Omeros Corporation Announces EBMT Case Report of Resolution of Gastrointestinal Hematopoietic Stem Cell Transplant-Associated Thrombotic Microangiopathy Following Narsoplimab Treatment

— Growing Identification of HSCT-TMA a Focus of Recent Annual Meeting
of the European Society for Blood and Marrow Transplantation —

SEATTLE–(BUSINESS WIRE)–Omeros Corporation (Nasdaq: OMER) today announced the recent
presentation of a case report describing resolution of gastrointestinal
hematopoietic stem cell transplant-associated thrombotic microangiopathy
(HSCT-TMA) following narsoplimab treatment under a compassionate-use
protocol. The case was presented at the 2019 Annual Meeting of the
European Society for Blood and Marrow Transplantation (EBMT) held March
24-27 in Frankfurt, Germany. Omeros is reporting the case to ensure
broad availability of the information presented. Narsoplimab, Omeros’
antibody to inhibit the lectin pathway of complement, has received
breakthrough therapy designation from FDA and is in Phase 3 development
for the treatment of HSCT-TMA.

The case was presented by Rafael Duarte M.D., Ph.D., F.R.C.P., Associate
Professor, Head of Hematopoietic Transplantation and Hemato-oncology
Section, University Hospital Puerta de Hierro
Majadahonda, Madrid, Spain, and Secretary of the EBMT. Dr. Duarte
described an 18-year-old patient with biopsy-proven HSCT-TMA of the
gastrointestinal tract causing severe gastrointestinal bleeding
requiring transfusions. The patient received narsoplimab, her TMA
resolved, and all transfusions have been discontinued. The patient
continues to do well after cessation of narsoplimab treatment.

Hematopoietic stem cell transplant-associated TMA was a focus of the
EBMT meeting program. In addition to the educational course on early
transplant complications that included Dr. Duarte’s presentation, the
program included a review session on renal complications of HSCT-TMA and
an Omeros-sponsored symposium entitled “How Do I Diagnose HSCT-TMA.” All
of these sessions were well attended. The meeting program also contained
several other podium and poster presentations directed to complications
related to endothelial injury, which include HSCT-TMA, graft-versus-host
disease and diffuse alveolar hemorrhage.

The interest in HSCT-TMA shown at the EBMT meeting tracks a broadening
recognition of the high incidence and severity of this transplant
complication. This growing awareness within the stem-cell transplant
community is further reflected by the increasing frequency of
compassionate-use requests from physicians worldwide seeking narsoplimab
treatment for adult and pediatric patients with HSCT-TMA. Historically,
the literature-based incidence of HSCT-TMA has been varied, with some
smaller centers and national registries reporting low numbers of cases
while major research institutions reported incidences in the range of
15-25 percent. More recently, however, as TMA has become better
understood and identified, its reported occurrence has been
approximately 40 percent in patients undergoing allogeneic HSCT in
centers that screen for the disease. The condition is associated with an
increased mortality rate and, even in those patients who survive, it
often causes chronic kidney damage.

Omeros is preparing both a U.S. biologics license application (BLA) and
a European marketing authorization application for narsoplimab in the
treatment of HSCT-TMA. The FDA has agreed that a rolling BLA submission
is appropriate and discussions with European regulators are ongoing.

About Omeros’ MASP Programs

Omeros controls the worldwide rights to MASP-2 and all therapeutics
targeting MASP-2, a novel pro-inflammatory protein target involved in
activation of the complement system, which is an important component of
the immune system. The complement system plays a role in the
inflammatory response and becomes activated as a result of tissue damage
or microbial infection. MASP-2 is the effector enzyme of the lectin
pathway, one of the principal complement activation pathways.
Importantly, inhibition of MASP-2 does not appear to interfere with the
antibody-dependent classical complement activation pathway, which is a
critical component of the acquired immune response to infection, and its
abnormal function is associated with a wide range of autoimmune
disorders. MASP-2 is generated by the liver and is then released into
circulation. Gene-targeted MASP-2-deficient mice and humans with MASP-2
gene polymorphisms that affect MASP-2 serum levels and MASP-2 functional
activity are generally healthy with no obvious adverse phenotype.

Phase 3 clinical programs are in progress for narsoplimab, Omeros’ lead
MASP-2 inhibitor also referred to as “OMS721,” in hematopoietic stem
cell transplant-associated thrombotic microangiopathy (HSCT-TMA), in
immunoglobulin A (IgA) nephropathy, and in atypical hemolytic uremic
syndrome (aHUS). Narsoplimab can be administered both intravenously and
subcutaneously, and Omeros expects to commercialize each formulation of
narsoplimab for different therapeutic indications. In
parallel, Omeros is developing small-molecule inhibitors of MASP-2.
Based on requests from treating physicians, Omeros has established a
compassionate-use program for narsoplimab, which is active in both the
U.S. and Europe. The FDA has granted narsoplimab breakthrough therapy
designation for IgA nephropathy and for HSCT-TMA, orphan drug status for
the prevention (inhibition) of complement-mediated thrombotic
microangiopathies, for the treatment of IgA nephropathy, for the
treatment of HSCT-TMA, and fast track designation for the treatment of
patients with aHUS. The European Medicines Agency has granted orphan
drug designation to narsoplimab for treatment of primary IgA nephropathy
and for treatment in HSCT.

Omeros also has identified MASP-3 as responsible for the conversion of
pro-factor D to factor D and as a critical activator of the human
complement system’s alternative pathway. The alternative pathway is
linked to a wide range of immune-related disorders. In addition to its
lectin pathway inhibitors, the company is advancing its development of
antibodies and small-molecule inhibitors against MASP-3 to block
activation of the alternative pathway. Omeros has initiated the
manufacturing scale-up process of its MASP-3 antibodies in preparation
for clinical trials.

About Omeros Corporation

Omeros is a commercial-stage biopharmaceutical company committed to
discovering, developing and commercializing small-molecule and protein
therapeutics for large-market as well as orphan indications targeting
inflammation, complement-mediated diseases, disorders of the central
nervous system and immune-related diseases, including cancers. The
company’s drug product OMIDRIA (phenylephrine and ketorolac intraocular
solution) 1% / 0.3% is marketed for use during cataract surgery or
intraocular lens (IOL) replacement to maintain pupil size by preventing
intraoperative miosis (pupil constriction) and to reduce postoperative
ocular pain. In the European Union, the European Commission has approved
OMIDRIA for use in cataract surgery and other IOL replacement procedures
to maintain mydriasis (pupil dilation), prevent miosis (pupil
constriction), and to reduce postoperative eye pain. Omeros has multiple
Phase 3 and Phase 2 clinical-stage development programs focused on:
complement-associated thrombotic microangiopathies; complement-mediated
glomerulonephropathies; cognitive impairment; and addictive and
compulsive disorders. In addition, Omeros has a diverse group of
preclinical programs and a proprietary G protein-coupled receptor (GPCR)
platform through which it controls 54 new GPCR drug targets and
corresponding compounds, a number of which are in preclinical
development. The company also exclusively possesses a novel
antibody-generating platform.

Forward-Looking Statements

This press release contains forward-looking statements within the
meaning of Section 27A of the Securities Act of 1933 and Section 21E of
the Securities Exchange Act of 1934, which are subject to the “safe
harbor” created by those sections for such statements. All statements
other than statements of historical fact are forward-looking statements,
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to,” “may,” “plan,” “potential,” “predict,” “project,” “prospects,”
“should,” “slated,” “targeting,” “will,” “would” and similar expressions
and variations thereof. Forward-looking statements are based on
management’s beliefs and assumptions and on information available to
management only as of the date of this press release. Omeros’ actual
results could differ materially from those anticipated in these
forward-looking statements for many reasons, including, without
limitation, risks associated with product commercialization and
commercial operations, unproven preclinical and clinical development
activities, regulatory oversight, intellectual property claims,
competitive developments, litigation, and the risks, uncertainties and
other factors described under the heading “Risk Factors” in the
company’s Annual Report on Form 10-K filed with the Securities and
Exchange Commission on March 1, 2019. Given these risks, uncertainties
and other factors, you should not place undue reliance on these
forward-looking statements, and the company assumes no obligation to
update these forward-looking statements, even if new information becomes
available in the future.

Contacts

Jennifer Cook Williams
Cook Williams Communications, Inc.
Investor
and Media Relations
360.668.3701
jennifer@cwcomm.org