Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is the single biggest infectious killer worldwide, and current antimicrobial treatment strategies are increasingly ineffective due to skyrocketing multi-drug resistance [1]. Host-directed therapies acting on the host-pathogen interface to induce apoptosis of infected cells offer a promising avenue to clear the pathogen and promote adaptive immune responses while limiting the risk of drug resistance [2]. We have provided proof-of-principle for the potential success of this strategy by using small-molecule IAP antagonists to degrade key regulators of host cell apoptosis, cellular inhibitors of apoptosis (cIAP1/cIAP2), promoting TB clearance in vivo [3]. However, the need for systemic administration of these inhibitors increases the risk of unwanted side effects and toxicity in patients.
In its early stages, Mtb is predominantly found in alveolar macrophages, and thus, precise drug delivery is desirable to limit off-target effects [4]. Lipid nanoparticles (LNPs) have revolutionised the targeted delivery of RNA therapeutics. We have developed LNPs that enable improved RNA transfection and preferential targeting of alveolar macrophages in vivo. These LNPs allow for direct RNA delivery to the lung, with luciferase mRNA expression shown 16h post intranasal instillation.
Leveraging this versatile delivery platform, we were able to induce cell death in Mtb-infected primary human macrophages using siRNAs against cIAP1 and 2. Additionally, we raised nanobodies against the major Mtb virulence factor, ESAT-6, which acts by limiting host cell apoptosis. LNP-encapsulated mRNA coding for these nanobodies has great potential to complement our siRNA approach. By combining these approaches we aim to generate a multiplexed RNA therapeutic to further boost apoptosis of infected macrophages and promote pathogen clearance. We currently assess the potential of these LNP-delivered RNA therapeutics in our clinically relevant mouse model of TB infection.