Poster Sessions

CANCER-4

Samuel Baron

S. Baron, J . Horowitz, J. Poast, A. Morrow, S. Fey, J. Finbloom, H. Schmeisser, J. Bekisz, K. Zoon

Eradication of Cultured Human Tumor Cells by Interferon-activated Monocytes

We previously reported eradication of low concentrations of human tumors treated with interferon-activated monocytes. Four out of five of the tumors were eradicated. In comparison, three human diploid cell types were not killed. This strong killing of tumor cells in 0.1 ml microtiter wells required104-5 monocytes, tumor cell contact and physiologic concentrations of types 1 and/or 2 interferons. The present study of much higher concentrations of tumor cells determined the mechanisms and conditions required for eradication. When the target dose of Ovcar 3 ovarian tumor cells or A549 lung tumor cells was increased from 103 to 105, the required number of interferon- activated monocytes was increased tenfold. Our studies indicated that the combined conditions for eradication of up to106 Ovcar 3 cells in microtiter wells were: (a) increasing the concentration of monocytes from 105 to 106; (b) interferon concentrations of greater than 0.1 ng per ml; (c) continuous presence of interferon; and (d) incubation of Ovcar 3 tumor cells with interferon-activated monocytes for at least two days. In addition, contaminating lymphocytes were shown not to cause the killing. These findings indicate for the first time that eradication of clinically-relevant concentrations of cultured human tumors by interferon-activated monocytes may be possible.