Subclinical Reactivation of Cytomegalovirus Drives CD4+CD28null T-Cell Expansion and Impaired Immune Response to Pneumococcal Vaccination in Antineutrophil Cytoplasmic Antibody-Associated Vasculitis

Background. Infection is the leading cause of death in antineutrophil cytoplasmic antibody-associated vasculitis (AAV). Expansion of CD4(+)CD28(null) T cells is associated with increased risk of infection and mortality, but is only present in cytomegalovirus (CMV)-seropositive individuals. We hypothesized that subclinical CMV reactivation drives CD4(+)CD28(null) T-cell expansion, that this is associated with impaired immune response to heterologous antigens, and that antiviral therapy may ameliorate this. Methods. In a proof-of-concept open-label clinical trial, 38 CMV-seropositive AAV patients were randomized to receive valacyclovir for 6 months or no intervention. CMV reactivation was measured monthly in plasma and urine. CD4(+)CD28(null) T cells were enumerated at baseline and at 6 months. At 6 months, 36 patients were vaccinated with a 13-valent pneumococcal vaccine. Serotype-specific immunoglobulin G was assayed before and 4 weeks postvaccination to calculate the antibody response ratio. Results. Valacyclovir treatment suppressed subclinical CMV reactivation and reduced CD4(+)CD28(null) T-cell proportion. CD4(+)CD28(null) T-cell reduction correlated with improved vaccine response, whereas CMV reactivation associated with reduced response to vaccination. Furthermore, expansion of CD4(+)CD28(null) T cells was associated with a reduction in the functional capacity of the CD4 compartment. Conclusions. Suppression of CMV may improve the immune response to a T-cell-dependent pneumococcal vaccination in patients with AAV, thus offering potential clinical benefit.