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Viral Epidemiology Branch [J. J. G.] and Genetic Epidemiology Branch [M. C. F.], National Cancer Institute, Rockville, Maryland 20852; Abteilung Virologie, Universitätskliniken des Saarlandes, Homburg/Saar, Germany [M. E. S., N. G. M-L.]; Department of Epidemiology, Johns Hopkins University School of Hygiene and Public Health, Baltimore, Maryland [L. P. J.]; Department of Urology, University of Washington, Seattle, Washington [R. L. V.]; Department of Pediatrics, New York Hospital-Cornell Medical Center, New York, New York [M. W. H.]; and Department of Transfusion Medicine, NIH, Bethesda, Maryland [S. F. L.]
| Abstract |
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Stored, frozen serum samples from 52 patients with testicular cancer (8 patients with HIV and 30 patients with samples near the time of diagnosis) and 84 controls (40 patients with HIV) were diluted 1:40 and tested by immunofluorescence against SF158 cells transfected with HERV-K10 env [ENV1.9(+)] or gag (pACGAG). Seroprevalence rates were compared cross-sectionally in cases and controls, excluding those with indeterminate results (3 of 30 cases and 7 of 84 controls), and also were examined longitudinally in the cases before or after diagnosis of testicular cancer.
Seroprevalence to HERV-K10 Env or Gag was 17 of 27 testicular cancer patients (63%) around the time of diagnosis, compared to 4 of 77 controls (5%; P < 0.0001). Seroprevalence was similar (50% to 60%) with seminoma, teratocarcinoma, or embryonal carcinoma, and it was not increased with HIV infection in either cases (33%) or controls (3%). HERV-K10 antibodies were detected in 12 of 19 cases (63%) more than 6 months before seminoma diagnosis, as well as in four cases with residual or recurrent malignancy more than 1 month after initial diagnosis.
Thus, HERV-K10 antibodies are detected frequently with testicular cancer and seem to resolve rapidly with effective therapy of the malignancy. Antibody reactivity also occurs in
5% of controls, perhaps because of nonspecific or cross-reactive epitopes. HIV and AIDS were not associated with HERV-K10 antibodies, thus, leaving their higher risk of testicular cancer unexplained.
| Introduction |
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We and others (6 , 7) have recently noted an increased risk of seminoma among persons with AIDS. We postulated that severe immune deficiency, such as AIDS, might result in the activation of HERV-K10 and lead to an increased risk of seminoma or other malignant germ cell tumors. We evaluated the relationship of HERV-K10 antibodies to testicular cancer, as well as the possibility that HERV-K10 antibody prevalence might be increased with HIV infection or AIDS.
| Materials and Methods |
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As reported previously (4 , 5) , sera or plasma samples were tested for HERV-K10 Env or Gag antibody reactivity using indirect immunofluorescence against SF158 cells that had been transfected with the ENV1.9(+) or pACGAG fragments. Wild-type baculovirus-infected SF158 cells served as controls. Positive samples, those that demonstrated specific immunofluorescence at a 1:40 dilution, were titered with further 4-fold serial dilutions. Samples with high background reactivity were considered indeterminate; those with indeterminate results against both Env and Gag were excluded from seroprevalence calculations. Aliquots of selected samples also were tested for levels of HCG and AFP by a commercial reference laboratory using licensed kits. In addition to longitudinal HERV-K10 seroprevalence rates among cases, cross-sectional results for samples collected near the time of diagnosis (30 of 52 cases) were compared with those of the control groups. Differences in seroprevalence were evaluated with a two-sided Fishers exact test.
| Results |
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Considering the HERV-K10 assays in more depth, 820% of the sera had indeterminate results due to high background, nonspecific reactivity (Table 1)
. The assay for Env had higher sensitivity (59% positive among cases) but lower specificity (4% positive among controls) than did the Gag assay (23% among cases, 1% among controls). Similarly, antibody titers tended to be higher against Env than against Gag. Among the HERV-K10 seropositive testicular cancer cases, median antibody titers were 1:1280 (range, 1:801:10240; n = 22) against Env, compared with 1:160 (range, 1:801:5120; n = 6) against Gag.
Using sera that had been collected and frozen prospectively, antibodies against HERV-K10 Env or Gag were detected >6 months before diagnosis in 12 of 19 seminoma cases (63%) and likewise were detected 16 months before diagnosis in 3 of 4 seminoma cases (75%; Fig. 1
). One of five seminoma cases (20%) was positive 112 months after diagnosis, and one of 13 cases (8%) was positive thereafter. Among the nonseminoma cases, 0 of 11 with prediagnostic sera had HERV-K10 antibodies; but, six of nine nonseminoma cases (67%) were seropositive within 2 months of diagnosis, as were three of six (50%) and one of three cases (33%) who were tested 112 months and >12 months, respectively, after diagnosis. Residual or recurrent malignancy was documented in four of the six cases that were seropositive after diagnosis. The fifth case was last tested on completion of radiation therapy 61 days after diagnosis but, thereafter, he was lost to follow-up. The sixth case was seropositive 16 months after orchiectomy for stage I teratoma and remains free of tumor more than 15 years later. None of the six cases who had HERV-K10 antibodies after diagnosis were infected with HIV. Appearance of antibodies before diagnosis and disappearance after successful therapy was observed in those individual cases that had closely spaced samples (data not shown).
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| Discussion |
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Men with AIDS have a nearly 3-fold increased risk of testicular cancer (6) . Because a hallmark of HIV infection and AIDS is the reactivation of certain latent viruses and other infections (often those that are readily controlled by intact cellular immunity), we postulated that HERV-K10 may become derepressed with HIV-related immune deficiency, leading to the expression of env or gag and to the development of antibodies. Our data did not support this hypothesis. The prevalence of HERV-K10 antibodies was only one (3%) of 36 HIV-infected men, not different from the one (5%) found among 20 healthy HIV-uninfected male blood donors. None of 20 HIV-infected subjects with very severe immune deficiency had antibodies against either HERV-K10 protein.
As is true for HCG and AFP, which are the classical markers of testicular cancer, the HERV-K10 env and gag genes probably are repressed in most adult cells and function only during embryonic development, if ever. On the off chance of a strong inheritance pattern in the regulation of these HERV-K10 genes, we included as controls unaffected members of families that are prone to testicular or renal cell carcinomas. HERV-K10 antibody prevalence in these family members was low and similar to the low prevalence seen in the other control subjects. The lack of anything in common among the four seropositive control subjects suggests that their antibody reactivity may have been nonspecific. In addition, although these sera had been stored frozen under good conditions, indeterminate results due to high background reactivity were found in 9% of the Env and 12% of the Gag slides.
We did confirm a high prevalence of HERV-K10 antibodies at the time of testicular cancer diagnosis. Seminoma cases frequently had such antibodies for 6 months or more before diagnosis. Despite its relatively high sensitivity of
60%, testicular cancer is such a rare disease even among white men during peak ages (13/100,000 per annum from age 2034) that the positive predictive value of HERV-K10 would be extremely low. In addition, HERV-K10 antibodies in four control subjects yields a specificity of
95%. Thus, these assays may be very useful for research, but they would not be appropriate for large-scale screening.
In summary, HERV-K10 is an endogenous human retrovirus, which means that it is a constitutive part of the genome of all human cells. HERV-K10 env and gag genes seem to be expressed in embryonic, placental, and testicular cancer tissue. Moreover, the proteins produced by these genes are antigenic, and the resulting antibodies can be found frequently in the sera of testicular cancer patients. As with classical markers of testicular cancer, HERV-K10 antibodies resolve rapidly with effective treatment of the testicular cancer, supporting the theory that HERV-K10 expression is limited to the tumor. Whether expression of HERV-K10 contributes to the pathogenesis of testicular cancer and whether HERV-K10 serology might be useful for monitoring patients who have had testicular cancer or for other purposes remains to be seen.
| Acknowledgments |
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| Footnotes |
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1 The Multicenter AIDS Cohort Study is funded by the National Institute of Allergy and Infectious Diseases, with additional funding from National Cancer Institute Grants UO1-AI-35042, 5-MO1-RR-00722 (GCRC), UO1-AI-35043, UO1-AI-37984, UO1-AI-35039, UO1-AI-35040, UO1-AI-37613, and UO1-AI-35041. Additional support was provided by National Cancer Institute Contract NO1-CP-40521 with Research Triangle Institute. ![]()
2 To whom requests for reprints should be addressed, at 6120 Executive Boulevard, Suite 8012, Rockville, MD 20852. Phone: (301) 435-4724; Fax: (301) 402-0817; E-mail: goedertj{at}mail.nih.gov ![]()
3 The abbreviations used are: HERV, human endogenous retrovirus; MACS, Multicenter AIDS Cohort Study; HCG, human chorionic gonadotropin; AFP,
-fetoprotein. ![]()
Received 8/31/98; revised 1/14/99; accepted 1/23/99.
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