Different Mechanisms of Resistance to Lymphokine-activated Killer (LAK) Cells in Leukemic Cell Sublines Selected by Etoposide or by LAK Cells.

Two models of in vitro induction of human IM-9 lymphoblastoid cell line resistance to LAK cell-mediated killing were compared. IM-9 cell line variants were selected in vitro by prolonged exposure to LAK cells or to etoposide. Sensitivity to killing by LAK cells or by etoposide, conjugation with LAK cells and surface marker patterns were compared. Both LAK-cell-selected cell subline (IM-9/SL-15) and etoposide-selected cell subline (IM-9/ER) have acquired resistance to LAK cell-mediated death. IM-9/ER cells, but not IM-9/SL-15 cells, were 3.2-fold less sensitive to etoposide as compared to parental IM-9 cells. IM-9/SL-15 cells revealed decreased conjugation with LAK cells and augmented CDlla/CD18 surface molecule expression as compared to IM-9 line. In contrast, IM-9/ER cells displayed a level of conjugation with LAK cells equal to IM-9 cells, but loss of CD11a/C18 expression. Our results suggest different mechanisms of acquired resistance to LAK cells are operative in etoposide- or LAK-selected sublines, involving deterioration of LFA-1 molecule expression and altered conjugation properties, respectively.

[Regenerating hematopoietic tissue as a source for a low molecular weight factor that inhibits leukemic cell proliferation]. / Regeneriruiushchaia krovetvornaia tkan' kak istochnik polucheniia nizkomolekuliarnogo faktora, ingibiruiushchego proliferatsiiu leikoznykh kletok.

Using a successive set of chromatographic methods, a low molecular weight factor inhibiting leukemic cells proliferation has been isolated from an aqueous extract of regenerating hematopoietic tissue. This factor inhibits DNA synthesis in leukemic cells about 1000-fold more effectively than the original extract. The factor activity does not change after treatment by proteinase K; however, successive action of endo-alpha-N-acetylgalactose aminidase and proteinase K significantly decreases the efficiency of the factor action. This factor whose molecular mass is less than 3 kDa seems to be of glycopeptide origin.

[Isolation of low-molecular weight fractions from the splenic tissue of calves that inhibit the proliferation of leukemic cells in mice]. / Poluchenie nizkomolekuliarnykh fraktsii iz tkani selezenki teliat, ingibiruiushchikh proliferatsiiu leikoznykh kletok myshei.

The three-stage scheme of extracting the low-molecular weight biologically active substances from spleen tissue has been suggested. It includes the following steps: adsorption chromatography on hydroxyapatite, ion-exchange chromatography on DEAE-matrices and gel-filtration. The resulting pool of low-molecular substances inhibits the 3H-thymidine incorporation into DNA of cultured leukemic cells.