Researchers at the Indian Institute of Technology (IIT) Kanpur have uncovered the molecular structure of EP67, a synthetic vaccine adjuvant that could help develop safer and more effective vaccine boosters. Published in the Proceedings of the National Academy of Sciences (PNAS), the study provides a near-atomic view of how the molecule activates the immune system while minimising excessive inflammation, opening new possibilities for vaccine and immunotherapy development.

The findings could contribute to the design of next-generation vaccines that generate stronger and longer-lasting immune responses with fewer inflammatory side effects.

Decoding how EP67 activates the immune system

EP67 is a synthetic peptide made of 10 amino acids, engineered from the naturally occurring immune protein C5a. While C5a can trigger strong inflammatory responses, EP67 has been designed to selectively activate dendritic cells and macrophages—key immune cells involved in initiating protective immunity—without stimulating neutrophils, which are associated with excessive inflammation.

Using cryo-electron microscopy (cryo-EM) at IIT Kanpur's National Cryo-EM Facility, researchers captured EP67 binding to the C5aR1 receptor in remarkable detail. The images revealed that the peptide folds into a distinctive hook-like shape, allowing it to fit precisely into the receptor and activate immune signalling.

Blueprint for future vaccine design

The structural insights provide researchers with a molecular blueprint for designing improved vaccine adjuvants. By understanding exactly how EP67 interacts with its receptor, scientists can now explore modifications to its amino acid sequence to enhance stability, effectiveness, and precision.

The C5aR1 receptor belongs to the G protein-coupled receptor (GPCR) family, one of the most important classes of drug targets, with approximately one-third of prescription medicines acting on GPCRs.

Potential beyond vaccines

In addition to improving vaccine boosters, EP67 has shown promise in pre-clinical animal studies by enhancing immune responses against antibiotic-resistant bacteria, including Methicillin-resistant Staphylococcus aureus (MRSA).

Researchers believe the molecule could eventually find applications in vaccines targeting infectious diseases as well as therapies that strengthen immune responses against difficult-to-treat bacterial infections.

Next steps

The IIT Kanpur team plans to continue pre-clinical studies to optimise EP67's formulation and dosage before evaluating its safety and effectiveness in human clinical trials.

Future research will also investigate its potential use in vaccine platforms for diseases such as COVID-19 and its broader role in combating antimicrobial resistance.

The study represents a significant advance in structural immunology, offering new insights that could support the development of safer vaccine boosters and next-generation immune therapies.