CpG-Oligodeoxynucleotides activate tyrosinase-related protein 2-specific T lymphocytes but do not lead to a protective tumor-specific memory response.
OBJECTIVE
Peritumoral CpG-oligodeoxynucleotide (ODN) treatment has been successful in tumor mouse models expressing strong antigens to induce activation of tumor-specific CD8+ T lymphocytes which contribute to the control of tumor growth. To get near to clinical reality, the tumor-specific CD8+ response was investigated in mice bearing the weakly immunogenic B16 melanoma tumor and using the melanocyte differentiation tyrosinase-related protein 2 (TRP-2) as a tracking antigen.


METHODS
The expansion and activation of TRP-2-specific T lymphocytes by CpG-ODNs was analyzed by tetramer staining and IFN-gamma production assays, while the activity of these cells in both memory and primary response was evaluated in vivo.


RESULTS
After CpG-ODN treatment, the number of TRP-2 tetramer-stained CD8+ T lymphocytes was not significantly modified, but these cells produced higher levels of interferon gamma (IFN-gamma) in response to the antigen than those from untreated mice. Mice possessing these activated T lymphocytes, when evaluated for their antitumor memory response, showed marginal protection against intravenous (i.v.) and subcutaneous (s.c.) tumor rechallenge. These cells were not crucial for the control of primary tumor growth since strong reduction of subcutaneous tumor was observed after CpG-ODN treatment in both CD8+ T cell depleted or nondepleted mice. On the contrary, NK cell depletion markedly reduced CpG-ODN-induced tumor growth inhibition.


CONCLUSIONS
Altogether, these data indicate the CpG treatment activates tumor-reactive effector CD8+ T lymphocytes, but, paralleling recent clinical observations, our model indicates that the mere activation of antitumor T cells is insufficient to result in a clinical response.
Sfondrini
Lucia
L
Molecular Targeting Unit, Department of Experimental Oncology, Istituto Nazionale Tumori, Via Venezian 1, 20133, Milan, Italy.
Besusso
Dario
D
Bronte
Vincenzo
V
Macino
Beatrice
B
Rossini
Anna
A
Colombo
Mario Paolo
MP
Ménard
Sylvie
S
Balsari
Andrea
A
D000818:Animals; D000951:Antigens, Neoplasm / Q000378:metabolism; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D007156:Immunologic Memory; D007371:Interferon-gamma / Q000378:metabolism; D019746:Intramolecular Oxidoreductases / Q000378:metabolism*; D007694:Killer Cells, Natural / Q000276:immunology; D008213:Lymphocyte Activation; D008546:Melanoma, Experimental / Q000276:immunology* / Q000473:pathology / Q000628:therapy*; D051379:Mice; D008810:Mice, Inbred C57BL; D009838:Oligodeoxyribonucleotides / Q000008:administration & dosage*; D015996:Survival Rate; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology
D000951:Antigens, Neoplasm; C408982:CPG-oligonucleotide; D009838:Oligodeoxyribonucleotides; D007371:Interferon-gamma; D019746:Intramolecular Oxidoreductases; C042501:dopachrome isomerase