Objective: We recently defined that a critical mechanism of IVIG therapy in KD patients is the activation and expansion of natural regulatory T cells (nTreg) that recognize the heavy constant region (Fc) of IgG1. Lack of circulating Fc-specific nTreg in the sub-acute phase of KD strongly correlates with arterial complications. Notably, Fc-specific nTreg are always detectable in circulation in healthy donors, suggesting their importance in maintaining vascular homeostasis. Here we aim at the characterization of the fine specificity of these nTreg by testing the immunogenicity of synthetic peptides (> 97% purity) 15 amino acid long, overlapping 10 amino acids, spanning the whole Fc protein.
Methods: To define the immunodominat Fc sequences for nTreg expansion, T cell lines have been established with pools of two consecutive overlapping peptides been generated from PBMC ex vivo from: 1) healthy donors, 2) sub-acute KD subjects (2 weeks after IVIG), and 3) KD subjects that received IVIG 1-2 years earlier. IL-10 secretion and CD4+ CD25high T cell expansion have been the read-outs in these experiments.
Results: 14 peptides have been defined immunogenic in all the 3 cohorts with several peptides recognized by the large majority of the subject studied, including patients with arterial complication that did not respond to the whole Fc protein. The algorithm prediction of the HLA binding affinity of these nTreg peptide epitopes suggests that these immunodominant regions of the Fc protein are promiscous for HLA binding and very good candidate for future therapeutic use.
Clinical relevance of the findings: Immunodominat Fc peptides are an optimized, low cost alternative to IVIG, potentially capable to overcome the lack of nTreg responses in KD patients that develop arterial complications.