Feb 23 (Reuters) - Gilead Sciences said on Monday it will buy cancer therapy partner Arcellx for an implied equity value of $7.8 billion, expanding their cell therapy development collaboration that started in 2022.

Shares of Arcellx climbed 78.3% to $114.30 while Gilead fell about 1% in premarket trading.

Gilead will pay $115 per share in cash at the deal's closing, which is at a premium of 79% to the stock's last close.

Kite Pharma, a unit of Gilead Sciences, was partnering with Arcellx to jointly develop and sell anito-cel, an experimental CAR-T therapy for multiple myeloma, a type of blood cancer.

CAR-T cell therapy is a cancer treatment that uses a patient's own genetically modified immune cells to find and kill cancer cells.

The U.S. Food and Drug Administration is currently reviewing the therapy, with a decision expected by December 23 this year.

Upon FDA approval of anito-cel, the proposed transaction is expected to be accretive to earnings per share in 2028 and thereafter.

Gilead will also pay Arcellx shareholders $5 per share, contingent upon the achievement of cumulative global net sales of anito-cel of at least $6 billion from launch through year-end 2029.