Identification of T-Cell Epitopes

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Abstract
Summary: A novel method was developed to isolate immunogenic peptides (CD8+ T-cell epitopes) from class I complexes expressed at the cell surface of viable cells. Cells treated at pH 3.3 with citrate-phosphate buffer for periods as short as 15 s remained viable and became phenotypically class I deficient. Qualitative loss of class I determinants was verified both serologically and by the incapacity of acid-treated cells to be lysed by class I-restricted cytolytic T lymphocytes (CTLs) in contrast to non-acid-treated controls. Flow cytometric analysis of acid-treated cells suggests that class I heavy chains remain associated with the cell membrane, while the class I light chain (β2-microglobulin) is absent. Since the physical dissociation of β2-microglobulin from class I heavy chain is correlated with the release of previously class I-bound peptides, we examined acid-eluted cell-free supernatants for the presence of immunogenic peptides. Peptides were acid eluted from an influenza A strain-infected, HLA-A2+ cell line and were subsequently fractionated by reverse-phase high performancpe liquid chromatography (RP-HPLC). These fractionated peptides were examined for their capacity to sensitize an HLA-A2+ B cell line to lysis mediated by an influenza A matrix peptide- (Flu Ml 57-68) specific, HLA-A2- restricted CTL line. A single peak of biologic activity was identified in HPLC fractions 47 and 48 derived from influenza-infected cells. These fractions contained a peptide of Mr 968 with a sequence similar to the Flu Ml 58-66 sequence GILGFVFTL. The application of this technique to other T-cell-based systems may aid in the definition of peptide epitopes relevant to viral, autoimmune, or neoplastic disorders.

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