A human cytotoxic T-lymphocyte epitope and its agonist epitope from the nonvariable number of tandem repeat sequence of MUC-1.

PURPOSE

MUC-1/DF-3 remains an attractive target for vaccine therapy. It is overexpressed in the majority of human carcinomas and multiple myeloma. Clinical trials using MUC-1-based vaccines have demonstrated safety, clinical responses, and the induction of T-cell responses directed against MUC-1. Previous studies in experimental models and in clinical trials have demonstrated that altering the amino acid sequence of a "self" epitope can lead to the generation of an enhancer agonist epitope capable of eliciting stronger T-cell responses than the native epitope can.

EXPERIMENTAL DESIGN AND RESULTS

We describe here the identification of six novel class I HLA-A2 epitopes of MUC-1 that reside outside of the variable number of tandem repeat region. Each is shown to have the ability to activate human T cells as measured by IFN-gamma production. One epitope (ATWGQDVTSV, at amino acid position 92-101 and designated P-92), which demonstrated the highest level of binding to HLA-A2 and which induced the highest level of IFN-gamma in human T cells, was further studied for the generation of potential enhancer agonist epitopes. Of four potential agonists identified, one epitope (ALWGQDVTSV, designated P-93L) was identified as an enhancer agonist. Compared with the native P-92 peptide, the P-93L agonist (a). bound HLA-A2 at lower peptide concentrations, (b). demonstrated a higher avidity for HLA-A2 in dissociation assays, (c). when used with antigen-presenting cells, induced the production of more IFN-gamma by T cells than with the use of the native peptide, and (d). was capable of more efficiently generating MUC-1-specific human T-cell lines from normal volunteers and pancreatic cancer patients. Most importantly, the T-cell lines generated using the agonist epitope were more efficient than those generated with the native epitope in the lysis of targets pulsed with the native epitope and in the lysis of HLA-A2 human tumor cells expressing MUC-1.

CONCLUSIONS

In addition to the identification of novel MUC-1 epitopes outside the variable number of tandem repeat region, the studies reported here describe the first agonist epitope of MUC-1. The employment of this agonist epitope in peptide-, protein-, and vector-based vaccines may well aid in the development of effective vaccines for a range of human cancers.