Adenovirus-vectored SARS-CoV-2 vaccine expressing S1-N fusion protein

Abstract

Background Additional COVID-19 vaccines that are safe, easy to manufacture, and immunogenic are needed for global vaccine equity. Methods Here, we developed a recombinant type 5 adenovirus vector encoding for the SARS-CoV-2 S1 subunit antigen and nucleocapsid as a fusion protein (Ad5.SARS-CoV-2-S1N) delivered to BALB/c mice through multiple vaccine administration routes. Results A single subcutaneous (S.C.) immunization with Ad5.SARS-CoV-2-S1N induced a similar humoral response, along with a significantly higher S1-specific cellular response, as a recombinant type 5 adenovirus vector encoding for S1 alone (Ad5.SARS-CoV-2-S1). Immunogenicity was improved by homologous prime boost strategies, using either S.C. or intranasal (I.N.) delivery of Ad5.SARS-CoV-2-S1N, and further improved through heterologous prime boost, with traditional intramuscular (I.M.) injection, using subunit recombinant S1 protein. Priming with low dose (1x1010 v.p.) of Ad5.SARS-CoV-2-S1N and boosting with either wildtype recombinant rS1 or B.1.351 recombinant rS1 induced a robust neutralizing response, that was sustained against immune evasive Beta and Gamma SARS-CoV-2 variants, along with a long-lived plasma cell response in the bone marrow 29 weeks post vaccination. Conclusion This novel Ad5-vectored SARS-CoV-2 vaccine candidate showed promising immunogenicity in mice and supports the further development of COVID-19 based vaccines incorporating the nucleoprotein as a target antigen.

Trivalent SARS-CoV-2 S1 Subunit Protein Vaccination Induces Broad Humoral Responses in BALB/c Mice

“…Protein subunit vaccine approaches against COVID-19 are highly favorable for worldwide equitable distribution due to their low cost per dose, relative thermostability, and excellent safety profile [ 22 , 23 , 24 , 25 ]. Our previously published reports on vaccines against SARS-CoV-1, Middle-East respiratory syndrome coronavirus (MERS-CoV), and SARS-CoV-2 have demonstrated the ability of S1 subunit targeting vaccines to generate neutralizing antibody responses against Beta coronaviruses [ 26 , 27 , 28 , 29 , 30 ].…”

Tetravalent SARS-CoV-2 S1 Subunit Protein Vaccination Elicits Robust Humoral and Cellular Immune Responses in SIV-Infected Rhesus Macaque Controllers

“…Antigen-specific T-cell responses in the PBMC’s of RMs immunized as described above were analyzed after immunization by flow cytometry, adhering to the recently published guidelines. 21,82 PBMCs collected prior to immunization and on Day 42 post prime immunization were stimulated with PepTivator SARS-CoV-2-S1 (a pool of S1 MHC class I– and MHC class II– restricted peptides) overnight in the presence of protein transport inhibitors (Golgi Stop) for the last 4 hours. Unstimulated cells were used as negative controls.…”

“…RMs were also bled and serially euthanized after week 9 post-prime vaccination: on day 0 (RM177), 1 (RM175), 6 (RM176), 8 (RM101), and 15 (RM175). PMBC's from RMs were collected and analyzed on Days -1, 3,7,10,14,21,24,28,31,35,42,49, and 64 days post prime immunization. RMs were maintained under specific pathogen-free conditions at the University of Pittsburgh, and all experiments were conducted in accordance with animal use guidelines and…”

“…Antigen-specific T-cell responses in the PBMC's of RMs immunized as described above were analyzed after immunization by flow cytometry, adhering to the recently published guidelines. 21,82…”

“…[13][14][15][16][17] We have previously demonstrated the immunogenicity of S1 subunit targeting vaccines against various Beta-coronaviruses including SARS-CoV-1, SARS-CoV-2, and MERS. [18][19][20][21][22][23] A focus for next-generation SARS-CoV-2 vaccine design is the investigation of novel vaccines which may be able to induce a broader immune response effective against multiple SARS-CoV-2 variants. A multivalent vaccine is a traditional approach used to increase antigen immunity coverage against multi-variant viruses such as SARS-CoV-2.…”