Characterization of Endogenous Human FcγRIII by Mass Spectrometry Reveals Site, Allele and Sequence Specific Glycosylation.

The importance of IgG glycosylation, Fc-gamma receptor (FcγR) single nucleotide polymorphisms and FcγR copy number variations in fine tuning the immune response has been well established. There is a growing appreciation of the importance of glycosylation of FcγRs in modulating the FcγR-IgG interaction based on the association between the glycosylation of recombinant FcγRs and the kinetics and affinity of the FcγR-IgG interaction. Although glycosylation of recombinant FcγRs has been recently characterized, limited knowledge exists on the glycosylation of endogenous human FcγRs. In order to improve the structural understanding of FcγRs expressed on human cells we characterized the site specific glycosylation of native human FcγRIII from neutrophils of 50 healthy donors and from matched plasma for 43 of these individuals. Through this analysis we have confirmed site specific glycosylation patterns previously reported for soluble FcγRIII from a single donor, identified FcγRIIIb specific Asn45 glycosylation and an allelic effect on glycosylation at Asn162 of FcγRIIIb. Identification of FcγRIIIb specific glycosylation allows for assignment of FcγRIIIb alleles and relative copy number of the two alleles where DNA/RNA is not available. Intriguingly the types of structures found to be elevated at Asn162 in the NA2 allele have been shown to destabilize the Fc:FcγRIII interaction resulting in a faster dissociation rate. These differences in glycosylation may in part explain the differential activity reported for the two alleles which have similar in vitro affinity for IgG.

SRF617 Is a Potent Inhibitor of CD39 with Immunomodulatory and Antitumor Properties.

CD39 (ENTPD1) is a key enzyme responsible for degradation of extracellular ATP and is upregulated in the tumor microenvironment (TME). Extracellular ATP accumulates in the TME from tissue damage and immunogenic cell death, potentially initiating proinflammatory responses that are reduced by the enzymatic activity of CD39. Degradation of ATP by CD39 and other ectonucleotidases (e.g., CD73) results in extracellular adenosine accumulation, constituting an important mechanism for tumor immune escape, angiogenesis induction, and metastasis. Thus, inhibiting CD39 enzymatic activity can inhibit tumor growth by converting a suppressive TME to a proinflammatory environment. SRF617 is an investigational, anti-CD39, fully human IgG4 Ab that binds to human CD39 with nanomolar affinity and potently inhibits its ATPase activity. In vitro functional assays using primary human immune cells demonstrate that inhibiting CD39 enhances T-cell proliferation, dendritic cell maturation/activation, and release of IL-1ß and IL-18 from macrophages. In vivo, SRF617 has significant single-agent antitumor activity in human cell line-derived xenograft models that express CD39. Pharmacodynamic studies demonstrate that target engagement of CD39 by SRF617 in the TME inhibits ATPase activity, inducing proinflammatory mechanistic changes in tumor-infiltrating leukocytes. Syngeneic tumor studies using human CD39 knock-in mice show that SRF617 can modulate CD39 levels on immune cells in vivo and can penetrate the TME of an orthotopic tumor, leading to increased CD8+ T-cell infiltration. Targeting CD39 is an attractive approach for treating cancer, and, as such, the properties of SRF617 make it an excellent drug development candidate.

Elucidating the interplay between IgG-Fc valency and FcγR activation for the design of immune complex inhibitors.

Autoantibody immune complex (IC) activation of Fcγ receptors (FcγRs) is a common pathogenic hallmark of multiple autoimmune diseases. Given that the IC structural features that elicit FcγR activation are poorly understood and the FcγR system is highly complex, few therapeutics can directly block these processes without inadvertently activating the FcγR system. To address these issues, the structure activity relationships of an engineered panel of multivalent Fc constructs were evaluated using sensitive FcγR binding and signaling cellular assays. These studies identified an Fc valency with avid binding to FcγRs but without activation of immune cell effector functions. These observations directed the design of a potent trivalent immunoglobulin G-Fc molecule that broadly inhibited IC-driven processes in a variety of immune cells expressing FcγRs. The Fc trimer, Fc3Y, was highly efficacious in three different animal models of autoimmune diseases. This recombinant molecule may represent an effective therapeutic candidate for FcγR-mediated autoimmune diseases.

Acute lung injury with endotoxin or NO2 does not enhance development of airway epithelium from bone marrow.

Adult marrow-derived stem cells can localize to lung and acquire immunophenotypic characteristics of lung epithelial cells. Lung injury increases recruitment of the marrow-derived cells. We speculated that comparing patterns of lung engraftment following different lung injuries would provide insight into potential mechanisms by which marrow-derived cells were recruited to lung. To evaluate this, adult female C57Bl/6 mice irradiated and engrafted with marrow from adult male transgenic GFP mice were exposed to either intranasal inhalation of endotoxin (25 microg/mouse) or 3 days of 25 ppm NO(2) and then compared 1 or 3 months later to transplanted but otherwise uninjured mice. In all cases, the majority of marrow-derived cells recruited to lung were CD45(+) leukocytes. In lungs of transplanted but otherwise uninjured mice, small numbers of CD45(-) donor-derived cells in alveolar septae stained positively for pro-surfactant protein C. Rare donor-derived cells located in the airway epithelium stained positively with cytokeratin. Subsequent exposure of engrafted mice to NO(2) or endotoxin did not significantly increase the number or pattern of donor-derived CD45(-) cells found in recipient lungs. These results suggest that NO(2) or endotoxin lung injury does not result in significant engraftment of marrow-derived cells in lung.