Background. Sickle cell disease (SCD) is caused by a single mutation of the ¿-globin gene and is the most
common form of inherited blood disorder. In the US, approximately 100,000 of Americans are affected.
Patients with SCD suffer from repeated red cell sickling and vaso-occlusion episodes, which, since early age,
lead to acute and chronic pain, stroke, anemia, infections, organ failure and premature death. Vaso-occlusion
episodes cause ischemia-reperfusion injury, activation of endothelial cells, immune cells and the coagulation
cascade. These processes lead to a state of chronic inflammation in SCD, associated with increased pro-
inflammatory cytokines, TLR4 activation and oxidative stress in all organs, including the bone marrow (BM).
To date, little is known about how inflammation impacts the BM microenvironment and HSC functions in SCD
patients. Notably, few and limited studies have been conducted on human samples. Preliminary results.
Our previous studies using different animal models have shown that TLR4 activation and upregulation of
miR155 and NF-kB signaling during inflammation results in the remodeling of the BM niche, myeloid lineage
skewing and loss of hematopoietic stem cell self-renewal. Preliminary results that we obtained in SCD patient
samples enrolled in a HSC transplantation (HSCT) clinical trial at City of Hope demonstrated a decrease in
frequency and number of CD34+ progenitor cells, decreased ability to generate colonies and increased
miR155 and NF-kB signaling in SCD BM-derived mesenchymal cells (MSC). Hypothesis. We hypothesize
that SCD-induced chronic inflammation remodels the BM niche and impairs HSC function in SCD patients,
and that these changes impact the engraftment of donor HSC during transplant. Aims and Strategy. This
study will be conducted on BM specimens of SCD patients (n=21) prior HSCT and at day +15, +30 and +1yr
after HSCT. Characterization of the cellular components and inflammatory pathways will be carried on BM
biopsies and aspirates by using complementary approaches such as multiparametric flow cytometry analysis,
immunohistochemistry and nanostring assays; CD34+ cells will be isolated at baseline, used for RNA-seq
and tested for colony-forming assay and ability to engraft NSG mice in vivo; BM and peripheral blood serum
will be probed for inflammatory cytokines; MSC will be BM derived in vitro and analyzed characterization and
persistence of the inflammatory signature. Results will be correlated with HSCT outcomes. Aged matched
healthy donors will be used as controls. Relevance. This study represents a unique opportunity to better
understand the biology of SCD in human specimens. Important, the dissection of the mechanisms involved in
BM niche dysfunction and inflammatory state in severe SCD should offer avenues for therapeutic intervention
to improve engraftment and hematopoietic reconstitution in patients with SCD.