Lymphocyte-mediated cytotoxicity against tumor cells

Spleen cells from Con A injected mice were cytotoxic to allogeneic tumor target cells in vitro. The degree of cytotoxicity was dependent upon the dose of Con A injected. Cytotoxicity did not occur when the lymphocytes were syngeneic to the targets. However, when extraneous Con A was added to the mixture of syngeneic lymphocytes and target cells, cytotoxicity occurred to the same extent as that found in allogeneic combinations without addition of Con A. Analogous findings were made in vitro by activating spleen cells with Con A. Only allogeneic lymphocytes caused cytotoxicity after treatment with α MM to remove surface bound Con A. However, extraneously added Con A also caused expression of cytotoxicity with syngeneic and semisyngeneic Con A activated lymphocytes. It is concluded that Con A transforms lymphocytes into cytotoxic effector cells, but these cells cannot express cytotoxicity unless they can bind to the target cells. Allogeneic Con A activated lymphocytes probably recognize the target cells by clonally distributed recognition receptors, and are therefore capable of binding to the targets by themselves. Syngeneic and semi-syngeneic cells, on the other hand, do not possess such receptors, and consequently can only express cytotoxicity when agglutinated to the targets by extraneous agents such as Con A.