Primary and metastatic brain tumors exhibit resistance to immunotherapies that demonstrate efficacy in peripheral cancer settings. While many immunotherapies aim to enhance CD8+ T cell infiltration and functionality in established tumors, identification of neoantigens support emerging immunopreventative tactics against brain cancer. Functionally potent tissue-resident memory CD8+ T cells (TRM) can be generated in the brain following peripheral infection or vaccination. However, the ability of brain TRM to prevent intracranial malignancy remains unknown. Here, mice were seeded with tumor-specific or bystander brain TRM via peripheral infection prior to depletion of circulating memory T cells (TCIRCM) and subsequent brain tumor challenge. Tumor-specific brain TRM durably protected mice against intracranial malignancy even in the absence TCIRCM. These brain TRM persisted in tumor-surviving mice and protected against a second antigen-matched challenge. Importantly, a translationally-relevant mRNA-lipid nanoparticle (LNP) vaccine phenocopied peripheral infection-induced outcomes, generating functional brain TRM that controlled tumor growth. Altogether, this work points to the utility of brain TRM in cancer immunoprevention, supporting the development of antitumor mRNA-LNP vaccines to bolster brain immunity.

Whole sporozoite vaccines (WSVs) are the most effective malaria vaccines developed to date. However, their durable efficacy declines sharply when moving from homologous CHMI studies to field trials in endemic regions. We argue this reduced efficacy reflects the complex context of vaccine deployment rather than a single cause. The antigen mismatch hypothesis postulates that limited genetic diversity in current vaccines fails to capture the diversity of field parasites, reducing immune recognition. The host-context hypothesis describes how genetics, infection history, microbiome, and nutrition influence vaccine outcomes. We propose that the future of malaria vaccines will depend on integrating parasite genomics, systems immunology, and the development of animal models which more accurately depict the context of individuals living in malaria endemic regions.

Immunization with radiation-attenuated sporozoites (RAS) drives effective sterilizing immunity against liver-stage Plasmodium infection. However, protection is compromised in individuals living in malaria endemic regions and the mechanisms of vaccine failure are unclear. Here we show that previous blood-stage exposure in a mouse model of Plasmodium yoelii infection compromises Plasmodium berghei RAS-induced essential CD8+ T cell responses and subsequent protection. The persisting malarial pigment haemozoin mediates impaired CD8+ T cell responses owing to impaired antigen uptake by dendritic cells, leading to reduced T cell activation. We designed a lipid nanoparticle-encapsulated mRNA vaccine that encodes a string of Plasmodium CD8+ T cell epitopes, which overcomes the defective T cell response and restores protection in Plasmodium-exposed mice. A combined RAS-plus-mRNA vaccine regimen enhances liver-resident memory T cells and protection in murine malaria-experienced hosts. The identification of haemozoin as a potential obstacle to vaccine efficacy in malaria endemic areas can inform the design of more effective malaria vaccines.

Malaria is a persistent global public health threat. Immunization with Radiation Attenuated Sporozoites (RAS) drives efficient CD8+ T cell dependent sterilizing immunity to malaria in humans. However, this protection is compromised in individuals living in malaria endemic regions and the mechanism(s) of the vaccine failure remain incompletely understood. In this study, we develop a murine model of Plasmodium infection where prior blood-stage exposure compromises RAS-induced CD8+ T cell responses and subsequent protection. We further identify the persisting malarial pigment hemozoin as a mediator of impaired CD8+ T cell responses. Mechanistically, we link this defect to impaired antigen uptake by dendritic cells, leading to reduced T cell activation. Importantly, we designed a lipid nanoparticle-encapsulated mRNA vaccine that encodes a string of Plasmodium CD8+ T cell epitopes and found that this vaccine overcomes the T cell defect and restores protection in Plasmodium exposed mice. Moreover, a combined RAS+mRNA vaccine regimen enhances liver resident memory T cells and protection even in malaria experienced hosts. These findings support the identification of hemozoin as a long-lived obstacle to vaccine efficacy in malaria endemic areas and provide a rational framework for designing malaria vaccines that are effective in endemic settings.

Patients infected with SARS-CoV-2 experience variable disease susceptibility, and patients with comorbidities such as sepsis are often hospitalized for COVID-19 complications. However, the extent to which initial infectious inoculum dose determines disease outcomes and whether this can be used for immunological priming in a genetically susceptible host has not been completely defined. We used an established SARS-like murine model in which responses to primary and/or secondary challenges with murine hepatitis virus type 1 (MHV-1) were analyzed. We compared the response to infection in genetically susceptible C3H/HeJ mice, genetically resistant C57BL/6J mice, and genetically diverse, variably susceptible outbred Swiss Webster mice. Although defined as genetically susceptible to MHV-1, C3H/HeJ mice displayed decreasing dose -dependent pathological changes in disease severity and lung infiltrate/edema, as well as lymphopenia. Importantly, an asymptomatic dose (500 PFU) was identified that yielded no measurable morbidity/mortality postinfection in C3H/HeJ mice. Polymicrobial sepsis induced via cecal ligation and puncture converted asymptomatic infections in C3H/HeJ and C57BL/6J mice to more pronounced disease, modeling the impact of sepsis as a comorbidity to I3-coronavirus infection. We then used low -dose infection as an immunological priming event in C3H/HeJ mice, which provided neutralizing Ab-dependent, but not circulating CD4/CD8 T cell -dependent, protection against a high -dose MHV-1 early rechallenge. Together, these data define how infection dose, immunological status, and comorbidities modulate outcomes of primary and secondary I3-coronavirus infections in hosts with variable susceptibility. The Journal of Immunology, 2024, 212: 563-575.

Radiation exposure occurs during medical procedures, nuclear accidents, or spaceflight, making effective medical countermeasures a public health priority. Naïve T cells are highly sensitive to radiation-induced depletion, although their numbers recover with time. Circulating memory CD8+ T cells are also depleted by radiation; however, their numbers do not recover. Critically, the impact of radiation exposure on tissue-resident memory T cells (TRM) remains unknown. Here, we found that sublethal thorax-targeted radiation resulted in the rapid and prolonged numerical decline of influenza A virus (IAV)–specific lung TRM in mice, but no decline in antigen-matched circulating memory T cells. Prolonged loss of lung TRM was associated with decreased heterosubtypic immunity. Importantly, boosting with IAV-epitope expressing pathogens that replicate in the lungs or peripheral tissues or with a peripherally administered mRNA vaccine regenerated lung TRM that was derived largely from circulating memory CD8+ T cells. Designing effective vaccination strategies to regenerate TRM will be important in combating the immunological effects of radiation exposure.

Malaria is a vector-borne disease caused by Plasmodium parasites. In an exciting new study, Ganley et al. harness the power of mRNA vaccines to summon tissue-resident memory T cells to battle the parasite as it replicates in the liver.

The increasing use of nuclear energy sources inevitably raises the risk of accidental or deliberate radiation exposure and associated immune dysfunction. However, the extent to which radiation exposure impacts memory CD8 T cells, potent mediators of immunity to recurring intracellular infections and malignancies, remains understudied. Using P14 CD8 T cell chimeric mice (P14 chimeras) with an lymphocytic choriomeningitis virus (LCMV) infection model, we observed that sublethal (5Gy) whole-body irradiation (WBI) induced a rapid decline in the number of naive (TN) and P14 circulating memory CD8 T cells (TCIRCM), with the former being more susceptible to radiation-induced numeric loss. While TN cell numbers rapidly recovered, as previously described, the number of P14 TCIRCM cells remained low at least 9 mo after radiation exposure. Additionally, the remaining P14 TCIRCM in irradiated hosts exhibited an inefficient transition to a central memory (CD62L+) phenotype compared to nonirradiated P14 chimeras. WBI also resulted in long-lasting T cell intrinsic deficits in memory CD8 T cells, including diminished cytokine and chemokine production along with impaired secondary expansion upon cognate Ag reencounter. Irradiated P14 chimeras displayed significantly higher bacterial burden after challenge with Listeria monocytogenes expressing the LCMV GP33-41 epitope relative to nonirradiated controls, likely due to radiation-induced numerical and functional impairments. Taken together, our findings suggest that sublethal radiation exposure caused a long-term numerical, impaired differentiation, and functional dysregulation in preexisting TCIRCM, rendering previously protected hosts susceptible to reinfection.

Exposure to sublethal ionizing radiation can occur through various mechanisms, including purposeful medical exposure, nuclear accidents, and acts of nuclear terrorism, making the development of effective medical countermeasures a high public health priority. The induction of DNA damage through reactive oxygen species makes rapidly dividing cells, such as naïve T cells highly sensitive to radiation induced depletion. A previous study demonstrated that broadly, circulating memory T cells are more resistant to numerical loss following radiation exposure compared to naïve T cells. However, the effects of radiation on the more recently described memory T cell subset, tissue resident memory T cells (T RM) remain unknown. T RMhave been identified as a critical T cell subset in protection from a number of infections including influenza, respiratory syncytial virus and malaria. In particular, lung T RMare critical for strain-transcending heterosubtypic immunity to influenza virus. In a murine model of influenza infection (IAV), we have found that sublethal thorax targeted radiation resulted in the rapid numerical decline of lung T RMwithout major alterations in circulating IAV-specific memory CD8+ T cells. The depletion of anti-IAV lung T RMwas long-lasting, and resulted in the loss of heterosubtypic immunity to IAV. Interestingly, any surviving T RMdisplay elevated granzyme B expression, indicating functional consequences for T RMfollowing radiation exposure, which could have implications for immune-mediated pathology. Designing effective vaccination strategies to reinvigorate this critical T cell subset will be an important step in combating the immunological effects of radiation exposure. 1F32AI174382-01

Introduction Vaccination is the most effective mechanism to prevent severe COVID-19. However, breakthrough infections and subsequent transmission of SARS-CoV-2 remain a significant problem. Intranasal vaccination has the potential to be more effective in preventing disease and limiting transmission between individuals as it induces potent responses at mucosal sites. Methods Utilizing a replication-deficient adenovirus serotype 5-vectored vaccine expressing the SARS-CoV-2 RBD (AdCOVID) in homozygous and heterozygous transgenic K18-hACE2, we investigated the impact of the route of administration on vaccine immunogenicity, SARS-CoV-2 transmission, and survival. Results Mice vaccinated with AdCOVID via the intramuscular or intranasal route and subsequently challenged with SARS-CoV-2 showed that animals vaccinated intranasally had improved cellular and mucosal antibody responses. Additionally, intranasally vaccinated animals had significantly better viremic control, and protection from lethal infection compared to intramuscularly vaccinated animals. Notably, in a novel transmission model, intranasal vaccination reduced viral transmission to naïve co-housed mice compared to intramuscular vaccination. Discussion Our data provide convincing evidence for the use of intranasal vaccination in protecting against SARS-CoV-2 infection and transmission.

Nearly half of the world's population is at risk of malaria, a disease caused by the protozoan parasite Plasmodium, which is estimated to cause more than 240,000,000 infections and kill more than 600,000 people annually. The emergence of Plasmodia resistant to chemoprophylactic treatment highlights the urgency to develop more effective vaccines. In this regard, whole sporozoite vaccination approaches in murine models and human challenge studies have provided substantial insight into the immune correlates of protection from malaria. From these studies, CD8+ T cells have come to the forefront, being identified as critical for vaccine-mediated liver-stage immunity that can prevent the establishment of the symptomatic blood stages and subsequent transmission of infection. However, the unique biological characteristics required for CD8+ T cell protection from liver-stage malaria dictate that more work must be done to design effective vaccines. In this review, we will highlight a subset of studies that reveal basic aspects of memory CD8+ T cell-mediated protection from liver-stage malaria infection.

Historically, the gold-standard benchmark for vaccine immunogenicity has been the induction of neutralizing antibodies detectable in the serum of peripheral blood. However, in recent years there has been a new appreciation for the mucosa as an important site for vaccine induced immunity. As a point of first contact, the mucosal tissue represents a major site of immune based detection and restriction of pathogen entry and dissemination. Tissue resident memory T cells (T rm ) are one of the critical cell types involved in this early detection and restriction of mucosal pathogens. Following tissue-specific infection or vaccination, T rm lodge themselves within tissues and can perform rapid sensing and alarm functions to control local re-infections, in an effort that has been defined as important for restriction of a number of respiratory pathogens including influenza and respiratory syncytial virus. Despite this characterized importance, only minor attention has been paid to the importance of T rm as a benchmark for vaccine immunogenicity. The purpose of this review is to highlight the functions of T rm with particular emphasis on respiratory infections, and to suggest the inclusion of T rm elicitation as a benchmark for vaccine immunogenicity in animal models, and where possible, human samples.

Rift Valley fever virus (RVFV) is a veterinary and human pathogen and is an agent of bioterrorism concern. Currently, RVFV treatment is limited to supportive care, so new drugs to control RVFV infection are urgently needed. RVFV is a member of the order Bunyavirales, whose replication depends on the enzymatic activity of the viral L protein. Screening for RVFV inhibitors among compounds with divalent cation-coordinating motifs similar to known viral nuclease inhibitors identified 47 novel RVFV inhibitors with selective indexes from 1.1-103 and 50% effective concentrations of 1.2-56 μM in Vero cells, primarily α-Hydroxytropolones and N-Hydroxypyridinediones. Inhibitor activity and selective index was validated in the human cell line A549. To evaluate specificity, select compounds were tested against a second Bunyavirus, La Crosse Virus (LACV), and the flavivirus Zika (ZIKV). These data indicate that the α-Hydroxytropolone and N-Hydroxypyridinedione chemotypes should be investigated in the future to determine their mechanism(s) of action allowing further development as therapeutics for RVFV and LACV, and these chemotypes should be evaluated for activity against related pathogens, including Hantaan virus, severe fever with thrombocytopenia syndrome virus, Crimean-Congo hemorrhagic fever virus.

Powassan virus (POWV) is a tick-borne pathogen for which humans are an incidental host. POWV infection can be fatal or result in long-term neurological sequelae; however, there are no approved vaccinations for POWV. Integral to efficacious vaccine development is the identification of correlates of protection, which we accomplished in this study by utilizing a murine model of POWV infection. Using POWV lethal and sub-lethal challenge models, we show that (1) robust B and T cell responses are necessary for immune protection, (2) POWV lethality can be attributed to both viral- and host-mediated drivers of disease, and (3) knowledge of the immune correlates of protection against POWV can be applied in a virus-like particle (VLP)-based vaccination approach that provides protection from lethal POWV challenge. Identification of these immune protection factors is significant as it will aid in the rational design of POWV vaccines.

Dengue virus (DENV) is the most common vector-borne viral disease, with nearly 400 million worldwide infections each year concentrated in the tropical and subtropical regions of the world. Severe dengue complications are often associated with a secondary heterotypic infection of one of the four circulating serotypes. In this scenario, humoral immune responses targeting cross-reactive, poorly neutralizing epitopes can lead to increased infectivity of susceptible cells via antibody-dependent enhancement (ADE). In this way, antibodies produced in response to infection or vaccination are capable of contributing to enhanced disease in subsequent infections. Currently, there are no available therapeutics to combat DENV disease, and there is an urgent need for a safe and efficacious vaccine. Here, we developed a nucleotide-modified mRNA vaccine encoding the membrane and envelope structural proteins from DENV serotype 1 encapsulated in lipid nanoparticles (prM/E mRNA-LNP). Vaccination of mice elicited robust antiviral immune responses comparable to viral infection, with high levels of neutralizing antibody titers and antiviral CD4(+) and CD8(+) T cells. Immunocompromised AG129 mice vaccinated with the prM/E mRNA-LNP vaccine were protected from a lethal DENV challenge. Vaccination with either a wild-type vaccine or a vaccine with mutations in the immunodominant fusion loop epitope elicited equivalent humoral and cell-mediated immune responses. Neutralizing antibodies elicited by the vaccine were sufficient to protect against a lethal challenge. Both vaccine constructs demonstrated serotype-specific immunity with minimal serum cross-reactivity and reduced ADE in comparison to a live DENV1 viral infection. IMPORTANCE With 400 million worldwide infections each year, dengue is the most common vector-borne viral disease. Forty percent of the world's population is at risk, with dengue experiencing consistent geographic spread over the years. With no therapeutics available and vaccines performing suboptimally, the need for an effective dengue vaccine is urgent. Here, we develop and characterize a novel mRNA vaccine encoding the dengue serotype 1 envelope and premembrane structural proteins that is delivered via a lipid nanoparticle. Our DENV1 prM/E mRNA-LNP vaccine induces neutralizing antibody and cellular immune responses in immunocompetent mice and protects an immunocompromised mouse from a lethal DENV challenge. Existing antibodies against dengue can enhance subsequent infections via antibody-dependent enhancement (ADE). Importantly our vaccine induced only serotype-specific immune responses and did not induce ADE.

Zika virus (ZIKV) is an arbovirus belonging to the flaviviridae family with a risk assessment that has been increasing in recent years and was labeled a global health emergency by the World Health Organization in 2016. There are currently no Food and Drug Administration-approved treatment options available for ZIKV, so expeditious development of treatment options is urgent. To expedite this process, an on-market drug, tamoxifen (TAM), was selected as a promising candidate for repurposing due to its wide range of biological activities and because it has already been shown to possess activity against hepatitis C virus, a flavivirus in a separate genus. Anti-ZIKV activity of TAM was assessed by compound screens using an infectious virus and mechanistic details were gleaned from time of addition and virucidal studies. TAM and an active metabolite, 4-hydroxytamoxifen (TAM-OH), both showed promising antiviral activity (EC50 approximate to 9 and 5 mu M, respectively) in initial compound screening and up to 8-h postinfection, though the virucidal assay indicated that they do not possess any direct virucidal activity. Additionally, TAM was assessed for its activity against ZIKV in the human male germ cell line, SEM-1, due to the sexually transmitted nature of ZIKV owing to its extended survival times in germ cells. Virus titers show diminished replication of ZIKV over 7 days compared to controls. These data indicate that TAM has the potential to be repurposed as an anti-ZIKV therapeutic and warrants further investigation.