The lifespan of major histocompatibility complex class I/peptide complexes determines the efficiency of cytotoxic T-lymphocyte responses

Abstract

Major histocompatibility complex (MHC)/peptide association and stability are determined by specific amino acid interactions between peptide antigens and the MHC groove, and are regarded as a critical feature in ensuring efficient monitoring by T cells. In this investigation we examined the relationship between MHC/peptide stability and the immunostimulatory capacity of MHC/peptide complexes. For this purpose we compared synthetic peptide analogues derived from the immunodominant HLA-A11-presented IVTDFSVIK (IVT) epitope, for their capacity to reactivate IVT-specific memory cytotoxic T-lymphocyte (CTL) responses. The analogues differentiated from the wild-type epitope by single amino acid substitution at position 2. All peptides showed similar affinity for HLA-A11 molecules and were recognized by IVT-specific CTL clones, but induced HLA-A11 complexes at the cell surface with different lifespan. This model offered the possibility of comparing the capacity of an immunogenic epitope to stimulate a unique population of T-cell precursors depending on the lifespan of its presentation at the cell surface. We demonstrated that stable HLA-A11/peptide complexes efficiently stimulate IVT-specific CTL responses, while HLA-A11/peptide complexes with short lifespan do not. The precise identification of the role of amino acid residues in the formation of stable MHC/peptide complexes may be relevant for the design of wild-type-derived epitopes with high immunogenicity. These analogues may have important applications in the immunotherapy of infectious diseases and immunogenic tumours.

Figure 1

Recognition of IVT analogues by IVT-specific CTL clones. The IVT-specific CTL clone ZAN-43 was tested for its ability to lyse HLA-A11-matched PHA-blasts pulsed with different concentrations of IVT, 2Abu, 2T, and 2alloT peptides before CTL were added to the assay. The percentage specific lysis recorded at 10:1 effector/target ratio is shown in the figure.

Figure 2

Expression of HLA-A11/peptide complexes at the cell surface. T2/A11 cells were preincubated overnight at 37° with the indicated concentrations of IVT and 2T peptides. Surface expression of HLA class I molecules was detected by indirect immunofluorescence using the W6.32 mAb. Data are expressed as mean luorescence intensity measured with a FACS analyser. Mean of three different experiments.

Figure 3

Stimulation of IVT-specific CTL responses by peptides. Freshly isolated lymphocytes derived from the HLA-A11-positive, EBV-seropositive donor MF were stimulated with T2/A11 cells preincubated overnight at 26°, and pulsed with 10⁻⁸ m, 10⁻¹⁰ m,10⁻¹² m, 10⁻¹⁴ m of the indicated peptides for 3 hr at 37°. CTL cultures obtained after two consecutive stimulations were tested in cytotoxicity assays against HLA-A11 positive PHA-blasts (open circle) or PHA-blasts pulsed with 10⁻⁷ m IVT peptide for 1 hr before the assay (closed circle). The percentage specific lysis recorded in one representative experiment is shown in the figure.