Evaluation of 4 Recently Discovered Human Polyomaviruses in Primary Cutaneous B-Cell and T-Cell Lymphoma FREE

Primary cutaneous lymphomas make up a heterogeneous spectrum of cutaneous B-cell lymphomas (CBCLs) and cutaneous T-cell lymphomas (CTCLs) that affect the skin without extracutaneous disease at first diagnosis. The cause of these lymphomas remains largely unknown. Some epidemiologic findings such as old age and acquired or iatrogenic immunosuppression are suggestive for an infectious cause, especially in CTCL.¹ However, all of the suspected agents, including retroviruses and herpesviruses, have failed to reveal a consistent association. The recent discovery of a novel polyomavirus (PyV) associated with Merkel cell carcinoma has rekindled research interest in the possibility that human PyVs (HPyVs) might induce cancer in humans. The present study was initiated to analyze a broad spectrum of CBCLs and CTCLs for the presence of 4 recently discovered cutaneous HPyVs.

A total of 130 archival paraffin-embedded biopsy specimens from 83 patients with CBCL or CTCL treated at the Department of Dermatology, Ruhr-University Bochum, Bochum, Germany, between January 1999 and December 2010, were available for virologic analysis. The tumors were classified according to the current WHO-EORTC classification system for cutaneous lymphomas.² Samples were analyzed by real-time polymerase chain reaction for the presence of Merkel cell PyV (MCPyV), HPyV6, HPyV7, and trichodysplasia spinulosa –associated PyV (TSPyV) DNA using type-specific primers and locked nucleic acid probes (Roche, Mannheim, Germany).^3- 5 Type-specific viral DNA load was defined as viral DNA copies per beta-globin gene copy.⁵ The expression of MCPyV large T(umor) antigen in MCPyV DNA –positive samples was evaluated by immunohistochemical analysis using the monoclonal antibody CM2B4 (dilution of 1:100; Santa Cruz Biotechnology, Santa Cruz, California), as previously reported.⁶ The study was approved by the ethics review board of Ruhr-University Bochum.

Results of MCPyV, HPyV6, HPyV7, and TSPyV analyses are listed in the Table. Merkel cell PyV DNA was found in 23.1% of the 130 lymphoma biopsy specimens. The percentage of MCPyV DNA positivity was similar in the different tumor groups, ranging from 20% in the mycosis fungoides (MF) group (n  =  71) to 31% in S ézary syndrome (n  =  13) (CD30⁺ lymphoproliferative disorders and rare CTCLs, 25% each [n  =  20 and n  =  12] ; CBCL, 28.6% [n  =  14]) (P  =  .88). The MCPyV DNA loads were low ( <1 viral DNA copies per beta-globin gene copy) in the vast majority of samples (Table). However, when looking at mycosis fungoides (MF) variants, we found that 6 of 8 folliculotropic MF samples harbored MCPyV DNA, and 3 of the biopsy specimens had MCPyV DNA loads higher than 1 viral DNA copies per beta-globin gene copy. However, none of the 30 MCPyV DNA-positive lymphomas expressed the MCPyV T antigen (Figure). There was no correlation between the presence of MCPyV and patient age or sex.

Human PyV6 was found in 6 samples (4.6%), and HPyV7 was detected in only 1 patient with folliculotropic MF (0.8%), with very low viral DNA loads (Table). Trichodysplasia spinulosa –associated PyV DNA was found in none of the 130 samples.

Infectious agents, in particular viruses, have long been suspected to be involved in the development of cutaneous lymphoma, especially in CTCL. However, previous attempts to evaluate viral pathogens in cutaneous lymphoma have yielded conflicting results.¹

The findings of the present study argue against a pathogenetic role of MCPyV, HPyV6, HPyV7, and TSPyV in primary cutaneous lymphoma. Merkel cell PyV, the acknowledged cause of approximately 80% of Merkel cell carcinomas, was recently shown to be absent in 4 patients with CTCL using a monoclonal antibody against the MCPyV T antigen.¹ In line with this, fewer than one-quarter of the samples evaluated in the present study were positive for MCPyV DNA; MCPyV DNA loads were generally low, and the MCPyV T antigen was not expressed in any of the MCPyV DNA –positive lymphomas. Interestingly, 75% of folliculotropic MF cases were found to be positive for MCPyV DNA (n  =  6), supporting the assumption that cells of the hair follicles are particularly predisposed to MCPyV infection.⁷

Two other human polyomaviruses, HPyV6 and HPyV7, have recently been discovered.³ Merkel cell PyV, HPyV6, and HPyV7 are chronically shed from healthy human skin.³ So far, HPyV6 and HPyV7 have not been found to be associated with any disease. Based on their low prevalence and low viral loads found in the present study, HPyV6 and HPyV7 do not seem to be causally linked to CBCLs and CTCLs.

Trichodysplasia spinulosa is a rare skin disease characterized by follicular papules and keratin spines that is exclusively found in immunocompromised patients. Trichodysplasia spinulosa PyV, another newly identified PyV, is the likely cause of trichodysplasia spinulosa.⁴ However, TSPyV has also been detected in 4% of unaffected long-term immunosuppressed renal transplant recipients.⁴ Our finding that none of the biopsy specimens analyzed contained TSPyV DNA strongly argues against a role of TSPyV in cutaneous lymphoma.

The findings presented herein should be interpreted in light of the limitations of the study. Although a relatively large number of samples were analyzed, the number of rare lymphoma subtypes was small for most tumor groups. Moreover, in most patients, only a single lesional specimen was available, possibly underestimating the prevalence of the respective PyVs. Finally, we did not evaluate nonlesional skin of the patients with lymphoma. In conclusion, our observations argue against a pathogenetic role of cutaneous PyVs in primary cutaneous lymphoma.