G-CSF-stimulated PMN in immunotherapy of breast cancer with a bispecific antibody to Fc gamma RI and to HER-2/neu (MDX-210)

CRISPR/Cas9-based genome-wide screening for metastasis ability identifies FCGR1A regulating the metastatic process of ovarian cancer by targeting LSP1

BACKGROUND

Metastasis is a main cause of death from ovarian cancer (OC). Identifying key markers involved in OC metastasis can aid in the effective detection of early postoperative metastasis. However, the role of FCGR1A in OC metastasis has yet to be fully established. A genome-wide CRISPR/Cas9-based screening system was used to identify regulatory factors involved in metastasis.

METHODS

The expression of FCGR1A and LSP1 in ovarian cancer cell lines was examined by quantitative real-time polymerase chain reaction (qRT‒PCR). The functions of FCGR1A and LSP1 in OC cell migration, invasion and proliferation were determined using wound healing, Transwell invasion and CKK-8 assays. A transcription-activated library was used to identify the potential downstream genes of FCGR1A. FCGR1A expression was detected by immunohistochemistry and the immunity risk score (IRS) scores were calculated.

RESULTS

FCGR1A was upregulated in OC cells compared with normal ovarian cells. Downregulation of FCGR1A inhibited metastasis, proliferation and epithelial-mesenchymal transition (EMT) progression in OC cells in vitro and intraperitoneal metastasis in vivo. Moreover, downregulation of FCGR1A was accompanied by decreased LSP1 expression. Overexpression of LSP1 partially reversed the tumor suppressive effect of FCGR1A downregulation. Higher FCGR1A expression was related to metastasis, higher grade, higher stage, and lymph node metastasis in OC. Survival analysis suggested that the group with higher FCGR1A expression had a lower tumor-free survival rate and a lower overall survival rate than did the group with low FCGR1A expression.

CONCLUSIONS

FCGR1A enhances OC metastasis by regulating LSP1, and FCGR1A is associated with poor prognosis, suggesting that FCGR1A is a potential predictive factor for detecting early postoperative metastasis.

Bispecific antibodies revolutionizing breast cancer treatment: a comprehensive overview

Breast cancer (BCa) is known as a complex and prevalent disease requiring the development of novel anticancer therapeutic approaches. Bispecific antibodies (BsAbs) have emerged as a favorable strategy for BCa treatment due to their unique ability to target two different antigens simultaneously. By targeting tumor-associated antigens (TAAs) on cancer cells, engaging immune effector cells, or blocking critical signaling pathways, BsAbs offer enhanced tumor specificity and immune system involvement, improving anti-cancer activity. Preclinical and clinical studies have demonstrated the potential of BsAbs in BCa. For example, BsAbs targeting human epidermal growth factor receptor 2 (HER2) have shown the ability to redirect immune cells to HER2-positive BCa cells, resulting in effective tumor cell killing. Moreover, targeting the PD-1/PD-L1 pathway by BsAbs has demonstrated promising outcomes in overcoming immunosuppression and enhancing immune-mediated tumor clearance. Combining BsAbs with existing therapeutic approaches, such as chemotherapy, targeted therapies, or immune checkpoint inhibitors (ICIs), has also revealed synergistic effects in preclinical models and early clinical trials, emphasizing the usefulness and potential of BsAbs in BCa treatment. This review summarizes the latest evidence about BsAbs in treating BCa and the challenges and opportunities of their use in BCa.

Targeting myeloid cells with bispecific antibodies as novel immunotherapies of cancer

INTRODUCTION

Most bispecific antibody (BsAb) therapies focus on stimulating the adaptive immune system, in particular T cells, to promote tumor cell killing. Another method to promote tumor eradication is through the engagement of myeloid cells, including macrophages and neutrophils, which are abundantly present and possess intrinsic cytotoxic mechanisms for tumor cell killing, making them interesting effector cells to recruit for BsAb therapy.

AREAS COVERED

In this review, we describe the evolving knowledge of the role of macrophages and neutrophils in cancer in scientific literature. Moreover, we address the BsAbs that have been developed over the years to recruit these cell types as effector cells in immunotherapy of cancer. This includes the discussion of BsAbs that target Fc receptors (i.e. FcγR and FcαRI) to induce antibody-dependent cellular phagocytosis (ADCP) by macrophages or trogoptosis via neutrophils, as well as BsAbs that interfere with checkpoint inhibition, including the SIRPα-CD47 pathway.

EXPERT OPINION

Elucidating the complexity of macrophage and neutrophil heterogeneity in cancer may help to specifically enlist the cytotoxic ability of these cells through targeting Fc receptors and checkpoint pathways, which may further enhance anti-cancer immunity.

Therapeutic exploitation of neutrophils to fight cancer

Antibody-based immunotherapy is a promising strategy in cancer treatment. Antibodies can directly inhibit tumor growth, induce complement-dependent cytotoxicity and induce Fc receptor-mediated elimination of tumor cells by macrophages and natural killer cells. Until now, however, neutrophils have been largely overlooked as potential effector cells, even though they are the most abundant type of immune cells in the circulation. Neutrophils display heterogeneity, especially in the context of cancer. Therefore, their role in cancer is debated. Nevertheless, neutrophils possess natural anti-tumor properties and appropriate stimulation, i.e. specific targeting via antibody therapy, induces potent tumor cell killing, especially via targeting of the immunoglobulin A Fc receptor (FcαRI, CD89). In this review we address the mechanisms of tumor cell killing by neutrophils and the role of neutrophils in induction of anti-tumor immunity. Moreover, possibilities for therapeutic targeting are discussed.

Fever and breast cancer: A critical review of the literature and possible underlying mechanisms

Fever is a common feature in various pathological conditions that manifests a series of molecular events in the internal milieu. Much less attention has been paid to the clinical importance and the management of fever in breast cancer patients. However, several studies have reported an association between postoperative fever and poor treatment outcomes in breast cancer patients. The fever is a side effect of chemotherapy and a manifestation of cancer recurrence. The postmenopausal breast cancer patients experience another body temperature disturbance that is known as a hot flashes. Here, we reviewed the literature regarding postoperative fever and the possible underlying molecular and cellular mechanisms. Then the efficacy of non-steroidal anti-inflammatory drugs was discussed as a therapeutic option to control postoperative fever. Finally, we reviewed the chemotherapy-induced neutropenic fever and cancer vaccination-induced fever.

A Phase I/IIa Study of Antidisialoganglioside Antibody Dinutuximab in Japanese Patients With Neuroblastoma

Japanese patients with neuroblastoma completing induction therapy and high-dose chemotherapy received antidisialoganglioside antibody dinutuximab 17.5 mg/m2 for 4 days during each of 5 consecutive 28-day cycles. Patients also received macrophage colony-stimulating factor (M-CSF) or granulocyte colony-stimulating factor (G-CSF) during cycles 1, 3, and 5 combined with interleukin-2 teceleukin during cycles 2 and 4. A total of 25 patients (11 in the M-CSF group and 14 in the G-CSF group) were enrolled, and dose-limiting toxicity was assessed in the first 12 patients (6 in each group). The recommended doses of dinutuximab, M-CSF, and G-CSF were determined to be 17.5 mg/m2, 6.0×106 U/m2, and 5 µg/kg/d, respectively, whereas that of teceleukin was 0.75×106 IU/m2 during week 1 and 1×106 IU/m2 during week 2. The most common grade 3 or 4 adverse events in both groups were neutrophil count decreased, platelet count decreased, pyrexia, and alanine aminotransferase increased. Four patients (2 in each group) discontinued the treatment because of adverse events. At the end of the study, survival was confirmed in 22 patients (9 in the M-CSF group and 13 in the G-CSF group). From these results, we concluded that this combination regimen is a feasible treatment for Japanese patients with neuroblastoma.

Development of optimal medium for production of commercially important monoclonal antibody 520C9 by hybridoma cell

Hybridoma HB-8696 produces monoclonal antibody (mAb) 520C9 (mouse IgG(1)), which recognizes breast cancer oncoprotein c-erbB2. The objective of this study was to optimize the medium recipe of HB 8696 cell for production of mAb 520C9. The optimization consisted of two steps: (1) screening of significant nutrients to make subsequent experiments more efficient with less runs and (2) locating their optimal concentrations. 29 variables including essential and non-essential amino acids, glucose, serum and 6 salts, namely NaCl, KCl, CaCl(2), NaH(2)PO(4), MgSO(4) and Na-pyruvate were chosen in screening phase. The Plackett-Burman method was used to screen the variables influencing mAb production. Seven factors namely glucose, serum, asparagine, threonine, serine, NaCl and NaH(2)PO(4) were identified to have a positive influencing role on mAb production with a confidence level >90 % (p < 0.1). Finally, Response surface methodology revealed the optimal level of the variables. The mAb production and average specific mAb production rate were enhanced by 111.05 and 105 %, respectively, compared to control medium.

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.

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.

Fucose removal from complex-type oligosaccharide enhances the antibody-dependent cellular cytotoxicity of single-gene-encoded bispecific antibody comprising of two single-chain antibodies linked to the antibody constant region

Bispecific antibodies (bsAbs) have the potential to extend binding selectivity, increase avidity and exert potent cytotoxicity due to the combination of dual specificities. scFv2-Fc type of single-gene-encoded bispecific antibody, composed of two different single-chain Fvs and an Fc, has been reported to be capable of binding to different antigens. The aim of this study was to determine the effect of fucose removal on effector functions of scFv2-Fc since fucose depletion from oligosaccharide of human IgG1 and scFv-Fc results in significant enhancement of ADCC. We generated novel single-gene-encoded bsAb with dual specificity against tumor associated glycoprotein (TAG)-72 and MUC1 mucin as fucose-negative scFv2-Fc from alpha-1,6-fucosyltransferase knock-out CHO cells and a highly fucosylated scFv2-Fc comparator from parental CHO cells. Expression, assembly and the antigen-binding activity of the scFv2-Fc were not influenced by removal of fucose. The fucose negative scFv2-Fc bound with higher avidity to FcgammaRIIIa and enhanced ADCC compared to the highly fucosylated scFv2-Fc. These results demonstrate that ADCC-enhancement by removal of fucose is effective in not only whole IgG1 and scFv-Fc, but also scFv2-Fc targeting two different antigens, and thus increases the potential of fucose-negative scFv2-Fcs as novel therapeutic candidates.

Bispecific antibodies for the treatment of tumours and infectious diseases

Bispecific antibodies are in clinical and preclinical development for the treatment of various cancers and life-threatening infectious diseases. Designed to direct and enhance the body's immune response to specific tumours and pathogens, bispecific antibodies have shown promising results in Phase I and Phase II clinical trials, leading in some cases to complete or partial responses in cancer patients. These bispecific antibodies consist of a 'targeting' domain, typically a fragment of a monoclonal antibody that binds to a tumour, linked to a 'triggering' arm that is specific for a molecule capable of mediating a phagocytic or lytic response by macrophages, natural killer cells, T-cells or other effector cells. By mediating an immune assault on tumours or pathogens, bispecific antibodies may also lead to antigen presentation and a vaccine-like response in patients. Over the next few years, we expect several bispecific antibodies to enter the late stages of clinical trials and ultimately emerge as new pharmaceutical products.

Bispecific antibody conjugates in therapeutics

Bispecific monoclonal antibodies have drawn considerable attention from the research community due to their unique structure against two different antigens. The two-arm structure of bsMAb allows researchers to place a therapeutic agent on one arm while allowing the other to specifically target the disease site. The therapeutic agent can be a drug, toxin, enzyme, DNA, radionuclide, etc. Furthermore, bsMAb may redirect the cytotoxicity of immune effector cells towards the diseased cells or induce a systemic immune response against the target. BsMAb holds great promise for numerous therapeutic needs in the light of: (1) recent breakthroughs in recombinant DNA technology, (2) the increased number of identified disease targets as the result of the completion of human genomic map project, and (3) a better understanding of the mechanism of human immune system. This review focuses on therapeutic applications and production of bsMAb while providing the up-to-date clinical trial information.

The CY domain of the Fcgamma RIa alpha-chain (CD64) alters gamma-chain tyrosine-based signaling and phagocytosis

Although the cytoplasmic domain of the human FcgammaRIa alpha-chain lacks tyrosine-based phosphorylation motifs, it modulates receptor cycling and receptor-specific cytokine production. The cytoplasmic domain of FcgammaRIa is constitutively phosphorylated, and the inhibition of dephosphorylation with okadaic acid, an inhibitor of type 1 and type 2A protein serine/threonine phosphatase, inhibits both receptor-induced activation of the early tyrosine phosphorylation cascade and receptor-specific phagocytosis. To explore the basis for these effects of the cytoplasmic domain of FcgammaRIa, we developed a series of human FcgammaRIa molecular variants, expressed in the murine macrophage cell line P388D1, and demonstrate that serine phosphorylation of the cytoplasmic domain is an important regulatory mechanism. Truncation of the cytoplasmic domain and mutation of the cytoplasmic domain serine residues to alanine abolish the okadaic acid inhibition of phagocytic function. In contrast, the serine mutants did not recapitulate the selective effects of cytoplasmic domain truncation on cytokine production. These results demonstrate for the first time a direct functional role for serine phosphorylation in the alpha-chain of FcgammaRIa and suggest that the cytoplasmic domain of FcgammaRI regulates the different functional capacities of the FcgammaRIa-receptor complex.

Best hope or last hope: access to phase III clinical trials of HER-2/neu for advanced stage breast cancer patients

Breast cancer is a major public health problem, with a 12% incidence among women. The over-expression of the proto-oncogene HER-2/neu is associated with 30% of breast and ovarian cancers that are very aggressive and do not respond to standard therapeutic regimens. Entrance into clinical trials can represent the best hope and even the last hope for these patients. Entrance, however, is based on satisfying eligibility criteria. In examining advanced stage breast cancer patients' access to phase III clinical trials for HER-2/neu, two specific arguments regarding eligibility will be addressed. First, if research is to provide the utilitarian goal of the 'greatest good to the greatest number', delineation of the population receiving the 'good', rather than a homogeneous sub-set of this population, must be addressed, along with patients' values and goals, very relevant to determining a 'good life', how to achieve it, and whether a treatment is a part of that process. Second, the 'good' being generated should involve realistic, practical values of quality ways of living with advanced breast cancer and not just increased survival, or cure. Arguments for relaxing criteria are based on an accurate versus over-simplified interpretation of utilitarian principles and concepts of human flourishing. Only through addressing these issues can the true 'good' of clinical trials and research be given to the greatest number of people.

Antibody dependent cellular phagocytosis (ADCP) and antibody dependent cellular cytotoxicity (ADCC) of breast cancer cells mediated by bispecific antibody, MDX-210

BACKGROUND

MDX-210 is a bispecific antibody (BsAb) with specificity for both the proto-oncogene product of HER-2/neu (c-erbB-2) and FcgammaRI (CD64). HER-2/neu is overexpressed in malignant tissue of approximately 30% of patients with breast cancer, and FcgammaRI is expressed on human monocytes, macrophages, and IFN-gamma activated granulocytes. We investigated phagocytosis and cytolysis of cultured human breast cancer cells by human monocyte-derived macrophages (MDM) mediated by BsAb MDX-210, its partially humanized derivative (MDX-H210), and its parent MoAb 520C9 (anti-HER-2/neu) under various conditions.

MATERIALS AND METHODS

Purified monocytes were cultured with GM-CSF, M-CSF, or no cytokine for five or six days. Antibody dependent cellular phagocytosis (ADCP) and cytolysis (ADCC) assays were performed with the MDM and HER-2/neu positive target cells (SK-BR-3). ADCP was measured by two-color fluorescence flow cytometry using PKH2 (green fluorescent dye) and phycoerythrin-conjugated (red) monoclonal antibodies (MoAb) against human CD14 and CD11b. ADCC was measured with a non-radioactive LDH detection kit.

RESULTS

Both BsAb MDX-210 (via FcgammaRI) and MoAb 520C9 (mouse IgG1, via FcgammaRII) mediated similar levels of ADCP and ADCC. ADCP mediated by BsAb MDX-H210 was identical to that mediated by BsAb MDX-210. Confocal microscopy demonstrated that dual-labeled cells represented true phagocytosis. Both ADCP and ADCC were higher when MDM were pre-incubated with GM-CSF than when incubated with M-CSF.

CONCLUSIONS

BsAb MDX-210 is as active in vitro as the parent MoAb 520C9 in inducing both phagocytosis and cytolysis of MDM. MDX-210 and its partially humanized derivative, MDX-H210, mediated similar levels of ADCP. GM-CSF appears to superior to M-CSF in inducing MDM-mediated ADCC and ADCP. These studies support the ongoing clinical investigations of BsAb MDX-210 and its partially humanized derivative.

The immunology and immunotherapy of breast cancer: an update

Adenocarcinomas of the breast behave clinically and epidemiologically in ways that show host resistance factors are important for outcome in addition to grade and stage of malignancy. Immune reactivity to autologous tumors is indicated by the general presence of lymphoid infiltration (LI) and regional lymph node changes; however, these changes predict favorable outcome only in non-metastatic disease. LI is characterized by CD4+ and CD8+ tumor infiltrating lymphocytes reflecting latent cell-mediated immunity (CMI). CMI and humoral immune reactivity have been demonstrated to autologous tumor and a variety of tumor-associated antigens (TAA) have been implicated including CEA, HER-2/neu, MAGE-1, p53, T/Tn and MUC-1. Immune incompetence involving CMI is progressive with the stage of breast cancer and is prognostically significant. Immunotherapy of several types has been designed to address this immunodeficiency and the TAAs involved. Animal models have employed drug therapy, cytokine transfection, vaccines with autologous tumor, cytokines like interferon alpha (IFN-alpha) and interleukin-2 (IL-2), TAA tumor vaccines, and immunotoxins with evidence of tumor regression by immunologic means. Immunotherapy of human breast cancer is a rapidly growing experimental area. Positive results have been obtained with natural IFN and interleukins, particularly in combination strategies (but not with high dose recombinant IFN or IL-2), with autologous tumor vaccine (but not yet with transfected autologous tumor); with a mucin carbohydrate vaccine (Theratope) in a combination strategy (but not with mucin core antigen) and with several immunotoxins. Combination strategies involving immunorestoration, contrasuppression, adjuvant, and immunotoxins are suggested for the future.

Monoclonal antibodies in solid tumours: approaches to therapy with emphasis on gynaecological cancer

Monoclonal antibodies have progressed from the laboratory to the clinic. Although recognised in diagnosis there are still problems as far as their therapeutic use is concerned. This review looks at the history, principles of active specific immunotherapy, clinical experience with monoclonal antibodies in therapy of solid tumours, in particular the development of new bispecific monoclonal antibodies, and trials in ovarian, breast and colorectal cancer. Immunoconjugates, linked with radionuclides and cytotoxic drugs, indicate future developments. Conditions for successful therapy, especially with adjuvants in patients with small tumour residues, are also described.

Fc receptors as targets for immunotherapy

Human membrane and soluble Fc epsilon receptors (Fc epsilon RI, Fc epsilon RII/CD23) and Fc gamma receptors (Fc gamma RI/CD64, Fc gamma RII/CD32, Fc gamma RIII/CD16) have been implicated in a number of diseases. Their functional roles such as capture and clearance of immune complexes, antibody-dependent cell cytotoxicity, or cytokine or inflammatory mediator release, make them potential targets for immuno-intervention. In the present review, we will describe how membrane and soluble human Fc epsilon R and Fc gamma R have been already used as targets/tools for immuno-interventions by using monoclonal and bispecific engineered antibodies. Some therapeutic uses of these molecules both in cancer, infectious, and auto-immune diseases are presented.

Bispecific antibodies for treatment of cancer in experimental animal models and man

Immunotherapy is a powerful anti-cancer treatment modality. However, despite numerous encouraging results obtained in pre-clinical studies, a definite breakthrough towards an established clinical treatment modality has as yet not occurred. Antibodies against tumor antigens have been shown to localise at the site of the tumor, but inadequate triggering of immune effector mechanisms have thwarted clinical efficacy thus far. Cellular immunotherapy has been hampered by limitations such as lack of specificity, down-regulation of major histocompatibility complex (MHC)-expression or Fas ligand up-regulation on tumor cells. This review focuses on the use of bispecific antibodies (BsAbs) for immunotherapy of cancer. Using BsAbs, it is possible to take advantage of the highly specific binding characteristics of antibodies and combine these with the powerful effector functions of cytotoxic immune effector cells. BsAbs share two different, monoclonal antibody-derived, antigen-recognizing moieties within one molecule. By dual binding, BsAbs reactive with a trigger molecule on an immune effector cell on the one hand and a surface antigen on a tumor target cell on the other are thus able to functionally focus the lytic activity of the immune effector cell towards the target cell. Over the last few years, the concept of BsAb-mediated tumor cell killing has been studied extensively both in preclinical models and in a number of phase I clinical trials. Promising pre-clinical results have been reported using tumor models in which diverse immune effector cell populations have been used. Despite this pre-clinical in vivo efficacy, the first clinical trials indicate that we are still not in a position to successfully treat human malignancies. This review discusses the production of BsAbs, the choice of trigger molecules in combination with potential effector cells and the preclinical models that have led to the current use of BsAbs in experimental clinical trials. It has become clear that appropriate immune cell activation and establishing a favourable effector-to-target cell ratio will have direct impact on the efficacy of the therapeutic approaches using BsAbs. New directions are discussed, i.e. finding appropriate dosage schemes by which immune effector cells become redirected without inducing hyporesponsiveness, defining possibilities for combining different immune effector cell populations and creating an in situ tumor environment that allows maximal tumoricidal activity

Antibody engineering

The development of recombinant techniques for the rapid cloning, expression, and characterization of cDNAs encoding antibody (Ab) subunits has revolutionized the field of antibody engineering. By fusion to heterologous protein domains, chain shuffling, and inclusion of self-assembly motifs, novel molecules such as bispecific Abs can now be generated which possess the subset of functional properties designed to fit the intended application. Rapid technological developments in phage display of peptides and proteins have led to a plethora of applications directed towards immunology and antibody engineering. Many of the problems associated with the therapeutic use of Abs are being addressed by the application of these new techniques.

Clinical significance of IgG Fc receptors and Fc gamma R-directed immunotherapies

Fc receptors for IgG (Fc gamma Rs) can trigger the inflammatory, cytotoxic and hypersensitivity functions of immune effector cells. Activation or deactivation of effector cells via Fc gamma Rs can be exploited to develop novel therapies for cancer, infectious diseases and autoimmune disorders. Initial results of clinical trials for several Fc gamma R-directed immunotherapies show the potential promise of this approach.

Minimal residual disease: detection, clinical relevance, and treatment strategies

Improvement of established treatment strategies for cancer has resulted in increased survival times for patients with malignancies. However, success of surgery, chemotherapy, and radiotherapy is limited, as even combined and repeated therapy regimens and high-dose chemotherapy can only reduce tumor burden by several logarithmic steps and are not able to completely eradicate all neoplastic cells. If clinically complete remission is achieved--that is, if no sign of the tumor is detectable by standard diagnostic procedures, remaining minimal residual disease (MRD) can eventually give rise to clinically manifest relapse. More sensitive methods are, therefore, necessary to detect single tumor cells for exact staging, to assess the metastatic potential of an individual tumor, to evaluate the sensitivity to prior therapy, and to detect MRD-positive patients with remaining malignant cells who are at higher risk for relapse. Novel treatment approaches must be created to eradicate minimal residual disease after conventional therapy.

A human Fc gamma RI/CD64 transgenic model for in vivo analysis of (bispecific) antibody therapeutics

The human high-affinity IgG receptor, hFc gamma RI (CD64), is exclusively expressed on myeloid cells, where it serves an important role as a (cytotoxic) trigger molecule. To establish an in vivo model for analysis of the role of hFc gamma RI in immunity, we developed a novel transgenic mouse model. The human Fc gamma RIA gene, with endogenous regulatory sequences, was used to generate two lines of transgenic FVB/N mice. Immunohistochemical and flow cytometric studies showed that hFc gamma RI expression was restricted to myeloid cells. Monocytes, macrophages, and polymorphonuclear neutrophils (PMN) expressed physiologic hFc gamma RI levels, whereas lymphocytes and mast cells lacked expression. Human Fc gamma RI expression was regulated in vivo by the cytokines IFN-gamma (exactly as in humans) and IL-10. The transgenic receptor proved functional and bound human tumor cells via anti-hFc gamma RI-based bispecific antibodies. hFc gamma RI could, furthermore, be efficiently targeted in vivo by CD64 antibodies. These data demonstrate that the hFc gamma RI transgenic mouse model closely parallels the situation in humans. This mouse model seems useful for in vivo evaluation of the therapeutic potential of novel bispecific reagents in tumor and infection models.