Macrophages eliminate circulating tumor cells after monoclonal antibody therapy

The use of monoclonal antibodies (mAbs) as therapeutic tools has increased dramatically in the last decade and is now one of the mainstream strategies to treat cancer. Nonetheless, it is still not completely understood how mAbs mediate tumor cell elimination or the effector cells that are involved. Using intravital microscopy, we found that antibody-dependent phagocytosis (ADPh) by macrophages is a prominent mechanism for removal of tumor cells from the circulation in a murine tumor cell opsonization model. Tumor cells were rapidly recognized and arrested by liver macrophages (Kupffer cells). In the absence of mAbs, Kupffer cells sampled tumor cells; however, this sampling was not sufficient for elimination. By contrast, antitumor mAb treatment resulted in rapid phagocytosis of tumor cells by Kupffer cells that was dependent on the high-affinity IgG-binding Fc receptor (FcγRI) and the low-affinity IgG-binding Fc receptor (FcγRIV). Uptake and intracellular degradation were independent of reactive oxygen or nitrogen species production. Importantly, ADPh prevented the development of liver metastases. Tumor cell capture and therapeutic efficacy were lost after Kupffer cell depletion. Our data indicate that macrophages play a prominent role in mAb-mediated eradication of tumor cells. These findings may help to optimize mAb therapeutic strategies for patients with cancer by helping us to aim to enhance macrophage recruitment and activity

Generation of human IgG1 and IgG3 TA99 mAb with histidine-arginine rearrangements in Fc domains at amino acid position 435.

<p>Human IgG1 was mutated to contain an arginine at position 435 (IgG1 H435R), whereas the arginine at position 435 in human IgG3 was changed to histidine (IgG3 R435H). (<b>A</b>) Specific anti-human IgG1 or (<b>B</b>) anti-human IgG3 ELISA confirmed the correct isotype of mAbs. Staining of B16F10-gp75 with (<b>C</b>) different human TA99 mAb and (<b>D</b>) mouse TA99 IgG2a confirmed binding to surface gp75 and equal binding efficiency to gp75 of all human TA99 mAb. Concentration curves of human IgG1 and IgG3 mAb (<b>E</b>) and mouse IgG2a TA99 (<b>F</b>) on B16F10-gp75. Of note, scales of human (<b>E</b>) and mouse (<b>F</b>) antibodies are different.</p

Cytotoxicity assays using murine macrophages and B16F10-gp75 tumour cells.

<p>(<b>A</b>) Remaining B16F10-gp75 cells after a 24 hour incubation with macrophages and 2 μg/ml TA99 mAbs (different isotypes). (<b>B</b>) FACS analysis of co-cultures of DiO labelled murine macrophages (FL1) and DiI labelled B16F10-gp75 (FL2) tumour cells after 24 hours of treatment with 1 μg/ml mouse IgG2a or human IgG1 or IgG3 TA99 mAb. Macrophages, which have phagocytosed B16F10-gp75 tumour cells are encircled in FACS plots. (<b>C</b>) Percentage of remaining viable tumour cells and (<b>D</b>) increase in number of macrophages, which have phagocytosed B16F10-gp75 tumour cells after treatment of co-cultures with different concentrations of mAb. Percentages of tumour cells after culture with isotype antibodies were set at 100%. Double-positive macrophages were depicted relative to the co-cultures with isotype antibodies (set to 1), as described previously [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177736#pone.0177736.ref004" target="_blank">4</a>]. Mouse MG4 or human HEPC mAb were used as isotypes controls, which were set to 100%. *P<0.05, **P<0.01, ***p<0.001, ****p<0.0001.</p

Afucosylated igg targets fcγriv for enhanced tumor therapy in mice

Promising strategies for maximizing IgG effector functions rely on the introduction of natural and non-immunogenic modifications. The Fc domain of IgG antibodies contains an N-linked oligosaccharide at position 297. Human IgG antibodies lacking the core fucose in this glycan have enhanced binding to human (FcγR) IIIa/b, resulting in enhanced antibody dependent cell cytotox-icity and phagocytosis through these receptors. However, it is not yet clear if glycan-enhancing modifications of human IgG translate into more effective treatment in mouse models. We gener-ated humanized hIgG1-TA99 antibodies with and without core-fucose. C57Bl/6 mice that were injected intraperitoneally with B16F10-gp75 mouse melanoma developed significantly less metastasis outgrowth after treatment with afucosylated hIgG1-TA99 compared to mice treated with wildtype hhIgG1-TA99. Afucosylated human IgG1 showed stronger interaction with the murine FcγRIV, the mouse orthologue of human FcγRIIIa, indicating that this glycan change is functionally conserved between the species. In agreement with this, no significant differences were observed in tumor outgrowth in FcγRIV-/- mice treated with human hIgG1-TA99 with or without the core fucose. These results confirm the potential of using afucosylated therapeutic IgG to increase their efficacy. Moreover, we show that afucosylated human IgG1 antibodies act across species, supporting that mouse models can be suitable to test afucosylated antibodies

Epidermal Growth Factor Receptor as Target for Perioperative Elimination of Circulating Colorectal Cancer Cells

Surgical resection of the tumor is the primary treatment of colorectal cancer patients. However, we previously demonstrated that abdominal surgery promotes the adherence of circulating tumor cells (CTC) in the liver and subsequent liver metastasis development. Importantly, preoperative treatment with specific tumor-targeting monoclonal antibodies (mAb) prevented surgery-induced liver metastasis development in rats. This study investigated whether the epidermal growth factor receptor (EGFR) represents a suitable target for preoperative antibody treatment of colorectal cancer patients undergoing surgery. The majority of patients with resectable colorectal liver metastases were shown to have EGFR + CTCs. Three different anti-EGFR mAbs (cetuximab, zalutumumab, and panitumumab) were equally efficient in the opsonization of tumor cell lines. Additionally, all three mAbs induced antibody-dependent cellular phagocytosis (ADCP) of tumor cells by macrophages at low antibody concentrations in vitro, independent of mutations in EGFR signaling pathways. The plasma of cetuximab-treated patients efficiently opsonized tumor cells ex vivo and induced phagocytosis. Furthermore, neither proliferation nor migration of epithelial cells was affected in vitro, supporting that wound healing will not be hampered by treatment with low anti-EGFR mAb concentrations. These data support the use of a low dose of anti-EGFR mAbs prior to resection of the tumor to eliminate CTCs without interfering with the healing of the anastomosis. Ultimately, this may reduce the risk of metastasis development, consequently improving long-term patient outcome significantly

Trichuris suis induces human non-classical patrolling monocytes via the mannose receptor and PKC: implications for multiple sclerosis

Introduction: The inverse correlation between prevalence of auto-immune disorders like the chronic neuro-inflammatory disease multiple sclerosis (MS) and the occurrence of helminth (worm) infections, suggests that the helminth-trained immune system is protective against auto-immunity. As monocytes are regarded as crucial players in the pathogenesis of auto-immune diseases, we explored the hypothesis that these innate effector cells are prime targets for helminths to exert their immunomodulatory effects. Results: Here we show that soluble products of the porcine nematode Trichuris suis (TsSP) are potent in changing the phenotype and function of human monocytes by skewing classical monocytes into anti-inflammatory patrolling cells, which exhibit reduced trans-endothelial migration capacity in an in vitro model of the blood-brain barrier. Mechanistically, we identified the mannose receptor as the TsSP-interacting monocyte receptor and we revealed that specific downstream signalling occurs via protein kinase C (PKC), and in particular PKC delta. Conclusion: This study provides comprehensive mechanistic insight into helminth-induced immunomodulation, which can be therapeutically exploited to combat various auto-immune disorder

Human IgG3 with extended half-life does not improve Fc-gamma receptor-mediated cancer antibody therapies in mice

Current anti-cancer therapeutic antibodies that are used in the clinic are predominantly humanized or fully human immunoglobulin G1 (IgG1). These antibodies bind with high affinity to the target antigen and are efficient in activating the immune system via IgG Fc receptors and/or complement. In addition to IgG1, three more isotypes are present in humans, of which IgG3 has been found to be superior compared to human IgG1 in inducing antibody dependent cell cytotoxicity (ADCC), phagocytosis or activation of complement in some models. Nonetheless, no therapeutic human IgG3 mAbs have been developed due to the short in vivo half-life of most known IgG3 allotypes. In this manuscript, we compared the efficacy of V-gene matched IgG1 and IgG3 anti-tumour mAb (TA99) in mice, using natural variants of human IgG3 with short- or long half-life, differing only at position 435 with an arginine or histidine, respectively. In vitro human IgG1 and IgG3 did not show any differences in opsonisation ability of B16F10-gp75 mouse melanoma cells. IgG1, however, was superior in inducing phagocytosis of tumour cells by mouse macrophages. Similarly, in a mouse peritoneal metastasis model we did not detect an improved effect of IgG3 in preventing tumour outgrowth. Moreover, replacing the arginine at position 435 for a histidine in IgG3 to enhance half-life did not result in better suppression of tumour outgrowth compared to wild type IgG3 when injected prior to tumour cell injection. In conclusion, human IgG3 does not have improved therapeutic efficacy compared to human IgG1 in a mouse tumour mode