Anthony R. Hayward

Decline in Varicella-Zoster Virus (VZV)–Specific Cell-Mediated Immunity with Increasing Age and Boosting with a High-Dose VZV Vaccine

The safety and immunogenecity of a booster dose of live attenuated varicella-zoster virus (VZV) vaccine was evaluated in 196 healthy subjects, >or=60 years old, who had already received a VZV vaccine >5 years before. This repeat booster dose was well tolerated. Cell-mediated immunity (CMI) to VZV was measured by an interferon-gamma (IFN-gamma) enzyme-linked immunosorbent spot-forming cell (ELISPOT) assay and a limiting dilution responder cell frequency (RCF) assay. Prevaccination responses decreased as a function of increasing age but were detectable in all subjects by use of the IFN-gamma ELISPOT assay. In most subjects, VZV-specific CMI was increased at 6 weeks postvaccination. The magnitude of the vaccine-induced IFN-gamma ELISPOT response was inversely related to prevaccination values. Although there was a significant correlation between the IFN-gamma ELISPOT and RCF assays, the ELISPOT assay had greater sensitivity and a wider dynamic range. A live attenuated VZV vaccine is safe and immunogenic in an elderly population, and the vaccine-induced immunity may be monitored by the IFN-gamma ELISPOT assay.

Use of a Live Attenuated Varicella Vaccine to Boost Varicella-Specific Immune Responses in Seropositive People 55 Years of Age and Older: Duration of Booster Effect

Varicella-zoster virus (VZV)-specific T cell immunity was measured in 130 persons > or = 55 years of age 6 years after they received a live attenuated VZV vaccine. Circulating T cells, which proliferated in vitro in response to VZV antigen, were enumerated (VZV responder cell frequency assay). Six years after the booster vaccination, the VZV-responding cell frequency (1/61,000 circulating cells) was still significantly (P < .05) improved over the baseline measurements (1/70,000) and appears to have diminished the expected decline in frequency as these vaccinees aged (to 1/86,000). Ten herpes-zoster--like clinical events were recorded. Although the frequency of these events, approximately 1/100 patient-years, is within the expected range of such events for this age cohort, the number of lesions was small, there was very little pain, and there was no postherpetic neuralgia. These results support the development of a vaccine to prevent or attenuate herpes zoster.

PREVENTION OF HERPES ZOSTER

The live attenuated varicella vaccine offers some hope that the frequency or severity of herpes zoster might be reduced. Universal immunization with this vaccine should result in less latent varicella-zoster virus in dorsal root and cranial nerve ganglia than that which occurs following varicella. Moreover, the vaccine virus is not well adapted for growth in human cells at normal body temperature. Thus, reduced virus for reactivation, and less robust replication, may lessen the problem of herpes zoster in vaccinees. For those individuals who have already had varicella, the risk of herpes zoster is closely related to the loss of varicella-zoster virus cell-mediated immune responses, which decline with aging (or immune suppression). In aging individuals these immune responses can be enhanced by booster immunization with the varicella vaccine, suggesting that a vaccine to prevent herpes zoster is feasible.

Development of lymphocyte responses and interactions in the human fetus and newborn.

Information concerning immunity development in humans was initially obtained during the course of devising immunization schedules which were suitable for infants. The recognition of the severe structural malformations which could result from congenital infection stimulated interest in the immunological responsiveness of the fetus and in ways by which the immunity development of the fetus might be adversely affected by the infection. As pregnancies were terminated by hysterotomy on account of proven or suspected congenital infection an increased number of fetal tissues became available for study. One use that these aborted tissues were put to was the grafting of infants with severe congential immunodeficiencies, mostly severe combined immunodeficiency (reviewed by Kay 1972). Some of the recipients developed graft versus host disease, making it clear that fetal lymphocytes were not necessarily incompetent. Further studies on fetal lymphoid tissues were therefore directed towards identifying a critical stage in lymphoid development when the cells could learn to tolerate a new host but would retain their potential for anti• microbial immunity. Since hysterotomy has been abandoned as a common means for terminating pregnancy, and since the advent of rubella immunization.

Cellular Immunity to Varicella-Zoster Virus in Patients with Major Depression

The incidence of herpes zoster increases markedly with advancing age, and this appears to be causally related to an age-dependent decline in varicella-zoster virus (VZV)-specific cellular immunity. Psychologic stress has also been linked to the occurrence of herpes zoster, but the mechanism involved has not been investigated. This study examined the relationship between major depression and VZV-specific cellular immunity by comparing VZV-specific responder cell frequency (RCF) in adults with major depression (n = 11) to that in age- and sex-matched nondepressed controls (n = 11) and in a larger group of nondepressed adults who were > or = 60 years old. VZV-specific RCF in depressed patients was markedly reduced compared with the RCF in matched controls (t = 2.7, P < .02). In fact, the levels of VZV-specific RCF in the depressed patients were comparable in magnitude to the low levels found in adults > or = 60 years of age. These data indicate that major depression is associated with a marked decline in VZV-specific cellular immunity.

Influence of Age and Nature of Primary Infection on Varicella-Zoster Virus—Specific Cell-Mediated Immune Responses

BACKGROUND Varicella-zoster virus (VZV)-specific cell-mediated immunity is important for protection against VZV disease. We studied the relationship between VZV cell-mediated immunity and age after varicella or VZV vaccination in healthy and human immunodeficiency virus (HIV)-infected individuals. METHODS VZV responder cell frequency (RCF) determinations from 752 healthy and 200 HIV-infected subjects were used to identify group-specific regression curves on age. RESULTS In healthy individuals with past varicella, VZV RCF peaked at 34 years of age. Similarly, VZV-RCF after varicella vaccine increased with age in subjects aged <1 to 43 years. In subjects aged 61-90 years, VZV RCF after zoster vaccine decreased with age. HIV-infected children had lower VZV RCF estimates than HIV-infected adults. In both groups, VZV RCF results were low and constant over age. Varicella vaccination of HIV-infected children with CD4 levels 20% generated VZV RCF values higher than wild-type infection and comparable to vaccine-induced responses of healthy children. CONCLUSIONS In immunocompetent individuals with prior varicella, VZV RCF peaked in early adulthood. Administration of varicella vaccine to HIV-infected or uninfected individuals aged >5 years generated VZV RCF values similar to those of immunocompetent individuals with immunity induced by wild-type infection. A zoster vaccine increased the VZV RCF of elderly adults aged <75 years to values higher than peak values induced by wild-type infection.

Interferon-γ Is Required for Innate Immunity to Cryptosporidium parvum in Mice

Although CD4 T cells are required for recovery from cryptosporidial infection, mice with severe combined immunodeficiency (SCID) remain infected for long periods without ill effect. In contrast, mice whose ability to use interferon(IFN)‐g is impaired, by neutralization or gene knockout, experience heavy cryptosporidial infection that may lead to death. To determine whether the innate immunity of SCID mice to Cryptosporidium parvum (CP) requires IFNg, doubly immunodeficient C57BL/6 SCID‐IFN-g knockout mice were bred. These mice experienced heavy CP infections of the gut; a significantly greater number became moribund or died, compared with mice carrying the SCID mutation alone or carrying disrupted IFNg genes alone. Mice with gene disruptions of inducible nitric oxide synthetase or Fas/Fas ligand recovered normally from CP infection. The results indicate that mice unable to produce specific immune responses because of the SCID mutation require IFN-g to avoid death after infection with CP. Cryptosporidium parvum (CP) is an apicomplexan parasite that infects epithelial cells in the intestine and the biliary tree. CP has attracted attention recently because it is difficult to eradicate from water supplies and can cause large outbreaks of infection. CP causes only transient diarrhea in healthy individuals, but it is responsible for severe enteritis and cholangitis in immunodeficient individuals, including individuals infected with AIDS. Experience in humans indicates that CD4 cells and an intact CD40‐CD154 pathway [1] are required for recovery from CP infections. These conclusions are confirmed in mice, where cytokine neutralization studies have identified interleukin (IL)‐12 and interferon (IFN)‐g as important or essential cytokines [2‐4]. Roles of these potentially separate effector mechanisms have been explored, in part, by infecting gene-knockout mice with CP. B6 mice with disrupted IFN-g genes have been

Clinical application of responder cell frequency estimates with four years of follow up

Limiting dilution cultures have been used to estimate the frequency of T cells which respond to antigen stimulation in vitro, but nothing is known of the reproducibility of this assay when applied to human blood. We developed a simplified form of limiting dilution culture in which blood mononuclear cells were diluted in round bottom 96-well plates and cultured for 10 days. The assay was used to estimate the frequency of blood mononuclear cells proliferating in response to varicella-zoster virus antigen. 250 subjects aged 25-87 years were studied: 95 of these subjects had annual measurements repeated over a 4 year period. The coefficients of variation for intra-assay replicates was 5%, and for inter-assay comparisons was 17.6% and 26% for tests at a 1 or 3 month interval respectively. For subjects studied at 1 year intervals the coefficient of variation was 42% with the total variability equally distributed between the variation between subjects and the variation within subjects. These data provide the first quantitative data to validate limiting dilution cultures for the long term in vitro measurement of human T cell responses.

Varicella-zoster virus infection of human mononuclear cells

Varicella-zoster virus (VZV) DNA was detected in mononuclear cells (MNC) of 7 humans with acute zoster 1-23 days after the onset of skin lesions. To further study the interaction of VZV with human MNC, cells obtained from seropositive normal donors were infected with VZV and analyzed for the presence of viral DNA and proteins. VZV-DNA was detected in T, B, and OKM 1 (monocyte-macrophage) positive cells, and virus-specific proteins were demonstrated by indirect immunofluorescence and immunoprecipitation. Hybridization studies revealed that VZV-DNA did not replicate in human MNC.

Persistence of varicella-zoster virus DNA in blood mononuclear cells of patients with varicella or zoster

Varicella-zoster virus (VZV) DNA was detectable by in-situ hybridization in blood mononuclear cells (MNCs) of patients with varicella or zoster for 2–56 days after the onset of a rash. VZV DNA was present in many MNCs from one acute varicella patient 2 days after the onset of the rash and was rarely found in MNCs during acute zoster, convalescent zoster, and convalescent varicella. The morphology of MNCs containing VZV was heterogenous, although most viral-DNA-containing MNCs were large monocytoid cells. Serial examination of blood MNCs from one adult with varicella revealed VZV DNA up until 8 weeks, but not 16 weeks, after the appearance of the rash; parallel studies in four zoster patients showed VZV DNA up until 3 weeks, but not later than 7 weeks after the appearance of the rash. These results indicate that MNCs become infected with VZV during the primary encounter with VZV (varicella) and during reactivation (zoster) and that infection continues for weeks after the onset of the skin rash. Furthermore, the detection of VZV DNA in blood MNCs of uncomplicated zoster patients coincides with the period during which these patients experience pain.