Multimeric gitr binding molecules and uses thereof

A multimeric binding molecule comprising two, five, or six bivalent binding units or variants or fragments thereof,

• wherein each binding unit comprises two IgA or IgM heavy chain constant regions or fragments thereof, each associated with an antigen-binding domain,
• wherein at least three of the antigen-binding domains of the binding molecule can specifically and agonistically bind to a GITR monomer on a cell expressing GITR, and
• wherein the binding molecule can induce GITR-mediated signal transduction in the cell in the absence of a secondary cross-linking moiety.