Quantitative assay of the lytic action of immune lymphoid cells on 51-Cr-labelled allogeneic target cells in vitro; inhibition by isoantibody and by drugs.

The in vitro cytotoxic effect of spleen cells of mice immunized by tumour allografts was studied by measuring target cell inactivation as a function of release of radioactive label (51Cr) or loss of cloning efficiency. When sensitized lymphoid cells were incubated with target cells at a ratio of 100:1, up to 90 per cent of the incorporated label was released within 6–9 hours, while the number of clone-forming cells was reduced by up to 99 per...