Development and implementation of a direct detection, quantitation and validation system for class I MHC self-peptide epitopes

Gene and protein expression studies demonstrate that viral-infected and malignant cells undergo a complex series of transcriptional and translational changes. As class I MHC molecules reflect the proteome (and changes therein) by presenting intracellular peptide epitopes, the development of a direct discovery and validation technology for the identification of these epitopes is needed. We developed our technology using HIV-1-infected cells as a model. A combination of hollow fiber class I HLA protein production and mass spectrometric epitope analysis indicated a 3-fold increase in the host-peptide VLMTEDIKL_720-728, [eIF4G₍₇₂₀₎] presented by the HLA-A^*0201 of HIV-1-infected cells. This peptide is derived from the host-protein translation of eukaryotic initiation factor 4-gamma (eIF4G) that plays a pivotal role in cellular protein synthesis. Direct confirmation of expression of this self-encoded antigen was performed through development of a T cell receptor mimic (TCRm) monoclonal antibody (mAb). The resulting 4F7 TCRm demonstrated specific recognition of the eIF4G₍₇₂₀₎-A^*0201 complex. Staining of normal PBMCs with 4F7 showed only low levels of endogenous eIF4G₍₇₂₀₎ presentation by HLA-A^*0201, while 4F7 staining of HIV-1-infected PBMCs revealed a ∼ 3-fold increase in eIF4G₍₇₂₀₎-A^*0201. The MHC-peptide complex was initially detectable by 4F7 at 3 days post-infection, with a steady increase through day 8. We therefore demonstrate the successful development and implementation of an integrated discovery and validation technology system for direct identification and confirmation of class I MHC-peptide epitopes on cells.