Repertoire of HLA-DR1-Restricted CD4 T-Cell Responses to Capsular Caf1 Antigen ofYersinia pestisin Human Leukocyte Antigen Transgenic Mice

Abstract

Yersinia pestis is the causative agent of plague, a rapidly fatal infectious disease that has not been eradicated worldwide. The capsular Caf1 protein of Y. pestis is a protective antigen under development as a recombinant vaccine. However, little is known about the specificity of human T-cell responses for Caf1. We characterized CD4 T-cell epitopes of Caf1 in "humanized" HLA-DR1 transgenic mice lacking endogenous major histocompatibility complex class II molecules. Mice were immunized with Caf1 or each of a complete set of overlapping synthetic peptides, and CD4 T-cell immunity was measured with respect to proliferative and gamma interferon T-cell responses and recognition by a panel of T-cell hybridomas, as well as direct determination of binding affinities of Caf1 peptides to purified HLA-DR molecules. Although a number of DR1-restricted epitopes were identified following Caf1 immunization, the response was biased toward a single immunodominant epitope near the C terminus of Caf1. In addition, potential promiscuous epitopes, including the immunodominant epitope, were identified by their ability to bind multiple common HLA alleles, with implications for the generation of multivalent vaccines against plague for use in humans.

The Signal Peptide of the Tumor-shared Antigen Midkine Hosts CD4+ T Cell Epitopes

“…To our knowledge, few CD4 ϩ T cell epitopes contained in signal peptides have been reported (22,23). They have been delineated in signal peptides of the tumor antigen Muc-1 (23) and the Caf1 antigen of Yersinia pestis (22). As stated by the authors, BALB/c mice inoculated with metastatic MUC1-transfected murine DA3 mammary tumor cells exhibited significantly prolonged survival following vaccination with MUC1 signal peptide (23).…”

“…As stated by the authors, BALB/c mice inoculated with metastatic MUC1-transfected murine DA3 mammary tumor cells exhibited significantly prolonged survival following vaccination with MUC1 signal peptide (23). Some HLA-DR1-transgenic mice infected with Y. pestis responded to peptides contained in the signal peptide of Caf1, suggesting that after cleavage from Caf1, the signal sequence is available for antigen presentation during infection (22). Signal peptides contain numerous hydrophobic residues that serve to anchor the nascent polypeptide to the membrane (31).…”

“…As we previously identified CD8 ϩ T cell epitopes in the signal peptide, we considered the entire sequence of MDK including the mature form of the protein secreted by tumors and the signal peptide, which remains in the cell (21). Few CD4 ϩ T cell epitopes have been found in signal peptides (22,23), but here, we demonstrate that the MDK signal peptide contains both subdominant and cryptic CD4 ϩ T cell epitopes.…”

“…Peptide peptidase has been implicated in the processing of the preprocalcitonin tumor antigen (19). Presentation of the preprocalcitonin [16][17][18][19][20][21][22][23][24][25] ϩ T cell epitope is inhibited by the preincubation of tumor cells with the serine protease inhibitor dichloroisocoumarin. However, in our experiments dichloroisocoumarin was toxic to the A375 melanoma cell line, even a low dose, such that they were uninformative (data not shown).…”

“…To our experience, this peptide induces a substantial T cell response. To our knowledge, few CD4 ϩ T cell epitopes contained in signal peptides have been reported (22,23). They have been delineated in signal peptides of the tumor antigen Muc-1 (23) and the Caf1 antigen of Yersinia pestis (22).…”