Identification of a MHC class II-restricted human gp100 epitope using DR4-IE transgenic mice

CD4(+) T cells play a central role in the induction and persistence of CD8( +) T cells in several models of autoimmune and infectious disease. To impro ve the efficacy of a synthetic peptide vaccine based on the self-Ag, gp100, we sought to provide Ag-specific T cell help. To identify a gp100 epitope restricted by the MHC class II allele with the highest prevalence in patien ts with malignant melanoma (HLA-DRB1*0401), we immunized mice transgenic fo r a chimeric human-mouse class II molecule (DR4-IE) with recombinant human gp100 protein. We then searched for the induction of CD4(+) T cell reactivi ty using candidate epitopes predicted to bind to DRB1*0401 by a computer-as sisted algorithm. Of the 21 peptides forecasted to bind most avidly, murine CD4(+) T cells recognized the epitope (human gp100(44-59), WNRQLYPEWTEAQRL D) that was predicted to bind best. Interestingly, the mouse helper T tells also recognized human melanoma cells expressing DRB1*0401. To evaluate whe ther human CD4(+) T cells could be generated from the peripheral blood of p atients with melanoma, we used the synthetic peptide h-gp100(44-59) to sens itize lymphocytes ex vivo. Resultant human CD4(+) T cells specifically reco gnized melanoma, as measured by tumor cytolysis and the specific release of cytokines and chemokines. NI,A class II transgenic mice may be useful in t he identification of helper epitopes derived from Ags of potentially great clinical utility.