Accordingly, there was no recovery of FVIII activity 30 min after FVIII injection to the BM/FVIII, while FVIII c-Met inhibitor recovery in BM/PBS was 0·69 ± 0·15 IU/ml (Supporting information
Fig. S1). In the case of BM/PBS mice, an anti-FVIII immune response developed with kinetics similar to that previously described;12 anti-FVIII IgG developed from the third FVIII administration and titres reached 767·6 ± 271·5 μg/ml after the fifth FVIII administration. In contrast, BM/FVIII mice developed negligible anti-FVIII IgG titres even 5 days after the fourth administration of FVIII (15 ± 19·4 μg/ml), compared with BM/PBS mice (179·5 ± 138 μg/ml, P < 0·01). In BM/FVIII mice, however, anti-FVIII IgG development initiated after the fifth injection of FVIII (103·3 ± 94 μg/ml) and reached 460 ± 278·2 μg/ml after a sixth FVIII administration. Similar results were obtained when inhibitory titres were measured in the serum of the mice using a Bethesda assay (Fig. 2b). Importantly, transfer of maternal anti-FVIII IgG influenced neither the total levels of circulating
IgG in the offspring (Fig. 2c), nor the capacity of the histone deacetylase activity offspring to mount classical immune responses to an unrelated exogenous antigen such as OVA (Fig. 2d). We then analysed the effect of the transfer of maternal anti-FVIII IgG on FVIII-specific cellular immune responses. Splenocytes from BM/FVIII and BM/PBS mice administered five times with FVIII, were stimulated with FVIII in vitro. T cells from BM/FVIII and BM/PBS mice demonstrated identical capacities to proliferate in the presence of concanavalin A (Fig. 2e). In contrast, splenocytes from BM/FVIII mice marginally proliferated upon stimulation with FVIII compared
with splenocytes from BM/PBS mice; the ratios of stimulation indices being 1·63 ± 0·38 versus 3·09 ± 0·83, respectively (P < 0·05). Together, the data suggest that the transfer of anti-FVIII IgG from the mother to the progeny is associated with a reduced capacity to develop an anti-FVIII immune response. The transfer of maternal IgG to the offspring occurs during gestation through the placenta and during lactation through the intestinal epithelium.4 We investigated which of the two types of transfer is critical to impair the capacity of the progeny to develop an antigen-specific during immune response. Mothers of BM/FVIII and BM/PBS mouse pups were interchanged at the time of birth so that some BM/PBS pups received anti-FVIII IgG during lactation (B/PBSM/FVIII) and some BM/FVIII pups did not receive antibodies from birth until the start of the FVIII immunization protocol (B/FVIIIM/PBS). In parallel, some BM/FVIII and BM/PBS pups were kept with their original mothers (referred to as B/FVIIIM/FVIII and B/PBSM/PBS, respectively). The pups were weaned at 5 weeks of age. At 8 weeks of age, B/FVIIIM/PBS mice did not have residual maternal anti-FVIII IgG, as assessed by ELISA (Fig.