Phenotypic analysis of fetal blood leucocytes: potential for prenatal diagnosis of immunodeficiency disorders.

Recent technological advances allow the detection and quantitation of subsets of leucocytes using monoclonal antibodies. We have taken advantage of this to study the ontogeny of fetal blood leucocytes, using very small blood samples obtained at fetoscopy. By 14 weeks gestation T cells represent 35 per cent or more of fetal leucocytes and the distribution of the helper/inducer and suppressor/cytotoxic subsets is similar to that of adults. B lymphocytes before 16 1/2 weeks are low (4-20 per cent), but rise to a mean of 28 per cent in 17-26 week fetuses. Granulocytic cells, many of which are phenotypically immature, represent 18-34 per cent of total leucocytes. The methodology employed is very reliable and offers the opportunity for the prenatal diagnosis of some immunodeficiency disorders, since using the same reagents we have diagnosed children with severe combined immunodeficiency shortly after birth.