Introduction: The subcutaneous site is a promising transplantation site because it is possible to monitor and remove the graft to ensure safety for the clinical application of islet-like cells derived from ES/iPS cells. It is required to induce a vascular bed in advance, but the optimal conditions for this are unclear. We evaluated the immunological environment of the transplantation site after prevascularization.

Method: 500 islets of C57BL/6 mice were transplanted into the prevascularized subcutaneous site of C57BL/6 mice by implanting agarose rods with bFGF. The agarose rod implantation period was set at 7 days and 14 days, and the blood glucose levels, cell infiltration, and cytokines before transplantation were evaluated. We also evaluated the transplant results when anti-TNF antibody was used.

Results: The 14-day group showed early glycemic normalization (At 30 days post-transplantation: 17% in the 7-day group, 83% in the 14-day group; At 40 days: 67% in the 7-day group, 83% in the 14-day group). The 14-day group showed numerous macrophage accumulation at the transplant site (7-day group: 7.8%; 14-day group: 24%; p = [Editor1] 0.03). The ratio of macrophage 1 to macrophage 2 was higher in the 7-day group (2.12 in the 7-day group; 0.10 in the 14-day group; p = 0.001), and IL-6 and TNF were locally higher at the transplant site (273 pg/mL in the 7-day group; 48.4 pg/mL in the 14-day group; p = 0.04, 40 pg/mL in the 7-day group for TNF; 14 pg/mL in the 14-day group for IL-6). The use of anti-TNF antibody in the 7-day group resulted in early glycemic normalization (glycemic normalization rate at 30 days after transplantation: 83%).

Conclusion: In the early stage of the prevascularization before subcutaneous transplantation, the accumulation of macrophage 1 prevented early engraftment due to the production of inflammatory cytokines. For clinical application, it is necessary to explore the optimal setting of the transplantation environment after prevascularization.