Haploidentical mixed chimerism cures autoimmunity in established type 1 diabetic mice.

Clinical trials are currently testing whether induction of MHC-haploidentical mixed chimerism (Haplo-MC) induces organ transplantation tolerance. Whether Haplo-MC can be used to treat established autoimmune diseases remains unknown. Here, we show that established autoimmunity in euthymic and adult-thymectomized NOD (H-2g7) mice was cured by induction of Haplo-MC under a non-myeloablative anti-thymocyte globulin-based conditioning regimen and infusion of CD4+ T-depleted hematopoietic graft from H-2b/g7 F1 donors that express autoimmune-resistant H-2b or from H-2s/g7 F1 donors that express autoimmune susceptible H-2s. The cure was associated with enhanced thymic negative selection, increased thymic Treg (tTreg) production, and anergy or exhaustion of residual host-type autoreactive T cells in the periphery. The peripheral tolerance was accompanied with expansion of donor- and host-type CD62L1Helios+ tTreg as well as host-type Helios-Nrp1+ peripheral Treg (pTreg) and PD-L1hi plasmacytoid DCs (pDC). Depletion of donor- or host-type Treg cells led to reduction of host-type PD-L1hi pDCs and recurrence of autoimmunity; whereas PD-L1 deficiency in host-type DCs led to reduction of host-type pDCs and Helios-Nrp1+ pTreg cells. Thus, induction of Haplo-MC re-established both central and peripheral tolerance through mechanisms that depend on allo-MHC+ donor-type DC, PD-L1hi host-type DCs, and the generation and persistence of donor and host-type tTreg and pTreg cells.