Quantification of a cell-mediated immune response against varicella zoster virus by assessing responder CD4 high memory cell proliferation in activated whole blood cultures

Herpes zoster (HZ) is caused by reactivation of a latent varicella zoster virus (VZV). The potential to develop HZ increases with age due to waning of memory cell-mediated immunity (CMI), mainly the CD4 response. Therefore, VZV-CD4-memory T cells (CD4-M) count in blood could serve as a barometer for HZ protection. However, direct quantification of these cells is known to be difficult because they are few in number in the blood. We thus developed a method to measure the proliferation level of CD4-M cells responding to VZV antigen in whole blood culture. Blood samples were collected from 32 children (2-15 years old) with or without a history of varicella infection, 18 young adults (28-45 years old), and 80 elderly (50-86 years old) with a history of varicella infection. The elderly group was vaccinated, and blood samples were taken 2 months and 1 year after VZV vaccination. Then, 1 mL of blood was mixed with VZV, diluted 1/10 in medium, and cultured. CD4-M cells were identified and measured by flow cytometry. There was distinct proliferation of CD3 CD4 CD45RA RO (CD4 -M) cells specific to VZV antigen at day 9. The majority of CD4 -M cells had the effector memory phenotype CCR7 and was granzyme B-positive. CD4 -M cells were detected in blood culture from varicella-immune but not varicella-non-immune children. Meanwhile, a higher level of CD4 -M proliferation was observed in young adults than in the elderly. The CD4 -M proliferation level was boosted 2 months after VZV vaccination and maintained for at least 1 year in the elderly. Quantifying VZV responder CD4 -M cell proliferation is a convenient way to measure VZV CMI using small blood volumes. Our method can be applied to measure VZV vaccine-induced CMI in the elderly. Clinical study registry numbers: (www.clinicaltrials.jp) 173532 and 183985.