Vaxcyte, Inc. announced the publication of preclinical data supporting the potential of VAX-24, its lead vaccine candidate, in the journal Vaccine. VAX-24 is an investigational 24-valent pneumococcal conjugate vaccine (PCV) designed to prevent invasive pneumococcal disease, which can be most serious for infants, young children, older adults and those with immune deficiencies or certain chronic health conditions. The paper, “Non-clinical Immunological Comparison of a Next-Generation 24-Valent Pneumococcal Conjugate Vaccine (VAX-24) Using Site-Specific Carrier Protein Conjugation to the Current Standard of Care (PCV13 and PPV23),” which includes previously disclosed data, uses a rabbit model to evaluate the immune response of Vaxcyte’s 24-valent PCV candidate compared to Prevnar13® (PCV13) and Pneumovax®23 (PPV23). In this study, all serotype conjugates in VAX-24 met the primary objective to elicit immune responses that were more robust compared to PPV23 and at least comparable to PCV13. Highlights of Study Design and Findings: In this study, VAX-24, PCV13 and PPV23 were administered to New Zealand White rabbits to compare the resulting opsonophagocytic, or neutralizing antibody, activity (OPA) and anti-capsular IgG antibodies generated that specifically bind to all the individual serotypes included in each respective vaccine. The rabbits were dosed at either 0.11µg or 1.1µg of VAX-24 at the start of the study and a booster was given 21 days later. Immunogenicity was measured 14 days after both the initial and booster doses and compared to the 13 serotypes contained in PCV13 and the incremental 11 serotypes contained in PPV23. In the study, VAX-24 showed conjugate-like immune responses to all 24 serotypes based on comparable OPA and IgG responses to PCV13 and higher responses than PPV23. This study demonstrated the utility of Vaxcyte’s site-specific conjugation technology in a preclinical setting and the potential for a PCV with broader serotype coverage. Pneumococcal disease is an infection caused by Streptococcus pneumoniae bacteria. This infection can lead to a wide range of serious invasive infections including pneumonia, meningitis and blood stream infections, as well as less severe, non-invasive ear and sinus infections, and can also cause secondary infections due to other respiratory pathogens. In the U.S. alone, approximately 900,000 people get pneumococcal pneumonia each year, including as many as 400,000 requiring hospitalization and approximately 28,000 deaths. Antibiotics are used to treat pneumococcal disease, but some strains of the bacteria have developed resistance to treatments. The morbidity and mortality due to pneumococcal disease are highly significant, particularly for young children and older adults, which underscores the need for a more broad-spectrum vaccine. VAX-24 is designed to improve upon the standard-of-care PCV vaccine by covering the additional strains that are responsible for the majority of residual pneumococcal disease currently in circulation. Vaxcyte’s cell-free protein synthesis platform, which is comprised of the XpressCFTM platform exclusively licensed from Sutro Biopharma, and its proprietary know-how, offer several advantages over conventional cell-based protein expression methods, which Vaxcyte believes enables it to generate a more broad-spectrum PCV. Vaxcyte’s approach is focused on expanding coverage by adding more antigenic strains without compromising the overall immune response. Vaxcyte achieved preclinical proof of concept for VAX-24 by demonstrating that VAX-24 has the potential to protect against the pneumococcal strains collectively covered by PCV13 and PPV23 and showed the durable, boostable immune response of a conjugate vaccine. The incremental 11 strains covered by VAX-24 and not covered by PCV13 are responsible for the majority of circulating invasive pneumococcal disease in both the United States and European Union and are associated with high case-fatality rates, antibiotic resistance and/or serious invasive infections.