SOMATIC CELL HYBRIDIZATION

It has been known since the 60's that somatic cells from the same or different species in culture could spontaneously fuse to form polyploid cells. The product of fusion was called Homokaryon if the two parental cells come from the same species, and Heterokaryon or Somatic Cell Hybrid if the fusion was interspecific. The hybrid cells could divide by mitosis and proliferate and thus could be maintained in culture. Cell fusion is followed by nuclear fusion to produce uninucleate hybrid cells or Synkaryons. The rate of cell fusion is very low; about one cell fuses in million of cells. In 1962 Okada discovered that inactivated Sandai virus could greatly increase the rate of cell fusions. Since then several agents causing cell fusion has been tried among which Polyethylene Glycol (PEG) has some advantages. The exact mechanism of cell fusion is not known. In case of UV-inactivated Sandai virus, it seems that the virus absorbs to the cell surface leading to agglutination of cells. The protein coat of virus forms the connecting bridge between the cells. The membrane of two cells swell into this region and when they come in contact they get dissolved. The cell contents mix up, the nuclei fuse and a heterokaryon is formed. When cell fusion is mediated by Polyethylene Glycol the two cell membranes directly come in contact.

Basic Hybridoma Technology

The term Hybridoma is applied to fused cells resulting due to fusion of following two types of cells:

1. An antibody producing lymphocyte cell e.g. spleen cells of mouse.
2. Myeloma (cancer) cells which are capable of multiplying indefinately.

These fused hybrid cells or hybridoma haves the antibody producing capability inherited from lymphocytes and have the ability to grow continuously like cancer cells. Following steps are involved in the production of monoclonal antibodies (specific antibody for specific antigen).

• A rabbit is immunized to a specific antigen for the production of specific antibody.
  
• Tumour is produced in a mouse or rabbit ( It is done by injecting tumour causing antigens).
  
• From the above two types of animals, spleen cells (that produces antibodies) and myeloma cells (that produces tumour) are isolated and cultured seperately. The myeloma cell that is cultured is unusual in two ways, first it has stopped synthes