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Short Communication |
Department of Epidemiology, The Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland 21205 [D. E. M. R., K. J. H., A. J. A., S. H.]; Department of Molecular Microbiology and Immunology, The Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland 21205 [R. D., K. V. S.]; and National Institute of Neurological Disorders and Stroke, Bethesda, Maryland 20852 [J. H., E. O. M.]
| Abstract |
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| Introduction |
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100%, respectively (3)
. Initial infections with JCV and BKV are largely asymptomatic and occur predominately in childhood, after which the viruses persist in kidney and B lymphocytes (2)
. Reactivation of latent JCV and BKV infections in immunocompromised individuals causes diseases, such as progressive multifocal leukoencephalopathy in AIDS patients (JCV) and nephropathy in renal transplant recipients (BKV; Ref. 2
). SV40, discovered in the early 1960s, was an accidental contaminant of licensed inactivated polio vaccines manufactured between 1955 and 1961 (1) . The prevalence of SV40 infection in the general population resulting from vaccination with contaminated lots is unknown. Serum antibodies to SV40 have been detected in study populations with prevalences ranging from 4 to 14% (4, 5, 6, 7) . There have been no population-based seroepidemiologic prevalence studies of SV40 antibodies.
Brain tumors, including medulloblastomas, glioblastomas, astrocytomas and ependymomas, and neuroblastomas, have been induced with inoculated polyomaviruses in several animal species (8) . The "tumor antigen" (T antigen), a nonstructural protein expressed by the viruses, is responsible for cell transformation in animal models. The T antigen complexes with and subsequently inactivates the tumor suppressor proteins p53 and pRb (8) . Genomic sequences from all three viruses have been reported from human brain tumor tissue of different types: (a) SV40 in choroid plexus tumors (9, 10, 11, 12) and ependymomas (9, 10, 11, 12, 13) ; (b) JCV in medulloblastomas (14) ; (c) BKV (11 , 15, 16, 17) and SV40 (11 , 18) in meningiomas; (d) JCV (19) , BKV (10 , 11 , 15) , and SV40 (10, 11, 12 , 20) in glioblastomas; and (e) JCV (19 , 21) , BKV (11 , 15) , and SV40 (11 , 12 , 18) in astrocytomas.
No statistically significant associations have been observed between SV40 exposure from potentially contaminated polio vaccines and brain tumors in seven cohort studies conducted since 1963 (reviewed in Refs. 22 and 23 ). These studies did not incorporate direct measurements of SV40 infection in individuals. No observational studies have investigated the possible associations between either JCV or BKV and brain tumors.
We conducted a population-based, nested case-control study, comparing the presence of polyomavirus antibodies in serum collected years before diagnosis between incident cases of primary brain tumors and cancer-free controls.
| Materials and Methods |
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Cases were defined as adults diagnosed with primary malignant tumors of the brain (ICD-9 191) or meninges (ICD-9 192) with no previous history of cancer, except possibly for nonmelanoma skin cancer and cervical cancer in situ. Cases diagnosed through December 31, 2000 were identified using the Washington County Cancer Registry and, since 1992, the Maryland Cancer Registry. The ratio of observed to expected number of cases, based on Surveillance, Epidemiology, and End Results incidence rates (24) , was 0.94. Of the 46 cases of primary brain tumors identified, 2 of those coded as ICD-9 192 (a spinal cord tumor and benign meningioma) were excluded, leaving 44 cases in the study. Brain tumor diagnosis was confirmed by pathology reports for 36 of the cases. Analyses conducted with and without the histologically confirmed cases yielded similar results; thus all are included.
Two controls were individually matched to each case on cohort participation, age within 2 years, race, gender, date of blood draw within 45 days, and freezer/thaw history of the serum sample. Controls were cancer free up to the time of cases diagnosis, with the possible exceptions of nonmelanoma skin cancer and cervical cancer in situ.
Laboratory Assays.
Serum samples were frozen and stored at -70°C, until thawed for the study. The presence of IgG antibodies to the capsid proteins of JCV and BKV was tested with an ELISA using virion particles as antigen, as described previously (25)
. Plaque neutralization assays were performed for SV40 antibodies, as described previously (26)
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Titers of
640 were considered positive for antibodies to JCV and BKV using ELISA (25)
. Plaque neutralization assays were performed at 1:10 and 1:40 dilutions in serum. Specimens that tested negative (<50% plaque reduction) at both dilutions were scored negative, those that tested positive at both dilutions were scored positive, and those specimens that tested positive at 1:10 dilution and negative at 1:40 dilution were called "weak positive." Plaque inhibition data were unavailable for one control who was classified as negative in the analysis. Laboratory personnel were masked to case-control status.
Sera from monkeys shown previously to be positive for SV40 antibodies served as positive controls for the plaque neutralization assays. Positive controls for ELISA were derived from individuals known to be infected with JCV or BKV, whereas negative controls were derived from pediatric patients <3 years old. All ELISA positive controls tested positive, and negative controls tested negative. Pairs of duplicate specimens were tested blindly to assess the reliability of the ELISA assay. The percentage of agreement among duplicate pairs, within one dilution, was 93% for JCV and 87% for BKV. No correlation was observed between JCV and BKV antibody titers, indicating little cross-reactivity between antibodies to these two viruses in the ELISA assays.
Statistical Methods.
To assess the association between polyomavirus antibodies and brain tumors, matched ORs and 95% CIs were estimated using conditional logistic regression. To investigate dose-response relationships, JCV- and BKV-positive titers were further divided into two categories (640 or 2,560 and
10,240), and SV40 plaque neutralization results were considered as three categories: (a) negative; (b) weak positive; and (c) positive.
JCV and BKV data were stratified by cohort participation, and no differences in ORs were observed. For the subset of individuals who donated blood in both 1974 (CLUE I) and 1989 (CLUE II), the results of assays performed on the 1989 specimens were used in subsequent analyses. Stratification was used to explore potential differences in the association between antibodies to JCV and BKV and brain tumors by tumor type, age at diagnosis, and time from blood draw to diagnosis. All analyses were conducted using SAS, version 8 (SAS Institute, Inc., Cary, NC).
| Results |
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| Discussion |
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Our findings are not likely confounded by other brain tumor risk factors. Except for exposure to ionizing radiation and the exceptionally rare cancer syndromes (27) , there are few established risk factors for brain cancer. These factors are not suspected risk factors for polyomavirus infection, so although not measured in this study, they are unlikely to have confounded the results.
Concerns over the health effects of exposure to SV40 through contaminated polio vaccines have been addressed in a recent Institute of Medicine report (28) . Our results suggest that 11% of a community-based population, most of whom had potential exposure to contaminated vaccine, had evidence of possible infection, but no association with brain tumors was observed. Circulating antibodies to the SV40 capsid protein may be an imperfect marker of past SV40 infection, because the formalin inactivation used in the polio vaccine may have completely or partially inactivated SV40, resulting in formation of antibodies in the absence of active infection. This would lead to individuals being misclassified as having been actively infected with SV40 and likely bias results toward the null, because this misclassification would be expected to be nondifferential with respect to brain tumor status.
Characteristics of both polyomaviruses and brain tumors present unique challenges for research into their relationship. The high prevalence of JCV and BKV antibodies and low prevalence of SV40 antibodies in the general population, in combination with the low incidence of brain tumors, limits statistical power of any prospective investigation of serum antibodies to these viruses and cancer, including the present study. Although our sample size was small, the lack of a dose-response association observed between polyomavirus antibodies and brain tumor development, in light of the temporal relationship of the data, argues against the association. This study should be replicated in other prospective cohorts. Given the high prevalence of JCV and BKV latent infections and the millions who were potentially exposed to SV40 through contaminated polio vaccines, additional investigations of polyomavirus infections as cancer risk factors have potential important public health significance.
| Acknowledgments |
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| Footnotes |
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1 Supported by the Training Center for Public Health Research, Johns Hopkins Bloomberg School of Public Health (JHBSPH), the Institutional Research Cancer Epidemiology Fellowship (to D. E. M. R.), 2 T32 CA093-14-19 [National Cancer Institute (NCI)], and the Early Detection Research Network, 5U01 CA86308-04 [NCI]. A. J. A. is a recipient of a KO7 award from the NCI (CA73790). ![]()
2 To whom requests for reprints should be addressed, at Johns Hopkins University, Bloomberg School of Public Health, 615 North Wolfe Street, Suite 6030, Baltimore, MD 21205. ![]()
3 The abbreviations used are: JCV, JC virus; BKV, BK virus; SV40, simian virus 40; ICD, International Classification of Diseases; CI, confidence interval; OR, odds ratio. ![]()
4 The term serum will be used for all samples. ![]()
Received 6/19/02; revised 1/10/03; accepted 1/31/03.
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