Generation of stable cellular phenotypes in a human malignant cell line conditioned by alterations in the cellular microenvironment.

Microenvironmental conditions may result in phenotypic changes of malignant cells and/or selection of preexisting variants with a growth advantage under the new growth conditions. The present study was initiated to evaluate the stability of changes in crucial cellular attributes as induced in vivo by nonimmunological mechanisms. Expression of major histocompatibility antigens, membrane immunoglobulin, in vitro growth rate, chromosome complement, and modal chromosome number were thus examined in a human B-lymphoma line (RH-L4) prior to and after short-term passage through the peritoneal cavity or spleen of newborn mice. Seven sublines (four from spleen and three from peritoneal cavity) of RH-L4 cells were established after the passage. These lines were found to differ phenotypically from the original line in respect to several or all of the attributes that were studied. These differences were stable for greater than 100 cell generations. Analyses of major histocompatibility complex Class II antigen expression indicated that the modulation of this antigen was independent of the immunological competence of the mice and unrelated to cell cycle-dependent variations. The emergence of the variant sublines seemed not to reflect a microenvironmentally determined selection of minority subpopulation in the original RH-L4 lymphoma line but, instead, induced by the growth conditions in the cellular microenvironment in the mouse. It is suggested that inductive processes may be of importance in the generation of phenotypic diversity within individual tumor cell populations, including the generation of phenotypic variants with high metastatic activity.