Project 3: Determine the consequences of perinatal inflammation on the function of HSPCs later in life.

There has been growing interest in how inflammation regulates adult HSC function. On a population level, inflammation can favor the expansion of certain clones of HSCs over others, leading to hematologic malignancies. On a per cell level, inflammation modulates HSPCs by inducing epigenetic modifications in myeloid-priming genes in a way that confers “memory” of the challenge, a process termed trained immunity.

Upon subsequent exposure, adult mice that are re-challenged mount a response characterized by increased myeloid production compared to naïve mice. This can be either protective when it leads to improved survival or maladaptive when it leads to increased disease severity. Importantly, these responses can be attributed to HSPCs, as bone marrow transplantation transfers the “exposed” phenotype to the recipient mouse. Whether inflammation shapes the fetal or neonatal HSPC compartment on either a population or a per cell level has not been addressed.

We hypothesize that given the increased susceptibility of mice and humans to inflammation during the fetal and neonatal periods, and the unique impact of exposures during this window on imprinting responses later in life, that fetal and neonatal HSPCs are shaped by inflammation with distinct consequences for hematopoietic function across the lifespan.

A significant challenge in addressing these questions is that some of the inflammatory stimuli shown to elicit trained immunity in adult mice lead to fetal and/or neonatal demise. To overcome this challenge, we employ an anti-Ly6G antibody model that depletes Ly6G-expressing granulocytes and triggers demand-adapted myelopoiesis. We have previously shown that this model can be used in pregnant dams, depleting fetal granulocytes and altering the HSPC compartment, without leading to fetal or neonatal demise. We have also established that anti-Ly6G administration in adult mice functions to elicit trained immunity as measured by increased myeloid cell output upon HSC transplantation and improved clearance of a Staphylococcus aureus challenge, and that this is not observed in young adult mice that were exposed to anti- Ly6G as fetuses.

We are using this model to compare the population level and per cell level changes that anti-Ly6G induces in adult HSCs compared to fetal HSCs, using functional, transcriptional, and epigenetic approaches.

These studies will establish how perinatal inflammation and infection imprint on the immune system throughout the lifespan, with implications for the establishment of immune memory in the context of infection and vaccination as well as the development of allergies and susceptibility to leukemia development.