No evidence for human cytomegalovirus infection in pediatric medulloblastomas

Human cytomegalovirus (HCMV), a member of the herpesvirus family, remains present after primary infection during a patient’s entire life. The overall seroprevalence of HCMV is around 20.7% for children and adolescents, of whom 0.7% are born with a congenital HCMV infection in the United States.¹ In the last decade, several studies have suggested a role for HCMV as a driver of tumorigenesis in pediatric brain tumors (eg, medulloblastoma,² glioma,³ and adult glioblastoma multiforme).^4,5 Therefore, HCMV is considered to be a potentially interesting therapeutic candidate for immunotherapy against these cancers.⁶ In pediatric medulloblastoma, however, there is conflicting evidence for HCMV positivity in tumor cells. Several studies show no HCMV positivity even in HCMV-seropositive patients with current standard procedures,^7,8 while others detect HCMV in the majority of tumors.² In the present study, we surveyed a panel of pediatric medulloblastomas for HCMV infection.

A total of 26 formalin-fixed, paraffin-embedded pediatric medulloblastoma tissue samples were retrieved from the archives of the Department of Pathology at the University Medical Center Utrecht in the Netherlands. Since we are using archival pathology material, which does not interfere with patient care and does not involve physical involvement of the patient, no ethical approval was required according to Dutch legislation. Each sample was independently reclassified by 2 experienced neuropathologists (W.G.M.S. and W.V.H.) according to the 4th edition of WHO Classification of Tumours of the Central Nervous System. We analyzed HCMV expression by immunohistochemistry for immediate-early (clone E13, Abserotec; 1:500) and late antigens (MAB8127,Chemicon; 1:100). We incorporated the critical steps for detecting low copy number HCMV detection according Cobbs et al. to avoid false negative results.⁹ The cohort was characterized as follows. Of the 26 cases, 17 were male (65.4%), and 9 were female (34.6%); the mean age at diagnosis was 8.5±5.3 years. Classical medulloblastoma was diagnosed in 16 cases, desmoplastic nodular in 6 cases, extensive nodularity in 3 cases, and anaplastic medulloblastoma in 1 case. In contrast with earlier reports,² we could not detect any positivity for HCMV immediate-early (IE1/2) antigens and late antigens in our cohort of pediatric medulloblastomas (Fig. 1). These findings are in line with recent studies showing that no HCMV could be detected in the tumor cells in HCMV-seropositive patients.^7,8

Fig. 1.

Immunohistochemistry of HCMV IE1/2 and late antigens in pediatric medulloblastoma. A sample medulloblastoma case shows no staining for both HCMV IE1/2 and late antigens, whereas the positive control (HCMV-infected placenta) shows evident positivity. Images taken at 200x magnification. Scale bar equals 50μm.

Our study shows no evidence for HCMV infection in pediatric medulloblastomas. This lowers the likelihood that HCMV enhances malignancy in these tumors. The reason for the discrepancy between different studies in detecting HCMV in medulloblastoma and brain cancer in general remains unclear. It might be related to technical issues including differences in pathology workup of clinical specimens, immunohistochemistry protocols, type of antibody used (specificity), and/or arbitrary cutoffs for determining HCMV positivity. Furthermore, positive controls are frequently lacking, which hampers quality assessment and increases the risk for nonspecific staining and false positivity of HCMV in brain tumors.

Clinical trials in gliomas evaluating immunotherapeutic strategies against HCMV using valganciclovir, dendritic cell-based vaccines, and adoptive T-cell therapy are in progress.¹⁰ However, our findings strongly suggest that caution has to be taken when applying such HCMV-targeted immunotherapy for pediatric medulloblastomas.

Funding

This work was supported by a research grant from Cancer Foundation Koppie-Au.

Conflict of interests statement. The authors declare no conflict of interest.