CD200 and cancer: High levels of CD200 have been associated with poor prognosis in certain cancers, suggesting that CD200 may be protecting the tumor by inhibiting myeloid cells through CD200R, and CD200 mAb are being tested to restore myeloid cell activity and help eliminate tumor cells (Kretz-Rommel et al., 2007; Moreaux et al., 2006; Tonks et al., 2007).