Antibody Targeting Program

Antibody Characterization

The detailed antibody characterization performed by LICR not only increases the chance that the antibody will be therapeutically beneficial, it also decreases the risk that the antibody will have harmful side-effects.

Introduction

Within the Antibody Targeting Program, each antibody is extensively characterized to determine its: tumor targeting (whether, and to what extent, the antibody enters the tumor mass); biodistribution (where the antibody travels in the body); pharmacokinetics (how long the antibody remains in the body); biological and biophysical aspects (whether the antibody is internalized by the cell to which it binds, and whether the antibody can be chelated to a radioisotope or toxin); immunogenicity (whether the antibody itself is a target of the patient’s immune system); and effector function (the antibody’s ability to direct the immune system to eliminate the cancer cells).

LICR’s model of antibody characterization is comprised of two parts: pre-clinical and clinical characterization.

Pre-clinical Characterization

NY-ESO-1

Immunohistochemical staining of cancer-testis antigen NY-ESO-1 in lung cancer and in testes cells (more...)

To assess the antibody’s binding characteristics, LICR scientists use: immunohistochemistry, to assess whether the antibody is binding only to cancer cells; hemadsorption assays, to assess whether the antibody is being internalized into the cell upon binding; and an assay that measures the affinity (strength of binding) of the antibody for the antigen. A detailed analysis of the antibody’s specificity of binding to the molecular target (protein or polysaccharide) is also performed, in order to map the epitope (the region of the antigen recognized by the antibody).

Another important aspect of the characterization is determining if the antibody has an effector function, that is, the antibody is cytotoxic (causes cell death). The effector function may be via complement-dependent cytotoxicity (CDC) which is part of the humoral (CD4+/CD8+ T cell) immune response, or antibody-dependent cellular-cytotoxicity (ADCC) which is part of the cellular immune response. The binding of an antibody may also induce apoptosis (programmed cell death). LICR investigators use a variety of methods to investigate effector function, some of which (particularly the T cell monitoring methodologies) have been developed through LICR’s Cancer Vaccine Program.

Clinical Characterization

Much of this characterization is performed using the ‘standard LICR protocol’ in which the first dose of an antibody is labelled with a small (‘trace’) amount of radioisotope. The radioisotope is not strong enough to harm the patient, but is strong enough to be picked up by gamma imaging cameras in vivo. Thus the trace-labelled antibody is ‘followed’, first in mice, and then in humans using non-invasive imaging technology, so that the investigators are able to analyse the targeting (whether the antibody binds to normal tissues or only the tumor), biodistribution (where the antibody goes in the body), and pharmacokinetics (it rate of clearing from the blood and organs).

The immunogenicity of the antibody is an extremely important aspect for antibody development. If the antibody is immunogenic, that is the immune system destroys the injected antibody, the antibody’s therapeutic effect will be nullified. LICR scientists use serum from treated patients to determine if the patients have produced their own antibodies against the therapeutic antibody. If the antibody is immunogenic, LICR scientists will then use Antibody Engineering to reduce the immunogenicity.

Finally, the clinical response to the therapy, although not an endpoint in early-phase clinical trials, is assessed by measuring tumor shrinkage and/or an extension of relapse-free survival in the Clinical Trials Program.

Key Publications

Centers Involved in this Research