Abstract
We investigated the in vivo role of CD69 by analyzing the susceptibility of CD69-/- mice to tumors. CD69-/- mice challenged with MHC class I- tumors (RMA-S and RM-1) showed greatly reduced tumor growth and prolonged survival compared with wild-type (WT) mice. The enhanced anti-tumor response was NK cell and T lymphocyte-mediated, and was due, at least in part, to an increase in local lymphocytes. Resistance of CD69-/- mice to MHC class I- tumor growth was also associated with increased production of the chemokine MCP-1, diminished TGF-beta production, and decreased lymphocyte apoptosis. Moreover, the in vivo blockade of TGF-beta in WT mice resulted in enhanced anti-tumor response. In addition, CD69 engagement induced NK and T cell production of TGF-beta, directly linking CD69 signaling to TGF-beta regulation. Furthermore, anti-CD69 antibody treatment in WT mice induced a specific down-regulation in CD69 expression that resulted in augmented anti-tumor response. These data unmask a novel role for CD69 as a negative regulator of anti-tumor responses and show the possibility of a novel approach for the therapy of tumors.