Microvascular phenomena during pancreatic islet graft rejection

Area of Science:

• Transplantation Biology
• Immunology
• Vascular Biology

Background:

• Free islet transplantation offers a potential cure for diabetes but faces challenges in achieving insulin independence.
• Unlike whole organ grafts, free islet grafts require revascularization for survival, a process vulnerable to rejection.
• Understanding the microvascular dynamics during islet graft revascularization and rejection is crucial for improving outcomes.

Purpose of the Study:

• To visualize and analyze the in vivo process of revascularization in free islet xenografts.
• To identify microvascular phenomena associated with graft rejection.
• To evaluate the efficacy of a specific immunosuppressive agent in mitigating microvascular rejection.

Main Methods:

• Rat islet xenografts were prepared and transplanted into hamster dorsal skinfold chambers.
• Intravital fluorescence microscopy was used to analyze graft microvasculature at 6, 10, and 14 days post-transplantation.
• Microvascular parameters including network size, capillary density, red blood cell velocity, permeability, and white blood cell interactions were assessed.

Main Results:

• Xenografts initially revascularized similarly to syngeneic grafts within the first 6 days.
• By day 10, a significant reduction in microvascular network size and functional capillary density was observed.
• Microvascular rejection signs included increased permeability, edema, capillary widening, and white blood cell accumulation and interaction.

Conclusions:

• Free islet xenografts undergo a complex revascularization process that is susceptible to microvascular rejection.
• Early signs of rejection involve detrimental changes in microvascular function and increased inflammatory cell activity.
• (+/-)-15-deoxyspergualin treatment showed limited success in preventing these microvascular rejection phenomena.