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

Abstract

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.

Keywords: Africa; BCG; cytokines; heterologous immunity; infants; nonspecific effects.

© The Author 2014. Published by Oxford University Press on behalf of the Infectious Diseases Society of America.

Figures

Figure 1.

Flow chart of the study participants and the outline of study. The infants in the present study were recruited from the participants of the randomized trial of early BCG in low-birth-weight infants during the period between 18 April 2011 and 12 January 2012. Infants were visited and bled 4 weeks (±7 days) after randomization. The figures presented are the number of participants (Early BCG / control). Abbreviations: BCG, bacillus Calmette–Guerin; EDTA, ethylenediaminetetraacetic; OPV, oral polio vaccine.

Figure 2.

Geometric means (GM) of in vitro cytokine concentrations for BCG-vaccinated and non-vaccinated infants, estimated by use of Tobit regression. Note the log-scale of the axis. Observations outside the assay range are included as missing in the model producing the GM estimates. Responses of IL-17 and IFN-γ to PMA/ionomycin; IL-6 to Pam3CSK4; IL-1β, IL-6 and TNF-α to LPS; and IFN-γ to CL075 have >50% of observations outside assay range; hence the estimated GM for these are subject to some uncertainty. *P < .05; **P < .01; ***P < .001. Abbreviations: BCG, bacillus Calmette–Guerin; IFN, interferon; IL, interleukin; LPS, lipopolysaccharide; PMA, phorbol 12-myristate 13-acetate; TNF, tumor necrosis factor.

Figure 3.

Geometric mean ratio (GMR) of in vitro cytokine production, comparing BCG-vaccinated to nonvaccinated overall and stratified by sex. The cytokine concentrations are analyzed collectively for all innate stimuli (medium alone, PMA/ionomycin, Pam3CSK4, LPS, CL075, excluding PPD). Estimates are adjusted for weight at randomization. For IL-10 a collective estimate could not be obtained due to rejected test of homogeneity of estimates of the BCG effect across the stimulations. A GMR >1 may be interpreted as an increasing effect of BCG on the outcome. *P < .05; **P < .01. Abbreviations: BCG, bacillus Calmette–Guerin; IL, interleukin; LPS, lipopolysaccharide; PMA, phorbol 12-myristate 13-acetate; PPD, purified protein derivative; TNF, tumor necrosis factor.

Figure 4.

Geometric mean ratio-ratio (GMRR) of TNF-α vs IL-10 and IFN-γ vs IL-5 in vitro cytokine production, comparing BCG-vaccinated to nonvaccinated. Estimates are adjusted for weight at randomization. A GMRR >1 may be interpreted as an increasing effect of BCG on the ratio. *P < .05; **P < .01; ***P < .001. Abbreviations: BCG, bacillus Calmette–Guerin; IFN, interferon; IL, interleukin; LPS, lipopolysaccharide; PMA, phorbol 12-myristate 13-acetate; PPD, purified protein derivative; TNF, tumor necrosis factor.

Figure 5.

Geometric mean ratio (GMR) of in vitro cytokine production, comparing BCG-vaccinated to nonvaccinated stratified by season at randomization. The cytokine concentrations are analyzed collectively for all innate stimuli (medium alone, PMA/ionomycin, Pam3CSK4, LPS, CL075, excluding PPD). Estimates are adjusted for weight at randomization. A GMR >1 may be interpreted as an increasing effect of BCG on the outcome. A significant interaction (P < .05) between BCG and season is indicated with a triangle. *P < .05; **P < .01; ***P < .001. Abbreviations: BCG, bacillus Calmette–Guerin; IFN, interferon; IL, interleukin; LPS, lipopolysaccharide; PMA, phorbol 12-myristate 13-acetate; PPD, purified protein derivative; TNF, tumor necrosis factor.