May 8, 2024
SymBio Pharmaceuticals Limited
Fuminori Yoshida
Representative Director
President and Chief Executive Officer(Securities Code: 4582)

SymBio Announces Initiation of Phase 2a Clinical Trial (ATHENA)
of Intravenous Brincidofovir for Treatment of Cytomegalovirus Infection
after Hematopoietic Stem Cell Transplantation

TOKYO, Japan, May 8, 2024 – SymBio Pharmaceuticals Limited (Headquarters: Tokyo, “SymBio” or
the “Company") today announced that its Phase 2a clinical trial of the intravenous formulation ofbrincidofovir (“BCV”) for treatment of adenovirus (AdV) infection after hematopoietic stem celltransplantation is on schedule to be completed as planned in H1 2024. In February 2024, the U.S.
Food and Drug Administration (FDA) accepted our protocol amendment to add a second indication,
cytomegalovirus (CMV) infection after hematopoietic stem cell transplantation, to the clinical trial
and we are now working diligently with major transplant centers in the United States to prepare forthe first patient administration.
Although effective therapeutic agents are currently available for CMV infection after hematopoietic
stem cell transplantation, a significant number of reactivation cases have been observed, and there
are cases of patients who are resistant or refractory to the treatment. Therefore, there is an extremely
high unmet medical need for this therapeutic area. Clinical trials of oral BCV have shown that BCV ishighly effective against CMV infection, and this clinical trial is to be conducted using intravenous
BCV, which has a superior safety profile.
Because of this protocol change, the cohorts for CMV infection will become part of the ATHENA
study, and the duration of the ATHENA study will be extended to reflect the duration of the CMVcohorts. Regarding AdV infection, cohort 4 of the trial has been completed and the Company does notexpect the protocol change to have any impact on the development plan for AdV infection.
[Contact]
Investor Relations
Tel: +81 (0)3 5472 1125

1

(Note)About the anti-viral drug Brincidofovir
Brincidofovir (BCV) has a new mechanism of action as a lipid conjugate of cidofovir (CDV). CDV is anantiviral drug already approved and marketed in the United States, but unapproved in Japan. BCV isexpected to be an effective treatment against a wide spectrum of dsDNA virus infections(cytomegalovirus, adenovirus, Epstein-Barr virus (EBV), herpes virus, BK virus, papillomavirus andsmallpox virus including monkeypox, etc.), with superior features such as high activity antiviral effectin comparison with CDV and other antiviral drugs. Due to the breakthrough nature of the BCV
molecule, in which a specific length of lipid chain is attached to the CDV, BCV is converted into a
molecule that acts directly within the cell, thereby dramatically increasing the efficiency of cellular
uptake and showing a high antiviral activity. In September 2019, SymBio entered into a license
agreement with Chimerix for the exclusive worldwide rights to develop, market, and manufacture
BCV for all diseases except orthopoxviruses (such as smallpox and monkeypox). The tablets and oralsuspension (oral formulation) were approved on June 4, 2021, for the treatment of smallpox in adults
and pediatric patients, including neonates. In addition to its high antiviral activity, BCV is also
expected to have anti-tumor effects. We are currently conducting collaborative studies with theNational Cancer Centre Singapore, the University of California, San Francisco, and other institutions
to confirm its anti-cancer activity and to identify synergistic effects when combined with its antiviralactivity.
Clinical trials and important R&D collaborations with prominent research institutions include:- Initiated a Phase II clinical trial in patients with adenovirus infection after hematopoietic stem celltransplantation (March 2021) and received Fast Track designation from the FDA (April 2021). Proofof Concept (POC) of antiviral efficacy established based on data up to cohort 3 (May 2023).
- Initiated a non-clinical trial at the University of California, San Francisco Neurosurgery Brain
Tumor Center to evaluate the anti-tumor effect of BCV on refractory brain tumors (September 2021).
- A number of recent studies have demonstrated that EBV is a risk factor for MS. SymBio entered into
CRADA with the NINDS in March 2023 to establish a new antiviral treatment method for MS andhas been conducting collaborative research to develop a clinical trial.
- CRADA with the National Institute of Allergy and Infectious Diseases (NIAID), affiliated with the 3NIH, to evaluate the efficacy of BCV for EB virus-associated lymphoproliferative diseases (April2023).
- Research on the involvement of infection by reactivation of latent viruses in various neurologicalseverity diseases of the brain, including Alzheimer's disease, has been ongoing for the past severalyears, and a simple three-dimensional mimicry of human neural stem cell cultures and brain tissue
established by Tufts University in the United States, the A Sponsored Research Agreement wassigned (December 2022) to examine the effect of BCV on HSV infection using a herpes simplex virus(HSV) infection/reactivation model established by Tufts University in the U.S., which uses humanneural stem cells cultured to mimic brain tissue in three dimensions.

2About SymBio Pharmaceuticals Limited
SymBio Pharmaceuticals Limited was established in March 2005 by Fuminori Yoshida who previouslyserved concurrently as Corporate VP of Amgen Inc. and founding President of Amgen Japan. In May
2016, the Company incorporated its wholly-owned subsidiary in the U.S., SymBio Pharma USA, Inc.
(Headquarters: Durham, North Carolina, Representative: John Houghton).
The Company’s underlying corporate mission is to “deliver hope to patients in need” as it aspires to bea leading global specialty biopharmaceutical company dedicated to addressing underserved medicalneeds.

3