The cytotoxic T cell response to peptide analogs of the HLA-A*0201-restricted MUC1 signal sequence epitope,M1.2 |
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| Authors: | Malcolm S Mitchell Teri A Lund Andrew K Sewell Francesco M Marincola Elyse Paul Kim Schroder Darcy B Wilson June Kan-Mitchell |
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| Institution: | (1) Department of Medicine, Wayne State University School of Medicine, Detroit, MI 48201, USA;(2) Department of Immunology and Microbiology, Wayne State University School of Medicine, Detroit, MI 48201, USA;(3) Karmanos Cancer Institute, Wayne State University School of Medicine, 110 East Warren Avenue, Detroit, MI 48201, USA;(4) T Cell Modulation Group, Nuffield Department of Medicine, University of Oxford, Oxford, UK;(5) Immunogenetics Section, Department of Transfusion Medicine, Clinical Center, National Institutes of Health, Bethesda, MD 20892, USA;(6) Torrey Pines Institute for Molecular Studies, La Jolla, CA, USA;(7) Present address: Hudson-Webber Cancer Research Center, Karmanos Cancer Institute, 110 East Warren Avenue, Detroit, MI 48201, USA |
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| Abstract: | The mucin MUC1 molecule is overexpressed on a variety of adenocarcinomas and is thus, a potential target for immunotherapy.
Of the MUC1 peptides that bind to HLA-A*0201(A2), M1.2 (LLLLTVLTV) from the signal sequence appears to be the most immunogenic
in humans. Here we have shown that large numbers (109) of tetramer-binding M1.2-specific cytotoxic T lymphocytes (CTL) can be generated ex vivo from circulating precursors, derived
from healthy adults. However, there was significant interpersonal variation in the level of co-stimulatory signal required.
Tetramer-binding cells also required maturation in culture to become proficient killers of the HLA-A2+ MUC1+ MCF7 cell line, known to express a low number of endogenously processed M1.2. The functional avidity of M1.2-specific CTL,
however, was low as compared to CTL specific for an HIV-1 epitope. Despite the low avidity, M1.2-specific CTL were polyfunctional,
secreting multiple cytokines upon degranulation with antigen recognition. To identify potential agonist peptides that may
be superior immunogens, an M1.2-specific CTL culture was used to scan a large nonameric combinatorial peptide library. Of
54 predicted peptides, 4 were “consensus” agonists because they were recognized by CTL from two other donors. Two agonists,
p29 (LLPWTVLTV) and p15 (VLLWTVLTV), were equally stimulatory when loaded onto C1R target cells transfected with wild-type HLA-A2. Both agonists induced
IL-2, TNF-α, IFN-γ, and degranulation with M1.2-specific CTL. In contrast, production of these cytokines, which are tightly
regulated by specific activation through the T cell receptor, was restricted when the CTL were stimulated with peptides loaded
onto C1R cells that were transfected with an HLA-A2 molecule bearing a mutation that abrogates binding to the CD8 co-receptor.
Thus, activation by both M1.2 and its agonists was dependent upon CD8, showing that compensation by the co-receptor was necessary
for the human T cell response to M1.2. |
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| Keywords: | Cancer CTL epitope Agonist peptide Immunotherapy |
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