Advances in protein subunit vaccines against tuberculosis

Tuberculosis (TB), also known as the "White Plague", is caused by Mycobacterium tuberculosis (Mtb). Before the COVID-19 epidemic, TB had the highest mortality rate of any single infectious disease. Vaccination is considered one of the most effective strategies for controlling TB. Despite the limitations of the Bacille Calmette-Guérin (BCG) vaccine in terms of protection against TB among adults, it is currently the only licensed TB vaccine. Recently, with the evolution of bioinformatics and structural biology techniques to screen and optimize protective antigens of Mtb, the tremendous potential of protein subunit vaccines is being exploited. Multistage subunit vaccines obtained by fusing immunodominant antigens from different stages of TB infection are being used both to prevent and to treat TB. Additionally, the development of novel adjuvants is compensating for weaknesses of immunogenicity, which is conducive to the flourishing of subunit vaccines. With advances in the development of animal models, preclinical vaccine protection assessments are becoming increasingly accurate. This review summarizes progress in the research of protein subunit TB vaccines during the past decades to facilitate the further optimization of protein subunit vaccines that may eradicate TB.

Maternal Immunization Using a Protein Subunit Vaccine Mediates Passive Immunity against Zaire ebolavirus in a Murine Model

The Ebola virus has caused outbreaks in Central and West Africa, with high rates of morbidity and mortality. Clinical trials of recombinant virally vectored vaccines did not explicitly include pregnant or nursing women, resulting in a gap in knowledge of vaccine-elicited maternal antibody and its potential transfer. The role of maternal antibody in Ebola virus disease and vaccination remains understudied. Here, we demonstrate that a protein subunit vaccine can elicit robust humoral responses in pregnant mice, which are transferred to pups in breastmilk. These findings indicate that an intramuscular protein subunit vaccine may elicit Ebola-specific IgG capable of being transferred across the placenta as well as into the breastmilk. We have previously shown protective efficacy with these vaccines in non-human primates, offering a potential safe and practical alternative to recombinant virally vectored vaccines for pregnant and nursing women in Ebola endemic regions.

Chemical Conjugation Strategies for the Development of Protein-Based Subunit Nanovaccines

The production of subunit nanovaccines relies heavily on the development of a vaccine delivery system that is safe and efficient at delivering antigens to the target site. Nanoparticles have been extensively investigated for vaccine delivery over the years, as they often possess self-adjuvanting properties. The conjugation of antigens to nanoparticles by covalent bonds ensures co-delivery of these components to the same subset of immune cells in order to trigger the desired immune responses. Herein, we review covalent conjugation strategies for grafting protein or peptide antigens onto other molecules or nanoparticles to obtain subunit nanovaccines. We also discuss the advantages of chemical conjugation in developing these vaccines.

Characterization and Protective Efficacy of Type III Secretion Proteins as a Broadly Protective Subunit Vaccine against Salmonella enterica Serotypes

Nontyphoidal Salmonella enterica serotypes (NTS) are the leading cause of hospitalization and death due to foodborne illnesses. NTS are the costliest of the foodborne pathogens and cause ∼$4 billion annually in health care costs. In Africa, new invasive NTS are the leading cause of bacteremia, especially in HIV-positive children and adults. Current vaccines against S. enterica are not broadly protective and most are directed at the typhoid-causing serotypes, not the NTS. All S. enterica strains require two type III secretion systems (T3SS) for virulence. The T3SS needle tip protein and the first translocator are localized to the T3SS needle tip and are required for pathogenesis of S. enterica Collectively they are 95 to 98% conserved at the amino acid sequence level among all S. enterica strains. The Salmonella pathogenicity island 1 or 2 tip and first translocator proteins were genetically fused to produce the S1 and S2 fusion proteins, respectively, as potential vaccine candidates. S1 and S2 were then characterized using spectroscopic techniques to understand their structural and biophysical properties. Formulated at the proper pH, S1, S2, or S1 plus S2 (S1S2), admixed with adjuvant, was used to immunize mice followed by a lethal challenge with S. enterica serotype Typhimurium or S. enterica serotype Enteritidis. The S1S2 formulation provided the highest protective efficacy, thus demonstrating that an S1S2 subunit vaccine can provide broad, serotype-independent protection, possibly against all S. enterica serotypes. Such a finding would be transformative in improving human health.