Protective MCMV immunity by vaccination of the salivary gland via Wharton's duct: replication-deficient recombinant adenovirus expressing individual MCMV genes elicits protection similar to that of MCMV

Spatial kinetics and immune control of murine cytomegalovirus infection in the salivary glands

Human cytomegalovirus (HCMV) is the most common congenital infection. Several HCMV vaccines are in development, but none have yet been approved. An understanding of the kinetics of CMV replication and transmission may inform the rational design of vaccines to prevent this infection. The salivary glands (SG) are an important site of sustained CMV replication following primary infection and during viral reactivation from latency. As such, the strength of the immune response in the SG likely influences viral dissemination within and between hosts. To study the relationship between the immune response and viral replication in the SG, and viral dissemination from the SG to other tissues, mice were infected with low doses of murine CMV (MCMV). Following intra-SG inoculation, we characterized the viral and immunological dynamics in the SG, blood, and spleen, and identified organ-specific immune correlates of protection. Using these data, we constructed compartmental mathematical models of MCMV infection. Model fitting to data and analysis indicate the importance of cellular immune responses in different organs and point to a threshold of infection within the SG necessary for the establishment and spread of infection.

Systemic immune response development in Albino rats after retrograde instillation of COVID-19 vaccine to submandibular salivary gland: An experimental study

Objective

This study aimed to investigate whether using the submandibular gland duct (SMD) as an alternative mucosal route for vaccine administration induced anti-COVID-19 specific immunity.

Material and methods

Forty rats were randomized equally into four groups; Group I: Rats did not receive any intervention. Group II: Rats were subjected to intramuscular (IM) injection of COVID-19 vaccine. Group III: Rats were subjected to ductal cannulation by retrograde instillation of sterile saline into right SMD. Group IV: Rats in this group who had 0.5 ml of COVID-19 vaccine retrogradely injected into the right SMD. Subsequently, rats were examined for anti-COVID-19 specific antibodies (IgG). Also, light microscopic observation of glandular changes and immunohistochemical staining for CD20 was performed.

Results

The obtained results demonstrated a significant increase in anti-COVID-19 IgG levels in all rats vaccinated via intraductal immunization (group IV) compared to group II. Histologically, ectopic follicles were found within the glandular lobules of the inoculated submandibular gland (SMG) in group IV. In addition, the nearby lymph node in group IV demonstrated reactive follicle characteristics in the form of activated secondary follicles with germinal centers (GCs). Immunohistochemically, CD20 was localized in group IV in GCs of the ectopic lymphoid tissue and the nearby lymph nodes while group I, group II, and III demonstrated negative immunoreactivity.

Conclusion

The immune response demonstrated by intraductal SG immunization is generally more significant than that elicited by IM inoculation of the same vaccine.

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Salivary gland intraductal vaccination developed a systemic immune response.

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High antibody levels are obtained via salivary glands intraductal vaccination.

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Salivary glands are a potential mucosal route for administering vaccines.

SARS-CoV-2 Antibodies Are Persisting in Saliva for More Than 15 Months After Infection and Become Strongly Boosted After Vaccination

SARS-CoV-2 antibodies in saliva serve as first line of defense against the virus. They are present in the mucosa, more precisely in saliva, after a recovered infection and also following vaccination. We report here the antibody persistence in plasma and in saliva up to 15 months after mild COVID-19. The IgG antibody response was measured every two months in 72 participants using an established and validated in-house ELISA assay. In addition, the virus inhibitory activity of plasma antibodies was assessed in a surrogate virus neutralization test before and after vaccination. SARS-CoV-2-specific antibody concentrations remained stable in plasma and saliva and the response was strongly boosted after one dose COVID-19 vaccination.

Inhibitory Molecules PD-1, CD73 and CD39 Are Expressed by CD8+ T Cells in a Tissue-Dependent Manner and Can Inhibit T Cell Responses to Stimulation

The salivary gland is an important tissue for persistence and transmission of multiple viruses. Previous work showed that salivary gland tissue-resident CD8⁺ T cells elicited by viruses were poorly functional ex vivo. Using a model of persistent murine cytomegalovirus (MCMV) infection, we now show that CD8⁺ T cells in the salivary gland and other non-lymphoid tissues of mice express multiple molecules associated with T cell exhaustion including PD-1, CD73 and CD39. Strikingly however, these molecules were expressed independently of virus or antigen. Rather, PD-1-expressing T cells remained PD-1⁺ after migration into tissues regardless of infection, while CD73 was activated on CD8⁺ T cells by TGF-β signaling. Blockade of PD-L1, but not CD73, improved cytokine production by salivary gland T cells ex vivo and increased the expression of granzyme B after stimulation within the salivary gland. Nevertheless, salivary-gland localized CD8⁺ T cells could kill PD-L1-expressing targets in vivo, albeit with modest efficiency, and this was not improved by PD-L1 blockade. Moreover, the impact of PD-L1 blockade on granzyme B expression waned with time. In contrast, the function of kidney-localized T cells was improved by CD73 blockade, but was unaffected by PD-L1 blockade. These data show that tissue localization per se is associated with expression of inhibitory molecules that can impact T cell function, but that the functional impact of this expression is context- and tissue-dependent.

Modeling Human Cytomegalovirus in Humanized Mice for Vaccine Testing

Human cytomegalovirus (HCMV or HHV-5) is a globally spread pathogen with strictly human tropism that establishes a life-long persistence. After primary infection, high levels of long-term T and B cell responses are elicited, but the virus is not cleared. HCMV persists mainly in hematopoietic reservoirs, whereby occasional viral reactivation and spread are well controlled in immunocompetent hosts. However, when the immune system cannot control viral infections or reactivations, such as with newborns, patients with immune deficiencies, or immune-compromised patients after transplantations, the lytic outbursts can be severely debilitating or lethal. The development of vaccines for immunization of immune-compromised hosts has been challenging. Several vaccine candidates did not reach the potency expected in clinical trials and were not approved. Before anti-HCMV vaccines can be tested pre-clinically in immune-compromised hosts, reliable in vivo models recapitulating HCMV infection might accelerate their clinical translation. Therefore, immune-deficient mouse strains implanted with human cells and tissues and developing a human immune system (HIS) are being explored to test anti-HCMV vaccines. HIS-mice resemble immune-compromised hosts as they are equipped with antiviral human T and B cells, but the immune reactivity is overall low. Several groups have independently shown that HCMV infections and reactivations can be mirrored in HIS mice. However, these models and the analyses employed varied widely. The path forward is to improve human immune reconstitution and standardize the analyses of adaptive responses so that HIS models can be forthrightly used for testing novel generations of anti-HCMV vaccines in the preclinical pipeline.

Salivary gland immunization via Wharton's duct activates differential T-cell responses within the salivary gland immune system

Salivary glands are a major component of the mucosal immune system that confer adaptive immunity to mucosal pathogens. As previously demonstrated, immunization of the submandibular gland with tissue culture-derived murine cytomegalovirus (tcMCMV) or replication-deficient adenoviruses expressing individual murine cytomegalovirus (MCMV) genes protected mice against a lethal MCMV challenge. Here, we report that salivary gland inoculation of BALB/cByJ mice with tcMCMV or recombinant adenoviruses differentially activates T helper (Th)1, -2, and -17 cells in the salivary glands vs. the associated lymph nodes. After inoculation with tcMCMV, lymphocytes from the submandibular gland preferentially express the transcription factor T-cell-specific T-box transcription factor (T-bet), which controls the expression of the hallmark Th1 cytokine, IFN-γ. Lymphocytes from the periglandular lymph nodes (PGLNs) express both T-bet and GATA-binding protein 3 (GATA3), which promotes the secretion of IL-4, -5, and -10 from Th2 cells. In contrast, after inoculation with replication-deficient adenoviruses, lymphocytes from the submandibular gland express T-bet, GATA3, and RAR-related orphan receptor γ, thymus-specific isoform (RORγt) (required for differentiation of Th17 cells) and forkhead box P3 (Foxp3) (required for the differentiation of regulatory T cells). Lymphocytes from the PGLNs were not activated. The differential induction of Th responses in the salivary gland vs. the PGLNs after inoculation with attenuated virus vs. a nominal protein antigen supports the use of the salivary as an alternative mucosal route for administering vaccines.-Liu, G., Zhang, F., Wang, R., London, S. D., London, L. Salivary gland immunization via Wharton's duct activates differential T-cell responses within the salivary gland immune system.

The salivary gland as a target for enhancing immunization response

Background

An organism’s immune response to a vaccine is dependent on a number of factors, including the site of immunization. While muscle is the most common site for vaccine administration, other sites, including the salivary gland, are poised to confer stronger and broader immunoprotection.

Findings

Studies exploring the salivary gland as an immunization site have involved protein antigens, as well as live pathogens and DNA vaccines. While intraductal instillation of protein antigens into the salivary gland may result in a relatively transient increase in antibody production, DNA or attenuated pathogen vaccination appear to confer a lasting widespread mucosal immune response that includes robust salivary and enteric IgA, as well as high levels of circulating IgG. Furthermore, vaginal and lung antibodies are also seen. For enteric pathogens, a common class of pathogen encountered by travelers, this type of immune response provides for a level of redundant protection against foreign microbes with mucosal targets.

Conclusion

The strength of immune response conferred by salivary gland vaccination is generally stronger than that seen in response to the same vaccine at a comparison site. For example, where other routes fail, immunization of the salivary gland has been shown to confer protection in lethal challenge models of infectious pathogens. A host of vaccines currently under development suffer from immunogenicity challenges, adding to the widespread interest and search for novel routes and adjuvants. With its capability to facilitate a strong and broad immune response, the salivary gland warrants consideration as an immunization site, especially for vaccines with immunogenicity challenges, as well as vaccines that would benefit from combined systemic and mucosal immunity.

The Cellular Localization of Human Cytomegalovirus Glycoprotein Expression Greatly Influences the Frequency and Functional Phenotype of Specific CD4+ T Cell Responses

CMV infection is a significant cause of morbidity and mortality in immunocompromised individuals, and the development of a vaccine is of high priority. Glycoprotein B (gB) is a leading vaccine candidate but the glycoprotein H (gH) pentameric complex is now recognized as the major target for neutralizing Abs. However, little is known about the T cell immune response against gH and glycoprotein L (gL) and this is likely to be an important attribute for vaccine immunogenicity. In this study, we examine and contrast the magnitude and phenotype of the T cell immune response against gB, gH, and gL within healthy donors. gB-specific CD4(+) T cells were found in 95% of donors, and 29 epitopes were defined with gB-specific response sizes ranging from 0.02 to 2.88% of the CD4(+) T cell pool. In contrast, only 20% of donors exhibited a T cell response against gH or gL. Additionally, gB-specific CD4(+) T cells exhibited a more cytotoxic phenotype, with high levels of granzyme B expression. Glycoproteins were effectively presented following delivery to APCs but only gB-derived epitopes were presented following endogenous synthesis. gB expression was observed exclusively within vesicular structures colocalizing with HLA-DM whereas gH was distributed evenly throughout the cytoplasm. Grafting of the C-terminal domain from gB onto gH could not transfer this pattern of presentation. These results reveal that gB is a uniquely immunogenic CMV glycoprotein and this is likely to reflect its unique pattern of endogenous Ag presentation. Consideration may be required toward mechanisms that boost cellular immunity to gH and gL within future subunit vaccines.

Animal models of human cytomegalovirus congenital infection

Human cytomegalovirus (HCMV) infection is highly species-specific, which means that it is unable to productively infect laboratory animals. Despite this caveat, studies of animal CMV counterparts in their natural hosts have revealed significant correlations with observed neuropathological effects of congenital HCMV infection and have improved our understanding of host responses to vaccination. The biological relatedness between human and animal CMVs has been confirmed by phylogenetic analyses; the conservation of ‘core' genes that are essential for virus replication as well as genes that contribute similar mechanisms for virus persistence in their respective host species. The common animal models of HCMV congenital infection include Rhesus CMV (RhCMV), guinea-pig CMV (GPCMV) and mouse CMV (MCMV). Whilst animal models of CMV do not fully recapitulate HCMV infection, they each offer specific advantages in understanding HCMV congenital/perinatal infection (summarised in Table 1).