Biotin
Lowering the total level of Immunoglobulin G (IgG) in circulation is a promising general treatment option for many autoimmune diseases driven by pathogenic autoantibodies. The half-life of IgG in circulation is unusually long as a consequence of its interaction with the neonatal Fc receptor (FcRn), which protects it from lysosomal degradation by cells in contact with blood. Blocking the IgG/FcRn interaction prevents FcRn-mediated rescue, which may lead to increased catabolism and a lowering of the total IgG level. Here, we find that an engineered alternative scaffold protein, an affibody molecule, interacting specifically with FcRn, is able to block the IgG/FcRn interaction in vitro. The affibody molecule (ZFcRn) was expressed alone or as a fusion to an albumin binding domain (ABD), to extend its half-life in circulation, in both cases with retained affinity and blocking potential. Repeated i.v. injections in mice of ZFcRn and ZFcRn-ABD were found to result in an up to 40% reduction of the IgG serum-level after 5 days. Potential applications of ZFcRn as a general treatment modality for autoimmune diseases are discussed.
Cell therapy with autologous donor-specific regulatory T cells (Tregs) is a promising strategy to minimize immunosuppression in transplant recipients. Chimeric antigen receptor (CAR) technology has recently been used successfully to generate donor-specific Tregs and overcome the limitations of enrichment protocols based on repetitive stimulations with alloantigens. However, the ability of CAR-Treg therapy to control alloreactivity in immunocompetent recipients is unknown. We first analyzed the effect of donor-specific CAR Tregs on alloreactivity in naive, immunocompetent mice receiving skin allografts. Tregs expressing an irrelevant or anti-HLA-A2-specific CAR were administered to Bl/6 mice at the time of transplanting an HLA-A2+ Bl/6 skin graft. Donor-specific CAR-Tregs, but not irrelevant-CAR Tregs, significantly delayed skin rejection and diminished donor-specific antibodies (DSAs) and frequencies of DSA-secreting B cells. Donor-specific CAR-Treg-treated mice also had a weaker recall DSA response, but normal responses to an irrelevant antigen, demonstrating antigen-specific suppression. When donor-specific CAR Tregs were tested in HLA-A2-sensitized mice, they were unable to delay allograft rejection or diminish DSAs. The finding that donor-specific CAR-Tregs restrain de novo but not memory alloreactivity has important implications for their use as an adoptive cell therapy in transplantation.
