ABSTRACT
Initially, immunotherapy in humans utilized nonspecific immunostimulants such as BCG and Cryptosporidium parvum, which resulted in some tumor cell killing but overall did little to reduce the tumor cell burden. These results probably reflect the development of strong immune responses against antigens associated with these microbes, including production of cytokines capable of activating immune effector cells. The resulting activated cells (e.g., macrophages) then mediated increased tumor cell lysis.
