ABSTRACT
BACKGROUND: Heterologous effects of vaccines are mediated by 'trained immunity' whereby myeloid cells are metabolically and epigenetically reprogrammed resulting in heightened responses to subsequent insults. Adenovirus vaccine vector has been reported to induce trained immunity in mice. Therefore, we sought to determine if the ChAdOx1 nCoV-19 vaccine (AZD1222), which uses an adenoviral vector, could induce trained immunity in vivo in humans. METHODS: Ten healthy volunteers donated blood on the day before receiving the ChAdOx1 nCoV-19 vaccine and on day 14, 56 and 90 post vaccination. Monocytes were purified from PBMC; cell phenotype was determined by flow cytometry, expression of metabolic enzymes were quantified by RT-qPCR and production of cytokines and chemokine in response to stimulation ex vivo were analyzed by multiplex ELISA. RESULTS: Monocyte frequency and count were increased in peripheral blood up to 3 months post vaccination compared with their own pre-vaccine control. Expression of HLA-DR, CD40 and CD80 was enhanced on monocytes for up to 3 months following vaccination. Moreover, monocytes had increased expression of glycolysis-associated enzymes 2 months post vaccination. Upon stimulation ex vivo with unrelated antigens, monocytes produced increased IL-1ß, IL-6, IL-10, CXCL1, and MIP-1α, and decreased TNF, compared with pre-vaccine controls. Resting monocytes produced more IFN-γ, IL-18, and MCP-1 up to 3 months post vaccination compared with pre-vaccine controls. CONCLUSION: These data provide evidence for the induction of trained immunity following a single dose of the ChAdOx1 nCoV-19 vaccine. FUNDING: This work was funded by The Health Research Board (EIA-2019-010) and Science Foundation Ireland Strategic Partnership Programme (Proposal ID 20/SPP/3685).