Maxygen Initiates Phase IIa Clinical Trial Of MAXY-G34 In Breast Cancer Patients

Maxygen, Inc.
(Nasdaq: MAXY) today announced that it has initiated a phase IIa trial to
evaluate the efficacy, safety and tolerability of MAXY-G34 in the treatment
of chemotherapy-induced neutropenia. MAXY-G34 is a novel pegylated
granulocyte colony stimulating factor (PEG-GCSF) shown in preclinical and
Phase I studies to have novel and potentially superior properties compared
to the current PEG- GCSF therapy.



"Patients and physicians have limited options for treatment of
neutropenia," said Russell Howard, chief executive officer of Maxygen.
"With MAXY-G34, we hope to expand those options and improve the outcome for
many chemotherapy patients. During this first Phase II trial we will begin
to learn more about how our drug might play a role in the large,
undifferentiated GCSF market."



The Phase IIa trial, which will be conducted at multiple centers in
Eastern Europe, is the first trial of MAXY-G34 in patients. Approximately
30 patients with Stage I-III breast cancer will undergo TAC (docetaxel,
adriamycin and cyclophosphamide) chemotherapy followed by next-day
administration of either MAXY-G34 or Neulasta (control population). The
trial is designed as a multiple ascending dose study, with planned doses at
10, 30, 60, or 100 micrograms per kilogram of MAXY-G34 compared to 6mg of
Neulasta. Both MAXY-G34 and Neulasta will be administered as a single
subcutaneous injection once per chemotherapy cycle.



The primary objective of the Phase IIa trial is to identify one or more
doses of MAXY-G34 that effectively treat chemotherapy-induced neutropenia.
Patient tolerability, safety, and immunogenicity will be monitored and
assessed. Data will also be collected on the pharmacokinetic properties of
MAXY-G34 and the mobilization of CD34+ stem cells.



Phase I Results



A Phase I trial was previously conducted to assess the safety and
tolerability of MAXY-G34 in 40 healthy volunteers. This study showed
MAXY-G34 to be a potent, long-lasting stimulator of neutrophils and an
efficient mobilizer of CD34+ stem cells. The drug exhibited a median
half-life approximately 2.3 times that of Neulasta. No serious adverse
events were reported, and there were no dose-limiting toxicities. No
binding or neutralizing antibodies were found at any dose level, with dose
levels ranging from 10 - 150 micrograms per kilogram.



About GCSF



GCSF is a natural protein that stimulates the body's bone marrow to
produce neutrophils, a specific type of white blood cell that plays an
important role in the defense against bacterial infections. Worldwide sales
of GCSF products were approximately $3.9 billion in 2006.
















About Neutropenia



Neutropenia is a severe decrease in neutrophil cell counts in the
blood. Neutropenia is a common side effect of chemotherapeutic treatments
for many forms of cancer, including breast cancer, lung cancer, lymphomas
and leukemias. Neutropenic patients are at increased risk of contracting
bacterial infections, some of which can be life threatening. Further, and
most importantly, neutropenic patients may receive reduced or delayed
chemotherapy treatment, which can result in cancer progression.



About Maxygen



Maxygen is a biopharmaceutical company focused on developing improved
versions of protein drugs. We look for opportunities where our proprietary
protein modification technologies can address significant therapeutic
needs. Products developed by Maxygen now in clinical trials include a novel
interferon-alpha for the treatment of hepatitis C virus (HCV) infection and
a novel GCSF for the treatment of neutropenia. Maxygen's approach may allow
us to leverage the established development and regulatory paths of approved
drugs. We believe this advantage translates to a greater chance of
successfully bringing important new drugs to market. maxygen



Forward Looking Statements



This news release contains forward-looking statements about our
research and business prospects, including those relating to our ability to
develop any human therapeutic products suitable for commercialization; our
ability or plans to continue the clinical development of MAXY-G34, and the
timing and status of such development; whether MAXY-G34 will demonstrate
any benefit in treating chemotherapy-induced neutropenia or exhibit novel
or improved properties in humans as compared to currently marketed drugs;
and whether this product, if commercialized, will be competitive in its
relevant markets. Such statements involve risks and uncertainties that may
cause results to differ materially from those set forth in these
statements. Among other things these risks and uncertainties include, but
are not limited to, changing research and business priorities of Maxygen,
the inherent uncertainties of pharmaceutical research and drug development,
our ability to develop human therapeutic drugs in an increasingly
competitive biotechnology industry and the uncertain timing of such
development, the development of superior products by competitors, and our
ability to establish and maintain our manufacturing arrangements. These and
other risk factors are more fully discussed in our Form 10-K for the year
ended December 31, 2006, including under the caption "Risk Factors", and in
our other periodic SEC reports, all of which are available from Maxygen at
maxygen. Maxygen disclaims any obligation to update or revise any
forward-looking statement contained in this release as a result of new
information or future events or developments.



Neulasta is a registered trademark of Amgen Inc.


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