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.