Washington D.C. 20549

                            Report of Foreign Issuer

                      Pursuant to Rule 13a-16 or 15d-16 of
                       the Securities Exchange Act of 1934

                    For period ending April 23, 2008

                               GlaxoSmithKline plc
                              (Name of registrant)

               980 Great West Road, Brentford, Middlesex, TW8 9GS
                    (Address of principal executive offices)

             Indicate by check mark whether the registrant files or
                 will file annual reports under cover Form 20-F
                                  or Form 40-F

                              Form 20-F x Form 40-F

         Indicate by check mark whether the registrant by furnishing the
        information contained in this Form is also thereby furnishing the
       information to the Commission pursuant to Rule 12g3-2(b) under the
                        Securities Exchange Act of 1934.

                                    Yes No x

Issued -  Tuesday 22 April 2008, London, UK, Philadelphia PA, Cambridge, MA

GlaxoSmithKline To Acquire Sirtris Pharmaceuticals, A World Leader In 'Sirtuin'
Research and Development

GlaxoSmithKline (GSK) and Sirtris Pharmaceuticals Incorporated (Nasdaq: SIRT)
announced today that they have entered into a definitive agreement pursuant to
which GlaxoSmithKline will acquire Sirtris Pharmaceuticals for approximately
USD720 million (or approx. GBP362 million) through a cash tender offer of
USD22.50 (or approx. GBP11.33) per share.

Through the acquisition of Sirtris, GSK will significantly enhance its
metabolic, neurology, immunology and inflammation research efforts by
establishing a presence in the field of sirtuins, a recently-discovered class of
enzymes that are believed to be involved in the ageing process.  Sirtris
Pharmaceuticals has established a drug discovery capability to exploit sirtuin
modulation for the treatment of human disease, an approach that has the
potential to generate multiple clinically and commercially important products.
Their focus to date has been on the development of SIRT1 activators for the
treatment of Type 2 Diabetes Mellitus (T2DM).

"Modulation of this family of enzymes is a potentially transformative science
that could address diseases associated with metabolism and ageing such as
diabetes, muscle wasting, and neurodegeneration," commented Moncef Slaoui,
Chairman GSK R&D. "This acquisition continues GSK's strategy of pursuing the
best new science, externally or internally, to bring new medicines to patients
and value to the GSK pipeline.  Our intent is to retain all Sirtris employees
and continue the entrepreneurial and innovative culture they created."

Sirtris will become part of GSK's Drug Discovery organisation, while continuing
to operate from laboratories in Cambridge, Massachusetts as an autonomous drug
discovery unit.  Christoph Westphal, CEO and Vice Chair of Sirtris and the
management team will continue to lead this autonomous unit.

Dr Westphal commented, "We have built a dynamic and scientifically-driven
organisation.  We expect this transaction will accelerate our vision to target
sirtuins to treat diseases of metabolism and ageing and deliver tremendous value
to patients, our shareholders and our employees.   We look forward to working
with GlaxoSmithKline and their world-class research, development and
commercialisation organisation."

Under the agreement, a subsidiary of GSK will commence a cash tender offer to
purchase all of the outstanding shares of Sirtris, at USD22.50 (or approx.
GBP11.33) per share followed by a second step merger in which any untendered
Sirtris shares would be acquired at the same price per share.  All outstanding
stock options will be cancelled with holders receiving the excess of the
transactions price over the exercise price. The acquisition has been approved by
the board of directors of each company and is subject to customary closing
conditions, including the tender of at least a majority of Sirtris's shares and
clearance under the Hart-Scott-Rodino Antitrust Improvements Act.  The parties
anticipate that the tender offer will be commenced in early May and close in the
second quarter of 2008.

About GSK

GSK - 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 company information
including a copy of this announcement and details of the company's updated
product development pipeline, visit GSK at

About Sirtris Pharmaceuticals

Sirtris Pharmaceuticals is a biopharmaceutical company focused on discovering
and developing proprietary, orally available, small molecule drugs with the
potential to treat diseases associated with ageing, including metabolic diseases
such as Type 2 Diabetes. Our drug candidates are designed to mimic certain
beneficial health effects of calorie restriction by activation of sirtuins, a
recently discovered class of enzymes that the Company believes control the
ageing process. The company's headquarters are in Cambridge, Massachusetts.

Cautionary statement regarding forward-looking statements

Under the safe harbor provisions of the US Private Securities Litigation Reform
Action of 1995, the company cautions investors that any forward-looking
statements or projections made by the company, including those made in this
Announcement, are subject to risks and uncertainties that may cause actual
results to differ materially from those projected.  Factors that may affect the
Group's operations are described under 'Risk factors' in the 'Business Review'
in the company's Annual Report 2007.

Important Additional Information Will Be Filed with the Securities Exchange
Commission (SEC)

This press release is neither an offer to purchase nor a solicitation of an
offer to sell shares of Sirtris Pharmaceuticals, Inc. The tender offer for
shares of Sirtris's stock described in this press release has not yet been

At the time the tender offer is commenced, a subsidiary of GSK intends to file
with the SEC and mail to Sirtris's stockholders a Tender Offer Statement on
Schedule TO and related exhibits, including the offer to purchase, letter of
transmittal and other related documents, and Sirtris intends to file with the
SEC and mail to its stockholders a Tender Offer Solicitation/Recommendation
Statement on Schedule 14D-9 in connection with the transaction. These will
contain important information about GSK, Sirtris, the transaction and other
related matters. Investors and security holders are urged to read each of these
documents carefully when they are available.

Investors and security holders will be able to obtain free copies of the Tender
Offer Statement, the Tender Offer Solicitation/Recommendation Statement and
other documents filed with the SEC by GSK and Sirtris through the Web site
maintained by the SEC at In addition, investors and security
holders will be able to obtain free copies of these documents by contacting the
Investor Relations departments of GSK or Sirtris.

GlaxoSmithKline Enquiries:

UK Media enquiries:                     Philip Thomson          (020) 8047 5502
                                        Alice Hunt              (020) 8047 5502
                                        Gwenan White            (020) 8047 5502

US Media enquiries:                     Nancy Pekarek           (215) 751 7709
                                        Mary Anne Rhyne         (919) 483 2839

European Analyst/Investor enquiries:    David Mawdsley          (020) 8047 5564
                                        Sally Ferguson          (020) 8047 5543
                                        Gary Davies             (020) 8047 5503

US Analyst/ Investor enquiries:         Frank Murdolo           (215) 751 7002
                                        Tom Curry               (215) 751 5419

Sirtris Enquiries:

Investor and Media                      John Lacey              (617) 252 6920
                                                                 (781)354 7452

Pure Communications               Andrea Johnston               (910) 616 5858


Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant has duly caused this report to be signed on its behalf by the
undersigned, thereunto duly authorised.

                                                             GlaxoSmithKline plc

Date: April 23, 2008                                      By: VICTORIA WHYTE
                                                              Victoria Whyte
                                                 Authorised Signatory for and on
                                                   behalf of GlaxoSmithKline plc