Varicella-zoster virus-specific cell-mediated immune responses in HIV-infected adults

Characterization of Varicella-Zoster (VZV) Specific T Cell Response in Healthy Subjects and Transplanted Patients by Using Enzyme Linked Immunospot (ELISpot) Assays

Solid organ transplant recipients, due to the administration of post-transplant immunosuppressive therapies, are at greater risk of viral reactivation episodes, mainly from herpes viruses, including varicella-zoster virus (VZV). The aim of this pilot study was to develop functional immunological assays (VZV-ELISpot) for the quantification and characterization of the VZV-specific effector-memory and central-memory responses in healthy subjects and transplanted patients. Glycoprotein gE and immediate-early 63 (IE-63) were used as antigens for in vitro stimulation. VZV-seropositive healthy subjects showed higher responses in respect to seronegative subjects. Even if differences were observed between VZV-seropositive healthy subjects and transplanted subjects at pre-transplant, the VZV-specific T-cell response was reduced at 60 days after transplant, mainly for the high level of immunosuppression. Phenotypical characterization revealed that response against VZV was mainly mediated by CD4 T cells. The results obtained in this study might be useful for the definition of personalized follow-up of the transplanted patients, providing useful information on the status of the patient potentially at risk of viral reactivation or other opportunistic infections.

Herpes zoster in HIV-1 infection: The role of CSF pleocytosis in secondary CSF escape and discordance

HIV cerebrospinal fluid (CSF) escape is defined by a concentration of HIV-1 RNA in CSF above the lower limit of quantification of the employed assay and equal to or greater than the plasma HIV-1 RNA level in the presence of treatment-related plasma viral suppression, while CSF discordance is similarly defined by equal or higher CSF than plasma HIV-1 RNA in untreated individuals. During secondary CSF escape or discordance, disproportionate CSF HIV-1 RNA develops in relation to another infection in addition to HIV-1. We performed a retrospective review of people living with HIV receiving clinical care at Sahlgrenska Infectious Diseases Clinic in Gothenburg, Sweden who developed uncomplicated herpes zoster (HZ) and underwent a research lumbar puncture (LP) within the ensuing 150 days. Based on treatment status and the relationship between CSF and plasma HIV-1 RNA concentrations, they were divided into 4 groups: i) antiretroviral treated with CSF escape (N = 4), ii) treated without CSF escape (N = 5), iii) untreated with CSF discordance (N = 8), and iv) untreated without CSF discordance (N = 8). We augmented these with two additional cases of secondary CSF escape related to neuroborreliosis and HSV-2 encephalitis and analyzed these two non-HZ cases for factors contributing to CSF HIV-1 RNA concentrations. HIV-1 CSF escape and discordance were associated with higher CSF white blood cell (WBC) counts than their non-escape (P = 0.0087) and non-discordant (P = 0.0017) counterparts, and the CSF WBC counts correlated with the CSF HIV-1 RNA levels in both the treated (P = 0.0047) and untreated (P = 0.002) group pairs. Moreover, the CSF WBC counts correlated with the CSF:plasma HIV-1 RNA ratios of the entire group of 27 subjects (P = <0.0001) indicating a strong effect of the CSF WBC count on the relation of the CSF to plasma HIV-1 RNA concentrations across the entire sample set. The inflammatory response to HZ and its augmenting effect on CSF HIV-1 RNA was found up to 5 months after the HZ outbreak in the cross-sectional sample and, was present for one year after HZ in one individual followed longitudinally. We suggest that HZ provides a ‘model’ of secondary CSF escape and discordance. Likely, the inflammatory response to HZ pathology provoked local HIV-1 production by enhanced trafficking or activation of HIV-1-infected CD4+ T lymphocytes. Whereas treatment and other systemic factors determined the plasma HIV-1 RNA concentrations, in this setting the CSF WBC counts established the relation of the CSF HIV-1 RNA levels to this plasma set-point.

Reactivation of Simian Varicella Virus in Rhesus Macaques after CD4 T Cell Depletion

Rhesus macaques intrabronchially inoculated with simian varicella virus (SVV), the counterpart of human varicella-zoster virus (VZV), developed primary infection with viremia and rash, which resolved upon clearance of viremia, followed by the establishment of latency. To assess the role of CD4 T cell immunity in reactivation, monkeys were treated with a single 50-mg/kg dose of a humanized monoclonal anti-CD4 antibody; within 1 week, circulating CD4 T cells were reduced from 40 to 60% to 5 to 30% of the total T cell population and remained low for 2 months. Very low viremia was seen only in some of the treated monkeys. Zoster rash developed after 7 days in the monkey with the most extensive CD4 T cell depletion (5%) and in all other monkeys at 10 to 49 days posttreatment, with recurrent zoster in one treated monkey. SVV DNA was detected in the lung from two of five monkeys, in bronchial lymph nodes from one of the five monkeys, and in ganglia from at least two dermatomes in three of five monkeys. Immunofluorescence analysis of skin rash, lungs, lymph nodes, and ganglia revealed SVV ORF63 protein at the following sites: sweat glands in skin; type II cells in lung alveoli, macrophages, and dendritic cells in lymph nodes; and the neuronal cytoplasm of ganglia. Detection of SVV antigen in multiple tissues upon CD4 T cell depletion and virus reactivation suggests a critical role for CD4 T cell immunity in controlling varicella virus latency.IMPORTANCE Reactivation of latent VZV in humans can result in serious neurological complications. VZV-specific cell-mediated immunity is critical for the maintenance of latency. Similar to VZV in humans, SVV causes varicella in monkeys, establishes latency in ganglia, and reactivates to produce shingles. Here, we show that depletion of CD4 T cells in rhesus macaques results in SVV reactivation, with virus antigens found in zoster rash and SVV DNA and antigens found in lungs, lymph nodes, and ganglia. These results suggest the critical role of CD4 T cell immunity in controlling varicella virus latency.

Evaluation of Varicella-zoster virus-specific cell-mediated immunity by interferon-γ Enzyme-Linked Immunosorbent Assay in adults ≥50 years of age administered a herpes zoster vaccine

Varicella-zoster virus (VZV)-specific cell-mediated immunity (CMI) is critical for preventing and controlling the onset of herpes zoster (HZ). To assess VZV CMI, an interferon-γ (IFN-γ) enzyme-linked immunosorbent assay (ELISA) was validated by examining the influence of VZV-specific antigen content, incubation time, and interval from whole blood collection on the assay. In phase II clinical trial, VZV-specific CMI in adults ≥50 years of age administered an HZ vaccine were evaluated by IFN-γ ELISA, as determined by measuring IFN-γ production in the whole blood in response to stimulation with ultraviolet light-inactivated VZV. The VZV-specific IFN-γ levels varied among individuals from prevaccination (baseline) to 6 weeks postvaccination. In most subjects, VZV-specific CMI was increased at 6 weeks postvaccination. The HZ vaccine elicited a significant increase in the VZV-specific CMI response as measured by ELISA; the geometric mean fold-rises from baseline to 6 weeks postvaccination were 3.50, 4.22, and 5.24 in the 4.3, 4.7, and 4.9 log plaque-forming unit vaccine groups, respectively, which was significantly higher than in the placebo group (P < 0.05). These results indicate that vaccination enhances the VZV-specific CMI responses in subjects; IFN-γ ELISA is an effective method for evaluating the CMI response and may be useful for identifying individuals at a high risk of HZ infection.

Increased incidence of herpes zoster in patients on renal replacement therapy cannot be explained by intrinsic defects of cellular or humoral immunity to varicella-zoster virus

BACKGROUND

Patients in need of long-term renal replacement therapy (RRT) are known to be at increased risk of herpes zoster, occurring when the latently present varicella-zoster virus (VZV) reactivates. In this study we investigated immunity to VZV in patients receiving RRT, with the aim of better understanding the mechanism behind the increased risk.

METHODS

Patients treated for at least three months with hemodialysis or peritoneal dialysis, and matched healthy controls (HC) were included. Cellular immunity to varicella-zoster virus (VZV) was studied using an interferon-γ (IFNγ) enzyme-linked immunospot (ELISpot) assay, flow-cytometric analysis of cytokine production and a proliferation assay. Humoral immunity was determined by measuring immunoglobulin (Ig)G antibody levels to VZV using an in-house glycoprotein enzyme-linked immunosorbent assay (ELISA). Multiple regression was used to assess variables of influence on measures of cellular and humoral immunity to VZV in patients receiving RRT.

RESULTS

Similar numbers of IFNγ spot-forming cells and levels of VZV-IgG were found in 97 patients and 89 HC. Age and transplantation history were negatively associated with cellular immunity (p = 0.001 and p = 0.012, respectively) while treatment modality, gender and urea levels were not. No variables were found to be associated with VZV-IgG levels.

CONCLUSIONS

Increased incidence of herpes zoster in patients receiving RRT cannot be explained by intrinsic defects of cellular or humoral immunity to VZV as measured by the methods used in this study, although older age and previous transplantation were associated with decreased cellular immunity to VZV. Herpes zoster susceptibility might be caused by a diminished function of otherwise capable T cells in a uremic environment.

Herpes Zoster in Persons Living with HIV-1 Infection: Viremia and Immunological Defects Are Strong Risk Factors in the Era of Combination Antiretroviral Therapy

In a cohort of 4,225 persons living with human immunodeficiency virus type 1 (HIV-1) infection (PLWH) enrolled at a southeastern US clinic, the overall rate of incident herpes zoster (HZ) was 101 per 10,000 person-years (PY) between January 1999 and 2017, which nearly quadruples the rate reported for the general US population. In the same cohort, the median age of HZ diagnosis was 39.5 years [interquartile range (IQR) 31.5-49.2] in African American (AA) and 39.1 years (IQR 34.9-45.2) in European American (EA) PLWH, with the highest incidence seen in PLWH who were over 50 years old (144 and 93 per 10,000 PY in AA and EA, respectively, P = 0.18), showing no bias between men (100 per 10,000 PY) and women (101 per 10,000 PY). In multivariable models that were applicable to 245 HZ cases and 3,713 controls, age, nadir CD4+ T-cell (CD4) count, plasma viral load (VL), and duration of combination antiretroviral therapy were independent correlates of incident HZ (adjusted P ≤ 0.006 for all). Regardless of other factors, viremic PLWH (VL > 50 copies/mL) was at the highest risk of HZ [adjusted odds ratio (OR) > 3.0, P < 0.0001]. PLWH with a nadir CD4 count of ≥500 cells/μL showed a relatively low risk (adjusted OR = 0.48, P = 0.003). By contrast, similar risk estimates were observed with three advancing age groups (30-39, 40-49, and ≥50) when compared with age <30 (adjusted OR = 1.86-2.17, P ≤ 0.010). These findings indicate that efforts for HZ diagnosis and prophylaxis should target viremic PLWH who are over 30 years old and with CD4 count <500 cells/μL.

Development of an IFN-γ ELISpot assay to assess varicella-zoster virus-specific cell-mediated immunity following umbilical cord blood transplantation

Varicella zoster virus (VZV) is a significant cause of morbidity and mortality following umbilical cord blood transplantation (UCBT). For this reason, antiherpetic prophylaxis is administrated systematically to pediatric UCBT recipients to prevent complications associated with VZV infection, but there is no strong, evidence based consensus that defines its optimal duration. Because T cell mediated immunity is responsible for the control of VZV infection, assessing the reconstitution of VZV specific T cell responses following UCBT could provide indications as to whether prophylaxis should be maintained or can be discontinued. To this end, a VZV specific gamma interferon (IFN-γ) enzyme-linked immunospot (ELISpot) assay was developed to characterize IFN-γ production by T lymphocytes in response to in vitro stimulation with irradiated live attenuated VZV vaccine. This assay provides a rapid, reproducible and sensitive measurement of VZV specific cell mediated immunity suitable for monitoring the reconstitution of VZV specific immunity in a clinical setting and assessing immune responsiveness to VZV antigens.  

Age and immune status of rhesus macaques impact simian varicella virus gene expression in sensory ganglia

Simian varicella virus (SVV) infection of rhesus macaques (RMs) recapitulates the hallmarks of varicella-zoster virus (VZV) infection of humans, including the establishment of latency within the sensory ganglia. Various factors, including age and immune fitness, influence the outcome of primary VZV infection, as well as reactivation resulting in herpes zoster (HZ). To increase our understanding of the role of lymphocyte subsets in the establishment of viral latency, we analyzed the latent SVV transcriptome in juvenile RMs depleted of CD4 T, CD8 T, or CD20 B lymphocytes during acute infection. We have previously shown that SVV latency in sensory ganglia of nondepleted juvenile RMs is associated with a limited transcriptional profile. In contrast, CD4 depletion during primary infection resulted in the failure to establish a characteristic latent viral transcription profile in sensory ganglia, where we detected 68 out of 69 SVV-encoded open reading frames (ORFs). CD-depleted RMs displayed a latent transcriptional profile that included additional viral transcripts within the core region of the genome not detected in control RMs. The latent transcriptome of CD20-depleted RMs was comparable to the latent transcription in the sensory ganglia of control RMs. Lastly, we investigated the impact of age on the establishment of SVV latency. SVV gene expression was more active in ganglia from two aged RMs than in ganglia from juvenile RMs, with 25 of 69 SVV transcripts detected. Therefore, immune fitness at the time of infection modulates the establishment and/or maintenance of SVV latency.

Systemic varicella zoster virus reactive effector memory T-cells impaired in the elderly and in kidney transplant recipients

Varicella zoster virus (VZV) infections cause varicella and subsequently herpes zoster upon reactivation. Immune-compromised individuals and the elderly are at high risk of developing herpes zoster due to waning of VZV-specific T-cell immunity. In the present study, a novel functional T-cell assay was developed to test the correlation between age and VZV-specific T-cell responses in peripheral blood from healthy individuals. Secondly, VZV-specific T-cell responses from renal transplant recipients were compared with healthy individuals. Monocytes were differentiated into mature monocyte-derived dendritic cells (moDCs) and were infected with VZV. T-cells were co-cultured with autologous moDCs infected with VZV and subjected to flowcytometric analysis to identify the phenotype (i.e., naïve [NA: CCR7(+) CD45RO(-) ], central [CM: CCR7(+) CD45RO(+) ] and effector memory [EM: CCR7(-) CD45RO(+) ] T-cells) and the frequency of VZV-reactive T-cell subsets by intra-cellular IFN-γ flowcytometry. In contrast to NA and CM T-cells, the frequency of VZV-reactive CD4 and CD8 EM T-cells was inversely correlated with age (P = 0.0007 and P = 0.01). No difference was found in the percentage of VZV-reactive CD4 NA, CM and EM T-cells between transplant recipients and controls. However, the percentage of VZV-reactive CD8 EM T-cells was significantly lower in transplant recipients compared to controls (P = 0.02). In conclusion, moDCs infected with VZV are efficient antigen presenting cells applicable to enumerate and characterize the phenotype and differentiation status of the systemic VZV-specific T-cell response ex-vivo. The data suggest that VZV-reactive EM T-cells are impaired in the elderly and renal transplant recipients.

The host immune response to varicella zoster virus

Varicella zoster virus (VZV) is a highly successful human pathogen, which is never completely eliminated from the host. VZV causes two clinically distinct diseases, varicella (chickenpox) during primary infection and herpes zoster (shingles) following virus reactivation from latency. Throughout its lifecycle the virus encounters the innate and adaptive immune response, and in order to prevent eradication it has developed many mechanisms to evade and overcome these responses. This review will provide a comprehensive overview of the host immune response to VZV infection, during the multiple stages of the virus lifecycle and at key sites of VZV infection. We will also briefly describe some of the strategies employed by the virus to overcome the host immune response and the ongoing challenges in further elucidating the interplay between VZV and the host immune response in an attempt to lead to better therapies and a ‘second generation’ vaccine for VZV disease.