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

 描述（由申请人提供）：对于I型糖尿病患者，胰岛移植提供了外源性胰岛素注射无法实现的即时胰岛素精细调节。由移植排斥、毒性免疫抑制药物的存在和/或缺乏血液和营养供应引起的胰岛细胞死亡仍然是成功治疗的重要障碍。一段时间以来，通过用藻酸盐包封胰岛来实现免疫保护已经取得了进展，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差。从活组织检查可知，目前使用的藻酸盐胶囊组合物远不是最佳的，因为它们可以引发异物宿主免疫应答，最终导致胶囊的纤维化过度生长和随后的胰岛细胞死亡。不幸的是，目前还没有手段来探测随时间推移无创地植入的微胶囊的机械稳定性和生物相容性，从而延迟了包封的胰岛细胞疗法的进一步开发和改进。我们的目标是开发一种双模式磁共振成像（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，我们将分别采用氟（19 F）和磁化传递（MT）MRI，这两种MRI都是临床可用的。混合藻酸盐梯度（MAG）氟胶囊将被开发为一种新的胶囊制剂，无需使用潜在毒性的聚阳离子来实现胶囊渗透性的选择性。我们假设，这些MAG荧光帽具有比传统藻酸盐澄清剂更好的生物相容性。我们将首先开发具有不同机械强度的MAG氟胶囊，并测试它们的稳定性、渗透选择性和胰岛包封性。 体外功能性。然后我们将空胶囊皮下移植。在非糖尿病、免疫活性Balb/c小鼠中进行腹腔注射，并随访180天。MRI研究和免疫组织病理学的结果将用于选择最有前途的制剂，以包封小鼠（同种异体）和猪及人（异种）胰岛，这些胰岛将通过腹腔内和皮下移植。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。将在180天内收集19 F MRI（机械稳定性）和MT MRI（宿主免疫应答）信号，并与免疫组织学和血液（c肽、葡萄糖）参数进行比较。相对胰岛细胞存活率将用生物发光成像（BLI）定量，并与氟和MTR信号相关。通过遵循来自不同来源的同种异体移植和异种移植胰岛的逐步方法，随着对免疫保护，生物相容性和机械稳定性的要求越来越高，我们希望证明双模式MRI在开发具有临床转化潜力的新型封装材料中的有用性。

 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.