Targeting Trained Immunity in Trauma-Induced Immune Dysregulation

PROJECT SUMMARY/ABSTRACT Traumatic injuries from burns, blasts, or major surgery dysregulates immune system function predisposing the injured people to life-threatening opportunistic infections or persistent critical illness. Targeted immunotherapies for traumatic injuries to restore immune system function and homeostasis have not yet been developed and are urgently needed. The immunophenotypic diversity in humans provides a solid justification to target evolutionarily conserved innate immunoregulatory networks that are less heterogenous for treatment. As such, the reprogramming of innate immune cells by a process called “trained immunity” is a promising concept for targeting therapeutics to reduce the morbidity and mortality from trauma-induced complications. Trained immunity can occur in short-lived innate immune cells by epigenetically modifying accessibility to immune regulatory genes in hematopoietic stem cells (HSC), which are then passed on by differentiation to innate effector cells, leaving them better poised to respond to infection. We have developed Toll-like receptor 9 (TLR9) agonists – unmethylated CpG-DNA sequences, which are naturally found in bacterial DNA and eukaryotic cell mitochondria - as immunotherapeutic medical countermeasures to promote immune system recovery after radiation and traumatic injuries. We recently discovered that mesenchymal stromal cells (MSCs), which are critical cellular residents in the bone marrow hematopoietic stem cell (HSC) niche, express high TLR9 levels, strongly react to CpG-DNA stimulation, and mediate emergency granulopoiesis responses to infection in neutropenic mice. This discovery prompted us to consider trained immunity as a central mechanism contributing to the immune protection from systemic CpG-DNA treatment in our burn trauma and infection model. Here, we address the hypothesis that TLR9 agonist therapy mediates protective immunity and restores immune homeostasis by trained immunity mechanisms involving bone marrow MSCs and HSCs. To test this hypothesis, we propose the following specific aims: 1) To delineate hematopoietic and peripheral immune consequences of trauma with CpG-DNA therapeutic intervention, 2) To identify transcriptional and epigenetic changes in bone marrow MSCs and HSCs from injured and uninjured mice treated with CpG-DNA, and 3) To generate and use chimeric mouse models to delineate injury and CpG-DNA induced trained immunity phenotypes transferred by HSCs. We anticipate that the results from this research program will provide pre-clinical mechanistic insights towards translating CpG-DNA as an immunotherapeutic strategy for trauma-induced immune dysregulation.