CAMBRIDGE, Mass, USA, and TOKYO, Japan, July 13, 2021?--?Affinivax, Inc.?("Affinivax") and Astellas Pharma Inc. (?Astellas?) announced results from the Phase 2 clinical trial of ASP3772, a novel vaccine candidate targeting?Streptococcus pneumoniae. Developed using Affinivax?s proprietary MAPS^??(Multiple Antigen-Presenting System) platform technology, ASP3772 is designed to offer both B-cell (antibody) and T-cell immune protection against?Streptococcus pneumoniae. ASP3772 includes 24 pneumococcal polysaccharides, as well as two conserved pneumococcal proteins. The results from the Phase 2 clinical trial demonstrated that ASP3772 was well tolerated. ?ASP3772 also exhibited an antibody response to each of the 24 polysaccharides, as well as an additional antibody response to the conserved pneumococcal proteins. The Phase 2 data for ASP3772 were delivered in an oral presentation at the 31^st?European Congress of Clinical Microbiology & Infectious Diseases (ECCMID), taking place online from 9 ? 12 July 2021. The U.S. Food and Drug Administration (FDA) has also granted Breakthrough Therapy designation for ASP3772 for the prevention of pneumonia and invasive disease caused by?Streptococcus pneumoniae?serotypes included in ASP3772 in adults aged 50 years and older. The FDA decision is informed by the results of the Phase 2 data. The FDA?s Breakthrough Therapy process is designed to expedite the development and review of drugs that are intended to treat a serious or life-threatening condition. Designation is based upon preliminary clinical evidence indicating that the drug may demonstrate substantial improvement over available therapies on one or more clinically significant endpoints. The Phase 2 clinical trial¹?of ASP3772 was conducted in 503 adults 65 to 85 years of age, and 293 adults received ASP3772, 97 adults received Prevnar13^??and 113 adults (who were previously vaccinated with Prevnar13^?) received Pneumovax^?23. The primary objective was to evaluate safety/tolerability and reactogenicity of ASP3772 compared to Prevnar13^?. The secondary objective was to evaluate the immunogenicity of ASP3772, versus Prevnar13 or Pneumovax^?23. A summary of the results is below:

• ASP3772 was observed to be well tolerated with mild and self-limited injection site and systemic reactions, similar to those seen in the Prevnar13^??group. Frequently reported local reactions were tenderness and pain, occurring within the first 2-3 days with no clear difference across ASP3772 and Prevnar13^??cohorts. ?Neither serious vaccine-related adverse events, nor clinically relevant abnormalities (vital signs, ECGs, laboratory parameters), were observed. No serious adverse events or medically attended adverse events related to immunization and no potentially immune mediated adverse events were observed in subjects through the 180-day safety assessment period post-immunization.
• At the three dose levels studied, ASP3772 induced a robust immune response to all 24 pneumococcal serotypes in the MAPS^??vaccine, as measured by both immunoglobulin G (IgG) and opsonophagocytic activity (OPA).
• When compared to Prevnar13^??alone, ASP3772 demonstrated a similar or better IgG and OPA immune response to the 13 shared serotypes included in both ASP3772 and Prevnar13?. Of note, ASP3772 demonstrated a statistically higher immune response to serotype 3 at all ASP3772 dose levels, as well as a statistically higher immune response to serotypes 5 and 19F at the highest ASP3772 dose tested. ASP3772 also demonstrated a statistically higher immune responses for all remaining 11 serotypes that are not included in Prevnar13^?.
• When compared to Prevnar13^??plus Pneumovax^?23, ASP3772 demonstrated a similar or better IgG and OPA immune response to the 13 shared serotypes with Prevnar13?. Of note, ASP3772 demonstrated a statistically higher immune responses for serotypes 3, 4, 5, 6A, 7F, 9V, and 18C at the highest dose tested. ASP3772 also demonstrated a similar, and in most cases statistically higher, immune response for all remaining 11 serotypes.
• ASP3772 also demonstrated an increase in antibodies (more than 2-fold, as measured by geometric mean fold rise in IgG) response to the conserved proteins included in the MAPS^??vaccine design (i.e., each polysaccharide was combined to a fusion of the two conserved pneumococcal proteins). There were no increases observed in the Prevnar13^??group.

?Extending the coverage to 24?Streptococcus pneumoniae?strains, we believe that ASP3772 has the potential to offer broader protection than any pneumococcal vaccine currently on the market or in clinical testing today , and we look forward to continuing to advance this important vaccine candidate through clinical trials in both adults and infants,? said Steven B. Brugger, CEO of Affinivax. ?Demonstrating strong immunogenicity to both the polysaccharides and proteins in our ASP3772 vaccine also represents a significant step forward in clinically validating our MAPS^??technology platform and highlights the promising potential for future MAPS? vaccines in our pipeline.? ?The MAPS^??technology offers new ways to address unmet needs for infectious diseases, such as?Streptococcus pneumoniae, that affect millions of people? said Salim Mujais, M.D., Senior Vice President and Therapeutic Area Head, Medical Specialties, Astellas. ??We believe that ASP3772 can offer significant potential to provide broader protection from pneumococcal infections that impact both infants and adults in our global community.? The ASP3772 clinical development program includes indications for protection against?Streptococcus pneumoniae?infections in both adults and infants. The pivotal Phase 3 registration clinical trials in adults are under preparation. A Phase 2 clinical trial with ASP3772 in infants is planned to start following the successful completion of the?ongoing Phase 1 study in healthy toddlers?12 to 15 months of age. In February 2017, Affinivax and Astellas entered into an exclusive worldwide license agreement to develop and commercialize a ASP3772 using Affinivax?s proprietary MAPS^?.