Transfusion-driven hyperhemolysis in sickle cell disease - Red blood cell (RBC) transfusions remain a cornerstone treatment in the management of sickle cell disease
(SCD). However, patients may experience delayed hemolytic transfusion reaction (DHTR) which in this patient
population has an unpredictable progression from mild to life-threatening severe reactions where both transfused
and patient’s own RBCs are destroyed along with reticulocytopenia at the time of hemolytic crisis, exacerbating
the anemia. The mechanisms underlying severe DHTR progression are poorly understood, posing challenges
for prevention and effective treatments for this transfusion complication which is disproportionately encountered
in patients with SCD. We recently found that acute hemolysis induces type I interferon (IFN-I) production in innate
immune cells, leading to increased differentiation and activation of monocyte-derived macrophages (MoMΦ) in
SCD, and exacerbating destruction of antibody (Ab)-coated transfused RBCs. Our preliminary data showed that
Ab-sensitized RBC destruction alone also led to IFN-I production but with even higher levels if destruction
occurred under hemolytic conditions, which interestingly also induced bystander hemolysis of sickle RBCs,
mimicking hyperhemolysis reaction in SCD. We also found that hemolysis-induced IFN-I impairs erythropoiesis
along with inhibition of EPO/EPOR signaling. Based on these data, we hypothesize that Fc receptor crosslinking
in a hemolytic backdrop of SCD leads to increase in IFN-I levels, causing heightened IFN-I signaling in
phagocytes and erythroid cells which trigger increased RBC destruction and further suppression of RBC
production, respectively, leading to severe DHTR. In aim 1, we will focus on identifying mechanisms of bystander
hemolysis by examining the role of key phagocytosis activation molecules, specifically SCD associated eat me
signals including thrombospondin (TSP-1) and its ligands which are upregulated in hyperhemolytic models. We
will compare the role of Ab-mediated erythrophagocytosis versus Ab-independent RBC engulfment in triggering
bystander hemolysis and interrogate the relative contribution of inhibiting FcR/SYK phosphorylation and heme
activation pathways in autologous sickle RBC destruction. We will also examine the potential of IFN-I as a
biomarker of DHTR severity by examining IFN-I/STAT1 driven changes in monocytes in SCD patient samples,
comparing patients experiencing severe and mild DHTR and after recovery to steady state. For aim 2, we will
define the mechanisms by which IFN-I suppresses erythropoiesis using primary erythroid cell culture system and
targeted deletion of key downstream pathways in human erythroblast cell lines and mouse models. We will also
test the therapeutic effects of inhibiting IFN-I production/IFN-I signaling or/and increasing EPO/EPOR signaling
on reversing impaired BM erythropoiesis in SCD mice and on human erythropoiesis in vitro and in cultures
treated with SCD patient plasma. We believe that our proposed studies to examine the basis for progression to
DHTR severity may help stratify risk and aid in development of novel targeted therapies to reverse or prevent
hyperhemolysis, a devastating complication of an otherwise life-saving treatment in SCD.
