Bex is a Clever-1 antibody. It works where there are many Clever-1 expressing cells, i.e., in tumor-associated macrophages (TAMs), which are specifically found in immunologically cold tumors.
In other words, the Clever-1 antibody specifically targets macrophages in an immunosuppressive state. These macrophages are not evenly distributed in the body but are concentrated in the cancerous tumors that are the problem. This allows Bex to be administered systemically, but its effect is (due to the distribution of Clever-1 expressing macrophages) somewhat localized to where the cancer is.
If, on the other hand, CD47 on cancer cells is targeted directly, then all CD47 on the body’s own tissues will also be targeted, resulting in a large part of the effect occurring in places where it is not wanted or needed.