IDENTIFICATION OF VACCINE RESPONSIVENESS BIOMARKERS THROUGH KINOME ANALYSIS IN PIGLETS

Abstract

Individual variability in immune responses to vaccination can result in vaccinated individuals who fail to develop protective immunity. These “vaccine low-responders” remain at risk for infection and compromise the protection achieved through herd immunity. Biomarkers of vaccine unresponsiveness could enable rapid identification of susceptible low-responders while discerning mechanisms of vaccine-induced immune responses. To investigate biomarkers of vaccine unresponsiveness, piglets (n=117) were vaccinated with a commercial Mycoplasma hyopneumoniae bacterin, and vaccine-induced serum IgG titers were quantified 35 days following vaccination. High (HR) and low (LR) vaccine responders within the 80th and 20th percentile of serum IgG titers were stratified, respectively, and split into discovery (n=12) and validation (n=8) cohorts. Within the discovery cohort, kinome analysis conducted on peripheral blood mononuclear cells collected from HR and LR revealed multiple differential phosphorylation events before and 6-days following vaccination. Differential phosphorylation events before vaccination were enriched in cytokine signaling pathways, a result supported by the quantification of higher plasma interferon-gamma (IFNγ) and interleukin-1beta (IL-1β) in LR compared to HR before vaccination. Additionally, LR had lower birth weight than HR, thus establishing significant associations between vaccine responsiveness and kinase signaling, plasma cytokines, and birth weight. Analysis of the validation cohort verified the differential phosphorylation events identified within the discovery cohort, but there were no differences in birth weight or plasma cytokines between LR and HR. In a second trial, piglets (n=67) from a different facility were vaccinated with the same Mycoplasma hyopneumoniae bacterin to further evaluate plasma cytokines and birth weight as biomarkers of vaccine unresponsiveness. Piglets in the second trial all seroconverted, and serum IgG titers varied less than the first trial. While the second trial found no associations between vaccine unresponsiveness and either birth weight or plasma cytokines, it revealed piglets had age- and litter-dependent differences in plasma IFNγ and IL-1β concentrations within the first 2-months of life. Collectively, these data suggest that though plasma cytokines or birth weight can be associated with vaccine unresponsiveness, their temporal and individual variability can make them inconsistent biomarkers. Phosphorylation biomarkers offered consistent discrimination of HR and LR and provided insight into potential mechanisms regulating vaccine-induced immunity.