Immunogenicity and safety of a live herpes zoster vaccine in hematopoietic stem cell transplant recipients

This was a clinical study conducted at Seoul National University Hospital (SNUH), which is a tertiary care university-affiliated hospital in South Korea.

From July 2017 to August 2018, we prospectively enrolled patients with a hematologic malignancy who had survived with either autologous or allogeneic HSCT. Additional inclusion criteria were as follows: age older than 50 years and provision of informed consent for participation. Exclusion criteria included GvHD, use of immunosuppressants or antiviral agents, HZ reactivation within 1 year of the study period, or receipt of HZ vaccines. These patients were stratified according to time since transplantation: 2–5 years and > 5 years (hereafter referred to as HSCT 2–5 yr and HSCT > 5 yr, respectively).

Controls included patients with a hematologic malignancy who had undergone cytotoxic chemotherapy and survived without relapse for at least 6 months before enrollment (referred to as the chemotherapy group). Inclusion and exclusion criteria were applied in the same manner as for the HSCT groups. Lastly, healthy volunteers aged > 50 years without recent HZ reactivation within 1 year were recruited (referred to as the healthy group).

Study participants were given a single dose (0.65 mL) of ZOSTAVAX®. Blood samples were collected to test both humoral and cellular immune responses against VZV prior to vaccination and at 6 weeks post-vaccination. Baseline characteristics included age, sex, underlying diseases, type of HSCT or cytotoxic chemotherapy, and previous history of HZ.

Although correlates of protection (CoP) for HZ vaccines have not been defined clearly, fold rises in antibody titers in the glycoprotein enzyme-linked immunosorbent assay (gpELISA) are thought to be an excellent immune correlate of protection [15]. VZV-specific antibodies were measured quantitatively using a SERION ELISA classic Varicella Zoster Virus IgG kit (Institut Virion/Serion GmbH, Würzburg, Germany). This gpELISA assay uses a lentil-lectin affinity-purified preparation of glycoprotein from VZV-infected MRC-5 cells as the antigen [16, 17]. Antigen-coated 96-well plates were incubated with test sera. Human immunoglobulin G antibodies (IgGs) bound to antigen were detected by incubation with anti-human IgG antibodies. Color was developed after reaction with a substrate. Optical density was read at 405 nm.

Peripheral blood mononuclear cells (PBMCs) collected and frozen during the study period were tested using a BD™ IFN-γ ELISPOT kit (BD Bioscience, San Jose, CA, USA). Briefly, 96-well plates were coated with 100 μL of an anti-human-IFN-γ antibody at a concentration of 5 μg/mL overnight at 4 °C. Next, 1 × 10⁶ PBMCs/100 μL/well were activated with 5 μg/mL phytohemagglutinin (mitogen), UV-inactivated VZV culture supernatants (at a dilution of 1:80) and mock antigen supernatants for 16–20 h at 37 °C in a 5% CO₂ humidified incubator [18]. After washing, a solution containing a biotinylated anti-human-IFN-γ detection antibody was added to each well, and streptavidin-HRP solution and substrate were used for color development. Spots were counted with a CTL-ImmunoSpot® reader (CTL ImmunoSpot, Cleveland, OH, USA) and reported as the net number of VZV-specific IFN-γ spot-forming cells (sfc) per 10⁶ PBMCs (the difference between responses to VZV antigen and control antigen) [19]. Samples lacking sufficient PMBCs and results with phytohemagglutinin responses < 300 sfc were not included in the analysis [20].

Vaccine adverse events (AEs) were monitored based on spontaneous reports from participants, subject daily review, and history taking by investigators. All vaccinated individuals were requested to inform the study nurse or physician immediately if they noticed any serious AEs after vaccination. The participants were also requested to fill in a self-reported structured questionnaire up to 6 weeks post-vaccination and submit it on the second visit. The type and severity of local and systemic adverse events were assessed again by the study nurse 6 weeks after vaccination. Adverse events were graded on a standard scale [21]. The causality of an adverse event after immunization was classified as follows: unlikely (inconsistent), possible (indeterminate), or likely (consistent) [22].

For continuous variables, mean (standard deviation, SD) and median (interquartile range, IQR) were used for normally and abnormally distributed data. Categorical variables were expressed as numbers and percentages. A t-test was used to compare continuous variables and the Chi-square or Fisher’s exact test was used to compare categorical variables. One-way ANOVA with Dunnett’s adjustment or Kruskal-Wallis test was used to calculate P-values for comparisons of more than two variables. All tests were two-sided and P-values < 0.05 were considered statistically significant. All statistical analyses were performed using SPSS for Windows (version 22; IBM Corp., Armonk, NY, USA).

The study screened 60 hematology patients at baseline; four patients dropped out due to follow-up loss (n = 3) and disease recurrence (n = 1). Among the remaining 56 subjects, 26 were assigned to the HSCT 2–5 yr group and 15 to the HSCT > 5 yr group. The chemotherapy group included 15 patients. In addition, 30 healthy volunteers were enrolled (Fig. 1).

Participants in each group were balanced by age; however, the male-to-female ratio of the healthy group was lower (1:2) than that in the other groups (Table 1). Leukemia and lymphoma were the most common (> 50% of participants in each group) underlying malignancies. Twenty patients in the HSCT 2–5 yr group (77%), and nine in the HSCT > 5 yr group (60%) underwent allogeneic HSCT. A history of HZ reactivation was documented in study groups. Twelve patients in the HSCT 2–5 yr group (46%), nine in the HSCT > 5 yr group (60%), and six in the chemotherapy group (40%) had shingles before enrollment in the study (Table 1). Among those reactivated, nine in the HSCT 2–5 yr group (75%), six in the HSCT > 5 yr group (67%), and five in the chemotherapy group (83%) had history within 2 years after HSCT or last cytotoxic chemotherapy.

At baseline, the gpELISA geometric mean titers (GMTs) in the HSCT 2–5 yr, chemotherapy, and healthy groups were similar (841.08, 95% CI [439.58–1609.29] vs 515.92, 95% CI [302.03–881.28] vs 657.15, 95% CI [424.18–1018.09]); values were significantly lower in the HSCT > 5 yr group (262.89, 95% CI [149.59–462.00], p = 0.041). At 6 weeks post-vaccination, immune responses measured in the gpELISA increased significantly in all four groups, compared with the baseline (Fig. 2a, Supplementary Table 1). The GMFR in the chemotherapy group was significantly lower than in the other groups (1.42; 95% CI, 1.08–1.86) (Fig. 2c). The GMFRs of the HSCT 2–5 yr, HSCT > 5 yr, and healthy groups were not significantly different (3.15, 95% CI [1.96–5.07] vs 5.05, 95% CI [2.50–10.20] vs 2.97, 95% CI [2.30–3.83]) (Fig. 2c). Patients with a history of shingles showed higher baseline gpELISA GMTs than those without, but the GMFRs were uninfluenced (Supplementary Table 2).

The ELISPOT assay was performed in only 52 subjects due to lack of qualified blood samples (HSCT 2–5 yr [n = 12], HSCT > 5 yr [n = 7], chemotherapy [n = 13], and healthy group [n = 20]). At baseline, the geometric mean concentrations (GMCs) of IFN-γ-secreting VZV-specific PBMCs were higher in the healthy group (51.39, 95% CI [34.36–76.88], p = 0.006) than in the other three groups (9.00, 95% CI [3.43–23.60] vs 27.99, 95% CI [8.45–92.65] vs 14.76, 95% CI [6.57–33.16]). Six weeks post-vaccination, the GMCs of IFN-γ-secreting VZV-specific PBMCs increased significantly in all groups (Fig. 2b, Supplementary Table 1). The GMFR of the IFN-γ ELISPOT assay was highest in the HSCT 2–5 yr group (8.39, 95% CI [3.30–21.32]) and lowest in the chemotherapy group (1.64, 95% CI [1.23–2.17]) (Fig. 2d). The GMFRs in the HSCT > 5 yr and healthy groups were 5.08 (95% CI, [1.86–13.86]) and 1.82 (95% CI, [1.32–2.49]), respectively. Patients with a history of shingles tended to have higher baseline GMCs than those without, but the GMFRs were uninfluenced (Supplementary Table 3).

There were no reported cases of VZV reactivation up to 6 weeks post-vaccination in any of the study groups. Injection site reactions such as local pain, redness, edema, and itching were the most common adverse events reported by vaccine recipients (Table 2). Three patients in the HSCT 2–5 yr group (11.5%) and one each in the HSCT > 5 yr (6.6%) and chemotherapy (6.6%) groups reported vaccine-related systemic adverse events such as headache, myalgia, and fatigue (Table 2). All adverse events were mild (grade 1) and occurred within 7 days of vaccination.