Glycine, a nonessential amino acid, plays a crucial role in various biological processes. Its versatile nature allows it to be involved in protein synthesis, neurotransmission, and energy metabolism. In recent years, glycine has also emerged as a potential candidate for vaccine development due to its immunomodulatory properties.
The Role of Glycine in Vaccines
Generally speaking, glycine is not directly used as an active ingredient in vaccines, but it is commonly used as a stabilizer, buffering agent and osmolytes in vaccine formulations. It helps maintain the stability, potency, and effectiveness of vaccine antigens during storage and transportation.
- Glycine as Stabilizer
Glycine works as a stabilizer by controlling the pH level (acidity or alkalinity) of the vaccine solution. It acts as a buffering agent, which helps maintain pH within a desired range, preventing any pH fluctuations that may degrade or denature the vaccine components.
Additionally, glycine also serves as a stabilizer for some proteins and viruses present in vaccines. Its presence can help protect these sensitive biological components from deterioration caused by various environmental factors such as temperature changes, light exposure, or chemical reactions.
- Glycine As Osmolyte in Vaccine Flocculation
Another important strategy in vaccine development is the purification of organisms for use as vaccines. Osmolytes are often used to purify these organisms. Glycine was reported to be the best osmolyte for flocculating non-enveloped viruses, while for enveloped viruses, the same concentration inactivated it, indicating that the choice of the osmolyte concentration should depend on the organism type involved in the flocculation process. 
Furthermore, the pH of the medium also has a significant impact on the quality of flocculation in the presence of osmotic agents. In the presence of glycine, flocculation is enhanced when the pH equals the pI of the virus particles. But as the negative charge on the virus increases with increasing pH, charge-charge repulsion between virus particles reduces flocculation efficiency.
Osmolytes enhance the rate of antibody production. 
Development of Glycine-based Vaccine Candidates
Glycine-based vaccine candidates are being actively developed in the field of immunology. By conjugating glycine to target antigens or incorporating it into peptide structures, researchers are able to enhance the immunogenicity of vaccine candidates and promote a strong immune response.
For example, Ghazal Karevan et al. evaluated specific immune responses in a mouse model using glycine nanoparticles as an adjuvant and a chimeric antigen delivery system containing the triggering factors, Omp31 and Bp26. The results suggest that chimeric antigen-loaded glycine nanoparticles can serve as vaccine candidates to induce cellular and humoral immune responses against brucellosis.
Glycine nanoparticles for Brucella vaccine candidate. 
- Tauheed Hasan, et al. Human Vaccines & Immunotherapeutics, 2019, 15(2): 514-525.
- Ghazal Karevan, et al. Clin Exp Vaccine Res. 2021 Jan; 10(1): 35-43.
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