Investigating the MHC class-II processing and presentation “network” via high-throughput small molecule screening.

Abstract

Abstract CD4+ T cells, activated by peptides presented in complex with MHCII, are key players in adaptive immune responses against most pathogens and cancers. Classically, MHCII presentation involves uptake of exogenous antigen, digestion in the endocytic compartment, and loading onto nascent MHCII in the late endosome. However, recent studies show viral pathogens do not exclusively adhere to the classical model. Two notable examples of non-classical MHC-II presentation are: 1) “Recycling” presentation (internalized MHCII molecules capture proteolytically unstable epitopes in the early endosome) and 2) endogenous presentation (the source of antigen is nascent viral protein). We have constructed a model in which these three MHCII processing and presentation pathways are mechanistically distinct and largely non-overlapping. To test this model, we have employed high throughput screening (HTS) using a 2240 member “known target” small molecule library with the goal of differentiating which cellular components are involved in the generation of influenza epitopes produced via the classical, recycling, and endogenous pathways. The preliminary HTS data strongly support our hypothesis, clearly identifying distinct pathways that are exclusively involved with either classical or endogenous antigen presentation. Among the 21 validated hit compounds, the screen identified 3 inhibitors of the proteasome (previously shown to figure prominently in endogenous processing). The remaining 18 compounds target pathways not previously known to contribute to MHCII antigen presentation. Compounds of particular interest are being investigated in vivo to assess their ability to bias the TCD4+ response in the context of an influenza infection.