Research Article
Rational design of a hydrolysis-resistant mycobacterial phosphoglycolipid antigen presented by CD1c to T cells

https://doi.org/10.1016/j.jbc.2021.101197Get rights and content
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Whereas proteolytic cleavage is crucial for peptide presentation by classical major histocompatibility complex (MHC) proteins to T cells, glycolipids presented by CD1 molecules are typically presented in an unmodified form. However, the mycobacterial lipid antigen mannosyl-β1-phosphomycoketide (MPM) may be processed through hydrolysis in antigen presenting cells, forming mannose and phosphomycoketide (PM). To further test the hypothesis that some lipid antigens are processed, and to generate antigens that lead to defined epitopes for future tuberculosis vaccines or diagnostic tests, we aimed to create hydrolysis-resistant MPM variants that retain their antigenicity. Here, we designed and tested three different, versatile synthetic strategies to chemically stabilize MPM analogs. Crystallographic studies of CD1c complexes with these three new MPM analogs showed anchoring of the lipid tail and phosphate group that is highly comparable to nature-identical MPM, with considerable conformational flexibility for the mannose head group. MPM-3, a difluoromethylene-modified version of MPM that is resistant to hydrolysis, showed altered recognition by cells, but not by CD1c proteins, supporting the cellular antigen processing hypothesis. Furthermore, the synthetic analogs elicited T cell responses that were cross-reactive with nature-identical MPM, fulfilling important requirements for future clinical use.

Keywords

T-cell receptor (TCR)
antigen presentation
glycolipid
lipid synthesis
protein crystallization
CD1c

Abbreviations

MHC
major histocompatibility complex
MPM
mannosyl-β1-phosphomycoketide
PM
phosphomycoketide
Pks12
polyketide synthase 12
MDDC
monocyte-derived dendritic cell
TCR
T cell receptor
HD
healthy donor
GMM
glucose monomycolate

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These authors contributed equally to this work.

These authors jointly supervised this work.