Hematopoietic stem cells (HSCs) are the source of all blood cells over an individual’s lifetime. Diseased HSCs can be replaced with gene-engineered or healthy HSCs through HSC transplantation (HSCT). However, current protocols carry major side effects and have limited access. We developed CD117/LNP–messenger RNA (mRNA), a lipid nanoparticle (LNP) that encapsulates mRNA and is targeted to the stem cell factor receptor (CD117) on HSCs. Delivery of the anti–human CD117/LNP–based editing system yielded near-complete correction of hematopoietic sickle cells. Furthermore, in vivo delivery of pro-apoptotic PUMA (p53 up-regulated modulator of apoptosis) mRNA with CD117/LNP affected HSC function and permitted nongenotoxic conditioning for HSCT. The ability to target HSCs in vivo offers a nongenotoxic conditioning regimen for HSCT, and this platform could be the basis of in vivo genome editing to cure genetic disorders, which would abrogate the need for HSCT.

Summary: In an attempt to find new types of anti‐sickling agents that specifically bind to intracellular sickle haemoglobin (HbS) without inhibition by plasma and tissue proteins or other undesirable consequences, we identified 5‐hydroxymethyl‐2‐furfural (5HMF), a naturally occurring aromatic aldehyde, as an agent that fulfils this criterion. Preliminary studies in vitro showed that 5HMF forms a high‐affinity Schiff‐base adduct with HbS and inhibits red cell sickling by allosterically shifting oxygen equilibrium curves towards the left. Further studies with transgenic (Tg) sickle mice showed that orally administered 5HMF was rapidly absorbed into the bloodstream from the gastrointestinal tract without being destroyed, traversed the red blood cell membrane and specifically bound with, and modified, HbS molecules at levels as high as 90%. Pretreatment of Tg sickle mice with 5HMF inhibited the formation of sickle cells and significantly prolonged survival time under severe hypoxia, compared with untreated mice, which died within 15 min because of sickling‐dependent pulmonary sequestration. These results indicate the feasibility of 5HMF as an attractive potential candidate for therapy of sickle cell disease.

A CRISPR screen for RBC regulators: Hemoglobin in red blood cells (RBCs) carries oxygen to the tissues. Sickle cell disease is an inherited condition that involves abnormal hemoglobin. Current treatments entail modulating the level of fetal hemoglobin expression. Grevet et al. performed a CRISPR-Cas9 screen for regulators of fetal hemoglobin in RBCs and identified heme-regulated eIF2α kinase (HRI). Depleting the kinase in RBCs led to an increase in fetal hemoglobin levels and reduced sickling of cultured human RBCs. Thus, HRI may be a therapeutic target for sickle cell disease and other hemoglobin disorders. Science , this issue p. 285

Quantification of blood oxygen saturation on the basis of a measurement of its magnetic susceptibility demands knowledge of the difference in volume susceptibility between fully oxygenated and fully deoxygenated blood (Δχ_do). However, two very different values of Δχ_do are currently in use. In this work we measured Δχ_do as well as the susceptibility of oxygenated blood relative to water, Δχ_oxy, by MR susceptometry in samples of freshly drawn human blood oxygenated to various levels, from 6 to 98% as determined by blood gas analysis. Regression analysis yielded 0.273 ± 0.006 and −0.008 ± 0.003 ppm (cgs) respectively, for Δχ_do and Δχ_oxy, in excellent agreement with previous work by Spees et al. (Magn Reson Med 2001;45:533–542). Magn Reson Med, 2012.

Erythrocyte precursors produce abundant α- and β-globin proteins, which assemble with each other to form hemoglobin A (HbA), the major blood oxygen carrier. αHb-stabilizing protein (AHSP) binds free α subunits reversibly to maintain their structure and limit their ability to generate reactive oxygen species. Accordingly, loss of AHSP aggravates the toxicity of excessive free α-globin caused by β-globin gene disruption in mice. Surprisingly, we found that AHSP also has important functions when free α-globin is limited. Thus, compound mutants lacking both Ahsp and 1 of 4 α-globin genes (genotype Ahsp^–/–α-globin*^α/αα) exhibited more severe anemia and Hb instability than mice with either mutation alone. In vitro, recombinant AHSP promoted folding of newly translated α-globin, enhanced its refolding after denaturation, and facilitated its incorporation into HbA. Moreover, in erythroid precursors, newly formed free α-globin was destabilized by loss of AHSP. Therefore, in addition to its previously defined role in detoxification of excess α-globin, AHSP also acts as a molecular chaperone to stabilize nascent α-globin for HbA assembly. Our findings illustrate what we believe to be a novel adaptive mechanism by which a specialized cell coordinates high-level production of a multisubunit protein and protects against various synthetic imbalances.