Provided herein are therapeutic compositions that include albumin (such as human serum albumin) and therapeutic proteins, such as a modified proaerolysin protein or an apoptosis-modulating fusion protein, as well as kits that include such compositions in containers. Also provided are methods of using such compositions in decreasing the antigenicity of therapeutic proteins such as modified proaerolysin proteins or apoptosis-modulating fusion protein antibodies (for example as evidenced by a decrease in the production of neutralizing antibodies).