In the context of the notion that the activation of the CD200:CD200R axis was implicated in the attenuation of immune responses, we hypothesized that the growth of EMT6 (a CD200-expressing tumor) and 4THM (a CD200-tumor) would differ where transplantation occurred in mice with various manipulations of CD200/CD200R in mice or tumor cells. The gene discussed is CD200R1; the disease is neoplasm.