Ii- tumor cells present novel MHC II peptides that are tumor specific and immunogenic (52.18)

Abstract

Abstract We have generated tumor cell-based vaccines to activate patients’ CD4+ T-cells to facilitate tumor immunity. The vaccines are based on the hypothesis that invariant chain negative (Ii-), MHC II+ , CD80+ human breast cancer cells (MCF10) present novel MHC II peptides and circumvent patients’ tolerance to their cancer. We sequenced MHC II peptides from Ii- (MCF10/DR7/CD80 and MCF10/CIITA/CD80/Ii siRNA) and Ii+ (MCF10/DR7/CD80/Ii and MCF10/CIITA/CD80) cells using LC-MS/MS. 64/116 peptides identified were unique to MCF10/DR7/CD80 and 176/228 peptides were unique to MCF10/DR7/CD80/Ii cells. 102/108 and 22/28 peptides were uniquely identified for MCF10/CIITA/CD80 and MCF10/CIITA/CD80/Ii siRNA cells, respectively. Therefore, the absence of Ii enables the presentation of unique peptides that are not presented by Ii+ or professional antigen presenting cells. Five peptides unique to Ii- and 2 peptides shared by Ii- and Ii+ cells and with the highest MHC II binding affinity, as predicted by artificial neural net analysis, were tested for their ability to activate T-cells from the blood of healthy donors or breast cancer patients. All peptides expanded tumor-reactive T-cells and induced IFNγ production. This is the first study to compare the human MHC II peptide repertoire in the absence or presence of Ii and to identify novel immunogenic MHC II-restricted peptides that are potential therapeutic reagents for cancer patients.