A synthetic delivery vector for mucosal vaccination

The success of mRNA-based vaccines during the Covid-19 pandemic has highlighted the value of this new platform for vaccine development against infectious disease. However, the CD8+ T cell response remains modest with mRNA vaccines, and these do not induce mucosal immunity, which would be needed to prevent viral spread in the healthy population. To address this drawback, we developed a dendritic cell targeting mucosal vaccination vector, the homopentameric STxB. Here, we describe the highly efficient chemical synthesis of the protein, and its in vitro folding. This straightforward preparation led to a synthetic delivery tool whose biophysical and intracellular trafficking characteristics were largely indistinguishable from recombinant STxB. The chemical approach allowed for the generation of new variants with bioorthogonal handles. Selected variants were chemically coupled to several types of antigens derived from the mucosal viruses SARS-CoV-2 and type 16 human papillomavirus. Upon intranasal administration in mice, mucosal immunity, including resident memory CD8+ T cells and IgA antibodies was induced against these antigens. Our study thereby identifies a novel synthetic antigen delivery tool for mucosal vaccination with an unmatched potential to respond to an urgent medical need.

Engineered Synthetic STxB for Enhanced Cytosolic Delivery

Many molecular targets for cancer therapy are located in the cytosol. Therapeutic macromolecules are generally not able to spontaneously translocate across membranes to reach these cytosolic targets. Therefore a strong need exists for tools that enhance cytosolic delivery. Shiga toxin B-subunit (STxB) is used to deliver therapeutic principles to disease-relevant cells that express its receptor, the glycolipid Gb3. Based on its naturally existing membrane translocation capacity, STxB delivers antigens to the cytosol of Gb3-positive dendritic cells, leading to the induction of CD8⁺ T cells. Here, we have explored the possibility of further increasing the membrane translocation of STxB to enable other therapeutic applications. For this, our capacity to synthesize STxB chemically was exploited to introduce unnatural amino acids at different positions of the protein. These were then functionalized with hydrophobic entities to locally destabilize endosomal membranes. Intracellular trafficking of these functionalized STxB was measured by confocal microscopy and their cytosolic arrival with a recently developed highly robust, sensitive, and quantitative translocation assay. From different types of hydrophobic moieties that were linked to STxB, the most efficient configuration was determined. STxB translocation was increased by a factor of 2.5, paving the path for new biomedical opportunities.

A67 RISK FACTORS ASSOCIATED WITH CRITICAL CARE AFTER INPATIENT GASTROINTESTINAL ENDOSCOPY: A 5-YEAR TERTIARY HOSPITAL STUDY

Background

A subset of hospitalized patients will require critical care after their gastrointestinal endoscopy (GIE) and predicting which patients are at high risk of requiring critical care remains an important challenge.

Purpose

To identify protective and aggravating clinical risk factors associated with critical care involvement within 7 days of inpatient GIE in adults and to develop a tool that could assist in risk-stratifying patients at high risk of requiring critical care post-endoscopy.

Method

This was a single-centre retrospective case-control study of adult patients who underwent inpatient GIE while admitted to ward-level care at Toronto General Hospital from years 2015 to 2019. Cases were defined by inpatients who required critical care response team and/or critical care admission within 7 days of GIE, compared to control patients who did not require critical care throughout admission. Chart review and linked secondary sources were used with defined inclusion and exclusion criteria. Both univariate and multivariate analyses were performed comparing patient baseline, clinical history (including cardiovascular, respiratory, other co-morbidities) and endoscopy characteristics.

Result(s)

We identified a total of 275 patients with 302 endoscopies as cases and 2069 patient controls who satisfied inclusion criteria. Critical care involvement was most commonly due to cardiovascular-related complications (n=175, 58%) followed by respiratory complications (n=117, 39%). Amongst cases, death occurred in 9 (3%), 25 (9%) and 67 (22%) within 72 hours, 7 days and 30 days respectively post endoscopy. The strongest associations with critical care involvement within 7 days after GIE included a history of discharge from critical care (OR 2.29 CI 1.70-3.04) and/or recent mechanical ventilatory support (OR 2.27 CI 1.30-3.91) in the 30 days prior to endoscopy, having several co-morbidities involving major organ systems (elevated troponin OR 3.20 CI 2.26-4.52, cirrhosis OR 2.5 CI 1.80-3.46, renal dysfunction 2.09 CI 1.57-2.78) and patients admitted under surgical (OR 3.82 CI 2.54-5.71) or transplant services (OR 4.63 CI 2.94-7.26). The majority of adverse events among cases were not found to be complications directly related to GIE (64% unlikely, 20% possible, 9% probable, 7% definite). Patients with a history of pulmonary hypertension (OR 5.68 CI 0.53-60.70) and ASA score III/IV (OR 3.28 CI 1.01-10.73) had the highest odds of probable or definite endoscopy-related adverse events.

Conclusion(s)

This study is the largest to date to examine risk factors associated with critical care requirements post GIE in the tertiary care inpatient setting. The risk factors we have identified can be used to create a tool to determine which inpatients may benefit from anesthesia consultation and support during their endoscopic procedure.

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Disclosure of Interest

None Declared

From a Cone Snail Toxin to a Competitive MC4R Antagonist

The melanocortin 4 receptor (MC4R) plays a role in energy homeostasis and represents a target for treating energy balance disorders. For decades, synthetic ligands have been derived from MC4R endogenous agonists and antagonists, such as setmelanotide used to treat rare forms of genetic obesity. Recently, animal venoms have demonstrated their capacity to provide melanocortin ligands with toxins from a scorpion and a spider. Here, we described a cone snail toxin, N-CTX-Ltg1a, with a nanomolar affinity for hMC4R but unrelated to any known toxins or melanocortin ligands. We then derived from the conotoxin the linear peptide HT1-0, a competitive antagonist of G_s, G₁₅, and β-arrestin2 pathways with a low nanomolar affinity for hMC4R. Similar to endogenous ligands, HT1-0 needs hydrophobic and basic residues to bind hMC4R. Altogether, it represents the first venom-derived peptide of high affinity on MC4R and paves the way for the development of new MC4R antagonists.