Novartis buys remaining rights to GSK treatment for up to $1 bln

* Will make initial $300 mln payment to buy compound

* Further $200 mln after start of a phase III study

* Up to $534 mln to be paid if milestones met

* Will pay royalties of up to 12 pct on future net sales (Adds comment from head of Novartis Pharmaceuticals, detail)

ZURICH, Aug 21 (Reuters) - Novartis (Xetra: 904278 - news) has agreed to buy all remaining rights to Ofatumumab from Britain's GlaxoSmithKline (Other OTC: GLAXF - news) for up to $1 billion, boosting the Swiss drugmaker's stable of multiple sclerosis (MS) treatments.

Basel-based Novartis had previously acquired the rights to Ofatumumab for oncology indications, but it is currently being developed for relapsing remitting multiple sclerosis and other auto-immune conditions.

"Novartis is pleased to further reinforce our commitment to neuroscience and to add an exciting new treatment to our strong MS portfolio," David Epstein, head of Novartis Pharmaceuticals, said in a statement.

Novartis will pay GSK $300 million up front to buy the compound and a further $200 million is payable after the start of a phase III study in MS by Novartis.

Payments of up to $534 million will be made if pre-agreed milestones are met.

Novartis will also pay royalties of up to 12 percent to GSK on any future net sales of Ofatumumab in auto-immune conditions.

(Reporting by Joshua Franklin; Editing by Gopakumar Warrier and David Goodman)