Autophagy Creates a CTL Epitope That Mimics Tumor-Associated Antigens

Ayako Demachi-Okamura,Tamotsu Yoshimori,Yoshiki Akatsuka,Hiroki Torikai,Kiyotaka Kuzushima,Hiroyuki Miyoshi,Hiroshi Shiku

doi:10.1371/journal.pone.0047126

Abstract

The detailed mechanisms responsible for processing tumor-associated antigens and presenting them to CTLs remain to be fully elucidated. In this study, we demonstrate a unique CTL epitope generated from the ubiquitous protein puromycin-sensitive aminopeptidase, which is presented via HLA-A24 on leukemic and pancreatic cancer cells but not on normal fibroblasts or EBV-transformed B lymphoblastoid cells. The generation of this epitope requires proteasomal digestion and transportation from the endoplasmic reticulum to the Golgi apparatus and is sensitive to chloroquine-induced inhibition of acidification inside the endosome/lysosome. Epitope liberation depends on constitutively active autophagy, as confirmed with immunocytochemistry for the autophagosome marker LC3 as well as RNA interference targeting two different autophagy-related genes. Therefore, ubiquitously expressed proteins may be sources of specific tumor-associated antigens when processed through a unique mechanism involving autophagy.

Highlights

Exploring the mechanisms underlying cancer-specific CTL recognition is important in the establishment of safe and effective immunotherapy
To establish the K562-based Artificial Antigen Presenting Cells (aAPCs), K562 cells were stably transduced with HLA-A24, CD86 and 4-1BBL with lentiviral vectors, and a positive population was isolated (Figure 1A) to generate tumor-specific T cells from HLA-A24-positive donors
16F3 recognized three out of five pancreatic cancer cell lines (Figure 1D) in an effect that was blocked by anti-HLA class I Abs

Summary

Introduction

Exploring the mechanisms underlying cancer-specific CTL recognition is important in the establishment of safe and effective immunotherapy. The discrimination of normal and malignant cells by CTLs depends on the repertoire of antigenic peptides displayed via the MHC class I molecules of these cells As both normal and malignant cells possess antigen-processing machinery, the repertoire displayed depends on the expression level of the target proteins. These target proteins are degraded in the cytoplasm by the proteasome, with the resulting short peptides being translocated into the endoplasmic reticulum, where they bind to MHC class I molecules [1]. If malignant cells possess unique antigen-processing machinery, they may create cancerspecific antigenic peptides, even from ubiquitously expressed proteins

Methods

Results

Conclusion