Non-depleting down-modulation of human B-cells through inhibitory coupling of FcγRIIB (CD32B) and the BCR with bi-specific DART molecules with extended pharmacokinetics. (51.8)

Abstract

Abstract We have previously demonstrated the ability of bi-specific Dual-Affinity ReTargeting (DART) molecules to coligate the inhibitory FcγRIIb (CD32B) receptor and the BCR component, CD79B, to inhibit B-cell activation and dampen autoimmunity (Veri et al, Arthritis. Rheum. 2010). Here we describe development and characterization of CD32BxCD79B DARTs with enhanced pharmacokinetic (PK) properties through incorporation of an albumin binding domain (ABD) or an Fc region. These second generation CD32BxCD79B DARTs, expressed in CHO cells and purified to homogeneity, demonstrated anticipated multi-specific binding properties and effectively reduced naïve and memory B-cell responses in both healthy subjects and SLE patients. Both the ABD and Fc- bearing DARTs displayed increased serum half-life resulting in prolonged ability to functionally block human B-cell responses resulting in reduced circulating IgM and IgG levels in mice engrafted with human PBMC. In contrast to rituximab, CD32BxCD79B DARTs did not induce B-cell depletion in a human fetal liver CD34+ HSC reconstituted mouse model. In summary, CD32BxCD79B DARTs with extended PK properties have been developed that inhibit human B-cell activation in the absence of depletion, forming the basis for an alternate B-cell intervention strategy for controlling autoimmune disease through convenient dosing, while avoiding the more general immune suppression associated with existing B-cell targeted strategies.