MARKERS OF IN VITRO INDUCED RESISTANCE OF B-LYMPHOBLASTOID CELL LINE IM-9 TO LYSIS BY LYMPHOKINE-ACTIVATED KILLER (LAK) CELLS
Interleukin-2-induced human lymphokine-activated killer cells were used for in vitro selection of resistance of B-lymphoblastoid cell line IM-9 to lysis by LAK cells. After eight procedures of treatment with effector cells selected IM-9 cells (termed as IM-9/SL-15 subline) reduced their susceptibility in JAM-test to LAK-induced cytolysis from 27.7 ± 5.6 to 5.0 ± 2.2%. The comparison of LAK-resistant IM-9/SL-15 cells with parental cell line revealed consistent changes in expression of phenotypic markers, cytogenetic features, and parameters of effector-to-target cell conjugation. Cytogenetic analysis clearly demonstrated that in contrast to parental cell line LAK-resistant IM-9/SL-15 subline was monoclonal cell population. IM-9/SL-15 cells overexpressed CD11a, CD11c, and CD18 while expression of CD21 and CD58 surface molecules decreased. IM-9/SL-15 cells revealed markedly decreased ability of conjugate formation with LAK cells in comparison with parental tumor cells. The binding curves for IM-9 and IM-9/SL-15 conjugation with LAK cells were markedly distinguished. The value of dissociation constant KD for [LAK]/[IM-9/SL-15] cell system was 2.4-fold higher as compared to one for [LAK]/[IM-9]. Cold target inhibition assay confirmed the differences observed in IM-9/SL-15 binding to LAK cells. At the same time no defined difference was found in the level of cell proliferation, expression of surface CD95/Fas and intracellular Bcl-2 proteins between IM-9 and IM-9/SL-15 cells. Thus the immune (LAK cell-mediated) selection of the resistance of B-lymphoblastoid IM-9 cells to killing by LAK cells is associated with the development of cytogenetic monoclonality of tumor cells, shift in adhesion molecules expression, decrease of conjugate formation with effector cells, but not with the changes in expression of apoptosis-related markers.
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