The present invention relates to the discovery that inhibition of Dickkopf2 (DKK2) increases CD8+ cytotoxic T lymphocyte (CTL) activity, attenuates tumor, and hence suppresses tumor formation. Thus, in various embodiments described herein, the methods of the invention relate to methods of treating cancer by administering to a patient an effective amount of a humanized anti-DKK2 antibody, methods for providing anti-tumor immunity in a subject, methods of stimulating a T cell mediated immune response to a cell population or a tissue and suppressing tumor in a subject. Additionally, the current invention includes methods of diagnosing a cancer or a predisposition of developing a cancer or a metastasis and methods for determining the use of immunotherapy treatment or cancer vaccine for treating cancer. Furthermore, the invention encompasses a pharmaceutical composition for treating cancer as well as a kit for carrying out the aforementioned methods.