Resistance to recombinant human granulocyte colony-stimulating factor in neonatal alloimmune neutropenia associated with anti-human neutrophil antigen-2a (NB1) antibodies.

Neonatal alloimmune neutropenia is the neutrophil counterpart of the erythrocyte disorder of hemolytic disease of the newborn. Fetal neutrophil antigens, which are inherited from the father but foreign to the pregnant mother, provoke the formation of maternal antibodies, which, on transplacental passage, cause fetal/neonatal neutropenia. Because infants with this disorder are at a higher risk of infection, recombinant hematopoietic growth factors, such as recombinant human granulocyte colony-stimulating factor, have been tried, with generally good results, to treat those with severe and prolonged neutropenia. We report a neonate who had neonatal alloimmune neutropenia associated with antibodies directed against human neutrophil antigen-2a (NB1) and initially failed to respond to even very high doses of recombinant human granulocyte colony-stimulating factor but eventually had a therapeutic response.