Heterologous immunological effects of early BCG vaccination in low-birth-weight infants in Guinea-Bissau: a randomized-controlled trial

Background: Bacillus Calmette-Guérin (BCG) seems to have beneficial nonspecific effects; early BCG vaccination of low-birth-weight (LBW) newborns reduces neonatal mortality by >40% due to prevention of primarily septicemia and pneumonia.

Methods: Within a randomized trial in LBW infants in Guinea-Bissau of early BCG vs the usual postponed BCG, a subgroup was bled 4 weeks after randomization. Levels of interleukin (IL)-1β, IL-5, IL-6, IL-10, IL-17, interferon (IFN)-γ and tumor necrosis factor (TNF)-α were measured from whole-blood assays stimulated with innate agonists to Toll-like receptor (TLR)-2, -4 or -7/8, or purified protein derivative (PPD).

Results: Among 467 infants, BCG significantly increased the in vitro cytokine responses to purified protein derivative of Mycobacterium tuberculosis (PPD), as expected. BCG was also associated with increased responses to heterologous innate stimulation, particularly of the cytokines IL-1β, IL-6, TNF-α, and IFN-γ.

Conclusion: Four weeks after immunization, BCG-vaccinated infants have a significantly increased production of cytokines upon heterologous challenge, particularly T helper cell type 1 polarizing and typically monocyte-derived pro-inflammatory cytokines. BCG may accelerate the development of the neonatal immune system, mediating comprehensive protection against infections and mortality.