Cytomegalovirus infection and progressive differentiation of effector-memory T cells [version 1; referees: 3 approved]

Primary cytomegalovirus (CMV) infection leads to strong innate and adaptive immune responses against the virus, which prevents serious disease. However, CMV infection can cause serious morbidity and mortality in individuals who are immunocompromised. The adaptive immune response to CMV is characterized by large populations of effector-memory (EM) T cells that are maintained lifelong, a process termed memory inflation. Recent findings indicate that infection with CMV leads to continuous differentiation of CMV-specific EM-like T cells and that high-dose infection accelerates this progression. Whether measures that counteract CMV infection, such as anti-viral drugs, targeting of latently infected cells, adoptive transfer of CMV-specific T cells, and vaccination strategies, are able to impact the progressive differentiation of CMV-specific EM-like cells is discussed

Improved innate and adaptive immunostimulation by genetically modified HIV-1 protein expressing NYVAC vectors

Attenuated poxviruses are safe and capable of expressing foreign antigens. Poxviruses are applied in veterinary vaccination and explored as candidate vaccines for humans. However, poxviruses express multiple genes encoding proteins that interfere with components of the innate and adaptive immune response. This manuscript describes two strategies aimed to improve the immunogenicity of the highly attenuated, host-range restricted poxvirus NYVAC: deletion of the viral gene encoding type-I interferon-binding protein and development of attenuated replication-competent NYVAC. We evaluated these newly generated NYVAC mutants, encoding HIV-1 env, gag, pol and nef, for their ability to stimulate HIV-specific CD8 T-cell responses in vitro from blood mononuclear cells of HIV-infected subjects. The new vectors were evaluated and compared to the parental NYVAC vector in dendritic cells (DCs), RNA expression arrays, HIV gag expression and crosspresentation assays in vitro. Deletion of type-I interferon-binding protein enhanced expression of interferon and interferoninduced genes in DCs, and increased maturation of infected DCs. Restoration of replication competence induced activationof pathways involving antigen processing and presentation. Also, replication-competent NYVAC showed increased Gag expression in infected cells, permitting enhanced cross-presentation to HIV-specific CD8 T cells and proliferation of HIVspecific memory CD8 T-cells in vitro. The recombinant NYVAC combining both modifications induced interferon-induced genes and genes involved in antigen processing and presentation, as well as increased Gag expression. This combined replication-competent NYVAC is a promising candidate for the next generation of HIV vaccines

Improved Innate and Adaptive Immunostimulation by Genetically Modified HIV-1 Protein Expressing NYVAC Vectors.

Attenuated poxviruses are safe and capable of expressing foreign antigens. Poxviruses are applied in veterinary vaccination and explored as candidate vaccines for humans. However, poxviruses express multiple genes encoding proteins that interfere with components of the innate and adaptive immune response. This manuscript describes two strategies aimed to improve the immunogenicity of the highly attenuated, host-range restricted poxvirus NYVAC: deletion of the viral gene encoding type-I interferon-binding protein and development of attenuated replication-competent NYVAC. We evaluated these newly generated NYVAC mutants, encoding HIV-1 env, gag, pol and nef, for their ability to stimulate HIV-specific CD8 T-cell responses in vitro from blood mononuclear cells of HIV-infected subjects. The new vectors were evaluated and compared to the parental NYVAC vector in dendritic cells (DCs), RNA expression arrays, HIV gag expression and cross-presentation assays in vitro. Deletion of type-I interferon-binding protein enhanced expression of interferon and interferon-induced genes in DCs, and increased maturation of infected DCs. Restoration of replication competence induced activation of pathways involving antigen processing and presentation. Also, replication-competent NYVAC showed increased Gag expression in infected cells, permitting enhanced cross-presentation to HIV-specific CD8 T cells and proliferation of HIV-specific memory CD8 T-cells in vitro. The recombinant NYVAC combining both modifications induced interferon-induced genes and genes involved in antigen processing and presentation, as well as increased Gag expression. This combined replication-competent NYVAC is a promising candidate for the next generation of HIV vaccines

Murine cytomegalovirus infection via the intranasal route offers a robust model of immunity upon mucosal CMV infection.

Cytomegalovirus (CMV) is a ubiquitous virus, causing the most common congenital infection in humans, yet a vaccine against this virus is not available. The experimental study of immunity against CMV in animal models of infection, such as the infection of mice with the mouse CMV (MCMV), has relied on systemic intraperitoneal infection protocols, although the infection naturally transmits by mucosal routes via body fluids containing CMV. To characterize the biology of infections by mucosal routes, we have compared the kinetics of virus replication, the latent viral load, and CD8 T cell responses in lymphoid organs upon experimental intranasal and intragastric infection to intraperitoneal infection of two unrelated mouse strains. We have observed that intranasal infection induces robust and persistent virus replication in lungs and salivary glands, but a poor one in the spleen. CD8 T cell responses were somewhat weaker than upon intraperitoneal infection, but showed similar kinetic profiles and phenotypes of antigen-specific cells. On the other hand, intragastric infection resulted in abortive or poor virus replication in all tested organs, and poor T cell responses to the virus, especially at late times after infection. Consistent with the T cell kinetics, the MCMV latent load was high in the lungs, but low in the spleen of intranasally infected mice and lowest in all tested organs upon intragastric infection. In conclusion, we show here that intranasal, but not intragastric infection of mice with MCMV represents a robust model to study short and long-term biology of CMV infection by a mucosal route

The Breadth of Synthetic Long Peptide Vaccine-Induced CD8⁺ T Cell Responses Determines the Efficacy against Mouse Cytomegalovirus Infection

<div><p>There is an ultimate need for efficacious vaccines against human cytomegalovirus (HCMV), which causes severe morbidity and mortality among neonates and immunocompromised individuals. In this study we explored synthetic long peptide (SLP) vaccination as a platform modality to protect against mouse CMV (MCMV) infection in preclinical mouse models. In both C57BL/6 and BALB/c mouse strains, prime-booster vaccination with SLPs containing MHC class I restricted epitopes of MCMV resulted in the induction of strong and polyfunctional (i.e., IFN-γ⁺, TNF⁺, IL-2⁺) CD8⁺ T cell responses, equivalent in magnitude to those induced by the virus itself. SLP vaccination initially led to the formation of effector CD8⁺ T cells (KLRG1^hi, CD44^hi, CD127^lo, CD62L^lo), which eventually converted to a mixed central and effector-memory T cell phenotype. Markedly, the magnitude of the SLP vaccine-induced CD8⁺ T cell response was unrelated to the T cell functional avidity but correlated to the naive CD8⁺ T cell precursor frequency of each epitope. Vaccination with single SLPs displayed various levels of long-term protection against acute MCMV infection, but superior protection occurred after vaccination with a combination of SLPs. This finding underlines the importance of the breadth of the vaccine-induced CD8⁺ T cell response. Thus, SLP-based vaccines could be a potential strategy to prevent CMV-associated disease.</p></div

CMV immune evasion and manipulation of the immune system with aging.

Human cytomegalovirus (HCMV) encodes numerous proteins and microRNAs that function to evade the immune response and allow the virus to replicate and disseminate in the face of a competent innate and acquired immune system. The establishment of a latent infection by CMV, which if completely quiescent at the level of viral gene expression would represent an ultimate in immune evasion strategies, is not sufficient for lifelong persistence and dissemination of the virus. CMV needs to reactivate and replicate in a lytic cycle of infection in order to disseminate further, which occurs in the face of a fully primed secondary immune response. Without reactivation, latency itself would be redundant for the virus. It is also becoming clear that latency is not a totally quiescent state, but is characterized by limited viral gene expression. Therefore, the virus also needs immune evasion strategies during latency. An effective immune response to CMV is required or viral replication will cause morbidity and ultimately mortality in the host. There is clearly a complex balance between virus immune evasion and host immune recognition over a lifetime. This poses the important question of whether long-term evasion or manipulation of the immune response driven by CMV is detrimental to health. In this meeting report, three groups used the murine model of CMV (MCMV) to examine if the contribution of the virus to immune senescence is set by the (i) initial viral inoculum, (ii) inflation of T cell responses, (iii) or the balance between functionally distinct effector CD4+ T cells. The work of other groups studying the CMV response in humans is discussed. Their work asks whether the ability to make immune responses to new antigens is compromised by (i) age and HCMV carriage, (ii) long-term exposure to HCMV giving rise to an overall immunosuppressive environment and increased levels of latent virus, or (iii) adapted virus mutants (used as potential vaccines) that have the capacity to elicit conventional and unconventional T cell responses

Polyfunctional CD4⁺ T Cell Responses to Immunodominant Epitopes Correlate with Disease Activity of Virulent <em>Salmonella</em>

<div><p><em>Salmonella enterica</em> serovars are intracellular bacteria capable of causing typhoid fever and gastroenteritis of significant morbidity and mortality worldwide. Current prophylactic and therapeutic treatment is hampered by the emergence of multidrug-resistant (MDR) strains of <em>Salmonella</em>, and vaccines provide only temporal and partial protection in vaccinees. To develop more effective <em>Salmonella</em> vaccines, it is important to understand the development of protective adaptive immunity to virulent <em>Salmonella</em>. Here we report the identification of novel CD4⁺ T cell peptide epitopes, which are conserved among <em>Salmonella</em> serovars. Immunization of <em>Salmonella</em>-infected mice with these peptide epitopes reduces the burden of <em>Salmonella</em> disease. Furthermore, we show that distinct polyfunctional (interferon-γ⁺, tumor necrosis factor⁺, and interleukin-2⁺) <em>Salmonella</em>-specific CD4⁺ T cell responses develop with respect to magnitude and kinetics. Moreover, we found that CD4⁺ T cell responses against immunodominant epitopes are predictive for active <em>Salmonella</em> disease. Collectively, these data could contribute to improved diagnosis of <em>Salmonella</em>-related diseases and rational design of <em>Salmonella</em> vaccines.</p> </div