ENGRAFTING SENSITIZED HOSTS WITH NONABLATIVE REGIMENS

移植已在非致敏的主要组织相容性复合体(MHC)相合的受体中建立，并采用非清髓性预适应方案。以前输血的受者对供者的次要组织相容抗原敏感，增加了移植排斥反应的风险。遗传性红细胞疾病患者需要输血，移植物排斥反应的可能性更高。在这项提议中，非清髓性调节方案将被开发用于1)缺乏清髓性方案所特有的毒性，以及2)可以在门诊环境中安全地给药的致敏受者。针对致敏患者的非清髓方案的开发将基于两个假设：1)致敏受者的宿主抗移植物(HVG)反应可以被大剂量放化疗以外的免疫抑制剂抑制；2)移植物中的T细胞可以抑制宿主免疫系统，包括致敏的免疫效应细胞。这些假说将在输血诱导致敏的临床前犬模型中得到验证，非清髓方案将被开发出来。移植前输血使受者致敏，可通过常规的大剂量调节产生均匀的移植排斥反应。在目标1中，将在剂量降低研究中确定在CSP的基础上进一步加强移植前免疫抑制是否能成功促进植入。移植后免疫抑制(MMF/CSP)将被单独评估，以确定它是否在920cGyTBI致敏受者中防止移植物排斥反应。如果有效，移植后免疫抑制的加强将在目标1A完成时发生移植物排斥反应的最大TBI剂量下进行。在目标2中，将确定促进GVH是否通过抑制致敏的宿主T细胞和在骨髓中创造空间来实现植入。如果这些研究成功，那么捐赠者的T细胞将被体外扩增并转导“自杀(HSVtk)基因”，以预防严重的GVHD。在目标3中，最佳免疫抑制方案将与GVH增强方案相结合。这项建议的最终目标是消除预适应方案中的细胞毒剂。通过降低与常规调节相关的发病率和死亡率，这些研究可以显著改变对选定的遗传性红细胞疾病的治疗。

Engraftment has been established in nonsensitized major histocompatibility complex (MHC)-matched recipients with nonmyeloablative conditioning regimens. Recipients previously transfused with blood products become sensitized to donor minor histocompatibility antigens, increasing the risk of graft rejection. Patients with inherited red blood cell diseases require blood transfusions and have a higher probability of graft rejection. In this proposal, nonmyeloablative conditioning regimens will be developed for sensitized recipients which 1) lack the toxicities characteristic of myeloablative regimens, and 2) could be safely administered in an outpatient setting. The development of the nonmyeloablative regimen for sensitized patients will be based on two hypotheses: 1) host-versus-graft (HVG) reactions of sensitized recipients can be suppressed with immunosuppressive agents other than high-dose chemoradiotherapy; 2) T cells from the graft can suppress the host immune system including sensitized immune effector cells. These hypotheses will be tested and nonmyeloablative regimens will be developed in a preclinical canine model of transfusion-induced sensitization. Sensitizing recipients with blood transfusions prior to transplant results in uniform graft rejection with conventional high-dose conditioning. In Aim 1, it will be determined if further stepwise intensification of pretransplant immunosuppression in addition to CSP will successfully promote engraftment in a dose de-escalation study of TBI. Posttransplant immunosuppression (MMF/CSP) will be assessed separately to determine if it prevents graft rejection in sensitized recipients at TBI 920 cGy. If effective, intensification of posttransplant immunosuppression will be done at the maximal TBI dose at which graft rejection occurs at the completion of Aim 1A. In Aim 2, it will be determined if promoting GVH will achieve engraftment by suppressing sensitized host T cells and "creating space" in the marrow. If these studies are successful, then donor T cells will be ex vivo expanded and transduced with a "suicide (HSVtk) gene" for prevention of severe GVHD. In Aim 3, the optimal immunosuppressive regimen will be combined with a GVH enhancing regimen. The ultimate goal of this proposal is the elimination of cytotoxic agents from the conditioning regimen. By lessening the morbidity and mortality associated with conventional conditioning, these studies could significantly change the management of selected inherited red blood cell diseases.