Correction of β-thalassemia mutant by base editor in human embryos

β-Thalassemia is a global health issue, caused by mutations in the HBB gene. Among these mutations, HBB -28 （A〉G） mutations is one of the three most common mutations in China and Southeast Asia patients with β-thalassemia. Correcting this mutation in human embryos may prevent the disease being passed onto future generations and cure anemia. Here we report the first study using base editor （BE） system to correct disease mutant in human embryos. Firstly, we produced a 293T cell line with an exogenous HBB -28 （A〉G） mutant fragment for gRNAs and targeting efficiency evaluation. Then we collected primary skin fibroblast cells from a β-thalassemia patient with HBB -28 （A〉G） homozygous mutation. Data showed that base editor could precisely correct HBB -28 （A〉G） mutation in the patient＇s primary cells. To model homozygous mutation disease embryos, we consb＇ucted nuclear transfer embryos by fusing the lymphocyte or skin fibroblast cells with enucleated in vitro matured （IVM） oocytes.Notably, the gene correction efficiency was over 23.0% in these embryos by base editor. Although these embryos were still mosaic, the percentage of repaired blastomeres was over 20.0%. In addition, we found that base editor variants, with narrowed deamination window, could promote G-to-A conversion at HBB -28 site precisely in human embryos. Collectively, this study demonstrated the feasibility of curing genetic disease in human somatic cells and embryos by base editor system.

HBB-deficient Macaca fascicularis monkey presents with human β-thalassemia

Dear Editor,β-Thalassemia is a common severe genetic disease caused by mutations in HBB and affects approximately 1.5% of the global population (Origa, 2017). In southern China, the carrier rate of β-thalassemia is as high as 6.43%, creating a high socio-economic burden (Xiong et al., 2010). In adult humans, there are three types of hemoglobin: HbA1 (~97%), HbA2 (~2%) and HbF (~1%). HbA1 (α2β2) is composed of two a-globin and two β-globi n sub units en coded by HBA and HBB, respectively;HbF (α2β2)is made up of two α-globin subunits and two β-globin sub units en coded by HBG. Mutations in the coding region or regulatory region of HBB are involved in β-thalassemia pathogenesis. Except for some rare dominant mutations, most HBB mutations are recessive (Origa, 2017). Depending on the mutation type, the β-globin level will either be reduced or completely depleted, resulting in α-globin accumulation and precipitation. These α-globin precipitates lead to red blood cell death, resulting in anemia and tissue damage, and even death in thalassemia major patients. Blood transfusions can help slow disease progression but lead to iron overload, ultimately resulting in iron toxicity. Bone marrow transfer is the only cure in the clinic and is available only to a small percentage of patients with human leukocyte antigervmatched donors. Recently, gene therapy and gene editing therapy have shown great promise in curing β-thalassemia (Glaser et al., 2015;Thompson et al., 2018). However, no appropriate animal models are available for evaluating the safety and efficacy of such advanced therapeutic strategies in vivo.β-thalassemia mice are the sole animal model available for research. However, substantial differences have been reported between the types and expressi on patter ns of human and mouse globins (McColl and Vadolas, 2016). Moreover, mice contain no fetal globin gene equivalent, and homozygous mutations of HBB in mouse for early models of β-thalassemia major or Cooley anemia are all embryonic lethal (Huo et al., 2009). Recently, significant phenotype and physiology differences have been reported between SIRT6- null mice and the non-human primate model (Zhang et al., 2018). Thus, an appropriate non-human primate model is needed for human β-thalassemia studies and treatments.

Treatment of childhood cancer in China:Current status and future direction

Introduction China has a population of 1.3 billion and 16.6%of the population(212 million)is below age of 15 years according to the sixth national census in 2010.1 Chinese National Central Cancer Registry(NCCR)collected data from 219 cancer registries distributed in different parts of China.In 2010 data from NCCR reported that childhood cancer comprised approximately 0.6%of all cancers.In a recent study analyzed data from 145 cancer registries in China,the age-standardized incidence rate of childhood cancer was 87.1 per million.The top five commonest childhood cancers were leukemia(35.6 per million),central nervous system(CNS)tumor(15.0 per million),lymphoma(6.4 per million),bone cancer(4.4 per million)and kidney cancer(3.7 per million).2 The incidence is lower than western countries but similar to those reported by other low-middle income countries.The reasons for lower incidence of childhood cancer may be related to incomplete data collection.In China,there is a large floating population,221 million,who were not permanent residents in locations they worked and might not be included in the city registration.The projected number of new cases of childhood cancer in 0-14 years is 22875,and new cases of leukemia projected to be 8943 in 2015.It is important to have accurate data on incidence and survival that will help the government in policy making on health care delivery.