Rituximab-dependent cytotoxicity by natural killer cells: influence of FCGR3A polymorphism on the concentration-effect relationship

The N-linked oligosaccharide at Fc gamma RIIIa Asn-45: an inhibitory element for high Fc gamma RIIIa binding affinity to IgG glycoforms lacking core fucosylation

Human leukocyte receptor IIIa (FcγRIIIa) plays an important role in mediating therapeutic antibodies’ antibody-dependent cellular cytotoxicity (ADCC), which is closely related to the clinical efficacy of anticancer processes in humans in vivo. The removal of the core fucose from oligosaccharides attached to the Fc region of antibodies improves FcγRIIIa binding, allowing the antibodies to enhance dramatically the antibody effector functions of ADCC. In this study, the contribution of FcγRIIIa oligosaccharides to the strength of the FcγRIIIa/antibody complex was analyzed using a serial set of soluble human recombinant FcγRIIIa lacking the oligosaccharides. A nonfucosylated antibody IgG1 appeared to have a significantly higher affinity to the wild-type FcγRIIIa fully glycosylated at its five N-linked oligosaccharide sites than did the fucosylated IgG1, and this increased binding was almost abolished once all of the FcγRIIIa glycosylation was removed. Our gain-of-function analysis in the FcγRIIIa oligosaccharide at Asn-162 (N-162) confirmed that N-162 is the element required for the high binding affinity to nonfucosylated antibodies, as previously revealed by loss-of-function analyses. Interestingly, beyond our expectation, the FcγRIIIa modified by N-162 alone showed a significantly higher binding affinity to nonfucosylated IgG1 than did the wild-type FcγRIIIa. Attachment of the other four oligosaccharides, especially the FcγRIIIa oligosaccharide at Asn-45 (N-45), hindered the high binding affinity of FcγRIIIa to nonfucosylated IgG1. Our data clearly demonstrated that N-45 is an inhibitory element for the high FcγRIIIa binding affinity mediated by N-162 to nonfucosylated antibodies. This information can be exploited for the structural-based functional study of FcγRIIIa.

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

Treatment of chronic lymphocytic leukemia patients with anti-CD20 mAb rituximab (RTX) leads to substantial CD20 loss on circulating malignant B cells soon after completion of the RTX infusion. This CD20 loss, which we term shaving, can compromise the therapeutic efficacy of RTX, and in vitro models reveal that shaving is mediated by effector cells which express Fc gammaRI. THP-1 monocytes and PBMC promote shaving, but PBMC also kill antibody-opsonized cells by antibody-dependent cellular cytotoxicity (ADCC), a reaction generally considered to be due to NK cells. We hypothesized that within PBMC, monocytes and NK cells would have substantially different and competing activities with respect ADCC or shaving, thereby either enhancing or inhibiting the therapeutic action of RTX. We measured ADCC and RTX removal from RTX-opsonized Daudi cells promoted by PBMC, or mediated by NK cells and monocytes. NK cells take up RTX and CD20 from RTX-opsonized B cells, and mediate ADCC. PBMC depleted of NK cells show little ADCC activity, whereas PBMC depleted of monocytes have greater ADCC than the PBMC. Pre-treatment of RTX-opsonized B cells with THP-1 cells or monocytes suppresses NK cell-mediated ADCC, and blockade of Fc gammaRI on monocytes or THP-1 cells abrogates their ability to suppress ADCC. Our results indicate NK cells are the principal cells in PBMC that kill RTX-opsonized B cells, and that monocytes can suppress ADCC by promoting shaving. These results suggest that RTX-based immunotherapy of cancer may be enhanced based on paradigms which include infusion of compatible NK cells and inhibition of monocyte shaving activity.

NK cell-mediated targeting of human cancer and possibilities for new means of immunotherapy

Insights into the molecular basis for natural killer (NK) cell recognition of human cancer have been obtained in recent years. Here, we review current knowledge on the molecular specificity and function of human NK cells. Evidence for NK cell targeting of human tumors is provided and new strategies for NK cell-based immunotherapy against human cancer are discussed. Based on current knowledge, we foresee a development where more cancers may be subject to treatment with drugs or other immunomodulatory agents affecting NK cells, either directly or indirectly. We also envisage a possibility that certain forms of cancers may be subject to treatment with adoptively transferred NK cells, either alone or in combination with other therapeutic interventions.

Human natural killer cells

Natural killer (NK) cells were discovered more than 30 years ago. NK cells are large granular lymphocytes that belong to the innate immune system because unlike T or B lymphocytes of the adaptive or antigen-specific immune system, NK cells do not rearrange T-cell receptor or immunoglobulin genes from their germline configuration. During the past 2 decades there has been a substantial gain in our understanding of what and how NK-cells "see," lending important insights into their functions and purpose in normal immune surveillance. The most recent discoveries in NK-cell receptor biology have fueled translational research that has led to remarkable results in treating human malignancy.

Antibody and immunomodulatory agents in the treatment of indolent non-Hodgkin's lymphoma

Immunomodulatory agents, including cytokines, CpG oligonucleotides, and anti-idiotype vaccines have properties that suggest they have the ability to augment rituximab in the treatment of non-Hodgkin's lymphoma (NHL). Although several clinical trials have shown promising results, no randomized trials of reasonable size have been reported to date, limiting the ability to discern whether combinations of immunomodulatory agents with rituximab impact clinical outcome. Until such trials are mature, we do not recommend using these agents in combination outside of the research setting.

Use of natural killer cells as immunotherapy for leukaemia

Natural killer (NK) cells potentially play a significant role in eradicating residual disease following allogeneic haematopoietic cell transplantation, and have been explored as tools for adoptive immunotherapy for chemotherapy-refractory patients. NK cell cytotoxicity is modulated by multiple activating and inhibitory receptors that maintain a balance between self-tolerance and providing surveillance against pathogens and malignant transformation. The functional characteristics of NK cells are dictated by the strength of inhibitory receptor signalling. Major histocompatibility complex (MHC)-specific inhibitory receptor acquisition occurs sequentially during NK cell development, and is determined by the nature of immunological reconstitution after allogeneic haematopoietic cell transplantation. Polymorphisms of inhibitory receptors [killer immunoglobulin-like receptors (KIRs)] and their ligands (MHC) contribute to interindividual variability. As a result, the functional NK cell repertoire of individual donors has variable potential for graft-vs-leukaemia reactions. Models predicting NK cell alloreactivity, including KIR ligand mismatch and missing KIR ligand strategies, are discussed as algorithms for optimal NK cell donor selection. Future modifications to improve NK cell adoptive immunotherapy by means of increasing target recognition and reducing inhibitory signalling are being explored.

A novel subset of NK cells expressing high levels of inhibitory FcgammaRIIB modulating antibody-dependent function

NK cells can kill antibody-coated target cells following engagement of FcgammaRIIIA, the major activating FcgammaR expressed by these cells. The presence of FcgammaRIIC (CD32C) has also been reported, but its contribution to the FcgammaR-dependent effector functions of NK cells remains debated. We demonstrate here that inhibitory FcgammaRIIB is also expressed by a small subset of CD56+/NKp46+ NK cells and can efficiently down-modulate their FcgammaR-dependent effector function. Immunofluorescence analyses of NK cells from 52 healthy donors showed the presence of CD56bright/FcgammaRII(-) (5.2%+/-3.4), CD56dim/FcgammaRII(lo/-) (94.1%+/-3.4), and CD56dim/FcgammaRIIbright (0.64%+/-0.72) cells. QRT-PCR and protein analyses performed on isolated FcgammaRIIbright NK cells indicated that FcgammaRIIB is strongly expressed by these cells but not by FcgammaRII(lo/-) cells. In addition, FcgammaRIIbright cells showed a weaker antibody-dependent degranulation when incubated with IgG-coated target cells compared with FcgammaRII(lo/-) NK cells, although a strong FcgammaRIIIA expression was detected in both cells. Furthermore, the addition of anti-FcgammaRII Fab paralleled a higher degranulation of FcgammaRIIbright NK cells, indicating a direct role for FcgammaRIIB in this down-modulating effect. Thus, it is proposed that FcgammaRIIBbright NK cells represent a new NK cell compartment able to down-modulate NK cell functions triggered by the engagement of activating FcgammaR.

Complement activation on B lymphocytes opsonized with rituximab or ofatumumab produces substantial changes in membrane structure preceding cell lysis

Binding of the CD20 mAb rituximab (RTX) to B lymphocytes in normal human serum (NHS) activates complement (C) and promotes C3b deposition on or in close proximity to cell-bound RTX. Based on spinning disk confocal microscopy analyses, we report the first real-time visualization of C3b deposition and C-mediated killing of RTX-opsonized B cells. C activation by RTX-opsonized Daudi B cells induces rapid membrane blebbing and generation of long, thin structures protruding from cell surfaces, which we call streamers. Ofatumumab, a unique mAb that targets a distinct binding site (the small loop epitope) of the CD20 Ag, induces more rapid killing and streaming on Daudi cells than RTX. In contrast to RTX, ofatumumab promotes streamer formation and killing of ARH77 cells and primary B cells from patients with chronic lymphocytic leukemia. Generation of streamers requires C activation; no streaming occurs in media, NHS-EDTA, or in sera depleted of C5 or C9. Streamers can be visualized in bright field by phase imaging, and fluorescence-staining patterns indicate they contain membrane lipids and polymerized actin. Streaming also occurs if cells are reacted in medium with bee venom melittin, which penetrates cells and forms membrane pores in a manner similar to the membrane-attack complex of C. Structures similar to streamers are demonstrable when Ab-opsonized sheep erythrocytes (non-nucleated cells) are reacted with NHS. Taken together, our findings indicate that the membrane-attack complex is a key mediator of streaming. Streamer formation may, thus, represent a membrane structural change that can occur shortly before complement-induced cell death.

Immunotherapeutic mechanisms of anti-CD20 monoclonal antibodies

The anti-CD20, B-cell-specific mAb rituximab (RTX) has been approved for treatment of non-Hodgkin's B cell lymphoma and rheumatoid arthritis. Under conditions of high B cell burden, exhaustion of the body's effector mechanisms, for example, NK-cell-mediated killing, may lead to substantial decreases in the immunotherapeutic efficacy of this mAb. Moreover, RTX treatment of patients with chronic lymphocytic leukemia and high levels of circulating B cells can lead to removal of CD20 from the cells, thus allowing them to persist and resist clearance. RTX therapy for several autoimmune diseases has proven to be effective, but in numerous instances there has been little correlation between reductions in disease activity and changes in titers of pathogenic autoantibodies. This paradox may be explained by a separate mechanism: Binding of RTX to B cells generates immune complexes that act as decoys to attract monoycte/macrophages and thus reduce their inflammatory activity in certain autoantibody-mediated diseases. Several second-generation anti-CD20 mAbs with enhanced cytotoxic action have been developed and are being tested in the clinic for treatment of cancer and autoimmune diseases. The application of these mAbs, potentially in combination with immune effector modifying drugs, may successfully address the shortcomings of current anti-CD20 immunotherapy.

Fc gamma RIIIa expression is not increased on natural killer cells expressing the Fc gamma RIIIa-158V allotype

The presence of a valine (V) versus a phenylanaline (F) at position 158 of Fc gamma RIIIa/CD16a improves the affinity for IgG and is associated with higher therapeutic response to rituximab. Increased CD16 expression on natural killer (NK) cells from donors with the VV or VF versus FF genotype has recently been reported. We indeed observed higher binding of the anti-CD16 monoclonal antibody (mAb) 3G8 on NK cells from V carriers (VV = VF > FF). However, the binding of two other anti-CD16 mAbs, LNK16 and DJ130c, decreased with the number of V allele (VV < VF < FF). CD16 transcript levels were independent on the genotype. Rituximab binding to NK cells from V carriers was higher than its binding to FF NK cells at low concentrations (10 and 100 microg/mL). However, the difference was nearly completely abolished at saturating concentrations (>or=1,000 microg/mL). Finally, nearly 100% of CD16-expressing NK cells displayed a complete down-modulation of the receptor after optimal engagement by plate-bound 3G8, whatever the genotype. By contrast, the percentages of NK cells down-modulating CD16 after competitive engagement of the receptor by plate-bound rituximab increased with the number of V allele (FF, 18.2 +/- 8.6%; VF, 32.0 +/- 4.9%; and VV, 42.4 +/- 9.9%). These results are in discrepancy with the expected increased competition that would result from an increased expression of CD16 on VV and VF NK cells. We conclude that increased binding and functional and clinical responses associated with the high-affinity Fc gamma RIIIa-158V are unrelated to an increased expression of this allotype.

Blockade of CD200 in the presence or absence of antibody effector function: implications for anti-CD200 therapy

CD200 is an immunosuppressive molecule overexpressed in multiple hematologic malignancies such as B cell chronic lymphocytic leukemia, multiple myeloma, and acute myeloid leukemia. We previously demonstrated that up-regulation of CD200 on tumor cells suppresses antitumor immune responses and that antagonistic anti-human CD200 mAbs enabled human PBMC-mediated tumor growth inhibition in xenograft NOD/SCID human (hu)-mouse models. Ab variants with effector function (IgG1 constant region (G1)) or without effector function (IgG2/G4 fusion constant region (G2G4)) exhibited high antitumor activity in a human tumor xenograft model in which CD200 was expressed. In this report, we seek to select the best candidate to move forward into the clinic and begin to decipher the mechanisms of tumor cell killing by comparing anti-CD200-G1 vs anti-CD200-G2G4 in two related animal models. In a CD200-expressing xenograft NOD/SCID hu-mouse model where CD200 ligand/receptor interactions are already established before initiating treatment, we find that anti-CD200-G1 is a less effective Ab compared with anti-CD200-G2G4. Separately, in a model that evaluates the effect of the Abs on the immune cell component of the xenograft NOD/SCID hu-mouse model distinctly from the effects of binding to CD200 on tumor cells, we find that the administration of anti-CD200-G1 Abs completely abolished human PBMC-mediated tumor growth inhibition. Along with supporting in vitro studies, our data indicate that anti-CD200-G1 Abs efficiently mediate Ab-dependent cellular cytotoxicity of activated T cells, critical cells involved in immune-mediated killing. These studies suggest important implications regarding the selection of the constant region in anti-CD200 immunotherapy of cancer patients.

Dependence of surface monoclonal antibody binding on dynamic changes in FcgammaRIIb expression

Receptors for the Fc region of immunoglobulin G (FcgammaRs) are expressed on a broad range of haematopoietic cell types and are responsible for regulating antibody production and linking the humoral and effector responses. In response to a number of stimuli, such as cytokine signals or inflammation, FcgammaR expression at the cell surface is dynamically regulated. On B cells, we observed what appeared to be a correlation between CD22 expression and FcgammaRIIb expression when the latter was varied in a number of models. Further investigation revealed that this was specific to a particular anti-CD22 monoclonal antibody, which appeared to require stabilization by interaction with FcgammaRIIb for optimal binding to CD22. Since alterations in the regulation of FcgammaR expression are important in controlling immune responses and have been associated with a number of immune-mediated disease states, we suggest that it might be prudent to confirm the expression of cell surface markers by two independent methods. Furthermore, because the efficacy of therapeutic antibodies may depend upon their interaction with FcgammaRs, our results are relevant to their design and assessment.

Elements related to heterogeneity of antibody-dependent cell cytotoxicity in patients under trastuzumab therapy for primary operable breast cancer overexpressing Her2

Preliminary results from a pilot trial on trastuzumab's mechanism of action against operable breast tumors overexpressing Her2 suggested a role for antibody-dependent cell cytotoxicity (ADCC). To examine factors affecting ADCC intensity and variability, we extended this study to the phenotypic and functional analysis of circulating mononuclear cells in 18 patients. ADCC was induced by trastuzumab therapy in 15 of 18 patients (83%). Inability to develop ADCC in three patients did not depend on inadequate levels of trastuzumab because further increase in its concentration in vitro was ineffective. Rather, susceptibility to develop ADCC was fairly predicted by test with trastuzumab before therapy and was correlated to the number of lymphocytes coexpressing CD16 and CD56. Phenotypic analysis at the end of ADCC evaluating down-regulation of CD16, and up-regulation of CD69 and CD107a, confirmed that natural killer (NK) cells and CD56(+) T cells were involved in productive engagement of trastuzumab. Also, the killing efficiency of CD16(+) lymphocytes was influenced by 158 V/F polymorphism of Fc gamma RIII (CD16), whereas variations of CD247 on NK cells were consistent with trends between ADCC before and after therapy. Complete pathologic response was observed in one patient showing ADCC of outstanding intensity, whereas four cases of partial response showed intermediate ADCC; none of the three patients unable to mount ADCC had significant tumor regression. These data indicate that quantity and lytic efficiency of CD16(+) lymphocytes are major factors for ADCC induction by trastuzumab, and confirm that breast cancer responses to short-term trastuzumab monotherapy may depend on involvement of the ADCC mechanism.

Complement-induced cell death by rituximab depends on CD20 expression level and acts complementary to antibody-dependent cellular cytotoxicity

PURPOSE

The use of the CD20-specific antibody rituximab has greatly improved the response to treatment of CD20+ follicular lymphoma. Despite the success of rituximab, resistance has been reported and prognostic markers to predict individual response are lacking. The level of CD20 expression on tumors has been related to response, but results of several studies are contradictory and no clear relationship could be established. Complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC) are thought to be important effector mechanisms, but the exact mechanism of rituximab-mediated cell kill is still unknown. Importantly, no data have been reported on the combined contribution of CDC and ADCC.

EXPERIMENTAL DESIGN

We have developed a system of clonally related CEM-CD20 cells by retroviral transfer of the human CD20 cDNA (n = 90). This set of cells, with the CD20 molecule as the only variable, was used to study the importance of CD20 expression level on rituximab-mediated CDC, ADCC, and the combination.

RESULTS

We show a sigmoidal correlation of CD20 expression level and rituximab-mediated killing via CDC but not ADCC. On both high and low CD20-expressing cells, all CD20 molecules were translocated into lipid rafts after rituximab binding. Furthermore, CDC and ADCC act simultaneously and CDC-resistant cells are sensitive to ADCC and vice versa.

CONCLUSIONS

These findings suggest that CDC depends on CD20 expression level and that both CDC and ADCC act complementary. These data give new insights into novel strategies to improve the efficacy of CD20-specific antibodies for the treatment of CD20+ tumors.

Pharmacogenetics of EGFR and VEGF inhibition

Even though treatment of several types of solid tumours has improved in the past few years with the introduction of the monoclonal antibodies against epidermal growth factor receptor (EGFR) and vascular endothelial growth factor (VEGF), response rates to these targeted therapies are modest. Pharmacogenetic factors have the potential to select patients with higher chance of response to agents that target these pathways. This review provides an overview over germ-line variations in genes that are potentially involved in the pharmacodynamics of the monoclonal antibodies cetuximab, panitumumab and bevacizumab, and which may underlie variable anti-tumour response.

Mechanisms of killing by anti-CD20 monoclonal antibodies

CD20 is a cell-surface marker expressed on mature B cells and most malignant B cells, but not stem or plasma cells. It is an ideal target for monoclonal antibodies (mAb), such as rituximab and ofatumumab, as it is expressed at high levels on most B-cell malignancies, but does not become internalized or shed from the plasma membrane following mAb treatment. This allows mAb to persist on the cell surface for extended periods and deliver sustained immunological attack from complement and FcR-expressing innate effectors, particularly macrophages. CD20 can also generate transmembrane signals when engaged by certain mAb which, although unproven, might provide an important element of the therapeutic success of anti-CD20 mAb. These favourable characteristics have led to anti-CD20 mAb being developed and exploited for use in immunotherapy, where they have proven remarkably efficacious in both the treatment of malignant disease and autoimmune disorders by deleting malignant or normal B cells, respectively. In this review, we discuss how these mAb have driven research in the immunotherapy field over the last decade, detail their likely modes of action and their limitations in terms of effector exhaustion, and explore ways in which they might be enhanced and further exploited in the future.

Non-fucosylated therapeutic antibodies: the next generation of therapeutic antibodies

Therapeutic antibody IgG1 has two N-linked oligosaccharide chains bound to the Fc region. The oligosaccharides are of the complex biantennary type, composed of a trimannosyl core structure with the presence or absence of core fucose, bisecting N-acetylglucosamine (GlcNAc), galactose, and terminal sialic acid, which gives rise to structural heterogeneity. Both human serum IgG and therapeutic antibodies are well known to be heavily fucosylated. Recently, antibody-dependent cellular cytotoxicity (ADCC), a lytic attack on antibody-targeted cells, has been found to be one of the critical effector functions responsible for the clinical efficacy of therapeutic antibodies such as anti-CD20 IgG1 rituximab (Rituxan((R))) and anti-Her2/neu IgG1 trastuzumab (Herceptin((R))). ADCC is triggered upon the binding of lymphocyte receptors (FcgammaRs) to the antibody Fc region. The activity is dependent on the amount of fucose attached to the innermost GlcNAc of N-linked Fc oligosaccharide via an alpha-1,6-linkage, and is dramatically enhanced by a reduction in fucose. Non-fucosylated therapeutic antibodies show more potent efficacy than their fucosylated counterparts both in vitro and in vivo, and are not likely to be immunogenic because their carbohydrate structures are a normal component of natural human serum IgG. Thus, the application of non-fucosylated antibodies is expected to be a powerful and elegant approach to the design of the next generation therapeutic antibodies with improved efficacy. In this review, we discuss the importance of the oligosaccharides attached to the Fc region of therapeutic antibodies, especially regarding the inhibitory effect of fucosylated therapeutic antibodies on the efficacy of non-fucosylated counterparts in one medical agent. The impact of completely non-fucosylated therapeutic antibodies on therapeutic fields will be also discussed.

NK cells stimulated with IL-15 or CpG ODN enhance rituximab-dependent cellular cytotoxicity against B-cell lymphoma

OBJECTIVE

Antibody-dependent cellular cytotoxicity (ADCC) is an important mechanism in the clinical activity of rituximab for treatment of B-cell malignancies. Natural killer (NK) cells, through the activating receptor FcgammaRIIIa (CD16), play a major role in rituximab-mediated ADCC. We have studied the in vitro effect of NK stimulators, such as interleukin-15 (IL-15) and CpG oligodeoxynucleotides A-Class (CpG ODN A), in the enhancement of rituximab-mediated ADCC against B-cell lymphoma.

METHODS

Peripheral blood mononuclear cells (PBMC), purified NK cells, or NK-depleted PBMC from healthy donors, were activated with IL-15 or CpG ODN A, and cocultured with B-lymphoma cells in the presence of rituximab to evaluate the enhancement of the cytotoxicity.

RESULTS

The rituximab-mediated ADCC of IL-15-activated PBMC was twofold compared to unstimulated PBMC (73% +/- 7% vs 37% +/- 5% respectively, p < 0.001). Similarly, rituximab-mediated ADCC was enhanced when PBMC were activated with CpG ODN A as compared to CpG ODN control (61% +/- 11% vs 36% +/- 8%, respectively, p = 0.02). Nevertheless, the ADCC of purified NK cells was increased only with IL-15. NK-depleted PBMC activated with either IL-15 or CpG ODN A showed no ADCC, suggesting that NK are the major effector cells. Furthermore, IL-15 or CpG ODN A-activated PBMC, but not activated purified NK cells, secreted large amounts of interferon-gamma in the presence of rituximab-coated lymphoma cells.

CONCLUSIONS

IL-15 and CpG ODN A enhance rituximab-mediated ADCC against B-cell lymphoma. Under these conditions, NK cells seem to be the main effector cells mediating ADCC. These findings suggest that these agents could be used as adjuvants in combination with rituximab for patients with B-cell lymphoma.

Increased natural killer cell expression of CD16, augmented binding and ADCC activity to rituximab among individuals expressing the Fc{gamma}RIIIa-158 V/V and V/F polymorphism

The presence of valine (V) at position 158 of FcgammaRllla (CD16) is known to improve clinical response to rituximab in indolent non-Hodgkin lymphoma (NHL). Little is known about the basic mechanisms for this observation. We examined natural killer (NK) cells from healthy donors representing the FcgammaRIIIa-158 polymorphic subgroups (V/V, V/F, and F/F) for gene transcript and cell surface CD16 expression, rituximab binding, and rituximab-dependent NK cell-mediated cytotoxicity. We observed higher levels of FcgammaRIIIa transcripts among individuals with the FcgammaRIIIa-158 V/V versus V/F or F/F genotype (P < .001); increased cell surface CD16 expression by quantitative flow cytometry on NK cells from individuals expressing at least one valine at FcgammaRIIIa-158 versus F/F (P = .029); as well as augmented rituximab binding and rituximab-mediated, antibody-dependent cellular cytotoxicity (ADCC). These results suggest that individuals expressing at least one valine at FcgammaRIIIa-158 might, in part, have better clinical outcomes due to increased CD16 expression, rituximab binding, and rituximab-mediated ADCC.

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

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 FcgammaRI 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.

Macrophage colony-stimulating factor enhances rituximab-dependent cellular cytotoxicity by monocytes

Recent studies suggest that monocytes are the dominant effectors by which rituximab induces cell death in B-cell lymphoma. Because macrophage colony-stimulating factor (M-CSF) can enhance the cytotoxicity of monocytes, the authors examined whether this growth factor can enhance their ability to kill lymphoma cells in vitro. Monocytes derived from a healthy volunteer were cultured for 48 h in the presence or absence of M-CSF. Monocytes stimul ated with M-CSF were significantly more cytotoxic to Daudi B-cell lymphomas than unstimulated monocytes. Flow cytometry revealed that M-CSF increased monocyte expression of Fcgamma receptors III and I by 1.6- and 1.5-fold, whereas the expression of Fcgamma receptor II remained unchanged. These results suggest that pretreatment with M-CSF can improve the therapeutic efficacy of rituximab against intractable CD20(+) lymphoma.

Recombinant therapeutic monoclonal antibodies: mechanisms of action in relation to structural and functional duality

Naked therapeutic recombinant monoclonal antibodies (mAbs) are bifunctional molecules. On the one hand, they recognize their antigen through the variable regions of the antigen binding portion (Fab). The recombinant mAb binding to a soluble or a membrane antigen may interfere with one or several functions of this antigen, leading to the therapeutic effect. On the other hand, since their crystalisable portion (Fc) is humanized (usually IgG1), they interact efficiently with human Fc-binding molecules, such as C1q and receptors for the Fc portion of IgG (FcgammaR). Thus, they initiate the classical pathway of complement and activate FcgammaR-expressing cells. The recruitment of these patient immune effector functions is essential in the therapeutic effect of several recombinant mAbs used in oncology. The aim of this review is to describe the main mechanisms of action of recombinant mAbs in relation to this structural and functional duality.

High level of MUC1 in serum of ovarian and breast cancer patients inhibits huHMFG-1 dependent cell-mediated cytotoxicity (ADCC)

The huHMFG-1 (AS1402) antibody is a humanised IgG1 directed against MUC1 and is currently in clinical trials for the treatment of breast carcinoma. Adenocarcinomas over-express and shed MUC1, and high MUC1 serum levels are associated with progressive disease. Here, we have investigated the effects of MUC1 present in sera from breast and ovarian cancer patients and that of NK cells on in vitro huHMFG-1-mediated ADCC, performed with and without the addition of various cytokines. Screening for patients with high levels of NK cells bearing the FcgammaRIIIa-158V polymorphism, adjusting the dosage to circulating levels of MUC1 and co-administration of NK cell activating cytokines may increase the efficacy of huHMFG-1 treatment.

Antibody-dependent cellular cytotoxicity of cetuximab against tumor cells with wild-type or mutant epidermal growth factor receptor

Cetuximab (Erbitux, IMC-C225) is a monoclonal antibody targeted to the epidermal growth factor receptor (EGFR). To clarify the mode of antitumor action of cetuximab, we examined antibody-dependent cellular cytotoxicity (ADCC) activity against several tumor cell lines expressing wild-type or mutant EGFR. ADCC activity and complement-dependent cytolysis activity were analyzed using the CytoTox 96 assay. ADCC activities correlated with the EGFR expression value (R = 0.924). ADCC activities were detected against all tumor cell lines, except K562 cells in a manner dependent on the cellular EGFR expression level, whereas complement-dependent cytolysis activity was not detected in any of the cell lines. The ADCC activity mediated by cetuximab was examined in HEK293 cells transfected with wild-type EGFR (293W) and a deletional mutant of EGFR (293D) in comparison with the mock transfectant (293M). ADCC activity was detected in 293W and 293D cells, in a cetuximab dose-dependent manner, but not in 293M cells (<10%). These results indicate that ADCC-dependent antitumor activity results from the degree of affinity of cetuximab for the extracellular domain of EGFR, independent of EGFR mutation status. These results suggest ADCC activity to be one of the modes of therapeutic action of cetuximab and to depend on EGFR expression on the tumor cell surface.

Interindividual variability in the concentration-effect relationship of antilymphocyte globulins - a possible influence of FcgammaRIIIa genetic polymorphism

AIMS

Polyclonal antilymphocyte globulins (ALGs) are currently used in transplantation, but the sources of interindividual variability of their effect are poorly understood. No pharmacokinetic-pharmacodynamic (PK-PD) study of ALG is available. Moreover, the genetic polymorphism of FcgammaRIIIa, a receptor for the Fc portion of immunoglobulins involved in antibody-dependent cellular cytotoxicity (ADCC), may influence their concentration-effect relationship.

METHODS

Fourteen kidney transplant patients treated by horse ALG were included in a prospective, noncomparative study. A population two-compartment PK model including a time dependence of the central volume of distribution was developed. Total lymphocyte count was used as biomarker of effect. Concentration-effect data were described using a physiological indirect response model, combining concentration-dependent and -independent inhibitions of lymphocyte input into the circulation. In addition, six kidney transplant patients in whom ALG concentrations were not available were included retrospectively. All patients were genotyped for FCGR3A.

RESULTS

Both the PK and the PK-PD model described the data satisfactorily and showed high interindividual variability. Asymptotic T(1/2)-alpha and T(1/2)-beta-values were 1.3 and 25 days, respectively. The concentration of ALG leading to a 50% inhibition of lymphocyte input (IC(50)) was lower in FCGR3A-V carriers than in FCGR3A-F/F patients (383 +/- 199 vs. 593 +/- 209 mg l(-1), P = 0.008).

CONCLUSIONS

This is the first description of the ALG effect on lymphocyte count using PK-PD modelling. Our results show that part of the variability in their concentration-effect relationship may be explained by FcgammaRIIIa genetic polymorphism and therefore that horse ALG may deplete lymphocytes by ADCC.

Autotransplant conditioning regimens for aggressive lymphoma: are we on the right road?

High-dose chemotherapy and autologous stem cell transplant (ASCT) is the standard approach for chemosensitive, relapsed aggressive non-Hodgkin's lymphoma (NHL). Various conditioning regimens have been used as treatment before ASCT and disease-free (DFS) and overall survival (OS) rates range from 34 to 60% and 26 to 46%, respectively. To date, few comparative randomized trials have been performed and no regimen has demonstrated superiority to another. Reduction of disease relapse remains the major hurdle for improving patient outcome and in vitro and in vivo purging of lymphoma cells has not necessarily enhanced results. Rituximab pre-mobilization and post-transplant appear to provide better response rates with OS approaching 87-91% at 2-3 years. Newer approaches with radioimmunotherapy may raise DFS to 78% and OS to 93%, albeit with short follow-up. Advances in the conditioning regimens and supportive care have reduced transplant-related mortality to less than 10%. In this review we discuss commonly utilized conditioning regimens, describe their pros and cons and address purging and present conditioning strategies. Owing to the poor outcome with conventional chemotherapy in mantle cell, Burkitt's and T-cell lymphoma, we propose the standard approach of front-line ASCT for these high-risk lymphoma patients. Finally, we will present novel strategies, which can enhance the anti-lymphoma effect, at the same time reducing toxicity, to improve the outcome of ASCT in NHL patients.

Prospects for the use of NK cells in immunotherapy of human cancer

Current insights into the molecular specificities that regulate natural killer (NK)-cell function suggest that it might be possible to design NK-cell-based immunotherapeutic strategies against human cancer. Here, we describe evidence for NK-cell targeting of human tumours and address crucial questions that, in our opinion, require consideration for the development of successful NK-cell-based therapies. Appropriately used, we predict that NK cells will have a role, both directly and in combination with other treatment modalities, in future treatment of cancer.

Relevance, advantages and limitations of animal models used in the development of monoclonal antibodies for cancer treatment

Antibody humanisation through recombinant DNA technology was a key step in allowing monoclonal antibodies (mAbs) to reach the clinic, particularly for the treatment of cancer. As a consequence, they are less adapted to animal studies, although these studies continue to be important tools to study antibody distribution and action at the level of a whole organism. Moreover, preclinical studies in animals are mandatory before the approval of biologics license applications for mAbs by the U.S. Food and Drug Administration (FDA) or European Agency for the Evaluation of Medicinal Products (EMEA). Different parameters should be taken in consideration before starting animal experiments with recombinant mAbs, including antibody cross-reactivity, immunogenicity, pharmacokinetics, and possible interactions with the host immune system. The various interspecies differences are reviewed and discussed in light of the pharmacological properties expected in patients. In doing so, this article aims to provide a critical review of the animal models used in preclinical studies of mAbs for cancer treatment. In particular, their relevance, advantages and limitations will be discussed.

Enhanced binding affinity for FcgammaRIIIa of fucose-negative antibody is sufficient to induce maximal antibody-dependent cellular cytotoxicity

Antibody-dependent cellular cytotoxicity (ADCC) is considered to be an important therapeutic function for clinical efficacy of monoclonal antibodies. Recent studies have revealed two methods to increase binding affinity for FcgammaRIIIa and enhance ADCC more efficiently for antibodies: (i) fucose removal from antibody N-linked complex oligosaccharides and (ii) amino acid mutations in the antibody Fc region. In this study, we compare the biological activities of the methods of generating high ADCC antibodies. We used a fucose-negative antibody and two antibodies with sets of mutations, demonstrated previously to optimally enhance ADCC using the chimeric anti-CD20 antibody, rituximab, as the model. Both amino acid mutant antibodies showed a significantly higher affinity for recombinant FcgammaRIIIa than fucose-negative antibody when compared using biosensor analysis. The removal of fucose from the antibodies bearing amino acid mutations exhibited a further enhancement of binding to recombinant FcgammaRIIIa and significantly increased binding to natural killer (NK) cells. Despite the differences manifested in binding for the FcgammaR, ADCCs were indistinguishable between methods and even when the methods were combined. These results indicate that the affinity of binding to FcgammaRIIIa does not predict ADCC beyond a certain threshold and that each method alone is sufficient to induce maximal ADCC of the antibody.

Pharmacokinetics of rituximab and its clinical use: thought for the best use?

Rituximab (MabThera, Rituxan) is a chimaeric monoclonal antibody increasingly used in the treatment of B-lymphoproliferative disorders and autoimmune diseases. Rituximab is now associated with chemotherapy for the treatment of non-Hodgkin's lymphoma and should be approved soon in maintenance strategies. During its rapid clinical development, rituximab schedules were dictated more often by logistical rather than by scientific considerations. In addition, early clinical phases have shown that rituximab exposure was variable in patients receiving similar doses and that clinical response was related to rituximab concentrations. There is however limited information on rituximab pharmacokinetics and on factors influencing individual exposure to this monoclonal antibody, although a better understanding of these factors is needed to optimise its dosing regimen. This review focuses on the current knowledge on rituximab pharmacokinetics and on factors influencing individual exposure and suggests ways to improve its clinical use.

Systemic lupus erythematosus: multiple immunological phenotypes in a complex genetic disease

Systemic lupus erythematosus (SLE) is a complex polygenic autoimmune disease characterized by the presence of anti-nuclear autoantibodies (ANAs) that are often detectable years prior to the onset of clinical disease. The disease is associated with a chronic activation of the immune system, with the most severe forms progressing to inflammatory damage that can impact multiple organ systems in afflicted individuals. Current therapeutic strategies poorly control disease manifestations and are generally immunosuppressive. Recent studies in human patient populations and animal models have associated elements of the innate immune system and abnormalities in the immature B lymphocyte receptor repertoires with disease initiation. A variety of cytokines, most notably type I interferons, play important roles in disease pathogenesis and effector mechanisms. The genetic basis for disease susceptibility is complex, and analyses in humans and mice have identified multiple susceptibility loci, several of which are located in genomic regions that are syntenic between humans and mice. The complexities of the genetic interactions that mediate lupus have been investigated in murine model systems by characterizing the progressive development of disease in strains expressing various combinations of susceptibility alleles. These analyses indicate that genetic epistasis dramatically impact disease development and support the feasibility of identifying molecular pathways that can suppress disease progression without completely impairing normal immune function.

Non-fucosylated therapeutic antibodies as next-generation therapeutic antibodies

Most of the existing therapeutic antibodies that have been licensed and developed as medical agents are of the human IgG1 isotype, the molecular weight of which is approximately 150 kDa. Human IgG1 is a glycoprotein bearing two N-linked biantennary complex-type oligosaccharides bound to the antibody constant region (Fc), in which the majority of the oligosaccharides are core fucosylated, and it exercises the effector functions of antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity through the interaction of the Fc with either leukocyte receptors (FcgammaRs) or complement. Recently, therapeutic antibodies have been shown to improve overall survival as well as time to disease progression in a variety of human malignancies, such as breast, colon and haematological cancers, and genetic analysis of FcgammaR polymorphisms of cancer patients has demonstrated that ADCC is a major antineoplasm mechanism responsible for clinical efficacy. However, the ADCC of existing licensed therapeutic antibodies has been found to be strongly inhibited by serum due to nonnpecific IgG competing for binding of the therapeutics to FcgammaRIIIa on natural killer cells, which leads to the requirement of a significant amount of drug and very high costs associated with such therapies. Moreover, enhanced ADCC of non-fucosylated forms of therapeutic antibodies through improved FcgammaRIIIa binding is shown to be inhibited by the fucosylated counterparts. In fact, non-fucosylated therapeutic antibodies, not including the fucosylated forms, exhibit the strongest and most saturable in vitro and ex vivo ADCC among such antibody variants with improved FcgammaRIIIa binding as those bearing naturally occurring oligosaccharide heterogeneities and artificial amino acid mutations, even in the presence of plasma IgG. Robust stable production of completely non-fucosylated therapeutic antibodies in a fixed quality has been achieved by the generation of a unique host cell line, in which the endogenous alpha-1,6-fucosyltransferase (FUT8) gene is knocked out. Thus, the application of non-fucosylated antibodies is expected to be a promising approach as next-generation therapeutic antibodies with improved efficacy, even when administrated at low doses in humans in vivo. Clinical trials using non-fucosylated antibody therapeutics are underway at present.

Activation, coactivation, and costimulation of resting human natural killer cells

Natural killer (NK) cells possess potent perforin- and interferon-gamma-dependent effector functions that are tightly regulated. Inhibitory receptors for major histocompatibility complex class I display variegated expression among NK cells, which confers specificity to individual NK cells. Specificity is also provided by engagement of an array of NK cell activation receptors. Target cells may express ligands for a multitude of activation receptors, many of which signal through different pathways. How inhibitory receptors intersect different signaling cascades is not fully understood. This review focuses on advances in understanding how activation receptors cooperate to induce cytotoxicity in resting NK cells. The role of activating receptors in determining specificity and providing redundancy of target cell recognition is discussed. Using Drosophila insect cells as targets, we have examined the contribution of individual receptors. Interestingly, the strength of activation is not determined simply by additive effects of parallel activation pathways. Combinations of signals from different receptors can have different outcomes: synergy, no enhancement over individual signals, or additive effects. Cytotoxicity requires combined signals for granule polarization and degranulation. The integrin leukocyte function-associated antigen-1 contributes a signal for polarization but not for degranulation. Conversely, CD16 alone or in synergistic combinations, such as NKG2D and 2B4, signals for phospholipase-C-gamma- and phosphatidylinositol-3-kinase-dependent degranulation.

Fc gamma receptors play a dominant role in protective tumor immunity against a virus-encoded tumor-specific antigen in a murine model of experimental pulmonary metastases

Simian virus 40 (SV40) large tumor antigen (Tag) represents a virus-encoded tumor-specific antigen expressed in many types of human cancers and a potential immunologic target for antitumor responses. Fc receptors are important mediators in the regulation and execution of host effector mechanisms against conditions including infectious diseases, autoimmunity, and cancer. By examining tumor protection in SV40 Tag-immunized wild-type BALB/c mice using an experimental pulmonary metastasis model, we attempted to address whether engagement of the immunoglobulin G Fc receptors (FcgammaRs) on effector cells is necessary to mediate antitumor responses. All immunized BALB/c FcgammaR-/- knockout mice developed anti-SV40 Tag antibody responses prior to experimental challenge with a tumorigenic cell line expressing SV40 Tag. However, all mice deficient in the activating FcgammaRI (CD64) and FcgammaRIII (CD16) were unable to mount protective immunologic responses against tumor challenge and developed tumor lung foci. In contrast, mice lacking the inhibitory receptor FcgammaRII (CD32) demonstrated resistance to tumorigenesis. These results underscore the importance of effector cell populations expressing FcgammaRI/III within this murine tumor model system, and along with the production of a specific humoral immune response, antibody-dependent cell-mediated cytotoxicity (ADCC) may be a functioning mechanism of tumor clearance. Additionally, these data demonstrate the potential utility of ADCC as a viable approach for targeting vaccination strategies that promote FcgammaRI/III scavenging pathways against cancer.

Critical issues of current and future developments in the treatment of immune thrombocytopenic purpura

B-cell depletion with rituximab has become a reasonable option for thrombocytopenic purpura (ITP) patients who are refractory for corticosteroids and/or splenectomy, with a response rate of about 55%. The side effects are mostly mild and easily manageable. Long lasting responses are likely in patients who achieve normal platelet counts. The mechanism of action of rituximab in immune-mediated disease in general and ITP in particular is not completely clear. Most probably, depletion of the memory B-cell compartment causes a decrease in autoantibody formation. To date it is impossible to predict the response to rituximab, although the presence of a high affinity Fc receptor for IgG seems to have positive predictive value. Future studies will have to clarify these issues, as well as possible effects of repeated rituximab treatment on primary and secondary immune responses.

Application and potential limitations of animal models utilized in the development of trastuzumab (Herceptin): a case study

The preclinical and clinical development of trastuzumab, a humanized monoclonal antibody directed against a juxtamembrane epitope in the HER2 receptor ectodomain, relied heavily on the use of animal models to validate HER2 as a potential MAb target. The identification of HER2 (neu) as a proto-oncogene was first established in a carcinogen-induced brain tumor in the rat. Transgenic mouse technology led to an understanding of the role of HER2 in pathogenesis of breast cancer. Transfection studies of human HER2 cDNA into murine xenograft models further explored the role HER2 plays in tumor progression and metastasis. A murine subrenal capsule fresh human tumor explant assay was utilized to test efficacy of various murine monoclonal anti-HER2 antibodies, and the data were helpful in choosing the most efficacious for subsequent human engineering for clinical use. HER2-overexpressing xenograft models in athymic mice were used to test the efficacy of anti-HER2 antibodies, develop dose-response relationships, measure drug interactions between trastuzumab and chemotherapy, and optimize dosing schedules of chemotherapeutics combined with trastuzumab. In this work, we will highlight the utility of animal models exploited in the development of trastuzumab - noting not only their contribution to drug development but also their limitations in translation of preclinical data into the clinic. It is likely that the experience we gained in the case of preclinical animal models to study in vivo effects of trastuzumab have parallels in the development of other monoclonal antibodies since overcoming the species boundaries (i.e. cross-reactivity with antigenic determinant, development of cross-species neutralizing antibodies, and cross-species interaction with activating Fc receptors on immune effector cells) are major limitations in the design and interpretation of preclinical/translational experiments designed to fulfill various regulatory requirements prior to initiation of phase I human clinical trials.

The anti-lymphoma effect of antibody-mediated immunotherapy is based on an increased degranulation of peripheral blood natural killer (NK) cells

BACKGROUND

In patients treated with rituximab and alemtuzumab for lymphomas or CLL, antibody-dependent cellular cytotoxicity (ADCC) is a major mechanism of action. Therefore, assessment of ADCC is mandatory to understand the complex mechanisms leading to the anti-lymphoma effects of monoclonal antibodies (mAb). Due to methodical difficulties, little is yet known about the relevant cell subpopulations and effector mechanisms leading to tumor lysis in ADCC.

METHODS

We used a novel flow cytometric assay that detects CD107a as a marker for NK-cell degranulation to characterize and quantify peripheral blood natural killer (NK) cells mediating ADCC in vitro and in vivo.

RESULTS

We observed specific and dose-dependent NK-cell activation after administration of rituximab and alemtuzumab. The number of degranulating NK cells was closely related to the concentration of mAb and the effector:target ratio. We were able to quantify and characterize the peripheral blood NK cells mediating ADCC. The majority of degranulating NK cells had the phenotype: CD56(dim), CD69(+), NKG2D(+), NKp30(-), NKp46(-), and CD94(-). Furthermore, we found that the CD107a assay can also visualize ADCC under clinical conditions as we observed increased numbers of NK cells degranulating in response to CD20(+) lymphoma cell lines in patients with non-Hodgkin's lymphoma treated with rituximab.

CONCLUSIONS

We were able to quantify and characterize NK cells mediating ADCC with a new and feasible method. The CD107a assay may be useful for predicting treatment responses of individual patients and may help find the optimal dosage and timing for treatment with mAb.

Protein therapeutics: new applications for pharmacogenetics

Pharmacogenetic studies have traditionally focused on genes involved in processes that affect the pharmacokinetics of small-molecule drugs, such as drug metabolism. However, attention is shifting to the effects of genetic variations in drug targets and associated pathway components on drug responses. We describe how these variations are important for understanding differences in responses to the growing number of protein therapeutics that are entering clinical practice. Pharmacogenetic studies of these drugs are surveyed, and issues important to the success of such endeavours are discussed. As novel protein therapeutics are introduced, we anticipate that the use of pharmacogenetics will assume a key role in their development and clinical application.

Anti-CD20 monoclonal antibody with enhanced affinity for CD16 activates NK cells at lower concentrations and more effectively than rituximab

Growing evidence indicates that the affinity of monoclonal antibodies (mAbs) for CD16 (FcgammaRIII) plays a central role in the ability of the mAb to mediate antitumor activity. We evaluated how CD16 polymorphisms, and mAb with modified affinity for target antigen and CD16, affect natural killer (NK) cell phenotype when CD20(+) malignant B cells were also present. The mAb consisted of rituximab (R), anti-CD20 with enhanced affinity for CD20 (AME-B), and anti-CD20 with enhanced affinity for both CD20 and CD16 (AME-D). Higher concentrations of mAb were needed to induce CD16 modulation, CD54 up-regulation, and antibody-dependent cellular cytotoxicity (ADCC) on NK cells from subjects with the lower affinity CD16 polymorphism. The dose of mAb needed to induce NK activation was lower with AME-D irrespective of CD16 polymorphism. At saturating mAb concentrations, peak NK activation was greater for AME-D. Similar results were found with measurement of CD16 modulation, CD54 up-regulation, and ADCC. These data demonstrate that cells coated with mAb with enhanced affinity for CD16 are more effective at activating NK cells at both low and saturating mAb concentrations irrespective of CD16 polymorphism, and they provide further evidence for the clinical development of such mAbs with the goal of improving clinical response to mAb.

Modulation of therapeutic antibody effector functions by glycosylation engineering: influence of Golgi enzyme localization domain and co-expression of heterologous beta1, 4-N-acetylglucosaminyltransferase III and Golgi alpha-mannosidase II

The effector functions elicited by IgG antibodies strongly depend on the carbohydrate moiety linked to the Fc region of the protein. Therefore several approaches have been developed to rationally manipulate these glycans and improve the biological functions of the antibody. Overexpression of recombinant beta1,4-N-acetylglucosaminyltransferase III (GnT-III) in production cell lines leads to antibodies enriched in bisected oligosaccharides. Moreover, GnT-III overexpression leads to increases in non-fucosylated and hybrid oligosaccharides. Such antibody glycovariants have increased antibody-dependent cellular cytotoxicity (ADCC). To explore a further variable besides overexpression of GnT-III, we exchanged the localization domain of GnT-III with that of other Golgi-resident enzymes. Our results indicate that chimeric GnT-III can compete even more efficiently against the endogenous core alpha1,6-fucosyltransferase (alpha1,6-FucT) and Golgi alpha-mannosidase II (ManII) leading to higher proportions of bisected non-fucosylated hybrid glycans ("Glyco-1" antibody). The co-expression of GnT-III and ManII led to a similar degree of non-fucosylation as that obtained for Glyco-1, but the majority of the oligosaccharides linked to this antibody ("Glyco-2") are of the complex type. These glycovariants feature strongly increased ADCC activity compared to the unmodified antibody, while Glyco-1 (hybrid-rich) features reduced complement-dependent cytotoxicity (CDC) compared to Glyco-2 or unmodified antibody. We show that apart from GnT-III overexpression, engineering of GnT-III localization is a versatile tool to modulate the biological activities of antibodies relevant for their therapeutic application.

Nonfucosylated Therapeutic IgG1 Antibody Can Evade the Inhibitory Effect of Serum Immunoglobulin G on Antibody-Dependent Cellular Cytotoxicity through its High Binding to FcγRIIIa

PURPOSE

Recent studies have revealed that fucosylated therapeutic IgG1s need high concentrations to compensate for FcgammaRIIIa-competitive inhibition of antibody-dependent cellular cytotoxicity (ADCC) by endogenous human plasma IgG. Here, we investigated whether ADCC of nonfucosylated therapeutic IgG1 is also influenced by plasma IgG in the same way as fucosylated IgG1s.

EXPERIMENTAL DESIGN

Ex vivo ADCC upon CD20+ human B cells was induced by incubation of human whole blood with nonfucosylated and/or fucosylated anti-CD20 IgG1s rituximab, and quantified by measuring the remaining CD19+ human B cells using flow cytometry.

RESULTS

Nonfucosylated anti-CD20 showed markedly higher (over 100-fold based on EC50) ex vivo B-cell depletion activity than its fucosylated counterpart in the presence of plasma IgG. The efficacy of fucosylated anti-CD20 was greatly diminished in plasma, resulting in the need for a high concentration (over 1.0 microg/mL) to achieve saturated efficacy. In contrast, nonfucosylated anti-CD20 reached saturated ADCC at lower concentrations (0.01-0.1 microg/mL) with much higher efficacy than fucosylated anti-CD20 in all nine donors through improved FcgammaRIIIa binding. Noteworthy, the high efficacy of nonfucosylated anti-CD20 was inhibited by addition of fucosylated anti-CD20. Thus, the efficacy of a 1:9 mixture (10 microg/mL) of nonfucosylated and fucosylated anti-CD20s was inferior to that of a 1,000-fold dilution (0.01 microg/mL) of nonfucosylated anti-CD20 alone.

CONCLUSIONS

Our data showed that nonfucosylated IgG1, not including fucosylated counterparts, can evade the inhibitory effect of plasma IgG on ADCC through its high FcgammaRIIIa binding. Hence, nonfucosylated IgG1 exhibits strong therapeutic potential through dramatically enhanced ADCC at low doses in humans in vivo.