Periodic Reporting for period 4 - FatemapB (High Resolution Mapping of Fetal and Adult B Cell Fates During Ontogeny)
Período documentado: 2022-04-01 hasta 2022-09-30
The overall objectives of FatemapB are as follows:
Aim 1. Determine the quantitative and qualitative contribution of early life B cell output to the adult B cell pool through ‘time stamping’.
Aim 2. Resolve the developmental relationship between fetal and adult derived B cells by single cell lineage-tracing.
Aim 3. Characterize the basis for and immune functions of induced fetal-like B cell output from adult HSPCs.
The societal impact of FateMapB extends beyond academic understanding of the formation of a diverse immune system to implications amenable for clinical exploitation within the areas of immune regeneration, neonatal immune imprinting and the development and optimization of vaccination strategies.
In addition we have demonstrated that the developmentally restricted expression of Lin28b temporarily relaxes the autoimmune checkpoint during B cell development allowing for augmented B cell positive selection and peripheral output (Science Immunology 2019). Thus, Lin28b breeches the censorship of developing B cells with perceived self-antigen engagement and the output of poly-reactive B-1 cells early in life. Furthermore, ectopic Lin28b expression in adult B cell precursors reinitiates the fetal-like augmented state of positive selection. The latter was quantified using cellular barcoding, a single cell lineage tracing method allowing for the relative quantification of precursor-progeny ratio of pre- and post-selection B cells in vivo. We propose that this neonatal mode of B cell selection represents a cell intrinsic cue to accelerate the de novo establishment of the adaptive immune system and incorporate a layer of natural antibody mediated immunity throughout life.
Our research has also demonstrated the ability of Lin28b to relax the autoimmune checkpoint to augment positive selection and overall B cell output early in life. Lin28b therefore offers a potential mechanism to explain the long-known fact that neonatal B cells are frequently self-reactive in mice and men. Of particular interest is the timing of Lin28b expression which in mice lasts until the third week of life. This overlaps with the immune formative event of weaning associated gut microbial colonisation, and offers an attractive possible explanation to the time-limited effects of neonatal exposure that cannot be recapitulated later in life.