Cancer cells seen on a large screen connected to a microscope at the CeBit computer fair in Hanover, Germany, in 2012. Reuters Gilead is acquiring the cancer-immunotherapy biotech Kite Pharma for $11.9 billion.

Gilead, known for its HIV and hepatitis C drugs, has been growing a cash pile over the past few years since the approval of its hepatitis C drug in 2013, leading investors to speculate what company it might buy. Gilead's purchase of Kite is the first big deal the company's had since.

Kite's shares were up 29% on the news before markets opened Monday.

Kite has been one of the companies leading development for a new form of highly personalized cancer treatment is called CAR T-cell therapy. It's a type of cancer immunotherapy, a therapy that harnesses the body's immune system to take on cancer cells.

Short for chimeric antigen receptor T-cell therapy, CAR-T treatment removes a person's cells from the body, reengineers them, and then puts the cells back in the body, where they can attack cancer cells. In July, a Food and Drug Administration panel voted in favor of approving one of these treatments made by Novartis. One of the panelists called it "most exciting thing I've seen in my lifetime." The FDA is expected to decide whether to approve that therapy, a treatment for pediatric acute lymphoblastic lymphoblastic leukemia, by October.

One month later, in November, Kite is expected to get an answer from the FDA regarding its CAR-T treatment for a type of blood cancer called aggressive B-cell non-Hodgkin lymphoma. In data Kite released in February, the company found that out of 101 patients, 36% had a complete response to the treatment after six months.