CELLULAR IMMUNOLOGY 45, l- 14 (1979) Cell-Mediated Cytostasis: A Critical Analysis of Methodological Problems M. I. C. GY~NGY~SSY,~ A. LIABEUF, AND P. GOLSTEIN Cenire d’lmmunologie INSERM-CNRS de Marseille-Luminy, Case 906. 13288 Marseille cPdex 2. France Received October 20. 1978 The experimental evidence supporting the existence of cell-mediated cytostasis (CMS) was examined according to some of the known various interactions taking place in culture systems. Possible sources of misinterpretation were (i) the culture conditions affecting label uptake, e.g., the shape of the culture vessel and the specific activity of the radiolabeled nucleoside; (ii) the degree of effector cell activation, stimulated effector cells taking up more label than nonstimulated cells; (iii) the effects of supematant giving a non-H-2 specific inhibition of label uptake but no corresponding decrease in cell number; and (iv) cytolytic effects generated during the culture. These effects, some of which can mimic CMS, were demonstrated experimentally and discussed. The reports in the literature on CMS were reviewed and compared to our experimental findings. It is concluded that experimental conditions for unambiguous demonstration of CMS may be very difficult to meet. INTRODUCTION The culture of tumor cells in the presence of a range of immunologically compe- tent. cells has led to results suggesting that some effector cells can exert an in- hibitory effect on the multiplication of their tumor targets. This in vitro phenomenon is called cell-mediated cytostasis (CMS). That one cell, by acting on another, can block its proliferation would not only be a potentially interesting immuno- logical phenomenon, but would have serious implications on surface-mediated cell interactions in general. However, a critical review of the literature and some experimental evidence prompts us to ask, does CMS exist as a distinct in vitro phenomenon? By definition, CMS is the inhibition of single tumor target cells’ ability to multiply, exerted by immunologically competent cells. It should be distinguished from population phenomena such as contact inhibition which occur in a population of normal but not tumor-derived or transformed cells in culture. It should also be reversible and as such distinct from cell-mediated cytolysis. The concept of CMS would be best supported if it included a component of immunological specificity, which, however, is not an essential part of its definition. Based on a critical examination of the CMS literature, as well as on our own ’ Present address: Department of Microbiology, University of Saskatchewan, Saskatoon, Saskatche- wan, Canada. 0008-8749/79/070001-14$02.00/O Copyright 0 1979 by Academic hess, Inc. All rights of reproduction in any form reserved.