Enhancement of the anti-melanoma response of Hu14.18K322A by αCD40 + CpG

Targeted monoclonal antibodies (mAb) can be used therapeutically for tumors with identifiable antigens such as disialoganglioside GD2, expressed on neuroblastoma and melanoma tumors. Anti-GD2 mAbs (αGD2) can provide clinical benefit in patients with neuroblastoma. An important mechanism of mAb therapy is antibody-dependent cellular cytotoxicity (ADCC). Combinatorial therapeutic strategies can dramatically increase the anti-tumor response elicited by mAbs. We combined a novel αGD2 mAb, hu14.18K322A, with an immunostimulatory regimen of agonist CD40 mAb and class B CpG-ODN 1826 (CpG). Combination immunotherapy was more effective than the single therapeutic components in a syngeneic model of GD2-expressing B16 melanoma with minimal tumor burden. NK cell depletion in B6 mice showed that NK cells were required for the anti-tumor effect; however, anti-tumor responses were also observed in tumor-bearing SCID/beige mice. Thus, NK cell cytotoxicity did not appear to be essential. Peritoneal macrophages from anti-CD40 + CpG-treated mice inhibited tumor cells in vitro in an hu14.18K322A antibody-dependent manner. These data highlight the importance of myeloid cells as potential effectors in immunotherapy regimens utilizing tumor-specific mAb and suggest that further studies are needed to investigate the therapeutic potential of activated myeloid cells and their interaction with NK cells.     

Humanized Affinity-matured Monoclonal Antibody 8H9 Has Potent Antitumor Activity and Binds to FG Loop of Tumor Antigen B7-H3

B7-H3 (CD276) is both an inhibitory ligand for natural killer cells and T cells and a tumor antigen that is widely expressed among human solid tumors. Anti-B7-H3 mouse monoclonal antibody 8H9 has been successfully used for radioimmunotherapy for patients with B7-H3(+) tumors. We present the humanization, affinity maturation, and epitope mapping of 8H9 based on structure determination, modeling, and yeast display methods. The crystal structure of ch8H9 Fab fragment was solved to 2.5-Å resolution and used as a template for humanization. By displaying the humanized 8H9 single chain Fv (scFv) on the surface of yeast, the affinity was matured by sequential random mutagenesis and fluorescence-activated cell sorting. Six mutations (three in the complementarity-determining region and three in the framework regions) were identified and incorporated into an affinity-matured humanized 8H9 construct (hu8H9-6m) and an affinity-matured chimeric 8H9 construct (ch8H9-6m). The hu8H9-6m scFv had a 160-fold improvement in affinity (0.9 nm K_D) compared with parental hu8H9 scFv (144 nm K_D). The IgG formats of ch8H9-6m and hu8H9-6m (nanomolar to subnanomolar K_D) had 2–9-fold enhancements in affinity compared with their parental forms, potent in vitro antibody-dependent cell-mediated cytotoxicity (0.1–0.3 μg/ml EC₅₀), and high tumor uptake in mouse xenografts. Based on in silico docking studies and experimental validation, the molecular epitope of 8H9 was determined to be dependent on the FG loop of B7-H3, a region critical to its function in immunologic blockade and unique among anti-B7-H3 antibodies published to date.     

Ocaratuzumab,an Fc-engineered antibody demonstrates enhanced antibody-dependent cell-mediated cytotoxicity in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is common in both developed and developing nations where the need for inexpensive and convenient administration of therapy is apparent. Ocaratuzumab is a novel Fc-engineered humanized IgG1 anti-CD20 monoclonal antibody (mAb) designed for effective antibody-dependent cell-mediated cytotoxicity (ADCC) at very low concentrations that may facilitate sub-cutaneous (vs. intravenous) dosing. Here, we report ocaratuzumab’s potency against CLL cells. In vitro assessment of ocaratuzumab’s direct cytotoxicity (DC), complement-dependent cytotoxicity (CDC), antibody-dependent cellular phagocytosis (ADCP), and ADCC was performed on CLL cells. Ocaratuzumab induced DC, CDC, and ADCP similarly to rituximab or ofatumumab (anti-CD20 mAbs). However, ocaratuzumab showed an advantage in NK cell-mediated ADCC over these antibodies. In allogeneic ADCC, [E:T (effector:target) ratios = 25:1, 12:1, 6:1], ocaratuzumab (10 µg/mL) improved ADCC by ~3-fold compared with rituximab or ofatumumab (P < 0.001 all tested E:T ratios). Notably, the superiority of ocaratuzumab-induced ADCC was observed at low concentrations (0.1–10 ug/ml; P < 0.03; allogeneic assays). In extended allogeneic ADCC E:T titration, ocaratuzumab (0.1 µg/mL) demonstrated 19.4% more cytotoxicity than rituximab (E:T = 0.38:1; P = 0.0066) and 21.5% more cytotoxicity than ofatumumab (E:T = 1.5:1; P = 0.0015). In autologous ADCC, ocaratuzumab (10 µg/mL) demonstrated ~1.5-fold increase in cytotoxicity compared with rituximab or ofatumumab at all E:T ratios tested (E:Ts = 25:1,12:1,6:1; all P < 0.001). Obinutuzumab, a glyco-engineered anti-CD20 mAb, showed no improvement in ADCC activity compared with ocaratuzumab. The enhanced ADCC of ocaratuzumab suggests that it may be effective at low concentrations. If supported by clinical investigation, this feature could potentially allow for subcutaneous dosing at low doses that could expand the potential of administering chemoimmunotherapy in developing countries.     

Monoclonal antibodies to disialogangliosides: characterization of antibody-mediated cytotoxicity against human melanoma and neuroblastoma cells in vitro

We previously reported the binding specificities of two anti-ganglioside GD2 murine monoclonal antibodies (MAbs), A1-425 and A1-267, both of which are of IgG3 isotype. A1-425 reacts specifically with ganglioside GD2, whereas A1-267 binds preferentially to GD2 but also reacts with GD3 [Tai, T., Kawashima, I., Tada, N., & Dairiki, K. (1988) J. Biochem. 103, 682-687]. In this paper, they were used for comparative analyses of antibody-mediated cytotoxicity, i.e., antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) against human melanoma and neuroblastoma cell lines. Melanoma cells were found to contain GD2 and/or GD3, whereas neuroblastoma cells expressed only GD2. Both antibodies induced high levels of ADCC and CDC to GD2/GD3-positive cells with human peripheral large granular lymphocytes (LGL) as effector cells and in the presence of human serum, respectively. A good correlation was obtained between the contents of disialogangliosides and the binding level of the antibodies; both melanoma and neuroblastoma cells with larger amounts of GD2/GD3 showed a higher level of antibody binding than did the cells with a smaller amount of GD2/GD3. Surprisingly, ADCC did not correlate well with the binding level of the antibodies. Thus, A1-425 showed stronger lytic activity than A1-267 in spite of the binding level of A1-425 being similar to or lower than that of A1-267 on the cell surfaces. Antigen-antibody complexes composed of GD2 and A1-425 showed higher binding levels to LGL than complexes of GD2 and A1-267. In contrast, free MAb molecules gave minimum binding to LGL.(ABSTRACT TRUNCATED AT 250 WORDS)     

Enhanced ADCC Activity of Affinity Maturated and Fc-Engineered Mini-Antibodies Directed against the AML Stem Cell Antigen CD96

CD96, a cell surface antigen recently described to be preferentially expressed on acute myeloid leukemia (AML) leukemic stem cells (LSC) may represent an interesting target structure for the development of antibody-based therapeutic approaches. The v-regions from the CD96-specific hybridoma TH-111 were isolated and used to generate a CD96-specific single chain fragment of the variable regions (scFv). An affinity maturated variant resulting in 4-fold enhanced CD96-binding was generated by random mutagenesis and stringent selection using phage display. The affinity maturated scFv CD96-S32F was used to generate bivalent mini-antibodies by genetically fusing an IgG1 wild type Fc region or a variant with enhanced CD16a binding. Antibody dependent cell-mediated cytotoxicity (ADCC) experiments revealed that Fc engineering was essential to trigger significant effector cell-mediated lysis when the wild type scFv was used. The mini-antibody variant generated by fusing the affinity-maturated scFv with the optimized Fc variant demonstrated the highest ADCC activity (2.3-fold enhancement in efficacy). In conclusion, our data provide proof of concept that CD96 could serve as a target structure for effector cell-mediated lysis and demonstrate that both enhancing affinity for CD96 and for CD16a resulted in mini-antibodies with the highest cytolytic potential.     

Ab-IL2 fusion proteins mediate NK cell immune synapse formation by polarizing CD25 to the target cell-effector cell interface

The huKS-IL2 immunocytokine (IC) consists of IL2 fused to a mAb against EpCAM, while the hu14.18-IL2 IC recognizes the GD2 disialoganglioside. They are under evaluation for treatment of EpCAM(+) (ovarian) and GD2(+) (neuroblastoma and melanoma) malignancies because of their proven ability to enhance tumor cell killing by antibody-dependent cell-mediated cytotoxicity (ADCC) and by antitumor cytotoxic T cells. Here, we demonstrate that huKS-IL2 and hu14.18-IL2 bind to tumor cells via their antibody components and increase adhesion and activating immune synapse (AIS) formation with NK cells by engaging the immune cells' IL-2 receptors (IL2R). The NK leukemia cell line, NKL (which expresses high affinity IL2Rs), shows fivefold increase in binding to tumor targets when treated with IC compared to matching controls. This increase in binding is effectively inhibited by blocking antibodies against CD25, the α-chain of the IL2R. NK cells isolated from the peritoneal environment of ovarian cancer patients, known to be impaired in mediating ADCC, bind to huKS-IL2 via CD25. The increased binding between tumor and effector cells via ICs is due to the formation of AIS that are characterized by the simultaneous polarization of LFA-1, CD2 and F-actin at the cellular interface. AIS formation of peritoneal NK and NKL cells is inhibited by anti-CD25 blocking antibody and is 50-200% higher with IC versus the parent antibody. These findings demonstrate that the IL-2 component of the IC allows IL2Rs to function not only as receptors for this cytokine but also as facilitators of peritoneal NK cell binding to IC-coated tumor cells.     

Neutrophils are cytotoxic and growth-inhibiting for neuroblastoma cells with an anti-GD2 antibody but, without cytotoxicity, can be growth-stimulating

Neutrophils and mononuclear cells (MNC) can mediate antibody-dependent cellular cytotoxicity (ADCC) against cancer cells. To study cytotoxicity and growth inhibition of neuroblastoma cells by neutrophils and MNC with chimeric anti-disialoganglioside (GD2) monoclonal antibody (mAb) ch14.18, we developed digital image microscopy scanning (DIMSCAN) assays that measure fluorescence of target cells in 96-well plates after 6–18 h (cytotoxicity assay) or 7 days (growth assay). Neuroblastoma cell lines (GD2-positive: SMS-KCN, SMS-LHN, LA-N-1; GD2-negative: SK-N-SH) were preloaded with calcein acetoxymethyl ester for the cytotoxicity assay or labeled in situ after 7 days of culture with fluorescein diacetate in the growth assay. Fluorescence, as quantified by DIMSCAN, was correlated with neuroblastoma cell number in both assays (100–2000 cells/well). In the cytotoxicity test, both neutrophils and MNC effectively mediated ADCC of GD2-positive but not GD2-negative neuroblastoma cell lines. Cytotoxicity of both neutrophils and MNC increased with effector to target cell (E:T) ratio (5–50:1) and mAb ch.14.18 dose (0.1–10 μg/ml). ADCC of neutrophils, but not MNC, increased with addition of GM-CSF. Neutrophils, especially with rhGM-CSF, significantly suppressed growth of GD2-positive cell lines at a high E:T ratio (50:1) and mAb dose (10 μg/ml). Without antibody, neutrophils inhibited growth of one cell line (LA-N-1) but stimulated growth of two others (SMS-KCN, SMS-LHN). If neuroblastoma cells did not express GD2 (SK-N-SH), neutrophils stimulated growth whether or not antibody was present. Neutrophil culture supernatants increased growth of SK-N-SH, LA-N-1, and SMS-KCN cells, and MNC culture supernatants increased growth of SK-N-SH. In conclusion, neutrophils can mediate cytotoxicity and growth inhibition with a chimeric anti-GD2 antibody but also can promote tumor cell growth if antibody is not present or if GD2 is not expressed. Received: 18 November 1998 / Accepted: 24 September 1999     

Polymorphonuclear leukocyte function triggered through the high affinity Fc receptor for monomeric IgG

While it is extensively documented that gamma-interferon (IFN-gamma) is a potent stimulator of cells of the monocyte lineage, relatively little is known about its effects on granulocytes. We and others have found that immunoglobulin G (IgG) antibody-dependent cell cytotoxicity (ADCC) by polymorphonuclear cells (PMN) is significantly enhanced in a dose-dependent fashion by 16 hours incubation with recombinant IFN-gamma, resulting in 2- to 16-fold increases in ADCC. Incubation of PMN with lipopolysaccharide for 16 hours did not augment ADCC. Since IFN-gamma enhancement of ADCC is accompanied by increased expression of Fc receptors, we used monoclonal antibodies to compare control and IFN-gamma treated PMN for expression of the high affinity Fc receptor for monomeric IgG1 (FcgRI) and the PMN receptor for polymeric IgG (FcgR1o). Freshly isolated PMN or PMN cultured without IFN-gamma expressed FcgR1o but not detectable quantities of FcgRI. However, while FcgR1o were not increased on IFN-gamma-treated PMN, these cells expressed moderate amounts of FcgRI. To determine whether FcgRI contributed to PMN function, heteroantibodies consisting of Fab 3G8 or Fab 32 linked to Fab anti-target antibody were produced. ADCC of untreated PMN was promoted only by Fab 3G8 heteroantibody, whereas IFN-gamma-treated PMN killed through both FAB 3G8 and Fab 32 heteroantibodies. Thus, FcgRI can be induced on PMN by IFN-gamma, can mediate cytotoxicity by these cells, and probably accounts for the IFN-gamma stimulation of ADCC.     

Exchanging human Fcγ1 with murine Fcγ2a highly potentiates anti-tumor activity of anti-EpCAM antibody adecatumumab in a syngeneic mouse lung metastasis model

An important mode of action shared by human IgG1 antibody therapies is antibody-dependent cellular cytotoxicity (ADCC). ADCC relies on the interaction of the antibody’s Fc portion with Fc-gama receptors (FcγR) on immune effector cells. The anti-tumor activity of human IgG1 antibodies is frequently assessed in mouse models. Binding of human IgG1 to murine FcγRs is however of reduced affinity. We here show that ADCC of adecatumumab (MT201), a fully human IgG1 antibody specific for epithelial cell adhesion molecule (EpCAM/CD326), is drastically lower if human peripheral blood mononuclear cells are replaced by murine splenocytes as effector cells. When the variable domains of adecatumumab were genetically fused to a murine IgG2a backbone (yielding mu-adecatumumab), ADCC with murine effector cells was much improved, but at the same time significantly reduced with human effector cells. The serum half-lives of adecatumumab and mu-adecatumumab were determined in mice and dosing schedules established that gave similar serum trough levels during a 4-week antibody treatment. The anti-tumor activities of adecatumumab and mu-adecatumumab were then compared side-by-side in a lung metastasis mouse model established with a syngeneic B16 melanoma line expressing human EpCAM at physiologically relevant levels. Treatment of mice with mu-adecatumumab led to an almost complete prevention of lung metastases, while the human version of the antibody was much less active. This shows that adecatumumab has high anti-tumor activity when tested in a form that is better compatible with the species’ immune system. Moreover, our data suggest to routinely compare in mouse models human IgG1 and murine IgG2a versions of antibodies to properly assess the contribution of ADCC to overall anti-tumor activity.     

Tumor cell killing by in vitro affinity-matured recombinant human monoclonal antibodies

We have developed a method that allows the rapid improvement of the affinity of phage-displayed antibody fragments by selection on intact eukaryotic cells. A single chain Fv fragment, specific for the tumor-associated Ep-Cam molecule, was mutagenized by shuffling of the immunoglobulin light chain variable region and DNA shuffling of both heavy and light chain variable regions. Higher-affinity mutants were selected from small phage display libraries by cell panning under stringent conditions. When converted to an intact fully human antibody, the mutagenized anti-tumor monoclonal antibody displayed an affinity of 0.4 nM, a 15-fold improvement over the affinity of the original antibody. Compared to previously reported affinity maturation schemes, panning on intact cells does not require purified targets for selection and may be particularly useful when the target molecule can not be expressed as a recombinant molecule or easily purified without disrupting its native configuration. In vitro tumor cell killing assays demonstrated an improved performance of the higher-affinity antibody in complement-mediated tumor cell killing. In contrast, the lower-affinity antibody performed somewhat better in antibody-dependent cellular cytotoxicity assays and penetrated better in multicell spheroids of tumor cells, an in vitro model for the tumor penetration capacity of antibodies. Received: 26 February 2000 / Accepted: 26 January 2001     

Differences in binding and effector functions between classes of TNF antagonists

There are currently two Food and Drug Administration-approved classes of biologic agents that target tumor necrosis factor-α (TNF-α): anti-TNF monoclonal antibodies (mAbs) (adalimumab and infliximab), and soluble TNF receptors (etanercept). This study examined the ability of the TNF antagonists to: (1) bind various polymorphic variants of cell surface-expressed Fc receptors (FcγRs) and the complement component C1q, and (2) mediate Ab-dependent cellular cytotoxicity (ADCC) and complement-mediated cytotoxicity (CDC) killing of cells expressing membrane-bound TNF (mTNF) in vitro. Both mAbs and the soluble TNF receptor demonstrated low-level binding to the activating receptors FcγRI, FcγRIIa, and FcγRIIIa, and the inhibitory receptor FcγRIIb, in the absence of exogenous TNF. However, upon addition of TNF, the mAbs, but not etanercept, showed significantly increased binding, in particular to the FcγRII and FcγRIII receptors. Infliximab and adalimumab induced ADCC much more potently than etanercept. In the presence of TNF, both mAbs bound C1q in in vitro assays, but etanercept did not bind C1q under any conditions. Infliximab and adalimumab also induced CDC in cells expressing mTNF more potently than etanercept. Differences in the ability to bind ligand and mediate cell death may account for the differences in efficacy and safety of TNF antagonists.     

The mononuclear cell in human blood which mediates antibody-dependent cellular cytotoxicity to virus-infected target cells. II. Identification as a K cell.

Studies were carried out to determine whether the mononuclear cell in human blood which mediates antibody-dependent cellular cytotoxicity (ADCC) to herpes simplex virus (HSV)-infected target cells has surface Fc receptors which participate in the reaction. The F (ab')2 fragment of human IgG antibody was inactive both in ADCC and in complement-mediated cytolysis, but retained the capacity to neutralize infectious virus, to agglutinate erythrocytes coated with viral antigens, and to bind to the surface of virus-infected cells. Treatment of sensitized virus-infected target cells with staphylococcus protein A, which has affinity for the Fc epitope of IgG, strongly reduced their susceptibility to lysis by ADCC in a dose-dependent relationship. These findings indicate that the Fc portion of IgG antibody to the virus is necessary for cytotoxicity. Treatment of blood mononuclear cells with either heat-aggregated gamma-globulin or HSV immune complexes inhibited effector cell activity. The presence of "third party" cellular immune complexes also strongly inhibited ADCC. Adsorption of mononuclear cells to plastic surfaces coated with soluble third party immune complexes resulted in a significant reduction in effector cell activity. These findings demonstrate that the ADCC effector cell possesses surface Fc receptors which are utilized in the ADCC reaction. The presence of Fc receptors on the surface of the effector cell indicates that it is a K cell rather than a null cell.     

Glycoengineered Pichia produced anti-HER2 is comparable to trastuzumab in preclinical study

Mammalian cell culture systems are used predominantly for the production of therapeutic monoclonal antibody (mAb) products. A number of alternative platforms, such as Pichia engineered with a humanized N-linked glycosylation pathway, have recently been developed for the production of mAbs. The glycosylation profiles of mAbs produced in glycoengineered Pichia are similar to those of mAbs produced in mammalian systems. This report presents for the first time the comprehensive characterization of an anti-human epidermal growth factor receptor 2 (HER2) mAb produced in a glycoengineered Pichia, and a study comparing the anti-HER2 from Pichia, which had an amino acid sequence identical to trastuzumab, with trastuzumab. The comparative study covered a full spectrum of preclinical evaluation, including bioanalytical characterization, in vitro biological functions, in vivo anti-tumor efficacy and pharmacokinetics in both mice and non-human primates. Cell signaling and proliferation assays showed that anti-HER2 from Pichia had antagonist activities comparable to trastuzumab. However, Pichia–produced material showed a 5-fold increase in binding affinity to FcγIIIA and significantly enhanced antibody dependant cell-mediated cytotoxicity (ADCC) activity, presumably due to the lack of fucose on N-glycans. In a breast cancer xenograft mouse model, anti-HER2 was comparable to trastuzumab in tumor growth inhibition. Furthermore, comparable pharmacokinetic profiles were observed for anti-HER2 and trastuzumab in both mice and cynomolgus monkeys. We conclude that glycoengineered Pichia provides an alternative production platform for therapeutic mAbs and may be of particular interest for production of antibodies for which ADCC is part of the clinical mechanism of action.     

Correlation of ADCC activity with cytokine release induced by the stably expressed,glyco-engineered humanized Lewis Y-specific monoclonal antibody MB314

A major limitation to the application of therapeutic monoclonal antibodies (mAbs) is their reduced in vivo efficacy compared with the high efficacy measured in vitro. Effector functions such as antibody-dependent cell-mediated cytotoxicity (ADCC) are dramatically reduced in vivo by the presence of high amounts of endogenous IgG in the serum. Recent studies have shown that modification of the glycosylation moieties attached to the Fc part of the mAb can enhance binding affinity to FcγRIIIα receptors on natural killer cells and thus may counteract the reduced in vivo efficacy. In the present study, a humanized IgG1/κ monoclonal antibody recognizing the tumor-associated carbohydrate antigen Lewis Y was stably produced in a moss expression system that allows glyco-engineering. The glyco-modified mAb (designated MB314) showed a highly homogeneous N-glycosylation pattern lacking core-fucose. A side-by-side comparison to its parental counterpart produced in conventional mammalian cell-culture (MB311, formerly known as IGN311) by fluorescence-activated cell sorting analysis confirmed that the target specificity of MB314 is similar to that of MB311. In contrast, ADCC effector function of MB314 was increased up to 40-fold whereas complement dependent cytotoxicity activity was decreased 5-fold. Notably, a release of immunostimulatory cytokines, including interferon γ, monocyte chemotactic protein-1 (MCP-1), interleukin-6 and tumor necrosis factor (TNF) was particularly induced with the glyco-modified antibody. TNF release was associated with CD14⁺ cells, indicating activation of monocytes.     

Antibody-dependent cellular cytotoxicity against murine leukemia viral antigens: studies with human lymphoblastoid cell lines and human peripheral lymphocytes as effector cells comparing rabbit, goat, and mouse antisera.

A thymic lymphoblastoid cell line derived from a New Zealand Black mouse produces murine leukemia virus (MuLV) and was used as a target in model systems for the in vitro study of antibody-dependent cellular cytotoxicity (ADCC). Several human lymphoblastoid cell lines were investigated as potential effector cells. The most promising (Raji cells) bound to antibody-coated target cells but caused only modest levels of ADCC at 25:1 effector-to-target cell ratio with substantial lysis in the absence of antiserum. Human peripheral lymphocytes were active as effector cells in ADCC at a 5:1 ratio and produced no lysis in the absence of antibody. These cells were used to demonstrate that high dilutions of rabbit antisera to MuLV antigens p30, p15, p12, and p10 were capable of mediating lysis of MuLV-producing target cells but not of a virus-negative murine cell line. A murine antiserum to Thy 1.2 and three caprine antisera to MuLV antigens that were active in complement-mediated cytotoxicity functioned poorly in inducing ADCC; however, rabbit antisera to similar antigens were 16- to 512-fold more efficient in cell-mediated than in complement lysis. The inefficiency of goat antisera was not due to shedding of cell surface antigens or generation of blocking factors but rather to lack of lytic interaction of antibody-coated targets with the effector cells.     

Killing of human tumor cell lines by human monocytes and murine monoclonal antibodies

We evaluated the capacity of freshly isolated blood monocytes to mediate antibody-dependent cellular-mediated cytotoxicity (ADCC) in cooperation with murine anti-tumor monoclonal antibodies (MAbs). Blood monocytes isolated from most donors by adherence selection to fibronectin-coated plastic surfaces and subsequently depleted of natural killer/killer (NK/K) cells exhibited significant ADCC activity against tumor cell lines in combination with an IgG3 antitumor MAb (BR55-2). However, significant variation in ADCC competence was observed among donors. Culture parameters influencing monocyte ADCC activity were evaluated and optimized. The influence of MAb isotype on ADCC capacity of anti-tumor MAbs was also evaluated using anti-tumor class-switch variant hybridoma proteins and a panel of anti-tumor MAbs. MAbs of the IgG2a and IgG3 subclasses exhibited high ADCC potential, whereas MAbs of the IgG2b subclass exhibited no ADCC activity. One of two IgG1 MAbs tested exhibited high ADCC activity with monocyte effectors. The role of monocytes or macrophages in tumor remission of cancer patients undergoing MAb immunotherapy is not known. However, correlative studies of monocyte ADCC capacity and responsiveness of cancer patients to MAb immunotherapy may help to establish the role of these effectors in MAb-mediated tumor remissions.     

Aberrantly glycosylated MUC1 is expressed on the surface of breast cancer cells and a target for antibody-dependent cell-mediated cytotoxicity

Protein glycosylation often changes during cancer development, resulting in the expression of cancer-associated carbohydrate antigens. In particular mucins such as MUC1 are subject to these changes. We previously identified an immunodominant Tn-MUC1 (GalNAc-α-MUC1) cancer-specific epitope not covered by immunological tolerance in MUC1 humanized mice and man. The objective of this study was to determine if mouse antibodies to this Tn-MUC1 epitope induce antibody-dependent cellular cytotoxicity (ADCC) pivotal for their potential use in cancer immunotherapy. Binding affinity of mAb 5E5 directed to Tn-MUC1 was investigated using BiaCore. The availability of Tn-MUC1 on the surface of breast cancer cells was evaluated by immunohistochemistry, confocal microscopy, and flow cytometry, followed by in vitro assessment of antibody-dependent cellular cytotoxicity by mAb 5E5. Biacore analysis demonstrated high affinity binding (K_D?=?1.7 nM) of mAb 5E5 to its target, Tn-MUC1. Immunolabelling with mAb 5E5 revealed surface expression of the Tn-MUC1 epitope in breast cancer tissue and cell lines, and mAb 5E5 induced ADCC in two human breast cancer cell lines, MCF7 and T47D. Aberrantly glycosylated MUC1 is expressed on the surface of breast cancer cells and a target for antibody-dependent cell-mediated cytotoxicity suggesting that antibodies targeting glycopeptide epitopes on mucins are strong candidates for cancer-specific immunotherapies.     

Ocaratuzumab,an Fc-engineered antibody demonstrates enhanced antibody-dependent cell-mediated cytotoxicity in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is common in both developed and developing nations where the need for inexpensive and convenient administration of therapy is apparent. Ocaratuzumab is a novel Fc-engineered humanized IgG1 anti-CD20 monoclonal antibody (mAb) designed for effective antibody-dependent cell-mediated cytotoxicity (ADCC) at very low concentrations that may facilitate sub-cutaneous (vs. intravenous) dosing. Here, we report ocaratuzumab’s potency against CLL cells.

In vitro assessment of ocaratuzumab’s direct cytotoxicity (DC), complement-dependent cytotoxicity (CDC), antibody-dependent cellular phagocytosis (ADCP), and ADCC was performed on CLL cells.

Ocaratuzumab induced DC, CDC, and ADCP similarly to rituximab or ofatumumab (anti-CD20 mAbs). However, ocaratuzumab showed an advantage in NK cell-mediated ADCC over these antibodies. In allogeneic ADCC, [E:T (effector:target) ratios = 25:1, 12:1, 6:1], ocaratuzumab (10 µg/mL) improved ADCC by ~3-fold compared with rituximab or ofatumumab (P < 0.001 all tested E:T ratios). Notably, the superiority of ocaratuzumab-induced ADCC was observed at low concentrations (0.1–10 ug/ml; P < 0.03; allogeneic assays). In extended allogeneic ADCC E:T titration, ocaratuzumab (0.1 µg/mL) demonstrated 19.4% more cytotoxicity than rituximab (E:T = 0.38:1; P = 0.0066) and 21.5% more cytotoxicity than ofatumumab (E:T = 1.5:1; P = 0.0015). In autologous ADCC, ocaratuzumab (10 µg/mL) demonstrated ~1.5-fold increase in cytotoxicity compared with rituximab or ofatumumab at all E:T ratios tested (E:Ts = 25:1,12:1,6:1; all P < 0.001). Obinutuzumab, a glyco-engineered anti-CD20 mAb, showed no improvement in ADCC activity compared with ocaratuzumab.

The enhanced ADCC of ocaratuzumab suggests that it may be effective at low concentrations. If supported by clinical investigation, this feature could potentially allow for subcutaneous dosing at low doses that could expand the potential of administering chemoimmunotherapy in developing countries.     

Correlation of ADCC activity with cytokine release induced by the stably expressed,glyco-engineered humanized Lewis Y-specific monoclonal antibody MB314

A major limitation to the application of therapeutic monoclonal antibodies (mAbs) is their reduced in vivo efficacy compared with the high efficacy measured in vitro. Effector functions such as antibody-dependent cell-mediated cytotoxicity (ADCC) are dramatically reduced in vivo by the presence of high amounts of endogenous IgG in the serum. Recent studies have shown that modification of the glycosylation moieties attached to the Fc part of the mAb can enhance binding affinity to FcγRIIIα receptors on natural killer cells and thus may counteract the reduced in vivo efficacy. In the present study, a humanized IgG1/κ monoclonal antibody recognizing the tumor-associated carbohydrate antigen Lewis Y was stably produced in a moss expression system that allows glyco-engineering. The glyco-modified mAb (designated MB314) showed a highly homogeneous N-glycosylation pattern lacking core-fucose. A side-by-side comparison to its parental counterpart produced in conventional mammalian cell-culture (MB311, formerly known as IGN311) by fluorescence-activated cell sorting analysis confirmed that the target specificity of MB314 is similar to that of MB311. In contrast, ADCC effector function of MB314 was increased up to 40-fold whereas complement dependent cytotoxicity activity was decreased 5-fold. Notably, a release of immunostimulatory cytokines, including interferon γ, monocyte chemotactic protein-1 (MCP-1), interleukin-6 and tumor necrosis factor (TNF) was particularly induced with the glyco-modified antibody. TNF release was associated with CD14⁺ cells, indicating activation of monocytes.     

Glycoengineered Pichia produced anti-HER2 is comparable to trastuzumab in preclinical study

Mammalian cell culture systems are used predominantly for the production of therapeutic monoclonal antibody (mAb) products. A number of alternative platforms, such as Pichia engineered with a humanized N-linked glycosylation pathway, have recently been developed for the production of mAbs. The glycosylation profiles of mAbs produced in glycoengineered Pichia are similar to those of mAbs produced in mammalian systems. This report presents for the first time the comprehensive characterization of an anti-human epidermal growth factor receptor 2 (HER2) mAb produced in glycoengineered Pichia, and a study comparing the anti-HER2 from Pichia, which had an amino acid sequence identical to trastuzumab, with trastuzumab. The comparative study covered a full spectrum of preclinical evaluation, including bioanalytical characterization, in vitro biological functions, in vivo anti-tumor efficacy and pharmacokinetics in both mice and non-human primates. Cell signaling and proliferation assays showed that anti-HER2 from Pichia had antagonist activities comparable to trastuzumab. However, Pichia-produced material showed a 5-fold increase in binding affinity to FcγIIIA and significantly enhanced antibody dependent cell-mediated cytotoxicity (ADCC) activity, presumably due to the lack of fucose on N-glycans. In a breast cancer xenograft mouse model, anti-HER2 was comparable to trastuzumab in tumor growth inhibition. Furthermore, comparable pharmacokinetic profiles were observed for anti-HER2 and trastuzumab in both mice and cynomolgus monkeys. We conclude that glycoengineered Pichia provides an alternative production platform for therapeutic mAbs and may be of particular interest for production of antibodies for which ADCC is part of the clinical mechanism of action.Key words: glycoengineered Pichia, anti-HER2, trastuzumab, xenograft, PK, ADCC