Goal: To determine the mechanisms by which IgM restores immune homeostasis in new-onset diabetic NOD mice.

Methods: 1) 5wks old non-obese diabetic (NOD) mice received mouse or human IgM (mIgM, hIgM, 50ugs/wk) or saline, beginning at 5wks until 18wks of age. 2) New-onset diabetic mice were treated with 2 doses (100ug on Day1 and 4) of prediabetic NOD or naive BL6 IgM. Blood glucose (BG) was monitored serially. 3) 5wks-old BL6 and NOD mice, BL6 and NOD VH125 mice, and humanized BLT mice received 50ug IgM (5X) followed by spleen and bone-marrow cell harvest. VH125 mice have a heavy chain specific for human insulin knocked into the endogenous IgM locus, that combines with endogenous light chains to produce insulin-reactive B lymphocytes. Humanized BLT mice are NOD/SCIDs cotransplanted with human liver/thymus tissues and autologous CD34+ hematopoietic stem cells. Flow cytometry and CyTOF were performed.

Results: Both mIgM and hIgM prevented the onset of diabetes compared to saline injected controls wherein 80% of mice became diabetic by 18wks of age (p<0.0001). More importantly, IgM reversed hyperglycemia in new-onset diabetic mice (BG220-350mg/dL) and maintained normoglycemia (BG<200mg/dL) in 63% of mice post IgM therapy (n=11). While serum IgM levels in NOD mice were similar to wild-type BL6 mice, IgM derived from prediabetic NOD donors did not reverse diabetes. IgM expanded myeloid derived suppressor cell and peripheral regulatory T cell (Treg) populations in NOD mice. Thymic Tregs were also expanded in a regulatory B cell-dependent manner. In humanized BLT mice, hIgM expanded the Helios+Foxp3+Treg population. IgM diminished autoreactivity in NOD mice by reducing marginal zone B cells, a subset associated with perpetuating autoimmunity (p<0.05). Significantly, IgM inhibited insulin autoantibody production in NODs (p<0.0001), eliminated autoreactive insulin-binding B cells in NODVH125 mice (p<0.0001), and normalized B cell homeostatic defects.

Conclusions: IgM reverses diabetes in the NOD mouse by inducing protective regulatory immune cells, restoring immune homeostasis and diminishing autoreactivity. The potential clinical relevance of IgM therapy is confirmed in the humanized BLT mouse model where hIgM induces the expansion of Tregs. This beneficial effect may be translatable to new onset diabetic patients and islet graft recipients.

CITATION INFORMATION: Brayman K., Chhabra P., Wilson C., Marshall A., Moore D. Prevention and Reversal of Diabetes through Restoration of B and T Cell Regulation and Immune Homeostasis Am J Transplant. 2017;17 (suppl 3).

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