Glucose-responsive mature β cells derived from human embryonic stem cells (SC-β cells) are a potential therapy for patients with type 1 diabetes mellitus (T1DM). However, the need for lifelong immunosuppressive therapy has hampered the introduction of this treatment. In a new study published in Nature Medicine, a team of researchers demonstrate that long-term glycaemic control can be achieved in mice using SC-β cells encapsulated with an alginate derivative, without the need for immunosuppression.

Representative image of immunofluorescence analysis of retrieved implants. Permission obtained from NPG © Vegas, A. J. et al. Nat. Med. doi:10.1038/nm.4030 (2016).

The team encapsulated SC-β cells using one of three formulations: 500 μm SLG20 alginate microcapsules; 1.5 mm SLG20 alginate spheres; and 1.5 mm triazole-thiomorpholine dioxide (TMTD) alginate spheres. Each of the formulations (with three different doses of SC-β cells) were transplanted into streptozotocin-treated C57BL/6J mice and the mice were followed up for 90 days.

Mice transplanted with the 500 μm SLG20 alginate microcapsules had the shortest duration of glycaemic control (15 days), and only the highest dose of SC-β cells was effective. The 1.5 mm SLG20 alginate spheres resulted in normoglycaemia for 20–30 days when either of the two highest doses of SC-β cells were used. However, mice transplanted with the 1.5 mm TMTD alginate spheres maintained normoglycaemia for >70 days, with all three doses of SC-β cells having similar effects.

The immune response to the encapsulation formulations was tested in a separate cohort of mice. The three types of alginate spheres were implanted intraperitoneally, and retrieved after 14 days. Analysis of the cells associated with the outside of the spheres revealed that far fewer macrophages, neutrophils and B cells were associated with the TMTD alginate spheres compared with the SLG20 alginate spheres. In addition, fibrotic deposits were present at much lower levels on the TMTD alginate spheres than on the SLG20 spheres. These findings suggest that the immune response to TMTD alginate spheres is not as strong as that to SLG20 alginate spheres.

Importantly, the researchers were able to show that the TMTD alginate spheres are able to 'shield' the SC-β cells from the host's immune system. Freeze-fracture cryogenic scanning electron microscopy revealed that the spheres have a heterogeneous pore structure of <1–3 μm, which prevents cells or large proteins from entering the sphere. Using intravital imaging of transplanted spheres, the team found that CCR6+ T cells localized to regions containing SC-β cells, but were unable to make contact.

The study mice maintained glycaemic control for the length of the follow-up

The long-term effectiveness of the TMTD alginate spheres was tested in another cohort of streptozotocin-treated C57BL/6J mice. The implants were retrieved after 174 days, before complications of streptozotocin treatment start. The study mice maintained glycaemic control for the length of the follow-up, with blood levels of glucose similar to those seen in wild-type mice. In response to a glucose challenge test, the transplanted mice were able to restore normoglycaemia at a similar rate to wild-type mice. Furthermore, the retrieved implants showed minimal signs of fibrotic overgrowth.

The researchers hope that these findings will help achieve the goal of long-term β-cell replacement therapy for T1DM, with patients becoming insulin independent.