Anti-human B7-H4 antibody “6H3”, antigen-binding fragments, derivatives, and humanized variants thereof that are capable of immunospecifically binding to B7-H4, and the uses of such molecules in the diagnosis and the treatment of cancer and other diseases are disclosed. In preferred embodiments, the molecules are used to retard or prevent tumor growth, inhibit tumor-mediated suppression, eliminate tumors and/or deplete or block the activity of tumor-associated macrophages (“TAMs”) so as to alter their activity and/or decrease TAM-mediated immune suppression.
