Risk of transmission of herpesviruses through cord blood transplantation

Human herpes simplex virus-6 (HHV-6) detection and seroprevalence among Qatari nationals and immigrants residing in Qatar

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The prevalence of anti-human herpes virus-6 immunoglobulin G (IgG) was 71.7% among healthy donors in Qatar.

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One-quarter (24.3%) of healthy donors in Qatar had detectable viraemia.

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No strong association was found between viraemia and IgG positivity.

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A significant association was found between viraemia and the nationality of healthy donors.

Background

Human herpes simplex virus-6 (HHV-6) is the causative agent of exanthema subitum. Transmission mainly occurs through salivary secretions, yet blood transfusions and organ transplantations have also been reported as routes of transmission. Studies of seroprevalence of HHV-6 in the Middle East and North Africa (MENA) region and other parts of Asia are scarce. As such, this study aimed to estimate the seroprevalence of HHV-6 among healthy blood donors in Qatar.

Methods

In total, 620 healthy blood donors from different nationalities residing in Qatar, mainly from the MENA region and Southeast Asia, were tested using a commercial anti-HHV-6 immunoglobulin G (IgG) enzyme-linked immunosorbent assay kit. In addition, HHV-6 DNA from randomly selected samples was tested and quantified using quantitative reverse transcriptase polymerase chain reaction.

Results

Anti-HHV-6 IgG was detected in 71.7% (445/620) [95% confidence interval (CI) 68.2–75.3%] of the tested samples, while 24.3% (61/251) (95% CI 20.0–29.6%) had detectable HHV-6 viraemia. Only 22.5% of individuals with positive IgG status had detectable HHV-6 DNA in their blood, indicating a weak association between viraemia and IgG positivity (P=0.08). Furthermore, no significant difference was associated between HHV-6 viraemia and demographic characteristics, except for nationality.

Conclusion

The seroprevalence of HHV-6 in Qatar was found to be similar to rates reported in other parts of the world.

Transfusion-related Epstein-Barr virus (EBV) infection: A multicenter prospective cohort study among pediatric recipients of hematopoietic stem cell transplants (TREASuRE study)

BACKGROUND

Epstein-Barr virus (EBV) is carried in the blood of most adults, and transfusion-related infections have been reported. EBV is particularly deleterious in immunosuppressed transplant patients. The aim was to determine if EBV transmission occurred through leukodepleted blood product transfusion in pediatric recipients of hematopoietic stem cell transplants (HSCT).

STUDY DESIGN AND METHODS

This prospective Canadian multi-center cohort study includes 156 allogeneic HSCT pediatric recipients. The association between EBV and transfusion was analyzed using Cox regressions. EBV infection, defined by a PCR+ test in the blood of seronegative recipients of an EBV-negative graft, was monitored in order to correlate the recipient EBV strain with that of the blood donors. EBV genotypes were determined by PCR amplification followed by DNA sequencing at two loci (EBNA3b and LMP1).

RESULTS

No statistically significant associations were found between transfusions and EBV. One case of post-transplant EBV infection was identified among the 21 EBV-seronegative recipients receiving an EBV-negative graft. A total of 22 blood donors were retraced to determine whether the recipient's EBV strain matched that of a donor. One donor strain showed 100% sequence homology at the EBNA3b locus, but differed by one or two point mutations and by a 132-bp deletion at the LMP1 locus. The blood donor in question was alone among the 22 donors to show amplifiable virus in plasma. Blood from this donor readily produced an immortalized lymphoblastoid cell line in culture.

CONCLUSION

While considered a rare event, EBV transmission through transfusion may occur in the context of severe immunosuppression.

Human cord blood-derived viral pathogens as the potential threats to the hematopoietic stem cell transplantation safety: A mini review

Umbilical cord blood (UCB) is a valuable source of hematopoietic stem cells (HSCs) and potential alternative for bone marrow transplantation for patients who lack human leukocyte antigen (HLA)-matched donors. The main practical advantages of UCB over other HSC sources are the immediate availability, lower incidence of graft-versus-host disease, minimal risk to the donor, and lower requirement for HLA compatibility. However, the use of UCB is limited by delayed engraftment and poor immune reconstitution, leading to a high rate of infection-related mortality. Therefore, severe infectious complications, especially due to viral pathogens remain the leading cause of morbidity and mortality during the post-UCB transplantation (UCBT) period. In this context, careful screening and excluding the viral-contaminated UCB units might be an effective policy to reduce the rate of UCBT-related infection and mortality. Taken together, complete prevention of the transmission of donor-derived viral pathogens in stem cell transplantation is not possible. However, having the knowledge of the transmission route and prevalence of viruses will improve the safety of transplantation. To the best of our knowledge, there are few studies that focused on the risk of virus transmission through the UCB transplant compared to other HSC sources. This review summarizes the general aspects concerning the prevalence, characteristics, and risk factors of viral infections with a focus on the impact of viral pathogens on cord blood transplantation safety.

Quantification of viral genome in cord blood donors by real time PCR to investigate human herpesvirus type 8 active infection

Umbilical cord blood (UCB) is one of the most important sources of hematopoietic stem cells which can be used for transplantation. The transplanted CB stem cells might cause infections in recipients. The aim of this study is to evaluate Human Herpes Virus8 (HHV8) as a Rhadinovirus among CB samples in order to assess safety of cord blood stem cells transplantation. To assess this aim, we surveyed 800 cord blood specimens by Real Time PCR.The overall HHV8 incidence in cord blood mononuclear cells was 1.38% and none of them was in lytic phase of HHV8. The authors suggest further HHV8 study on CB samples for transplantation.

Quantitative polymerase chain reaction for detection of human herpesvirus-7 infection in umbilical cord blood donors

OBJECTIVE

Umbilical cord blood (UCB) has been a reasonable alternative to granulocyte colony-stimulating factor-mobilized peripheral blood or bone marrow, as a source of hematopoietic stem cells with a lower risk of graft-versus-host disease. In immunocompromised hosts after transplantation, the risk of viral infection in adults, especially with beta-herpesviruses such as human herpesvirus-7 (HHV-7), may be increased. This virus in immunocompromised patients can be reactivated from latency and converted to an active phase. Therefore, light-upon-extension real-time polymerase chain reaction (PCR) was developed to assess the prevalence and load of HHV-7 in the plasma and buffy coat of donors.

METHODS

About 825 UCB samples under standard protocol from donors were collected. Then, DNA from plasma and buffy coat was extracted and quantitative real-time PCR was performed with light-upon-extension primers.

RESULTS

Overall, HHV-7 was detected in 3.64% (30/825) of UCB donors. HHV-7 DNA was detected in 26 (3.2%) buffy coat samples (latent infection), and only 4 (0.48%) of them were positive for HHV-7 DNA in plasma samples (active infection); the mean HHV-7 viral load was 1.31 × 10(1) copies/mL in latent infection, and 1.94 × 10(5) copies/mL in active infection.

CONCLUSIONS

We suggest that real-time PCR in plasma and buffy coat could be a useful method to detect active and latent HHV-7 infection in UCB donors and determine its role in subsequent transmission events.

Human herpesvirus 6 infection after hematopoietic cell transplantation: is routine surveillance necessary?

Human herpesvirus 6 (HHV6) may be an important pathogen following allogeneic hematopoietic cell transplantation (HCT). We prospectively evaluated weekly HHV6 viremia testing after allogeneic HCT using a quantitative polymerase chain reaction (PCR)-based assay. HHV-6 viremia was detected in 46 of 82 (56%) patients at a median of 23 days post-HCT (range: day +10 to +168). More males (65% vs females 39%, P = .03) and recipients of umbilical cord blood (UCB 69% vs unrelated donor [URD], 46% vs sibling donor [20%] grafts, P = 0.01) reactivated HHV-6. Patients with HHV6 viremia had more cytomegalovirus (CMV) reactivation (26% vs 5.5%, P = .01) and unexplained fever and rash (23.9% vs 2.7%, P = .01) compared with patients without HHV6 viremia. High-level HHV6 (≥ 25,000 copies/mL) versus lower levels were associated with more culture-negative pneumonitis (72.7% vs 22.8%, P = .01). Twenty HHV6-positive patients were treated with foscarnet, ganciclovir, or cidofovir for HHV6 or other coexistent viruses. Within 2 weeks, HHV6 viremia resolved more commonly in treated (65%) than untreated patients (31%), P = .02. Survival at 3 months was similar in treated and untreated patients (90% vs 81%, P = .4). Survival at 3 and 6 months post-HCT were not affected by HHV6 positivity (3 months HHV6+ 85% vs 78%, P = .46; 6 months HHV6+ 70% vs 72%, P = .89) or by HHV6 level (3-month high level 73% vs 89%, P = .23; 6-month high level 64% vs 71%, P = .54). Neither the occurrence of HHV6, degree of viremia, nor use of antiviral drugs influenced short-term survival after HCT.

Functionally active virus-specific T cells that target CMV, adenovirus, and EBV can be expanded from naive T-cell populations in cord blood and will target a range of viral epitopes

The naive phenotype of cord blood (CB) T cells may reduce graft-versus-host disease after umbilical cord blood transplantation, but this naivety and their low absolute numbers also delays immune reconstitution, producing higher infection-related mortality that is predominantly related to CMV, adenovirus (Adv), and EBV. Adoptive immunotherapy with peripheral blood-derived virus-specific cytotoxic T lymphocytes (CTLs) can effectively prevent viral disease after conventional stem cell transplantation, and we now describe the generation of single cultures of CTLs from CB that are specific for multiple viruses. Using EBV-infected B cells transduced with a clinical-grade Ad5f35CMVpp65 adenoviral vector as sources of EBV, Adv, and CMV antigens, we expanded virus-specific T cells even from CB T cells with a naive phenotype. After expansion, each CTL culture contained both CD8(+) and CD4(+) T-cell subsets, predominantly of effector memory phenotype. Each CTL culture also had HLA-restricted virus-specific cytotoxic effector function against EBV, CMV, and Adv targets. The CB CTLs recognized multiple viral epitopes, including CD4-restricted Adv-hexon epitopes and immunosubdominant CD4- and CD8-restricted CMVpp65 epitopes. Notwithstanding their naive phenotype, it is therefore possible to generate trivirus-specific CTLs in a single culture of CB, which may be of value to prevent or treat viral disease in CB transplant recipients. This study is registered at www.clinicaltrials.gov as NCT00078533.

Infections in 100 cord blood transplantations: spectrum of early and late posttransplant infections in adult and pediatric patients 1996-2005

Cord blood-derived stem cells are successfully used in the treatment of cancer and congenital disorders in children. This alternative source of stem cells is also explored for adult cancer patients with limited donor options. However, delayed engraftment, prolonged neutropenia, secondary graft loss, and graft-versus-host disease (GVHD) in recipients of cord blood transplantation (CBT) make opportunistic infections a serious concern. We evaluated the spectrum of infections in adults and children undergoing CBT at our National Cancer Institute-designated comprehensive cancer center. The infection incidence rate ratio (total infection episodes/days at risk [survival after CBT] x 100) was 2.4 times higher in 35 adult patients than in 62 children, especially in adults with neutropenia (3 x higher) and GVHD (1.9 x higher). Ninety-two percent of fungal infection episodes occurred within 100 days after transplantation; half of these infections occurred in the first 30 days after CBT. Most bacterial infections (80%) were also diagnosed in the first 100 days, whereas late (>100 d) post-CBT cytomegalovirus and varicella zoster virus infections occurred only in children with chronic GVHD. Multivariate analysis showed that resolution of lymphocytopenia (> or =1000 cells/microL) (hazard ratio [HR] 0.71; p < 0.0001) and successful engraftment (HR 0.20; p < 0.0001) were associated with a low risk of serious infection. Children (HR 0.36; p < 0.0002) with sustained engraftment (HR 0.39; p < 0.004) and those with cancer in remission (HR 0.47; p < 0.007) were less likely to die from infection. More effective measures for surveillance and prevention of late cytomegalovirus and varicella zoster virus infections in children with CBT and chronic GVHD are needed.

Infectious complications following unrelated cord blood transplantation

INTRODUCTION

Infections following cord blood transplantation are just beginning to be defined in the literature. This review will outline infections at death, the epidemiology of individual infections, and the impact of stem cell source.

METHODS

A review of studies published since 2000.

RESULTS

Based on registry data, most studies demonstrate an approximate rate of infection at death of 30-40% among cord blood recipients. Bacterial infections often occur prior to engraftment and increase among patients with graft failure. In addition, there is delayed recovery of the immune response among patients with graft-versus-host disease that leads to viral infections at later time points. The risk of serious infection among children receiving umbilical cord blood (UCB) grafts is comparable to that of children receiving unmanipulated marrow and is lower than that of recipients of a T-cell-depleted stem cell source. Among adult patients, despite an overall higher incidence of serious infections after UCB transplantation as compared with unrelated donor grafts, non-relapse mortality and overall survival were not significantly different between haematopoietic stem cell sources.

CONCLUSIONS

Further studies are needed to confirm these observations and determine whether the risk of infection for cord blood recipients is comparable to that of recipients of unmanipulated marrow.

Biological and clinical advances in human herpesvirus-6 and -7 research

Since its isolation more than 20 years ago, human herpesvirus (HHV)-6 has been considered an opportunistic pathogen whose infection and/or reactivation is associated with diseases such as roseola, organ transplant anomalies and central nervous system disorders. The lack of relevant animal models, standardized diagnostic reagents and specific anti-HHV-6 drugs has impaired our ability to prove a causal relationship between the presence of this virus and the development of many diseases. Unless such models and reagents are developed and clinical trials performed, speculations on the role for this virus in various pathologies will continue to grow. In this review, recent biological, clinical and epidemiological research advances in the HHV-6 field as well as that of its closest relative, HHV-7, will be presented. Additionally, priority research areas that will help move the field forward are discussed.