The anti-tuberculosis vaccine Bacillus Calmette-Guérin (BCG) reduces overall infant mortality. Induction of innate immune memory, also termed trained immunity, contributes towards protection against heterologous infections. Since immune cells display oscillations in numbers and function throughout the day, we investigated the effect of BCG administration time on the induction of trained immunity.
18 volunteers were vaccinated with BCG at 6pm and compared with 36 age- and sex-matched volunteers vaccinated between 8-9 am. Peripheral blood mononuclear cells were stimulated with Staphylococcus aureus and Mycobacterium tuberculosis before, as well as two weeks and three months after BCG vaccination. Cytokine production was measured to assess the induction of trained immunity and adaptive responses, respectively. Additionally, the influence of vaccination time on induction of trained immunity was studied in an independent cohort of 302 individuals vaccinated between 8am-12pm with BCG.
Compared to evening vaccination, morning vaccination elicited both a stronger trained immunity and adaptive immune phenotype. In a large cohort of 302 volunteers, early morning vaccination resulted in a superior cytokine production capacity compared with later morning. A cellular, rather than soluble, substrate of the circadian effect of BCG vaccination was demonstrated by the enhanced capacity to induce trained immunity in vitro in morning compared to evening isolated monocytes.
BCG vaccination in the morning induces stronger trained immunity and adaptive responses compared to evening vaccination. Future studies should take vaccine administration time into account when studying specific and non-specific effects of vaccines: early morning should be the preferred moment of BCG administration.FUNDING Spinoza grant of the Netherlands Organization for Scientific Research, ERC Advanced Grant (TRAIN-OLD nr. 833247), Danish National Research Foundation (DNRF108).