Location: Immunity and Disease Prevention Research
Project Number: 2032-53000-001-11-T
Project Type: Trust Fund Cooperative Agreement
Start Date: Jan 1, 2014
End Date: Jun 30, 2017
Vitamin A deficiency in infants and young children increases the risk of death from infectious diseases. Thus the World Health Organization (WHO) recommends vitamin A supplementation (VAS) from 6-59 m of age to decrease mortality. VAS at birth also decreases mortality during the first year of life in some settings though overall results are inconclusive. In an ongoing study funded as part of a WHO initiative we are evaluating the effect of VAS within 48 of birth on immune function through 15 wk of age in 300 infants (150 VAS, 150 placebo) recruited in Dhaka, Bangladesh (ClinicalTrials.gov Identifier: NCT01583972). Vitamin A deficiency impairs T-cell mediated immunity. Our ongoing study is thus evaluating the effect of VAS at birth on thymic function and T-cell responses to four vaccines (BCG, oral polio, tetanus, hepatitis B) given as part of the WHO Expanded Program of Immunization (EPI) Program. Previous mortality studies suggest that the benefits of VAS at birth may extend through 1 yr of age. We thus propose to recruit participants from our ongoing study into the study described here to evaluate the effect of VAS at birth on thymic function and T-cell-mediated responses at 1 yr of age. Vitamin A deficiency particularly affects development of effector and regulatory T-cells in the intestinal immune system. Since the intestinal immune system affects colonization of the gut with microbiota, vitamin A deficiency at birth may create a state of dysbiosis in the gut that adversely affects immune function, including responses to oral and systemic vaccines. We hypothesize that VAS at birth will improve intestinal immunity and thus minimize dysbiosis. For this reason we are also currently evaluating the impact of VAS at birth on the gut microbiome by metagenomic analysis using sequence from the bacterial 16S ribosome gene in a subset of 60 infants from our ongoing study. In the study described here we propose to expand our pilot study of the effect of VAS at birth on the gut metagenome to all 300 infants and to include analysis at 1 yr of age. In the present study we propose to recruit infants from the ongoing study of VAS at birth to evaluate immune function at 1 yr of age, including (1) thymic function by evaluating levels of naïve T-cells in peripheral blood; (2) responses to vaccines given early in infancy, including T-cell proliferation, systemic and secretory antibody responses; (3) the IgA antibody response in stool to a booster dose of oral polio vaccine given at 1 yr; and (4) the effect of VAS at birth on the gut metagenome assessed early in infancy and at 1 yr of age, and the relationship of dysbiosis to oral and systemic vaccine responses. The study protocol will involve (1) a home visit by a health worker to collect stool; (2) a subsequent clinic visit to collect anthropometric measures, questionnaire data and a blood sample; (3) administration of the oral polio vaccine after the blood collection; and (4) two subsequent home visits 1 and 4 wk after vaccination to collect stool for evaluating the secretory IgA response to the polio booster vaccine.
Hypothesis 1: Vitamin A supplementation (VAS) at birth will improve thymic function at 1 yr of age. Specific Aim 1: Determine if (A) the concentration of naïve T-cells in peripheral blood and (B) the thymic output of naïve T cells at 1 yr of age differ between infants who received VAS or placebo at birth. The concentration of naïve T-cells will be measured by flow cytometric analysis and the relative levels of recent thymic emigrant (naïve) T-cells will be measured by measuring T-cell receptor excision circle (TREC) levels in DNA purified from peripheral blood mononuclear cells (PBMC). Hypothesis 2: VAS at birth will result in greater persistence of immunologic memory to T-cell dependent vaccine antigens given orally or systemically early in infancy, as indicated by responses measured at 1 yr of age. Specific Aim 2: Determine if antibody and T-cell responses to T-cell dependent vaccine antigen given early in infancy differ between infants who received VAS or placebo at birth when the responses are measured at 1 yr of age. The responses measured at 1 yr of age include: (A) Serum IgG and IgA responses to oral polio virus vaccine (OPV; given at birth, 6 wk, 10 wk, 14 wk and 9 m); (B) serum IgG response to tetanus toxoid vaccine (TT; given at 6, 10 and 14 wk) and (C) Hepatitis B virus vaccine (HBV; given at 6, 10 and 14 wk); (D) the IgA response to OPV in stool; the (E) proliferative and (F) cytokine response of peripheral blood CD4 T-cells to OPV, TT, HBV vaccines and to the tuberculosis vaccine (BCG; given at birth). Antibody responses will be measured by ELISA, T-cell proliferation by flow cytometric analysis after 6 d of culture with corresponding vaccine antigens, and cytokines will be measured in supernatant after 3 and 6 d of culture with the same antigens. Hypothesis 3: VAS at birth will increase intestinal colonization with Bifidobacterium and other commensal bacteria early in infancy and at 1 yr of age and the greater percentage representation of these beneficial gut flora will be associated with a greater immunologic responses to oral and systemic vaccines. Specific Aim 3: (A) Determine if the relative abundance of Bifidobacterium and other commensal gut bacteria from stool collected near the time of vaccination with oral (OPV) and parenteral (BCG, HBV and TT) vaccines early in infancy affect the antibody and T-cell proliferative response to these vaccines shortly after vaccination (15 wk) and later in infancy (1 yr). (B) Determine if these measures of gut microflora in stool collected at 1 yr of age affect the magnitude of these vaccine responses assessed at 1 yr of age.