Issued: Thursday 10 May 2012, London UK

GlaxoSmithKline plc (LSE: GSK) today announced that it has commenced its previously announced tender offer to acquire all of the outstanding shares of Human Genome Sciences (NASDAQ: HGSI) for US$13.00 per share in cash.  GSK’s offer represents a premium of 81 percent to HGS’s closing share price of US$7.17 on 18 th April, the last trading day before HGS publicly disclosed GSK’s private offer. 

The closing of the tender offer is subject to the terms and conditions detailed in the offer document.  The tender offer and withdrawal rights are scheduled to expire at 12:00 midnight New York City time on 7 June 2012 unless the offer is extended. 

The offering documents for the Offer are being filed today with the SEC and may be obtained by contacting the information agent for the Offer: 

D.F. King & Co., Inc. 48 Wall Street, 22nd Floor New York, NY 10005

Banks and Brokerage Firms Please Call Collect: (212) 269-5550 All Others Call Toll Free: (800) 848-2998 Email: HGStender@dfking.com  

Lazard and Morgan Stanley are acting as financial advisors to GSK and Cleary Gottlieb Steen & Hamilton and Wachtell, Lipton, Rosen & Katz are providing legal advice. 

GlaxoSmithKline – one of the world’s leading research-based pharmaceutical and healthcare companies – is committed to improving the quality of human life by enabling people to do more, feel better and live longer.  For further information please visit www.gsk.com .