Which one of the following antibiotic is used?

In hybridoma technology for monoclonal Ab production antibiotic is used to select hybridoma cell over myeloma cells.

Aminopterin is used to select hybridoma over myeloma . Aminoptorine inhibits the denovo nucleotide synthesis pathway . However normal cells survive in a medium as they are able to use salvage pathway for nucleic acid biosynthesis. But if the cell unable to produce the enzyme Hypoxanthine Guanine Phospho Ribosyl –Transferase ( HGPRT ) utilized in salvage pathway, they die. Here in this method, myeoloma cell lack that particular enzyme thus, they die in Aminopterin containing medium.