Chromosomally integrated HHV-6 in renal transplant patients Paolo Lusso, NIAID, NIH 27 October 2011 Sir: The recent report by Csoma et al.1 identifies HHV-6A as the viral variant most frequently detected in patients who received renal transplantation, but we noticed some important drawbacks in the study that suggest caution in the interpretation of these results. First and foremost, although the authors introduce the issue of chromosomally integrated HHV-6 (ciHHV-6) in the discussion, they did not test their patients for ciHHV-6. Individuals with ciHHV-6 have high levels of both cell-associated and cell-free HHV-6 DNA in the absence of active infection2. For these reasons, clinical studies should exclude, or at least consider separately, such individuals. Although in this study viral load data are not specified for each PCR-positive patient (only mean values and ranges are presented in the text), the numbers of HHV-6 DNA copies at the high end in both plasma (6x105mL) and blood cells (2.1x106/1.5x106 cells) are those typically detected in individuals with ciHHV-62,3. Active HHV-6 infection rarely causes a viral load of over 1 million copies per ml and in these situations the elevated viral load is transient and correlates with dramatic clinical manifestations. Since all of the patients with HHV-6 viremia in this study had mild disease, ciHHV-6 status can be presumed in at least some of these patients. The estimated prevalence of ciHHV-6 is approximately 0.85% among blood donors and newborns in the US and UK2, 6. However, the prevalence of ciHHV-6 in two small studies of renal transplant patients was 1.92% and 2.13%, respectively8, 9. Based on these figures, one might expect to find 4 ciHHV-6 individuals out of 200 as tested in this study. Another issue that deserves attention is the low level of HHV-6 latency (6-9%) reported by Csoma et al., which suggests a poor PCR sensitivity, making it difficult to interpret the data on the incidence of active HHV-6 infection. Since HHV-6, especially variant B, is a ubiquitous virus that infects >95% of the population at an early age and persists in a latent form predominantly in blood cells10, 11, the majority of adults harbor HHV-6 DNA sequences in their blood cells. Finally, the authors report that 8 out of 9 patients with viremia had the A variant of HHV-6, which is in contrast with previous studies of post-renal transplant patients in which the B variant was predominantly detected12, 13. However, detection of the two variants is influenced by the compartment investigated as well as, possibly, by the method used. HHV-6B is found more frequently in PBMCs while HHV-6A is found more frequently in plasma. Nitsche et al. used a variant-specific PCR and found HHV-6A in 92% of plasma samples, but in only 4% of PBMC samples from 336 HSCT patients14. Lack of identification of ciHHV-6 has led to a great deal of confusion in the HHV-6 field. The finding of high HHV-6 DNA levels in the blood of mildly ill or asymptomatic individuals with ciHHV-6 may lead to the faulty conclusion that HHV-6 can replicate at significant levels without causing disease, as also suggested in this study. A simple quantitative test on whole blood can establish ciHHV-6 status in almost all cases. Conversely, serum and plasma PCR DNA tests are not sufficient to identify ciHHV-6 status15. Confirmation can be made by hair follicle or fingernail DNA PCR testing15, 16. Sincerely, Paolo Lusso, National Institute of Allergy and Infectious Diseases, NIH, USA Dharam Ablashi, HHV-6 Foundation, USA Kristin Loomis, HHV-6 Foundation, USA Sylvie Rogez, Department of Virology, CHRU Dupuytren, France Louis Flamand, Rheumatology and Immunology Research Center, Université Laval, Canada 1. Csoma E, Meszaros B, Gall T, Asztalos L, Konya J, Gergely L: Dominance of variant A in Human Herpesvirus 6 viraemia after renal transplantation, Virol J 2011, 8:403 2. Leong HN, Tuke PW, Tedder RS, Khanom AB, Eglin RP, Atkinson CE, Ward KN, Griffiths PD, Clark DA: The prevalence of chromosomally integrated human herpesvirus 6 genomes in the blood of UK blood donors, J Med Virol 2007, 79:45-51 3. Ward KN, Leong HN, Thiruchelvam AD, Atkinson CE, Clark DA: Human herpesvirus 6 DNA levels in cerebrospinal fluid due to primary infection differ from those due to chromosomal viral integration and have implications for diagnosis of encephalitis, J Clin Microbiol 2007, 45:1298-1304 4. Brands-Nijenhuis AV, van Loo IH, Schouten HC, van Gelder M: Temporal relationship between HHV 6 and graft vs host disease in a patient after haplo-identical SCT and severe T-cell depletion, Bone Marrow Transplant 2010, 5. Tohyama M, Hashimoto K: [Drug-induced hypersensitivity syndrome], Nippon Rinsho 2007, 65 Suppl 8:341-343 6. Hall CB, Caserta MT, Schnabel KC, Boettrich C, McDermott MP, Lofthus GK, Carnahan JA, Dewhurst S: Congenital infections with human herpesvirus 6 (HHV6) and human herpesvirus 7 (HHV7), J Pediatr 2004, 145:472-477 7. Pellett PEaGT: Human herpesviruses 6, 7, and 8. Edited by J. Versalovic KCC, G. Funke, J.H. Jorgensen, M.L. Landry, and D.W. Warnock,. Washington, DC, ASM Press, 2011, 8. Lee SO, Brown RA, Eid AJ, Razonable RR: Chromosomally integrated human herpesvirus-6 in kidney transplant recipients, Nephrol Dial Transplant 2011, 26:2391-2393 9. Kidd IM, Clark DA, Sabin CA, Andrew D, Hassan-Walker AF, Sweny P, Griffiths PD, Emery VC: Prospective study of human betaherpesviruses after renal transplantation: association of human herpesvirus 7 and cytomegalovirus co-infection with cytomegalovirus disease and increased rejection, Transplantation 2000, 69:2400-2404 10. Clark DA, Ait-Khaled M, Wheeler AC, Kidd IM, McLaughlin JE, Johnson MA, Griffiths PD, Emery VC: Quantification of human herpesvirus 6 in immunocompetent persons and post-mortem tissues from AIDS patients by PCR, J Gen Virol 1996, 77 ( Pt 9):2271-2275 11. Yoshikawa T, Goshima F, Akimoto S, Ozaki T, Iwasaki T, Kurata T, Asano Y, Nishiyama Y: Human herpesvirus 6 infection of human epidermal cell line: pathogenesis of skin manifestations, J Med Virol 2003, 71:62-68 12. Chapenko S, Folkmane I, Ziedina I, Chistyakovs M, Rozentals R, Krumina A, Murovska M: Association of HHV-6 and HHV-7 reactivation with the development of chronic allograft nephropathy, J Clin Virol 2009, 46:29-32 13. Loginov R, Karlsson T, Hockerstedt K, Ablashi D, Lautenschlager I: Quantitative HHV-6B antigenemia test for the monitoring of transplant patients, Eur J Clin Microbiol Infect Dis 2010, 29:881-886 14. Nitsche A, Muller CW, Radonic A, Landt O, Ellerbrok H, Pauli G, Siegert W: Human herpesvirus 6A DNA Is detected frequently in plasma but rarely in peripheral blood leukocytes of patients after bone marrow transplantation, J Infect Dis 2001, 183:130-133 15. Ward KN, Leong HN, Nacheva EP, Howard J, Atkinson CE, Davies NW, Griffiths PD, Clark DA: Human herpesvirus 6 chromosomal integration in immunocompetent patients results in high levels of viral DNA in blood, sera, and hair follicles, J Clin Microbiol 2006, 44:1571-1574 16. Hubacek P, Virgili A, Ward KN, Pohlreich D, Keslova P, Goldova B, Markova M, Zajac M, Cinek O, Nacheva EP, Sedlacek P, Cetkovsky P: HHV-6 DNA throughout the tissues of two stem cell transplant patients with chromosomally integrated HHV-6 and fatal CMV pneumonitis, Br J Haematol 2009, 145:394-398 Competing interests The authors have no competing interests. This research was supported in part by the Intramural Research Program of the NIAID, NIH and by the HHV-6 Foundation.