Soluble Antigen Arrays utilize molecular and physical features to suppress Experimental Autoimmune Encephalomyelitis

Abstract

Blockade of immune cell adhesion during antigen recognition may suppress the inflammatory immune response in autoimmune diseases. Employing a novel N-oxime chemistry, Soluble Antigen Arrays (SAgAs) were synthesized to simultaneously display intracellular cell-adhesion molecule-1 (ICAM-1) inhibitor and antigen. Hyaluronic acid (HA) was used as a backbone and two peptides were grafted, an ICAM-1 inhibitor (LABL) derived from αL-integrin and an encephalitogenic epitope of proteolipid protein (PLP). Mice with experimental autoimmune encephalomyelitis (EAE) that received subcutaneous (s.c.) injections of SAgAs displaying both peptides showed significantly lower clinical disease scores and incidence, as well as better body weight maintenance than those treated with HA polymer alone. Multivalent presentation of cell-adhesion inhibitor (LABL) alone or antigen (PLP) alone was also evaluated. Treatment with hyaluronic acid grafted with only PLP antigen or only LABL peptide did not provide significant disease suppression and, in the case of LABL, actually exacerbated the disease. When hyaluronic acid was replaced with a PLGA nanoparticle displaying grafted LABL and PLP (NP-ArrayLABL-PLP), an analogous treatment strategy with the NP-Array¬LABL-PLP did not provide significant EAE suppression. Next, the effect of SAgA molecular weight and cell-adhesion molecule target were evaluated. SAgAs with inhibitors targeting intracellular cell-adhesion molecule-1 (ICAM-1) or its ligand leukocyte-associated function antigen-1 (LFA-1) were equally effective. Also, the disease onset was delayed and severity was significantly reduced when the molecular weight of the SAgA was decreased. Animal imaging suggested that the smaller SAgA drained from the injection site more quickly than the larger SAgA, which may suggest enhanced transit to the regional lymphatics. Analysis of the cytokine production profiles of all treatments demonstrated that reducing SAgA size also provided the largest change in inflammatory cytokine response. SAgA performance, therefore, depended on lymphatic drainage as dictated by size, as well as molecular signaling resulting from co-grafting cell-adhesion inhibitor and antigen. Future research should attempt to correlate SAgA transport with efficacy and explore the effect of grafting different inhibitors or activators of co-stimulation.