The cells of origin of lymphocyte clones grown by limiting dilution

A high proportion of the mononuclear cells separated from peripheral blood by Ficoll-Hypaque centrifugation show extensive proliferation when cloned at limiting dilution. The nature of clone-forming cells (CFCs) and the cells generated during clone formation were studied by cytotoxicity with antibody and complement and by immunofluorescence. Cytotoxicity prior to cloning with OKT3 plus OKT11 eliminated 99.34% of clones, indicating that virtually all CFCs are T-lymphocytes, and cytotoxicity with OKT4 or OKT8 indicated that helper and suppressor subclasses each contribute approximately half of the CFCs. Immunofluorescence of cells proliferating in clones confirmed that all clones were T-lymphocytes and showed that 47% were OKT4 positive and 47% were OKT8 positive; 6% were negative with both OKT4 and OKT8. The results indicate that in the nearly optimal conditions for proliferation provided by limiting dilution, clones arise entirely from T-lymphocytes and clone formation is a property of a variety of lymphocyte subclasses.