STALLERGENES: Persistent Efficacy Demonstrated After a Year on Actair(R) Followed by a Second Treatment-Free Year

ANTONY, France, June 28, 2010 - After having announced positive results for the first year of
its phase IIb/III clinical trial (VO 57.07) conducted on Actair(R) sublingual
allergen immunotherapy tablets in allergic rhinitis triggered by house dust
mites in April 2009, Stallergenes S.A. today announces the results of the
second year of this study.

Following this first year which demonstrated positive results
for both the dosages tested (300 IR[1] and 500 IR) and which is key for the
marketing authorization application, the second year of the study involved an
exploratory evaluation of the persistence of the therapeutic effect of
Actair(R) in the following year. Out of the 509 patients originally included
in the study, 397 participated until the end of the second year. The primary
endpoint for this second year was the Average Adjusted Symptom Score
(AAdSS)[2] measured one year after the end of treatment.

The results of this second year demonstrate not only that the
efficacy of Actair(R) persists well beyond the first six months after
treatment is stopped but also that the size effect is globally equivalent to
that observed in the first year. Thus in the main assessment period for the
efficacy endpoint (between 10 and 12 months after the discontinuation of
treatment), both active groups demonstrated a persistent effect of the
treatment, with a statistically significant difference for the AAdSS versus
placebo [(p=0.0342) for the 300 IR dosage; (p=0.0229) for the 500 IR dosage],
still with no difference between the two treated groups.

This study is a world first in that, for the first time, it
indisputably demonstrates the persistence of the effect of sublingual
allergen immunotherapy in perennial allergic rhinitis triggered by house dust
mites, as well as the early onset of this effect, from the end of the first
year. The duration and the dynamics of this effect will have to be explored.

"We're clearly delighted with these results. For the first
time ever, the persistence of the therapeutic effect of allergen
immunotherapy has been demonstrated after only a year. This is yet another
illustration of the contribution that the large-scale studies conducted as
part of the Stalair(R) clinical development program can make to our
understanding of allergen immunotherapy", says Albert Saporta, Chairman and
CEO of Stallergenes. "Like the trial conducted in asthma triggered by house
dust mites with Staloral(R) 300 in China, this study will help us construct a
development plan for Actair(R) that is ambitious in terms of the indications
envisaged and realistic, proposing discontinuous protocols that meet the
expectations of both patients and health system paying authorities."

ABOUT ALLERGIC RHINITIS TRIGGERED BY HOUSE DUST MITES

In Europe, almost 40% of allergic respiratory diseases, on
average, are triggered by house dust mites, making this the leading cause of
respiratory allergy, ahead of grass pollens. Dust mites are responsible for
allergic rhinitis that begins in early childhood, gradually worsens over time
and naturally progresses to asthma. These conditions have marked symptoms
that significantly impair patients' quality of life.

ABOUT STALAIR(R)

Stalair(R) is the name of the pharmaceutical and clinical
development program for immunotherapy tablets being implemented by
Stallergenes with a view to obtaining market authorizations for
pharmaceutical products in Europe and in other strategic markets.

Oralair(R) is the first project resulting from this program. A
Mutual Recognition Procedure has been completed in Europe. Having recently
demonstrated its efficacy after 3 years of treatment (study VO53.06 conducted
in Europe), Oralair(R) has been the subject of a positive phase III trial in
adults in the United States (VO61.08).

The second project in the program is Actair(R), dust mite
immunotherapy tablet. Following the results of the first year of the phase
IIb/III study in allergic rhinitis in adults, a phase III pediatric study has
been launched.

The Stalair(R) r Bet v 1 tablet (birch pollen recombinant
allergen) has been the subject of a positive phase IIb/III clinical trial
conducted in allergic rhinitis caused by birch pollen. A confirmatory phase
III study is currently being prepared with a view to EMA registration.

The other allergens concerned by the program are ragweed
pollen for the North American market and Japanese cedar pollen for the
Japanese market. Altogether, the program covers 80% of the epidemiology for
all markets.

ABOUT STALORAL(R) 300

Staloral(R) 300 is a sublingual solution of allergen extracts
for allergen immunotherapy. It is indicated in the treatment of allergic
rhinitis, rhinoconjunctivitis and seasonal or perennial mild to moderate
allergic asthma in adults and children over the age of 5 years. Prescribed by
allergy specialists, Staloral(R) 300 is particularly aimed at patients
suffering from severe allergic diseases inadequately controlled by the use of
symptomatic treatments.

In the context of a phase III clinical trial (VO55.06)
conducted in China, Staloral(R) 300 has demonstrated its efficacy in the
control of asthma triggered by house dust mites on the basis of
"well-controlled asthma" and "total asthma control" criteria in adult GINA 3
patients (moderate asthma stabilized by inhaled corticosteroids).

ABOUT STALLERGENES

Stallergenes is a European biopharmaceutical company dedicated
to immunotherapy treatments for the prevention and treatment of
allergy-related respiratory diseases, such as allergic rhinoconjunctivitis,
rhinitis and asthma. Stallergenes is the seventh-ranked French pharmaceutical
company. A pioneer and leader in sublingual immunotherapy treatments,
Stallergenes devotes more than 20% of its turnover, in gross terms, to
Research and Development and is actively involved in the development of a new
therapeutic class: sublingual immunotherapy tablets. In 2009, Stallergenes
had a turnover of 193 million euros and more than 500,000 patients were
treated with Stallergenes immunotherapy products.

[1] Reactivity index for standardized extracts

[2] AAdSS: Average Adjusted Symptom Score taking into account the total
daily rhinoconjunctivitis symptom score and recourse to authorized rescue
treatments.

    Euronext Paris (Compartment B)
    SBF 120.

    ISIN code: FR0000065674
    Reuters code: GEN.PA
    Bloomberg code: GEN.FP

Additional information is available at:
www.stallergenes.com

Contacts: Albert Saporta - Chairman and CEO, Tel.: +33-1-55-59-20-04;
Christian Thiry - Financial Director, Tel.: +33-1-55-59-20-95,
e-mail: investorrelations at stallergenes.fr ; Press relations, Lise Lemonnier - Communication Manager, Tel.: + 33-1-55-59-20-96, e-mail: llemonnier at stallergenes.fr;
Investor and analyst relations, Lucile de Fraguier - Pavie Finance,
Tel.: + 33-1-42-15-04-39, e-mail: contact at pavie-finance.com;