title: Surface levels of CD20 determine anti-CD20 antibodies mediated cell death in vitro.
abstract: BACKGROUND
  The sensitivity of human Burkitt's lymphoma cells to rituximab (Rtx) and tositumomab (Tst) was assessed on cells expressing different levels of CD20 on surface. Cells that harbor low CD20 levels may resists against therapeutics response to CD20-specific antibodies. We postulated that, radiation-induced modulation of CD20 surface levels may play a crucial and central role in determining the relative efficacy of rituximab and tositumomab in treating Burkitt's lymphoma disease. Here, we examined the γ-radiation-induced CD20 expression in the Burkitt lymphoma cell line 'Daudi' and the relation of differential levels of CD20 with anti-CD20 mAbs mediated cell death.
  
  
  METHODS
  In this study we examined kinetics of CD20 expression following sub lethal doses ofγ-radiation to Daudi cells and thereafter anti-CD20 mAbs (rituximab and tositumomab) were added in cell suspensions. The correlation of kinetics of CD20 expression and cells treated with anti-CD20 mAbs/or corresponding isotype Abs with special reference to changes in mitochondrial membrane potential and reactive oxygen species generation was also examined. Further, we also investigated the efficacy of anti-CD20 mAbs and possible induction of cell death in relation to levels of CD20 cell surface expression.
  
  
  CONCLUSIONS
  This report provides evidence that CD20 expression can be induced by exposure of cells to γ-radiation. In addition, these findings demonstrated that the efficacy of anti-CD20 mAbs is dependent on the surface levels of CD20. Based on these findings, we hypothesized (i) irradiation just prior to immunotherapy may provide new treatment options even in aggressive B cell tumors, which are resistant to current therapies in vivo (ii) The efficacy of induction of apoptosis varies with type of monoclonal antibodies in vitro.
authors.affiliation: Division of Radiation Biosciences, Institute of Nuclear Medicine & Allied Sciences, Brig SK Mazumdar Marg, Timarpur, Delhi, India.
authors.forename: Vijay
authors.initials: V
authors.lastname: Singh
authors.affiliation: Division of Radiation Biosciences, Institute of Nuclear Medicine & Allied Sciences, Brig SK Mazumdar Marg, Timarpur, Delhi, India.
authors.forename: Damodar
authors.initials: D
authors.lastname: Gupta
authors.affiliation: Division of Radiation Biosciences, Institute of Nuclear Medicine & Allied Sciences, Brig SK Mazumdar Marg, Timarpur, Delhi, India.
authors.forename: Rajesh
authors.initials: R
authors.lastname: Arora
authors.affiliation: Division of Radiation Biosciences, Institute of Nuclear Medicine & Allied Sciences, Brig SK Mazumdar Marg, Timarpur, Delhi, India.
authors.forename: Rajendra Prashad
authors.initials: RP
authors.lastname: Tripathi
authors.affiliation: Department of Radiation Oncology, Taussig Cancer Institute, Cleveland Clinic, Cleveland, Ohio, United States of America; Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio, United States of America.
authors.forename: Alexandru
authors.initials: A
authors.lastname: Almasan
authors.affiliation: Department of Radiation Oncology, Taussig Cancer Institute, Cleveland Clinic, Cleveland, Ohio, United States of America.
authors.forename: Roger M
authors.initials: RM
authors.lastname: Macklis
mesh_terms: D058846:Antibodies, Monoclonal, Murine-Derived / Q000494:pharmacology*; D018951:Antigens, CD20 / Q000235:genetics / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D016130:Immunophenotyping; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D017382:Reactive Oxygen Species / Q000378:metabolism; D000069283:Rituximab
chemical_list: D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20; D000970:Antineoplastic Agents; D017382:Reactive Oxygen Species; D000069283:Rituximab