Diminished placental Factor XIIIA1 expression associates with pre-conception antiretroviral treatment and preterm birth in pregnant people living with HIV.

We previously showed a link between maternal vascular malperfusion and pre-term birth (PTB) in pregnant people living with HIV (PPLH) initiating antiretroviral treatment (ART) before pregnancy, indicating poor placental vascularisation. After measuring antenatal plasma angiogenic factors to seek mechanistic insights, low levels of plasma Factor XIIIA1 (FXIIIA1) and vascular-endothelial-growth-factor (VEGF) was significantly associated with PTB at the time closest to delivery (median 34 weeks) in PPLH initiating ART before pregnancy. Knowing that FXIIIA1 is crucial for haemostasis, angiogenesis, implantation and pregnancy maintenance and that expression is found on placental macrophages (Hofbauer cells), we examined placentae at delivery from matching participants who either initiating ART before pregnancy or during gestation. Highest FXIIIA1 expression was on Hofbauer cells but was significantly lower in PTB regardless of HIV infection, but was significantly lower in PPLH in PTB from women who initiated ART before pregnancy. To test the hypothesis that antiretroviral drugs may disrupt vascularisation in the placenta, we used a human umbilical vein endothelial cell (HUVEC) matrigel angiogenesis assay. We identified that addition of pre-treated FXIIIA1-expressing MCSF- and IL-10-induced placenta-like macrophages with physiological concentrations of tenofovir, 3TC, and efavirenz resulted in significantly inhibited angiogenesis; akin to the inhibition observed with titratable concentrations of ZED1301, an inhibitor of FXIIIA1. Overall, an efavirenz-containing ART combination inhibits vasculogenesis without causing toxicity and likely does so through inhibition of a FXIIIA1-mediated-placental macrophage pathway.