Role of Biologics in Fetal Hematologic Conditions: HDFN and FNAIT.

Maternal alloimmunization to fetal red cell and platelet antigens results in the formation of IgG antibodies that can be transported across the placenta. In more severe cases, the resulting hemolytic disease of the fetus/newborn (HDFN) is manifested by fetal anemia, hydrops and perinatal death. In the case of platelet alloimmunization, fetal/neonatal alloimmune thrombocytopenia (FNAIT) manifests as a decreased platelet count and intracranial hemorrhage. Intravenous immune globulin (IVIG) in red cell alloimmunization in cases where there has been early-onset HDFN in a previous pregnancy can result in a prolongation of the gestational age until intrauterine transfusions of red cells are needed in the treated pregnancy. In cases of maternal platelet alloimmunization, IVIG started at varying gestational ages and doses based on the severity of FNAIT in a previous pregnancy can improve perinatal outcomes. Nipocalimab, a humanized monoclonal antibody that blocks the neonatal Fc receptor, results in both a decrease in circulating levels of maternal IgG and decreased transplacental transport. This investigational drug is currently being studied through several randomized clinical trials in both HDFN and FNAIT.