PURIFICATION OF CORD-BLOOD LYMPHOCYTES

When cord blood is separated using standard methods based on Ficoll-Hy paque, the mononuclear fraction is contaminated with erythrocytes and also with nucleated cells that do not express the leucocyte marker CD4 5. The contamination with CD45-negative cells can exceed 50%, and will interfere with phenotypic, mRNA or functional analysis, A large propo rtion of these cells are erythrocyte precursors. The contaminating cel ls may be removed by lysis with hypotonic ammonium chloride; when the cells are required for studies which are adversely affected by ammoniu m chloride (such as antigen processing), high purity can be attained b y two rounds of density separation.