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.