ABSTRACT

T regulatory cells (Tregs) play an essential role in the induction of selftolerance by suppressing autoimmune responses (Sakaguchi et al. 2001). Many of these responses are tissue-specifi c, yet some are related to the development of tumors and can be detrimental to the anti-tumor T cell response. Despite this, T regulatory cells can be converted from naïve or antigen-specifi c T cells in the context of a growing tumor (Drake et al. 2006). This is indicative of an important anti-self-tolerance mechanism. Even though this is not the only immunosuppressive T cell mechanism controlling the anti-tumor T cell response (Edwards and Evavold 2010), it probably represents one of the main reasons why many anti-tumor T cell responses are ineffective. The activities of Tregs during an antitumor T cell response may be crucial to the success or failure of such a response while the tumor is growing (El Andaloussi and Lesniak 2006). Both “innate” and “adaptive” Tregs play a role in the anti-tumor T cell response, but the adaptive Treg in this situation may be a pivotal element because of the T cell/Treg conversion phenomenon (Bluestone and Abbas 2003). The conversion of naïve or tumor-specifi c T cells into Tregs, and Tregs into antigen-specifi c effector T cells, is mediated by DCs (Curiel 2007). Dendritic cells not only mediate this conversion or reprogramming process, but also are essential to the expansion and maintenance of the Treg (Yamazaki et al. 2003). They can also themselves come under the control of Tregs, and thus alter their function in such a way as to benefi t tumor growth (Liang et al. 2008).