Human Factor H Domains 6 and 7 Fused to IgG1 Fc Are Immunotherapeutic against Neisseria gonorrhoeae

Abstract

Novel therapeutics against multidrug-resistant Neisseria gonorrhoeae are urgently needed. Gonococcal lipooligosaccharide (LOS) often expresses lacto-N-neotetraose (LNnT), which becomes sialylated in vivo, enhancing factor H (FH) binding and contributing to the organism’s ability to resist killing by complement. We previously showed that FH domains 18–20 (with a D-to-G mutation at position 1119 in domain 19) fused to Fc (FHD1119G/Fc) displayed complement-dependent bactericidal activity in vitro and attenuated gonococcal vaginal colonization of mice. Gonococcal LOS phase-variation can result in loss of LNnT expression. Loss of sialylated LNnT, although associated with a considerable fitness cost, could decrease efficacy of FHD1119G/Fc. Similar to N. meningitidis, gonococci also bind FH domains 6 and 7 through Neisseria surface protein A (NspA). Here we show that a fusion protein comprising FH domains 6 and 7 fused to human IgG1 Fc (FH6,7/Fc) bound to 15 wild-type antimicrobial resistant isolates of N. gonorrhoeae and to each of six lgtA gonococcal deletion mutants. FH6,7/Fc mediated complement-dependent killing of 8 of the 15 wild-type gonococcal isolates and effectively reduced the duration and burden of vaginal colonization of three gonococcal strains tested in wild-type mice, including two strains that resisted complement-dependent killing, but on which FH6,7/Fc enhanced C3 deposition. FH/Fc lost efficacy when Fc was mutated to abrogate C1q binding and in C1q−/− mice, highlighting the requirement of the classical pathway for its activity. Targeting gonococci with FH6,7/Fc provides an additional immunotherapeutic approach against multidrug-resistant gonorrhea.

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

“…A similar strategy was successfully demonstrated in a recent study showing the effectiveness of a chimeric anti-gonococcal antibody that recognizes LOS epitope and was modified to enhance complement activation through a single amino acid mutation in Fc (37). Besides, previous studies hampering FH recruitment by gonococci using 2 types of FH-IgG chimeric proteins showed resolution of gonococcal colonization in the same mouse model used here (7,38). Thus, both strategies may be useful adjunctives to antimicrobials.…”

“…Serum bactericidal assay. Bactericidal assays with NHS in the presence of C4BP-IgM fusion protein were performed similarly to those described previously (38). Briefly, bacteria were cultured on a chocolate agar plate overnight and subcultured on new plates for at least 5 hours with or without CMP-Neu5Ac, the latter in case of sialylated gonococci.…”

Antibacterial Fusion Proteins Enhance Moraxella catarrhalis Killing

“…Specifically the authors noted no enhanced complement deposition in tissues sections taken from the eyes and kidneys of FH6-7/IgG treated and untreated animals, either infected or not with S. pyogenes ( 22 ). Lastly, Shaughnessy et al ( 44 ) also observed no short term renal (increases in creatinine) or hematologic (increases in lactate dehydrogenase or decrease in hematocrit) or adverse side effects following systemic administration of FH6–7/IgG. Although this data is encouraging, future toxicology assessments are required and will take place during the preclinical development of these fusion proteins.…”

Role of Gonococcal Neisserial Surface Protein A (NspA) in Serum Resistance and Comparison of Its Factor H Binding Properties with Those of Its Meningococcal Counterpart

“…Based on the finding that N. gonorrhoeae also binds FH domains 6 and 7, we have fused these two domains with human IgG1 Fc to create FH SCR6-7/Fc. Ongoing work has shown that FH SCR6-7/Fc is effective against N. gonorrhoeae both in vitro and in vivo (77,78). We speculate that the use of FH SCR18-20/Fc and FH SCR6-7/Fc may provide additive or synergistic activity because these molecules bind to distinct targets on the bacterial membrane.…”