Nonmyeloablative allogeneic PBSC in globin disorders

血液病，如地中海贫血和血红蛋白病，分别是由一种或多种珠蛋白分子亚基的缺失/减少或异常产生造成的，它们共同构成了人类单基因疾病中最普遍的一类。长期以来，旨在替代缺失或缺陷的珠蛋白基因的策略一直被认为是潜在的治疗方法，而针对造血干细胞的基因转移策略一直是这一目标的核心。当然，同种异体骨髓移植是一种基于造血干细胞的基因移植，通过用正常基因型的供体替换整个患病器官来完成，已经被证明是有效的，但程序上的毒性限制了应用。为了扩大应用范围，我们探索了非骨髓清除移植方案，该方案旨在允许同种异体造血干细胞植入，而没有传统骨髓清除条件的毒性。使用动员的外周血干细胞作为来源，我们证明了转移性癌症患者在没有骨髓消融的情况下可靠的移植1，并将这些观察结果扩展到由于合并症而不适合传统骨髓移植的患者2,3。虽然明确确立了在没有骨髓消融的情况下实现人类造血植入的能力，但主要以移植物抗宿主病形式出现的程序性毒性仍然太高，无法应用于非恶性疾病。因此，我们回到动物模型，最近开发了一种低强度调理方案，旨在促进对同种异体移植物的耐受性。基于一种独特的耐受诱导机制，我们在小鼠动员外周血移植排斥模型中比较了低剂量照射后雷帕霉素免疫抑制与环孢素常规免疫抑制的应用。只有接受雷帕霉素治疗的小鼠表现出长期的造血嵌合，并且在随访超过4个月时达到75%以上的水平。为了将这些观察结果用于成人镰状细胞性贫血的临床应用，我们确定了外周血干细胞动员在具有镰状细胞特征的个体中的安全性和可行性，因为这些杂合子约占兄弟姐妹供体池的一半。我们现在已经启动了一项针对成人镰状细胞性贫血和地中海贫血的临床试验，并筛选了100多名潜在受试者，累计有8人患有纯合子镰状细胞病。到目前为止，所有8名患者都接受了早期供体造血嵌合移植，导致表型逆转。两名患者无意中接受了低于计划的照射剂量，一名患者需要再次移植，目前供体红细胞嵌合完全稳定。另外三对患者/供体已被确定，计划在未来几个月内进行移植。应计项目正在进行中。

Hematologic disorders such as the thalassemias and hemoglobinopathies, resulting from absent/reduced or abnormal production of one or more of the globin-molecule subunits, respectively, together constitute the most prevalent group of human monogenic diseases. Strategies which aim to replace the absent or defective globin gene have long been envisioned as potentially curative, and gene transfer strategies targeting hematopoietic stem cells have been central to this goal. Certainly, allogeneic bone marrow transplantation, a form of hematopoietic stem cell based gene transfer accomplished by replacement of the entire diseased organ with that from a donor with a normal genotype, has proven curative, yet procedural toxicities limit application. In order to expand application, we have explored nonmyeloablative transplant regimens which are designed to allow engraftment of allogeneic hematopoietic stem cells without the toxicity of conventional marrow ablative conditioning. Using mobilized peripheral blood stem cells as the source, we demonstrated reliable engraftment in the absence of marrow ablation in patients with metastatic cancer1 and extended these observations to patients ineligible for conventional myeloablative transplantation due to comorbidities2,3. While clearly establishing the ability to achieve hematopoietic engraftment in humans without marrow ablation, procedural toxicity, mainly in the form of graft-versus-host disease, remained too high for application to nonmalignant disorders. We therefore returned to animal models and have recently developed a low intensity conditioning regimen designed to promote tolerance to the allograft. Based upon a unique mechanism for tolerance induction, we compared the use of immunosuppression with rapamycin to that with conventional immunosuppression with cyclosporine after low dose irradiation in a murine model of mobilized peripheral blood allograft rejection. Only mice treated with rapamycin demonstrated long-term hematopoietic chimerism, and the levels achieved exceeded 75% at greater than 4 months of follow up. In anticipation of moving these observations toward clinical application for adults with sickle cell anemia, we established the safety and feasibility of peripheral blood stem cell mobilization in individuals with sickle cell trait, as these heterozygotes represent approximately half of the sibling donor pool4. We have now initiated a clinical trial for adults with sickle cell anemia and thalassemia, and have screened over 100 potential subjects and accrued 8 with homozygous sickle cell disease. All eight patients have thus far undergone transplantation with early donor hematopoietic chimerism resulting in reversion of the phenotype. Two patients inadvertantly received a lower than planned irradiation dose and one has required retransplantation and is currently stable with complete donor erythroid chimerism. Three additional patient/donor pairs have been identified with transplantation planned in the coming months. Accrual is ongoing.