Toward the Discovery of Vaccine Adjuvants: Coupling In Silico Screening and In Vitro Analysis of Antagonist Binding to Human and Mouse CCR4 Receptors

Abstract

BackgroundAdjuvants enhance or modify an immune response that is made to an antigen. An antagonist of the chemokine CCR4 receptor can display adjuvant-like properties by diminishing the ability of CD4+CD25+ regulatory T cells (Tregs) to down-regulate immune responses.MethodologyHere, we have used protein modelling to create a plausible chemokine receptor model with the aim of using virtual screening to identify potential small molecule chemokine antagonists. A combination of homology modelling and molecular docking was used to create a model of the CCR4 receptor in order to investigate potential lead compounds that display antagonistic properties. Three-dimensional structure-based virtual screening of the CCR4 receptor identified 116 small molecules that were calculated to have a high affinity for the receptor; these were tested experimentally for CCR4 antagonism. Fifteen of these small molecules were shown to inhibit specifically CCR4-mediated cell migration, including that of CCR4+ Tregs.SignificanceOur CCR4 antagonists act as adjuvants augmenting human T cell proliferation in an in vitro immune response model and compound SP50 increases T cell and antibody responses in vivo when combined with vaccine antigens of Mycobacterium tuberculosis and Plasmodium yoelii in mice.

A CCR4 antagonist combined with vaccines induces antigen-specific CD8+ T cells and tumor immunity against self antigens

“…This CCR4 antagonist was previously shown to block in vitro the migration of human Tregs mediated by CCL22 or CCL17 and to increase humoral and cellular responses against various bacterial and viral Ags. 14,15 This study confirms and extends these results by showing the ability of this CCR4 antagonist to break tolerance in models, where Tregs play a main role in the control of anti-self CD8 ϩ T cells. Compared with conventional approaches to block Tregs (anti-CD25 mAb, cyclophosphamide), we show that this CCR4 antagonist appears to be a competitive strategy.…”

“…In vitro experiments in humans showed that these CCR4 antagonists inhibit the recruitment of Tregs mediated by CCL22 and CCL17 and, when administered in combination with vaccines, increased humoral responses against foreign Ags. 14, 15 The present study was designed to address whether a CCR4 antagonist (a small chemical molecule with a molecular weight of 565.93; contain six 5-or 6-membered aromatic rings; and 3 nitrogen atoms) previously described 14 was efficient to elicit CD8 ϩ T cells directed against various self Ags. Tregs are known to exert a stringent peripheral control on these anti-self CD8 ϩ T cells.…”

“…16 Mice were injected with 1.5 g of CCR4 antagonist, a dose that has been optimized in previous experiments. 14,15 Cyclophosphamide was used at 200 mg/kg (4 mg/mouse) as previously described. 23 IFA was emulsified with the vaccine (v/v).…”

Src Homology 3-interacting Domain of Rv1917c of Mycobacterium tuberculosis Induces Selective Maturation of Human Dendritic Cells by Regulating PI3K-MAPK-NF-κB Signaling and Drives Th2 Immune Responses

“…Importantly, we would like to speculate that our analysis would render the designing and development of peptidomimics that specifically inhibit interaction between Rv1917c and pattern recognition receptors as well as host signaling proteins of DCs or macrophages. Because expansion of regulatory T cells and Th2 cells is a hallmark of chronic tuberculosis infection, the molecular adjuvants such as CCR4 antagonists that block these two suppressive populations might benefit tuberculosis vaccination strategies (79,80). These insights, in our opinion, will broaden the understanding of the tuberculosis disease pathogenesis and might pave a way for their inclusion in drug development efforts against tuberculosis.…”

Characterizing the interaction of CCL17 with CCR4: Elucidating requirements to elicit cellular function

“…To understand the role of chemokine-mediated function in the immune response, attention has focused on receptor biology more so than that of the individual chemokines [2][3][4][5][6][7] . One approach to study CCR4 biology has been to employ knock-out (KO) mice which, while informative, fail to adequately address the different functional consequences of CCL17 and CCL22 engagement with CCR4.…”