Rituximab-CD20 Complexes Are Shaved from Z138 Mantle Cell Lymphoma Cells in Intravenous and Subcutaneous SCID Mouse Models

Abstract

Infusion of standard-dose rituximab (RTX) in chronic lymphocytic leukemia (CLL) patients promotes rapid complement activation and deposition of C3 fragments on CLL B cells. However, immediately after RTX infusions, there is substantial loss (shaving) of CD20 from circulating malignant cells. Because shaving can compromise efficacies of anticancer immunotherapeutic mAbs, we investigated whether shaving occurs in SCID mouse models. Z138 cells, a B cell line derived from human mantle cell lymphoma, were infused i.v. or s.c. The i.v. model recapitulates findings we previously reported for therapeutic RTX in CLL: i.v. infused RTX rapidly binds to Z138 cells in lungs, and binding is accompanied by deposition of C3 fragments. However, within 1 h targeted cells lose bound RTX and CD20, and these shaved cells are still demonstrable 40 h after RTX infusion. Z138 cells grow in tumors at s.c. injection sites, and infusion of large amounts of RTX (0.50 mg on each of 4 days) leads to considerable loss of CD20 from these cells. Human i.v. Ig blocked shaving, suggesting that FcγRI on cells of the mononuclear phagocytic system promote shaving. Examination of frozen tumor sections from treated mice by immunofluorescence revealed large areas of B cells devoid of CD20, with CD20 intact in adjacent areas; it is likely that RTX had opsonized Z138 cells closest to capillaries, and these cells were shaved by monocyte/macrophages. The shaving reaction occurs in neoplastic B cells in tissue and in peripheral blood, and strategies to enhance therapeutic targeting and block shaving are under development.

Within Peripheral Blood Mononuclear Cells, Antibody-Dependent Cellular Cytotoxicity of Rituximab-Opsonized Daudi cells Is Promoted by NK Cells and Inhibited by Monocytes due to Shaving

“…In contrast, the high affinity receptor Fc␥RI can rapidly recycle and promote very efficient endocytosis of small IgG-containing immune complexes (67)(68)(69)(70). Our in vitro experiments and findings in mouse models (46,71) suggest that it is this high affinity receptor that is primarily responsible for CD20 shaving when patients receive high doses of RTX, which temporarily saturates the clearance capacity of the body (46).…”

Plasma‐dependent, antibody‐ and Fcγ receptor‐mediated translocation of CD8 molecules from T cells to monocytes

“…Recently, another mechanism of trogocytosis mediated by Ag/Ab immune complexes and FccRs on acceptor cells was identified (6). This mechanism is well characterized as the phenomenon wherein CD20 molecules on malignant B cells are lost after infusion of the humanized anti-CD20 mAb, rituximab (23,24). In this situation, FccR 1 immune cells, such as monocytes, accept the CD20/anti-CD20 immune complexes from B cells.…”

Translational Medicine in Action: Anti-CD20 Therapy in Lymphoma

“…We found that the level of the complement defense molecules CD46, CD55, and CD59 on lymphoma cells did not correlate, either negatively or positively, with responses to rituximab (50). A series of comprehensive studies from Taylor and colleagues (51)(52)(53) showed trogocytosis as a potential mechanism of rituximab resistance. Trogocytosis is a process whereby phagocytic cells selectively remove bound Ag/IgG complexes (CD20/rituximab, in this case) from the surface of target cells rather than phagocytose them (51,52).…”

“…A series of comprehensive studies from Taylor and colleagues (51)(52)(53) showed trogocytosis as a potential mechanism of rituximab resistance. Trogocytosis is a process whereby phagocytic cells selectively remove bound Ag/IgG complexes (CD20/rituximab, in this case) from the surface of target cells rather than phagocytose them (51,52). Consequently, the target cells are no longer opsonized and are able to escape detection by immune effector cells.…”