Defining the anti-inflammatory activity of a potent myxomaviral chemokine modulating protein, M-T7, through site directed mutagenesis

Viral chemokine modulating proteins provide new and extensive sources for therapeutics. Purified M-T7, a poxvirus-derived secreted immunomodulatory protein, reduces mononuclear cell invasion and atheroma in rodent models of angioplasty injury as well as aortic and renal transplant, improving renal allograft survival. M-T7 is a rabbit species-specific interferon gamma receptor (IFNγR) homolog, but also inhibits chemokine/glycosaminoglycan (GAG) interactions for C, CC and CXC chemokines, with cross-species specific inhibitory activity. M-T7 anti-atheroma activity is blunted in GAG deficient mouse aortic transplants, but not in CC chemokine receptor deficient transplants, supporting M-T7 interference in chemokine/GAG interactions as the basis of the atheroma-inhibitory activity. We have assessed point mutants of M-T7 both in vivo in a mouse angioplasty model and in vitro in tissue culture and binding assays, in order to better define the primary mechanism of anti-atheroma activity. Of these M-T7 mutants, the R¹⁷¹E and E²⁰⁹I M-T7 mutants lost inhibitory activity for plaque growth in hyperlipidemic ApoE^-/- mice after angioplasty injury and R¹⁷¹E, moreover, greatly exacerbated plaque growth and inflammation. F¹³⁷D retained some inhibitory activity for plaque growth. In contrast, for cell migration assays, M-T7-His_6X, F¹³⁷D, R¹⁷¹E, and E²⁰⁹I all inhibited CC chemokine (RANTES) mediated cell migration. For the ligand binding assays, R¹⁷¹E and E²⁰⁹I had significantly reduced binding to RANTES and IFNγ, whereas F¹³⁷D retained wild-type binding activity. Heparin treatment further reduced RANTES binding of all three M-T7 mutants. In summary, point mutations of M-T7, R¹⁷¹E and E²⁰⁹I, exhibited reduced anti-inflammatory properties in vivo after mouse angioplasty with a loss of in vitro binding to RANTES and IFNγ, indicating these point mutations partially disrupt M-T7 ligand-binding activities. Unexpectedly, the M-T7 mutants all retained inhibitory activity for human monocyte THP-1 cell migration ex vivo, suggesting additional inhibitory properties against human monocyte THP-1 cells that are independent of chemokine inhibition.