Monoclonal antibodies (MAbs) are produced from a single B cell clone and can bind to a single type of antigen binding site. MAbs are homogenous antibodies that cannot form lattices with monomeric proteins as they can bind to only a single epitope on the antigen. Developed in the 1970s, MAbs can be produced against any given substance. Thus they can be used to detect and purify any substance of interest. This has made MAbs a powerful tool of molecular biology, biochemistry, and medicine.
Monoclonal Antibodies: Making Cancer a Target
Production of monoclonal antibodies
MAbs are produced using hybridoma technology. This method provides an unlimited homogeneous antibody supply with the desired specificities.
Hybridoma technology was developed in 1975 by Georges Köhler and César Milstein who shared the Nobel Prize in Physiology/Medicine in the year 1984. Their method takes advantage of the capacity of myeloma cells to divide and grow perpetually and produce antibodies.
In this method, B-lymphocytes from immunized mammals are fused with immortal myeloma cells. The fusion products are cloned to form hybridomas and propagated indefinitely. Hybridomas are assayed using ELISA in order to select the desired homogeneous immunoglobulin mix that can be used to induce a tumor in a second animal.
The tumor secretes a fluid rich in antibody called ascites, which is extracted and subjected to chromatography for isolation of MAbs. These MAbs are then purified to remove contaminants before being used in the lab for different purposes. As hybridomas are immortal, this technology offers a renewable source of MAbs.
Applications of monoclonal antibodies
The mono-specificity of MAbs is exploited for use in the following areas:
- Study of changes in molecular conformation
- Analysis of phosphorylation state
- Protein-protein interaction studies
- In structural analysis such as X-ray crystallography
- To identify single members of protein families
- In cancer diagnosis and treatment
- For prevention of allograft rejection
- In neoplastic and hematopoietic disease therapy
- To treat myocardial infarctions
- In the reversal of drug toxicity
Advantages of monoclonal antibodies
The key advantages of MAbs are listed below:
- MAbs are homogenous and consistent.
- They can be renewably generated once a suitable hybridoma is developed.
- The purity and concentration of a specific antibody is higher in MAbs as compared to polyclonal antibodies.
- MAbs are highly sensitive to small changes in both salt concentration and pH.
- They can be easily tested for cross-reactivity
Disadvantages of monoclonal antibodies
Some disadvantages of MAbs are listed below:
- MAbs’ mono-specificity also limits their applications
- Minor changes in antigen epitope structure affect the function of MAbs
- MAb production should be very specific to the antigen to which it needs to bind.
- They are not suitable for use in assays such as hemagglutination involving antigen cross-linking; slight modifications affect the binding site of the antibody
- Though these limitations can be overcome by pooling in multiple MAbs of required specificities, the identification of such MAbs can prove expensive, laborious, and time consuming.
Antibodies have been extraordinarily tools in laboratory research for many years. MAbs were developed about 25 years ago and have expanded the scope of antibodies to ex vivo diagnosis of a wide range of diseases. Scientists are taking more and more advantage of their high level of specificity and selective binding ability by employing them in immunotherapy.
The advent of hybridoma technology has led to the unlimited availability of MAbs. Numerous MAbs generated using this technology have aided the identification and analysis of tumor-associated antigens from several different human melanomas, carcinomas, lymphomas, and leukemias. Literature available till date reports over 100 unique MAbs against human carcinomas.