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

Abstract

Polymorphonuclear neutrophils (PMNs) have previously been reported to mediate phagocytosis of anti-CD20-opsonized B cells from patients with chronic lymphocytic leukemia (CLL). However, recent data have suggested that PMNs, like macrophages, can also mediate trogocytosis. We have performed experiments to more precisely investigate this point and to discriminate between trogocytosis and phagocytosis. In live-cell time-lapse microscopy experiments, we could not detect any significant phagocytosis by purified PMNs of anti-CD20-opsonized CLL B cells, but could detect only the repeated close contact between effectors and targets, which suggested trogocytosis. Similarly, in flow cytometry assays using CLL B-cell targets labeled with the membrane dye PKH67 and opsonized with rituximab or obinutuzumab, we observed that a mean of 50% and 75% of PMNs 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 occurs, 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 PMNs mediate mostly trogocytosis rather than phagocytosis of anti-CD20-opsonized CLL B cells, and we discuss the implications of this finding in patients with CLL treated with rituximab or obinutuzumab in vivo.