SPECIAL SECTION: MONOCLONAL ANTIBODIES
A method of creating molecules with high binding specificity was developed by Kohler and Milstein in 1975. This process uses the inducible immune response in mammals to create antibodies to injected foreign substances. These antibodies have become ubiquitous reagents in laboratories and their use in clinical applications is expanding. Advances in molecular biology since that time have allowed for the development of recombinant techniques that can generate molecules with increased versatility and better specificity than is achievable using historical methods, and is accomplished without the use of animals.
Monoclonal Antibodies (mAbs)
Antibodies are large molecules that are capable of recognizing small structural elements (epitopes) of larger molecules and marking them for phagocytosis. The epitopes that antibodies typically recognize are short amino acid sequences within proteins. The normal function of antibodies within an organism is to recognize and destroy foreign proteins. This antibody-epitope recognition system serves to maintain a disease-free state within organisms with adaptive immune systems. The precise specificity and strong affinity of binding that makes antibodies an irreplaceable component of adaptive immunity is what is harnessed in molecular biology, clinical medicine, and multiple other scientific disciplines to identify and label proteins of interest.
Monoclonal antibodies, (mAbs) in contrast to polyclonal antibodies, are specific for a single antigen and are produced by cells that are derived from a single antibody-producing cell (clonally-derived – hence “monoclonal”). This singular specificity makes mAbs valuable in both basic research and in medical research for disease diagnosis and treatment. Monoclonal antibodies have had a major impact on virtually every area of investigative science and applied research and are a commodity that has been a major focus in countless laboratories since the mid-1970s.
The Historical origins of mAb Production for Laboratory and Clinical Use
mAb Generation in Mice
Historically, mice have been used to generate and produce mAbs for laboratory and clinical use. Monoclonal antibodies were generated by immunizing an animal with the target antigen, allowing time for the animal’s immune system to produce antibodies against the foreign substance, and then dissecting the animal's spleen or lymph nodes to isolate the lymphocytes producing antibodies to that antigen. Isolated specific antibody-producing cells were then fused to immortalized myeloma cells. These “hybridomas” would then grow and divide indefinitely.
mAb Amplification in vivo
To produce large quantities of an antibody, the hybridoma cells were injected into the abdomen of mice where the cells multiplied and produced antibody-filled fluid (ascites) in the animal's abdomen. This method is known as the “mouse ascites method” of antibody production.
The use of in vivo ascites mAb amplification is so painful to the animals used that it has been banned or restricted in Australia, Germany, Switzerland, the Netherlands, and the United Kingdom. The United States National Institutes of Health and U.S. Department of Agriculture encourage the use of in vitro methods as the default procedure for mAb amplification (see below).
mAb Amplification in vitro
Advances in tissue culture technology made possible the large-scale amplification of mAbs in vitro as an alternative to the mouse ascites method. In the in vitro amplification methods, hybridomas that were derived from animals, are cultured in petri dishes and antibodies are collected from the medium. Various cell culture systems are applied to this amplification process depending on the volume of antibodies required. This process avoids the ethical and scientific shortcomings of using mice to produce ascites but still requires the formation of hybridomas in vivo, which continues to present ethical concerns and leads to the suffering and death of countless mice.
Generation of Antibody-like Molecules Without the Use of Animals
Recent advances in molecular biology have lead to the ability to generate molecules with the recognition properties of antibodies by completely in vitro processes.
In addition to being more humane, molecules such as recombinant antibodies rAb and aptamers have certain advantages over animal-generated antibodies, including the fact that they can be made to recognize a wider variety of targets with selected specificity and affinity.
Samantha Dozier, Ph.D.