Memory Recall Responses Research Articles

Adaptive features of innate immune cells and their relevance to graft rejection.

Allograft rejection involves both innate and adaptive immune cells, and the adaptive immune cells have dominated transplant studies for decades. Recent studies have identified surprising new features for the innate immune cells, including memory recall responses, which may have significant implications in further improvement of transplant outcomes. Transplant survival is excellent in the short-term, but the long-term graft outcomes are not so, and most grafts are continuously lost to chronic rejection in the clinic. In both animal models and clinical settings, graft loss to chronic rejection is often dominated by innate immune cells, especially macrophages and natural killer (NK) cells in the grafts. Recent studies suggest that innate immune cells can acquire features of adaptive cells in that they either directly sense allogeneic nonself or become 'trained' in the allogeneic milieu, where they show features of memory recall responses. In certain models, targeting the adaptive features of such innate immune cells can promote long-term allograft survival. These findings may open new therapeutic opportunities in promoting transplant survival in the clinic. The discovery of donor specificity and memory recall responses of certain innate immune cells, which are prominently featured in chronic allograft rejection, may open novel therapeutic opportunities in transplantation, as well as in treatment of cancers and autoimmune diseases.

“America First, the Netherlands Second” on YouTube: “spoofing” destination marketing with political satire

This study attempts to provide first tentative insights into the audience reception of intertwining of political satire and destination marketing imagery by analysing the “America First, the Netherlands Second” video and a student sample audience response. In 2017, a series of YouTube videos named “America First” went viral. The video that started the viral phenomenon was “America First, the Netherlands Second”, responding in a satirical manner to the “America First” message of the inaugural speech of U.S. president Donald J. Trump. They reached extreme popularity both in number of views and in number of new memetic videos with similar satirical messages. These videos were a form of political expression and at first sight did not seem to have much in common with communication in tourism. However, the videos included typical destination marketing imagery, intertwined with satirical representations and thus representing a humorous “spoof” on destination marketing. Currently, not much is known on how political satire affects the process of destination image formation. The study analyses participants’ memory recall, eye-tracking movements and focus group responses in order to provide first conclusions on how the audiences respond to intertwining of satirical political expression and destination marketing imagery

T cell-selective deletion of Oct1 protects animals from autoimmune neuroinflammation while maintaining neurotropic pathogen response

BackgroundTreatments for autoimmune diseases aim to dampen autoreactivity while preserving normal immune function. In CD4+ T cells, the transcription factor Oct1/Pou2f1 is a dispensable transcription factor for T cell development and response to primary infection, but promotes expression of target genes, including Il2 and Ifng, under conditions of antigen reencounter. As a result, they are more strongly expressed upon secondary stimulation. Such repeated antigen encounters occur in memory recall responses, in autoimmunity where self-antigen can be recognized multiple times, and in chronic infection where foreign antigen is persistent. Based on these previous findings, we hypothesized that Oct1 loss would protect animals from autoimmunity but maintain normal responses to pathogens in the CNS.ObjectiveWe used a conditional mouse Oct1 (Pou2f1) allele and a CD4-Cre driver to determine the effect of T cell-specific Oct1 loss on autoimmune- and viral-induced neuroinflammation using an autoantigen-driven EAE model of autoimmunity and a JHMV model of viral infection.ResultsOct1 conditional deletion mitigated clinical scores and reduced infiltrating T cells and cytokine production in the EAE model. Consistently, Oct1-deficient CD4+ T cells stimulated in vitro showed increased expression of markers associated with T cell anergy, particularly in the absence of co-stimulatory signals. In contrast, anti-viral T cell effector functions are intact in the absence of Oct1, with no changes in neuroinflammation, infiltrating T cells or cytokine production.ConclusionOur findings uncover a significant difference between the effect of Oct1 loss on autoimmune and anti-pathogen responses, which potentially could be exploited for therapeutic benefit.

Requirement for memory B-cell activation in protection from heterologous influenza virus reinfection

While two memory compartments, memory B cells and long-lived plasma cells, are thought to contribute to the successful establishment of memory recall responses, the unique roles of each cellular compartment are still unclear. Herein, by tracing influenza anti-hemagglutinin (HA)-specific antibodies in mice, we demonstrate that pre-existing antibodies secreted by long-lived plasma cells are essential for protection from reinfection with the same influenza virus, whereas protection from secondary infection with an antigenically distinct influenza virus requires memory B-cell activation. These activated memory B cells were largely specific for the conserved HA stem region, and generated sufficient levels of antibodies for protection from heterologous reinfection. Given that the anti-stem plasmablasts derived from the memory B cells were higher affinity than those from naive B cells, our results suggest that maturation of anti-stem memory B cells during primary influenza infection and their subsequent activation are required for protection from reinfection by mutant viruses.

Helios deletion in CD4+T cells induces pTregs that inhibit memory recall responses

Abstract The transcription factor Helios is required for the maintenance of the suppressive phenotype of Foxp3+ regulatory T cells (Tregs) as evidenced by the spontaneous autoimmune activation that develops in mice with a Foxp3− specific Helios deficiency. Helios is also upregulated in a subset of activated CD4+Foxp3−T conventional (Tconv) cells, but its role in Tconv cells remains unknown. Mice with a CD4-Cre driven Helios deletion do not exhibit autoimmunity despite the defect in the suppressor function of their Treg population, pointing to a requisite function of Helios in the activation of Tconv cells in response to antigen. We examined the capacity of Helios-deficient, naïve Tconv cells to respond to their cognate antigen in vivo and found that Helios was not required for proliferation, differentiation into helper subsets, or the production of effector cytokines. Unexpectedly, we observed that Helios deficiency increased the susceptibility of naïve T cells to differentiate into pTregs under inflammatory conditions. These pTregs were then subsequently able to suppress the reactivation of memory T cells in an antigen-specific manner upon challenge with antigen. These findings suggest that increased pTreg differentiation in the periphery in mice with a CD4-Cre driven Helios deletion may prevent the development of autoimmunity normally associated with Helios-deficient Tregs.

CD8+ T cell exhaustion.

CD8+ T cells are important for the protective immunity against intracellular pathogens and tumor. In the case of chronic infection or cancer, CD8+ T cells are exposed to persistent antigen and/or inflammatory signals. This excessive amount of signals often leads CD8+ T cells to gradual deterioration of T cell function, a state called "exhaustion." Exhausted T cells are characterized by progressive loss of effector functions (cytokine production and killing function), expression of multiple inhibitory receptors (such as PD-1 and LAG3), dysregulated metabolism, poor memory recall response, and homeostatic proliferation. These altered functions are closely related with altered transcriptional program and epigenetic landscape that clearly distinguish exhausted T cells from normal effector and memory T cells. T cell exhaustion is often associated with inefficient control of persisting infections and cancers, but re-invigoration of exhausted T cells with inhibitory receptor blockade can promote improved immunity and disease outcome. Accumulating evidences support the therapeutic potential of targeting exhausted T cells. However, exhausted T cells comprise heterogenous cell population with distinct responsiveness to intervention. Understanding molecular mechanism of T cell exhaustion is essential to establish rational immunotherapeutic interventions.

The transcription factor c-Myb regulates CD8+ T cell stemness and antitumor immunity

Stem cells are maintained by transcriptional programs that promote self-renewal and repress differentiation. Here we found that the transcription factor c-Myb was essential for generating and maintaining stem cells within the CD8+ T cell memory compartment. Following viral infection, CD8+ T cells lacking Myb underwent terminal differentiation and generated fewer stem cell–like central memory cells than Myb-sufficient T cells. c-Myb acted both as a transcriptional activator of Tcf7 (which encodes the transcription factor Tcf1) to enhance memory development and as a repressor of Zeb2 (which encodes the transcription factor Zeb2) to hinder effector differentiation. Domain-mutagenesis experiments revealed that the transactivation domain of c-Myb was necessary for restraining differentiation, whereas its negative regulatory domain was critical for cell survival. Myb overexpression enhanced CD8+ T cell memory formation, polyfunctionality and recall responses that promoted curative antitumor immunity upon adoptive transfer. These findings identify c-Myb as a pivotal regulator of CD8+ T cell stemness and highlight its therapeutic potential.

Intra-seasonal antibody repertoire analysis of a subject immunized with an MF59®-adjuvanted pandemic 2009 H1N1 vaccine

During the height of the 2009 H1N1 swine-derived influenza pandemic, a clinical trial was conducted in which seven subjects were immunized using a monovalent, MF59®-adjuvanted vaccine, developed from an egg-passaged candidate vaccine virus (CVV), A/California/07/2009 X-181. Whole blood was collected prior to immunization and at 8, 22, and 202 days post-vaccination, and subjects’ serological responses were evaluated. Here, we reconstruct and examine the longitudinal, influenza-specific circulating B cell repertoire of one subject in that study. Genotypic analysis of 390 total subject-derived antibodies (Abs) revealed a total of 29 germline genes in use among immunoglobulin heavy chain variable regions (IgHV), with the majority of those sequences isolated representing memory recall responses and two major lineages dominating the early response. In vitro phenotyping showed a diverse set of binding epitopes on the surface glycoproteins hemagglutinin (HA) and neuraminidase (NA), many of which are considered subdominant. Strong correlations were found between IgHV germline usage among non-related lineages and both binding epitope and neutralization breadth. Results here highlight the potential for Ab responses to be misdirected to egg-adaptive artifacts on CVVs while simultaneously stressing the ability to mount potent, broadly neutralizing responses to mostly novel antigens via recall of subdominant memory responses, as well as the need for evaluating alternative endpoint assays and anti-NA responses following clinical trials.

Therapeutic blockade of CD3-mediated signaling ameliorates memory Th2-driven allergic asthma

Abstract Allergic asthma is an inflammatory disease of the lungs characterized by Type 2 helper T cell (Th2)-driven immune responses to inhaled allergens. Memory Th2 cells are a major driving force behind asthma, secreting cytokines like IL-4, IL-5, and IL-13 as well as persisting in the host long after allergen encounter. The selective removal of pre-existing memory Th2 cells could be a key process resulting in enhanced tolerance. One such method could involve targeting CD3 through the use of monoclonal anti-CD3 antibodies, which have been shown to successfully induce tolerance in animal models of autoimmune diseases and have also shown promise in clinical trials. We tested blocking CD3 complex signaling in a HDM model of allergic inflammation, to determine if we could induce airway tolerance. Importantly, pre-sensitized C57BL/6J mice displayed strongly ablated lung inflammation and Th2 responses when treated at the time of memory T cell reactivation with F(ab′)2 anti-CD3 antibody. This treatment was found to specifically inhibit HDM-specific CD4+ T cell proliferation and Th2 cytokine production. Interestingly, mice treated with anti-CD3 also showed an increased frequency of Treg cells, improving the Treg:Th2 cell ratio in favor of airway tolerance. Additionally, a significant reduction in airway inflammation and Th2 responses was maintained with therapeutic anti-CD3 antibody even when given several months later during a further memory T cell recall response to allergen. These data suggest that blocking signaling mediated by the CD3 complex could be employed to inhibit memory recall responses to complex allergens thus promoting airway tolerance.

IL-2 producing and non-producing effector CD8 T cells phenotypically and transcriptionally coalesce to form memory subsets with similar protective properties.

Abstract Interleukin-2 (IL-2) acts as a differentiation factor that drives effector CD8 T cell formation and also programs robust memory recall responses. However, the roles of intrinsic IL-2 production in shaping effector and memory CD8 T cell differentiation remain uncertain. To address this, we utilized novel IL-2 and IFN-γ double cytokine reporter systems to trace the cytokine production profiles and fate decisions of effector and memory virus-specific CD8 T cells. Notably, effector and memory CD8 T cells segregate into populations that co-produce IL-2 and IFN-γ or populations that produce only IFN-γ. IL-2-producing effector CD8 T cells preferentially survive and develop memory traits, including the ability to mount protective recall responses. These cells also display transcriptional profiles more closely associated with memory formation. Additionally, cells that produce IL-2 appear refractory to signaling by IL-2 through their STAT5 pathways, which potentially directs their developmental choices. These data illustrate that the intrinsic ability of effector CD8 T cells to produce IL-2 can dictate their sensitivity to the cytokine milieu, predict their developmental fates, and forecast their ability to mount vigorous secondary responses, resist exhaustion, and protect the host. Despite having distinct properties during the effector phase of the response, IL-2-producing and non-producing CD8 T cells transcriptionally and phenotypically coalesce as memory matures to form subsets which respond similarly to secondary lymphocytic choriomeningitis virus challenge. Thus once memory is established, robust secondary responses are not limited to polyfunctional IL-2-producing virus-specific CD8 T cells.

T cell subtypes and reciprocal inflammatory mediator expression differentiate P. falciparum memory recall responses in asymptomatic and symptomatic malaria patients in southeastern Haiti

Asymptomatic Plasmodium falciparum infection is responsible for maintaining malarial disease within human populations in low transmission countries such as Haiti. Investigating differential host immune responses to the parasite as a potential underlying mechanism could help provide insight into this highly complex phenomenon and possibly identify asymptomatic individuals. We performed a cross-sectional analysis of individuals who were diagnosed with malaria in Sud-Est, Haiti by comparing the cellular and humoral responses of both symptomatic and asymptomatic subjects. Plasma samples were analyzed with a P. falciparum protein microarray, which demonstrated serologic reactivity to 3,877 P. falciparum proteins of known serologic reactivity; however, no antigen-antibody reactions delineating asymptomatics from symptomatics were identified. In contrast, differences in cellular responses were observed. Flow cytometric analysis of patient peripheral blood mononuclear cells co-cultured with P. falciparum infected erythrocytes demonstrated a statistically significant increase in the proportion of T regulatory cells (CD4+ CD25+ CD127-), and increases in unique populations of both NKT-like cells (CD3+ CD8+ CD56+) and CD8mid T cells in asymptomatics compared to symptomatics. Also, CD38+/HLA-DR+ expression on γδ T cells, CD8mid (CD56-) T cells, and CD8mid CD56+ NKT-like cells decreased upon exposure to infected erythrocytes in both groups. Cytometric bead analysis of the co-culture supernatants demonstrated an upregulation of monocyte-activating chemokines/cytokines in asymptomatics, while immunomodulatory soluble factors were elevated in symptomatics. Principal component analysis of these expression values revealed a distinct clustering of individual responses within their respective phenotypic groups. This is the first comprehensive investigation of immune responses to P. falciparum in Haiti, and describes unique cell-mediated immune repertoires that delineate individuals into asymptomatic and symptomatic phenotypes. Future investigations using large scale biological data sets analyzing multiple components of adaptive immunity, could collectively define which cellular responses and molecular correlates of disease outcome are malaria region specific, and which are truly generalizable features of asymptomatic Plasmodium immunity, a research goal of critical priority.

In Vivo Expansion of Melanoma-Specific T Cells Using Microneedle Arrays Coated with Immune-Polyelectrolyte Multilayers.

Microneedles (MNs) are micron-scale polymeric or metallic structures that offer distinct advantages for vaccines by efficiently targeting skin-resident immune cells, eliminating injection-associated pain, and improving patient compliance. These advantages, along with recent studies showing therapeutic benefits achieved using traditional intradermal injections in human cancer patients, suggest MN delivery might enhance cancer vaccines and immunotherapies. We recently developed a new class of polyelectrolyte multilayers based on the self-assembly of model peptide antigens and molecular toll-like receptor agonists (TLRa) into ultrathin, conformal coatings. Here, we reasoned that these immune polyelectrolyte multilayers (iPEMs) might be a useful platform for assembling cancer vaccine components on MN arrays for intradermal delivery from these substrates. Using conserved human melanoma antigens and a potent TLRa vaccine adjuvant, CpG, we show that iPEMs can be assembled on MNs in an automated fashion. These films, prepared with up to 128 layers, are approximately 200 nm thick but provide cancer vaccine cargo loading >225 μg/cm2. In cell culture, iPEM cargo released from MNs is internalized by primary dendritic cells, promotes activation of these cells, and expands T cells during coculture. In mice, application of iPEM-coated MNs results in the codelivery of tumor antigen and CpG through the skin, expanding tumor-specific T cells during initial MN applications and resulting in larger memory recall responses during a subsequent booster MN application. This study support MNs coated with PEMs built from tumor vaccine components as a well-defined, modular system for generating tumor-specific immune responses, enabling new approaches that can be explored in combination with checkpoint blockade or other combination cancer therapies.

Assembly and Immunological Processing of Polyelectrolyte Multilayers Composed of Antigens and Adjuvants.

While biomaterials provide a platform to control the delivery of vaccines, the recently discovered intrinsic inflammatory characteristics of many polymeric carriers can also complicate rational design because the carrier itself can alter the response to other vaccine components. To address this challenge, we recently developed immune-polyelectrolyte multilayer (iPEMs) capsules electrostatically assembled entirely from peptide antigen and molecular adjuvants. Here, we use iPEMs built from SIINFEKL model antigen and polyIC, a stimulatory toll-like receptor agonist, to investigate the impact of pH on iPEM assembly, the processing and interactions of each iPEM component with primary immune cells, and the role of these interactions during antigen-specific T cell responses in coculture and mice. We discovered that iPEM assembly is pH dependent with respect to both the antigen and adjuvant component. Controlling the pH also allows tuning of the relative loading of SIINFEKL and polyIC in iPEM capsules. During in vitro studies with primary dendritic cells (DCs), iPEM capsules ensure that greater than 95% of cells containing at least one signal (i.e., antigen, adjuvant) also contained the other signal. This codelivery leads to DC maturation and SIINFEKL presentation via the MHC-I antigen presentation pathway, resulting in antigen-specific T cell proliferation and pro-inflammatory cytokine secretion. In mice, iPEM capsules potently expand antigen-specific T cells compared with equivalent admixed formulations. Of note, these enhancements become more pronounced with successive booster injections, suggesting that iPEMs functionally improve memory recall response. Together our results reveal some of the features that can be tuned to modulate the properties of iPEM capsules, and how these modular vaccine structures can be used to enhance interactions with immune cells in vitro and in mice.

A Single Human Papillomavirus Vaccine Dose Improves B Cell Memory in Previously Infected Subjects

Although licensed human papillomavirus (HPV) vaccines are most efficacious in persons never infected with HPV, they also reduce infection and disease in previously infected subjects, indicating natural immunity is not entirely protective against HPV re-infection. The aim of this exploratory study was to examine the B cell memory elicited by HPV infection and evaluate whether vaccination merely boosts antibody (Ab) levels in previously infected subjects or also improves the quality of B cell memory. Toward this end, the memory B cells (Bmem) of five unvaccinated, HPV-seropositive subjects were isolated and characterized, and subject recall responses to a single HPV vaccine dose were analyzed. Vaccination boosted Ab levels 24- to 930-fold (median 77-fold) and Bmem numbers 3- to 27-fold (median 6-fold). In addition, Abs cloned from naturally elicited Bmem were generally non-neutralizing, whereas all those isolated following vaccination were neutralizing. Moreover, Ab and plasmablast responses indicative of memory recall responses were only observed in two subjects. These results suggest HPV vaccination augments both the magnitude and quality of natural immunity and demonstrate that sexually active persons could also benefit from HPV vaccination. This study may have important public policy implications, especially for the older ‘catch-up’ group within the vaccine's target population.

CD4(+) T-Cell-Independent Secondary Immune Responses to Pneumocystis Pneumonia.

Pneumocystis pneumonia is a major cause of morbidity and mortality among immunocompromised patients, especially in the context of HIV/AIDS. In the murine model of Pneumocystis pneumonia, CD4+ T-cells are required for clearance of a primary infection of Pneumocystis, but not the memory recall response. We hypothesized that the memory recall response in the absence of CD4+ T-cells is mediated by a robust memory humoral response, CD8+ T-cells, and IgG-mediated phagocytosis by alveolar macrophages. To investigate the role of CD8+ T-cells and alveolar macrophages in the immune memory response to Pneumocystis, mice previously challenged with Pneumocystis were depleted of CD8+ T-cells or alveolar macrophages prior to re-infection. Mice depleted of CD4+ T-cells prior to secondary challenge cleared Pneumocystis infection within 48 h identical to immunocompetent mice during a secondary memory recall response. However, loss of CD8+ T-cells or macrophages prior to the memory recall response significantly impaired Pneumocystis clearance. Specifically, mice depleted of CD8+ T-cells or alveolar macrophages had significantly higher fungal burden in the lungs. Furthermore, loss of alveolar macrophages significantly skewed the lung CD8+ T-cell response toward a terminally differentiated effector memory population and increased the percentage of IFN-γ+ CD8+ T-cells. Finally, Pneumocystis-infected animals produced significantly more bone marrow plasma cells and Pneumocystis-specific IgG significantly increased macrophage-mediated killing of Pneumocystis in vitro. These data suggest that secondary immune memory responses to Pneumocystis are mediated, in part, by CD8+ T-cells, alveolar macrophages, and the production of Pneumocystis-specific IgG.

PD-1 inhibition results in reduced dendritic cell (DC) activation of HIV-1-specific de novo CTL and enhancement of DC-induced CTL memory recall responses

Abstract Combination strategies consisting of DC vaccines and suppression of immunoregulatory pathways such as PD-1 blockade have been advocated to elicit optimal CTL responses in chronic diseases including cancer and HIV infection. We have shown that inactivated HIV-1 virus loaded, high IL-12 producing, mature, type-1 polarized DC (DC1) can activate CTL from naïve CD8+ T cell precursors that more effectively kill HIV-1-infected cells than CTL derived from memory CD8+ T cells. Here we tested DC1 transfected with an adenoviral (Ad) vector encoding anti-PD-1 antibody (DC.αPD1) enhancement of both primary as well as memory CTL responses to HIV-1. Ad-αPD1-transduced DC1 (DC.αPD1) secreted high levels of functional anti-PD1 Ab without affecting their phenotype or IL-12p70-producing capacity. We next compared HIV Gag peptide epitope-loaded DC.αPD1 to DC1 that were transfected with an empty vector for their ability to activate either purified, autologous naïve or memory HIV-1-specific CD8+ T cells from chronic HIV-1-infected participants of the Multicenter AIDS Cohort Study. When compared to the control DC1, antigen-loaded DC.αPD1 enhanced the overall magnitude of HIV-1-specific CTL responses induced, as determined by the expansion of HIV-1-peptide responsive CD107a and IFNγ expressing T cells. In contrast, the overall number HIV-1 antigen-reactive CTL derived from the naïve CD8+ T cell fraction sharply decreased when using the DC.αPD1-based approach. These results suggest previously unrecognized, opposing roles of the inhibitory receptor PD-1 in DC1-induced primary versus memory recall CD8+ T cell responses to HIV-1.

Cutting edge: stage-specific requirement of IL-18 for antiviral NK cell expansion.

Although NK cells are considered part of the innate immune system, recent studies have demonstrated the ability of Ag-experienced NK cells to become long-lived and contribute to potent recall responses similar to T and B cells. The precise signals that promote the generation of a long-lived NK cell response are largely undefined. In this article, we demonstrate that NK cells require IL-18 signaling to generate a robust primary response during mouse CMV (MCMV) infection but do not require this signal for memory cell maintenance or recall responses. IL-12 signaling and STAT4 in activated NK cells increased the expression of the adaptor protein MyD88, which mediates signaling downstream of the IL-18 and IL-1 receptors. During MCMV infection, NK cells required MyD88, but not IL-1R, for optimal expansion. Thus, an IL-18-MyD88 signaling axis facilitates the prolific expansion of NK cells in response to primary viral infection, but not recall responses.

Gp49B-mediated negative regulation of antibody production by memory and marginal zone B cells.

The rapid Ab responses observed after primary and secondary immunizations are mainly derived from marginal zone (MZ) and memory B cells, respectively, but it is largely unknown how these responses are negatively regulated. Several inhibitory receptors have been identified and their roles have been studied, but mainly on follicular B cells and much less so on MZ B, and never on memory B cells. gp49B is an Ig superfamily member that contains two ITIMs in its cytoplasmic tail, and it has been shown to negatively regulate mast cell, macrophage, and NK cell responses. In this study, we demonstrate that gp49B is preferentially expressed on memory and MZ B cells. We show that gp49B(-/-) mice produce more IgM after a primary immunization and more IgM and IgG1 after a secondary immunization than gp49B(+/+) mice in T cell-dependent immune responses. Memory and MZ B cells from gp49B(-/-) mice also produce more Abs upon in vitro stimulation with CD40 than those from gp49B(+/+) mice. The in vitro IgM production by MZ B cells from gp49B(+/+), but not gp49B(-/-), mice is suppressed by interaction with a putative gp49B ligand, the integrin αvβ3 heterodimer. In addition, gp49B(-/-) mice exhibited exaggerated IgE production in the memory recall response. These results suggest that plasma cell development from memory and MZ B cells, as well as subsequent Ab production, are suppressed via gp49B. In memory B cells, this suppression also prevents excessive IgE production, thus curtailing allergic diseases.

Hexon hypervariable region-modified adenovirus type 5 (Ad5) vectors display reduced hepatotoxicity but induce T lymphocyte phenotypes similar to Ad5 vectors.

Hexon modification of adenovirus type 5 (Ad5) vectors with the hypervariable regions (HVRs) of Ad48 has been shown to allow Ad5HVR48 vectors to circumvent the majority of the preexisting Ad5-neutralizing antibodies. However, it remains unclear whether modifying hexon HVRs impacts innate or adaptive immune responses elicited by this vector. In this study, we investigated the influence of the HVR substitution of Ad5 on innate and adaptive immune responses following vaccination. Ad5HVR48 displayed an intermediate level of innate immune cytokines and chemokines relative to those of Ad5 and Ad48, consistent with its chimeric nature. Hepatotoxicity was observed after Ad5 immunization but not after Ad5HVR48 or Ad48 immunization. However, the CD8(+) T-cell responses elicited by Ad5HVR48 vectors displayed a partially exhausted phenotype, as evidenced by the sustained expression of programmed death 1 (PD-1), decreased effector-to-central memory conversion, and reduced memory recall responses, similar to those elicited by Ad5 vectors and in contrast to those induced by Ad48 vectors. Taken together, these results indicate that although Ad5HVR48 largely bypasses preexisting Ad5 neutralizing antibodies and shows reduced hepatotoxicity compared to that of Ad5, it induces adaptive immune phenotypes that are functionally exhausted similar to those elicited by Ad5.

CpG immunization protects against a lethal influenza challenge and generates antigen specific memory T cells (VAC2P.932)

Abstract Despite extensive research, influenza A virus (IAV) remains a major cause of mortality and healthcare expenditure. Emerging pandemics from highly pathogenic IAV strains such as H5N1 and H1N1 highlight the need for universal, cross protective IAV vaccines. Current vaccine formulations generate strain-specific neutralizing antibodies primarily against the outer coat proteins hemagglutinin and neuraminidase. In contrast to these highly mutable proteins, internal proteins of IAV are more conserved and are therefore a favorable target for developing vaccines that induce strong T cell responses in the absence of humoral immunity. Here, we found that intranasal administration of a TLR 9 agonist (CpG) and inactivated x31 (H3N2) protects mice from a heterosubtypic challenge with a lethal dose of PR8 virus (H1N1). Vaccinated mice also showed less weight loss and lower viral titers compared to control mice following a lethal PR8 challenge. Both CD4 and CD8 effector functions were measured five days post challenge with significant increases in the number of Granzyme B positive cells as well as antigen specific IFN-γ cells. Additionally, vaccinated mice had higher memory recall responses following ex vivo restimulation with NP specific peptides as measured by IL-2 and IFN-γ production. Thus, CpG is a potent inducer of antiviral immunity highlighted by robust T cell responses underscoring the potential of this vaccination strategy as a prophylactic measure against pandemic IAV strains.