Sulfavant A as the first synthetic TREM2 ligand discloses a homeostatic response of dendritic cells after receptor engagement

Abstract

Objective The immune response arises from a fine balance of mechanisms that provide for surveillance, tolerance, and elimination of dangers. Sulfavant A (SULF A) is a sulfolipid with a promising adjuvant activity. Here we studied the mechanism of action of SULF A and addressed the identification of its molecular target in human dendritic cells (hDCs). Methods Adjuvant effect and immunological response to SULF A were assessed on DCs derived from human donors. In addition to testing various reporter cells, target identification and downstream signalling was supported by a reverse pharmacology approach based on antibody blocking and gene silencing, crosstalk with TLR pathways, use of human allogeneic mixed lymphocyte reaction. Results SULF A binds to the Triggering Receptor Expressed on Myeloid cells-2 (TREM2) and initiates an unconventional maturation of hDCs leading to enhanced migration activity and up-regulation of MHC and co-stimulatory molecules without release of conventional cytokines. This response involves the SYK-NFAT axis and is compromised by blockade or gene silencing of TREM2. Activation by SULF A preserved the DC functions to excite the allogeneic T cell response, and increased interleukin-10 release after lipopolysaccharide stimulation. Conclusion SULF A is the first synthetic small molecule that binds to TREM2. The receptor engagement drives differentiation of an unprecedented DC phenotype (homeDCs) that contributes to immune homeostasis without compromising lymphocyte activation and immunogenic response. This mechanism fully supports the adjuvant and immunoregulatory activity of SULF A. We also propose that the biological properties of SULF A can be of interest in various physiopathological mechanisms and therapies involving TREM2.

The immunoregulatory effect of the TREM2-agonist Sulfavant A in human allogeneic mixed lymphocyte reaction

“…One of the best-known examples of these mechanisms is the interaction of the costimulatory molecule CD28 and the inhibitory counterpart CTLA-4 along with their ligands CD80 and CD86 (25) (26). SULF A is a small organic molecule suitable for pharmaceutical applications due to the property of triggering an unconventional maturation of DCs and initiating an effective immune response in vivo (11) (14). In this study we showed that SULF A can modulate DC-T cell synapse in the context of the allogeneic MLR.…”

“…In this study we showed that SULF A can modulate DC-T cell synapse in the context of the allogeneic MLR. According to the previous reports (14), addition of SULF A to MLR determined DC maturation after 48h with increased expression of the costimulatory molecules ICOSL and OX40L in conjunction with down-regulation of cytokine IL-12 and up-regulation of IL-10. This condition led to additional T cell proliferation and, although T CD4+ and T CD8+ subsets were both promoted, it was skewed towards T CD4+ proliferation.…”

“…MoDCs (stimulators) and naïve CD3+ T lymphocytes (responders) deriving from six different donors were cultured in a ratio of 1:10 (10.000 stimulators:100.000 responders) in round-bottomed 96-well plates with RPMI medium completed with 10% human AB serum in the presence of 10 μg/mL SULF A in PBS (MLR+SULF A). The concentration of SULF A used was established on the basis of previous dose-response experiments ( 10 ) ( 14 ). Untreated co-cultures were used as control (MLR).…”

“…The molecule has been proposed as a vaccine adjuvant (EU Patent n. EP3007725B1) and despite the divergence from the inflammatory mechanisms of conventional adjuvants, retains the ability to activate immune protection in an experimental model of a prophylactic vaccine against melanoma in B16F10 mice ( 11 ). Very recently, we showed that SULF A can bind the triggering receptor expressed on myeloid cells (TREM2) which helps explain the unusual mechanism of action of the sulfolipid and the ability to trigger in vitro the differentiation of a homeostasis-inducing DC subpopulation that we named homeDC ( 14 ).…”

The therapeutic potential of TREM2 in cancer

“…Triggering receptor expressed on myeloid cells 2 (TREM2) is a transmembrane receptor of the immunoglobulin superfamily that binds an array of ligands including bacteria and polyanionic molecules (1), DNA (2), lipoproteins (3), phospholipids (4) and sulfoglicolipids such as Sulfavant A (5). TREM2 itself does not contain intrinsic signaling capabilities; therefore, it associates with the adaptor proteins DNAX activation protein (DAP) 12 and DAP10; which, upon TREM2-ligand interaction are phosphorylated and propagate signals within the cell (6).…”