Modeling diabetes in minipigs for more accurate testing of potential cell therapies

Since the discovery of human iPS cells, a principal goal for researchers worldwide has been to use them for various medical applications, including cell therapy. Among different human diseases, type 1 diabetes mellitus (T1DM) has been a top priority for cell therapy development.

While most basic research on human diseases utilizes rodents, such as mice and rats, differences between those species and humans, including anatomy, body size, and blood volume, make it challenging to translate findings for use in the clinic.

For a recent study published in Cell Transplantation, a team of researchers created a minipig type 1 diabetes model for testing new therapies based on iPS cell-derived pancreatic islets.

The team includes scientists from CiRA, Takeda Pharmaceutical Co. Ltd., Orizuru Therapeutics, Inc. and Axcelead Drug Discovery Partners, Inc., led by Junior Associate Professor Taro Toyoda (Department of Life Science Frontiers, CiRA) and Midori Yamasaki (R&D Research, Global Advanced Platform, Takeda Pharmaceutical Co., Ltd.).

As part of T-CiRA, or the Takeda-CiRA Joint Program for iPS Cell Applications, Toyoda has a long history of developing a viable cell therapy for T1DM using iPS cells. Through such efforts, his research group has developed a 7-stage differentiation process to generate iPS cell-derived pancreatic islet cells (iPICs) and, in this study, they created a minipig T1DM model for pre-clinical testing of iPIC transplantations.

First, before inducing the T1DM model, the thymus and spleen were surgically removed to initiate the immunosuppression required to test cell therapy using human cells. Next, streptozotocin (STZ) was administered to induce T1DM by specifically destroying endogenous pancreatic β-cells, responsible for insulin production and secretion to maintain blood glucose levels.

Blood glucose and C-peptide levels were monitored to confirm the onset of diabetic conditions. Higher fasting blood glucose and lower C-peptide levels after STZ administration suggested that T1DM was successfully and stably induced.

A week before iPIC transplantation, immunosuppressive drugs (i.e., cyclosporine, mycophenolate mofetil, and prednisolone) were also administered to minipigs, with effective concentrations of the drugs and their active metabolites measured to ensure proper immunosuppression. Then, iPICs were transplanted to different areas, including the pre-peritoneal and subcutaneous space, with different implant compositions.

Human C-peptide levels in the plasma were monitored as a measure of iPIC function. In addition, histological analyses were performed to compare implantation sites and/or compositions. Whereas engrafted cells tended to be more common when cells were transplanted into the pre-peritoneal space, other sites typically showed massive immune cell infiltration and fibrosis.

Further analyses showed that engrafted iPICs were only invaded slightly by CD3+ T cells and macrophages, with islet-like structures and expressing appropriate cell-type-specific markers.

Next, the research team implanted the same number of iPICs into the subcutaneous or pre-peritoneal space of different animals. They found that C-peptide levels were detected earlier and higher when iPICs were transplanted into pre-peritoneal space than the subcutaneous space, highlighting it as an ideal transplantation site.

From these results, the joint research team can further expand upon this work and begin the comprehensive testing of iPICs for their therapeutic effects in a T1DM model with more similarities to human physiology.

With such advantages, the researchers hope they can more accurately assess iPIC-based therapies and implant compositions to ensure their safety and therapeutic potential before moving toward clinical trials in human patients.