Induction of Protective Immunity by a Single Low Dose of a Master Cell Bank cGMP-rBCG-P Vaccine Against the Human Metapneumovirus in Mice

Abstract

Human metapneumovirus (hMPV) is an emergent virus, which mainly infects the upper and lower respiratory tract epithelium. This pathogen is responsible for a significant portion of hospitalizations due to bronchitis and pneumonia in infants and the elderly worldwide. hMPV infection induces a pro-inflammatory immune response upon infection of the host, which is not adequate for the clearance of this pathogen. The lack of knowledge regarding the different molecular mechanisms of infection of this virus has delayed the licensing of effective treatments or vaccines. As part of this work, we evaluated whether a single and low dose of a recombinant Mycobacterium bovis Bacillus Calmette-Guérin (BCG) expressing the phosphoprotein of hMPV (rBCG-P) can induce a protective immune response in mice. Immunization with the rBCG-P significantly decreased neutrophil counts and viral loads in the lungs of infected mice at different time points. This immune response was also associated with a modulated infiltration of innate cells into the lungs, such as interstitial macrophages (IM) and alveolar macrophages (AM), activated CD4+ and CD8+ T cells, and changes in the population of differentiated subsets of B cells, such as marginal zone B cells and plasma cells. The humoral immune response induced by the rBCG-P led to an early and robust IgA response and a late and constant IgG response. Finally, we determined that the transfer of cells or sera from immunized and infected mice to naïve mice promoted an efficient viral clearance. Therefore, a single and low dose of rBCG-P can protect mice from the disease caused by hMPV, and this vaccine could be a promising candidate for future clinical trials.

BCG-Based Vaccines Elicit Antigen-Specific Adaptive and Trained Immunity against SARS-CoV-2 and Andes orthohantavirus

“…On the other hand, for the rBCG-N-ANDV, we chose to explore the immunization schedule further, considering two doses of 1 × 10 8 CFU of rBCG-N-ANDV, with each dose separated by two weeks. This is in line with previous reports evaluating rBCGs in pre-clinical models [ 45 , 46 , 48 , 49 , 50 , 51 ]. As controls for this immunization schedule, mice were administered two doses of 1 × 10 8 CFU of BCG-WT or 1X PBS on the same days.…”

“…Here, we report data regarding two recombinant BCGs expressing either the N-SARS-CoV-2 or the N-ANDV proteins and their capacity to induce adaptive and trained immunity traits in mice. As reported for other rBCG vaccines, we observed favorable safety profiles for both vaccine prototypes [ 5 , 45 , 46 , 48 , 49 , 50 , 51 ]. Notably, mice immunized with the rBCG-N-SARS-CoV-2 vaccine in a single, low dose of this prototype exhibited no differences in weight changes, clinical score, and behavior compared to unimmunized or BCG-WT immunized mice.…”

“…This live-attenuated vaccine has been widely used for over a century to prevent tuberculosis disease, and it is one of the most used vaccines worldwide, with a well-characterized and documented safety profile [ 4 , 5 ]. Remarkably, BCG has also been used as a vector for the heterologous expression of recombinant antigens, with a positive correlation of protection against diseases caused by measles virus, hepatitis B virus, respiratory syncytial virus, and Bordetella pertussis , among others [ 5 , 45 , 46 , 48 , 49 , 50 , 51 ]. Hence, the rationale for using BCG as a vector for the expression of heterologous proteins, inducing a well-balanced immune response, leaning towards a Th1 polarization upon viral infections.…”

“…Details on the protein extraction can be found on the Supplementary Material . A total of 20 µg of purified protein or total protein extracts were loaded into SDS-PAGE gels, according to what was reported previously [ 44 , 45 , 46 , 47 ], and run for 30 min at 90 V and then for 90 min at 120 V. Then SDS-PAGE was transferred into a nitrocellulose membrane using a Semi-Dry Power Blotter Transfer System (Thermo Fisher, MA, USA). Upon transfer, the membranes were blocked and then incubated with a mouse monoclonal anti-N antibody for SARS-CoV-2 diluted 1:500 (Sinobiological, cat 40143-MM05) or a monoclonal anti-N-ANDV mouse IgG1 antibody diluted 1:1000 (Austral Biologicals, cat HNM-6021DZ1-5).…”

“…Six- to eight-week-old BALB/cJ mice from the animal facility at Pontificia Universidad Católica de Chile were randomly distributed and harboured in pathogen-free conditions. In order to evaluate the safety and immunogenicity of the rBCG-N-SARS-CoV-2 strain, mice were immunized in a single dose immunization scheme, as was previously reported for other rBGCs [ 45 , 48 ]. Six- to eight-week-old BALB/cJ male mice were vaccinated by subcutaneous (sc) injection with 1 × 10 5 CFU of rBCG-N-SARS-CoV-2, BCG-WT, or 1X PBS used as a vehicle in a final volume of 100 μL per dose.…”