Here, we investigated the impact of TPE on serum sB7-H4, an immunological checkpoint molecule, and placental proteins (Flt-1, Eng, B7-H4, iNOS, TNF-α) in TPE-treated early-onset preeclampsia patients (N = 12, 23 + 2–28 + 5 weeks), conventionally treated counterparts (N = 12, 23 + 5–30 weeks), and gestational age-matched controls (N = 8, 22 + 4–31 + 6 weeks). The gene discussed is FLT1; the disease is preeclampsia.