CD70 is a type II transmembrane protein. It is a member of the TNF superfamily, expressed on activated B cells, activated dendritic cells, and some activated T cells (low levels). CD70 interacts with CD27 to promote T-B cell cross-stimulation and co-stimulate B cell proliferation and immunoglobulin production. Cells expressing CD70 can co-stimulate T cell proliferation and enhance the production of cytokines. The FR70 antibody blocks CD70 binding to CD27.