Experimental Antibody Therapy of Liver Metastases Reveals Functional Redundancy between FcγRI and FcγRIV

Abstract

Many patients with colorectal cancer will develop liver metastases, even after successful surgical removal of the primary tumor at a time at which no visible metastases are present. We previously demonstrated that surgery--although mandatory--paradoxically enhances the risk of developing liver metastases. Because Ab therapy has been acknowledged as a successful strategy to treat malignancies, we studied the potential of postoperative adjuvant Ab therapy to prevent outgrowth of liver metastases. Treatment with murine anti-gp75 (TA99) mAb completely prevented outgrowth of B16F10 liver metastases in over 90% of mice. Therapeutic efficacy was maintained in either C1q- or complement receptor 3-deficient mice but was completely abrogated in FcR gamma-chain knockout mice. This indicates that the classical complement pathway was not essential, but interaction with activatory Fc gammaR was necessary for successful therapy. TA99-treatment was still effective in Fc gammaRI(-/-), Fc gammaRIII(-/-), Fc gammaRI/III(-/-), and Fc gammaRI/II/III(-/-) mice, suggesting an important role for Fc gammaRIV. However, wild-type mice that were treated with TA99 Abs and an Fc gammaRIV blocking Ab (mAb 9E9) were protected against development of liver metastases as well. Only when both Fc gammaRI and Fc gammaRIV functions were simultaneously inhibited, TA99-mediated curative Ab treatment was abrogated, indicating functional redundancy between both IgG receptors in the liver. Furthermore, depletion of liver macrophages (Kupffer cells) reduced the efficacy of Ab therapy, supporting that Kupffer cells are involved as effector cells. Importantly, since Ab treatment almost completely prevented development of liver metastases, postoperative adjuvant Ab therapy may help to improve patient prognosis.

FcγRIV deletion reveals its central role for IgG2a and IgG2b activity in vivo

“…Interestingly, blocking FcγRIV also afforded protection in model systems where FcγRIII knockout animals showed abrogation of IgG2a or IgG2b activity (20,22,23). A similar observation was made in models of antibody-mediated killing of melanoma cells, where blocking FcγRIV interfered with the activity of the therapeutic IgG2a antibody most severely on an FcγRI knockout background (14,21). Further studies in this direction are hampered by the fact that the available blocking antibody originates from hamster and becomes immunogenic after prolonged administration.…”

“…Several studies using blocking antibodies for FcγRIV indicated that this activating FcγR might play an important role for the activity of antitumor antibodies of the IgG2a and IgG2b subclass. Thus, in models of lung and liver metastases of melanoma cells and anti-CD20 antibody-dependent depletion of B cells, inhibition of FcγRIV activity resulted in the loss of the protective effects conferred by the therapeutic antibody (11,14,21). To gain further insight into the role of this receptor for the activity of anti-tumor antibodies of the IgG2a subclass, we turned to a s.c. melanoma model.…”

“…On the basis of protein sequence, genomic localization, and functional studies, mouse FcγRIV seems to be the ortholog to human CD16A, although it has some unique features, such as the capacity to bind to IgE with low affinity, and varies in its cellular expression pattern compared to its human counterpart (14,15,18,19). Using blocking antibodies, it was demonstrated that FcγRIV was essentially involved in IgG2a-and IgG2b-dependent killing of B cells, melanoma metastasis in the lung, and phagocytosis of platelets and red blood cells (11,14,15,(20)(21)(22). Moreover, blocking of this receptor protected animals from development of nephrotoxic nephritis and glomerular infiltration induced by IgG2a and IgG2b switch variants (23,24).…”

The role of Fcγ receptors in murine autoimmune thrombocytopenia

“…One of the dominant sources of FcγR expression in these organs are tissue-specific resident macrophages and endothelial cells. In the liver for example, Kupffer cells seem to express activating FcγRs in the spleen, red pulp macrophages are highly positive for FcγRs and thus could be involved in antibody-mediated platelet depletion [30]. In addition, strong FcγR expression can be detected on endothelial cells, although here, the dominant receptor seems to be the inhibitory FcγRIIB and probably FcγRIII to some degree.…”

“…This in vitro binding pattern reflects the importance of the individual FcγRs for the activity of the individual IgG subclasses in different in vivo model systems. Thus, IgG1 is essentially dependent on FcγRIII, whereas IgG2a and IgG2b are additionally dependent on FcγRI and FcγRIV [24][25][26][27][28][29][30][31]. The second distinguishing feature within the family of FcγRs is whether they transduce activating or inhibitory signals.…”