Evaluation of varicella zoster virus-specific cell-mediated immunity by using an interferon-γ enzyme-linked immunosorbent assay

Immunogenicity and safety of an ORF7-deficient skin-attenuated and neuro-attenuated live vaccine for varicella: a randomised, double-blind, controlled, phase 2a trial

BACKGROUND

The Oka varicella vaccine strain remains neurovirulent and can establish lifelong latent infection, raising safety concerns about vaccine-related herpes zoster. In this study, we aimed to evaluate the immunogenicity and safety of a skin-attenuated and neuro-attenuated varicella vaccine candidate (v7D vaccine).

METHODS

We did this randomised, double-blind, controlled, phase 2a clinical trial in Jiangsu, China. Healthy children aged 3-12 years with no history of varicella infection or vaccination were enrolled and randomly assigned (1:1:1:1) to receive a single subcutaneous injection of the v7D vaccine at 3·3 log10 plaque forming units (PFU; low-dose v7D group), 3·9 log10 PFU (medium-dose v7D group), and 4·2 log10 PFU (high-dose v7D group), or the positive control varicella vaccine (vOka vaccine group). All the participants, laboratory personnel, and investigators other than the vaccine preparation and management staff were masked to the vaccine allocation. The primary outcome was assessment of the geometric mean titres (GMTs) and seroconversion rates of anti-varicella zoster virus immunoglobulin G (IgG) induced by different dose groups of v7D vaccine at 0, 42, 60, and 90 days after vaccination in the per-protocol set for humoral immune response analysis. Safety was a secondary outcome, focusing on adverse events within 42 days post-vaccination, and serious adverse events within 6 months after vaccination. This study was registered on Chinese Clinical Trial Registry, ChiCTR2000034434.

FINDINGS

On Aug 18-21, 2020, 842 eligible volunteers were enrolled and randomly assigned treatment. After three participants withdrew, 839 received a low dose (n=211), middle dose (n=210), or high dose (n=210) of v7D vaccine, or the vOka vaccine (n=208). In the per-protocol set for humoral immune response analysis, the anti-varicella zoster virus IgG antibody response was highest at day 90. At day 90, the seroconversion rates of the low-dose, medium-dose, and high-dose groups of v7D vaccine and the positive control vOka vaccine group were 100·0% (95% CI 95·8-100·0; 87 of 87 participants), 98·9% (93·8-100·0; 87 of 88 participants), 97·8% (92·4-99·7; 91 of 93 participants), and 96·4% (89·8-99·2; 80 of 83 participants), respectively; the GMTs corresponded to values of 30·8 (95% CI 26·2-36·0), 31·3 (26·7-36·6), 28·2 (23·9-33·2), and 38·5 (31·7-46·7). The v7D vaccine, at low dose and medium dose, elicited a humoral immune response similar to that of the vOka vaccine. However, the high-dose v7D vaccine induced a marginally lower GMT compared with the vOka vaccine at day 90 (p=0·027). In the per-protocol set, the three dose groups of the v7D vaccine induced a similar humoral immune response at each timepoint, with no statistically significant differences. The incidence of adverse reactions in the low-dose, medium-dose, and high-dose groups of v7D vaccine was significantly lower than that in the vOka vaccine group (17% [35 of 211 participants], 20% [41 of 210 participants], and 13% [27 of 210 participants] vs 24% [50 of 208 participants], respectively; p=0·025), especially local adverse reactions (10% [22 of 211 participants], 14% [30 of 210 participants] and 9% [18 of 210 participants] vs 18% [38 of 208 participants], respectively; p=0·016). None of the serious adverse events were vaccine related.

INTERPRETATION

The three dose groups of the candidate v7D vaccine exhibit similar humoral immunogenicity to the vOka vaccine and are well tolerated. These findings encourage further investigations on two-dose vaccination schedules, efficacy, and the potential safety benefit of v7D vaccine in the future.

FUNDING

The National Natural Science Foundation of China, CAMS Innovation Fund for Medical Sciences, the Fundamental Research Funds for the Central Universities, and Beijing Wantai.

TRANSLATION

For the Chinese translation of the abstract see Supplementary Materials section.

Anti-varicella-zoster virus antibody titers and seroprotection status from before the first dose of varicella vaccination to before entering elementary school in one region in Japan

OBJECTIVE

We aimed to examine changes in anti-varicella-zoster virus (VZV) antibody titers and seroprotection status from before the first dose of vaccination to before 7 years old entering elementary school in children who received the routine two-dose varicella vaccination.

METHODS

Participants were 37 healthy children who received the routine two-dose varicella vaccination at our hospital. A total of five serum samples per child were collected immediately before and 4-6 weeks after each dose of the vaccination and in the year before entry to elementary school. We measured anti-VZV antibody titers by immune adherence hemagglutination (IAHA) method and glycoprotein-based enzyme-linked immunosorbent assay (gpELISA). A positive antibody titer and the seroprotection level were set as ≥2-fold and ≥16-fold, respectively, for IAHA antibody and as ≥50 units and ≥105 units, respectively, for gpELISA-IgG antibody.

RESULTS

The rates of IAHA antibody positivity in the five samples (in order of collection) were 0%, 65%, 38%, 100%, and 59%, and the rates of seroprotection were 0%, 43%, 8%, 100%, and 43%. The rates of gpELISA-IgG antibody positivity were 8%, 81%, 89%, 100%, and 100%, and the rates of seroprotection were 5%, 54%, 70%, 100%, and 89%. The mean IAHA antibody titer and mean gpELISA-IgG antibody titer before entering elementary school were both lower than the respective titers obtained after the second vaccination (both p < 0.01).

CONCLUSIONS

Routine two-dose varicella vaccination leads to good antibody production, but titers of acquired antibodies decrease before children enter elementary school.

A Simple-to-Perform ifn-γ mRNA Gene Expression Assay on Whole Blood Accurately Appraises Varicella Zoster Virus-Specific Cell-Mediated Immunity After Allogeneic Hematopoietic Stem Cell Transplantation

Herpes zoster, which is due to the reactivation of Varicella zoster virus (VZV), is a leading cause of morbidity after allogeneic hematopoietic stem cell transplantation (allo-HSCT). While cell-mediated immunity (CMI) is critical to inhibiting VZV reactivation, CMI is not routinely assessed due to a lack of reliable tests. In this study, we aimed to evaluate VZV-specific CMI among allo-HSCT recipients (n = 60) and healthy individuals (HI, n = 17) through a panel of three immune functional assays after ex vivo stimulation by VZV antigen: quantification of (i) IFN-γ release in the supernatants, (ii) T-cell proliferation after a 7-day stimulation of peripheral blood mononuclear cells (PBMC), and (iii) measurement of the ifn-γ mRNA gene expression level after 24 h of stimulation of a whole-blood sample. VZV responsiveness was defined according to IFN-γ release from VZV-stimulated PBMC. Upon VZV stimulation, we found that allo-HSCT recipients at a median time of 6 [5-8] months post-transplant had lower IFN-γ release (median [IQR], 0.34 [0.12–8.56] vs. 409.5 [143.9–910.2] pg/ml, P <.0001) and fewer proliferating T cells (0.05 [0.01–0.57] % vs. 8.74 [3.12–15.05] %, P <.0001) than HI. A subset of allo-HSCT recipients (VZV-responders, n = 15/57, 26%) distinguished themselves from VZV-non-responders (n = 42/57, 74%; missing data, n = 3) by higher IFN-γ release (80.45 [54.3–312.8] vs. 0.22 [0.12–0.42] pg/ml, P <.0001) and T-cell proliferation (2.22 [1.18–7.56] % vs. 0.002 [0.001–0.11] %, P <.0001), suggesting recovery of VZV-specific CMI. Interestingly, VZV responders had a significant fold increase in ifn-γ gene expression, whereas ifn-γ mRNA was not detected in whole blood of VZV-non-responders (P <.0001). This study is the first to suggest that measurement of ifn-γ gene expression in 24-h-stimulated whole blood could be an accurate test of VZV-specific CMI. The routine use of this immune functional assay to guide antiviral prophylaxis at an individual level remains to be evaluated.

Immune response of C57BL/6J mice to herpes zoster subunit vaccines formulated with nanoemulsion-based and liposome-based adjuvants

Herpes zoster (HZ) is a recurrent nerve tissue infection caused by the reactivation of varicella-zoster virus (VZV). At present, two vaccines, the live attenuated vaccine Zostavax™ and AS01B-adjuvanted recombinant subunit vaccine Shingrix™, are commercially available for HZ. The latter is superior to the former in terms of efficacy and duration of immunity in the elderly. In this study, we used glycoprotein E (gE) as an antigen, and investigated the effects of various adjuvants (MF59, MF59/CpG 2006, and MF59/QS-21) on the immune response of C57BL/6J mice to find an alternative adjuvant to AS01B-like adjuvant of liposome/QS-21/MPL. In addition to safety, the gE-specific antibody, IgG antibody subtype, and cytokine secretion by splenocytes, and cell-mediated immune responses were determined using ELISA and ELISPOT assays, respectively. Our results showed no significant effects on the body weight, temperature, or behavior of mice vaccinated with PBS or all adjuvanted vaccines. All adjuvanted vaccine groups showed significantly higher gE-specific IgG antibody levels than the gE-alone group on day 28 after the first vaccine dose. In addition, all adjuvants induced a remarkable increase in both IgG1 and IgG2b levels. However, MF59/QS-21 and MF59/CpG 2006 showed comparable capacities to those of liposome/QS-21/MPL in increasing the IgG2c levels, being superior to MF59. Further investigation revealed that MF59 only induced a limited increase in the levels of Th1 and Th2 cytokines, while MF59/QS-21, MF59/CpG 2006, and liposome/QS-21/MPL led to a significant increase in the secretion of interferon gamma (IFN-γ), IL-2, IL-4, and IL-10 and showed a Th1-biased immune response. Moreover, MF59/QS-21, MF59/CpG 2006, and liposome/QS-21/MPL adjuvanted vaccines resulted in comparable gE-specific IFN-γ + immune cell responses. These results suggest that the combination of MF59 with QS-21 or CpG 2006 may be a promising adjuvant candidate for subunit HZ vaccines. Further investigations are needed to illustrate their durability and efficacy in aged mice.

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.

Development of varicella vaccine in Japan and future prospects

In Japan, Dr. Michiaki Takahashi (1928-2013) successfully developed the first live attenuated varicella vaccine in the world. The virus used for this vaccine was varicella-zoster virus isolated from the vesicular fluid of a child with typical varicella and it was named the Oka strain after the family name of the child. In 1974, a patient with nephrosis developed varicella in the Pediatric Ward, and uninfected pediatric patients received varicella vaccine immediately. As a result, there were no cases of varicella in the other children and all of the vaccinated children acquired immunity to the disease. These results were published in the Lancet, demonstrating the safety and efficacy of varicella Oka strain vaccine for the first time. When clinical studies were conducted at the start of vaccine development, most of the subjects were pediatric patients with a high risk of contracting severe varicella. Therefore, the development process was different from that for other vaccines, since clinical studies are generally performed in healthy individuals. This vaccine was approved in Japan in 1986, and voluntary single-dose vaccination for children aged 1 year or older was started in 1987. However, the vaccination coverage rate remained low and the number of patients with varicella did not decrease significantly. Due to its voluntary status, the cost of vaccination was borne by the child's family and this was considered to be a reason for the low coverage rate. Moreover, although the vaccine achieved a good antibody response, the number of cases of breakthrough varicella (BV) was relatively high and showed an increasing trend that was also a concern. In order to increase the coverage rate and reduce BV, the Japanese government changed the varicella vaccination policy from voluntary to routine vaccination in October 2014. At the same time, a two-dose schedule was introduced that involved administration of the vaccine twice at an interval of at least 3 months up to the age of 3 years. At present, cases of varicella are only monitored at the pediatric sentinel clinics in Japan. Therefore, we need to establish a system to survey all patients, in order to demonstrate the efficacy of varicella vaccine based on detailed surveillance data. We also need to investigate the optimum timing of the second dose of the vaccine and the necessity for further booster vaccination. A combined live vaccine containing varicella vaccine has not yet been approved in Japan. Because of the greater convenience of combined vaccines, development and introduction of such a vaccine in the future would be desirable. Routine varicella vaccination is also expected to eventually reduce the occurrence of herpes zoster, although there are no supporting epidemiological data. The prevalence of herpes zoster has attracted attention, but it is necessary to develop a surveillance system for this disease. In March 2016, use of varicella vaccine to prevent herpes zoster in adults aged 50 years or older was approved in Japan, and the results of this policy change need to be assessed.

[Results of Booster Vaccination in Children with Primary Vaccine Failure after Initial Varicella Vaccination]

In October 2014, the varicella vaccination policy in Japan was changed from a single voluntary inoculation to two routine inoculations. This paper reports the results of booster vaccination in children who did not show seroconversion after initial vaccination (i.e., primary vaccine failure : PVF) over a 7-year period prior to the introduction of routine varicella vaccination. Between November 2007 and May 2014, 273 healthy children aged between 1.1 and 14.5 years (median : 1.7 years) underwent varicella vaccination. Before and 4 to 6 weeks after vaccination, the antibody titers were measured using an immune adherence hemagglutination (IAHA) assay and a glycoprotein-based enzyme-linked immunosorbent assay (gpELISA). In addition, side reactions were examined during the four-week period after vaccination. Children who did not show IAHA seroconversion (PVF) were recommended to receive a booster vaccination, and the measurement of antibody titers and an assessment of side reactions were performed after the booster dose. In May 2015, a questionnaire was mailed to each of the 273 participants to investigate whether they had developed varicella and/or herpes zoster after vaccination. After initial vaccination, the IAHA seroconversion rate was 75% and the mean antibody titer (Log2) with seroconversion was 4.7, while the gpELISA seroconversion rate was 84% and the mean antibody titer (Log10) with seroconversion was 2.4. Among children with PVF, 54 received booster vaccination within 81 to 714 days (median : 139 days) after the initial vaccination. After booster vaccination, the IAHA seroconversion rate was 98% and the mean antibody titer (Log2) with seroconversion was 5.8. Both the seroconversion rate and the antibody titer were higher compared with the values after the initial vaccination (p < 0.01). After booster vaccination, the gpELISA seropositive rate was 100% and the mean positive antibody titer (Log 10) was 3.6 ; similar results were obtained for the IAHA assay, with a significantly higher, antibody response than that after the initial vaccination (p < 0.01). Side reactions were generally minor, including fever (≥ 37.5 degrees C), rash at the injection site, and rash at other sites. There were no significant differences in the incidences of side reactions between the initial and booster vaccinations. A total of 185 participants responded to the questionnaire (response rate : 68%), and the period between receiving the initial vaccination and their response to the questionnaire ranged from 1.0 to 7.5 years (median : 4.0 years). The prevalence of breakthrough varicella after the initial vaccination was 17% among seroconverters who did not receive booster vaccination and 14% among non-seroconverters who received booster vaccination, showing no significant difference between the two groups. In conclusion, there are no safety issues regarding the administration of a booster vaccination to children with PVF after an initial varicella vaccination, and,a good antibody response can be expected.