Biology subjects

Broden, M. W.

Publications and source records attributed to Broden, M. W..

3 recordsLinked to original sources

bioRxiv2026

Pre-clinical efficacy of a C4BP hexameric IgG Fc fusion protein against Neisseria gonorrhoeae

Gonorrhea is the second most common bacterial sexually transmitted infection and affects about 80 million people worldwide annually. The causative agent, Neisseria gonorrhoeae, has become resistant to almost every antibiotic used for its treatment. There is no licensed vaccine against gonorrhea. Therefore, there is an urgent need to develop novel prevention and treatment strategies to curb the spread of gonorrhea. The gonococcus has evolved several mechanisms to evade complement, a key arm of immune defenses against this pathogen, including binding of the human complement inhibitors Factor H (FH) and C4b-binding protein (C4BP). We previously showed that chimeric molecules fusing the gonococcal binding domains of FH and C4BP to IgG Fc and IgM Fc, respectively, mediate complement-dependent killing of gonococci in vitro and attenuate gonococcal colonization of mouse vaginas when administered topically. Here, we fused C4BP domains 1 and 2, which contain the gonococcal binding region, to IgG Fc bearing the IgM tail-piece to facilitate Fc hexamerization. This molecule, called C4BP-Hexa IgG Fc, showed [~]650-fold greater complement-dependent bactericidal activity on a molar basis than monomeric C4BP-IgG1 Fc. C4BP-Hexa IgG Fc enhanced association with and uptake by human neutrophils in a complement-independent manner. Despite off-target complement activation in solution, C4BP-Hexa IgG Fc reduced both the duration and the bacterial burden of gonococcal vaginal colonization in human FH and C4BP transgenic mice when administered intravaginally daily. In conclusion, we show proof-of-concept of the efficacy of a hexameric C4BP IgG Fc fusion molecule against N. gonorrhoeae, which could aid in the fight against this multidrug-resistant pathogen.

immunology↗

bioRxiv2026

C4BP occludes the non-opsonic interaction of Neisseria gonorrhoeae with human neutrophil CEACAMs

Neisseria gonorrhoeae (Gc) causes the sexually transmitted infection gonorrhea, an urgent public health concern. Gc infection elicits a robust neutrophil response and serum leakage, but Gc has developed specialized defenses to evade both complement and neutrophils. We recently reported that the classical complement pathway inhibitor C4b-binding protein (C4BP) binds to Gc and reduces phagocytic killing by neutrophils in a complement-independent manner. Here, we used a Chinese hamster ovary (CHO) expression system and engineered C4BP constructs to define the underlying molecular mechanisms. C4BP inhibited interactions between opacity protein (Opa)-expressing Gc and carcinoembryonic antigen-related cell adhesion molecules (CEACAMs), receptors that drive non-opsonic phagocytosis of Gc by neutrophils. The degree of C4BP-mediated inhibition varied among CEACAMs. By using wild-type and chimeric CEACAMs, we found C4BP was more inhibitory towards the granulocyte-restricted CEACAM3 than the ubiquitously expressed CEACAM1, which we ascribed to CEACAM3s shorter extracellular domain. C4BP also inhibited the association between Opa-expressing Gc and the GPI-anchored CEACAM6. Molecules containing C4BP domains 1 and 2 fused to IgM (C4BP-IgM) or to a hexameric IgG Fc construct (C4BP-Hexa-IgG), proteins similar in diameter and degree of multimerization to native C4BP, inhibited the association of Opa-expressing Gc with CEACAM3-CHO cells to the same degree as C4BP, while C4BP domains 1 and 2 fused to dimeric Fc (C4BP-IgG) did not. C4BP-IgM, but not C4BP-IgG bearing mutations to abrogate Fc gamma receptor interactions, blocked Opa-mediated phagocytosis by primary human neutrophils. These results support a model in which C4BP occludes Opa-CEACAM interactions, which protects Gc from phagocytic killing by neutrophils.

microbiology↗

bioRxiv2024

Neisseria gonorrhoeae scavenges host sialic acid for Siglec-mediated, complement-independent suppression of neutrophil activation

Gonorrhea, caused by the bacterium Neisseria gonorrhoeae (Gc), is characterized by neutrophil influx to infection sites. Gc has developed mechanisms to resist killing by neutrophils that include modifications to its surface lipooligosaccharide (LOS). One such LOS modification is sialylation: Gc sialylates its terminal LOS sugars with cytidine-5-monophosphate-N-acetylneuraminic acid (CMP-NANA) scavenged from the host using LOS sialyltransferase (Lst), since Gc cannot make its own sialic acid. Sialylation enables sensitive strains of Gc to resist complement-mediated killing in a serum-dependent manner. However, little is known about the contribution of sialylation to complement-independent, direct Gc-neutrophil interactions. In the absence of complement, we found sialylated Gc expressing opacity-associated (Opa) proteins decreased the oxidative burst and granule exocytosis from primary human neutrophils. In addition, sialylated Opa+ Gc survived better than vehicle treated or {Delta}lst Gc when challenged with neutrophils. However, Gc sialylation did not significantly affect Opa-dependent association with or internalization of Gc by neutrophils. Previous studies have implicated sialic acid-binding immunoglobulin-type lectins (Siglecs) in modulating neutrophil interactions with sialylated Gc. Blocking neutrophil Siglecs with antibodies that bind to their extracellular domains eliminated the ability of sialylated Opa+ Gc to suppress oxidative burst and resist neutrophil killing. These findings highlight a new role for sialylation in Gc evasion of human innate immunity, with implications for the development of vaccines and therapeutics for gonorrhea. IMPORTANCENeisseria gonorrhoeae, the bacterium that causes gonorrhea, is an urgent global health concern due to increasing infection rates, widespread antibiotic resistance, and its ability to thwart protective immune responses. The mechanisms by which Gc subvert protective immune responses remain poorly characterized. One way N. gonorrhoeae evades human immunity is by adding sialic acid that is scavenged from the host onto its lipooligosaccharide, using the sialyltransferase Lst. Here, we found that sialylation enhances N. gonorrhoeae survival from neutrophil assault and inhibits neutrophil activation, independently of the complement system. Our results implicate bacterial binding of sialic acid-binding lectins (Siglecs) on the neutrophil surface, which dampen neutrophil antimicrobial responses. This work identifies a new role for sialylation in protecting N. gonorrhoeae from cellular innate immunity, which can be targeted to enhance the human immune response in gonorrhea.

microbiology↗