Oral Administration of Universal Bacterium-Vectored Nucleocapsid-Expressing COVID-19 Vaccine is Efficacious in Hamsters

Oral delivery of an inexpensive COVID-19 (coronavirus disease 2019) vaccine could dramatically improve immunization rates, especially in low- and middle-income countries. Previously, we described a potential universal COVID-19 vaccine, rLVS ΔcapB/MN, comprising a replicating bacterial vector, LVS (live vaccine strain) ΔcapB, expressing the highly conserved SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) membrane and nucleocapsid (N) proteins, which, when administered intradermally or intranasally, protects hamsters from severe COVID-19-like disease after high-dose SARS-CoV-2 respiratory challenge. Here, we show that oral administration of the vaccine also protects against high-dose SARS-CoV-2 respiratory challenge; its protection is comparable to that of intradermal, intranasal, or subcutaneous administration. Hamsters were protected against severe weight loss and lung pathology and had reduced oropharyngeal and lung virus titers. Protection against weight loss and histopathology by the vaccine, which in mice induces splenic and lung cell interferon gamma in response to N protein stimulation, was correlated in hamsters with pre-challenge serum anti-N TH1-biased IgG (IgG2/3). Thus, rLVS ΔcapB/MN has potential as an oral universal COVID-19 vaccine. IMPORTANCE The COVID-19 pandemic continues to rage into its fourth year worldwide. To protect the world's population most effectively from severe disease, hospitalization, and death, a vaccine is needed that is resistant to rapidly emerging viral variants of the causative agent SARS-CoV-2, inexpensive to manufacture, store, and transport, and easy to administer. Ideally, such a vaccine would be capable of oral administration, especially in resource-poor countries of the world where there are shortages of needles, syringes and trained personnel to administer injectable vaccines. Here, we show that oral administration of a bacterium-vectored vaccine meeting all these criteria protects naturally susceptible Syrian hamsters from severe COVID-19-like disease, including severe weight loss and lung pathology, after high-dose SARS-CoV-2 respiratory challenge. As the vaccine is based upon inducing immunity to highly conserved SARS-CoV-2 membrane and nucleocapsid proteins, as opposed to the rapidly mutating Spike protein, it should remain resistant to newly emerging SARS-CoV-2 variants.

The Diverse Applications of Recombinant BCG-Based Vaccines to Target Infectious Diseases Other Than Tuberculosis: An Overview

Live attenuated Bacillus Calmette-Guérin (BCG) is the world's most widely used vaccine which is mainly administered for its protection against tuberculosis (TB), particularly in young children. However, since its initial use over 100years ago, it has also proven to offer a level of protection against various other pathogens, as a consequence of its non-specific immune enhancing effects. Thus, over the past few decades, recombinant BCG (rBCG) technology has been used as a vector to create rBCG vaccines expressing heterologous antigens that elicit immunity against a range of bacterial, viral, and parasitic diseases. Our goal with this mini-review is to provide an up-to-date survey of the various techniques, approaches, and applications of rBCG-based vaccines for targeting infectious diseases other than TB.

An oral cancer vaccine using a Bifidobacterium vector suppresses tumor growth in a syngeneic mouse bladder cancer model

Cancer immunotherapy using immune-checkpoint inhibitors (ICIs) such as PD-1/PD-L1 inhibitors has been well established for various types of cancer. Monotherapy with ICIs, however, can achieve a durable response in only a subset of patients. There is a great unmet need for the ICI-resistant-tumors. Since patients who respond to ICIs should have preexisting antitumor T cell response, combining ICIs with cancer vaccines that forcibly induce an antitumor T cell response is a reasonable strategy. However, the preferred administration sequence of the combination of ICIs and cancer vaccines is unknown. In this study, we demonstrated that combining an oral WT1 cancer vaccine using a Bifidobacterium vector and following anti-PD-1 antibody treatment eliminated tumor growth in a syngeneic mouse model of bladder cancer. This vaccine induced T cell responses specific to multiple WT1 epitopes through the gut immune system. Moreover, in a tumor model poorly responsive to an initial anti-PD-1 antibody, this vaccine alone significantly inhibited the tumor growth, whereas combination with continuous anti-PD-1 antibody could not inhibit the tumor growth. These results suggest that this oral cancer vaccine alone or as an adjunct to anti-PD-1 antibody could provide a novel treatment option for patients with advanced urothelial cancer including bladder cancer.

Live bacterial vaccine vectors: an overview

Genetically attenuated microorganisms, pathogens, and some commensal bacteria can be engineered to deliver recombinant heterologous antigens to stimulate the host immune system, while still offering good levels of safety. A key feature of these live vectors is their capacity to stimulate mucosal as well as humoral and/or cellular systemic immunity. This enables the use of different forms of vaccination to prevent pathogen colonization of mucosal tissues, the front door for many infectious agents. Furthermore, delivery of DNA vaccines and immune system stimulatory molecules, such as cytokines, can be achieved using these special carriers, whose adjuvant properties and, sometimes, invasive capacities enhance the immune response. More recently, the unique features and versatility of these vectors have also been exploited to develop anti-cancer vaccines, where tumor-associated antigens, cytokines, and DNA or RNA molecules are delivered. Different strategies and genetic tools are constantly being developed, increasing the antigenic potential of agents delivered by these systems, opening fresh perspectives for the deployment of vehicles for new purposes. Here we summarize the main characteristics of the different types of live bacterial vectors and discuss new applications of these delivery systems in the field of vaccinology.

Applications of bacillus Calmette-Guerin and recombinant bacillus Calmette-Guerin in vaccine development and tumor immunotherapy

Bacillus Calmette-Guerin (BCG) vaccines are attenuated live strains of Mycobacterium bovis and are among the most widely used vaccines in the world. BCG is proven to be effective in preventing severe infant meningitis and miliary tuberculosis. Intravesical instillation of BCG is also a standard treatment for non-muscle invasive bladder cancer. In the past few decades, recombinant BCG (rBCG) technology had been extensively applied to develop vaccine candidates for a variety of infectious diseases, including bacterial, viral, and parasite infections, and to improve the efficacy of BCG in bladder cancer therapy. This review is intended to show the vast applications of BCG and recombinant BCG (rBCG) in the prevention of infectious diseases and cancer immunotherapy, with a special emphasis on recent approaches and trends on both pre-clinical and clinical levels.

Development of Streptococcus pneumoniae Vaccines Using Live Vectors

Streptococcus pneumoniae still causes severe morbidity and mortality worldwide, especially in young children and the elderly. Much effort has been dedicated to developing protein-based universal vaccines to conquer the current shortcomings of capsular vaccines and capsular conjugate vaccines, such as serotype replacement, limited coverage and high costs. A recombinant live vector vaccine delivering protective antigens is a promising way to achieve this goal. In this review, we discuss the researches using live recombinant vaccines, mainly live attenuated Salmonella and lactic acid bacteria, to deliver pneumococcal antigens. We also discuss both the limitations and the future of these vaccines.