The Evaluation of Recombinant, Chimeric, Tetravalent Antihuman CD22 Antibodies

Imaging and Targeting of the α(2-6) and α(2-3) Linked Sialic Acid Quantum Dots in Zebrafish and Mouse Models

Sialic acid-conjugated nanocarriers have emerged as attractive biomarkers with promising biomedical applications. The translation of these nanocarriers into clinical applications requires in-depth assessment in animal models. However, due to the complexity, ethical concerns, and cost of the high-order animal system, there is an immediate need of information-rich simple animal models to decipher the biological significance. Herein, we performed in vivo head-to-head comparison of Neu5Acα(2-6) and α(2-3)Gal conjugated quantum dots (QDs) toxicity, biodistribution, and sequestration in wild-type zebrafish ( Danio rerio) and mouse model (C57BL). The fluorescent properties and cadmium composition of quantum dots were used to map the blood clearance, biodistribution, and sequestration of the sialylated QDs in major organs of both models. We observed that α(2-6) sialylated QDs preferentially have prolonged circulating half-life and broader biodistribution in both models. On the contrary, α(2-3) sialic acid and galactose-conjugated QDs have shortened blood circulation time and are sequestered in the liver, and cleared after several hours in both models. These results demonstrate the applicability of the zebrafish and sialylated QDs to target specific organs, as well as drug delivery and biomedical diagnostics.

Thermostable ricin vaccine protects rhesus macaques against aerosolized ricin: Epitope-specific neutralizing antibodies correlate with protection

Ricin toxin (RT) is the second most lethal toxin known; it has been designated by the CDC as a select agent. RT is made by the castor bean plant; an estimated 50,000 tons of RT are produced annually as a by-product of castor oil. RT has two subunits, a ribotoxic A chain (RTA) and galactose-binding B chain (RTB). RT binds to all mammalian cells and once internalized, a single RTA catalytically inactivates all of the ribosomes in a cell. Administered as an aerosol, RT causes rapid lung damage and fibrosis followed by death. There are no Food and Drug Administration-approved vaccines and treatments are only effective in the first few hours after exposure. We have developed a recombinant RTA vaccine that has two mutations V76M/Y80A (RiVax). The protein is expressed in Escherichia coli and is nontoxic and immunogenic in mice, rabbits, and humans. When vaccinated mice are challenged with injected, aerosolized, or orally administered (gavaged) RT, they are completely protected. We have now developed a thermostable, aluminum-adjuvant-containing formulation of RiVax and tested it in rhesus macaques. After three injections, the animals developed antibodies that completely protected them from a lethal dose of aerosolized RT. These antibodies neutralized RT and competed to varying degrees with a panel of neutralizing and nonneutralizing mouse monoclonal antibodies known to recognize specific epitopes on native RTA. The resulting antibody competition profile could represent an immunologic signature of protection. Importantly, the same signature was observed using sera from RiVax-immunized humans.

Chimeric, divalent and tetravalent anti-CD19 monoclonal antibodies with potent in vitro and in vivo antitumor activity against human B-cell lymphoma and pre-B acute lymphoblastic leukemia cell lines

CD19 is an attractive therapeutic target for treating human B-cell tumors. In our study, chimeric (c) divalent (cHD37) and tetravalent (cHD37-DcVV) anti-CD19 monoclonal antibodies (MAbs) were constructed, expressed and evaluated for their binding to human 19-positive (CD19(+)) tumor cell lines. They were also tested for proapoptotic activity and the ability to mediate effector functions. The antitumor activity of these MAbs was further tested in mice xenografted with the CD19(+) Burkitt's lymphoma cell line, Daudi or the pre-B acute lymphoblastic leukemia (ALL) cell line, NALM-6. The cHD37 and cHD37-DcVV MAbs exhibited specific binding and comparable proapoptotic activity on CD19(+) tumor cell lines in vitro. In addition, the cHD37 and cHD37-DcVV MAbs were similar in their ability to mediate antibody-dependent cell-mediated phagocytosis (ADCP). However, the tetravalent cHD37-DcVV MAb bound more avidly, had a slower dissociation rate, and did not internalize as well. It also had enhanced antibody-dependent cellular cytotoxicity (ADCC) with human but not murine effector cells. The cHD37 and cHD37-DcVV MAbs exhibited comparable affinity for the human neonatal Fc receptor (FcRn) and similar pharmacokinetics (PKs) in mice. Moreover, all the HD37 constructs were similar in extending the survival of mice xenografted with Daudi or NALM-6 tumor cells. Therefore, the cHD37 and cHD37-DcVV MAbs have potent antitumor activity and should be further developed for use in humans. Although not evident in mice, due to its increased ability to mediate ADCC with human but not mouse effector cells, the cHD37-DcVV MAb should have superior therapeutic efficacy in humans.

Construction and characterization of a bispecific anti-CD20 antibody with potent antitumor activity against B-cell lymphoma

To develop more effective anti-CD20 reagents for B-cell lymphoma, we designed and constructed a bispecific tetravalent anti-CD20 antibody, 11B8/2F2(ScFvHL)(4)-Fc, derived from two fully human monoclonal antibodies (mAb), 2F2 and 11B8. 2F2 is a type I CD20 mAb, which is potent in complement-dependent cytotoxicity (CDC) assays but poor at inducing apoptosis, whereas 11B8 is a type II CD20 mAb, which is effective in induction of apoptosis but ineffective in CDC. Our results showed that 11B8/2F2(ScFvHL)(4)-Fc possessed apoptosis-inducing activity markedly superior to that of 2F2, and even 11B8, 11B8 plus 2F2, and 2F2(ScFvHL)(4)-Fc, a 2F2-derived monospecific tetravalent antibody developed previously. Interestingly, 11B8/2F2(ScFvHL)(4)-Fc displayed a similar ability to mediate CDC as 2F2(ScFvHL)(4)-Fc, although two of its four antigen-binding arms originated from 11B8. To explore why 11B8/2F2(ScFvHL)(4)-Fc was so potent in both CDC and apoptotic activity, a bispecific divalent antibody composed of 2F2 and 11B8, denoted as 11B8/2F2-ScFvFc, was constructed and characterized. Our results partially explained the reason for the potent CDC and apoptosis-inducing activity of 11B8/2F2(ScFvHL)(4)-Fc. Further in vivo therapy studies showed that 11B8/2F2(ScFvHL)(4)-Fc had a significantly more potent antitumor activity compared with 2F2, 11B8, 2F2 plus 11B8, and 2F2(ScFvHL)(4)-Fc. These data suggest that 11B8/2F2(ScFvHL)(4)-Fc may serve as a potential therapeutic agent for B-cell lymphoma.

Engineering therapeutic monoclonal antibodies

During last two decades, the chimerization and humanization of monoclonal antibodies (mAbs) have led to the approval of several for the treatment of cancer, autoimmune diseases, and transplant rejection. Additional approaches have been used to further improve their in vivo activity. These include combining them with other modalities such as chemotherapy and redesigning them for improved pharmacokinetics, effector function, and signaling activity. The latter has taken advantage of new insights emerging from an increased understanding of the cellular and molecular mechanisms that are involved in the interaction of immunoglobulin G with Fc receptors and complement as well as the negative signaling resulting from the hypercrosslinking of their target antigens. Hence, mAbs have been redesigned to include mutations in their Fc portions, thereby endowing them with enhanced or decreased effector functions and more desirable pharmacokinetic properties. Their valency has been increased to decrease their dissociation rate from cells and enhance their ability to induce apoptosis and cell cycle arrest. In this review we discuss these redesigned mAbs and current data concerning their evaluation both in vitro and in vivo.

Combined yeast-derived beta-glucan with anti-tumor monoclonal antibody for cancer immunotherapy

Beta-glucan is an immuno-stimulating agent that has been used to treat cancer and infectious disease for many years with varying and unpredictable efficacy. Recent studies have unraveled the action mode of yeast-derived beta-glucan in combination with anti-tumor monoclonal antibodies (mAbs) in cancer therapy. It has demonstrated that particulate or large molecular weight soluble beta-glucans are ingested and processed by macrophages. These macrophages secrete the active moiety that primes neutrophil complement receptor 3 (CR3) to kill iC3b-opsonized tumor cells. In vitro and in vivo data demonstrate that successful combination therapy requires complement activation and deposition on tumors and CR3 expression on granulocytes. Pre-clinical animal studies have demonstrated the efficacy of combined beta-glucan with anti-tumor mAb therapy in terms of tumor regression and long-term survival. Clinical trials are underway using anti-epidermal growth factor receptor mAb (cetuximab) in combination with beta-glucan for metastatic colorectal cancer. This review provides a brief overview of this combination therapy in cancer and describes in detail the beta-glucan composition and structure, mechanism of action, and preclinical studies in human carcinoma xenograft models. It is proposed that the addition of beta-glucan will further improve the therapeutic efficacy of anti-tumor mAbs in cancer patients.

Novel designs of multivalent anti-CD20 humanized antibodies as improved lymphoma therapeutics

Multivalent antibodies, either monospecific or bispecific, may improve the efficacy of current therapeutic interventions involving a single monoclonal antibody (mAb). We have applied the Dock-and-Lock (DNL) method, a new platform technology for the site-specific and covalent assembly of modular components into stably tethered complexes of defined composition, to prepare a hexavalent, anti-CD20 antibody, designated Hex-hA20, which comprises six Fabs with one Fc. We show that Hex-hA20 retains the binding activity of all six Fabs, associates with CD20 in lipid rafts, affects antibody-dependent cell-mediated cytotoxicity, but not complement-dependent cytotoxicity, and inhibits proliferation of Daudi, Raji, and Ramos cells in vitro at subnanomolar concentrations without the need for a cross-linking antibody. In addition, Hex-hA20 induces strong homotypical adhesion and is inefficient in stimulating calcium mobilization. Thus, Hex-hA20 exhibits biological properties attributable to both type I and type II anti-CD20 mAbs, as exemplified by rituximab and tositumomab, respectively. Although Hex-hA20 has a short serum half-life, it shows antitumor efficacy in tumor-bearing mice comparable with veltuzumab at equivalent doses. The versatile DNL method was also applied to generate two other multivalent anti-CD20 antibodies without the Fc region, Tri-hA20 and Tetra-hA20, comprising three and four Fabs of veltuzumab, respectively. Similar to Hex-hA20, these were purified to near homogeneity and shown to have potent antiproliferative activity in vitro, thus indicating the need for clustering three or more CD20 molecules on the cell surface to induce growth inhibition.

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.

Anti-CD19 and anti-CD22 monoclonal antibodies increase the effectiveness of chemotherapy in Pre-B acute lymphoblastic leukemia cell lines

The monoclonal antibodies (MAbs) HD37 and RFB4 bind to receptors on precursor B acute lymphoblastic leukemia (ALL) cells. These MAbs were tested alone and in combination with chemotherapy for their anti-leukemic activity. HD37 and not RFB4 increased the in vitro cytotoxicity of daunorubicin (DNR) and vincristine (VCR) in three Pre-B ALL cell lines. HD37 alone induced apoptosis in 30% of the cells versus 2% for RFB4. The treatment of SCID/ALL mice with either chemotherapy agent minimally prolonged their mean survival time (MST) versus controls but HD37 or RFB4 plus VCR significantly extended the MST. Forty percent of the mice treated with HD37 plus VCR survived. In conclusion, chemotherapy was made more effective when combined with HD37, and less so with RFB4.

Engineering antibodies for clinical applications

Molecular engineering has contributed immensely to the clinical success of antibodies in recent years. The modular structure of antibodies has permitted their modification in numerous ways, to meet various clinical requirements. With the help of antibody engineering, it has been possible to modify the molecular size, pharmacokinetics, immunogenicity, binding affinity, specificity and effector function of antibodies. In addition, fusion proteins of antibodies with various proteins and peptides have yielded targeted biological modifiers, toxins and imaging agents. This review focuses on the recent trends in antibody engineering for improving their clinical utility.

Complement as effector system in cancer immunotherapy

The contribution of the complement system to the control of tumour growth has been neglected for a long time as the major emphasis has been put mainly on cell-mediated immune response against cancer. With the introduction of monoclonal antibodies in cancer immunotherapy complement has come into play with a great potential as effector system. Complement has a number of advantages over other effector systems in that it is made of molecules that can easily penetrate the tumour tissue and a large majority, if not all, of the components of this system can be supplied locally by many cells at tissue site. Further advances are being made to increase the anti-tumour efficiency of the complements system using C-fixing antibodies that are modified in the Fc portion to be more active in complement activation. Another strategy currently investigated is essentially based on the use of a combination of two antibodies directed against different molecules or different epitopes of the same molecule expressed on the cell surface in order to increase the number of the binding sites for the antibodies on the tumor cells and the chance for them to activate complement more efficiently. One of the problems to solve in exploiting complement as an effector system in cancer immunotherapy is to neutralize the inhibitory effect of complement regulatory proteins which are often over-expressed on tumour cells and represent a mechanism of evasion of these cells from complement attack. This situation can be overcome using neutralizing antibodies to target onto tumour cells together with the specific antibodies directed against tumor specific antigens. This is an area of active investigation and the initial data that start to be available from animal models seem to be promising.

Generation and characterization of a novel tetravalent anti-CD22 antibody with improved antitumor activity and pharmacokinetics

The purpose of this study was to prepare a tetravalent anti-human CD22 recombinant antibody with improved antitumor activity and a half life longer than that of its divalent counterpart. We compared the ability of tetravalent vs. divalent antibody to associate/dissociate to/from CD22-positive Daudi cells, to interact with murine and human Fcgamma receptors (FcgammaR), to bind human complement component C1q, to inhibit the growth of tumor cells, to diffuse into various tissues, to be internalized by Daudi cells, to react with human neonatal Fc receptors (FcRn), and to persist in the circulation of normal mice. As compared to the murine or chimeric divalent antibodies, the chimeric tetravalent counterpart has a longer half life in mice. It also has an affinity for FcRns that is identical to that of human IgG. The tetravalent antibody has increased antitumor activity in vitro and completely conserved effector functions (binding to FcgammaR-positive cells and to C1q) in vitro. Despite its 33% higher molecular weight, it penetrates mouse tissues as well as its divalent antibody counterpart. Based on the improved in vitro performance and pharmacokinetics of the tetravalent antibody it will now be tested for its antitumor activity in vivo.

Complement Activated by Chimeric Anti–Folate Receptor Antibodies Is an Efficient Effector System to Control Ovarian Carcinoma

Two chimeric monoclonal antibodies (mAb), cMOV18 and cMOV19, recognizing distinct epitopes of folate receptor highly expressed on epithelial ovarian cancer (EOC) cells were analyzed for their ability to activate complement (C) as a means to enhance their antitumor activity. The individual cMOVs failed to activate C on six EOC cell lines as documented by the marginal deposition of C components and the negligible C-dependent cytotoxicity (CDC). Conversely, the mixture of cMOVs was more effective, although the percentage of cell killing did not exceed 25%. Fluorescence-activated cell sorting analysis of EOC cells for surface expression of the membrane C regulatory proteins (mCRP) revealed high levels of CD46, variable expression of CD59, and absence of CD55. This finding was confirmed in tumor tissue specimens obtained from advanced-stage EOC patients and analyzed for the expression of mCRPs mRNA using a cDNA microarray and for the presence of proteins by immunohistochemistry. Incubation of EOC cells with neutralizing mAbs to CD46 and CD59 led to a significant increase in the CDC from 10%-20% to 45%-50%. The relative contribution of antibody-dependent cell cytoxicity (ADCC) and C-dependent killing of two EOC cell lines induced by the mixture of cMOV18 and cMOV19 was about 15% and 25%-35%, respectively, bringing the total killing to about 40%-50%. This value increased to 60%-70% after neutralization of CD46 and CD59 without an appreciable change of ADCC. These results suggest that C is the major contributor to the killing of EOC cells induced by the mixture of cMOV18 and cMOV19.

The generation of immunotoxins using chimeric anti-CD22 antibodies containing mutations which alter their serum half-life

Murine and chimeric RFB4 (anti-human CD22) monoclonal antibodies (MAbs) with mutations in their Fc portions were conjugated to recombinant ricin toxin A chain to generate immunotoxins. The resulting immunotoxins (ITs) constructed with chimeric RFB4 MAbs were designed to have longer or shorter half-lives but similar binding and cytotoxic properties. These ITs can now be evaluated in vivo for improved therapeutic indices. The characteristics of these ITs are the subject of this report.