Fetal hemoglobin per erythrocyte (HbF/F-cell) after gene therapy for sickle cell anemia.
Fetal hemoglobin per erythrocyte (HbF/F-cell) after gene therapy for sickle cell anemia.
复制标题
镰状细胞性贫血基因治疗后每个红细胞的胎儿血红蛋白 (HbF/F-cell)。
DOI：
10.1002/ajh.26791
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发表时间：
2023
影响因子：
12.8
通讯作者：
Steinberg,MartinH
中科院分区：
文献类型：
--
作者：
Sebastiani,Paola;Steinberg,MartinH
致编辑：镰状细胞性贫血（和β地中海贫血）的基因治疗试验诱导高水平的胎儿血红蛋白（HbF，α2γ2）或胎儿样成人血红蛋白（HbAT 87 Q），这可能是其出色临床结果的原因。1-3 HbF及其杂合四聚体（α2γβS）在很大程度上被排除在镰状血红蛋白（HbS）聚合物相之外，从而防止驱动疾病病理生理学的红细胞损伤。4、5高浓度抗镰状化血红蛋白的广泛细胞分布完全保护大多数红细胞免受聚合物损伤，这是疾病表型逆转的原因。HbF通常限于少量红细胞（异细胞），但在某些遗传性疾病中，这种血红蛋白可以均匀分布在所有红细胞（泛细胞）中。响应于HbF诱导剂羟基脲，HbF更广泛地但仍然是异细胞分布的。当在婴儿期开始时，羟基脲是镰状细胞性贫血的第一种HbF诱导疗法，HbF水平维持在20%至40%之间，大多数症状消退。当在成人中开始时，HbF增加不到这个量的一半，并且患者仍然有症状。6由于HbF浓度在含HbF细胞（F细胞）中分布的变化，在羟基脲治疗之前或之后具有相似HbF水平的个体可能具有不同的疾病表型。7、8在HbS基因缺失遗传性持续性HbF（HbS-HPFH）的遗传条件下，杂合子的全部红细胞中约有30%的HbF。他们的平均红细胞血红蛋白（MCH）约为30 pg，因此每个红细胞含有约10 pg的HbF。9-11这些F细胞几乎正常存活，很少触发急性镰状血管闭塞，从而设定了HbF/F细胞的治愈性全细胞水平的治疗目标。具有类似高HbF水平的镰状细胞性贫血婴儿在临床上良好，直到他们的HbF水平随着年龄的增长而下降。12，13随着基因治疗的成功，婴儿期HbS-HPFH和镰状细胞贫血的临床和血液学结果似乎会重复。我们假设，基因治疗后的血液学结果诱导HbF水平约为40%，导致血红蛋白浓度接近正常，而MCH没有从基线增加，预示着几乎所有的镰状红细胞都有足够的HbF来逆转疾病的表型。为了模拟潜在的生理学，我们使用了在BCL 11 A增强子基因的CRISPR/Cas9破坏后观察到的血液学参数来下调BCL 11 A，并估计了F细胞中HbF浓度的分布。F细胞的荧光激活细胞分选（FACS）检测需要4- 6pg的HbF/F细胞，尽管一些较新的测定可以检测仅具有2 pg的细胞。7、14具有小于10 pg的HbF的F细胞可能部分但不完全免受HbS聚合物的影响，改善但不消除疾病表型。然而，使用约10 pg的HbF，细胞完全或几乎完全被保护免受HbS聚合物产生的损伤。我们在建模中设定了两个限制：不超过10%的细胞可以完全失活BCL 11 A表达。在小鼠和细胞系的研究中，显示完全失活伴随着多达20 pg的HbF/F-细胞。此外，2%的细胞可能具有小于5 pg的HbF，并且不被计数为F细胞。图1显示了基因治疗诱导40%HbF（4.4g/dL）后镰状红细胞中HbF浓度的可能分布。从左到右是具有2%至10%的细胞的图，所述细胞具有小于10 pg的HbF。虽然具有不同量的HbF的细胞的分布不改变，但当HbF浓度升高时，细胞的分布会发生变化。
To The Editor: Gene therapy trials for sickle cell anemia (and β thalassemia) induce high levels of fetal hemoglobin (HbF, α2γ2) or a fetal-like adult hemoglobin (HbAT87Q) that likely accounts for their outstanding clinical results. 1–3 HbF and its hybrid tetramer (α2γβS) are largely excluded from the sickle hemoglobin (HbS) polymer phase, preventing the erythrocyte injury that drives the disease pathophysiology. 4, 5 A broad cellular distribution of high concentrations of anti-sickling hemoglobin protects fully most erythrocytes from polymer damage accounting for the reversal of the disease phenotype. HbF is normally restricted to a small number of erythrocytes (heterocellular), but in some genetic disorders, this hemoglobin can be homogeneously distributed among all erythrocytes (pancellular). In response to the HbF-inducing agent hydroxyurea, HbF is more widely but still heterocellularly distributed. When started in infancy, hydroxyurea, the first HbF-inducing therapy for sickle cell anemia, sustained HbF levels between 20% and 40% with resolution of most symptoms. When started in adults, the HbF increase is less than half this amount and patients remain symptomatic. 6 Because of variation in the distribution of HbF concentrations among HbF-containing cells (F-cells) individuals with similar HbF levels before or after hydroxyurea treatment can have different disease phenotypes. 7, 8 In the inherited condition, HbS-gene deletion hereditary persistence of HbF (HbS-HPFH), heterozygotes have about 30% HbF in all their red cells. Their mean corpuscular hemoglobin (MCH) is about 30 pg, so each erythrocyte contains about 10 pg of HbF. 9–11 These F-cells survive nearly normally and rarely trigger acute sickle vasoocclusion setting a therapeutic goal for curative pancellular levels of HbF/F-cell. Infants with sickle cell anemia with similarly high HbF levels were clinically well until their HbF levels fell as they aged. 12, 13 With successful gene therapy, the clinical and hematologic outcomes of HbS-HPFH and sickle cell anemia in infancy appear to be repeated. We hypothesized that the hematologic results following gene therapy that induced HbF levels of about 40% and resulted in nearnormal hemoglobin concentration without an increase in MCH from the baseline, foreordained that nearly all sickle erythrocytes would have sufficient HbF to reverse the phenotype of the disease. To model the underlying physiology, we used the hematologic parameters observed following CRISPR/Cas9 disruption of the BCL11A enhancer gene to downregulate BCL11A and estimated the distribution of HbF concentrations among F-cells. 2 Fluorescence-activated cell sorting (FACS) detection of F-cells requires 4–6 pg of HbF/F-cell although some newer assays can detect cells with only 2 pg. 7, 14 F-cells with less than 10 pg of HbF are likely to be partially, but not fully protected from HbS polymer, improving but not abolishing the disease phenotype. However, with about 10 pg of HbF, the cell is totally or nearly totally protected from HbS polymer-generated injury. We set two limits in our modeling: no more than 10% of cells could have complete inactivation of BCL11A expression. Total inactivation was shown to be accompanied by as much as 20 pg of HbF/F-cell in studies of mice and cell lines. 15, 16 In addition, 2% of cells could have less than 5 pg of HbF and not be counted as F-cells. Figure 1 displays possible distributions of HbF concentrations in sickle erythrocytes after gene therapy induced 40% HbF (4.4 g/dL). From left to right are panels with 2% up to 10% cells with less than 10 pg of HbF. While the distribution of cells with various amounts of HbF does not change, when …