Effects of isolated tumor lymphocytes alone and with adherent cells.

The effect on the growth of gradient-isolated mouse mammary tumor cells of different populations of lymphoid cells were evaluated in microcytotoxicity assays. Variable effects were obtained with tumor-bearer lymph node and spleen cells: in some experiments growth stimulation occurred, whereas in others inhibition was observed. Mixed effector populations gave more regular results: adherent spleen cells added to lymph node or spleen lymphocytes inhibited tumor cell growth in six of nine experiments; inhibition occurred when either of the effector populations in the mixture was derived from the tumor-bearing mouse. Tumor-associated lymphoid cells (TAL) stimulated growth of the tumor cells in five of seven experiments. However, TAL inhibited tumor growth when combined with adherent spleen cells from tumor-bearing animals. In contrast with the peripheral lymphoid cells, admixture of control adherent cells from normal animals with TAL did not inhibit growth. No natural killer effect was seen in these growth inhibition assays. These data indicate that lymphoid populations capable of inhibiting tumor cell growth can be found in tumor-bearing animals, but such combination of active cells are not present in the tumor site.