To examine whether T cell can impair BMMSC in vivo, we adoptively transferred CD4+CD25−CD45RB+hi T cells, previously showed to induce inflammatory bowel disease (IBD) in nude mice [23] and in patients with IBD associated osteoporosis [24], [25], into OVX immunocompromised mice that lacked osteoporosis phenotype due to the absence of T lymphocytes (Fig. 2A). The gene discussed is CD4; the disease is osteoporosis.