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Melanoma-Specific Memory T Cells Are Functionally Active in Ret Transgenic Mice without Macroscopic Tumors

¹ Skin Cancer Unit, German Cancer Research Center and University Hospital Mannheim, Heidelberg, Germany and ² Unit of Environmental Health Sciences, Department of Biomedical Sciences, College of Life and Health Sciences, Chubu University, Kasugai-shi, Aichi, Japan

Requests for reprints: Viktor Umansky, Skin Cancer Unit (G300), German Cancer Research Center, Im Neuenheimer Feld 280, 69120 Heidelberg, Germany. Phone: 49-621-3833773; Fax: 49-621-3832163; E-mail: v.umansky{at}dkfz.de.

Key Words: Memory T cells • melanoma • transgenic mouse model • bone marrow

We previously reported that bone marrows of breast cancer patients contained tumor antigen–specific CD8⁺ T cells with central or effector memory phenotype. Using a recently developed ret transgenic mouse melanoma model, we now show that bone marrows and tumors of transgenic mice contain high frequencies of CD8⁺ T cells specific for the melanoma antigen tyrosinase-related protein 2 and showing mostly effector memory phenotype. Moreover, increased numbers of bone marrow tyrosinase-related protein-2–specific effector memory CD8⁺ T cells are also detected in transgenic animals older than 20 weeks with disseminated melanoma cells in the bone marrow and lymph nodes but showing no visible skin tumors and no further melanoma progression. After a short-term coincubation with dendritic cells generated from the bone marrow and pulsed with melanoma lysates, bone marrow memory T cells from mice without macroscopic melanomas produced IFN- in vitro and exerted antitumor activity in vivo after adoptive transfer into melanoma-bearing mice. Our data indicate that functionally active bone marrow–derived melanoma-specific memory T cells are detectable at the phase of microscopic tumor load, suggesting that thereby they could control disseminated melanoma cells. [Cancer Res 2008;68(22):9451–8]