Factor H–IgG Chimeric Proteins as a Therapeutic Approach against the Gram-Positive Bacterial PathogenStreptococcus pyogenes

Abstract

Bacteria can cause life-threatening infections, such as pneumonia, meningitis or sepsis. Antibiotic therapy is a mainstay of treatment, although antimicrobial resistance has drastically increased over the years. Unfortunately, safe and effective vaccines against most pathogens have not yet been approved, thus developing alternative treatments is important. We analyzed the efficiency of FH6-7/Fc, a novel antibacterial immunotherapeutic protein against the gram-positive bacterium Streptococcus pyogenes. This protein is composed of two domains of complement inhibitor human factor H (FH complement control protein modules 6 and 7) that bind to S. pyogenes, linked to the Fc region of IgG (FH6-7/Fc). FH6-7/Fc has previously been shown to enhance complement-dependent killing of and facilitate bacterial clearance in animal models of the gram-negative pathogens, Haemophilus influenzae and Neisseria meningitidis. We hypothesized that activation of complement by FH6-7/Fc on the surface of bacteria gram-positive bacteria such as S. pyogenes will enable professional phagocytes to eliminate the pathogen. We found that FH6-7/Fc alleviated S. pyogenes induced sepsis in a transgenic mouse model expressing human FH (S. pyogenes bind FH in a human-specific manner). Furthermore, FH6-7/Fc, which binds to Protein H and select M proteins, displaced FH from the bacterial surface, enhanced alternative pathway activation and reduced bacterial blood burden by opsonophagocytosis in a C3-dependent manner in an ex vivo human whole-blood model. In conclusion, FH-Fc chimeric proteins could serve as adjunctive treatments against multidrug-resistant bacterial infections.

C4BP-IgM protein as a therapeutic approach to treat Neisseria gonorrhoeae infections

“…Because complement-inhibitory activity of C4BP requires the third CCP domain (23), these fusion proteins should not inhibit complement, while they should preserve the ability to deposit on bacteria. Previous work by our groups have shown that a chimeric protein that comprises the microbial binding domains of another complement inhibitor, factor H (FH), fused to Fc is efficacious in vitro and in vivo against Streptococcus pyogenes (24), N. gonorrhoeae (7), N. meningitidis (25), and Haemophilus influenzae (26) and provided the rationale for targeting N. gonorrhoeae-C4BP interactions. The isolates are grouped according to their expressed subclass of PorB and anatomical site of isolation.…”

Antibacterial Fusion Proteins Enhance Moraxella catarrhalis Killing

“…FreeStyle Chinese hamster ovary (CHO) S suspension cells (Life Technologies), grown in FreeStyle CHO expression medium supplemented with 8 mM L-glutamine were used for the expression of FH6-7/IgG fusion protein as described ( 22 ). Cell cultures were grown in 250 ml Erlenmeyer flasks at 37°C with 8% CO 2 with shaking (130 rpm).…”

“…The net result is displacement of complement inhibitors from the bacterial surface with simultaneous complement activation via Fc-C1q interaction, which increases pathogen elimination. This approach has shown promise in enhancing killing of Non-typeable Haemophilus influenzae (NTHi) ( 20 ), Neisseria meningitidis ( 18 ), Neisseria gonorrhoeae ( 19 , 21 ), and Streptococcus pyogenes ( 22 ). In this study we tested the bactericidal activity of both fusion proteins against M. catarrhalis .…”

Catch Me if You Can: <b><i>Streptococcus pyogenes</i></b> Complement Evasion Strategies

“…Using S. pyogenes as an example, we investigated if FH-IgG would have an antibacterial effect on Gram-positive bacteria as well. Indeed, we observed binding of FH-IgG to the bacteria and a displacement of serum FH from the bacterial surface, leading to increased MAC deposition [22]. Increased killing, however, was not observed in serum sensitivity assays, but only when co-incubated in whole blood.…”

“…Similar to M proteins, protein H also presents a coiled-coil dimer structure with a heptad repeat pattern [21]. It can bind to a variety of human serum proteins, such as albumin, the complement inhibitors FH and C4BP, and IgG, via their Fc portion [12, 14, 15, 22]. Interestingly, certain ligands such as IgG or albumin as well as temperature can influence the structure of protein H and the M proteins [21, 23].…”