Protective effect of a synthetic peptide mimicking the b2GPI PL-binding site on aPL-induced placental damage

Purpose: b2GPI-dependent aPL can cause recurrent pregnancy loss & pregnancy complications by triggering placental thrombosis & by reacting with b2GPI expressed on trophoblast & decidual cells. aPL mediate a local inflammatory process & functional trophoblast/decidual cell abnormalities leading to a defective placentation. A 20 aa CMV derived synthetic peptide (TIFI) sharing similarity with the putative PL-binding site in the Vth domain of b2GPI reverses aPL-mediated thrombosis in vivo & inhibits in vitro binding of FITC b2GPI to human endothelium & murine monocytes. Aim of the study was to investigate the ability of TIFI to protect pregnant naïve mice from aPL-induced foetal loss. Methods: In vivo studies. Pregnant C57BL/6 mice were injected with IgG from APS patients (aPL-IgG) or with normal human IgG (NHS-IgG) (50 μg iv the day after mating - day 0). Treated animals were divided into: group A which received 40 ug of TIFI/mouse i.p. 30 min before the infusion of IgG at day 0, & at day 5 & 10 of pregnancy; group B which received 40 ug of a control peptide (VITT) & group C which received saline at the same times. 20 animals/group were studied. The animals were sacrificed at day 15 of pregnancy & the placentas/foetuses collected & analyzed for weight & histology as described (Martinez de la Torre et al PNAS 2007;104:2319-24). In vitro studies: binding of aPL-IgG & human b2GPI-dependent aPL IgG mAb (IS3) to human trophoblast & decidual cell monolayers was investigated as described (Di Simone et al Arthritis Rheum 2000;43:140-51); aPL binding was evaluated in the presence or in the absence of serial concentrations of TIFI or VITT (5-20 ug/ml). Results: aPL-IgG treated animals displayed: higher number of foetal losses & reduced placental/foetal weights vs animals treated with NHS-IgG (p< 0.01). Control peptide (VITT) treatment did not display any effect, while the number of animals with foetal loss & histological lesions at the foetal placental side were significantly reduced after TIFI injection (p<0.01).TIFI, but not VITT, displayed a dose-dependent inhibitory effect on both polyclonal aPL IgG fraction & IS3 mAb binding to trophoblast & decidual cell monolayers in vitro. Conclusions: a synthetic peptide sharing similarity with the putative b2GPI PL-binding site reverses aPL-mediated foetal loss in pregnant naïve mice & inhibits the binding of b2GPI-dependent aPL to human trophoblast & decidual cells. These findings further support the pathogenic role of anti-b2GPI antibodies on aPL-associated fetal loss & offer innovative therapeutic approaches.