异染性脑白质营养不良(MLD)是一种常染色体隐性遗传性疾病。据之前报告显示，其患病率约为四万分之一。它是由于单一基因缺陷诱发的。该基因编码溶酶体中的一种叫做芳基硫酸酯酶A(ARSA)的蛋白。由于该基因的缺陷，溶酶体不能发挥正常的生理功能，致使神经细胞内代谢废物沉积，从而导致神经系统退化。异染性脑白质营养不良患者通常在婴幼儿早期发病，一般在出现首次症状几年后死亡。

    由于神经系统具有非常完善的自我防御机制，在神经系统中替换有缺陷的基因是非常困难的。鉴于造血干细胞一般是存在于成人的骨髓中，研究团队故采用其作为隐形的芳基硫酸酯酶A基因载体。研究人员先从患者体内提取微量的造血干细胞，然后将携带芳基硫酸酯酶A基因的病毒转染进去，最后再将这些造血干细胞重新置入该患者的血液中。

    一方面，这些细胞随着血液循环流动，一部分进入骨髓，另一部分到达神经系统后，以自身正常芳基硫酸酯酶A基因修复那些基因缺陷的细胞。另一方面，由于这些细胞本身就是干细胞，它们也分化成为新的血液细胞。

    大多数异染性脑白质营养不良患者的芳基硫酸酯酶A基因编码错误，所以溶酶体内芳基硫酸酯酶A的蛋白水平非常低，导致溶酶体不能发挥正常的功能。如果想使患者恢复，仅仅使芳基硫酸酯酶A的蛋白水平部分提升显然是不够的。有一个使其大幅度地提升的办法，那就是将具有大量拷贝的相同的正常遗传信息包装到基因缺陷的细胞中。于是，科研人员将具有两到四个拷贝芳基硫酸酯酶A基因整合进病毒，然后转染造血干细胞，以求产生更多的芳基硫酸酯酶A蛋白。

    接受治疗后的患者，他们芳基硫酸酯酶A的蛋白水平急剧升高。经过一年多的治疗，通过对他们的脑脊液进行检测，发现芳基硫酸酯酶A蛋白水平已经达到正常值。这表明，他们的中枢神经系统功能已经趋于稳定。接受该项治疗的是三名儿童，他们都有和他们一样遭受异染性脑白质营养不良折磨的兄弟姐妹。经过治疗后，这三个孩子恢复得很好，现在能和同龄儿童一样进行思考、跳跃、翻滚和说话等一系列的活动了。

    意大利圣拉斐尔科学研究所另外一个由AlessandroAiuti领导的研究小组，用相同的方法，对三个年轻的Wiskott-Aldrich综合征(WAS)患者进行治疗后，发现可以极大地减轻他们的病情。这项研究也发表在《science 科学》上。

    和异染性脑白质营养不良一样，WAS也是一个由单基因缺陷引起的疾病，这种疾病会导致免疫系统功能障碍。用整合过该基因的正常序列的病毒转染造血干细胞，然后将其注入患者体内，可以使患者的免疫系统功能恢复正常。

    由此看来，这种基于干细胞研究的基因治疗技术，既可以用来治疗严重的退行性神经系统疾病，也可以用来治疗免疫性疾病。这些事实证明，该技术在治疗由单基因缺陷引起的疾病方面是一个重大的突破。

    推荐原文阅读：

    Science. 2013 Aug 23;341(6148):1233151. doi: 10.1126/science.1233151. Epub 2013 Jul 11.

    Lentiviral hematopoietic stem cell gene therapy in patients with Wiskott-Aldrich syndrome.

    Aiuti A, Biasco L, Scaramuzza S, Ferrua F, Cicalese MP, Baricordi C, Dionisio F, Calabria A, Giannelli S, Castiello MC, Bosticardo M, Evangelio C, Assanelli A,Casiraghi M, Di Nunzio S, Callegaro L, Benati C, Rizzardi P, Pellin D, Di Serio C, Schmidt M, Von Kalle C, Gardner J, Mehta N, Neduva V, Dow DJ, Galy A,Miniero R, Finocchi A, Metin A, Banerjee PP, Orange JS, Galimberti S, Valsecchi MG, Biffi A, Montini E, Villa A, Ciceri F, Roncarolo MG, Naldini L.

    Source

    San Raffaele Telethon Institute for Gene Therapy, Division of Regenerative Medicine, Stem Cells, and Gene Therapy, San Raffaele Scientific Institute, 20132 Milan, Italy. aiuti.alessandro@hsr.itAbstract

    Wiskott-Aldrich syndrome (WAS) is an inherited immunodeficiency caused by mutations in the gene encoding WASP, a protein regulating the cytoskeleton. Hematopoietic stem/progenitor cell (HSPC) transplants can be curative, but, when matched donors are unavailable, infusion of autologous HSPCs modified ex vivo by gene therapy is an alternative approach. We used a lentiviral vector encoding functional WASP to genetically correct HSPCs from three WAS patients and reinfused the cells after a reduced-intensity conditioning regimen. All three patients showed stable engraftment of WASP-expressing cells and improvements in platelet counts, immune functions, and clinical scores. Vector integration analyses revealed highly polyclonal and multilineage haematopoiesis resulting from the gene-corrected HSPCs. Lentiviral gene therapy did not induce selection of integrations near oncogenes, and no aberrant clonal expansion was observed after 20 to 32 months. Although extended clinical observation is required to establish long-term safety, lentiviral gene therapy represents a promising treatment for WAS.

    Science. 2013 Aug 23;341(6148):1233158. doi: 10.1126/science.1233158. Epub 2013 Jul 11.

    Lentiviral hematopoietic stem cell gene therapy benefits metachromatic leukodystrophy.

    Biffi A, Montini E, Lorioli L, Cesani M, Fumagalli F, Plati T, Baldoli C, Martino S, Calabria A, Canale S, Benedicenti F, Vallanti G, Biasco L, Leo S, Kabbara N,Zanetti G, Rizzo WB, Mehta NA, Cicalese MP, Casiraghi M, Boelens JJ, Del Carro U, Dow DJ, Schmidt M, Assanelli A, Neduva V, Di Serio C, Stupka E, Gardner J, von Kalle C, Bordignon C, Ciceri F, Rovelli A, Roncarolo MG, Aiuti A, Sessa M, Naldini L.

    Source

    San Raffaele Telethon Institute for Gene Therapy, San Raffaele Scientific Institute, 20132 Milan, Italy.biffi.alessandra@hsr.itAbstract

    Metachromatic leukodystrophy (MLD) is an inherited lysosomal storage disease caused by arylsulfatase A (ARSA) deficiency. Patients with MLD exhibit progressive motor and cognitive impairment and die within a few years of symptom onset. We used a lentiviral vector to transfer a functional ARSA gene into hematopoietic stem cells (HSCs) from three presymptomatic patients who showed genetic, biochemical, and neurophysiological evidence of late infantile MLD. After reinfusion of the gene-corrected HSCs, the patients showed extensive and stable ARSA gene replacement, which led to high enzyme expression throughout hematopoietic lineages and in cerebrospinal fluid. Analyses of vector integrations revealed no evidence of aberrant clonal behavior. The disease did not manifest or progress in the three patients 7 to 21 months beyond the predicted age of symptom onset. These findings indicate that extensive genetic engineering of human hematopoiesis can be achieved with lentiviral vectors and that this approach may offer therapeutic benefit for MLD patients.