Characterization of human lymphocyte subpopulations for cytotoxicity against tumor‐derived monolayer cultures

Lymphocyte fractions of three healthy donors were tested for cytotoxicity in a 48-h assay on several tumor-derived lines. Analysis of surface markers indicated that a non-T non-B fraction comprising about 50% Fc-receptor-positive cells was most potent. The cell yield in this fraction was on the average 6.5% of the non-fractionated population. Elimination of Slg positive cells did not influence the cytotoxic potential. Pure T cells isolated with E-rosetting subsequent to passage on nylon wool column had no or very low low cytotoxicity. We had indications that cells without conventional markers--"null" cells--were also cytotoxic.