Irrespective of host genetic factors, newborns and infants are characterised by a higher susceptibility to particular infections. Thus, these populations constitute privileged targets and reservoirs for existing and emerging diseases. They carry influenza virus, respiratory syncytial virus or B. pertussis leading to severe respiratory diseases in these fragile populations. Vaccination represents a powerful mean to provide protection against many infectious diseases, but with limited efficacy in the first few months of life. One main reason is that vaccine design does not take into account age-specific immune parameters of the populations receiving immunizations, i.e. neonates and infants. Systems biology has initiated the definition of a comprehensive picture to accurately define protection correlates. However age-specific immune parameters are still missing for appropriate signal deconvolution in high throughput immune system analyses. The gaps in the knowledge of the immune system of the newborn and the infant need to be filled to propose appropriate prophylactic and therapeutic treatments to these vulnerable populations.

We established a Human-Mouse experimental platform to study pathogen-neonatal immune host interactions and to design and evaluate age-specific vaccine strategies. Apart from the traditional view of immaturity, we recently evidenced immunological unfitness related to age-specific effector and regulatory mechanisms tuning immune responses in early life. We thus evidenced development of memory T cells and innate antibody responses during fetal life. We also characterised new innate inflammatory pathways in dendritic cells for future adjuvant setting in paediatric vaccination.