Alternative Complement Pathway Inhibition Abrogates Pneumococcal Opsonophagocytosis in Vaccine-Naïve, but Not in Vaccinated Individuals

Abstract

To assess the relative contribution of opsonisation by antibodies, classical and alternative complement pathways to pneumococcal phagocytosis, we analyzed killing of pneumococci by human blood leukocytes collected from vaccine-naïve and PCV13-vaccinated subjects. With serotype 4 pneumococci as model, two different physiologic opsonophagocytosis assays based on either hirudin-anticoagulated whole blood or on washed cells from EDTA-anticoagulated blood reconstituted with active serum, were compared. Pneumococcal killing was measured in the presence of inhibitors targeting the complement components C3, C5, MASP-2, factor B or factor D. The two assay formats yielded highly consistent and comparable results. They highlighted the importance of alternative complement pathway activation for efficient opsonophagocytic killing in blood of vaccine-naïve subjects. In contrast, alternative complement pathway inhibition did not affect pneumococcal killing in PCV13-vaccinated individuals. Independent of amplification by the alternative pathway, even low capsule-specific antibody concentrations were sufficient to efficiently trigger classical pathway mediated opsonophagocytosis. In heat-inactivated or C3-inhibited serum, high concentrations of capsule-specific antibodies were required to trigger complement-independent opsonophagocytosis. Our findings suggest that treatment with alternative complement pathway inhibitors will increase susceptibility for invasive pneumococcal infection in non-immune subjects, but it will not impede pneumococcal clearance in vaccinated individuals.

Iptacopan monotherapy in patients with paroxysmal nocturnal hemoglobinuria: a 2-cohort open-label proof-of-concept study

“…It also blocks the amplification of classical and lectin pathway-dependent–C5 activation, although it does not impact amplification-independent complement activation via these pathways, which may potentially lead to lower infection risk in vaccinated patients as compared with other proximal complement inhibitors. 1, 16, 22, 23 Based on data from nonclinical and phase 1 studies, the pharmacokinetics of iptacopan is characterized by high absorption and moderate clearance (data on file). The main clearance pathway is hepatic metabolism (cytochrome P450 2C8-mediated oxidation, direct glucuronidation), followed by direct renal excretion (∼25%).…”

Alternative Complement Pathway Inhibition With Iptacopan for the Treatment of C3 Glomerulopathy-Study Design of the APPEAR-C3G Trial

“…This may be important in immunized individuals such that membrane attack complex-dependent killing of bacteria, such as Neisseria meningitidis, is maintained. 28 , 29 , 30 …”

“…In contrast, iptacopan, does not fully block the generation of MAC initiated by the C5 convertases of the classical and lectin pathways (C4b2aC3b) and therefore infection risk is theoretically lower. This may be important in immunized individuals such that MAC-dependent killing of bacteria, such as Neisseria meningitidis, is maintained [27][28][29] .…”

Inhibition of the different complement pathways has varying impacts on the serum bactericidal activity and opsonophagocytosis against Haemophilus influenzae type b

“…Neisseria meningitidis infections dominate ( 31 , 32 ), but it is recommended that children treated with eculizumab also receive vaccinations to prevent Streptococcus pneumoniae and Hib infections. As potential alternatives to C3 and C5 inhibitors, AP inhibitors are being developed and we have previously shown that AP inhibition abrogates meningococcal SBA and pneumococcal opsonophagocytosis in vaccine-naïve, but not in vaccinated individuals ( 33 , 34 ). Here we assessed the impact of complement inhibitors targeting C3, the AP (fB, fD), the lectin pathway (LP) (MASP-2) and the terminal pathway (C5) on both SBA and opsonophagocytic killing of Hib isolates by serum or reconstituted blood from individuals before and after vaccination with a capsule conjugate vaccine.…”

“…We have previously shown that AP inhibitors, which are being developed as potential alternatives to therapeutic C3 and C5 inhibitors, abrogate the killing of meningococci by SBA in pre-vaccination serum and the killing of pneumococci by opsonophagocytosis in pre-vaccination blood (33,34). In contrast, in serum or blood from vaccinated individuals, AP inhibitors had only a limited effect on bacterial In the present study, C3 and C5 inhibition blocked killing of Hib by SBA both in pre-and post-vaccination serum completely, while LP inhibition had no effect.…”