaviruses in GenBank to ensure specificity. Cloned HPyV6 and 7 viral plasmids were used as positive controls. PCR for both HPyV6 and 7 was performed on all 38 cases and products detected by 2% agarose gel electrophoresis. To determine PCR sensitivity, a dilution series of viral plasmid DNA was constructed.
Results: The beta globin control gene was amplified in all 38 MCC cases. None (0/38) of the MCC cases, including both MCPyV positive and negative cases, had detectable HPyV6 or HPyV7. PCR sensitivity was estimated to be >5,000 viral copies.
Conclusions: While both MCPyV and HPyV6/7 are part of normal skin flora and show a high degree of similarity to MCPyV, we see no evidence of an association between HPyV6/7 and MCC. More importantly we see no evidence of HPyV6/7 in MCPyV negative MCC, arguing against the idea that another polyomavirus may be responsible for MCPyV negative MCC. While we cannot fully exclude the possibility of low level HPyV6/7 involvement in MCC, it seems unlikely that HPyV6/7 accounts for the pathogenicity of MCPyV negative MCC given that pathogenic MCPyV is present in very high copy numbers in MCPyV positive MCC.
Wednesday, March 2, 2011 1:00 PM
Poster Session VI # 102, Wednesday Afternoon