Varicella-zoster virus-specific cellular immunity in subjects given acyclovir after household chickenpox exposure

The effect of varicella-zoster virus reactivation on the long-term outcomes of patients undergoing allogeneic hematopoietic stem cell transplantation

BACKGROUND

A virus infection may lead the body to produce more immune cells of particular types or stimulate the production of new ones, both of which may have anti-leukemic effects. There has been no research on whether immune cells stimulated by varicella-zoster virus (VZV) infection have anti-leukemic effects. The objective of this investigation is to assess the impact of VZV infection on patients' long-term survival following allogeneic hematopoietic stem cell transplantation (allo-HSCT).

METHODS

This retrospective study investigated the association between varicella-zoster virus (VZV) reactivation and outcomes in 219 individuals who received allogeneic hematopoietic stem cell transplantation (allo-HSCT) at the Sun Yat-sen University's First Affiliated Hospital. According to being diagnosed with VZV infection or not, these patients were grouped into two groups. The comparison of cumulative incidence of relapse, non-recurrent mortality, and overall survival (OS) was conducted between the two groups.

RESULTS

Analyzing multivariate data, VZV reactivation was linked to lower relapse incidence in the group containing all individuals (hazard ratio [HR] = 0.27; 95% confidence interval [CI], 0.12-0.64), patients suffering from acute myeloid leukaemia (HR = 0.10; 95% CI, 0.01-0.83), and patients suffering from acute lymphoblastic leukaemia (HR = 0.25; 95% CI, 0.08-0.77). Moreover, VZV reactivation was linked with decreased non-relapse mortality in all individuals (HR = 0.20; 95% CI, 0.05-0.79), but no statistical significance was found for any disease subgroup. Further, VZV reactivation was an independent predictor for improved OS in the group containing all individuals (HR = 0.10; 95% CI, 0.03-0.29), patients suffering from acute myeloid leukaemia (HR = 0.09; 95% CI, 0.01-0.66), and patients suffering from acute lymphoblastic leukaemia (HR = 0.16; 95% CI, 0.04-0.68).

CONCLUSION

This is the first study to show that VZV reactivation following allo-HSCT is an independent predictor for lower relapse rates and improved OS, providing novel therapeutic approaches to improve patients' long-term survival following allo-HSCT.

Managing varicella zoster virus contact and infection in patients on anti-rheumatic therapy

Chickenpox and shingles can be more severe and occasionally life threatening in immunosuppressed patients. As such, some groups warrant a more detailed history, serological testing and consideration of prophylaxis following contact with the virus. Active disease may also require more aggressive treatment with antivirals. Guidance for the use of varicella zoster immunoglobulin has recently been updated by Public Health England with important implications for rheumatology patients.

Varicella Vaccination of Children With Leukemia Without Interruption of Maintenance Therapy: A Danish Experience

BACKGROUND

Varicella-zoster virus (VZV) can be fatal or cause severe complications in children with acute lymphoblastic leukemia (ALL). This analysis set out to investigate the morbidity and mortality of VZV vaccination without interruption of maintenance therapy in children with ALL.

METHODS

Files of 73 seronegative children with ALL were examined for data regarding VZV vaccination and infection, and long-term seroconversion was measured. Criteria before VZV vaccination were (1) seronegative, (2) in complete remission, (3) age ≥ 1.0 year, (4) lymphocyte count ≥ 0.6 × 10/L at time of vaccination and (5) receiving maintenance therapy.

RESULTS

Forty-five children were vaccinated. No child died or experienced serious adverse events due to VZV vaccination. Nine children developed late chickenpox despite vaccination. Long-term protection was found in 86% of children not receiving acyclovir and 78% of the entire population. Long-term seroconversion was found in 52% of the children. There were no severe cases of varicella infection. Acyclovir prophylaxis postvaccination was associated with an increased risk of late chickenpox [hazard ratio = 5.40 (1.43, 20.41), P = 0.01]. In contrast, a vaccine-induced rash reduced the risk of late chickenpox [hazard ratio = 0.08 (0.01, 0.66), P = 0.02]. No child had interruption of maintenance therapy at the time of vaccination, but 33% experienced discontinuation of therapy due to vaccine-induced rash. Dexamethasone was associated with an increased risk of vaccine-induced rash [hazard ratio = 2.9 (1.21, 6.90), P = 0.02].

CONCLUSIONS

This analysis indicates that VZV vaccination is feasible and justified in seronegative children with ALL, in countries where VZV vaccination is not part of the national vaccination program.

Virus specific cell-mediated immunity may play a role in controlling reactivated human herpesvirus 6B in patients under measles induced immunosuppression

For a better understanding of the cellular immune responses to reactivated HHV 6B the lymphoproliferative response to human herpesvirus 6B (HHV 6B) antigen was measured in three consecutive specimens obtained biweekly from 22 young children and infants suffering from acute measles, and in 19 influenza patients and nine healthy control subjects. HHV 6B DNA in peripheral blood mononuclear cells (PBMCs) was detected in 18 of 22 subjects with measles, but not in the influenza patients or the healthy population. A novel reactivation profile of HHV 6B was found in patients with measles in the milder form of immunosuppression than in patients with organ transplantation. HHV 6B specific lymphoproliferation activities increased correspondingly with reactivation of HHV 6B assessed by detecting HHV 6B DNA in PBMCs in patients with measles, but no significant change in either the antibody response to HHV 6B or DNAemia occurred in serial specimens obtained either from patients with influenza or healthy subjects. This novel form of HHV 6B reactivation without antibody response was observed in patients with measles. The dynamic fluctuations in lymphoproliferative responses in measles may represent the balance between HHV 6B reactivation and its suppression by the host immune system.

Preventing varicella in children with malignancies: what is the evidence?

PURPOSE OF REVIEW

The prevention of varicella in children with cancer is generally agreed to be an important goal, because of their elevated risk of varicella zoster virus (VZV)-associated morbidity and mortality. However, there is a lack of consensus on the best means of achieving this. Here, we review the existing evidence in relation to postexposure prophylaxis against varicella in this group and summarize data regarding the role of active vaccination.

RECENT FINDINGS

Death from varicella during treatment for cancer is now rare, but VZV disease and its prevention remain significant problems in paediatric oncology practice. Measures to reduce VZV exposure amongst seronegative individuals are often neglected. When exposure is known to have occurred, early administration of varicella zoster immune globulin (VZIG) is generally protective against severe and complicated varicella. However, many centres in the UK and Japan use an oral antiviral agent, aciclovir, in place of VZIG. Published evidence for the efficacy of aciclovir as postexposure prophylaxis (PEP) relates mostly to healthy children, with no controlled studies in the immunocompromised.

SUMMARY

Good evidence already supports the administration of varicella vaccine to healthy susceptible family contacts of children with malignancy, but not to patients themselves. Further data are urgently needed to inform the choice of PEP against VZV in the immunocompromised.

VZV T cell-mediated immunity

Primary varicella-zoster virus (VZV) infection (varicella) induces VZV-specific antibody and VZV-specific T cell-mediated immunity. T cell-mediated immunity, which is detected within 1-2 weeks after appearance of rash, and consists of both CD4 and CD8 effector and memory T cells, is essential for recovery from varicella. Administration of a varicella vaccine also generates VZV-specific humoral and cellular immune responses. The memory cell responses that develop during varicella or after vaccination contribute to protection following re-exposure to VZV. These responses are subsequently boosted either by endogenous re-exposure (silent reactivation of latent virus) or exogenous re-exposure (environmental). VZV-specific T cell-mediated immunity is also necessary to maintain latent VZV in a subclinical state in sensory ganglia. When these responses decline, as occurs with aging or iatrogenic immune suppression, reactivation of VZV leads to herpes zoster. Similarly, the magnitude of these responses early after the onset of herpes zoster correlates with the extent of zoster-associated pain. These essential immune responses are boosted by the VZV vaccine developed to prevent herpes zoster.

Varicella vaccination in pediatric kidney and liver transplantation

Reports about efficacy and safety of live-virus attenuated vaccines in patients before and after transplantation are mainly based on small patient numbers, making general recommendations for this patient population difficult. Children and adults as well as their close relatives and contact persons should be preferably immune to VZV before solid organ transplantation to avoid VZV-associated complications, thus making VZV vaccination necessary in susceptible individuals. The following literature review focused on efficacy and safety of VZV vaccination in pediatric kidney and liver transplant recipients. Review of literature also revealed that in all pediatric transplant candidates, humoral and cellular immunity against VZV should be consistently monitored to assess waning immunity under immunosuppressive treatment. This approach is desirable to estimate the risk of severe varicella disease after exposure in these patients.

Varicella

Varicella-zoster virus, a herpesvirus, causes varicella (chickenpox) and, after endogenous reactivation, herpes zoster (shingles). Varicella, which is recognised by a characteristic vesicular rash, arises mainly in young children, although older individuals can be affected. In immunocompetent patients, symptoms are usually mild to moderate, but an uncomplicated severe case can have more than 1000 lesions and severe constitutional symptoms. Serious complications--including central nervous system involvement, pneumonia, secondary bacterial infections, and death--are sometimes seen. Varicella can be prevented by vaccination. Vaccine is about 80-85% effective against all disease and highly (more than 95%) effective in prevention of severe disease. In the USA, a routine childhood immunisation programme has reduced disease incidence, complications, hospital admissions, and deaths in children and in the general population, indicating strong herd immunity. Similar immunisation programmes have been adopted by some other countries, including Uruguay, Germany, Taiwan, Canada, and Australia, and are expected to be implemented more widely in future.

Time course characteristics of human herpesvirus 6 specific cellular immune response and natural killer cell activity in patients with exanthema subitum

The time-course of cell-mediated immunity in exanthema subitum is not well documented. The lymphoproliferative response to purified human herpesvirus 6 (HHV-6) antigen and to phytohemagglutinin was measured and natural killer (NK) cell activities determined in three consecutive specimens obtained biweekly from 18 young children and infants with exanthema subitum. Virus isolation and PCR detection of virus DNA and determination of neutralization antibody to HHV-6 and -7 were also carried out. The magnitude of the HHV-6 specific lymphoproliferative response varied; however, in most cases the time course kinetics revealed a low response in the acute phase with a subsequent gradual increase. In contrast, NK cell activities were high in the acute phase and declined gradually during convalescence. The lymphoproliferative response to phytohemagglutinin did not show a consistent trend in kinetics of time; however, dynamic changes in activity were observed in patients during the acute and convalescent periods. The results suggest that NK cells play a major role in resolving acute phase infection while specific lymphocyte activity develops later. The cause of the delayed development of HHV-6 specific lymphoproliferative response is unknown. The lymphoproliferative response to phytohemagglutinin ratios implied that HHV-6 infection has some impact on host T-cell immunity during the course of exanthema subitum.

Preventing varicella-zoster disease

Varicella-zoster virus (VZV), the cause of chickenpox and shingles, is a pathogen in retreat following the introduction of mass vaccination in the United States in 1995. The live attenuated Oka vaccine, which is safe and immunogenic, gives good protection against both varicella and zoster in the short to medium term. It has undoubtedly been highly effective to date in reducing all forms of varicella, especially severe disease. However, the huge pool of latent wild-type virus in the population represents a continuing threat. Both the biology and the epidemiology of VZV disease suggest that new vaccination strategies will be required over time.

Viral diseases of the skin: diagnosis and antiviral treatment

Viral diseases in children can present with characteristic mucocutaneous manifestations. This article focuses, from a practical clinical point of view, on the laboratory and clinical diagnoses, and treatment of pediatric dermatological diseases that have specific antiviral therapies: herpes virus infections (including varicella), papillomavirus infections and molluscum contagiosum. Special issues, such as viral infections in pregnancy, therapy of viral infections in immunosuppressed children, as well as special problems associated with the epidemiology of genital herpes and papillomavirus infections in adolescents are discussed. The antivirals discussed in detail include: aciclovir, valaciclovir, famciclovir, penciclovir, cidofovir, foscarnet and the immune response modulator, imiquimod. Since these antiviral drugs generally have not been evaluated in children, caution should be exercised with their usage.

Nosocomial spread of viral disease

Viruses are important causes of nosocomial infection, but the fact that hospital outbreaks often result from introduction(s) from community-based epidemics, together with the need to initiate specific laboratory testing, means that there are usually insufficient data to allow the monitoring of trends in incidences. The most important defenses against nosocomial transmission of viruses are detailed and continuing education of staff and strict adherence to infection control policies. Protocols must be available to assist in the management of patients with suspected or confirmed viral infection in the health care setting. In this review, we present details on general measures to prevent the spread of viral infection in hospitals and other health care environments. These include principles of accommodation of infected patients and approaches to good hygiene and patient management. They provide detail on individual viral diseases accompanied in each case with specific information on control of the infection and, where appropriate, details of preventive and therapeutic measures. The important areas of nosocomial infection due to blood-borne viruses have been extensively reviewed previously and are summarized here briefly, with citation of selected review articles. Human prion diseases, which present management problems very different from those of viral infection, are not included.

Immunization of pediatric solid organ transplant candidates and recipients

Organ transplantation has evolved from an experimental procedure to an accepted treatment for otherwise irreversible or congenital disorders. The immunosuppression necessary to prevent rejection enhances the severity of many infectious diseases and may potentially attenuate the response to vaccines designed to prevent disease. In spite of the frequency and severity of infectious diseases in organ transplant recipients, many children are not fully vaccinated before transplantation. The safety and efficacy of many of the currently available vaccines for solid organ transplant recipients have not been evaluated. We review the currently available data on immunization safety and efficacy, discuss experimental vaccines, and outline strategies to avoid vaccine-preventable diseases in pediatric organ transplant recipients.