Dual-mode MRI for in vivo sensing of microcapsule stability and biocompatibility

 描述(申请人提供)：对于I型糖尿病患者，胰岛移植提供了一种时刻精细的胰岛素调节，这是外源性胰岛素注射无法实现的。胰岛细胞死亡，无论是由于移植排斥反应、毒性免疫抑制药物的存在，和/或缺乏血液和营养供应，仍然是成功治疗的重要障碍。一段时间以来，用藻酸盐包裹胰岛以实现免疫保护的方法取得了进展，但总体成功率有限，一旦移植到患者体内，胰岛的长期存活率很低。从活检中可以知道，目前使用的藻酸盐胶囊组合物远远不是最理想的，因为它们可以引发异物宿主免疫反应，最终导致胶囊的纤维性过度生长和随后的胰岛细胞死亡。遗憾的是，随着时间的推移，目前还没有手段无创地检测植入微囊的机械稳定性和生物相容性，从而延缓了囊化胰岛细胞治疗的进一步发展和改进。我们的目标是开发一种双模磁共振成像(MRI)方法，可以报告植入胶囊随时间的机械稳定性，同时询问是否存在主要的宿主免疫反应。为此，我们将分别使用氟(19F)和磁化转移(MT)磁共振，这两种方法都可用于临床。混合海藻酸盐梯度(MAG)氟胶囊将被开发为一种新的胶囊配方，而不需要使用潜在的有毒聚阳离子来实现胶囊通透性的选择性。我们推测，这些MAG氟胶囊比传统的藻酸盐胶囊具有更好的生物相容性。我们将首先开发不同机械强度的MAG氟胶囊，并测试它们的稳定性、渗透性和胰岛包封性 体外功能。然后我们将移植空胶囊S.C.和IP。在非糖尿病、免疫活性的Balb/c小鼠中，将被跟踪180天。核磁共振研究和免疫组织病理学的结果将被用来选择最有希望的配方来包裹小鼠(同种)、猪和人(异种)胰岛，这些胰岛将被移植到I.P.和S.C.在免疫活性NOD SHI/LTJ和链脲佐菌素(STZ)诱导的免疫缺陷NOD SCID/SCID小鼠中。19F MRI(机械稳定性)和MT MRI(宿主免疫反应)信号将在180天内收集，并与免疫组织学和血液参数(C-肽、葡萄糖)进行比较。胰岛细胞的相对存活率将用生物发光成像(BLI)进行量化，并与荧光和MTR信号相关联。随着对免疫保护、生物相容性和机械稳定性的要求不断提高，我们希望通过对不同来源的胰岛进行同种异体移植和异种移植的循序渐进的方法，展示双模MRI在开发具有临床翻译潜力的新型包囊材料方面的有效性。

 DESCRIPTION (provided by applicant): For patients with Type I diabetes mellitus, islet transplantation provides a moment-to-moment fine regulation of insulin that is unachievable by exogenous insulin injection. Islet cell death, caused either by transplant rejection, the presence of toxic immunosuppressive drugs, and/or the lack of blood and nutrient supply remains an important obstacle for successful therapy. For some time, advances have been made by encapsulating islets with alginate to achieve immunoprotection, but the overall success rate has been limited, with poor long-term survival of islets once transplanted into patients. From biopsies it is known that the currently used alginate capsule compositions are far from optimal, as they can elicit a foreign body host immune response culminating in fibrotic overgrowth of capsules and subsequent islet cell death. Unfortunately, there is currently no means to probe the mechanical stability and biocompatibility of engrafted microcapsules non-invasively over time, delaying further development and improvements of encapsulated islet cell therapy. Our goal is to develop a dual-mode magnetic resonance imaging (MRI) approach that can report on the mechanical stability of implanted capsules over time while simultaneously interrogating the absence or presence of a major host immune response. To this end, we will employ fluorine (19F) and magnetization transfer (MT) MRI, respectively, both of which are clinically available. Mixed Alginate Gradient (MAG) fluorocapsules will be developed as a new capsule formulation without the need for using potentially toxic polycations to achieve selectivity of capsule permeability. We hypothesize that these MAG fluorocapsules have improved biocompatibility profiles over conventional alginate encapsulants. We will first develop MAG fluorocapsules with different mechanical strengths, and test their stability, perm-selectivity, and islet- encapsulated functionality in vitro. We will then transplant empty capsules s.c. and i.p. in non-diabetic, immunocompetent Balb/c mice which will be followed for 180 days. The outcome of the MRI studies and immunohistopathology will be used to select the most promising formulation to encapsulate mouse (allogeneic) and porcine and human (xenogeneic) islets, which will be transplanted i.p. and s.c. in immunocompetent NOD Shi/Ltj and streptozotocin (STZ)-induced immunodeficient NOD scid/scid mice. 19F MRI (mechanical stability) and MT MRI (host immune response) signals will be collected over 180 days and compared to immunohistological and blood (c-peptide, glucose) parameters. The relative islet cell survival will be quantified with bioluminescent imaging (BLI) and correlated to the fluorine and MTR signals. By following a step-wise approach of allografting and xenografting islets from different sources, with increasing demand on immunoprotection, biocompatibility, and preservation of mechanical stability, we hope to demonstrate the usefulness of dual-mode MRI in developing novel encapsulating materials with potential for clinical translation.