Paternal HLA-Derived Epitopes and Live Birth in Secondary Recurrent Pregnancy Loss: New Insights From a Clinical Trial

Recurrent pregnancy loss (RPL), defined as two or more pregnancy losses before the 24th week of gestation, affects 1%–3% of women worldwide. Approximately, 40% of RPL cases are secondary RPL (sRPL), where women have given birth before facing pregnancy losses. The underlying causes of RPL remain unclear, but immune-related factors may play a role. Previously, a randomised controlled trial using immunoglobulin (IVIG) in sRPL women with a history of four pregnancy losses performed in our RPL unit did not show significant effects of IVIG treatment overall. Yet, some evidence suggests potential benefits for a subset of sRPL patients. In the cohort used for the randomised controlled trial, we examined the role of maternal HLA class II-presented fetal HLA-derived epitopes in sRPL using the predicted indirectly recognisable HLA epitopes (PIRCHE-II) algorithm. In the placebo group, sRPL mothers with an anti-HLA antibody response had higher PIRCHE-II scores when having a live birth compared with sRPL women who experienced another pregnancy loss. This difference was not observed in the IVIG-treated group. Furthermore, as a proxy for T-cell memory, the number of overlapping peptides between the two paternal haplotypes in couples having live births without treatment displayed a larger number of overlapping peptides. This effect was primarily driven by class II-derived peptides. These results suggest that specific combinations of sRPL mothers and fathers, particularly those with an anti-HLA antibody response, may generate higher PIRCHE-II scores, which could contribute to successful live births. Understanding these immune interactions may provide insights for personalised diagnostic and therapeutic strategies in sRPL.