Research

The HIV-1 envelope spike (Env) bears a cluster of oligomannose-type glycans that is a target for broadly neutralizing antibodies (bnAbs). However, while nAbs to this cluster, dubbed the high-mannose patch (HMP), are known to develop in at least some HIV-infected individuals, past attempts to elicit similar antibodies by immunization have been largely unsuccessful. Most previous approaches have involved presenting clusters of natural or synthetic high-mannose glycans on the surface of carrier proteins. The difficulty in eliciting high-mannose-targeting nAbs by immunization is believed to relate, at least in part, to the ‘self’ nature of the targeted glycans. The approach that we are pursuing is based on the scientific premise that antigenic mimicry of mammalian host structures can stimulate cross-reactive antibodies if such mimics are presented in the proper ‘foreign’ milieu. Our overarching hypothesis is that, upon immunization, an antigenic mimic of mammalian oligomannose will more readily elicit antibodies that bind the HMP than native or synthetic oligomannose. In our progress report, we show that a CRM197-conjugate of our lead oligomannose mimetic is bound with high avidity by various HMP-specific bnAbs as well as their germline precursors. Furthermore, human antibody transgenic mice immunized with this neoglycoconjugate yield antibodies that bind recombinant HIV-1 SOSIP trimers, albeit only when the conjugate is formulated in the TLR4-stimulating Th1-adjuvant GLA-SE. We expect our findings to help sharpen our strategy and critically inform the pursuit of future preclinical studies. Results from this research could inform other HIV vaccine design strategies also.

C-type lectin-like receptor 2 (CLEC-2) is involved in two important processes of platelet biology: separation of blood and lymphatic vessels and thrombosis. Besides being considered a potential drug target in settings of wound healing, inflammation, infection, and cancer, CLEC-2 is gaining interest as a therapeutic target for a variety of thrombo-inflammatory disorders with treatment also predicted to cause minimal disruption to hemostasis. While the last few years have seen major advances in our understanding of CLEC-2 ligand interactions and the resulting signaling cascades, the mechanisms by which the different biological functions are controlled are still insufficiently understood. Elucidation of these pathways is bottlenecked by a lack of chemical tools to investigate and visualize the effects of receptor multimerization on signaling and ligand fate. This project aims at establishing a platelet-specific liposomal platform for mechanistic and targeted-delivery studies. Liposomal nanoparticles are decorated with natural as well as newly developed high-affinity ligands of CLEC-2 prepared by chemical synthesis. The opportunity to control ligand affinity and density on the nanoparticles will enable detailed studies into CLEC-2 biology and thus exploration of CLEC-2 as a therapeutic target for small-molecule inhibitors and for delivery devices for nucleic acids and other drugs.

Wider research context: The demand of current societies, with ever-increasing populations, for food, energy, and materials grows dramatically, resulting in a clear need for increased crop productivity. Crop improvement for food, fiber, and biofuels production will greatly benefit from a more detailed understanding of plant immune function. Plants sense and respond to pathogen attacks by using an arm of the plant immune system that relies on the detection of exogeneous Microbe-Associated Molecular Patterns (MAMPs) and endogenous Danger-Associated Molecular Patterns (DAMPs) by Pattern-Recognition-Receptors (PRRs), such as Receptor-Like-Kinases (RLKs). Despite the large number of RLKs in plants and the dominating presence of glycans in the cell walls of plants, bacteria, and fungi, only a handful of glycans were found to elicit plant immune responses, and only for two of those the cognate receptors have been described. We recently identified two novel glycan-RLK pairs by interrogating glycan arrays with heterologously expressed extracellular RLK domains and further confirmed the immune activities of these glycans in vivo. Objectives: We aim at establishing the plant polysaccharides rhamnogalacturonan-I (RG-I) and galactomannan (GM) as novel DAMPs for activation of plant innate immunity as well as determining the exact molecular patterns recognized by their cognate RLKs. Approach: Chemical synthesis of collections of RG-I and GM oligosaccharides will enable the glycan array-based characterization of recently discovered RG-I- and GM-binding RLKs. After hit validation in further biophysical assays, the identified oligosaccharides will be investigated in vivo towards their potential to stimulate ROS-production, MAP-kinase activation, and defense genes induction as hallmarks of immune activation. Innovation: The unique approach to combine synthetic carbohydrate chemistry and glycan arrays with plant immunity research will enable the elucidation of refined molecular structures with maximum capacity to elicit immune responses. The generated knowledge will facilitate the development of preparations of glycan molecules to boost the plant immune system, avoiding the need for using traditional pesticides.