The cells that were collected from the spleen having the ability to produce antibody survives for a definite period of time. In stage 3 these cells are fused with immortal tumor of lymphocytes. The resulting product is known as hybridoma and its core characteristic is that it shows indefinite growth. Such tumor cells are known as myeloma cells and such cells are grown with 8-azaguanine and thus it make sure its susceptibility to the hypoxanthine-aminopterin-thymidine(HAT) medium. HAT medium is the culture medium that will be used following the fusion step.
The myeloma cells are developed in 8-azaguanine one week prior to fusion. Elevated durability and enhanced development is highly desired from the cells.