Human Genome Sciences : ANNOUNCES REQUIRED OFFER TO REPURCHASE IN RESPECT OF ITS 3.00% CONVERTIBLE SENIOR NOTES DUE 2018

• Holders that Convert Notes by September 5, 2012 (Instead of Tendering for Repurchase) Will Receive $1,241.475675 in Cash per $1,000 Principal Amount of Notes Converted

ROCKVILLE, Maryland, August 3, 2012 -- Human Genome Sciences ("HGS"), a wholly owned subsidiary of GlaxoSmithKline plc ("GSK"), announced today (1) a temporary increase in the conversion rate applicable to conversions of its 3.00% Convertible Senior Notes due 2018 (CUSIP: 444903AN8) (the "notes"), (2) a change in the consideration deliverable upon conversion of the notes, and (3) a required offer to repurchase the notes. As a result of the transactions and provisions described below, holders that convert notes on or before 5:00 pm, New York City time, September 5, 2012 will receive $1,241.475675 in cash per $1,000 principal amount of notes converted.

As previously announced, GSK has acquired all outstanding shares of HGS for $14.25 per share, in cash, through a tender offer and subsequent merger. Under the indenture governing the notes, the tender offer and the merger constituted a "Make-Whole Fundamental Change" requiring a temporary increase in the conversion rate applied to conversions of notes. This increase will apply to conversions validly submitted between July 30, 2012 and 5:00 pm, New York City time, on September 5, 2012 (referred to as the "Make-Whole Period").

In addition, because each outstanding share of HGS's common stock was converted into the right to receive cash consideration in the course of GSK's acquisition, the convertible notes have become convertible into the amount of cash that the holder would have been entitled to receive had their notes been converted into common stock immediately prior to the merger (and then further converted into cash, upon the merger).

As a result of the transactions and provisions described above, any holder that converts notes between the merger referred to above (which occurred on August 2, 2012) and the end of the Make-Whole Period (at 5:00 pm, New York City time, on September 5, 2012) will receive $1,241.475675 in cash per $1,000 principal amount of notes converted.

After the Make-Whole Period, the notes will be convertible only if the conditions to conversion contained in the indenture are met, and holders that convert after the Make-Whole Period will receive $1,069.418325 in cash per $1,000 principal amount of notes converted.

Conversion consideration will be delivered to any converting holder on the third business day following the relevant conversion date.

The tender offer and the merger described above, and the related delisting of HGS' common stock constituted a "Fundamental Change" under the indenture, requiring GSK to offer to repurchase the notes for cash equal to 100% of their principal amount, plus accrued and unpaid interest to, but excluding, the related repurchase date. This repurchase date, referred to as the Fundamental Change Repurchase Date, will be September 6, 2012.

The amount of interest accrued and unpaid per $1,000 principal amount of notes from May 15, 2012, the last interest payment date prior to the Fundamental Change Repurchase Date, to, but excluding, the Fundamental Change Repurchase Date is expected to be approximately $9.25, so that the total payment for each $1000 principal amount of Convertible Notes repurchased will be $1,009.25.

Because the price offered in the required offer to repurchase is lower than the amount of cash deliverable upon conversion of the notes, HGS does not anticipate that holders will participate in the required offer. However, the indenture for the note requires that information regarding the offer to repurchase be made available through a press release.

Holders may exercise their right to elect repurchase from the date hereof up to 5:00 pm, New York City time, on September 4, 2012 (the "Expiration Time").

A form of repurchase exercise notice has been sent to holders as an attachment to the repurchase notice. As described in the repurchase notice, in order to exercise a repurchase right in connection with a Fundamental Change, a holder of notes must deliver, prior to the Expiration Time, the notes to be purchased to the paying agent, duly endorsed for transfer, or effect book-entry transfer of the notes to the paying agent, together with the repurchase notice.

If the notes are in global form, the repurchase exercise notice must comply with the rules and procedures of The Depository Trust Company to the extent applicable.

Notes that are delivered as described above may be withdrawn only by written notice of withdrawal delivered to the paying agent prior to the Expiration Time. Withdrawal of the repurchase exercise notice must be made in accordance with the indenture. If a repurchase exercise notice is properly withdrawn, HGS shall not be obligated to repurchase the notes in respect of such repurchase exercise notice.

The trustee is the paying agent and conversion agent for the notes and its address is as follows:

of New York Mellon Corporation
Corporate Trust Operations
Reorganization Unit
101 Barclay Street - 7 East
New York, N.Y. 10286
Attn: William Buckley

The CUSIP number of the notes is 444903AN8.

Human Genome Sciences exists to place new therapies into the hands of those battling serious disease.

For more information about HGS, please visit the Company's web site at www.hgsi.com. Health professionals and patients interested in clinical trials of HGS products may inquire via email to This e-mail address is being protected from spam bots, you need JavaScript enabled to view it or by calling HGS at 1-240-314-4430.

HGS, Human Genome Sciences and BENLYSTA are trademarks of Human Genome Sciences, Inc. Other trademarks referenced are the property of their respective owners.

This communication contains forward-looking statements. HGS cautions readers that any forward-looking statements made by HGS, including those made in this communication, are subject to risks and uncertainties that may cause actual results to differ materially from those contained in the forward-looking statements. In particular, whether holders of the notes exercise their conversion rights will depend upon holders' individual decisions, which are not currently known to HGS.