Aminopterin inhibits dHFR enzyme and block denovo pathway of nucleotide synthesis, which further allow the survival of only hybridoma cells and B-cells in HAT media.

Monoclonal antibodies are specific against the particular antigen and these are used to treat the cancer as they release their toxins in the growing cells which interfere with their cellular processes. Herceptin is particularly for breast cancer while erbutir is for colorectal cancer.

Different classes of antibodies have variable amino acid sequences at the Nterminal end which interacts with different types of antigens. Four theories have been proposed for generating antibody diversity.