title: Molecular basis of cross-species reactivities of human versus porcine CTLA-4.
abstract: The binding motif of human CTLA-4 is well known to be MYPPPY and for porcine CTLA-4 the binding motif is LYPPPY. Is this single amino acid difference of methionine (M) versus leucine (L) critical for the CTLA-4 binding? Recently, we have reported that the recombinant soluble porcine CTLA-4 was incapable of binding to human CD80. In this study we mutated L to M in the binding motif of the soluble porcine CTLA-4 and mutated M to L in the binding motif of the soluble human CTLA-4. We then analyzed how these mutations affected the binding affinity of the mutants to both porcine and human CD80(+) cells. The soluble porcine CTLA-4-L97M mutant partially lost its binding affinity to porcine CD80 compared to the wild-type and conferred very weak binding ability to human CD80. These results indicate that the L in the binding motif of porcine CTLA-4 is important for determining its binding ability to porcine CD80. Wild-type soluble human CTLA-4 binds to both human and porcine CD80 with comparable affinity, however, the soluble human CTLA-4-M97L mutant almost lost its binding ability to human CD80 and increased its binding ability to porcine CD80. These results indicate that M in the human CTLA-4 binding motif is extremely critical for its binding to human CD80. Those data suggest that the human CTLA-4 based recombinant protein drugs such as human CTLA-4-Ig can be used and/or tested in a porcine model. Conversely, the use of porcine CTLA-4 based recombinant protein drugs such as porcine CTLA-4-Ig is restricted to swine models. The difference in binding specificity of CTLA-4 observed in this study may be useful for studies such as pig to nonhuman primate xeno-transplantation. Porcine CTLA-4- and human CTLA-4-M97L mutant-based recombinant protein drugs can be used to specifically block the direct presentation by donor antigen presenting cells in pig to nonhuman primate xeno-transplantation. Human CTLA-4-M97L mutant-based recombinant protein drugs will be more ideal as it is without immunogenicity to human being.
authors.affiliation: Transplantation Biology Research Center, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02129, USA.
authors.forename: Jaclyn Stromp
authors.initials: JS
authors.lastname: Peraino
authors.forename: Huiping
authors.initials: H
authors.lastname: Zhang
authors.forename: Guoying
authors.initials: G
authors.lastname: Li
authors.forename: Christene A
authors.initials: CA
authors.lastname: Huang
authors.forename: Zhirui
authors.initials: Z
authors.lastname: Wang
mesh_terms: D000818:Animals; D018122:B7-1 Antigen / Q000276:immunology*; D060908:CTLA-4 Antigen / Q000235:genetics / Q000276:immunology*; D003429:Cross Reactions / Q000235:genetics; D015195:Drug Design; D006084:Graft Rejection / Q000276:immunology / Q000517:prevention & control*; D006801:Humans; D007167:Immunotherapy; D016297:Mutagenesis, Site-Directed; D016377:Organ Transplantation; D011485:Protein Binding / Q000235:genetics; D054730:Protein Interaction Domains and Motifs / Q000235:genetics; D013045:Species Specificity; D013552:Swine / Q000276:immunology*; D014183:Transplantation, Heterologous
chemical_list: D018122:B7-1 Antigen; D060908:CTLA-4 Antigen