Modeling Inflammation, Neutropenia, Bone Marrow Failure, and Lymphoproliferation caused by TLR8 (INFLTR8) in B6 Mice 2259831

Abstract

Abstract Introduction Toll-like receptor 8 (TLR8) is an endosomal sensor of ssRNA expressed primarily in myeloid cells. TLR8 activation leads to expression of type I interferons and inflammatory cytokines. Recently, 12 patients who presented with neutropenia, lymphoproliferation, infections, and bone marrow failure were found to have gain of function (GOF) mutations in TLR8 (“INFLTR8”). Strikingly, many of these patients were mosaic for the mutations with variant allele frequencies of < 30% (Aluri et al; Blood 2021). It is unclear how these mutant harboring cells lead to such profound immune system dysfunction. We hypothesize that TLR8 mutant myeloid cells produce inflammatory cytokines leading to T cell activation and marrow failure. Methods To interrogate mechanisms of INFLTR8, we developed a transgenic B6 mouse model conditionally expressing wild type or GOF human TLR8 (TLR8WT or TLR8GOF) in the myeloid lineage. We verified expression of TLR8, obtained peripheral blood counts, analyzed serum cytokines, and performed competitive bone marrow transplants with peripheral blood and bone marrow chimerism tracking. Results TLR8GOF mice exhibit increased serum cytokines, cytopenias, and decreased engraftment potential in competitive bone marrow transplants. In addition, HSCs have decreased differentiation potential after transplantation. Ongoing experiments are aimed at identifying abnormal signaling pathways and cytokine production in the TLR8 GOF myeloid cells, as well as the cell non-autonomous effects on T cells and other bone marrow populations. In addition, we are testing potential anti-TLR therapies, including IRAK inhibition. Conclusion Our B6 mouse model of INFLTR8 recapitulates several hallmarks of the disease found in patients: cytopenias, inflammation, and bone marrow dysfunction. Our model reveals HSC dysfunction as an important component of the pathogenesis of this disease. Ongoing experiments will elucidate the mechanisms by which TLR8GOF cells impact HSCs and other cell populations. Funding Source Children’s Discovery Institute of WashU Topic Categories Immune Mechanisms of Human Disease (HUM)