The Penicillins are a group of β-lactam antibiotics that provide a first line of defence against microbial infections. However, 11.5% of individuals prescribed penicillin develop allergic responses to the drug, which if left unchecked can have serious implications on patient health. Traditionally, these allergies were considered to be predominantly IgE mediated, although new evidence points towards the involvement of T-cells. The ability of penicillins to haptenate serum proteins (through covalent binding) can lead to the generation of neoantigens, thereby triggering an immune response. These haptenated neoantigens, following processing and presentation by antigen presenting cells, may be displayed in the form of peptides by the human leukocyte antigen (HLA) molecules for recognition by T-cells. Activation of these drug-specific T-cells can mediate a range of pathologies, ranging from mild cutaneous reactions to more severe clinical conditions such as drug-induced liver injury.
We have recruited 11 penicillin-induced hypersensitivity patients, with only 40% having elevated serum IgE against the causative drug. This suggests that other factors/cellular populations (e.g. T-cells) may contribute to adverse reactions observed in these individuals. Here, we describe that penicillin-responsive T-cells isolated from a hypersensitive patient are activated upon exposure to penicillin and restricted to the common Caucasian HLA-A*02:01 allomorph. We hypothesised that a HLA-A*02:01-restricted penicillin-haptenated neoepitope was presented to these drug-specific T-cells and this contributed to the adverse drug reaction.
Applying an immunopurification LC-MS/MS workflow, we analysed the immunopeptidome of HLA-A*02:01 from patient-derived B-LCLs treated with or without penicillin. In combination with a robust set of criteria for the identification of haptenated peptides, based on haptenated human serum albumin, we identified three HLA-A*02:01 presented penicillin-haptenated peptides.
Together, these results will allow us to utilise the fragmentation patterns of penicillin-modified peptides to conduct further, more targeted MS analysis that will provide novel molecular insights into this common drug reaction.