Search

Engagement of the low-affinity Ab receptor FcγRIIb downregulates B cell activation, and its dysfunction is associated with autoimmunity in mice and humans. We engineered the Fc domain of an anti-human CD19 Ab to bind FcγRIIb with high affinity, promoting the coengagement of FcγRIIb with the BCR complex. This Ab (XmAb5871) stimulated phosphorylation of the ITIM of FcγRIIb and suppressed BCR-induced calcium mobilization, proliferation, and costimulatory molecule expression of human B cells from healthy volunteers and systemic lupus erythematosus (SLE) patients, as well as B cell proliferation induced by LPS, IL-4, or BAFF. XmAb5871 suppressed humoral immunity against tetanus toxoid and reduced serum IgM, IgG, and IgE levels in SCID mice engrafted with SLE or healthy human PBMC. XmAb5871 treatment also increased survival of mice engrafted with PBMC from a unique SLE patient. Unlike anti-CD20 Ab, coengagement of FcγRIIb and BCR complex did not promote B cell depletion in human PBMC cultures or in mice. Thus, amplification of the FcγRIIb inhibitory pathway in activated B cells may represent a novel B cell-targeted immunosuppressive therapeutic approach for SLE and other autoimmune diseases that should avoid the complications associated with B cell depletion.

TNF is a pleiotropic cytokine required for normal development and function of the immune system; however, TNF overexpression also induces inflammation and is associated with autoimmune diseases. TNF exists as both a soluble and a transmembrane protein. Genetic studies in mice have suggested that inflammation in disease models involves soluble TNF (solTNF) and that maintenance of innate immune function involves transmembrane TNF (tmTNF). These findings imply that selective pharmacologic inhibition of solTNF may be anti-inflammatory and yet preserve innate immunity to infection. To address this hypothesis, we now describe dominant-negative inhibitors of TNF (DN-TNFs) as a new class of biologics that selectively inhibits solTNF. DN-TNFs blocked solTNF activity in human and mouse cells, a human blood cytokine release assay, and two mouse arthritis models. In contrast, DN-TNFs neither inhibited the activity of human or mouse tmTNF nor suppressed innate immunity to Listeria infection in mice. These results establish DN-TNFs as the first selective inhibitors of solTNF, demonstrate that inflammation in mouse arthritis models is primarily driven by solTNF, and suggest that the maintenance of tmTNF activity may improve the therapeutic index of future anti-inflammatory agents.

A dominant hypomorphic allele of Tnf, PanR1, was identified in a population of G(1) mice born to N-ethyl-N-nitrosourea-mutagenized sires. Macrophages from homozygotes produced no detectable TNF bioactivity, although normal quantities of immunoreactive TNF were secreted. The phenotype was confined to a critical region on mouse chromosome 17, and then ascribed to a C-->A transversion at position 3480 of the Tnf gene, corresponding to the amino acid substitution P138T. As a result of subunit exchange, the protein exerts a dominant-negative effect on normal TNF trimers, interfering with the trimer/receptor interaction. Homozygotes are highly susceptible to infection by Listeria monocytogenes, confirming the essential role of TNF in innate immune defense. However, PanR1 mutant mice show normal architecture of the spleen and Peyer's patches, suggesting that TNF is not essential for the formation of these lymphoid structures.