The present invention relates to antibodies. Specifically, the present invention relates to antibodies composed of novel combinations of inter-species antibody domains ("domain-grafted antibodies"). The present invention further relates to compositions comprising such domain-grafted antibodies, as well as methods for producing such domain-grafted antibodies. Finally, the present invention relates to methods of evaluating the in vivo biological effect of such domain-grafted antibodies as well as uses of such domain-grafted antibodies for cross-species evaluation of the in vivo activity antibodies intended for human therapy.