The Cancer Research Institute's biennial symposium on monoclonal antibodies supplied insights into diverse investigations occupied with one common goal-using this versatile therapeutic entity in an effort to halt cancer. Advances in the state-of the-art spanned the areas from basic research to the clinic.

Clinical Trials
    Sydney Welt (Memorial Sloan-Kettering Cancer Center and the Ludwig Institute for Cancer Research, NY) opened the meeting by detailing an increment in the successful development of an antibody targeted at A33, an antigen expressed in 95% of colon cancers. A humanized antibody construct used in combination with a last resort chemotherapeutic regimen was shown to produce partial responses in 3 of 11 evaluable patients. Unfortunately seven patients developed immune responses against the monoclonal. The three partial responses lasted for durations ranging from 5 to 10 months. An additional mixed response (4.5 months) and stable disease (9 months) were also observed. All four responders experienced a drop in their serum CEA (carcino-embyronic antigen). The study paves the way for a newer A33 antibody construct that is less likely to prompt an immune reaction.

    Andrew Scott of the Ludwig Institute for Cancer Research in Melbourne, Australia discussed a novel antigenic target located within the stromal compartment of tumors or the support structure of a tumor. Fibroblast activation protein (FAP) is expressed on the stroma of most epithelial cancers. During Phase I trials with a humanized anti-FAP antibody (BIBH 1), the antibody honed in on the tumorous stroma and steered cleared of the rest of the body's organs. A subsequent trial now underway is using the antibody to deliver b-emitting isotopes. The group is also investigating another antigenic target GD3, a ganglioside expressed on melanoma cells. Indium labelled - KM871 demonstrated specific targeting during a Phase I trial and further trials in patients with metastatic melanoma are planned.

    Gert Riethmüller of the University of Munich presented data on what he described as "the most suitable target for immunological intervention"-minimal residual cancer. The presence of residual cancer cells in the bone marrow of patients has been shown to have a prognostic impact on overall and relapse free survival. Genetic analysis of the cell population of one patient group showed a high level of heterogeneity, yet distinct patterns for epithelial mesencymal transformation, cell migration and DNA repair were observed. Further investigation proved EpCAM to be a reliable surface marker for disseminated cells. An EpCAM-antibody depleted metastatic cells in breast cancer patients presenting with more than 20 tumor cells per 106 bone marrow cells. The success has prompted Riethmüller to develop a humanized version of the antibody and a diagnostic test to detect the residual cells.

    Dennis Slamon of the University of California, Los Angeles, shared data on the topic of HER-2/neu overexpression and chemosensitivity. According to Slamon, strategies using anti HER-2/neu in combination with therapeutic modalities indicate that these antibodies can have an additive or a more remarkable synergistic effect with chemotherapeutic agents. In vitro, taxotere demonstrated a synergistic effect and has been included as a treatment option in a large Phase III clinical trial comparing available standard therapy plus herceptin to standard therapy.

    The HAHAs heard throughout the clinical presentations could hardly be an expression of jovial amusement. The potential development of human anti-human antibodies (HAHA), human anti-mouse antibodies (HAMA) and human anti-chimeric antibodies (HACA) makes it "absolutely critical to monitor immunogenicity," according to Gerd Ritter of the Ludwig Institute for Cancer Research in NY. Ritter and colleagues developed a biosensor assay (BIACORE) capable of identifying and quantitating the immune responses to infused antibodies in patient sera. Monitoring HAHA reactivities in more than 40 patients receiving the humanized A33 antibody showed Type I and Type II reactions against the antibody. Interestingly, Type I occurrences (49%) were transient while Type II incidences necessitated termination of the treatment.

Effector Mechanisms
    Mike Clark stressed that it was not only hitting the target but attracting the attention of the patients' effector systems that was the true measure of a monoclonal antibody's therapeutic effects. He and his colleagues at Cambridge University in the UK have sought to design antibodies specific for effector recruitment. Comparative studies to identify human IgG constant regions with differential effector abilities have helped the group to select several candidates for clinical development.

    Immune tolerance is an asset to tumorigenesis. Investigations with a model for autoimmune disease conducted by Jeffrey Ravetch (The Rockefeller University, NY) have demonstrated that both activation and inhibitory signals mediate antibody coupling to effector cells. By removing the inhibitory pathway, the cytotoxic effects of an anti-tumor antibody can be increased.

    Noting that recognition is not the sole factor that can influence recruitment of T cells against a tumor or tumor cell, James Allison (University of California, Berkeley) has been manipulating interactions that when inhibited augment T-cell killing of tumor cells. Allison has enhanced T-cell responses by blocking inhibitory CTLA-4 signals (these signals interact with B7 on antigen presenting cells). The strategy proved effective in prostate and melanoma tumor models and Phase I clinical trials for prostate cancer and melanoma are underway.

Targets and Constructs
    The clinical analysis of a renal cell carcinoma trial presented by Egbert Oosterwijk of the University of Nijmegen, The Netherlands, showed that factors other than antigen expression are also important for antibody targeting. The G250 antigen (MN/CAIX) is highly and specifically expressed in clear cell renal carcinoma. While investigating a monoclonal antibody developed against G250, the group in Nijmegen demonstrated excellent targeted uptake in tumor. Even so, uptake of the monoclonal was slightly heterogeneous, and internalization of the antibody seemed to be a determining factor in these results.

The Major Histocompatability Complexes (MHC) became the target of two new experimental therapeutic constructs-peptide conjugates being developed by Jean Pierre Mach at the University of Lausanne and antibodies derived by phage display libraries developed by Hennie Hoogenboom (Dyax Corp. and Liège University, Belgium).

    James Marks and others at the University of California, San Francisco, are developing a library of monoclonal antibody fragments capable of triggering receptor-mediated endocytosis.
        
    Renata Pasqualini of the University of Texas MD Anderson Cancer Center is exploiting the diversity associated with angiogenesis. Pasqualini is using in vivo phage display to identify the unique molecular characteristics of the vessels in human cancers. The information could be useful for several applications including making diagnostic tests more predictive. For example, the group has isolated a novel peptide marker present only in advanced prostate patients that could better predict disease progression than traditional tests.

    Several B cell surface receptors serve as targets for immunotherapy of malignancies. Thomas Tedder's (Duke University, NC) emphasis is on the function elicited in the target molecules. For example, monoclonal antibody binding to CD20 alters calcium homeostasis and arrests the cell cycle. A better understanding of CD20 or the tyrosine kinase activity prompted by CD19, or the induction of apoptosis by CD22 and their comparative biological functions may shed light on why B-cell therapies are not uniformly successful.

    Developing intrabodies may be a strategy for flying under the immune system's radar. Carlos Barbas III and colleagues at The Scripps Research Institute in La Jolla have isolated a single chain antibody (CCR5) that was expressed intracellularly and retained in the endoplasmic reticulum. Introduction of the CCR5-intrabody was enough to render human and rhesus cells refractory to HIV challenge. The group is extending the approach to cancer therapy through their exploration of Tie 2 (a receptor kinase that plays a role in angiogenesis) as a possible target. Arne Skerra from the Technical University, Munich, put forth the idea that proteins from the lipocalin family would better serve as a scaffold for the generation of ligand receptor proteins. These cellular transport or storage proteins are much smaller than monoclonals. A synthetic library of recombinations has been developed and Skerra hopes to find both bioanalytic and therapeutic agents.

Conclusions
    Monoclonal antibodies hold great promise for treating cancer because they are naturally selective and specific. In the concluding remarks of the meeting, Andrew Scott commented that the search for antigenic targets has to date been a great success, however the ability to identify new targets through genomics and proteomics approaches provides great promise for the future. The challenge for monoclonal antibody therapy of cancer is to effectively translate laboratory discoveries including construct design and preclinical development into carefully designed early Phase clinical trials, and optimization of therapeutic efficacy in patients. Antibodies 2002 was a conference that surveyed a variety of ideas born out of the drive to rise to these and the other challenges ahead.

Abstracts

• Kari Alitalo.  Angiogenesis, Lymphangiogenesis and Metastasis. University of Helsinki, Helsinki, Finland.
• James P. Allison. Removing The Brakes: Antibody Blockade of Inhibitory T-Cell Costimulation in Tumor Immunotherapy. University of California, Berkeley, CA.
• Carlos F. Barbas III, Christoph Rader, Mikhail Popkov, Nina Jendreyko, Subash Sinha. Cancer—A Multidisciplinary Approach: Genes, Proteins, and Drugs. The Scripps Research Institute, La Jolla, CA.
• Mike Clark¹, Kathryn Armour¹, Lorna Williamson^1,2. Designing Antibodies for Effector Recruitment. ¹Cambridge University, Cambridge, U.K. ²National Blood Service, Cambridge, U.K.
• Chaitanya R. Divgi. Radioimmunotherapy in Solid and Hematologic Neoplasms. Memorial Sloan-Kettering Cancer Center, New York, NY.
• Hennie R. Hoogenboom. Targeting MHC-Peptide Complexes With Antibodies Derived From Phage Display Libraries. Dyax Corp., Liège, Belgium; Liège University, Liège, Belgium.
• Jean-Pierre Mach. Antibody-MHC/Peptide Conjugates as a New Bridge Between Antibody and T-Lymphocyte Attack on Cancer Cells. Bruno Robert Institute of Biochemistry University of Lausanne, Epalinges, Switzerland.
• James D. Marks, Bin Liu, Zhou Yu, Marie A. Poul, Tara Heitner, Ulrik B. Nielsen, Baltazar Becerill, Dave O’Connell, Mike Huie. Selection of Internalizing Antibodies from Phage Libraries for Targeted Drug Delivery. University of California, San Francisco, CA.
• Ira Mellman. Endocytosis and Antibody-Based Cancer Therapy. Ludwig Institute for Cancer Research, New York, NY; Yale University School of Medicine, New Haven, CT.
• Sherie L. Morrison. Use of Antibody Fusion Proteins as Therapeutic Agents. University of California, Los Angeles, CA.
• Dario Neri. Antibody-Based Targeting of Tumor Angiogenesis. Swiss Federal Institute of Technology, Zurich, Switzerland.
• Egbert Oosterwijk. Monoclonal Antibody G250 in Renal Cell Carcinoma: Issues of Specificity, Heterogeneity and Efficacy. University Medical Center Nijmegen, Nijmegen, The Netherlands.
• Renata Pasqualini, Wadih Arap. Mapping Vascular Diversity by Screening Peptide Libraries. The University of Texas M.D. Anderson Cancer Center, Houston, TX.
• Andreas Plückthun. Improving Antibodies by Evolution and Engineering. University of Zurich, Zurich, Switzerland.
• Jeffrey V. Ravetch. Antibody Triggered Effector Pathways. The Rockefeller University, New York, NY.
• Christoph Renner. Generation of Biological Active Antibody Constructs for Cancer Therapy. Saarland University Medical School, Homburg, Germany.
• Gert Riethmüller, C. Klein, Oleg Schmidt-Kittler, P. Kufer. Antibody Therapy for Minimal Residual Cancer: The Target, the Effects and the Perspectives. University of Munich, Munich, Germany.
• Gerd Ritter. Immunogenicity of Recombinant Antibodies: "In-Vivo Veritas" Ludwig Institute for Cancer Research, New York, NY.
• Gisela Schwab¹, R. Figlin², A. Belldegrun², J. Crawford³, M. Lohner¹, L. Roskos¹, X-D. Yang¹, K. Foon¹, L. Weiner⁴. Effects of ABX-EGF, A Fully Human Anti-EGFr Antibody, in Patients with Advanced Cancer. ¹Abgenix, Inc., Fremont, CA; ²University of California, Los Angeles, CA; ³Duke University, Durham, NC; ⁴Fox Chase Cancer Center, Philadelphia, PA.
• Andrew M. Scott. Tumor Stromal and Cell-Surface Targeting with Novel Recombinant Antibodies. Ludwig Institute for Cancer Research, Austin & Repatriation Medical Centre, Melbourne, Australia.
• Arne Skerra. Anticalins, Small Antibody-Like Proteins with Engineered Target Specificities. Technical University, Munich, Germany.
• Dennis J. Slamon. Use of the Anti HER-2/neu Antibody Herceptin in the Treatment of Human Breast Cancer: Biologic Rationale and Clinical Results. University of California, Los Angeles, CA.
• Thomas F. Tedder. B-Lymphocyte Targets for Immunotherapy: A Molecular Basis for How They Work? Duke University Medical Center, Durham, NC.
• Sydney Welt^1,2, Gerd Ritter², Achim A. Jungbluth², Nancy E. Kemeny¹, Lloyd J. Old². The A33 Antigen of Colorectal Cancer: A Model for the Development of Therapeutic Antibodies. ¹Memorial Sloan-Kettering Cancer Center, New York, NY; ²Ludwig Institute for Cancer Research, New York, NY.
• Larry Witte. Anti-Angiogenic and Anti-Tumor Activities of Antibodies Against VEGFR1 and VEGFR2. ImClone Systems Incorporated, New York, NY.