Two Populations of Mouse Lymphokine‐activated Killer Cells Separated by Use of Soybean Agglutinin

We separated lymphokine‐activated killer (LAK) cells induced from spleen cells of BALB/c mice by culturing with recombinant interleukin‐2 (rIL‐2) into soybean agglutinin‐positive (SBA(+)) and soybean agglutinin‐negative (SBA(‐)) fractions with a cell sorter at the time when LAK activity reached a maximum (day 3). We found that the cells with LAK activity were enriched in the SBA(+) fraction. Analysis of cell surface phenotypes revealed that the SBA(+) cells are of non‐T cell origin, while the SBA(‐) fraction consists of T cells. We also found that the large granular lymphocyte (LGL) fraction of spleen cells obtained with a Percoll gradient became SBA(+) after culture for 3 days with rIL‐2, whereas cells of high density did not. The change in SBA binding sites was also examined on C57BL/6 mouse spleen cells and we found that NK1.1(+) non‐T cells selectively acquire SBA binding sites at an early stage of activation with rIL‐2. On the other hand, sorted SBA(‐) cells gradually acquired SBA binding sites on extended culturing with rIL‐2. These results suggest that the expression of SBA binding sites is related to the stage of cell activation with rIL‐2, though cells of the NK‐lineage became SBA(+) at an earlier period of a culture with rIL‐2 than cells of the T‐lineage. Utilizing these findings, we separated NK‐derived LAK cells by means of SBA‐binding, and used the separated cells for adoptive immunotherapy for experimental pulmonary metastasis. We found that SBA(+)‐NK cell‐derived LAK cells showed stronger activity for the inhibition of experimental pulmonary metastasis than SBA ‐T cell‐derived LAK cells.