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RhCMV serostatus and vaccine adjuvant impact immunogenicity of RhCMV/SIV vaccines.

  • Author(s): Chang, WL William
  • Deere, Jesse D
  • Kieu, Hung T
  • Castillo, Luis D
  • Machmach, Kawthar
  • Shen, Xiaoying
  • Tomaras, Georgia D
  • Shacklett, Barbara L
  • Barry, Peter A
  • Hartigan-O'Connor, Dennis J
  • Sparger, Ellen E
  • et al.

Rhesus cytomegalovirus (RhCMV) strain 68-1-vectored simian immunodeficiency virus (RhCMV/SIV) vaccines are associated with complete clearance of pathogenic SIV challenge virus, non-canonical major histocompatibility complex restriction, and absent antibody responses in recipients previously infected with wild-type RhCMV. This report presents the first investigation of RhCMV/SIV vaccines in RhCMV-seronegative macaques lacking anti-vector immunity. Fifty percent of rhesus macaques (RM) vaccinated with a combined RhCMV-Gag, -Env, and -Retanef (RTN) vaccine controlled pathogenic SIV challenge despite high peak viremia. However, kinetics of viral load control by vaccinated RM were considerably delayed compared to previous reports. Impact of a TLR5 agonist (flagellin; FliC) on vaccine efficacy and immunogenicity was also examined. An altered vaccine regimen containing an SIV Gag-FliC fusion antigen instead of Gag was significantly less immunogenic and resulted in reduced protection. Notably, RhCMV-Gag and RhCMV-Env vaccines elicited anti-Gag and anti-Env antibodies in RhCMV-seronegative RM, an unexpected contrast to vaccination of RhCMV-seropositive RM. These findings confirm that RhCMV-vectored SIV vaccines significantly protect against SIV pathogenesis. However, pre-existing vector immunity and a pro-inflammatory vaccine adjuvant may influence RhCMV/SIV vaccine immunogenicity and efficacy. Future investigation of the impact of pre-existing anti-vector immune responses on protective immunity conferred by this vaccine platform is warranted.

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