Abstract 458: B cell precursor ALL cells alter their immunophenotype, cell cycle, and chemosensitivity through contact with mesenchymal stromal cells
Authors: Kihira Kentaro , Hori Hiroki , Iwamoto Shotaro , Komada Yoshihiro 
Published: June 2012

Background: The outcome of B cell precursor ALL (BCP-ALL) in childhood has steadily improved, but 10 to 20 % of the patients still have recurrence of the disease. We speculate that BCP-ALL cells may obtain a characteristic of chemoresistance and similar phenotype of leukemic stem cell through the interaction with mesenchymal stromal cells (MSCs).

Materials and methods: Five BCP-ALL cell lines established from pediatric patients at author's institution were cultured in serum free medium. Primary BCP-ALL samples and specimens were obtained from patients with informed consents. Human bone marrow mesenchymal cells transfected with telomerase reverse transcriptase (hTERT) gene were passaged in cell culture medium with 10% fetal bovine serum and moved into serum free medium when incubating with leukemic cells. The BCP-ALL cells were analyzed in doubling time with time-lapsing images, and examined for expression of stem cell markers, hematopoietic stem/progenitor cell markers, and multidrug-resistance transporters with flowcytometry or confocal microscopy. Chemosensitivity of each cells to different anti-cancer drug were estimated by cell counting kit-8 (Doujindo) for suspending cells, and Vybrant cell adhesion assay kit (Invitrogen) for adherent cells.

Results: The doubling time of BCP-ALL adherent with MSCs were prolonged, compared with that of suspending cells. The suspending BCP-ALL cells incubated with or without MSCs showed positive to CD38 and negative to CD34, CD133, P-glycoprotein (Pgp), and BCRP/ABCG2, whereas the cells adherent with MSCs altered the expressions into CD34+, CD38-, CD133+, Pgp+, and BCRP/ABCG2+. The stem cell markers, Oct3/4, Nanog, SSEA-1 and Sox-2 were all negative in any condition. The alterations in phenotype were universally observed in all 5 cells examined. The primary bone marrow sample biopsied from a BCP-ALL patient was positive to CD34, CD133, Pgp and BCRP/ABCG2+ although that aspirated was all negative to those antibodies. BCP-ALL cells adherent with MSCs demonstrated remarkably decreased chemosensitivity against methotrexate, predonisolone, 6-mercaptoprine, vincristine, and cytrabine, compared with suspending cells.

Discussions: Although leukemic stem cells in BCP-ALL have not been proved, our data showed that BCP-ALL cells become positive to hematopoietic stem/progeniter cell surface markers such as CD34 and CD133, and obtain chemoresistance through contact with MSCs. The chemoresistance in BCP-ALL cells adherent with MSCs were suspected to result from expression of multidrug-resistant proteins. BCP-ALL cells may escape from cytotoxic effect of chemotherapeutic agents through interaction with MSCs.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 458. doi:10.1158/1538-7445.AM2011-458