Author: Saoirse Benson
Benson, Saoirse, 2023 Characterising the mechanisms through which the microbiota influences immune responses to vaccination in early life, Flinders University, College of Medicine and Public Health
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Antibody-mediated responses play a critical role in vaccine-mediated immunity, however, for reasons that are poorly understood, responses are highly variable between individuals and different populations. In mice, antibiotic-driven dysbiosis in early-life leads to significantly dysregulated B and T cell responses to vaccines that are routinely administered to infants worldwide. To investigate whether this is also the case in infants we established the Antibiotics and Immune Responses (AIR) study, a clinical systems immunology study that assessed the effects of neonatal or intrapartum antibiotic exposure on the infant gut microbiota; blood gene expression; circulating immune cell populations; and antibody responses to multiple different infant vaccines in a cohort of 226 vaginally-born, healthy, term infants. Infants exposed to neonatal antibiotics had significantly lower antibody titres against multiple different vaccine antigens, most notably to polysaccharides in the 13-valent pneumococcal conjugate vaccine (PCV13) and altered transcriptional profiles pre- and post-vaccination. Multi-parameter immune profiling revealed that these transcriptional differences were not explained by differences in the frequency of major immune cell populations, though infants exposed to intrapartum antibiotics had a modest reduction in circulating CD45RA- iTregs compared to unexposed infants.
The mechanisms by which the gut microbiota influence vaccine responses remain poorly understood. I compared antibody responses to PCV13 in germ-free (GF) mice, in GF mice that were colonised at day 21 of life via fecal microbiota transplant (FMT), in mice that were born to GF dams that were recolonised prior to pregnancy (exGF) and in conventionally colonised SPF mice. GF mice immunized at 3-4 weeks of age had impaired polysaccharide-specific and conjugate protein-specific antibody responses to the PCV13 vaccine compared to normally colonised SPF mice. Responses were restored to levels comparable to SPF mice in exGF but not in GF mice recolonised by FMT at day 21 of life. Comprehensive multi-parameter flow cytometry analysis of the spleen and draining lymph nodes revealed that GF mice had significantly impaired germinal centre B cells and Tfh cells after the second dose of PCV13. In addition, GF mice had significantly fewer innate-like B-1a and B-1b cells in the peritoneum following primary immunisation with PCV13. My findings indicate that both T-dependent and T-independent humoral responses to the PCV13 vaccine are dependent on signals from the gut microbiota and that there is a critical window of opportunity for those signals to be received.
I hypothesised that products from the microbiota could act as natural adjuvant and prime innate responses to vaccination via Toll-like receptor (TLRs) signalling. To investigate this, I assessed responses to PCV13 in Myd88-/- mice, a key adapter protein downstream of most TLRs, and found that Myd88-/- mice had significantly impaired humoral and germinal centre responses to the PCV13 vaccine. Further experiments in Tlr2-/- and Tlr4-/- mice revealed that TLR2 but not TLR4 signalling was necessary for primary antibody responses to PCV13. Surprisingly, antibiotic treatment in early life resulted in an apparent ‘recovery’ of the impaired humoral responses observed in Myd88-/- mice. My data suggest that microbiota-targeted inventions may be beneficial to support optimal responses to vaccination.
Keywords: vaccine, microbiome, immunology, PCV13, infant
Subject: Microbiology & Infectious Diseases thesis
Thesis type: Doctor of Philosophy
Completed: 2023
School: College of Medicine and Public Health
Supervisor: David Lynn