With a goal of enhancing endogenous antigen trafficking to the cellular MHC II compartment of antigen-presenting cells, we employ the use of genetic vaccines encoding the antigens as chimeras containing the lysosomal targeting sequences of the lysosome-associated membrane protein (LAMP). Our rationale is that the delivery of antigen to the cellular site of MHC II processing and binding of antigen epitopes could result in an enhanced immune response through greater antigen-specific activation of CD4 ϩ T-cells. LAMP molecules have steady-state localization in the outer membrane of lysosomes (15-17) with a trafficking pathway from the Golgi complex (18, 19) mediated by adaptor protein binding (20) to the carboxyl-terminal YXXØ (where the Ø symbol represents any hydropholic amino acid) recognition sequence of an 11-amino acid cytoplasmic tail (21-23). This LAMP trafficking pathway was found to coincide with that of MHC II in specialized multilaminar vesicular compartments of immature APCs, termed MIIC, sites associated with the formation of antigenic peptide-MHC II complexes (24 -28).

No abstract

Vaccine-induced CD8+ T-cell responses can eradicate developing tumors in vivo in mouse models. Translating these successes into approved treatments for cancer patients has been challenging, since many of these models lack expression of clinically proven/relevant tumor antigens. We have shown that mesothelin is a clinically relevant CD8 + T-cell target in human pancreas cancer, which is also highly conserved among species. Here, we utilize the murine mesothelin-expressing pancreatic tumor model (Panc02) to identify the immunerelevant mesothelin-derived peptides and study interventions that enhance the antitumor response. We first screened overlapping peptides of the entire murine mesothelin protein to identify two new CD8 + mesothelin-restricted epitopes. These peptides were then evaluated for recognition by vaccine-induced T cells from mice treated with vaccine in sequence with low-dose cyclophosphamide (CY) and an anti-CD25 IL-2Rα monoclonal antibody (PC61). These treatments are both known to deplete subpopulations of T regulatory cells (Tregs). Our findings demonstrate that combined Treg-depleting therapies synergize to enhance vaccine efficacy. Furthermore, our data supports mesothelin as a relevant antigen in murine and clinical models and the use of Panc02 as a clinically relevant murine model of pancreatic cancer for evaluating antigen-targeted immunotherapies in immune-tolerant hosts.

No abstract