Biota Pharmaceuticals, Inc.

A total of nine unsolicited AEs were reported by six subjects during the active study period (through Day 57). All unsolicited AEs were mild in severity and resolved without the need for medical treatment. Subjects are currently within the safety follow-up period of between four and five months post initial vaccinations. No serious AEs have been reported to date.

The secondary objective of this study was to determine the immunogenicity of the vaccine. The vaccine was immunogenic, and immune responses against SARS-CoV-2 were observed in approximately 85% of subjects. In particular, increases in Th1 cytokines and markers were observed in the T cells that recognize the SARS-CoV-2 S and N proteins in the clinical trial. Cytotoxic T cells, those that express the surface marker CD8, at day eight had a high percentage of cells that made IFNg, TNFa, and/or CD107a in response to stimulation with the S protein, with substantial increases compared to the first day of the study. B cell plasmablasts increased in subjects post immunization, as well as upregulation of the mucosal homing receptor and surface IgA on those B cells in a dose dependent manner. While no neutralizing antibody responses were observed in the serum of subjects, preliminary analysis showed that increases in IgA responses to the S protein, the receptor binding domain, and the N protein could be found in some subjects and several different compartments including nasal and saliva samples. Given the dose dependent manner in which the B cells of interest were activated, future studies of this candidate will focus on dose ranging and boosting to increase the mucosal immune responses to SARS-CoV-2.

SARS-CoV-2 is an RNA virus that naturally evolves genetic mutations over time producing numerous viral variants. Since December of 2019 coordinated global efforts have traced the emergence of SARS-CoV-2 variants, and identified frequent genetic mutations occurring in multiple countries. Viral variants rapidly emerging in many regions of the world, have several genomic changes leading to significant shifts in amino acid sequence and protein structure. During the second half of 2020, three divergent SARS-CoV-2 variants quickly spread through populations in the United Kingdom (B.1.1.7), South Africa (B.1.351) and Brazil (P.1). These particular variants have alterations in key regions of the outer S protein which is utilized by the virus to infect human cells through a receptor called ACE2. Structural changes in the receptor binding portion of the S protein in these variants have been shown to enhanced viral transmission, possibly leading to higher viral loads and worse disease outcomes. Currently, most vaccine strategies under development or approved for emergency use by the FDA, employ the S protein as a vaccine antigen to elicit antibodies responses to block the SARS-CoV-2 virus from entering cells. All existing vaccine formulations comprise of the S protein are derived from the original strain, which may not elicit cross protective antibody responses that block new viral variants from binding to the receptor and entering cells. Recent data from a Johnson & Johnson Phase 3 trial, showed that 28 days after vaccination 66% of participants in Latin America and 57% in South Africa were protected from the circulating strains. The Oxford-AstraZeneca vaccine campaign in Africa has recently been halted due to efficacy being only 25% against the dominant circulating strain. While laboratory experiments indicate that Moderna and Pfizer-BioNTech vaccines are effective against the U.K. variant B.1.1.7, it seems unlikely that substantial cross-protection will extend to P1 or B.1.351 mutants. These results indicate as novel S protein variants continue to emerge current vaccination approaches will need to be updated to offer immune protection against new SARS-CoV-2 mutants.

In order to evaluate efficacy of our COVID-19 vaccine, we conducted a hamster challenge study at Lovelace Biomedical (Albuquerque, NM). Hamsters are a good model of SARS-CoV-2 infection because they can be infected via the intranasal route, and can get clinical symptoms such as weight loss, labored breathing, and ruffled fur. They also get lung problems similar to humans. Microcomputed tomographic imaging of hamsters given SARS-CoV-2 revealed severe lung injury that shared characteristics with SARS-CoV-2−infected human lung, including severe multi-lobular ground glass opacity, and regions of lung consolidation. A study by Janssen reported results showing that their vaccine can prevent disease in the same animal model. 

Our topline results showed that two oral administrations of VXA-CoV2-1 (rAd-S-N) at 1e9 IU could substantially protect hamsters from weight loss associated with infection (Fig. N1A), protect against the lung weight gain associated with lung CoV-2 mediated damage (Fig. N1B), and substantially protect against high viral titers in the lungs five days post challenge (Fig. N1C). Oral vaccination with VXA-CoV2-1 reduced the viral titers in the lungs four to five logs (Fig. N1C). Histopathological comparisons between the lungs of untreated animals and VXA-CoV2-1 oral immunized animals showed substantial differences. All untreated animals had mostly moderate (six of eight animals) to marked (two of eight animals) mixed cell inflammation, minimal (one of eight animals) to moderate (two of eight animals) epithelial hypertrophy/hyperplasia in centriacinar areas, mostly minimal (five of eight animals) to mild (three of eight animals) alveolar hemorrhage, and mild (eight of eight animals) epithelial hypertrophy/hyperplasia in the bronchi. All animals that received two doses of the vaccine VXA-CoV2-1 had minimal mixed cell inflammation. There was no evidence of epithelial hypertrophy/hyperplasia in centriacinar areas, alveolar hemorrhage or epithelial hypertrophy/hyperplasia in the bronchi of these animals. Control vaccination by intranasal (i.n.) delivery of VXA-CoV2-1 also induced a similar level of protection as oral delivery. 

B cell responses. The major goal of vaccination is to induce an immune response that mediates protection from infection or disease. B lymphocytes, also known as B cells, play an important role towards this goal by producing antibodies that can specifically recognize and inhibit infectious agents. B cells can produce antibodies in different forms, each type with distinct characteristics and roles. B cells with the isotype A (“IgA”) antibodies are the ones preferentially secreted at mucosal surfaces, such as the respiratory tract, where they prevent foreign substances from entering the body. The ability of our candidate vaccine to promote specific B cells capable of making high levels of antibodies (called ‘plasmablasts’) was tested using both flow cytometry-based measurements and an antibody-secreting cell (ASC) assay by ELISPOT. Flow cytometry allows measurement of proteins expressed by the cells, either on the surface or inside the cell. We explored immune cell populations in the peripheral blood. This analysis revealed a significant expansion in the overall plasmablast population 8 days after vaccination (p<0.0001, Wilcoxon test) with 69% of vaccinees in this study showing a twofold or higher increase in the frequencies of these antibody-secreting cells when compared to baseline levels (Figures N4A-B). Further investigation indicated upregulation of both IgA and the mucosal homing receptor b7 on the surface of circulating plasmablasts post vaccination, particularly in the higher dose cohort (p=0.0261, Mann-Whitney test), thus suggesting vaccine-induced migration of this IgA-producing B cell population to mucosal tissues (Figure N4c). Contextually, the ELISPOT assay also confirmed a strong production of IgA-secreting ASC on day 8 after vaccination (fourfold median increase over day 1 levels), additionally highlighting the ability for these cells to recognize and bind the S1 domain of the SARS-CoV-2 S protein (Figure N4d).

Antibody Responses.  Serum samples were measured for neutralizing antibodies. No neutralizing antibodies were found in the serum at day 29 (and day 56 for the five subjects given two low doses). Increases in IgG responses were measured in the serum of only a few subjects. Local immune responses at the site of infection are of particular interest due to their ability to block viral entry, and IgA is considered to be the first line of defense at most mucosal tissues. To measure the immune response in the mucosa, nasal and saliva samples were taken. Sera samples were taken as well, as serum can also contain IgA. Levels of IgA antibodies were measured using a multiplex assay on the Meso Scale Discovery platform that measures antibodies to SARS-CoV-2 S protein, N protein and the Spike Receptor Binding Domain (“RBD”). This platform allows capture of antibodies specific for multiple antigens at once using a lower sample volume than a traditional ELISA format. In a preliminary analysis, a twofold or more increase above pre-vaccination samples in SARS-CoV-2 specific IgA found in the various compartments was detected in 18 of 35 subjects (52%) 29 days post vaccination. 11 of 35 (32%) had a twofold or above response to S protein, 13 of 35 (37%) had a twofold or above response to N protein, 16 of 35 (46%) had a twofold or above response to RBD, with 14 of 35 (40%) having a twofold or above response to two or more antigens. In Cohort 1, where subjects had two doses, four of five (80%) had SARS-CoV-2 IgA responses twofold or above and five of five (100%) had responses 1.5-fold or above in one or more compartments. These results include all subjects. Because samples that may lack any IgA in them are unlikely to show specific antibody responses, future work will normalize samples by the total amount of IgA and discard samples without any IgA from the analysis.