Background: Sickle Cell Disease (SCD) is a devastating inherited disease, characterized by polymerization of sickle hemoglobin under deoxygenated conditions that can lead to acute pain crises, ischemia, and chronic organ damage. Pharmacologic anti-sickling agents that decrease polymerization are currently under investigation, however there is no consistent in vitro system to study these compounds; whole patient blood, subject to clinical variability and limited supply, is most often used. Human Umbilical Cord Derived Erythroid Progenitor 2 cells (HUDEP2) are an immortalized CD34+ hematopoietic stem cell (HSC) derived erythroid precursor cell line that can differentiate into red blood cells. We have engineered S-HUDEP2 cells to express sickle hemoglobin (HbS) via CRISPR/Cas9 gene editing. We hypothesized that this cell line will sickle under hypoxic conditions, produce dense red blood cells (DRBC, red cells with a density>1.11 mg/mL that are dehydrated and prone to sickling. If these intrinsic, essential SCD RBC properties are found, we propose to use this novel cell line to screen drug compounds for anti-sickling capabilities.

Methods: S-HUDEP cells were cultured as previously described (Kurita et al, 2013). %HbS and %HbA produced by parent HUDEP and S-HUDEP2 cells were measured by high performance liquid chromatography (HPLC). Hypoxia was induced by placing the cells at 2% O2 for four hours. Parent HUDEP and S-HUDEP2 cells were then fixed with glutaraldehyde and Giemsa stained. % sickling estimated at 40x magnification by a pathologist blinded to cell group counting sickle forms out of 1000 cells. The percentage of dense red blood cells (DRBCs) was quantified by an ADVIA hematology analyzer (Siemens). S-HUDEP2 cells were dosed with 0, 2.5 and 5 µM 5-hydroxymethylfurfural (5-HMF) and 75, 150, and 300 µM GBT440, two known anti-sickling agents, on day ten and day 14 of culture for one hour, subjected to hypoxic conditions and % sickling quantified as described above.

Results: S-HUDEP2 cells express 98% HbS. Under hypoxia, 20% of S-HUDEPs sickle at day 10 of differentiation; 30% of S-HUDEP2 cells sickle at Day +14 of differentiation. Parent HUDEP-2 cells, which produce 98% HbA, did not sickle under hypoxic conditions at any stage of differentiation. 70% of S-HUDEP2 cells were determined to be DRBC under hypoxia at Day 10 and 14 time points; parent HUDEP-2 cells did not produce DRBC under hypoxia. Treatment of S-HUDEP2 cells with 5μM of 5-HMF and 150 μM of GBT440 reduced sickling by 40-50% under hypoxic conditions compared with untreated S-HUDEP2 cells (p<0.01), and reduced %DRBC by 30% (p<0.01).

Conclusions: S-HUDEP2 cells express HbS, form DRBC, and sickle under hypoxic conditions, just like erythroid precursors and mature red blood cells from individuals with SCD. Exposure to two anti-sickling agents, one of which is currently in Phase III clinical trials, significantly decreased S-HUDEP2 sickling under hypoxic conditions, and reduced %DRBC, a marker of disease severity. Advantages of S-HUDEPs over patient samples include genetic and phenotypic uniformity, no human pathogens, and availability to groups without access to patient samples. We therefore conclude that S-HUDEP2s have utility in clinical research, may be used to screen anti-sickling and anti-dense cell compounds in vitro, and may lead to identification of new therapeutic options for SCD patients.


No relevant conflicts of interest to declare.

Author notes


Asterisk with author names denotes non-ASH members.