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 disproportionately is 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. Interestingly, only when the incompatible RBC
destruction occurs under hemolytic conditions inducing highest levels of IFN-I, we detect 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 inhibits RBC
production, respectively, in severe DHTR. In aim 1, we will focus on identifying mechanisms of bystander
hemolysis by examining the role of key phagocytosis activation molecules, including thrombospondin (TSP-1)
and its ligands which are upregulated in our 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 murine/human FcγR/SYK pathway and heme activation pathways in bystander
hemolysis. We will also examine the potential of IFN-I as a biomarker of DHTR severity by examining IFN-
I/STAT1 driven changes in monocyte phagocytosis associated profiles 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
from 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.

Grant Number: 5R01HL165202-03
NIH Institute/Center: NIH
Principal Investigator: Xiuli An