Magenta Therapeutics Announces First Subjects Dosed in Phase 1 Clinical Trial of MGTA-145, a First-Line Stem Cell Mobilization Product Candidate

CAMBRIDGE, Mass.–(BUSINESS WIRE)–Magenta
Therapeutics (NASDAQ: MGTA), a clinical-stage biotechnology company
developing novel medicines to bring the curative power of stem cell
transplant to more patients, today announced that it has dosed the first
subjects in a Phase 1 study of MGTA-145. Magenta intends to develop
MGTA-145 in autoimmune diseases, blood cancers and genetic diseases.

More than 85 percent of the 65,000 transplants in the US and Europe each
year use mobilized hematopoietic stem cells as a cell source. MGTA-145
is a biologic chemokine factor that Magenta is developing as a
first-line therapy for stem cell mobilization. MGTA-145 is designed to
enable single-day mobilization and collection of high numbers of stem
cells without G-CSF, the current standard of care. MGTA-145 works
synergistically with plerixafor, another stem cell mobilization product.

The Phase 1 study will investigate the safety and tolerability of
MGTA-145 alone and in combination with plerixafor in healthy volunteers
and establish recommended Phase 2 doses. The study will also measure the
number of hematopoietic stem cells in the blood after dosing with
MGTA-145 alone and in combination with plerixafor.

“There is a clear need for a better first-line stem cell mobilization
agent for both patients and donors that does not involve the use of
G-CSF,” said John DiPersio, M.D., Ph.D., Professor of Medicine,
Washington University School of Medicine. “G-CSF requires five to seven
days of injections in order to provide adequate numbers of stem cells
for transplant. There are significant side effects associated with
G-CSF, including severe bone pain that may require the use of narcotic
pain medications. A significant portion of patients do not mobilize an
adequate number of stem cells with G-CSF alone and require a second drug
and more days of stem cell collection. Further, approximately fifty
percent of donors decline to donate for patients undergoing allogeneic
transplant, in part because of the burden associated with donation with
current mobilization regimens.”

“MGTA-145 was developed based on our understanding of the physiological
mechanisms that control stem cell mobilization. Preclinical data suggest
that MGTA-145 in combination with plerixafor could reliably provide a
robust number of stem cells in a single day for both autologous and
allogeneic stem cell transplant. The cells that are mobilized have been
shown to contain a large number of high-quality stem cells, which is
associated with better disease outcomes,” said John Davis, M.D., M.P.H.,
Chief Medical Officer, Magenta Therapeutics. “We believe that MGTA-145
has the potential to become a new first-line standard of care for stem
cell mobilization that could improve stem cell collection for more
patients and donors.”

Forward-Looking Statement
This press release contains
forward-looking statements and information within the meaning of The
Private Securities Litigation Reform Act of 1995 and other federal
securities laws. The use of words such as “may,” “will,” “could”,
“should,” “expects,” “intends,” “plans,” “anticipates,” “believes,”
“estimates,” “predicts,” “projects,” “seeks,” “endeavor,” “potential,”
“continue” or the negative of such words or other similar expressions
can be used to identify forward-looking statements.

The express or implied forward-looking statements included in this press
release are only predictions and are subject to a number of risks,
uncertainties and assumptions, including, without limitation:
uncertainties inherent in clinical studies and in the availability and
timing of data from ongoing clinical studies; whether interim results
from a clinical trial will be predictive of the final results of the
trial; whether results from preclinical studies or earlier clinical
studies will be predictive of the results of future trials; the expected
timing of submissions for regulatory approval or review by governmental
authorities, including review under accelerated approval processes;
orphan drug designation eligibility; regulatory approvals to conduct
trials or to market products; whether Magenta’s cash resources will be
sufficient to fund Magenta’s foreseeable and unforeseeable operating
expenses and capital expenditure requirements; and other risks set forth
under the caption “Risk Factors” in Magenta’s Registration Statement on
Form S-1, as updated by Magenta’s most recent Annual Report on Form 10-K
and its other filings with the Securities and Exchange Commission. In
light of these risks, uncertainties and assumptions, the forward-looking
events and circumstances discussed in this press release may not occur
and actual results could differ materially and adversely from those
anticipated or implied in the forward-looking statements. You should not
rely upon forward-looking statements as predictions of future events.
Although Magenta believes that the expectations reflected in the
forward-looking statements are reasonable, it cannot guarantee that the
future results, levels of activity, performance or events and
circumstances reflected in the forward-looking statements will be
achieved or occur.

Moreover, except as required by law, neither Magenta nor any other
person assumes responsibility for the accuracy and completeness of the
forward-looking statements included in this press release. Any
forward-looking statement included in this press release speaks only as
of the date on which it was made. We undertake no obligation to publicly
update or revise any forward-looking statement, whether as a result of
new information, future events or otherwise, except as required by law.

Contacts

Magenta Therapeutics:
Manisha Pai, Vice President, Communications &
Investor Relations
617-510-9193
[email protected]