Background:
Clonal hematopoiesis (CH) is defined as a clonal expansion of hematopoetic stem cells (HSCs) with distinct phenotypes with age being one of the major risk factors. These altered HSCs subsequently give rise to dysfunctional leukocytes, but neutrophil specific alterations in this context are not yet fully described. To this date it is not clear if and how these changes in the immune cell composition are transferred to the next generation and if inherited changes of the HSC transcriptome persist through life and which immunological consequences are intertwined with them. It has also been suggested that there is a strong correlation between CH and cardiovascular diseases (CVD) driven by myeloid cells. We aimed to identify how chronic inflammation changes the pool of multipotent progenitors (MPPs), myeloid progenitors (MyPs), granulocyte macrophage progenitor (GMP), and common myeloid progenitors (CMPs). We further clarified how changes in the pool of HSCs affects the production of immune cells on a cellular and a genetic level and how these changes are passed on to the next generation.

Results:
We found an expansion of MyPs and megakaryocyte progenitors (MEPs) in the bone marrow following a chronic inflammatory stimulation. This was accompanied by an enlarged spleen with increased Ly6C⁺ monocytes and neutrophils. The F1 generation showed no alterations in spleen size, however the pool of MPPs and MPP subsets was remarkably different and showed a rapid change of some subsets (MPP2/3/4) upon further inflammatory stimulation. When analyzing the bone marrow compartment, we found that GMPs, CMPs, and MEPs are more prone to changes compared to the progenitors within the spleen. Additionally, we could identify transcriptional changes like upregulation of pro inflammatory genes as well as of genes involved in the cell cycle, like Mki67 and Ccnb2. We could identify a specific, niche dependent change of mature neutrophils, which tend to upregulate CD11b, GCSFR, CCR5, and C5aR. In contrast, expression levels of the IL1 receptor was dampened significantly in splenic neutrophils. Interestingly, we could observe sex-specific variations in stem cell composition and neutrophil phenotype and functionality in the different organs. However, the LSK to MyP ratio (roughly 10% and 90% respectively) in bone marrow samples of either gender showed a similar shift upon inflammatory challenge, with an accumulation of LSKs up to 50%.

Conclusions:
Our data indicate that inflammation-induced changes in the stem cell pool heavily impact on the maturation and functionality of mature immune cells. These effects translate to a different stem- and immune cell composition in the next generation, which results in an abnormal immune response upon immune challenge. We found that the composition of the stem cell pool in different organs is partly reflected in circulating immune cells. This could open the door for novel preventive screening panels to identify high risk patients with genetic disorders within their stem cells. Such screening assays could potentially spare the next generation from potentially life-threatening immune diseases and would offer the chance to detect and monitor affected subjects in the early stage of life.