The invention provides heterochimeric antibodies and/or fragments thereof comprising (i) hypervariable region sequences wholly or substantially corresponding to sequences found in antibodies from a donor species； (ii) constant region sequences wholly or substantially corresponding to sequences found in antibodies from a target species which is different from the donor species； and (iii) heavy and/or light chain variable framework sequences which contain at least three non-CDR residues corresponding to sequences found in antibodies from a target species and at least three contiguous non-CDR residues corresponding to sequences found in antibodies from a donor species. The invention further provides antibody to canine or feline or equine antigens, e.g., CD20 or CD52, and methods of making and using antibodies as described.
