Tumor necrosis factor (tnf) superfamily receptor binding molecules and uses thereof

An isolated IgM antibody or antigen-binding fragment thereof comprising five or six bivalent binding units fragments thereof,

• (a) wherein each binding unit comprises two IgM heavy chain constant regions or fragments thereof, each associated with an antigen-binding domain,
• (b) wherein at least three of the antigen-binding domains of the antibody or fragment thereof specifically and agonistically bind to a tumor necrosis factor (TNF) superfamily receptor protein,
• (c) wherein the antibody or fragment thereof can cross-link at least three identical TNF superfamily receptor proteins expressed on the surface of a cell, thereby activating signal transduction in the cell;
• and
• (d) wherein the antibody or fragment thereof can activate TNF superfamily receptor-mediated signal transduction in a TNF receptor superfamily-expressing cell at a higher potency than an equivalent amount of a bivalent IgG antibody or fragment thereof, which also specifically binds to and agonizes the same TNF superfamily receptor protein.