June 30 (Reuters) -

U.S. drugmaker AbbVie ( ABBV ) said on Monday it will

acquire cell therapy developer Capstan Therapeutics in a cash

deal worth up to $2.1 billion, expanding its pipeline with

experimental treatments for autoimmune diseases.

AbbVie ( ABBV ) has been diversifying its portfolio to make up

for a steep decline in the sales of Humira, its flagship

rheumatoid arthritis drug that is facing stiff competition.

Since Humira's patent expiration, AbbVie ( ABBV ) has spent over

$20 billion on acquisitions, including $8.7 billion for

neuroscience firm Cerevel, $10.1 billion for cancer drugmaker

ImmunoGen and $1.4 billion for Alzheimer's-focused biotech

Aliada.

Under the terms of the agreement, AbbVie ( ABBV ) will pay up to

$2.1 billion in cash to acquire Capstan, subject to certain

customary adjustments.

Capstan develops CAR-T therapies, a type of treatment

that uses a patient's own immune cells, specifically T cells, to

fight diseases. Its main drug, CPTX2309, is currently in

early-stage development for the treatment of autoimmune

diseases.

The drug works by using tiny fat-based particles called

lipid nanoparticles to deliver instructions to certain immune

cells, which find and remove harmful cells that mistakenly

attack the body.

The deal aims to strengthen AbbVie's ( ABBV ) already strong

position in immunology, building on the success of autoimmune

treatments Skyrizi and Rinvoq, which are expected to

generate

over $31 billion in combined sales by 2027.