Subacute SARS-CoV-2 replication can be controlled in the absence of CD8+ T cells in cynomolgus macaques

Intranasal pediatric parainfluenza virus-vectored SARS-CoV-2 vaccine is protective in monkeys

Pediatric SARS-CoV-2 vaccines are needed that elicit immunity directly in the airways as well as systemically. Building on pediatric parainfluenza virus vaccines in clinical development, we generated a live-attenuated parainfluenza-virus-vectored vaccine candidate expressing SARS-CoV-2 prefusion-stabilized spike (S) protein (B/HPIV3/S-6P) and evaluated its immunogenicity and protective efficacy in rhesus macaques. A single intranasal/intratracheal dose of B/HPIV3/S-6P induced strong S-specific airway mucosal immunoglobulin A (IgA) and IgG responses. High levels of S-specific antibodies were also induced in serum, which efficiently neutralized SARS-CoV-2 variants of concern of alpha, beta, and delta lineages, while their ability to neutralize Omicron sub-lineages was lower. Furthermore, B/HPIV3/S-6P induced robust systemic and pulmonary S-specific CD4+ and CD8+ T cell responses, including tissue-resident memory cells in the lungs. Following challenge, SARS-CoV-2 replication was undetectable in airways and lung tissues of immunized macaques. B/HPIV3/S-6P will be evaluated clinically as pediatric intranasal SARS-CoV-2/parainfluenza virus type 3 vaccine.

Intranasal pediatric parainfluenza virus-vectored SARS-CoV-2 vaccine candidate is protective in macaques

Pediatric SARS-CoV-2 vaccines are needed that elicit immunity directly in the airways, as well as systemically. Building on pediatric parainfluenza virus vaccines in clinical development, we generated a live-attenuated parainfluenza virus-vectored vaccine candidate expressing SARS-CoV-2 prefusion-stabilized spike (S) protein (B/HPIV3/S-6P) and evaluated its immunogenicity and protective efficacy in rhesus macaques. A single intranasal/intratracheal dose of B/HPIV3/S-6P induced strong S-specific airway mucosal IgA and IgG responses. High levels of S-specific antibodies were also induced in serum, which efficiently neutralized SARS-CoV-2 variants of concern. Furthermore, B/HPIV3/S-6P induced robust systemic and pulmonary S-specific CD4+ and CD8+ T-cell responses, including tissue-resident memory cells in lungs. Following challenge, SARS-CoV-2 replication was undetectable in airways and lung tissues of immunized macaques. B/HPIV3/S-6P will be evaluated clinically as pediatric intranasal SARS-CoV-2/parainfluenza virus type 3 vaccine.

Mild SARS-CoV-2 infection in rhesus macaques is associated with viral control prior to antigen-specific T cell responses in tissues

SARS-CoV-2 primarily replicates in mucosal sites, and more information is needed about immune responses in infected tissues. Here, we used rhesus macaques to model protective primary immune responses in tissues during mild COVID-19. Viral RNA levels were highest on days 1-2 post-infection and fell precipitously thereafter. 18F-fluorodeoxyglucose (FDG)-avid lung abnormalities and interferon (IFN)-activated monocytes and macrophages in the bronchoalveolar lavage (BAL) were found on days 3-4 post-infection. Virus-specific effector CD8+ and CD4+ T cells became detectable in the BAL and lung tissue on days 7-10, after viral RNA, radiologic evidence of lung inflammation, and IFN-activated myeloid cells had substantially declined. Notably, SARS-CoV-2-specific T cells were not detectable in the nasal turbinates, salivary glands, and tonsils on day 10 post-infection. Thus, SARS-CoV-2 replication wanes in the lungs of rhesus macaques prior to T cell responses, and in the nasal and oral mucosa despite the apparent lack of antigen-specific T cells, suggesting that innate immunity efficiently restricts viral replication during mild COVID-19.

Neutralizing-antibody-independent SARS-CoV-2 control correlated with intranasal-vaccine-induced CD8+ T cell responses

Effective vaccines are essential for the control of the coronavirus disease 2019 (COVID-19) pandemic. Currently developed vaccines inducing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S)-antigen-specific neutralizing antibodies (NAbs) are effective, but the appearance of NAb-resistant S variant viruses is of great concern. A vaccine inducing S-independent or NAb-independent SARS-CoV-2 control may contribute to containment of these variants. Here, we investigate the efficacy of an intranasal vaccine expressing viral non-S antigens against intranasal SARS-CoV-2 challenge in cynomolgus macaques. Seven vaccinated macaques exhibit significantly reduced viral load in nasopharyngeal swabs on day 2 post-challenge compared with nine unvaccinated controls. The viral control in the absence of SARS-CoV-2-specific NAbs is significantly correlated with vaccine-induced, viral-antigen-specific CD8⁺ T cell responses. Our results indicate that CD8⁺ T cell induction by intranasal vaccination can result in NAb-independent control of SARS-CoV-2 infection, highlighting a potential of vaccine-induced CD8⁺ T cell responses to contribute to COVID-19 containment.

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Anti-SARS-CoV-2 efficacy of an intranasal S-free vaccine is shown in macaques

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The SARS-CoV-2 control is associated with vaccine-induced CD8⁺ T cell responses

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Vaccine induction of CD8⁺ T cells can result in neutralization-free viral control

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Vaccine-induced CD8⁺ T cells may contribute to SARS-CoV-2 variant control