Frequent detection of human herpesvirus 6 DNA in peripheral blood mononuclear cells from kidney transplant patients

Human herpesvirus-6 infections in kidney, liver, lung, and heart transplantation: review

Human herpesvirus-6 (HHV-6), which comprises of HHV-6A and HHV-6B, is a common infection after solid organ transplantation. The rate of HHV-6 reactivation is high, although clinical disease is not common. Only 1% of transplant recipients will develop clinical illness associated with HHV-6 infection, and most are ascribable to HHV-6B. Fever, myelosuppression, and end-organ disease, including hepatitis and encephalitis, have been reported. HHV-6 has also been associated with various indirect effects, including a higher rate of CMV disease, acute and chronic graft rejection, and opportunistic infection such as invasive fungal disease. All-cause mortality is increased in solid organ transplant recipients with HHV-6 infection. HHV-6 is somewhat unique among human viruses because of its ability to integrate into the host chromosome. The clinical significance of chromosomally integrated HHV-6 is not yet defined, although a higher rate of bacterial infection and allograft rejection has been suggested. The diagnosis of HHV-6 is now commonly made using nucleic acid testing for HHV-6 DNA in clinical samples, but this can be difficult to interpret owing to the common nature of asymptomatic viral reactivation. Treatment of HHV-6 is indicated in established end-organ disease such as encephalitis. Foscarnet, ganciclovir, and cidofovir have been used for treatment.

Sequential measurement of human herpesvirus 6 DNA with polymerase chain reaction method in pediatric living-related liver transplantation

BACKGROUND

Human herpesvirus 6 (HHV-6), a causative virus of exanthem subitum, may occasionally present with a severe clinical form in immunosuppressed patients after transplantation. In this study, HHV-6 DNA was sequentially measured with a polymerase chain reaction (PCR) method, a quick and sensitive modality in pediatric living-related liver transplantation (LTx).

METHODS

Subjects consisted of 5 post-operative biliary atresia patients undergoing living-related LTx at ages from 8 months to 4 yr. Immunosuppression was performed with Tacrolimus (blood trough level 8-18 within 1 month and 5-10 ng/mL thereafter) and low-dose steroid. Specimens were peripheral blood mononuclear cells (PBMC), plasma, and liver biopsy tissue. The amount of HHV-6 DNA was semiquantified as follows: 1+, 1-10; 2+, 10-100; 3+, 100-1000; 4+, over 1000 copies/105 PBMCs.

RESULTS

A total of 69 blood samples and three liver biopsies were provided for the examination. HHV-6 DNA in PBMC was positive in 2 donors and 3 recipients before LTx. Two patients with negative DNA were converted to 3+ at 2-3 wk after LTx and 3 with positive DNA remained 2+ to 3+ throughout the post-LTx period. Only 1 patient developed clinical symptoms, such as fever, liver dysfunction, petechiae, idiopathic thrombocytopenic purpura, and finally bone marrow suppression. HHV-6 DNA in the liver biopsy tissue and plasma in this patient were 4+ and 2+, respectively.

CONCLUSION

HHV-6 DNA in PBMC measured by the PCR method may be persistently high in pediatric recipients after living-related LTx. Although HHV-6 DNA in PBMC may be positive in case of evident infection, positivity in PBMC may not be always associated with the clinical symptoms.

Human herpesvirus-6 antigenemia after liver transplantation

BACKGROUND

Human herpesvirus (HHV)-6 has recently been reported in liver transplant patients. It infects and causes dysfunction in hepatic transplants, which provides serious differential diagnostic problems between allograft rejection and viral infection. The diagnosis of posttransplantation HHV-6 infection is usually based on serology or on polymerase chain reaction detection of viral DNA in peripheral blood specimens. However, serology does not tell the exact time of the infection, and detection of viral DNA by polymerase chain reaction may also indicate a latent infection in seropositive patients. Here we report the diagnostic use of frequent monitoring of HHV-6 antigenemia after liver transplantation.

METHODS

Altogether 622 blood specimens from 51 consecutive adult liver transplant patients were analyzed. The diagnosis was based on demonstration of HHV-6-specific antigens in peripheral blood mononuclear cells using immunoperoxidase staining and monoclonal antibodies and on serology.

RESULTS

During the first year (7-280 days) after transplantation, HHV-6 infection was diagnosed in 11 (22%) of 51 patients. HHV-6 early antigens, as well as HHV-6 variant B antigens, were detected in all 11 patients. HHV-6 diagnosis was confirmed by serology. The episode of HHV-6 antigenemia usually lasted for several weeks together with mild, if any, clinical signs of the infection. A significant graft dysfunction was associated with HHV-6 antigenemia in 8 of 11 patients, and viral antigens were also detected in the liver biopsy specimens of 3 of these patients.

CONCLUSIONS

An active HHV-6 infection can be diagnosed from peripheral blood by detection of virus-specific antigens in mononuclear cells. HHV-6 antigenemia correlated with seroresponse.

Human herpesvirus 6 infection and associated pathogenesis following bone marrow transplantation

Human herpesvirus 6 (HHV-6) infections following bone marrow transplantation (BMT) have been shown to be associated with fever, skin rash, graft versus host disease, encephalitis, delay in engraftment, marrow suppression, and pneumonia. Unfortunately several of these studies were case reports and although the results were suggestive they prompted us to study these pathological events systematically. These associations were primarily based on either HHV-6 isolation, HHV-6 DNA detection, antigen detection or increases in HHV-6 specific antibodies. HHV-6 activity was more frequent during the post- rather than the pre-transplantation period. All HHV-6 isolates from BMT patients have been shown to be variant B. A better understanding of HHV-6 associated pathogenesis gained by larger prospective trials is needed to facilitate proper treatment of cases of idiopathic illnesses or those associated with symptoms (fever, skin rash) similar to those caused by HHV-6.

Correlation between the detection of viral DNA by the polymerase chain reaction in peripheral blood leukocytes and serological responses to human herpesvirus 6, human herpesvirus 7, and cytomegalovirus in renal allograft recipients

Diagnosis of significant infections by human herpesvirus 6 (HHV6) and 7 (HHV7) in transplant patients has proved difficult because both viruses are ubiquitous and can cause persistent infections in their hosts. The significance of viral DNA detected in peripheral blood leukocytes (PBLs; DNAemia) by PCR is therefore unclear. The interpretation of serological results is complicated by the fact that both primary and secondary infections with other herpesviruses may be associated with a concurrent antibody response to HHV6. Fifty-four renal allograft recipients were studied prospectively and their serological response to HHV6, HHV7 and CMV were compared with the detection of viral DNAemia from the homologous and heterologous viruses. Serum and heparinished blood samples were collected prospectively from 54 renal allograft recipients. DNA was extracted from PBLs and tested for the presence of HHV6, HHV7 and CMV DNA by PCR. Antibodies to HHV6 and HHV7 were measured by an indirect immunofluorescence test and to CMV by an anticomplement immunofluorescence (ACIF) test. CMV IgM antibodies were detected by a commercial enzyme immunoassay. CMV and HHV7 DNAemia were each significantly associated with serological responses to the homologous virus but no such association was found for HHV6 DNAemia. However, patients with consecutively positive DNAemia to any of the viruses (including HHV6) were more likely to have a homologous serological response. Patients who had detectable CMV IgM without a concurrent rise in CMV antibodies were significantly less likely to have CMV DNAemia (odds ratio = 0.16; 95% CI 0.02-0.9). CMV IgM antibodies may be associated with HHV6 or HHV7 DNAemia (odds ratio 2.3; 95% CI 0.5-15). This serological profile may reflect a crossreactive response to HHV6, HHV7 or other herpesviruses. CMV IgM should not be used in isolation for the diagnosis of CMV infection or disease in this group of patients.

Human herpesvirus-6 infection in renal allografts: retrospective immunohistochemical study in Japanese recipients

This study was conducted to determine the incidence and clinical significance of human herpesvirus-6 (HHV-6) infection in renal allografts. A total of 105 biopsy specimens from 72 recipients were immunohistochemically examined for the presence of HHV-6 antigen, which localized in the distal tubular epithelial cells and in a few lymphocytes infiltrating into the interstitium. HHV-6 antigen in the tubular epithelia was detected in 63 (61.2%) specimens. Categorically, a higher incidence of the antigen was noted in specimens of accelerated rejection (3/4, 75.0%), acute rejection (28/3, 73.7%), and cyclosporin nephropathy (8/11, 72.7%). The antigen was present and absent an almost equal number of times in the categories of chronic rejection, intraoperative and routine protocol biopsies. Repeated biopsies were performed in six cases showing HHV-6 antigen, only one of which underwent transplant nephrectomy due to severe chronic rejection. Single or multinucleated giant cells in distal tubuli occurred in 10 (9.5%) specimens in a scattered manner. All of them were diagnosed as acute or chronic rejection. The giant cells showed no immunoreactivity for HHV-6, cytomegalovirus, or herpes simplex virus. These results indicate overall that HHV-6 infection is common in renal allografts and might be reactivated in acute rejection or cyclosporin nephropathy. The presence of HHV-6 antigen, however, does not necessarily correlate with a poor prognosis for the renal graft nor with the occurrence of giant cells in distal tubuli.

Low-incidence latent infection with variant B or roseola type human herpesvirus 6 in leukocytes of healthy adults

Nested primer-based polymerase chain reaction was employed to determine the frequency of latent infection with human herpesvirus 6 (HHV-6) among healthy adults from Bratislava, Slovak Republic. A 592-bp region, upstream from the gene encoding the putative large tegument protein of HHV-6, was amplified from DNA extracted from peripheral blood mononuclear cells (PBMC) of only one of 29 seropositive adults, suggesting that as few as 1 in 10(5) PBMC may be infected with the virus. Direct sequencing of the 592-bp fragment indicated that the virus harbored by the seropositive Slovak subject (designated B38) differed by only 3 nucleotides from an HHV-6 variant B strain (R-147) isolated from an American infant with a roseola-like illness and by 32 bases from the variant A strain GS isolated from a patient with lymphadenopathy (5.4% sequence divergence). None of these strains had a deoxyadenosine at base position 1251, when compared to the published sequence of strain GS clone pZVH14. Although this discrepancy did not affect the large tegument protein gene, it altered the predicted amino acid sequences of two putative proteins coded by open-reading frames 1 and 2 (ORF 1 and ORF 2) located upstream from this gene.

Activation of the Epstein-Barr virus replicative cycle by human herpesvirus 6

One common attribute of herpesviruses is the ability to establish latent, life-long infections. The role of virus-virus interaction in viral reactivation between or among herpesviruses has not been studied. Preliminary experiments in our laboratory had indicated that infection of Epstein-Barr virus (EBV) genome-positive human lymphoid cell lines with human herpesvirus 6 (HHV-6) results in EBV reactivation in these cells. To further our knowledge of this complex phenomenon, we investigated the effect of HHV-6 infection on expression of the viral lytic cycle proteins of EBV. Our results indicate that HHV-6 upregulates, by up to 10-fold, expression of the immediate-early Zebra antigen and the diffuse and restricted (85 kDa) early antigens (EA-D and EA-R, respectively) in both EBV producer and nonproducer cell lines (i.e., P3HR1, Akata, and Raji). Maximal EA-D induction was observed at 72 h post-HHV-6 infection. Furthermore, expression of late EBV gene products, namely, the viral capsid antigen (125 kDa) and viral membrane glycoprotein gp350, was also increased in EBV producer cells (P3HR1 and Akata) following infection by HHV-6. By using dual-color membrane immunofluorescence, it was found that most of the cells expressing viral membrane glycoprotein gp350 were also positive for HHV-6 antigens, suggesting a direct effect of HHV-6 replication on induction of the EBV replicative cycle. No expression of late EBV antigens was observed in Raji cells following infection by HHV-6, implying a lack of functional complementation between the deleted form of EBV found in Raji cells and the superinfecting HHV-6. The susceptibility of the cell lines to infection by HHV-6 correlated with increased expression of various EBV proteins in that B95-8 cells, which are not susceptible to HHV-6 infection, did not show an increase in expression of EBV antigens following treatment with HHV-6. Moreover, UV light-irradiated or heat-inactivated HHV-6 had no upregulating effect on the Zebra antigen or EA-D in Raji cells, indicating that infectious virus is required for the observed effects of HHV-6 on these EBV products. These results show that HHV-6, another lymphotropic human herpesvirus, can activate EBV replication and may thus contribute to the pathogenesis of EBV-associated diseases.

Human herpesvirus-6 infection and bone marrow transplantation

Human herpesvirus-6 (HHV-6) is ubiquitous in the human population and causes exanthem subitum, a benign disease seen in infancy. However it also produces a wide spectrum of clinical manifestations including cases with a fatal outcome. The virus remains latent in several organs, including the kidneys, liver, lymph/nodes and salivary glands, after the primary infection and reactivates when immune function is impaired. Reactivation of the virus occurred in a half of the bone marrow recipients 2 to 4 weeks after bone marrow transplantation (BMT). It remains to be established whether HHV-6 in fact causes the fever and rash observed in recipients who have reactivation of the virus. The data reviewed here will be required to compare with those of human herpesvirus 7 and a different group of HHV-6.