Chromosomally Integrated HHV-6: Slow Decrease of HHV-6 Viral Load After Hematopoietic Stem-Cell Transplantation

Human herpesvirus (HHV)-6 belongs to the Betaherpesvirinae subfamily. Similar to other herpesviruses, HHV-6 has a latent stage (1) with problematic reactivation in immunocompromised subjects, leading to fatal infections including meningoencephalitis (2, 3). A less-frequent HHV-6 persistence form consists in integration in host chromosomes (4). The prevalence of HHV-6 integration, characterized by high viral load in healthy individuals, has been estimated at approximately 0.2% to 2% in the whole population (5–7) and can thus concern up to 2% of hemotopoietic stem-cell transplantation (HSCT) donors or recipients (8). Some previous publications have described cases of integrated HHV-6 transmission through HSCT (9–11). In those cases, the recipient has undetectable HHV-6 viral load before the transplantation and becomes positive to high values (∼106 genomic equivalent copies [gec]/106cells) for HHV-6 DNA early after transplantation (<10 days) (9, 12). The presence of high HHV-6 viral load in an HSCT recipient could also be misinterpreted as HHV-6 reactivation and lead to unnecessary treatment with antiviral compounds, such as ganciclovir, which have drawbacks (13). Here, we describe another type of case in which high HHV-6 viral load is also caused by integrated HHV-6 and could be misinterpreted as an active infection leading to unnecessary treatment. The patient is a 25-year-old woman diagnosed with Hodgkin’s lymphoma having experienced failure after a prior autologous transplant. The disease before transplantation was chemosensitive and in good partial remission. She was given an allogeneic HSCT mobilized from peripheral blood on July 11, 2008, from a 38-year-old unrelated matched (10 of 10 loci) female donor. The reduced-intensity conditioning regimen included Fludarabine (25 mg/m2/day) on days −7 to −3, Melphalan (140 mg/m2) on day −2, and ATG Fresenius (13 mg/kg/day) on days −5, −3, and −1. The prophylaxis of graft-versus-host disease included cyclosporin and mycophenolate mofetil. The recipient’s whole blood (WB) samples were tested weekly for adenovirus (14), Epstein-Barr virus, cytomegalovirus (CMV), and HHV-6 (EBV R-gene™ and CMV HHV6,7,8 R-gene™; Argène, Varilhes, France) by quantitative polymerase chain reaction (qPCR) after DNA isolation (Magna Pure LC system®, Roche, Meylan, France); the results were expressed as genomic equivalent copies per milliliter of WB. Moreover, albumin gene DNA was retrospectively amplified according to Laurendeau et al. (15) to quantify HHV-6 gec/106 cells, considering that each cell contains two copies of albumin genome (16). Retrospectively, HHV-6 DNA was tested in the donor’s peripheral blood mononuclear cells. Before the graft, a high HHV-6 viral load (1.30×108 gec/106 cells) led to treatment with intravenous foscarnet (180 mg/kg/day) from day −7 pretransplant to day +14 posttransplant, without decrease in the viral load. Other infectious events included fever of undocumented origin on day 1 and CMV infection on day 45, successfully treated with valganciclovir. The high HHV-6 viral load before transplantation was in favor of integrated HHV-6 and should have prevented patient treatment. Retrospectively, HHV-6 integration in the recipient was confirmed by HHV-6 DNA isolation in hair follicles (17) and mouth swab specimens. The recipient’s parents could not be tested for integrated HHV-6 (6). Besides, HHV-6 DNA was undetectable in donor peripheral blood mononuclear cells. Unexpectedly, 37 days after the transplantation, the HHV-6 viral load in WB remained up to 8.45×105 gec/106 cells. Quantitative analysis of hematopoietic chimerism was performed by real-time qPCR using TaqMan technology (Applied Biosystems, Foster City, CA) (18), and confirmed that there was still 1% of the recipient cells in blood samples at days 30 and 40 posttransplantation (Fig. 1). This could partially explain why the HHV-6 load was still so high (i.e., 1% of recipient cells containing 108 gec/106 cells fits with 106 gec/106 cells in WB).FIGURE 1.: HHV-6 viral load in whole blood expressed as log10 genomic equivalent copies per milliliter of whole blood (▴) and as log10 genomic equivalent copies/106 cells (▪), leukocyte count (⋄) and chimerism result in hematopoietic stem-cell transplantation recipient.Moreover, the HHV-6 viral load was still detectable (threshold of detection: 2500 gec/mL) at day 121 posttransplantation. The persistence of HHV-6 DNA in WB many months after transplantation is probably secondary to the release of chromosomal DNA from nonhematopoietic cells (19). Thus, the presence of integrated HHV-6 in HSCT recipients as well as in HSCT donors could lead to persistent high HHV-6 viral load, detected by sensitive qPCR. In those cases, viral integration must be confirmed by several analyses to prevent useless toxic antiviral treatments; indeed, to our knowledge, no case of symptomatic reactivation has been described in HHV-6-integrated patients. Moreover, the patients’ follow-up for HHV-6 viral load expressed as genomic equivalent copies/106 cells is more descriptive of a decrease in DNA during cell reconstitution (Fig. 1), as has been demonstrated previously in cases of integrated HHV-6 transmission through HSCT (9, 11). Hélène Jeulin Matthieu Guéry Laboratoire de Virologie CHU de Nancy Brabois Vandoeuvre-lès-Nancy, France Laurence Clément Alexandra Salmon Service de Transplantation Médullaire CHU de Nancy Brabois Vandoeuvre-lès-Nancy, France Mylène Beri Laboratoire de Génétique CHU de Nancy Brabois Vandoeuvre-lès-Nancy, France Pierre Bordigoni Service de Transplantation Médullaire CHU de Nancy Brabois Vandoeuvre-lès-Nancy, France Véronique Venard Laboratoire de Virologie CHU de Nancy Brabois Vandoeuvre-lès-Nancy, France