Generation, characterization, and in vivo studies of humanized anticarcinoma antibody CC49

Aberrant Glycosylation as Immune Therapeutic Targets for Solid Tumors

Glycosylation occurs at all major types of biomolecules, including proteins, lipids, and RNAs to form glycoproteins, glycolipids, and glycoRNAs in mammalian cells, respectively. The carbohydrate moiety, known as glycans on glycoproteins and glycolipids, is diverse in their compositions and structures. Normal cells have their unique array of glycans or glycome which play pivotal roles in many biological processes. The glycan structures in cancer cells, however, are often altered, some having unique structures which are termed as tumor-associated carbohydrate antigens (TACAs). TACAs as tumor biomarkers are glycan epitopes themselves, or glycoconjugates. Some of those TACAs serve as tumor glyco-biomarkers in clinical practice, while others are the immune therapeutic targets for treatment of cancers. A monoclonal antibody (mAb) to GD2, an intermediate of sialic-acid containing glycosphingolipids, is an example of FDA-approved immune therapy for neuroblastoma indication in young adults and many others. Strategies for targeting the aberrant glycans are currently under development, and some have proceeded to clinical trials. In this review, we summarize the currently established and most promising aberrant glycosylation as therapeutic targets for solid tumors.

Humanization and characterization of a murine monoclonal neutralizing antibody against human adenovirus 7

Human adenovirus type 7 (HAdV7) is commonly associated with febrile acute respiratory disease (ARD) outbreaks. We have reported that 10G12, a mouse monoclonal antibody (mAb) specifically recognizing and neutralizing HAdV7, is a promising candidate for humanization. In this study, we engineered the six variants of 10G12 with increased degree of humanization and investigated their biological activity. The humanized monoclonal antibody (mAb) 10G12-M2 was shown to retain the parental antibody's high binding affinity, specificity and potent efficacy of viral suppression. The mAb 10G12-M2 recognized a conformational neutralization epitope of the hexon protein. Complex structure-based molecular docking simulation showed that the hexon protein formed several interactions with 10G12-M2, including hydrogen bonds and salt bridges interaction. Physicochemical properties analysis of 10G12-M2 demonstrated that it is stable and desirable lead candidate. In general, 10G12-M2 had excellent biological activity after humanization combined with the potential for use in prophylactic or therapeutic applications against HAdV7.

Targeting Tumor Glycans for Cancer Therapy: Successes, Limitations, and Perspectives

Simple Summary

Aberrant glycosylation is a common feature of many cancers, and it plays crucial roles in tumor development and biology. Cancer progression can be regulated by several physiopathological processes controlled by glycosylation, such as cell–cell adhesion, cell–matrix interaction, epithelial-to-mesenchymal transition, tumor proliferation, invasion, and metastasis. Different mechanisms of aberrant glycosylation lead to the formation of tumor-associated carbohydrate antigens (TACAs), which are suitable for selective cancer targeting, as well as novel antitumor immunotherapy approaches. This review summarizes the strategies developed in cancer immunotherapy targeting TACAs, analyzing molecular and cellular mechanisms and state-of-the-art methods in clinical oncology.

Abstract

Aberrant glycosylation is a hallmark of cancer and can lead to changes that influence tumor behavior. Glycans can serve as a source of novel clinical biomarker developments, providing a set of specific targets for therapeutic intervention. Different mechanisms of aberrant glycosylation lead to the formation of tumor-associated carbohydrate antigens (TACAs) suitable for selective cancer-targeting therapy. The best characterized TACAs are truncated O-glycans (Tn, TF, and sialyl-Tn antigens), gangliosides (GD2, GD3, GM2, GM3, fucosyl-GM1), globo-serie glycans (Globo-H, SSEA-3, SSEA-4), Lewis antigens, and polysialic acid. In this review, we analyze strategies for cancer immunotherapy targeting TACAs, including different antibody developments, the production of vaccines, and the generation of CAR-T cells. Some approaches have been approved for clinical use, such as anti-GD2 antibodies. Moreover, in terms of the antitumor mechanisms against different TACAs, we show results of selected clinical trials, considering the horizons that have opened up as a result of recent developments in technologies used for cancer control.

Engineered CAR-T cells targeting TAG-72 and CD47 in ovarian cancer

Chimeric antigen receptor (CAR) T cells have revolutionized blood cancer immunotherapy; however, their efficacy against solid tumors has been limited. A common mechanism of tumor escape from single target therapies is downregulation or mutational loss of the nominal epitope. Targeting multiple antigens may thus improve the effectiveness of CAR immunotherapies. We generated dual CAR-T cells targeting two tumor antigens: TAG-72 (tumor-associated glycoprotein 72) and CD47. TAG-72 is a pan-adenocarcinoma oncofetal antigen, highly expressed in ovarian cancers, with increased expression linked to disease progression. CD47 is ubiquitously overexpressed in multiple tumor types, including ovarian cancer; it is a macrophage “don’t eat me” signal. However, CD47 is also expressed on many normal cells. To avoid this component of the dual CAR-T cells killing healthy tissue, we designed a truncated CD47 CAR devoid of intracellular signaling domains. The CD47 CAR facilitates binding to CD47⁺ cells, increasing the prospect of TAG-72⁺ cell elimination via the TAG-72 CAR. Furthermore, we could reduce the damage to normal tissue by monomerizing the CD47 CAR. Our results indicate that the co-expression of the TAG-72 CAR and the CD47-truncated monomer CAR on T cells could be an effective, dual CAR-T cell strategy for ovarian cancer, also applicable to other adenocarcinomas.

Humanized Anti-Tumor-Associated Glycoprotein-72 for Submillimeter Near-Infrared Detection of Colon Cancer in Metastatic Mouse Models

BACKGROUND

Tumor-associated glycoprotein (TAG)-72 is a pancarcinoma antigen that is overexpressed in greater than 80% of colorectal adenocarcinomas. CC49 is a TAG-72-specific antibody. The aim of the present study was to demonstrate selective imaging of colon tumors and metastases with the humanized TAG-72 antibody (anti-huCC49) conjugated to a near-infrared fluorophore in orthotopic mouse models.

METHODS

Anti-huCC49 was conjugated to near-infrared dye IR800CW. Mouse imaging was performed with the Pearl Trilogy Small Animal and FLARE Imaging Systems. Subcutaneous mouse models of colon cancer cell line LS174T were used to determine the optimal dose of administration and timing of imaging. Orthotopic mouse models of LS174T were established by surgical orthotopic implantation of LS174T tumors onto the serosa of the cecum. Peritoneal carcinomatosis models were established by injection of LS174T cells into the peritoneum of nude mice. Mice were administered anti-huCC49-IR800 via tail vein injection. Mice were euthanized 72 h later and imaged after laparotomy.

RESULTS

Subcutaneous LS174T xenografts demonstrated optimal tumor detection 72 h after administration with 50 μg anti-huCC49-IR800CW. Tumors were visualized with fluorescence imaging with a mean tumor-to-liver ratio of 7.39 (standard deviation: 2.76). In the orthotopic model, metastases smaller than 1 mm were fluorescently visualized that were invisible with bright light.

CONCLUSIONS

Anti-huCC49-IR800CW provides sensitive and specific imaging of colon cancer and metastases at a submillimeter resolution in metastatic nude mice models. This provides a promising near-infrared probe for the imaging of colon cancer and metastases for preoperative diagnosis and fluorescence-guided surgery.

Effective Targeting of TAG72+ Peritoneal Ovarian Tumors via Regional Delivery of CAR-Engineered T Cells

Impressive clinical efficacy of chimeric antigen receptor (CAR)-engineered T cell therapy for hematological malignancies have prompted significant efforts in achieving similar responses in solid tumors. The lack of truly restricted and uniform expression of tumor-associated antigens, as well as limited T cell persistence and/or tumor trafficking pose major challenges for successful translation of CAR T cell therapy in solid tumors. Recent studies have demonstrated that aberrantly glycosylated cell surface proteins on tumor cells are amenable CAR targets. Tumor-associated glycoprotein 72 (TAG72) antigen is the sialyl-Tn found on multiple O-glycoproteins expressed at high levels on the surface of several cancer types, including ovarian cancer. Here, we developed a humanized TAG72-specific CAR containing a 4-1BB intracellular co-stimulatory signaling domain (TAG72-BBζ). TAG72-BBζ CAR T cells showed potent antigen-dependent cytotoxicity and cytokine production against multiple TAG72⁺ ovarian cancer cell lines and patient-derived ovarian cancer ascites. Using in vivo xenograft models of peritoneal ovarian tumors, regional intraperitoneal delivery of TAG72-BBζ CAR T cells significantly reduced tumor growth, extended overall survival of mice, and was further improved with repeat infusions of CAR T cells. However, reduced TAG72 expression was observed in early recurring tumors, which coincided with a lack of T cell persistence. Taken together, we demonstrate efficacy with TAG72-CAR T cells in ovarian cancer, warranting further investigations as a CAR T cell therapeutic strategy for this disease.

Humanized anti-Sialyl-Tn antibodies for the treatment of ovarian carcinoma

The expression of Sialyl-Tn (STn) in tumors is associated with metastatic disease, poor prognosis, and reduced overall survival. STn is expressed on ovarian cancer biomarkers including CA-125 (MUC16) and MUC1, and elevated serum levels of STn in ovarian cancer patients correlate with lower five-year survival rates. In the current study, we humanized novel anti-STn antibodies and demonstrated the retention of nanomolar (nM) target affinity while maintaining STn antigen selectivity. STn antibodies conjugated to Monomethyl Auristatin E (MMAE-ADCs) demonstrated in vitro cytotoxicity specific to STn-expressing ovarian cancer cell lines and tumor growth inhibition in vivo with both ovarian cancer cell line- and patient-derived xenograft models. We further validated the clinical potential of these STn-ADCs through tissue cross-reactivity and cynomolgus monkey toxicity studies. No membrane staining for STn was present in any organs of human or cynomolgus monkey origin, and the toxicity profile was favorable and only revealed MMAE-class associated events with none being attributed to the targeting of STn. The up-regulation of STn in ovarian carcinoma in combination with high affinity and STn-specific selectivity of the mAbs presented herein warrant further investigation for anti-STn antibody-drug conjugates in the clinical setting.

Safety, tumor trafficking and immunogenicity of chimeric antigen receptor (CAR)-T cells specific for TAG-72 in colorectal cancer

Background

T cells engineered to express chimeric antigen receptors (CARs) have established efficacy in the treatment of B-cell malignancies, but their relevance in solid tumors remains undefined. Here we report results of the first human trials of CAR-T cells in the treatment of solid tumors performed in the 1990s.

Methods

Patients with metastatic colorectal cancer (CRC) were treated in two phase 1 trials with first-generation retroviral transduced CAR-T cells targeting tumor-associated glycoprotein (TAG)-72 and including a CD3-zeta intracellular signaling domain (CART72 cells). In trial C-9701 and C-9702, CART72 cells were administered in escalating doses up to 10¹⁰ total cells; in trial C-9701 CART72 cells were administered by intravenous infusion. In trial C-9702, CART72 cells were administered via direct hepatic artery infusion in patients with colorectal liver metastases. In both trials, a brief course of interferon-alpha (IFN-α) was given with each CART72 infusion to upregulate expression of TAG-72.

Results

Fourteen patients were enrolled in C-9701 and nine in C-9702. CART72 manufacturing success rate was 100% with an average transduction efficiency of 38%. Ten patients were treated in CC-9701 and 6 in CC-9702. Symptoms consistent with low-grade, cytokine release syndrome were observed in both trials without clear evidence of on target/off tumor toxicity. Detectable, but mostly short-term (≤14 weeks), persistence of CART72 cells was observed in blood; one patient had CART72 cells detectable at 48 weeks. Trafficking to tumor tissues was confirmed in a tumor biopsy from one of three patients. A subset of patients had ¹¹¹Indium-labeled CART72 cells injected, and trafficking could be detected to liver, but T cells appeared largely excluded from large metastatic deposits. Tumor biomarkers carcinoembryonic antigen (CEA) and TAG-72 were measured in serum; there was a precipitous decline of TAG-72, but not CEA, in some patients due to induction of an interfering antibody to the TAG-72 binding domain of humanized CC49, reflecting an anti-CAR immune response. No radiologic tumor responses were observed.

Conclusion

These findings demonstrate the relative safety of CART72 cells. The limited persistence supports the incorporation of co-stimulatory domains in the CAR design and the use of fully human CAR constructs to mitigate immunogenicity.

Development of oligoclonal nanobodies for targeting the tumor-associated glycoprotein 72 antigen

The tumor-associated glycoprotein 72 (TAG-72) is a membrane mucin whose over-expression is correlated with advanced tumor stage and increased invasion and metastasis. In this study, we identified a panel of four nanobodies, single variable domains of dromedary heavy-chain antibodies that specifically recognize the TAG-72 antigen. All selected nanobodies were shown to selectively bind to this cancer-related molecule with low-nanomolar affinities and do not cross-react with other antigens, such as MUC1 or HER2. Furthermore, they can detect TAG-72 in concentrations as low as 5 U/ml which is valuable in sensitive detection of this molecule in cancerous patients. Cell ELISA experiments proved their ability for binding to the native target antigen on TAG-72 expressing cells while not showing any reactivity to HT-29 cells, a TAG-72-negative cell line. Using competition studies, we found that each nanobody recognizes a distinct epitope on the TAG-72 antigen that is different from the one recognized by the mouse anti-TAG-72 antibody, CC49. Considering their high specificity, reduced immunogenicity and multi-targeting behavior, these oligoclonal nanobodies represent a promising tool to target TAG-72 over-expressing tumor cells.

Biodistribution and dosimetry of In-111/Y-90-HuCC49ΔCh2 (IDEC-159) in patients with metastatic colorectal adenocarcinoma

BACKGROUND

CC49, an antibody (mAb) reactive to tumor-associated glycoprotein (TAG-72), has been extensively studied for radioimmunotherapy for colon cancer. Myelotoxicity has been dose-limiting because of prolonged circulation time in the plasma, and human anti-mouse antibody responses were observed in the majority of patients. A CH2 domain deleted and humanized CC49 (HuCC49ΔCh2) was developed to ameliorate these problems. This study reports biodistribution and dosimetry of (111)In/(90)Y-HuCC49ΔCh2 (IDEC-159).

MATERIALS AND METHODS

Five (5) patients with colon cancer were enrolled. Each patient received intravenous administration of 185 MBq (111)In-HuCC49ΔCh2, followed by sequential gamma camera imaging, and blood counting. Uptakes and clearance half-lives for organs and tumors were quantified from images. Absorbed doses for (90)Y-HuCC49ΔCh2 were derived from (111)In-HuCC49ΔCh2 kinetic data.

RESULTS

Compared to reported (111)In/(90)Y-CC49 data in the literature, median blood circulation T(1/2β) was less at 38 (31-43) hours for (90)Y-HuCC49ΔCh2, than 50 hours for (90)Y-CC49. Median tumor-to-marrow absorbed dose ratio was 18 for (90)Y-HuCC49ΔCh2, and 9.53 for (90)Y-CC49. Median tumor-to-liver absorbed dose ratio was 3.14 for (90)Y-HuCC49ΔCh2, and 1.0 for (90)Y-CC49. Median tumor-to-spleen absorbed dose was 3.19 for (90)Y-HuCC49ΔCh2, and 1.07 for (90)Y-CC49.

CONCLUSIONS

A humanized and CH2 domain-deleted CC49 antibody radiolabeled with (111)In/(90)Y showed improved tumor-to-normal dose ratios over those reported from studies with intact CC49.

Identification of a high affinity TAG-72 binding peptide by phage display selection

PURPOSE

Phage display was used to select novel peptides that specifically bind the TAG-72 antigen and with properties suitable for imaging TAG-72 positive cancers.

RESULTS

After three rounds of selection against TAG-72 and using two different elution conditions including a long elution, the consensus sequences FRERCDKHPQKCTKFL and DPRHCQKRVLPCPAWL were expressed on phages G3-15 and T3-15 respectively. ELISA, fluorescence-activated cell sorting analysis and fluorescence microscopy provided evidence that both phages specifically bound TAG-72 in vitro. Both peptides are stable in 37oC serum. By a cell binding competition assay, the IC50 for T3-15 was measured as 0.29 nM and therefore 36-fold higher affinity than G3-15 at 10.32 nM. The biodistribution in mice carrying LS-174T tumors in one thigh were similar for both 99mTc-peptides at 30 min, but at 90 min the 99mTc-T3-15 peptide accumulated almost three times higher in the tumor. The SPECT/CT images were consistent with the biodistribution results.

PROCEDURES

The f88-4/Cys6 phage library and two different elution conditions were used to identify two new higher affinity binding peptides for the TAG-72 antigen. One, was a single brief elution with pH 2.2 glycine buffer, and the second began with the glycine elution but was followed with a longer elution with Tris buffered saline (TBS) at pH 7.4. The phages that bound TAG-72 were evaluated by fluorescence-activated cell sorting analysis using TAG-72 positive LS-174T cells and confirmed by immunofluorescence imaging. The consensus peptides displayed on the selected phages were synthesized and conjugated with NHS-MAG3 for radiolabeling with 99mTc. The IC50 for TAG-72 binding was evaluated by cell binding competition in vitro while binding affinity was evaluated in vivo by necropsy and SPECT/CT imaging in a tumor mouse model.

CONCLUSION

We have identified a peptide with a sub nanomolar inhibition constant for the TAG-72 antigen that may have application in cancer imaging.

A comprehensive overview of radioguided surgery using gamma detection probe technology

The concept of radioguided surgery, which was first developed some 60 years ago, involves the use of a radiation detection probe system for the intraoperative detection of radionuclides. The use of gamma detection probe technology in radioguided surgery has tremendously expanded and has evolved into what is now considered an established discipline within the practice of surgery, revolutionizing the surgical management of many malignancies, including breast cancer, melanoma, and colorectal cancer, as well as the surgical management of parathyroid disease. The impact of radioguided surgery on the surgical management of cancer patients includes providing vital and real-time information to the surgeon regarding the location and extent of disease, as well as regarding the assessment of surgical resection margins. Additionally, it has allowed the surgeon to minimize the surgical invasiveness of many diagnostic and therapeutic procedures, while still maintaining maximum benefit to the cancer patient. In the current review, we have attempted to comprehensively evaluate the history, technical aspects, and clinical applications of radioguided surgery using gamma detection probe technology.

Gamma probes and their use in tumor detection in colorectal cancer

The purpose of this article is to summarize the role of gamma probes in intraoperative tumor detection in patients with colorectal cancer (CRC), as well as provide basic information about the physical and practical characteristics of the gamma probes, and the radiopharmaceuticals used in gamma probe tumor detection. In a significant portion of these studies, radiolabeled monoclonal antibodies (Mabs), particularly 125I labeled B72.3 Mab that binds to the TAG-72 antigen, have been used to target tumor. Studies have reported that intraoperative gamma probe radioimmunodetection helps surgeons to localize primary tumor, clearly delineate its resection margins and provide immediate intraoperative staging. Studies also have emphasized the value of intraoperative gamma probe radioimmunodetection in defining the extent of tumor recurrence and finding sub-clinical occult tumors which would assure the surgeons that they have completely removed the tumor burden. However, intraoperative gamma probe radioimmunodetection has not been widely adapted among surgeons because of some constraints associated with this technique. The main difficulty with this technique is the long period of waiting time between Mab injection and surgery. The technique is also laborious and costly. In recent years, Fluorine-18-2-fluoro-2-deoxy-D-glucose (18F-FDG) use in gamma probe tumor detection surgery has renewed interest among surgeons. Preliminary studies during surgery have demonstrated that use of FDG in gamma probe tumor detection during surgery is feasible and useful.

Expression of TAG-72 in ovarian cancer and its correlation with tumor stage and patient prognosis

Tumor associated glycoprotein-72 (TAG-72), a pancarcinoma antigen, was initially identified in cancer tissues by its immunoreactivity to a monoclonal antibody B72.3. In this study, we have analyzed the expression and localization profiles of TAG-72 in ovarian cancer tissue samples of different stages and histological subtypes by immunohistochemistry using a second generation high affinity monoclonal antibody CC49. We have also studied the expression of TAG-72 in ovarian cancer cell lines by confocal microscopy and immunoblot analyses. A correlation between TAG-72 expression and localization with patients' prognosis was also analyzed using Kaplan-Meier analysis. Eighty eight percent of the ovarian cancer tissue samples (n=43) showed immunoreactivity with CC49 antibody. The expression of TAG-72 in advanced stage cancer tissues (mean composite score=3.7) was significantly higher (p=0.035) compared to the early stage tumors (mean composite score=2.3). However, no significant correlation of TAG-72 was observed with histological tumor types. A marginal correlation of TAG-72 staining with patients' survival was observed. Interestingly, the membrane localization of TAG-72 in tumors was significantly (p=0.0082) associated to the poor clinical outcome, while cytoplasmic staining was correlated significantly to a better prognosis (p=0.0051). Immunoblot analysis demonstrated the expression of TAG-72 in three ovarian cancer cell lines (OVCAR3, SB247 and COV362.4). In conclusion, the tumor-specific expression of TAG-72 and its association with disease stage indicate its potential as a marker for effective disease management and targeted cancer therapy.

Enzyme specific activation of benzoquinone ansamycin prodrugs using HuCC49DeltaCH2-beta-galactosidase conjugates

To activate prodrugs for cancer treatment, an anti-TAG-72 antibody (HuCC49DeltaCH2) was used for delivery of an activation enzyme (beta-galactosidase) to specifically activate a geldanamycin prodrug (17-AG-C2-Gal) against colon cancer. The geldanamycin prodrug 17-AG-C2-Gal was synthesized by coupling a galactose-amine derivative with geldanamycin at the C-17 position. Molecular docking with two different programs (Affinity and Autodock) showed that the prodrug (17-AG-C2-Gal) was unable to bind to Hsp90; however, the product (17-AG-C2), enzymatically cleaved by beta-galactosidase conjugate, bound to Hsp90 in a similar way as geldanamycin and 17-AG. The computational docking results were further confirmed in experimental testing by the tetrazolium [3-(4,5-dimethythiazol-2-yl)]-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay and mass spectrometry. HuCC49DeltaCH2 was chemically conjugated to beta-galactosidase. The antibody-enzyme conjugate was able to target tumor antigen TAG-72 with the well-preserved enzymatic activity to activate 17-AG-C2-Gal prodrug. The released active drug 17-AG-C2 was demonstrated to induce up to 70% AKT degradation and enhance anticancer activity by more than 25-fold compared to the prodrug.

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.

Pharmacokinetics and tumor localization of (111)in-labeled HuCC49DeltaC(H)2 in BALB/c mice and athymic murine colon carcinoma xenograft

The primary limitation of IgG antibodies for radioimmunotherapy of solid tumors is their prolonged serum half-life, leading to dose-limiting bone marrow toxicity at doses providing inadequate radiation to the tumor. A humanized C(H)2 domain-deleted variant of the anti-TAG-72 antibody CC49 (HuCC49DeltaC(H)2) has faster blood clearance, compared to the IgG, while retaining tumor targeting. We compared the pharmacokinetics and tumor uptake of (111)In-HuCC49DeltaC(H)2 in BALB/c mice and a colon carcinoma (LS-174T) mouse xenograft with that of (111)In-labeled chimeric CC49 (cCC49), an antibody with pharmacokinetics similar to the humanized CC49 parent. Immuno-conjugates of HuCC49DeltaC(H)2 and cCC49 prepared with the (111)In chelator Mx-DTPA (1-isothiocyantobenzyl-3-methyldiethylenetriaminepentaacetic acid) retained low nM affinity and radiolabeling protocols provided greater than 95% radio-incorporation with (111)In while retaining greater than 80% immunoreactivity. Blood clearance of (111)In-HuCC49DeltaC(H)2 in BALB/c mice was monoexponential (t(1/2) 5.4 hours) and faster than (111)In-cCC49 (biexponential clearance; t1/2Delta 1.5 hours; t1/2beta 162 hours). The (111)In-HuCC49DeltaC(H)2 also cleared more rapidly from the blood in the murine xenograft. At 1 hour postinjection, blood concentrations for (111)In-HuCC49DeltaC(H)2 and (111)In-cCC49 were comparable (25.5 injected dose per g [%ID/g] and 21.3 %ID/g, respectively); tumor uptake for (111)In- HuCC49DeltaC(H)2 was 7.9 %ID/g, compared to 7.5 %ID/g for (111)In-cCC49. However, at 24 hours, blood concentration for (111)In-HuCC49DeltaC(H)2 was less than (111)In-cCC49 (0.9 %ID/g versus 5.2 %ID/g, respectively) with comparable tumor retention (14.4 %ID/g versus 19.0 %ID/g, respectively). Faster blood clearance of (111)In-HuCC49DeltaC(H)2 and tumor localization comparable to that of (111)In-cCC49 provided a fourfold improved tumor-to-blood ratio for (111)In-HuCC49DeltaC(H)2 at 24 hours postinjection.

Intraperitoneal radioimmunotherapy with a humanized anti-TAG-72 (CC49) antibody with a deleted CH2 region

The application of intraperitoneal (i.p.) radioimmunotherapy to treat i.p. tumor loci has been limited by bone marrow toxicity secondary to circulating radiolabeled antibodies. The generation of novel genetically engineered monoclonal antibodies, which can achieve high tumor uptake and rapid blood clearance, should enhance the therapeutic index of i.p. radioimmunotherapy. In this regard, a novel humanized anti-TAG-72 monoclonal antibody with a deleted CH2 region (HuCC49DeltaCH2) has been described, which localized well to subcutaneous xenograft tumors and had a rapid plasma clearance. The aim of this study was to examine the characteristics of this radiolabeled reagent when administered through the i.p. route in mice bearing i.p. tumor (LS174T). The DeltaCH2 molecule and intact humanized CC49 (HuCC49) monoclonal antibody were conjugated to PA-DOTA and radiolabeled with (177)Lu. Both molecules retained high-affinity binding to TAG-72 positive LS174T tumor cells in vitro. The radiolabeled DeltaCH2 molecule had a modest decrease in tumor localization, as compared to the intact molecule when administered i.p. to tumor-bearing mice and a dramatically shorter plasma disappearance T(1/2) at 2.7 hours compared to 61.2 hours for the intact antibody. The radiolabeled DeltaCH2 molecule thus had very high tumor:blood ratios. Using an (131)I-labeled system, the maximum tolerated dose of DeltaCH2 was >3x that of intact HuCC49. Autoradiography of tumors showed low radiation dose rates at tumor centers early (1 and 4 hours), as compared to higher dose rates at tumor periphery but a more uniform distribution by 24 hours. Dose-rate distributions were similar for both reagents. Animals bearing LS174T i.p. tumors were treated with 300 microCi of (177)Lu-labeled DeltaCH2 or intact HuCC49 by i.p. route daily x 3. The (177)Lu-DeltaCH(2) molecule mediated an increase in median survival compared to controls (67.5 +/- 7.5 days versus controls of 32 +/- 3.3) while the same dose of (177)Lu-HuCC49 produced early toxic deaths. These studies suggest that i.p. radioimmunotherapy using radiolabeled HuCC49DeltaCH2 should allow higher radiation doses to be administered with less marrow toxicity and potentially improved efficacy.

Construction, affinity maturation, and biological characterization of an anti-tumor-associated glycoprotein-72 humanized antibody

The tumor-associated glycoprotein (TAG)-72 is expressed in the majority of human adenocarcinomas but is rarely expressed in most normal tissues, which makes it a potential target for the diagnosis and therapy of a variety of human cancers. Here we describe the construction, affinity maturation, and biological characterization of an anti-TAG-72 humanized antibody with minimum potential immunogenicity. The humanized antibody was constructed by grafting only the specificity-determining residues (SDRs) within the complementarity-determining regions (CDRs) onto homologous human immunoglobulin germ line segments while retaining two mouse heavy chain framework residues that support the conformation of the CDRs. The resulting humanized antibody (AKA) showed only about 2-fold lower affinity compared with the original murine monoclonal antibody CC49 and 27-fold lower reactivity to patient serum compared with the humanized antibody HuCC49 that was constructed by CDR grafting. The affinity of AKA was improved by random mutagenesis of the heavy chain CDR3 (HCDR3). The highest affinity variant (3E8) showed 22-fold higher affinity compared with AKA and retained the original epitope specificity. Mutational analysis of the HCDR3 residues revealed that the replacement of Asn(97) by isoleucine or valine was critical for the affinity maturation. The 3E8 labeled with (125)I or (131)I showed efficient tumor targeting or therapeutic effects, respectively, in athymic mice with human colon carcinoma xenografts, suggesting that 3E8 may be beneficial for the diagnosis and therapy of tumors expressing TAG-72.

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

Fucose removal from complex-type oligosaccharide of human IgG1-type antibody results in a great enhancement of antibody-dependent cellular cytotoxicity (ADCC). The aim of this study was to clarify the effect of fucose removal on effector functions of a single-gene-encoded antibody with an scFv used as the binding domain. We generated both a fucose-negative anti-tumor associated glycoprotein (TAG)-72 scFv-Fc using alpha-1,6-fucosyltransferase knock-out CHO cells and a highly fucosylated scFv-Fc from parental CHO cells. Expression, assembly and antigen binding activity of the scFv-Fcs were not influenced by fucose removal. The scFv-Fc lacking fucose exhibited significantly more potent FcgammaRIIIa binding and ADCC compared to highly fucosylated scFv-Fc. These results prove that ADCC enhancement by fucose-removal is effective in not only whole IgG1, but also scFv-Fc, and thus increases the potential of Fc-fusion proteins as therapeutic candidates.

SDR grafting--a new approach to antibody humanization

A major impediment to the clinical utility of the murine monoclonal antibodies is their potential to elicit human anti-murine antibody (HAMA) response in patients. To circumvent this problem, murine antibodies have been genetically manipulated to progressively replace their murine content with the amino acid residues present in their human counterparts. To that end, murine antibodies have been humanized by grafting their complementarity determining regions (CDRs) onto the variable light (V(L)) and variable heavy (V(H)) frameworks of human immunoglobulin molecules, while retaining those murine framework residues deemed essential for the integrity of the antigen-combining site. However, the xenogeneic CDRs of the humanized antibodies may evoke anti-idiotypic (anti-Id) response in patients. To minimize the anti-Id response, a procedure to humanize xenogeneic antibodies has been described that is based on grafting, onto the human frameworks, only the specificity determining residues (SDRs), the CDR residues that are most crucial in the antibody-ligand interaction. The SDRs are identified through the help of the database of the three-dimensional structures of the antigen-antibody complexes of known structures or by mutational analysis of the antibody-combining site. An alternative approach to humanization, which involves retention of more CDR residues, is based on grafting of the 'abbreviated' CDRs, the stretches of CDR residues that include all the SDRs. A procedure to assess the reactivity of the humanized antibody to sera from patients who had been administered the murine antibody has also been described.

Pharmacokinetics and clinical evaluation of 125I-radiolabeled humanized CC49 monoclonal antibody (HuCC49deltaC(H)2) in recurrent and metastatic colorectal cancer patients

INTRODUCTION

CC49 is an antitumor monoclonal antibody that is promising for use in radioimmunoguided surgery (RIGS). However, the murine antibody has been limited by human antimouse antibody (HAMA) response and slow clearance. This study examined the pharmacokinetics and tissue localization of a humanized domain-deleted CC49 antibody (HuCC49DeltaC(H)2 MAb) in humans.

METHODS

Twenty-one patients with colorectal carcinoma were given 1 mg intravenous (I.V.) bolus of HuCC49DeltaC(H)2 MAb radiolabeled with 2 mCi (125)I after thyroid blockade. The level of circulating HuCC49DeltaC(H)2 MAb was measured daily as precordial counts using a handheld gamma-detecting probe. Each patient underwent an exploratory laparotomy on postinjection days 3-20. Gamma counts were measured at normal organs, aortic bifurcation (AB), and both clinically evident and occult tumors.

RESULTS

Precordial and AB gamma counts showed an excellent linear correlation. HuCC49DeltaC(H)2 MAb followed a two-compartment pharmacokinetic model. Normal organs and AB showed similar exposures to HuCC49DeltaC(H)2 MAb, while HuCC49DeltaC(H)2 MAb favorably distributed into tumors from day 3. Intestinal and metastatic liver lesions showed the highest partition coefficients. All patients showed no HAMA response.

DISCUSSION

C(H)2 region deletion of HuCC49DeltaC(H)2 MAb did not alter the pharmacokinetics compared to murine CC49. The favorable partition coefficient K of HuCC49DeltaC(H)2 MAb into tumors supports its use in RIGS.

HGS-ETR1, a fully human TRAIL-receptor 1 monoclonal antibody, induces cell death in multiple tumour types in vitro and in vivo

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in a variety of tumour cells through activation of TRAIL-R1 and TRAIL-R2 death signalling receptors. Here, we describe the characterisation and activity of HGS-ETR1, the first fully human, agonistic TRAIL-R1 mAb that is being developed as an antitumour therapeutic agent. HGS-ETR1 showed specific binding to TRAIL-R1 receptor. HGS-ETR1 reduced the viability of multiple types of tumour cells in vitro, and induced activation of caspase 8, Bid, caspase 9, caspase 3, and cleavage of PARP, indicating activation of TRAIL-R1 alone was sufficient to induce both extrinsic and intrinsic apoptotic pathways. Treatment of cell lines in vitro with HGS-ETR1 enhanced the cytotoxicity of chemotherapeutic agents (camptothecin, cisplatin, carboplatin, or 5-fluorouracil) even in tumour cell lines that were not sensitive to HGS-ETR1 alone. In vivo administration of HGS-ETR1 resulted in rapid tumour regression or repression of tumour growth in pre-established colon, non-small-cell lung, and renal tumours in xenograft models. Combination of HGS-ETR1 with chemotherapeutic agents (topotecan, 5-fluorouracil, and irinotecan) in three independent colon cancer xenograft models resulted in an enhanced antitumour efficacy compared to either agent alone. Pharmacokinetic studies in the mouse following intravenous injection showed that HGS-ETR1 serum concentrations were biphasic with a terminal half-life of 6.9–8.7 days and a steady-state volume of distribution of approximately 60 ml kg⁻¹. Clearance was 3.6–5.7 ml⁻¹ day⁻¹ kg⁻¹. These data suggest that HGS-ETR1 is a specific and potent antitumour agent with favourable pharmacokinetic characteristics and the potential to provide therapeutic benefit for a broad range of human malignancies.

Minimizing the Immunogenicity of Antibodies for Clinical Application

The clinical utility of murine monoclonal antibodies has been greatly limited by the human anti-murine antibody responses they effect in patients. To make them less immunogenic, murine antibodies have been genetically engineered to progressively replace their murine content with that of their human counterparts. This review describes the genetic approaches that have been used to humanize murine antibodies, including the generation of mouse-human chimeric antibodies, veneering of the mouse variable regions, and the grafting of murine complementarity-determining regions (CDRs) onto the variable light (VL) and variable heavy (VH) frameworks of human immunoglobulin molecules, while retaining only those murine framework residues deemed essential for the integrity of the antigen-binding site. To minimize the anti-idiotypic responses that could still be evoked by the murine CDRs in humanized antibodies, two approaches have also been described. These are based on grafting onto the human frameworks the 'abbreviated' CDRs or only the specificity-determining residues (SDRs), the CDR residues that are involved in antigen interaction. The SDRs are identified through the help of the database of three-dimensional structures of antibody:antigen complexes or by mutational analysis of the antibody-combining site. In addition, we also describe the use of in vitro affinity maturation to enhance the binding affinity of humanized antibodies, as well as the manipulation of framework residues to maximize their human content and minimize their immunogenic potential.

A novel monoclonal antibody design for radioimmunotherapy

The generation of chimeric and complementary-determining region (CDR) grafted monoclonal antibodies (MAb) have reduced the immunogenicity problem in the clinical application of radioimmunotherapy with monoclonal antibodies. However, humanization (Hu) has prolonged the circulation (plasma T1/2) of radiolabeled antibodies, resulting in an increased normal tissue exposure to radioactivity and greater dose-limiting bone marrow suppression. To overcome this problem, a tumor-associated glycoprotein (TAG)-72-specific CDR grafted MAb with C(H)2 domain deletion (DeltaC(H)2) was developed from the MAb CC49. Preclinical studies have demonstrated that HuCC49 DeltaC(H)2 clears more rapidly from the plasma of mice than HuCC49. This preliminary report describes the initial human experience with HuCC49 DeltaC(H)2 radiolabeled with 131I and administered to patients with metastatic colorectal carcinoma. In this pilot study we enrolled four patients who received a single infusion of 20 mg of HuCC49 DeltaC(H)2 (total protein dose) labeled with 10 mCi of 131I. Pharmacokinetics, biodistribution, dosimetry, and immune response were evaluated over 2-6 weeks. No toxicity was observed in this group of patients. A one-compartment bolus model using the non-linear (NLIN) procedures in Statistical Analysis Software (SAS; SAS, Incorporated, Cary, NC) best describes the pharmacokinetics of the 131I-HuCC49 DeltaC(H)2 with a plasma mean T1/2 of 20 +/- 3 hours, a mean residence time (MRT) of 29 +/- 4 hours and a clearance rate (Cl) of 1.5 +/- 0.1 mL/hours/kg. The whole body and marrow radiation dose estimates were 0.55 +/- 0.06 rad/mCi and 1.00 +/- 0.14 rad/mCi, respectively. All patients had positive localization of antibody to metastatic tumor sites. The 131I-HuCC49 DeltaC(H)2 biodistribution was similar to murine CC49. Three patients had no evidence of antibody response to HuCC49 DeltaC(H)2 over 6 weeks of observation, and one patient had a marginal response by week 6. Intravenous administration of HuCC49 DeltaC(H)2 is safe and well tolerated. The deleted C(H)2 construct has a shorter half-life compared with prior studies of murine CC49 but with similar biodistribution and low immunogenicity. These studies support the further clinical investigation of this agent in phase I trials by intravenous and intraperitoneal routes.

Pharmacokinetics and biodistribution of genetically engineered antibodies

The engineering of monoclonal antibodies has created a new generation of pharmaceuticals with the desired pharmacokinetics and biodistribution properties. For radioimmunotherapy and radioscintigraphy, optimum tumor targeting can be achieved using engineered constructs that provide high antigen affinity and specificity, effective tumor penetration, circulation properties that allow high tumor uptake with acceptable doses to the normal tissues, and fast clearance allowing low background. Recent advances have made possible the development of antibodies with these properties.

Surface plasmon resonance-based competition assay to assess the sera reactivity of variants of humanized antibodies

While clinical trials are the only way to evaluate the immunogenicity, in patients, of murine or genetically engineered humanized variants of a potentially therapeutic or diagnostic monoclonal antibody (MAb), ethical and logistical considerations of clinical trials do not permit the evaluation of variants of a given MAb that are generated to minimize its immunogenicity. The most promising variant could be identified by comparing the reactivities of the parental antibody (Ab) and its variants to the sera of patients containing anti-variable region (anti-VR) Abs to the administered parental Ab. We have developed a surface plasmon resonance (SPR) biosensor-based assay to monitor the binding of the sera anti-VR Abs to the parental Ab and the inhibition of this binding by the variants. SPR biosensors allow the real-time detection and monitoring of the binding between an immobilized protein and its soluble ligand without the need for prior purification and labeling of the mobile analyte. This new assay requires no radiolabeling, is relatively less time-consuming, and uses only small amounts of serum (5-20 microl of diluted serum) through a new microfluidic sample handling technique. To validate the assay, we have tested the relative reactivities of the CDR-grafted anti-carcinoma Ab, HuCC49, and its two variants, designated V5 and V10, to the sera of patients who were earlier administered radiolabeled murine CC49 in a clinical trial. A comparison of IC(50)s (the concentrations of the competitor Abs required for 50% inhibition of the binding of sera to immobilized HuCC49) showed that V5 and V10 were less reactive than HuCC49 to the three patients' sera tested. We have also demonstrated, for the first time, the specific detection and comparison of relative amounts of anti-VR Abs present in the sera of different patients without prior removal of anti-murine Fc Abs and/or circulating antigen. This may facilitate the rapid screening, for the presence of anti-VR Abs, of the sera of patients undergoing clinical trials.

Grafting of "abbreviated" complementarity-determining regions containing specificity-determining residues essential for ligand contact to engineer a less immunogenic humanized monoclonal antibody

Murine mAb COL-1 reacts with carcinoembryonic Ag (CEA), expressed on a wide range of human carcinomas. In preclinical studies in animals and clinical trials in patients, murine COL-1 showed excellent tumor localization. To circumvent the problem of immunogenicity of the murine Ab in patients, a humanized COL-1 (HuCOL-1) was generated by grafting the complementarity-determining regions (CDRs) of COL-1 onto the frameworks of the variable light and variable heavy regions of human mAbs. To minimize anti-V region responses, a variant of HuCOL-1 was generated by grafting onto the human frameworks only the "abbreviated" CDRs, the stretches of CDR residues that contain the specificity-determining residues that are essential for the surface complementarity of the Ab and its ligand. In competition RIAs, the recombinant variant completely inhibited the binding of radiolabeled murine and humanized COL-1 to CEA. The HuCOL-1 and its variant showed no difference in their binding ability to the CEA expressed on the surface of a CEA-transduced tumor cell line. Compared with HuCOL-1, the HuCOL-1 variant showed lower reactivity to patients' sera carrying anti-V region Abs to COL-1. The final variant of the HuCOL-1, which retains its Ag-binding reactivity and shows significantly lower serum reactivity than that of the parental Ab, can serve as a prototype for the development of a potentially useful clinical reagent.

In vivo comparison of macrocyclic and acyclic ligands for radiolabeling of monoclonal antibodies with 177Lu for radioimmunotherapeutic applications

The studies reported herein present the first in vitro and in vivo comparison of radioimmunoconjugates (RIC) radiolabeled with 177Lu using the acyclic CHX-A"-DTPA ligand and the macrocyclic ligands, C-DOTA and PA-DOTA. The in vivo studies include pharmacokinetics and biodistribution of the formed 177Lu-labeled immunoconjugates in a tumor bearing murine model with engineered monoclonal antibody HuCC49DeltaCH2. The in vitro analysis indicated that the CHX-A" RIC was superior with respect to immunoreactivity, radiolabeling with 177Lu, and specific activity. The in vivo pharmacokinetic data by itself indicated that the Lu(III)-PA-DOTA complex may not be as stable as Lu(III) complexes with CHX-A" or C-DOTA. All three RICs demonstrated tumor targeting of human colon carcinoma xenografts in athymic mice. In these biodistribution studies, there appears to be no overall pattern or trend of one RIC over the other two. Based on these in vitro and in vivo studies, the CHX-A" DTPA ligand should be considered a suitable bifunctional chelate for the radiolabeling of monoclonal antibodies with 177Lu for radioimmunotherapy applications.

Effects of humanization and gene shuffling on immunogenicity and antigen binding of anti-TAG-72 single-chain Fvs

One major constraint in the clinical application of murine monoclonal antibodies (MAbs) is the development of a human antimurine antibody response. The immunogenicity of MAbs can be minimized by replacing nonhuman regions with corresponding human sequences. The studies reported in our article were undertaken to analyze the immunoreactivity and the immunogenicity of the CC49 single-chain antibody fragments (scFvs): (i) an scFv construct comprised of mouse CC49 VL and VH (m/m scFv), (ii) a light chain shuffled scFv with human VL (Hum4 VL) and mouse CC49 VH (h/m scFv), and (iii) a humanized scFv assembled from Hum4 VL and CC49 VH complementary determining regions (CDRs) grafted onto a VH framework of MAb 21/28' CL (h/CDR scFv). The CC49 scFvs competed for an antigen binding site with CC49 IgG in a similar fashion in a competition radioimmunoassay and were able to inhibit the binding of CC49 IgG to the antigen completely. The immunogenicity of CC49 scFvs was tested using sera with antiidiotypic antibodies to MAb CC49 obtained from patients treated by CC49 IgG in clinical trials. All tested sera exhibited the highest reactivity to the m/m scFv. However, the sera demonstrated differential reactivities to h/CDR scFv and h/m scFv. Replacement of the mouse chain in h/m scFv and h/CDR scFv decreased or completely averted serum reactivity. Our studies compared for the first time the antigen binding and immunogenicity of different scFv constructs containing the mouse, CDR grafted or human variable chains. These results indicate that the humanized CC49 scFv is potentially an important agent for imaging and therapeutic applications with TAG-72-positive tumors.

Intraperitoneal radioimmunochemotherapy of ovarian cancer: a phase I study

A phase I trial was designed to examine the feasibility of combining interferon and Taxol with intraperitoneal radioimmunotherapy (177Lu-CC49). Patients with recurrent or persistent ovarian cancer confined to the abdominal cavity after first line therapy, Karnofsky performance status > 60, adequate liver, renal and hematologic function, and tumor that reacted with CC49 antibody were enrolled. Human recombinant alpha interferon (IFN) was administered as 4 subcutaneous injections of 3 x 10(6) U on alternate days beginning 5 days before RIT to increase the expression of the tumor-associated antigen, TAG-72. The addition of IFN increased hematologic toxicity such that the maximum tolerated dose (MTD) of the combination was 40 mCi/m2 compared to 177Lu-CC49 alone (45 mCi/m2). Taxol, which has radiosensitizing effects as well as antitumor activity against ovarian cancer, was given intraperitoneally (i.p.) 48 hrs before RIT. It was initiated at 25 mg/m2 and escalated at 25 mg/m2 increments to 100 mg/m2. Subsequent groups of patients were treated with IFN + 100 mg/m2 Taxol + escalating doses of 177Lu-CC49. Three or more patients were treated in each dose group and 34 patients were treated with the 3-agent combination. Therapy was well tolerated with the expected reversible hematologic toxicity. The MTD for 177Lu-CC49 was 40 mCi/m2 when given with IFN + 100 mg/m2 Taxol. Interferon increased the effective whole body half-time of radioactivity and the whole body radiation dose. Taxol did not have a significant effect on pharmacokinetic or dosimetry parameters. Four of 17 patients with CT measurable disease had a partial response (PR) and 4 of 27 patients with non-measurable disease have progression-free intervals of 18+, 21+, 21+, and 37+ months. The combination of intraperitoneal Taxol chemotherapy (100 mg/m2) with RIT using 177Lu-CC49 and interferon was well tolerated, with bone marrow suppression as the dose-limiting toxicity.

Antibody constructs for radioimmunodiagnosis and treatment of human pancreatic cancer

Pancreatic cancer (PC) is a common disease that is seldom cured. Current approaches to the treatment of PC are not effective because the non-specific nature of both chemotherapy and external beam radiation results in toxicity to normal tissue. Monoclonal antibodies (MAbs) can be used as selective carriers for delivering radionuclides, toxins, or cytotoxic drugs to malignant cell populations. Therefore, MAb-technology has led to a significant amount of research in targeted therapy. Targeted therapy would generally allow the concentration of cytotoxic agents in tumors and would markedly lessen the toxicity to normal tissues, which limits the dosage and effectiveness of systemically administered drugs. A variety of MAbs are being pre-clinically evaluated for the diagnosis and treatment of PC. Novel recombinant antibody constructs hold a promising future in both the diagnosis and treatment of cancer. By genetic-engineering methods, several high affinity antibody fragments with optimum tumor targeting properties, such as higher functional affinity (divalent and multivalent scFvs) and blood residence time (good tumor localization with high radiolocalization index), have been generated. Animal models have permitted the in vivo assessment of these antibody-based reagents, therapeutic/diagnostic radionuclide, radiolabeling conditions, and efficacy of administration regimes. For PC, immunoscintigraphy using MAbs has taken new strides. The use of MAbs and their fragments for radioimmunoguided surgery and therapy of PC has shown encouraging results at preclinical levels and warrants further attention.

The integrity of the ball-and-socket joint between V and C domains is essential for complete activity of a humanized antibody

AF2 is a high affinity murine Ab possessing potent neutralizing activity against human IFN-gamma. In carrying out the modifications to humanize this Ab, we discovered that an initial version displayed affinity for IFN-gamma that was slightly less than that of AF2, but exhibited IFN-gamma-neutralizing activity that was severely diminished. Characterization via site-directed mutagenesis revealed that the majority of this loss in IFN-gamma-neutralizing activity was due to altering the V(H) framework residue at position 11. V(H) position 11 is distal to the binding surface of the Ab; however, it, along with residues 110 and 112, have been identified as forming the socket of a molecular ball-and-socket joint between the V and C domains of the Ig Fab, which influences the elbow angle between these domains. To determine whether disrupting the structure of this joint was the basis for reduced IFN-gamma-neutralizing capacity, we altered residue 148 of C(H1), which with residue 149 comprises the corresponding ball portion of the joint. Changing this single C(H1) domain residue diminished the ability of the Ab to neutralize IFN-gamma to a level similar to that observed with the V(H) alteration. Thus, an intact ball-and-socket joint between the V and C domains in AF2 is required for potent neutralization of IFN-gamma. These results suggest the importance of the elbow angle between Ig V and C domains in Ab activity, and support the hypothesis that this joint can be an important functional element of Ab structure.

Anti-Tumor CC49-zeta CD4 T cells possess both cytolytic and helper functions

The authors report that the nature of the T-cell-receptor--derived signal in normal CD4+ T cells can induce interleukin-2 (IL-2) secretion or perforin-mediated cytolytic activity. Normal human T cells were genetically modified to express the tumor antigen specific chimeric immune receptor, CC49-zeta. The CC49-zeta chimeric immune receptor is comprised of the intracellular signaling domains of the TCR CD3zeta protein fused to the single chain scFv of the humanized CC49 antibody, which binds the pan-adenocarcinoma tumor antigen TAG-72. Patient-specific T cells genetically modified to express the CC49-zeta receptor have been used in patients with colon cancer. The authors report that both CD4 and CD8 T cells expressing the CC49-zeta receptor mediated the major histocompatibility complex-unrestricted lysis of TAG-72--expressing tumor cells with comparable efficiency. However, although the CC49-zeta receptor mediated target cell lysis, it did not support the production of IL-2, even in the presence of CD28 stimulation. Robust IL-2 secretion and T-cell proliferation were observed when the same CD4 CC49-zeta T cells were stimulated through the CD28 receptor and endogenous T-cell receptor. These results indicate that CD4 T lymphocytes possess the capacity to act as both cytolytic and helper T cells and that this difference in effector function is controlled by the nature of the T-Cell receptor--derived signals.

Monoclonal antibody therapy for solid tumors

Monoclonal antibody therapy for solid tumors has many theoretical attractions and a long history. Until recently, with the approval and widespread use of rituximab (Rituxan) and trastuzumab (Herceptin), monoclonal antibody therapy for tumors had not had significant success. This article reviews basic theories behind antibody development and their clinical implementation as treatment for solid tumors. Medline was searched for articles over the past 15 years dealing with laboratory and clinical applications of antibody therapy for solid tumors. In addition, American Society of Clinical Oncology (ASCO) abstracts from the past 3 years were reviewed to complement the Medline search. This article focuses on treatment for common solid tumors, including breast, colon and lung cancers.

Radioimmunotherapy: designer molecules to potentiate effective therapy

The evolution of monoclonal antibody forms for radioimmunotherapy and other antibody-based applications has been driven by a series of problems that each new form has introduced. Ehrlich was the first to present the concept that antibodies could be exploited in such a manner. Four decades were required before technological advances allowed the exploration of the potential of antibodies for radioimaging and radioimmunotherapeutic applications. Advances in DNA technology have led to the ability to tailor and manipulate the immunoglobulin molecule for specific functions and in vivo properties. This article discusses the use of monoclonal antibodies for radiotherapy with an emphasis on the problems that have been encountered and the subsequent solutions.

Structural correlates of an anticarcinoma antibody: identification of specificity-determining residues (SDRs) and development of a minimally immunogenic antibody variant by retention of SDRs only

Clinical utility of murine mAbs is limited because many elicit Abs to murine Ig constant and variable regions in patients. An Ab humanized by the current procedure of grafting all the complementarity determining regions (CDRs) of a murine Ab onto the human Ab frameworks is likely to be less immunogenic, except that its murine CDRs could still evoke an anti-variable region response. Previous studies with anticarcinoma mAb CC49 showed that light chain LCDR1 and LCDR2 of humanized CC49 could be replaced with the corresponding CDRs of a human Ab with minimal loss of Ag-binding activity. The studies reported in this paper were undertaken to dissect the CC49 Ag-binding site to identify 1) specificity determining residues (SDRs), the residues of the hypervariable region that are most critical in Ag-Ab interaction, and 2) those residues that contribute to the idiotopes that are potential targets of patients' immune responses. A panel of variants generated by genetic manipulation of the murine CC49 hypervariable regions were evaluated for their relative Ag-binding affinity and reactivity to sera from several patients who had been immunized with murine CC49. One variant, designated HuCC49V10, retained only the SDRs of CC49 and does not react with the anti-variable region Abs of the sera from the murine CC49-treated patients. These studies thus demonstrate that the genetic manipulation of Ab variable regions can be accomplished by grafting only the SDRs of a xenogeneic Ab onto human Ab frameworks. This approach may reduce the immunogenicity of Abs to a minimum.

Improved synthesis of the bifunctional chelating agent 1,4,7,10-tetraaza-N-(1-carboxy-3-(4-nitrophenyl)propyl)-N',N'',N'''-tri s(acetic acid)cyclododecane (PA-DOTA)

A concise synthesis of the bifunctional chelating agent 1,4,7,10-tetraaza-N-(1-carboxy-3-(4-nitrophenyl)propyl)-N',N'',N'' '-tris(acetic acid)cyclododecane (PA-DOTA) is reported. Difficulties involving the production of partially alkylated products and their removal have been addressed and obviated. After the pure nitro form of PA-DOTA was obtained, conversion to the isothiocyanato form PA-DOTA (1, conjugation to HuCC49 and HuCC49deltaCH2 monoclonal antibodies was achieved. Subsequent radiolabeling with 177Lu was performed, demonstrating a useful bifunctional chelating agent suitable for clinical radioimmunotherapy applications.

CDR substitutions of a humanized monoclonal antibody (CC49): contributions of individual CDRs to antigen binding and immunogenicity

One of the major obstacles in the successful clinical application of monoclonal antibodies has been the development of host immune responses to murine Ig constant and variable regions. While the CDR grafting of MAbs may alleviate many of these problems, the potential remains that one or more murine CDRs on the human Ig backbone of a "humanized" MAb may still be immunogenic. Studies were undertaken employing a MAb of potential clinical utility, CC49, to define those CDRs that are essential for antigen binding and those that may be immunogenic in humans. We previously developed a humanized CC49 (HuCC49) by grafting the MAb CC49 hypervariable regions onto frameworks of human MAbs. To identify those CDRs essential for binding, a panel of variant HuCC49 MAbs was generated here by systematically replacing each of the murine CDRs with their human counterparts. The relative affinity constant of each variant was determined. Serum from a patient who received murine CC49 was used to determine the potential immunogenicity of each CDR in humans. The serum was shown to react with the anti-CC49 variable region. Results showed that patients' anti-idiotypic responses are directed mainly against LCDR3 and moderately against LCDR1 and HCDR2. These studies demonstrate for the first time that variants containing individual CDR substitutions of a humanized MAb can be constructed, and each CDR can be defined for the two most important properties for potential clinical utility: antigen binding and immunogenicity.

A single backmutation in the human kIV framework of a previously unsuccessfully humanized antibody restores the binding activity and increases the secretion in cos cells

Humanization of rodent mAbs by CDR-grafting (also called "reshaping") is now a standard procedure for reducing immunogenicity and recruiting human effector functions. However, the design of the humanized mAb can sometimes prove circuitous. Attempts were made to humanize L-25, a mouse antibody against the human alpha-4 integrin subunit using the usual protocols. Despite reaching eight backmutations in the light chain, it was not possible to recover the binding activity to the level of the chimeric. In an effort to restore the binding activity, an analysis of the human kappa IV acceptor frameworks was undertaken. This analysis highlighted the Asp at position 9 in framework 1, which although a common amino acid in human kappa IV frameworks, was an unusual residue in mouse kappa frameworks. Backmutating this position to the mouse amino acid completely restored the binding of the humanized antibody and as a by-product also increased the secretion levels in cos cells. Mutating position 9 to the consensus residue for human kappa I also restored the binding and secretion levels although not to the same extent. The resulting humanized antibody had a light chain with only a single backmutation to the mouse sequence.

Human Anti-Animal Antibody Interferences in Immunological Assays

Purpose: The scope and significance of human anti-animal antibody interference in immunological assays is reviewed with an emphasis on human anti-animal immunoglobulins, particularly human anti-mouse antibodies (HAMAs).

Issues: Anti-animal antibodies (IgG, IgA, IgM, IgE class, anti-isotype, and anti-idiotype specificity) arise as a result of iatrogenic and noniatrogenic causes and include human anti-mouse, -rabbit, -goat, -sheep, -cow, -pig, -rat, and -horse antibodies and antibodies with mixed specificity. Circulating antibodies can reach gram per liter concentrations and may persist for years. Prevalence estimates for anti-animal antibodies in the general population vary widely and range from <1% to 80%. Human anti-animal antibodies cause interferences in immunological assays. The most common human anti-animal antibody interferent is HAMA, which causes both positive and negative interferences in two-site mouse monoclonal antibody-based assays. Strategies to prevent the development of human anti-animal antibody responses include immunosuppressant therapy and the use of humanized, polyethylene glycolylated, or Fab fragments of antibody agents. Sample pretreatment or assay redesign can eliminate immunoassay interferences caused by anti-animal antibodies. Enzyme immunoassays, immunoradiometric assays, immunofluorescence, and HPLC assays have been designed to detect HAMA and other anti-animal antibodies, but intermethod comparability is complicated by differences in assay specificity and lack of standardization.

Conclusions: Human anti-animal antibodies often go unnoticed, to the detriment of patient care. A heightened awareness on the part of laboratory staff and clinicians of the problems caused by this type of interference in routine immunoassay tests is desirable. Efforts should be directed at improving methods for identifying and eliminating this type of analytical interference.

Large-scale manufacturing of safe and efficient retrovirus packaging lines for use in immunotherapy protocols

BACKGROUND

The use of gene modified T lymphocytes for immunotherapy in a cancer or AIDS clinical trial requires an efficient, safe ex vivo method for modification of these cells at manufacturing scale. Since retroviruses have been shown to be a moderately effective means of stably integrating therapeutic genes into T lymphocytes, we wanted to create packaging and producer cell lines that would produce replication competent retrovirus (RCR)-free supernatants, at large scale (> 200 l), and transduce with high efficiency.

METHODS

cDNA expression plasmids containing only coding sequences for gagpol or env were built and sequentially transfected into human 293 cells. Packaging and producer clones were characterized for stability, titer and RCR. A producer clone delivering chimeric immune receptors was scaled-up and supernatants used to transduce patient T lymphocytes for clinical studies. PCR and RT-PCR assays were utilized to evaluate the transmission of HERV-H sequences. Relative infectivity of producer clones pseudotyped with different envelopes was determined by transduction and RT assays.

RESULTS

RCR-free, human 293 split-genome packaging lines, pseudotyped with amphotropic, xenotropic, or 10A1 envelopes, were created. A CC49 zeta producer clone was scaled-up to 5 x 54 l lots and supernatants used to safely and efficiently transduce patient T lymphocytes with minimal ex vivo manipulation. While 293 cells express HERV-H mRNA, the transmission frequency in our packaging clones was less than 1 HERV-H sequence per 5 x 10(5) proviral integrations. Additionally, 10A1 and xenotropic packaging lines had higher infectivities than the amphotropic clone.

CONCLUSION

These packaging lines represent the safest configuration for the large-scale production of retroviral vectors, and are capable of producing high titer, RCR-free retroviral vector for large scale clinical use. While all three clones efficiently transduce human T lymphocytes, the 10A1 clone has the highest infectivity. These packaging cell lines will be valuable for use in human gene therapy protocols.

Anti-tumor activity of human T cells expressing the CC49-zeta chimeric immune receptor

A chimeric immune receptor consisting of an extracellular antigen-binding domain derived from the CC49 humanized single-chain antibody, linked to the CD3zeta signaling domain of the T cell receptor, was generated (CC49-zeta). This receptor binds to TAG-72, a mucin antigen expressed by most human adenocarcinomas. CC49-zeta was expressed in CD4+ and CD8+ T cells and induced cytokine production on stimulation. Human T cells expressing CC49-zeta recognized and killed tumor cell lines and primary tumor cells expressing TAG-72. CC49-zeta T cells did not mediate bystander killing of TAG-72-negative cells. In addition, CC49-zeta T cells not only killed FasL-positive tumor cells in vitro and in vivo, but also survived in their presence, and were immunoprotective in intraperitoneal and subcutaneous murine tumor xenograft models with TAG-72-positive human tumor cells. Finally, receptor-positive T cells were still effective in killing TAG-72-positive targets in the presence of physiological levels of soluble TAG-72, and did not induce killing of TAG-72-negative cells under the same conditions. This approach is being currently being utilized in a phase I clinical trial for the treatment of colon cancer.

A novel tumor-specific human single-chain Fv selected from an active specific immunotherapy phage display library

A colon tumor-associated antigen, CTAA 28A32-32K (CTA # 2E), related to the annexin family of proteins, was initially identified by its reactivity with a low affinity human IgM monoclonal antibody (mAb), 28A32. Both in vitro lymphoproliferative assays with human peripheral blood lymphocytes and delayed type hypersensitivity responses in patients immunized with autologous colon tumor cells indicated that CTA # 2E elicits potent T cell mediated responses and may be an important antigen in the development of a generic colorectal vaccine (Pomato et al. Vaccine Res 1994;3:145-161). A CTA # 2E-specific, murine hybridoma-derived mAb, 5-11A, which recognizes the amino-terminus of the tumor-associated antigen, exhibited qualitative human colon tumor-specific immunohistochemical reactivity. To rapidly develop a human mAb with similar antigen specificity and tumor reactivity as the murine 5-11A mAb, antibody phage display technology was employed. Two human antibody phage display libraries with 3.1 x 10(7) and 2.3 x 10(8) members were prepared from the variable region genes expressed by circulating B cells of patients undergoing active specific immunotherapy (ASI) with autologous tumor cells, predominantly from the colon, admixed with Bacille Calmette-Guerin (BCG). A CTA # 2E-reactive human single-chain (sc)Fv was selected by panning the larger library on decreasing concentrations of biotinylated tumor-associated antigen in solution. It exhibited similar antigen specificity as the murine hybridoma-derived 5-11A scFv, requiring the presence of the CTA # 2E amino-terminus for reactivity. This human scFv exhibited qualitative human colon tumor-specific immunohistochemical reactivity when displayed as a gene III fusion protein on phage. When reconstructed and expressed as an intact human IgG1, K mAb, its qualitative colon tumor-specificity was unaltered. Two other CTA # 2E-reactive human scFvs were selected from the smaller library by panning initially on decreasing concentrations of CTA # 2E coated to polystyrene and then on biotinylated CTA # 2E in solution. These human scFvs, which exhibited modest reactivity with different epitopes on the CTA # 2E antigen, did not exhibit human colon tumor-specific immunohistochemical reactivity.

Specific targeting of cytokine-secreting cells: a bispecific diabody recognizing human interleukin-6 and CD3 induces T cell-mediated killing

Cytokines have been implicated in the pathophysiology of many diseases. Although there have been many attempts to neutralize the activity of cytokines in vivo and in vitro, no strategies have been developed to specifically eliminate cells that overexpress cytokines. Considering the fact that cytokines in part remain cell associated on secretion, we have constructed a bispecific diabody consisting of a nonneutralizing scFv antibody recognizing human interleukin-6 (IL-6) and an scFv corresponding to the monoclonal antibody (mAb) OKT3, which recognizes and activates the human T cell receptor. Here we show that the diabody recognized both human IL-6 and human CD3. In the presence of human T cells, the diabody induced killing of human hepatoma cells that had been transfected with a human IL-6 cDNA. The extent of killing was dependent on the ratio of effector/target cells and increased with increasing concentrations of the diabody. Untransfected control cells or human hepatoma cells that secrete the IL-6-related cytokine leukemia inhibitory factor (LIF) remained unaffected. We conclude that diabodies recognizing cytokines can be used to specifically target cytokine-secreting cells.