Irish drugmaker Mallinckrodt said it plans to acquire US immunotherapy company Therakos for $1.33 billion from American private equity investor Gores Group. The deal is planned to close in the latter part of the calendar third quarter, which is Mallinckrodt’s fiscal fourth quarter.

The private equity group based in Los Angeles took over Therakos in December 2012 for an undisclosed sum from Ortho Clinical Diagnostics, a former unit of Johnson & Johnson.

Based in West Chester, Pennsylvania, the immunotherapy company focuses on treatment platforms that harness the power of each individual patient’s immune system to fight disease. It claims to be global leader in autologous immune cell therapy delivered through extracorporeal photopheresis (ECP).

Therakos’ Cellex system collects immune cells from a patient's blood, treats the cells with ultraviolet light to activate them, and returns them to the body in order to attack a disease.

In the US the system is used to treat skin problems in patients suffering from cutaneous T-cell lymphoma and who have not responded to other treatments. It is approved in other countries to treat conditions such as Crohn's disease and organ transplants.

The acquisition would allow Mallinckrodt’s specialty segment to expand its business in hospitals, giving it a larger presence in pain management and critical-care respiratory therapies in neonatal intensive care units.

According to Mallinckrodt, Therakos expects 2015 annual sales of around $185-195 million and expects high-single-digit percentage growth. It added that the Cellex system has strong profit margins.

The Irish drugmaker is under pressure due to recently slowing growth of its biggest product, HP Acthar Gel, which it picked up in the $5.6 billion acquisition of Questcor in 2014. Acthar is used to treat a variety of autoimmune and inflammatory conditions.