Therapeutic efficacy of FcγRI/CD64-directed bispecific antibodies in B-cell lymphoma

Serum immunoglobulin and the threshold of Fc receptor-mediated immune activation

Antibodies can mediate immune recruitment or clearance of immune complexes through the interaction of their Fc domain with cellular Fc receptors. Clustering of antibodies is a key step in generating sufficient avidity for efficacious receptor recognition. However, Fc receptors may be saturated with prevailing, endogenous serum immunoglobulin and this raises the threshold by which cellular receptors can be productively engaged. Here, we review the factors controlling serum IgG levels in both healthy and disease states, and discuss how the presence of endogenous IgG is encoded into the functional activation thresholds for low- and high-affinity Fc receptors. We discuss the circumstances where antibody engineering can help overcome these physiological limitations of therapeutic antibodies. Finally, we discuss how the pharmacological control of Fc receptor saturation by endogenous IgG is emerging as a feasible mechanism for the enhancement of antibody therapeutics.

Distinct phenotype of neutrophil, monocyte, and eosinophil populations indicates altered myelopoiesis in a subset of patients with multiple myeloma

Hematologic malignancies, including multiple myeloma (MM), promote systemic immune dysregulation resulting in an alteration and increased plasticity of myeloid cell subsets. To determine the heterogeneity of the myeloid cell compartment in the peripheral blood of patients with MM, we performed a detailed investigation of the phenotype and function of myeloid subpopulations. We report that a subset of MM patients exhibits a specific myeloid cell phenotype indicative of altered myelopoiesis characterized by significant changes in the properties of circulating granulocytic, monocytic, and eosinophilic populations. The subset, referred to as MM2, is defined by a markedly elevated level of CD64 (FcγRI) on the surface of circulating neutrophils. Compared to healthy controls or MM1 patients displaying intermediate levels of CD64, neutrophils from MM2 patients exhibit a less differentiated phenotype, low levels of CD10 and CXC chemokine receptor 2 (CXCR2), increased capacity for the production of mitochondrial reactive oxygen species, and an expansion of CD16^neg immature neutrophil subset. Classical and patrolling monocytes from MM2 patients express elevated levels of CD64 and activation markers. MM2 eosinophils display lower levels of C-C Chemokine receptor 3 (CCR3), Toll-like receptor 4 (TLR4, CD284), and tissue factor (TF, CD142). The MM2 (CD64^high) phenotype is independent of age, race, sex, and treatment type. Characteristic features of the MM2 (CD64^high) phenotype are associated with myeloma-defining events including elevated involved/uninvolved immunoglobulin free light chain (FLC) ratio at diagnosis. Detailed characterization of the altered myeloid phenotype in multiple myeloma will likely facilitate the identification of patients with an increased risk of disease progression and open new avenues for the rational design of novel therapeutic approaches.

Enabling the next steps in cancer immunotherapy: from antibody-based bispecifics to multispecifics, with an evolving role for bioconjugation chemistry

In the past two decades, immunotherapy has established itself as one of the leading strategies for cancer treatment, as illustrated by the exponentially growing number of related clinical trials. This trend was, in part, prompted by the clinical success of both immune checkpoint modulation and immune cell engagement, to restore and/or stimulate the patient's immune system's ability to fight the disease. These strategies were sustained by progress in bispecific antibody production. However, despite the decisive progress made in the treatment of cancer, toxicity and resistance are still observed in some cases. In this review, we initially provide an overview of the monoclonal and bispecific antibodies developed with the objective of restoring immune system functions to treat cancer (cancer immunotherapy), through immune checkpoint modulation, immune cell engagement or a combination of both. Their production, design strategy and impact on the clinical trial landscape are also addressed. In the second part, the concept of multispecific antibody formats, notably MuTICEMs (Multispecific Targeted Immune Cell Engagers & Modulators), as a possible answer to current immunotherapy limitations is investigated. We believe it could be the next step to take for cancer immunotherapy research and expose why bioconjugation chemistry might play a key role in these future developments.

Therapeutic Potential of Neu1 in Alzheimer's Disease Via the Immune System

Alzheimer's Disease (AD) is pathologically characterized by the accumulation of soluble oligomers causing extracellular beta-amyloid deposits in form of neuritic plaques and tau-containing intraneuronal neurofibrillary tangles in brain. One proposed mechanism explaining the formation of these proteins is impaired phagocytosis by microglia/macrophages resulting in defective clearance of soluble oligomers of beta-amyloid stimulating aggregation of amyloid plaques subsequently causing AD. However, research indicates that activating macrophages in M2 state may reduce toxic oligomers. NEU1 mutation is associated with a rare disease, sialidosis. NEU1 deficiency may also cause AD-like amyloidogenic process. Amyloid plaques have successfully been reduced using NEU1.Thus, NEU1 is suggested to have therapeutic potential for AD, with lysosomal exocytosis being suggested as underlying mechanism. Studies however demonstrate that NEU1 may activate macrophages in M2 state, which as noted earlier, is crucial to reducing toxic oligomers. In this review, authors discuss the potential therapeutic role of NEU1 in AD via immune system.

Monoclonal antibody-mediated killing of tumour cells by neutrophils

Neutrophils represent the most abundant population of circulating cytotoxic effector cells. Moreover, their number can be easily increased by treatment with granulocyte-colony stimulating factor or granulocyte macrophage-colony stimulating factor, without the need for ex vivo expansion. Because neutrophils express Fc receptors, they have the potential to act as effector cells during monoclonal antibody therapy of cancer. Additionally, as neutrophils play a role in the regulation of adaptive immune responses, exploiting neutrophils in mAb therapy may result in long-term antitumour immunity. There is limited evidence that neutrophils play a prominent role in current immunoglobulin G-based immunotherapy. However, as IgA induces neutrophil recruitment, novel therapeutic strategies that aim to target the IgA Fc receptor FcαRI may fully unleash the potential of enlisting neutrophils as cytotoxic effector cells in antibody therapy of cancer.

Neutrophils in cancer

Neutrophils play an important role in cancer. This does not only relate to the well-established prognostic value of the presence of neutrophils, either in the blood or in tumor tissue, in the context of cancer progression or for the monitoring of therapy, but also to their active role in the progression of cancer. In the current review, we describe what is known in general about the role of neutrophils in cancer. What is emerging is a complex, rather heterogeneous picture with both pro- and anti-tumorigenic roles, which apparently differs with cancer type and disease stage. Furthermore, we will discuss the well-known role of neutrophils as myeloid-derived suppressor cells (MDSC), and also on the role of neutrophils as important effector cells during antibody therapy in cancer. It is clear that neutrophils contribute substantially to cancer progression in multiple ways, and this includes both direct effects on the cancer cells and indirect effect on the tumor microenvironment. While in many cases neutrophils have been shown to promote tumor progression, for instance by acting as MDSC, there are also protective effects, particularly when antibody immunotherapy is performed. A better understanding of the role of neutrophils is likely to provide opportunities for immunomodulation and for improving the treatment of cancer patients.

bisFabs: Tools for rapidly screening hybridoma IgGs for their activities as bispecific antibodies

Bispecific antibodies are a growing class of therapeutic molecules. Many of the current bispecific formats require DNA engineering to convert the parental monoclonal antibodies into the final bispecific molecules. We describe here a method to generate bispecific molecules from hybridoma IgGs in 3-4 d using chemical conjugation of antigen-binding fragments (Fabs) (bisFabs). Proteolytic digestion conditions for each IgG isotype were analyzed to optimize the yield and quality of the final conjugates. The resulting bisFabs showed no significant amounts of homodimers or aggregates. The predictive value of murine bisFabs was tested by comparing the T-cell redirected cytotoxic activity of a panel of antibodies in either the bisFab or full-length IgG formats. A variety of antigens with different structures and expression levels was used to extend the comparison to a wide range of binding geometries and antigen densities. The activity observed for different murine bisFabs correlated with those observed for the full-length IgG format across multiple different antigen targets, supporting the use of bisFabs as a screening tool. Our method may also be used for the screening of bispecific antibodies with other mechanisms of action, allowing for a more rapid selection of lead therapeutic candidates.

Chemically synthesized molecules with the targeting and effector functions of antibodies

This article reports the design, synthesis, and evaluation of a novel class of molecules of intermediate size (approximately 7000 Da), which possess both the targeting and effector functions of antibodies. These compounds—called synthetic antibody mimics targeting prostate cancer (SyAM-Ps)—bind simultaneously to prostate-specific membrane antigen and Fc gamma receptor I, thus eliciting highly selective cancer cell phagocytosis. SyAMs have the potential to combine the advantages of both small-molecule and biologic therapies, and may address many drawbacks associated with available treatments for cancer and other diseases.

Of mice and men: the need for humanized mouse models to study human IgG activity in vivo

Antibodies of the IgG isotype have a variety of pro- and anti-inflammatory effector functions, making them attractive platforms for the development of novel therapeutic approaches. Animal model systems have been invaluable to the understanding of the underlying mechanisms of IgG activity. However, differences in the IgG subclasses and Fc receptors responsible for mediating IgG-dependent effector functions, even between such closely related species as humans and monkeys, make it difficult to predict the activity of human IgG in vivo. This review will focus on currently available animal model systems used to study human IgG activity and will propose novel model systems that might enable us to obtain a closer look at the molecular and cellular mechanisms underlying human IgG activity in vivo.

Polymorphonuclear neutrophils and cancer: intense and sustained neutrophilia as a treatment against solid tumors

Polymorphonuclear neutrophils (PMN) are the most abundant circulating immune cells and represent the first line of immune defense against infection. This review of the biomedical literature of the last 40 years shows that they also have a powerful antitumoral effect under certain circumstances. Typically, the microenvironment surrounding a solid tumor possesses many of the characteristics of chronic inflammation, a condition considered very favorable for tumor growth and spread. However, there are many circumstances that shift the chronic inflammatory state toward an acute inflammatory response around a tumor. This shift seems to convert PMN into very efficient anticancer effector cells. Clinical reports of unexpected antitumoral effects linked to the prolonged use of granulocyte colony-stimulating factor, which stimulates an intense and sustained neutrophilia, suggest that an easy way to fight solid tumors would be to encourage the development of intense peritumoral PMN infiltrates. Specifically designed clinical trials are urgently needed to evaluate the safety and efficacy of such drug-induced neutrophilia in patients with solid tumors. This antitumoral role of neutrophils may provide new avenues for the clinical treatment of cancer.

Fc-receptors and immunity to malaria: from models to vaccines

The complexity and number of antigens (Ags) seen during an immune response has hampered the development of malaria vaccines. Antibodies (Abs) play an important role in immunity to malaria and their passive administration is effective at controlling the disease. Abs represent approximately 25% of all proteins undergoing clinical trials, and these 'smart biologicals' have undergone a major revival with the realization that Abs lie at the interface between innate and adaptive immunity. At least 18 Abs have FDA approval for clinical use and approximately 150 are in clinical trials, the majority for the treatment of cancer, allograft rejection or autoimmune disease. Despite these triumphs none are in development for malaria, principally because they are perceived as being too expensive for a disease mainly afflicting poor and marginalized populations. Although unlikely, at least in the foreseeable future, that Ab-based prophylaxis will be made available to the millions of people at risk from malaria, they may be incorporated into current vaccine approaches, since Abs act as correlates of protection in studies aimed at defining the best Ags to include in vaccines. Abs may also form the basis for novel vaccination strategies by targeting Ags to appropriate antigen presenting cells. Therefore, to develop the most efficacious vaccines it will be necessary to fully understand which Abs and Fc-receptors (FcRs) are best engaged for a positive outcome.

Surfactant protein D/anti-Fc receptor bifunctional proteins as a tool to enhance host defence

BACKGROUND

Drug-resistant pathogens are an increasing threat, particularly for hospitalised patients. In search of a new approach in pathogen targeting, we developed bifunctional proteins that combine broad spectrum pathogen recognition with efficient targeting to phagocytes. Pathogen recognition is provided by a recombinant fragment of surfactant protein D (rfSP-D) while targeting to phagocytic cells is accomplished by coupling rfSP-D to F(ab') fragments directed against Fcalpha receptor I (FcalphaRI) or Fcgamma receptor I (FcgammaRI). FcalphaRI and FcgammaRI are expressed on myeloid cells, and induce rapid internalisation of particles after crosslinking.

OBJECTIVE/METHODS

In this review we discuss the roles of SP-D and Fc receptors in host defence as a rationale for rfSP-D/anti-FcR bifunctional proteins. Furthermore we summarise the available data on rfSP-D/anti-FcR proteins as well as opportunities and considerations for future use of such bifunctional proteins.

RESULTS/CONCLUSION

rfSP-D/anti-FcR bifunctional proteins could be of great value for the treatment of a variety of infectious diseases. The focus in the near future should be on proof-of-principle by testing the bifunctional proteins in different mouse models of infectious disease.

Neutrophils in antibody-based immunotherapy of cancer

Monoclonal antibodies (mAb) are presently considered key therapeutic drugs for the treatment of malignancies. They can be designed to specifically target tumour-associated antigens and initiate several effector mechanisms, which potentially leads to elimination of the tumour. Through their Fc tail mAbs interact with Fc receptors (FcR) that are expressed on immune cells. Neutrophils are the most abundant circulating FcR-expressing white blood cells with potent cytotoxic ability that is enhanced in the presence of antitumour mAbs. They furthermore play a role in regulating adaptive immunity, which may lead to the initiation of antitumour immune responses. Yet, neutrophils receive surprisingly little attention as potential effector cell population. This article reviews the scientific data that supports the possibility of exploiting neutrophils for mAb-based immunotherapy of cancer. An increasing awareness and understanding of this topic may allow for future development of new anticancer therapies.

Monoclonal antibodies in the treatment of lymphoid malignancies

Rituximab (Rit) was the first monoclonal antibody approved for therapeutic use in cancer patients. Rit is a chimeric mouse/human monoclonal antibody, consisting of the human IgG1 and k constant Fc region, and a mouse variable Fab region specific against the B-cell antigen CD20. Rit exerts its antilymphoma activity through many different mechanisms. Binding of antibody to CD20 antigen, provokes apoptosis through downstream signals that lead to caspase-3 activation. Complement activation by the Fc portion of the antibody results in complement-dependent cytotoxicity. However, the most effective mechanism of action seems to be antigen-dependent cellular cytotoxicity. Effector cytotoxic cells such as natural killer cells (NK) are activated after binding to the Fc portion of the anti-CD20 molecule. Activated NK cells kill the coated lymphoma cells with the use of granzyme-perforin system. More recently, pre-clinical data support the concept that Rituximab can provoke a vaccination-like effect. Finally in-vitro experiments and clinical trials have shown that co-administration of the antibody with cytotoxics confers a strong synergistic effect. The relative contribution of these mechanisms in vivo and in different lymphoma subtypes is not well known and remains to be further evaluated. Among the different histological groups, follicular lymphoma (FL) has been proven to be the most sensitive to Rit when used as a single agent, with overall response rates of 80% and 50% in untreated and previously treated patients, respectively. Moreover, Rit in combination with chemotherapy is superior to chemotherapy alone in terms of response rate and event-free survival, while early data indicate a significant prolongation in overall survival as well. Similarly, the addition of Rit to standard chemotherapy improves the disease-free and overall survival of patients with diffuse large B-cell lymphoma. There is no doubt that Rit represents one of the greatest achievements of biotechnology engineering. However, we need to understand better the mechanisms of its action as well as the mechanisms of resistance to Rit, in order to design more effective treatment modalities.

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.

The importance of human FcgammaRI in mediating protection to malaria

The success of passive immunization suggests that antibody-based therapies will be effective at controlling malaria. We describe the development of fully human antibodies specific for Plasmodium falciparum by antibody repertoire cloning from phage display libraries generated from immune Gambian adults. Although these novel reagents bind with strong affinity to malaria parasites, it remains unclear if in vitro assays are predictive of functional immunity in humans, due to the lack of suitable animal models permissive for P. falciparum. A potentially useful solution described herein allows the antimalarial efficacy of human antibodies to be determined using rodent malaria parasites transgenic for P. falciparum antigens in mice also transgenic for human Fc-receptors. These human IgG1s cured animals of an otherwise lethal malaria infection, and protection was crucially dependent on human FcγRI. This important finding documents the capacity of FcγRI to mediate potent antimalaria immunity and supports the development of FcγRI-directed therapy for human malaria.

Malaria rivals HIV and tuberculosis as the world's most deadly infection killing a child every 30 seconds. Antibodies and their receptors (Fc-receptors) have been shown to be vital for the development of protective immunity, and as such they act as correlates of protection in studies aimed at defining the best antigens to incorporate into current vaccines. Understanding antibody types and Fc-receptors that optimally induce immunity is therefore vital to developing the best vaccines. Surrogate markers of antibody efficacy currently rely on in vitro assays that are laborious and difficult to reproduce. It remains unclear if such in vitro assays are predictive of functional immunity in humans due to the lack of suitable animal models permissive for Plasmodium falciparum. Here, we create a transgenic in vivo mouse model that has significant advantage over the use of new world primates, the only other model for human malaria. We demonstrate that this model defines an Fc-dependent mechanism of parasite destruction that cannot be assessed in current in vitro assays. The model provides both a test for therapeutic antibody efficacy prior to clinical trials in humans and an important tool in malaria vaccine development.

Targeting antigens to dendritic cells in vivo

Dendritic cells (DCs) play a key role in antigen-specific immune regulation. DCs take up and process antigens and present these as peptides through MHC molecules to T cells. Recent pre-clinical and clinical studies have exploited DCs as a means to improve vaccine efficiency. In these studies, monocyte-derived autologous DCs are loaded ex vivo with antigens and re-administered to the patient. These tailor-made vaccines are costly and labor intensive, and therefore less suitable for large-scale immunization programs. As a next step in the development of DC vaccines, it is proposed to load DCs with antigens in vivo. Drug delivery systems harboring antigens have been targeted to DCs via specific surface receptors preferentially expressed by DCs, resulting in priming of humoral and cellular immune responses. The present review focuses on the various antigen delivery systems that are currently in use and the DC surface receptors they target.

Monocyte CD64 or CD89 targeting by surfactant protein D/anti-Fc receptor mediates bacterial uptake

We recently showed that a chimeric protein, consisting of a recombinant fragment of human surfactant protein D (rfSP-D) coupled to a Fab' fragment directed against the human Fcalpha receptor (CD89), effectively targets pathogens recognized by SP-D to human neutrophils. The present study evaluates the effectiveness of chimeric rfSP-D/anti-Fc receptor proteins targeting Escherichia coli to CD89 or to the Fcgamma receptor I (CD64) on monocytes. Both chimeric rfSP-D/anti-Fc receptor proteins increased internalization of E. coli by the human promonocytic cell line U937, but only after induction of monocytic differentiation, despite the fact that the expression levels of CD64 and CD89 on undifferentiated cells were at least as high as on differentiated cells. The two chimeric rfSP-D/anti-Fc receptor proteins did not enhance each other's effect on E. coli uptake. Targeting to differentiated U937 cells was inhibited by blocking the interaction either between the rfSP-D part of the chimeric molecule and E. coli, or between the anti-Fc receptor Fab' fragment and the Fc receptor on the U937 cell. In conclusion, both CD64 and CD89 on U937 cells prove to be suitable for targeting by rfSP-D/anti-Fc receptor proteins. However, in addition to mere Fc receptor expression, effective targeting requires monocytic differentiation.

Direct targeting of genetically modified tumour cells to FcγRI triggers potent tumour cytotoxicity

Expression of the type I receptor for Fc domain of immunoglobulin (Ig)G (Fc gammaRI or CD64) is restricted to myeloid effector cells, such as monocytes, macrophages and a subset of dendritic cells. Previous work has indicated a role for Fc gammaRI in antibody-dependent phagocytosis and lysis of tumour cells. We hypothesised that tagging of tumour cells with an anti-Fc gammaRI single chain Fv (sFv) may facilitate targeting to this receptor on effector cells, thereby initiating tumour cytotoxicity. A vector encoding the sFv for an Fc gammaRI-specific antibody (H22), linked to the transmembrane domain of platelet-derived growth factor was constructed. Transfected tumour cells expressed high surface levels of functional H22-sFv, which greatly enhanced susceptibility for phagocytosis and lysis by monocytes and macrophages. The expression of H22-sFv evoked the ability of tumour cells to directly activate monocytes, as evidenced by phosphorylation of mitogen-activated protein kinase and secretion of the inflammatory cytokines interleukin (IL)-1beta, tumour necrosis factor-alpha and IL-6. Moreover, growth of tumour cells in mice expressing H22-sFv was profoundly delayed (or absent) in transgenic mice expressing human Fc gammaRI. These results demonstrated that tumour cells can be readily modified to activate cell effector mechanisms, a strategy that may be useful for in vivo targeting in patients.

Phase I clinical trial of the bispecific antibody MDX-H210 (anti-FcgammaRI x anti-HER-2/neu) in combination with Filgrastim (G-CSF) for treatment of advanced breast cancer

A phase I study of the bispecific antibody MDX-H210 in combination with granulocyte colony-stimulating factor (G-CSF) was performed in stage IV breast carcinoma patients, overexpressing HER-2/neu. MDX-H210, constructed by crosslinking antigen binding fragments (F(ab') fragments) of monoclonal antibody (mAb) H22 to Fc gamma receptor I (FcgammaRI), and mAb 520C9 to HER-2/neu, respectively, mediates the lysis of tumour cells in vitro, and in human FcgammaRI transgenic mouse models. The proto-oncogene HER-2/neu is overexpressed in approximately 30% of breast cancer patients, and represents a promising target for antibody-based immunotherapy. Fc gamma receptor I (CD64) is an effective trigger molecule, which is expressed on monocytes/macrophages, immature dendritic cells, and G-CSF-primed polymorphonuclear cells (PMN). Patients received G-CSF (Filgrastim) for 8 consecutive days, and cohorts of three patients were treated on day 4 with escalating, single doses of MDX-H210. A total of 30 patients were included, and treatment was generally well tolerated, without reaching dose-limiting toxicity. Side effects consisted mainly of fever and short periods of chills, which were timely related to elevated plasma levels of interleukin 6 and tumour necrosis factor alpha. In the last two cohorts, MDX-H210 plasma levels exceeded 1 microg ml(-1), and on circulating myeloid cells >50% saturation of FcgammaRI was found until day 4. These effector cells were highly effective in antibody-dependent cell-mediated cytotoxicity. Immunohistochemical analyses of tumour biopsies in individual patients documented infiltration of monocytes and PMN after MDX-H210 infusion. Although the clinical course of the disease was not altered by the single dose of MDX-H210, a favourable toxicity profile--even at high doses--and remarkable biological effects were seen when combined with G-CSF. Therefore, the combination of G-CSF and MDX-H210 should be evaluated in further immunotherapeutical strategies.

A novel recombinant bispecific single-chain antibody, bscWue-1 × CD3, induces T-cell-mediated cytotoxicity towards human multiple myeloma cells

The development of antibody-based strategies for the treatment of multiple myeloma (MM) has been hampered so far by the fact that suitable plasma cell-specific surface antigens have been missing. However, recently a novel monoclonal antibody, designated Wue-1, has been generated that specifically recognizes normal and malignant human plasma cells. Therefore, Wue-1 is an interesting and promising candidate to develop novel immunotherapeutic strategies for the treatment of MM. One variant for an antibody-based strategy is the bispecific antibody approach. Recombinant bispecific single-chain (bsc) antibodies are especially interesting candidates because they show exceptional biological properties. We have generated a novel MM-directed recombinant bsc antibody, bscWue-1 x CD3, and analyzed the biological properties of this antibody using the MM cell line NCI-H929 and primary cells from the bone marrow of patients with MM. We were able to show that bscWue-1 x CD3 induces efficient and selective T-cell-mediated cell death of NCI-H929 cells and primary myeloma cells in nine out of 11 cases. The bscWue-1 x CD3 Ab is efficacious even at low E:T ratios, and with or without additional T-cell pre- or costimulation. Target cell lyses were specific for Wue-1 antigen-positive cells and could be blocked by the Wue-1 monoclonal antibody.

Two new trifunctional antibodies for the therapy of human malignant melanoma

Trifunctional antibodies are able to redirect T cells and Fcgamma receptor(+) accessory immune cells to tumor targets. The simultaneous activation of these different classes of effector cells results in efficient killing of the tumor cells by different mechanisms such as phagocytosis and perforin-mediated cytotoxicity. Here, we introduce 2 new trifunctional antibodies specific for human melanoma. These trifunctional antibodies recognize with one binding arm CD3 on human T cells. The other binding arm is directed against melanoma-associated proteoglycans or melanoma-associated gangliosides (GD2 as well as GD3). They mediate specific lysis of various melanoma cell lines in correlation with the level of antigen expression in short-term cytotoxicity experiments. A combination of the 2 trifunctional antibodies was equally or even more efficient. Moreover, they induced a strong Th1 cytokine pattern with high amounts of IFN-gamma and low or no IL-4. Accordingly, CD4(+) and especially CD8(+) T cells expanded, whereas B cells, NK cells and monocytes decreased. The cytokine response was up to 16-fold higher when tumor cells were present. IFN-gamma reached cytotoxic concentrations for SK-MEL-23 melanoma cells. The induction of a T-cell-activatory and melanoma cell-inhibitory cytokine milieu together with the redirection of T-cell- and accessory cell-mediated cytotoxicity are interesting features of these trifunctional antibodies. They may be a new option for the therapy of human malignant melanoma.

Polymorphonuclear Granulocytes Induce Antibody-Dependent Apoptosis in Human Breast Cancer Cells

Recent studies in HER-2/neu-targeted immunotherapy demonstrated that polymorphonuclear neutrophils (PMN) mediated Ab-dependent cellular cytotoxicity against HER-2/neu-positive breast cancer cell lines. However, the mechanism of cell death remained unclear. We used several assays to analyze the induction of apoptosis in the breast cancer cell line SK-BR-3 via PMN-dependent Ab-dependent cellular cytotoxicity. In the presence of the HER-2/neu Ab 520C9 and PMN from healthy donors, apoptosis occurred as detected by annexin V binding and disappearance of euploid SK-BR-3 nuclei, which can be differentiated from PMN nuclei by their increased DNA contents. Apoptosis induction was observed with E:T cell ratios as low as 10:1. Laser scanning fluorescence microscopy of TUNEL tumor cells or staining for cleaved cytokeratin-18 further confirmed apoptosis of the SK-BR-3 breast cancer cells. Killing via 520C9 was dependent on the interaction with FcR on PMN, because 1) F(ab')(2) fragments of 520C9 mediated no cytotoxicity, 2) target cell death was influenced by a biallelic polymorphism of FcgammaRIIa on the effector cells, and 3) a bispecific Ab against HER-2/neu and the IgA receptor (FcalphaRI) expressed on effector cells significantly induced apoptosis. Thus, PMN induce Ab-dependent apoptosis against human breast cancer cells targeted with HER-2/neu-directed mAbs or FcR directed bispecific Abs.

HLA class II antibodies in the treatment of hematologic malignancies

Promising results have suggested human leukocyte antigen (HLA) class II as potential target for antibody-based lymphoma therapy. Thus, antibodies against HLA class II induced apoptosis in vitro, as well as complement-dependent cytotoxicity (CDC) and effector cell-mediated cytotoxicity (ADCC). Furthermore, animal models demonstrated strong antitumor effects in vivo. Importantly, early clinical studies with antibodies Lym-1 or Hu1D10, both against HLA-DR variants, suggested therapeutic potential. However, the increased risk of serious toxicity may require an improved understanding of the clinically relevant mechanisms of action of HLA class II-directed antibodies, which may then allow generation of optimized antibody constructs to achieve optimal therapeutic efficacy.

Efficient elimination of chronic lymphocytic leukaemia B cells by autologous T cells with a bispecific anti-CD19/anti-CD3 single-chain antibody construct

Recently, we have shown that a novel recombinant bispecific single-chain antibody construct (bscCD19 x CD3), induces highly efficacious lymphoma-directed cytotoxicity mediated by unstimulated peripheral T lymphocytes. Functional analysis of bscCD19 x CD3 has so far been exclusively performed with human B lymphoma cell lines and T cells from healthy donors. Here we analysed the properties of bscCD19 x CD3 using primary B cells and autologous T cells from healthy volunteers or patients with B-cell chronic lymphocytic leukaemia (B-CLL). We show that bscCD19 x CD3 induces T-cell-mediated depletion of nonmalignant B cells in all four cases and depletion of primary lymphoma cells in 22 out of 25 cases. This effect could be observed at low effector-to-target (E:T) ratios and in the majority of cases without additional activation of autologous T cells by IL-2. Even in samples derived from patients heavily pretreated with different chemotherapy regimens, strong cytotoxic effects of bscCD19 x CD3 could be observed. The addition of bscCD19 x CD3 to patients' cells resulted in an upregulation of activation-specific cell surface antigens on autologous T cells and elevated levels of CD95 on lymphoma B cells. Although anti-CD95 antibody CH-11 failed to induce apoptosis in lymphoma cells, we provide evidence that B-CLL cell depletion by bscCD3 x CD3 is mediated at least in part by apoptosis via the caspase pathway.

Treatment of breast cancer with chemotherapy in combination with filgrastim: approaches to improving therapeutic outcome

Chemotherapy improves disease-free and overall survival in breast cancer, and its benefit is directly related to the percentage of the planned dose that is actually administered. In all current chemotherapeutic regimens, a substantial proportion of patients have reductions and/or delays in dosage due to side effects. In about half such cases, the delays or reductions are related to neutropenia. Overall, approximately 30% of patients have a reduction to less than 85% of the planned dosage. Women aged > or = 50 years are more likely to experience a reduction or delay in dose. Dose-intense regimens (excluding myeloablative high-dose chemotherapy) which increase the dose of chemotherapy or reduce the interval between cycles, or both, are a promising approach now under investigation. The human granulocyte colony-stimulating factor filgrastim reduces the incidence of neutropenia and facilitates adherence to full dose intensity in both standard and dose-intensified regimens. A model based on the first-cycle absolute neutrophil count nadir has been developed and validated to determine which patients should receive filgrastim. A cost benefit associated with the use of filgrastim in patients with breast cancer has been realised. This may lead to a re-evaluation of the current treatment guidelines.

Mac-1 (CD11b/CD18) is crucial for effective Fc receptor-mediated immunity to melanoma

Antibody-reliant destruction of tumor cells by immune effector cells is mediated by antibody-dependent cellular cytotoxicity, in which Fc receptor (FcR) engagement is crucial. This study documents an important role for the beta(2) integrin Mac-1 (CD11b/CD18) in FcR-mediated protection against melanoma. CD11b-deficient mice, those that lack Mac-1, were less protected by melanoma-specific monoclonal antibody TA99 than wild-type (WT) mice. Significantly more lung metastases and higher tumor loads were observed in Mac-1(-/-) mice. Histologic analyses revealed no differences in neutrophil infiltration of lung tumors between Mac-1(-/-) and WT mice. Importantly, Mac-1(-/-) phagocytes retained the capacity to bind tumor cells, implying that Mac-1 is essential during actual FcR-mediated cytotoxicity. In summary, this study documents Mac-1 to be required for FcR-mediated antimelanoma immunity in vivo and, furthermore, supports a role for neutrophils in melanoma rejection.

Current strategies of antibody-based treatment in Hodgkin's disease

Many new approaches involving antibody-based agents have given promising results in experimental Hodgkin's disease (HD) models. Clinical trials with monoclonal antibodies, immunotoxins, bispecific constructs and radioimmunoconjugates have demonstrated some clinical efficacy in patients with advanced refractory HD. Although it seems unlikely that resistant patients with larger tumor masses will be cured by either of these approaches, it might be feasible to treat bulky disease by conventional therapy and then administer biological agents to kill residual Hodgkin and Reed-Sternberg cells. Future phase III trials will have to prove a possible superior effect of this combined immunochemotherapy. Currently, the evaluation of the most promising approaches continues.

Phase 1 trial of the novel bispecific molecule H22xKi-4 in patients with refractory Hodgkin lymphoma

CD30 is an excellent target for immunotherapy of Hodgkin lymphoma (HL) because it is overexpressed on Hodgkin and Reed-Sternberg cells. We developed a novel bispecific molecule (BSM) consisting of F(ab') fragments derived from the murine anti-CD30 monoclonal antibody (MoAb) Ki-4 and the humanized CD64-specific MoAb H22. In vitro experiments of H22xKi-4 demonstrated specific phagocytosis of HL-derived cell lines. Patients (pts) with refractory CD30(+) HL were treated with escalating doses of H22xKi-4 at doses of 1, 2.5, 5, 10, and 20 mg/m(2)/d, respectively (administered intravenously on days 1, 3, 5, and 7). The main study objectives were to determine the maximum tolerated dose and the dose-limiting toxicities of H22xKi-4, to define its pharmacokinetic profile, and to document clinical response. Ten pts were enrolled and are evaluable for toxicity and response. Side effects were transient and mild with hypotension (4 of 10), tachycardia (6 of 10), fatigue (10 of 10), and fever (2 of 10 grade I, 3 of 10 grade II). Pharmacokinetic (PK) data revealed an elimination half-life of 11.1 hours, resulting in a significant accumulation of H22xKi-4. The BSM was shown to bind to both monocytes and malignant cells. Response to H22xKi-4 included 1 complete remission (CR), 3 partial remissions (PR), and 4 pts with stable disease. The new BSM H22xKi-4 can be given safely to pts with refractory CD30(+) HL in doses up to 80 mg/m(2) per cycle. Although this dose is not the maximum tolerated dose (MTD) as defined by toxicity criteria, surrogate parameters suggest a biologic effective regimen. H22xKi-4 shows activity in heavily pretreated HL patients warranting further clinical evaluation.

Enhanced killing of B lymphoma cells by granulocyte colony-stimulating factor-primed effector cells and Hu1D10--a humanized human leucocyte antigen DR antibody

Antibody-based approaches have become a novel treatment modality for lymphoma patients. Humanized 1D10 (Hu1D10; Remitogen) is among the antibodies that are currently under evaluation in phase II clinical trials in lymphoma patients. The 1D10 antibody is directed against a polymorphic epitope on the beta-chain of human leucocyte antigen (HLA) class II. We found expression of the 1D10 epitope on B cells and monocytes from approximately 50% of healthy donors. Analyses of 1D10 expression on malignant cells revealed that approximately half of the HLA class II-positive haematological malignancies expressed the 1D10 epitope. In whole blood antibody-dependent cellular cytotoxicity (ADCC) assays, Hu1D10 was more effective than rituxan in killing malignant ARH-77 B cells. Interestingly, Hu1D10-mediated lymphoma cell lysis was significantly enhanced when blood from granulocyte colony-stimulating factor (G-CSF)-treated patients was compared with blood from healthy controls. Analyses of the relevant effector cell populations revealed that FcgammaRI (CD64)-positive polymorphonuclear cells were critical for enhanced Hu1D10-mediated lymphoma killing during G-CSF therapy, while the same effector cell population induced only marginal lysis with rituxan. Furthermore, Hu1D10 was highly effective in inducing apoptosis in primary lymphoma cells from B chronic lymphocytic leukaemia patients. These preclinical results form the basis for a phase I/II clinical trial of Hu1D10 in combination with G-CSF.

Intracellular domains of target antigens influence their capacity to trigger antibody-dependent cell-mediated cytotoxicity

Ab-mediated signaling in tumor cells and Ab-dependent cell-mediated cytotoxicity (ADCC) are both considered as relevant effector mechanisms for Abs in tumor therapy. To address potential interactions between these two mechanisms, we generated HER-2/neu- and CD19-derived chimeric target Ags, which were expressed in experimental tumor target cells. HER-2/neu-directed Abs were documented to mediate effective ADCC with both mononuclear cells (MNCs) and polymorphonuclear granulocytes (PMNs), whereas Abs against CD19 were effective only with MNCs and not with PMNs. We generated cDNA encoding HER-2/CD19 or CD19/HER-2 (extracellular/intracellular) chimeric fusion proteins by combining cDNA encoding extracellular domains of HER-2/neu or CD19 with intracellular domains of CD19 or HER-2/neu, respectively. After transfecting wild-type HER-2/neu or chimeric HER-2/CD19 into Raji Burkitt's lymphoma cells and wild-type CD19 or chimeric CD19/HER-2 into SK-BR-3 breast cancer cells, target cell lines were selected for high membrane expression of transfected Ags. We then investigated the efficacy of tumor cell lysis by PMNs or MNCs with CD19- or HER-2/neu-directed Ab constructs. MNCs triggered effective ADCC against target cells expressing wild-type or chimeric target Ag. As expected, PMNs killed wild-type HER-2/neu-transfected, but not wild-type CD19-transfected target cells. Interestingly, however, PMNs were also effective against chimeric CD19/HER-2-transfected, but not HER-2/CD19-transfected target cells. In conclusion, these results demonstrate that intracellular domains of target Ags contribute substantially to effective Ab-mediated tumor cell killing by PMNs.

Efficient inhibition of human B-cell lymphoma xenografts with an anti-CD20 x anti-CD3 bispecific diabody

Bispecific antibodies have been exploited both as cancer immunodiagnostics and as cancer therapeutics, and have shown promise in several clinical trials in cancer imaging and therapy. A number of bispecific antibodies against B-cell markers have been shown to be effective in vitro in mediating tumor cell lysis and in vivo in inhibiting tumor growth in animal models. We have constructed a bispecific diabody from the variable genes encoding two hybridoma-derived monoclonal antibodies directed against human CD20 on B cells and CD3 on T cells. The anti-CD20 x anti-CD3 diabody was expressed in a single Escherichia coli host and purified by a one-step affinity chromatography. The bispecific diabody bound as efficiently to both CD20- and CD3-positive cells as the respective parental antibodies, and was capable of cross-linking CD20-positive tumor cells and human T lymphocytes as shown by cellular rosetting. The diabody effectively lysed human B-lymphoma cells in the presence of T-enriched human peripheral blood lymphocytes (PBL). Further, when combined with human PBL and interleukin-2, the diabody significantly prolonged the survival of nude mice inoculated with human B-lymphoma cells. Taken together, our results suggest that an anti-CD20 x anti-CD3 diabody may have significant clinical application in the treatment of human CD20-positive B-cell malignancies.

FcgammaRI (CD64) contributes substantially to severity of arthritis, hypersensitivity responses, and protection from bacterial infection

The high-affinity receptor for IgG, FcgammaRI, shares its capacity to bind IgG2a immune complexes (IgG2a-IC) with the low-affinity receptor FcgammaRIII and complement factors, hampering the definition of its biological role. Moreover, in vivo, FcgammaRI is occupied by monomeric IgG2a, reducing its accessibility to newly formed IgG2a-IC. By using a variety of FcgammaR(-/-) mice, we demonstrate that in the absence of FcgammaRI, the IgG2a-IC-induced cellular processes of phagocytosis, cytokine release, cellular cytotoxicity, and antigen presentation are impaired. FcgammaRI(-/-) mice showed impaired hypersensitivity responses, strongly reduced cartilage destruction in an arthritis model, and impaired protection from a bacterial infection. We conclude that FcgammaRI contributes substantially to a variety of IgG2a-IC-dependent immune functions and immunopathological responses.

Recombinant antibodies for cancer diagnosis and therapy

Recombinant antibodies now represent over 30% of biopharmaceuticals in clinical trials, highlighted by the recent approvals for cancer immunotherapy from the FDA which has awoken the biotechnology industry. Sales of these antibodies are increasing very rapidly to a predicted US$ 3 billion per annum worldwide by 2002. Since the development of new therapeutic reagent into commercial product takes 10 years, the recent FDA-approved antibodies are based on early antibody designs which are now considered primitive. Emerging technologies have created a vast range of novel, recombinant, antibody-based reagents which specifically target clinical biomarkers of disease. In the past year, radiolabelling of antibodies has increased their potential for cancer imaging and targeting. Recombinant antibodies have also been reduced in size and rebuilt into multivalent molecules for higher affinity. In addition, antibodies have been fused with many molecules including toxins, enzymes and viruses for prodrug therapy, cancer treatment and gene delivery. Recombinant antibody technology has enabled clever manipulations in the construction of complex antibody library repertoires for the selection of high-affinity reagents against refractory targets. Although phage display remains the most extensively used method, this year high affinity reagents have been isolated using alternative display and selection systems such as ribosome display and yeast display confirming the emergence of new display methods. Furthermore, innovative affinity maturation strategies have been developed to obtain high affinity reagents. This review focuses on developments in the last 12 months and describes the latest developments in the design, production and clinical use of recombinant antibodies for cancer diagnosis and therapy.

IgA antibodies for cancer therapy

Antibody-based therapy is a new treatment option for selected tumor patients. Today, human IgG(1) is the most widely used isotype, because it effectively activates human complement, recruits NK cells for ADCC, and has an extended plasma half life. In recent work, however, neutrophils--the most populous cytotoxic cells in humans--were more effectively recruited by human IgA than by IgG antibodies. IgA antibodies may have the additional advantages of forming natural dimers with improved signaling capacity on tumor cells, and being actively transported into mucosal secretions with the potential for improved targeting of certain carcinomas from the luminal surface.

Neutrophil Fc gamma RI as target for immunotherapy of invasive candidiasis

Invasive candidiasis represents a life-threatening disease for immunocompromised patients. This study focused on new immunotherapeutic approaches for systemic Candida albicans infections in a human FcgammaRI-transgenic mouse model. FcgammaRI (CD64) is a potent immunoactivating receptor on phagocytic and dendritic cells. In vivo targeting of C. albicans toward neutrophil-FcgammaRI by bispecific Abs and G-CSF effectively protected FcgammaRI-transgenic mice from lethal candidiasis. Nontransgenic mice were not protected, and treatment with bispecific Ab or G-CSF alone did not reduce mortality. Furthermore, infected FcgammaRI-transgenic mice developed high titers of anti-C. albicans IgG, and survival was extended on secondary infection without further treatment. These findings document the capacity of FcgammaRI to initiate potent anti-C. albicans immunity and support the development of FcgammaRI-directed immunotherapy of invasive fungal disease.

Mechanisms of G-CSF- or GM-CSF-stimulated tumor cell killing by Fc receptor-directed bispecific antibodies

Studies with gene-modified mice have recently reinforced the importance of Fc receptor-mediated effector mechanisms for the therapeutic efficacy of rituxan and herceptin - two clinically approved antibodies for the treatment of tumor patients. We investigated Fc receptor-dependent tumor cell killing by mononuclear and granulocytic effector cells - comparing human IgG1 antibodies against CD20 or HER-2/neu with their respective FcgammaRI (CD64)-, FcgammaRIII (CD16)-, or FcalphaRI (CD89)-directed bispecific derivatives. With blood from healthy donors as effector source, human IgG1 and FcgammaRIII (CD16)-directed bispecific antibodies proved most effective in recruiting mononuclear effector cells, whereas tumor cell killing by granulocytes was most potently triggered by FcalphaRI-directed bispecific constructs. Granulocyte-mediated tumor cell lysis was significantly enhanced when blood from G-CSF- or GM-CSF-treated patients was investigated. Interestingly, however, both myeloid growth factors improved effector cell recruitment by different mechanisms, which were furthermore dependent on the tumor target antigen, and on the selected cytotoxic Fc receptor.