Precision immunology for discovery and development of the Precision Vaccines Program (PVP)-037 small molecule series: imidazopyrimidine adjuvants identified via age-specific human in vitro modeling

Abstract Infection is a significant cause of mortality and immunization is the most promising biomedical intervention to reduce this burden. However, multiple booster doses are often required to protect those with distinct immunity such as the young, elders, and immunocompromised individuals. Adjuvants are molecules that potentiate vaccine responses. There is a need for a larger toolbox of adjuvants, since Alum is the only adjuvant currently incorporated into licensed vaccines in the pediatric setting. We utilized a unique in vitro approach to discover new adjuvants, screening a ~10k small molecule library via a no-wash 384-well quantitative TNF immunoassay in peripheral blood mononuclear cells (PBMCs) from 3 adult healthy human donors. Preliminary hits were based on induced TNF production in at least two of the three donors screened. We identified a novel imidazopyrimidine (IMP) scaffold named PVP-037 which demonstrated efficacy, potency, and adjuvanticity. PVP-037 demonstrated broad age-independent immune-stimulatory ability in human PBMCs and dendritic cells, including key Th-polarizing cytokines such as IL-12, and significant enhancement murine humoral responses to recombinant hemagglutinin (rHA) proteins in the quadrivalent influenza. PVP-037 further demonstrated limited activity in several common cell lines (THP-1) and murine/porcine primary leukocytes. Structure activity relationship (SAR) studies identified the analog PVP-144-3 with greater in vitro efficacy across species (porcine, non-human primates) and murine in vivo adjuvanticity. Overall, we discovered an IMP adjuvant via high throughput screening of human mononuclear cells in vitro which correlated with enhanced influenza immunization in mice.