5.21B - Producing monoclonal antibodies

5.21B · One clone, one target

An antibody works at the molecular scale. Its binding site has a shape that is complementary to a particular part of an antigen, so the two can bind. An antigen is the target molecule; the antibody is the protein that binds to it. They are not interchangeable terms.

Different lymphocytes can make antibodies with different binding sites. To make a monoclonal antibody supply, scientists select one cell that makes the required antibody and produce a clone of that cell. Every cell in the clone has the same origin and makes the same antibody type, so the collected antibodies bind the same specific target.

Monoclonal does not mean that only one antibody molecule is made. It means that a large supply of one identical antibody type comes from one selected cell clone. Specificity is what makes the same antibody useful as a detector, a location marker and a treatment carrier.

5.21B · Building an antibody-producing cell line

The production problem has two halves. A lymphocyte can make the desired antibody, but an isolated antibody-producing lymphocyte does not keep dividing in culture. A tumour cell, also called a myeloma cell in this method, divides repeatedly but does not make the desired antibody. Neither cell has both useful properties on its own.

The hybridoma method combines those properties in a stable sequence:

1. The target antigen is introduced into an animal, usually a mouse, stimulating some lymphocytes to produce antibodies against that antigen.
2. Antibody-producing lymphocytes are removed and mixed with tumour/myeloma cells.
3. A lymphocyte and a tumour cell are fused. The new fused cell is a hybridoma: hybrid because it combines two cells, and -oma because one parent is a tumour cell.
4. The hybridomas are screened to find one that produces the desired antibody. That selected cell is cloned, so all the resulting hybridoma cells come from the same original hybridoma.
5. The clone is grown in culture. The hybridoma cells divide repeatedly and produce the desired antibodies as they divide. The antibodies are then collected and purified.