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Human neutrophils mediate trogocytosis rather than phagocytosis of CLL B-cells opsonized with anti-CD20 antibodies

Rut Valgardsdottir, Irene Cattaneo, Christian Klein, Martino Introna, Marina Figliuzzi and Josée Golay

Key points

  • Human neutrophils mediate trogocytosis rather than phagocytosis of CD20 antibody opsonized CLL B cells

  • Trogocytosis is induced more effectively by rituximab compared to obinutuzumab

Abstract

Polymorphonuclear neutrophils (PMN) have previously been reported to mediate phagocytosis of anti-CD20 opsonized B-cells from CLL patients. However recent data have suggested that PMN, like macrophages, can also mediate trogocytosis. We have performed experiments to more precisely investigate this point and discriminate between trogocytosis and phagocytosis. In live cell time-lapse microscopy experiments, we could not detect any significant phagocytosis by purified PMN of anti-CD20-opsonized CLL B-cells, but only the repeated close contact between effectors and targets, suggesting trogocytosis. Similarly, in flow cytometry assays using CLL B-cell targets labeled with the membrane dye PKH67 and opsonized with rituximab or obinutuzumab, we could show that a mean of 50% and 75% of PMN had taken a fraction of the dye from CLL B-cells at 3 and 20 hours, respectively, with no significant decrease in absolute live or total CLL B-cell numbers, confirming that trogocytosis takes place, rather than phagocytosis. Trogocytosis was accompanied by loss of membrane CD20 from CLL B-cells, which was evident with rituximab but not obinutuzumab. We conclude that PMN mediate mostly trogocytosis rather than phagocytosis of anti-CD20-opsonized CLL B-cells and discuss the implications of this finding in CLL patients treated with rituximab or obinutuzumab in vivo.

  • Submitted August 23, 2016.
  • Accepted March 3, 2017.