title: Membrane microdomain sphingolipids are required for anti-CD20-induced death of chronic lymphocytic leukemia B cells.
abstract: BACKGROUND
  Chronic lymphocytic leukemia remains incurable, despite the addition of rituximab to chemotherapy as an available means of treatment. The resistance of certain patients to this monoclonal antibody prompted us to set up in vitro studies of another CD20-specific monoclonal antibody, B1 (later termed tositumomab). We hypothesized that the membrane lipid organization of leukemic B cells might be instrumental in the cells' sensitivity to the B1 monoclonal antibody.
  
  
  METHODS
  B lymphocytes from 36 patients with chronic lymphocytic leukemia and 13 patients with non-Hodgkin's lymphoma were investigated for B1-triggered cell death. Membrane components, such as sphingomyelin and ganglioside M1, were investigated by flow cytometry, immunofluorescence and co-immunoprecipitation, together with the Csk-binding protein.
  
  
  RESULTS
  Chronic lymphocytic leukemia patients segregated into two groups: B cells from one group were sensitive to B1, whereas those from the second group were not. Further results ascribed the resistance of these latter cases to a defective recruitment of Csk-binding protein, resulting in a lack of sphingomyelin and ganglioside M1 at the outer leaflet of the plasma membrane of their malignant B cells. Sphingolipids were indeed retained in the cytoplasm, because of lowered activity of P-glycoprotein. Supporting this mechanism, rifampicin, an inducer of P-glycoprotein, improved the activity of this transmembrane efflux pump, normalized the quantity of sphingomyelin within the membrane, and thereby restored the efficacy of the B1 monoclonal antibody in the formerly B1-resistant cases of chronic lymphocytic leukemia.
  
  
  CONCLUSIONS
  The lipid organization of membranes of B cells from patients with chronic lymphocytic leukemia differs from one patient to another. In practice, given the relevance of the membrane lipid distribution to the efficacy of biotherapies, this observation is of potential importance.
authors: EA2216 Immunology & Pathology, and IFR 148 ScInBioS, European University of Brittany, France.
authors: Mariam
authors: M
authors: Hammadi
authors: Pierre
authors: P
authors: Youinou
authors: Adrian
authors: A
authors: Tempescul
authors: Gabriel
authors: G
authors: Tobón
authors: Christian
authors: C
authors: Berthou
authors: Anne
authors: A
authors: Bordron
authors: Jacques-Olivier
authors: JO
authors: Pers
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000911:Antibodies, Monoclonal / Q000494:pharmacology* / Q000627:therapeutic use; D018951:Antigens, CD20 / Q000378:metabolism*; D001402:B-Lymphocytes / Q000187:drug effects / Q000378:metabolism*; D016923:Cell Death; D002478:Cells, Cultured; D005260:Female; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000188:drug therapy / Q000378:metabolism*; D008297:Male; D021962:Membrane Microdomains / Q000187:drug effects / Q000378:metabolism*; D008875:Middle Aged; D013107:Sphingolipids / Q000096:biosynthesis*
chemical_list: D000911:Antibodies, Monoclonal; D018951:Antigens, CD20; D013107:Sphingolipids