Effect of LAK cells against three-dimensional tumor tissue. In vitro study using multi-cellular human glioma spheroids as targets.

The anti-tumor mechanisms of local LAK cell therapy are difficult to study in vivo. We describe a method to study in vitro the action of LAK cells against three-dimensional tumor tissue. Spherical cell aggregates (spheroids) grown from human glioma cell lines H-2 and U-251 were labeled with 51Cr and then incubated for up to 24 h with LAK cells. After the incubation, most spheroids were still macroscopically identifiable, and the measured reduction of volume did not correlate to the extent of damage. LAK cells infiltrated into spheroid tissue slowly as a frontier which explains why the specific 51Cr release was clearly slower from spheroids than corresponding single cell suspensions. The infiltrated area was at 1 to 2 h very thin but by 8 to 12 h consisted already of several cell layers. Most H-2 spheroids became totally infiltrated by 16 to 24 h whereas in U-251 spheroids the infiltration usually remained peripheral. In accordance with the different extent of infiltration, H-2 spheroids were clearly more sensitive to LAK cells than U-251 spheroids: at E/T ratio 10:1 the mean specific 51Cr release by 24 h was 63 and 36%, respectively. A single exposure to LAK cells released 51Cr from H-2 spheroids approximately 12 h but over 24 h from U-251 spheroids. The spheroid model can be used to study the infiltrative capacity and cytotoxicity of LAK cells against three-dimensional tumor tissue, and the method may help to find an optimal mode of local LAK cell therapy, i.e., proper combination of lymphokines and LAK cells, and proper timing of their administration.