Thousand Oaks biotech Amgen Inc. has signed a licensing deal which gives it exclusive access to an antigen being developed by Massachusetts startup Tetragenetics Inc. The Cambridge company said the agreement will provide it with Amgen’s research and development resources and allow the biotech giant to use the antigen for drug development. Antigens cause the immune system to produce antibodies and are being used to develop many biotech drugs Tetragenetics has a technology for generating antigen proteins in an animal-like cell that can be reproduced in the lab. “Our collaboration with Amgen validates Tetragenetics’ proprietary drug discover platform,” said John Reilly, the company’s vice president of business development, in a statement. “We will be announcing further collaborations with leading biotech and pharmaceutical companies as we expand out partnering programs.” The firm also announced a partnership with Amgen rival Pfizer Inc. on Wednesday, and a grant from the Bill and Melinda Gates Foundation. The grant is the second from the foundation, which has been funding Tetragenetics’ research into malaria drugs. Financial terms of the deals were not disclosed. Shares of Amgen were down $1.69, or 1.6 percent, to $104.71 in midday trading on the Nasdaq.