Bacillus Calmette-Guérin vaccination induces a trained innate immunity phenotype in adults over 50 years of age: A randomized trial in Guinea-Bissau.

Background: The beneficial effects of Bacillus Calmette-Guérin (BCG) as an intervention against non-mycobacterial infections have been extensively studied in randomized trials. These non-specific effects have been linked to a heterologous increase of pro-inflammatory cytokine production by innate immune cells. It is unknown if BCG induces such responses in older individuals from TB-endemic countries.

Methods: In a single-blinded trial in Guinea-Bissau, 40 adults over 50 years of age were randomized 1:1 in a block of 40 to intradermal injection of BCG-Japan (intervention) or solvent (placebo). Production of interleukin (IL)-1β, IL-6, IL-10, interferon (IFN)-γ and tumor necrosis factor (TNF)-α was measured by ELISA in supernatant of peripheral blood mononuclear cells stimulated with Mycobacterium tuberculosis and heterologous pathogens. The trial was registered at clinicaltrials.gov (NCT02953327).

Findings: Between January 25 and March 7, 2017, 40 individuals were randomized. Two months after vaccination, BCG-Japan recipients (n = 11) had higher production of IFN-γ to M. tuberculosis stimulation (Geometric mean ratio (GMR): 3·91 [95 % Confidence Interval (CI), 1·53-9·96]) and increased release of the pro-inflammatory innate cytokines IL-1β, IL-6 and TNF-α to non-specific stimuli (GMR TNF-α: 1·47 [95 % CI, 0·98-2·19]) than their controls (n = 13). Both the specific and non-specific responses were more pronounced among those with a positive QuantiFERON at baseline.

Interpretation: BCG-Japan can induce a trained immunity phenotype in older adults. These effects were particularly strong in previously M. tuberculosis exposed individuals. Future randomized trials are needed to determine BCG's potential to protect the older populations from infections-driven morbidity and mortality.