SIRP-Alpha D1 Variants for Selective CD47 Binding

The patent applies local quality by creating SIRP-α D1 variants with specific amino acid mutations at particular positions (e.g., R80Q, R80L, R80P mutations combined with other residue changes) that locally modify the binding interface. These targeted mutations enhance binding affinity to human CD47 at the molecular interaction site without uniformly increasing binding to all CD47 variants, thereby improving therapeutic effectiveness while reducing off-target effects that cause acute anemia.

The patent employs parameter changes by systematically varying amino acid residues at specific positions in the SIRP-α D1 domain (such as changing residues at positions 6, 27, 31, 47, 53, 54, 56, 66, and 92) to optimize binding affinity. Through combinatorial mutagenesis and selection, variants are identified that achieve high affinity for human CD47 with dissociation constants in the nanomolar range, while the Fc domain modifications (e.g., L234A, L235A, G237A mutations) adjust effector function parameters to reduce hemolytic activity and prevent acute anemia.

The patent applies dynamics by creating a library of SIRP-α D1 variants with diverse amino acid substitutions that exhibit varying binding affinities and specificities. Through iterative selection and optimization processes, variants are identified that dynamically balance high affinity for cancer cell-associated CD47 with reduced binding to normal cell CD47. The Fc domain engineering further enables dynamic control of effector function, allowing selective activation in cancer contexts while minimizing normal cell toxicity.

The patent uses Fc domain variants as intermediaries that modulate the interaction between the SIRP-α D1 binding domain and the immune system. By engineering Fc domains with reduced binding to Fcγ receptors (through mutations like L234A, L235A, G237A) and reduced complement activation, the system achieves selective targeting of cancer cells via the SIRP-α D1-CD47 interaction while the modified Fc domain prevents excessive immune activation that would cause toxicity to normal cells.

The patent applies local quality by making specific, targeted mutations in the Fc domain (such as L234A, L235A, G237A, N297A mutations) that locally affect Fcγ receptor binding and complement activation sites. These localized modifications reduce immunogenicity and off-target immune activation while preserving the core therapeutic mechanism of CD47 blocking by the SIRP-α D1 domain. The selective nature of these mutations allows fine-tuning of effector function without completely abolishing therapeutic activity.

The patent employs partial action by implementing Fc domain modifications that partially reduce effector function rather than completely eliminating it. The mutations are designed to selectively reduce binding to certain Fcγ receptors and complement activation while maintaining other important functions. This partial modification approach allows the therapeutic to retain sufficient immune-mediated cytotoxicity against cancer cells while minimizing excessive immune activation and immunogenicity that would cause toxicity.