B-lymphoma cells escape rituximab-triggered elimination by NK cells through increased HLA class I expression
Received 6 October 2009; received in revised form 11 December 2009; accepted 28 December 2009. published online 06 January 2010.
Objective
Antibody-dependent cellular cytotoxicity (ADCC) by natural killer (NK) cells is a major effector mechanism of the monoclonal anti-CD20 antibody rituximab in eliminating B-cell lymphomas. Resistance to this treatment occurs, although CD20 antigen is expressed on the tumor cells.
Materials and Methods
A model of ADCC was established by stimulating human bulk NK cells and inhibitory killer immunoglobulin receptor (KIR)−defined NK cells from human leukocyte antigen (HLA)−typed donors. NK-cell activation was triggered via stimulation of the Fc receptor with immunoglobulin G aggregates, rituximab-labeled HLA-defined CD20-positive B-lymphoblast cell lines or CD20-positive B-lymphoma cell lines. The effect of KIR ligation by anti-KIR antibodies and HLA, the HLA expression density and rituximab concentrations on the efficacy of ADCC were analyzed in granzyme B ELISPOT measuring NK-cell activation and fluorescein-activated cell sorting cytotoxicity assay.
Results
HLA, but not CD20 expression density correlated with NK-cell activity against rituximab-labeled targets. ADCC was increased or decreased following HLA shielding or KIR activation by anti-KIR antibodies, respectively. Herein we show that rituximab-induced ADCC is attenuated upon ligation of KIR by HLA molecules expressed on human B-lymphoma target cells. Moreover, anti-KIR antibodies do not only block KIR/HLA interactions, but display agonistic effects at the KIR, which has to be considered for therapeutical applications.
Conclusion
KIR activation and HLA expression density are critical determinants for the efficacy of rituximab treatment. An explanation for the failure of rituximab treatment may be the protection of the tumor cells from ADCC by inhibiting NK-cell function with their surface HLA.
aDepartment of Haematology and Oncology, Georg-August University of Göttingen, Göttingen, Germany
bDepartment of Cellular and Molecular Immunology, Georg-August University of Göttingen, Göttingen, Germany
cAsklepios Clinic St. Georg, Department of Haematology and Stem Cell Transplantation, Hamburg, Germany
Offprint requests to: Andrea Borgerding, M.D., Department of Hematology and Oncology Georg-August University of Göttingen, Robert-Koch-Strasse 40, 37075 Göttingen, Germany
ABSTRACT