Production of atypical measles in rhesus macaques: evidence for disease mediated by immune complex formation and eosinophils in the presence of fusion-inhibiting antibody

Nebulized fusion inhibitory peptide protects cynomolgus macaques from measles virus infection

Measles is the most contagious airborne viral infection and the leading cause of child death among vaccine-preventable diseases. We show here that aerosolized lipopeptide fusion inhibitor, derived from heptad-repeat regions of the measles virus (MeV) fusion protein, blocks respiratory MeV infection in a non-human primate model, the cynomolgus macaque. We use a custom-designed mesh nebulizer to ensure efficient aerosol delivery of peptide to the respiratory tract and demonstrate the absence of adverse effects and lung pathology in macaques. The nebulized peptide efficiently prevents MeV infection, resulting in the complete absence of MeV RNA, MeV-infected cells, and MeV-specific humoral responses in treated animals. This strategy provides an additional means to fight against respiratory infection in non-vaccinated people, that can be readily translated to human trials. It presents a proof-of-concept for the aerosol delivery of fusion inhibitory peptides to protect against measles and other airborne viruses, including SARS-CoV-2, in case of high-risk exposure.

Vaccine-associated enhanced disease in humans and animal models: Lessons and challenges for vaccine development

The fight against infectious diseases calls for the development of safe and effective vaccines that generate long-lasting protective immunity. In a few situations, vaccine-mediated immune responses may have led to exacerbated pathology upon subsequent infection with the pathogen targeted by the vaccine. Such vaccine-associated enhanced disease (VAED) has been reported, or at least suspected, in animal models, and in a few instances in humans, for vaccine candidates against the respiratory syncytial virus (RSV), measles virus (MV), dengue virus (DENV), HIV-1, simian immunodeficiency virus (SIV), feline immunodeficiency virus (FIV), severe acute respiratory syndrome coronavirus 1 (SARS-CoV-1), and the Middle East respiratory syndrome coronavirus (MERS-CoV). Although alleviated by clinical and epidemiological evidence, a number of concerns were also initially raised concerning the short- and long-term safety of vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is causing the ongoing COVID-19 pandemic. Although the mechanisms leading to this phenomenon are not yet completely understood, the individual and/or collective role of antibody-dependent enhancement (ADE), complement-dependent enhancement, and cell-dependent enhancement have been highlighted. Here, we review mechanisms that may be associated with the risk of VAED, which are important to take into consideration, both in the assessment of vaccine safety and in finding ways to define models and immunization strategies that can alleviate such concerns.

Vaccine-Associated Enhanced Viral Disease: Implications for Viral Vaccine Development

Vaccine-associated enhanced disease (VAED) is a serious barrier to attaining successful virus vaccines in human and veterinary medicine. VAED occurs as two different immunopathologies, antibody-dependent enhancement (ADE) and vaccine-associated hypersensitivity (VAH). ADE contributes to the pathology of disease caused by four dengue viruses (DENV) through control of the intensity of cellular infection. Products of virus-infected cells are toxic. A partially protective yellow fever chimeric tetravalent DENV vaccine sensitized seronegative children to ADE breakthrough infections. A live-attenuated tetravalent whole virus vaccine in phase III testing appears to avoid ADE by providing durable protection against the four DENV. VAH sensitization by viral vaccines occurred historically. Children given formalin-inactivated measles or respiratory syncytial virus (RSV) vaccines experienced severe disease during breakthrough infections. Tissue responses demonstrated that VAH not ADE caused these vaccine safety problems. Subsequently, measles was successfully and safely contained by a live-attenuated virus vaccine. The difficulty in formulating a safe and effective RSV vaccine is troublesome evidence that avoiding VAH is a major research challenge. VAH-like tissue responses were observed during breakthrough homologous virus infections in monkeys given severe acute respiratory syndrome (SARS) or Middle East respiratory syndrome (MERS) vaccines.

Control theory helps to resolve the measles paradox

Measles virus (MV) is a highly contagious respiratory morbillivirus that results in many disabilities and deaths. A crucial challenge in studying MV infection is to understand the so-called 'measles paradox'-the progression of the infection to severe immunosuppression before clearance of acute viremia, which is also observed in canine distemper virus (CDV) infection. However, a lack of models that match in vivo data has restricted our understanding of this complex and counter-intuitive phenomenon. Recently, progress was made in the development of a model that fits data from acute measles infection in rhesus macaques. This progress motivates our investigations to gain additional insights from this model into the control mechanisms underlying the paradox. In this paper, we investigated analytical conditions determining the control and robustness of viral clearance for MV and CDV, to untangle complex feedback mechanisms underlying the dynamics of acute infections in their natural hosts. We applied control theory to this model to help resolve the measles paradox. We showed that immunosuppression is important to control and clear the virus. We also showed under which conditions T-cell killing becomes the primary mechanism for immunosuppression and viral clearance. Furthermore, we characterized robustness properties of T-cell immunity to explain similarities and differences in the control of MV and CDV. Together, our results are consistent with experimental data, advance understanding of control mechanisms of viral clearance across morbilliviruses, and will help inform the development of effective treatments. Further the analysis methods and results have the potential to advance understanding of immune system responses to a range of viral infections such as COVID-19.

Vaccine-associated enhanced disease: Case definition and guidelines for data collection, analysis, and presentation of immunization safety data

This is a Brighton Collaboration Case Definition of the term “Vaccine Associated Enhanced Disease” to be utilized in the evaluation of adverse events following immunization. The Case Definition was developed by a group of experts convened by the Coalition for Epidemic Preparedness Innovations (CEPI) in the context of active development of vaccines for SARS-CoV-2 vaccines and other emerging pathogens. The case definition format of the Brighton Collaboration was followed to develop a consensus definition and defined levels of certainty, after an exhaustive review of the literature and expert consultation. The document underwent peer review by the Brighton Collaboration Network and by selected Expert Reviewers prior to submission.

Measles immunity and immunosuppression

Effects of measles on the immune system are only partially understood. Lymphoid tissue is a primary site of measles virus (MeV) replication where CD150 is the receptor for infection of both B and T cells. Lymphocyte depletion occurs during the acute phase of infection, but initiation of the adaptive immune response leads to extensive lymphocyte proliferation, production of MeV-specific antibody and T cells, the rash and clearance of infectious virus. Viral RNA persists in lymphoid tissue accompanied by ongoing germinal center proliferation, production of antibody-secreting cells, functionally distinct populations of T cells and antibody avidity maturation to establish life-long immunity. However, at the same time diversity of pre-existing antibodies and numbers of memory and naive B cells are reduced and susceptibility to other infections is increased.

COVID-19 Vaccines: Should We Fear ADE?

Might COVID-19 vaccines sensitize humans to antibody-dependent enhanced (ADE) breakthrough infections? This is unlikely because coronavirus diseases in humans lack the clinical, epidemiological, biological, or pathological attributes of ADE disease exemplified by dengue viruses (DENV). In contrast to DENV, SARS and MERS CoVs predominantly infect respiratory epithelium, not macrophages. Severe disease centers on older persons with preexisting conditions and not infants or individuals with previous coronavirus infections. Live virus challenge of animals given SARS or MERS vaccines resulted in vaccine hypersensitivity reactions (VAH), similar to those in humans given inactivated measles or respiratory syncytial virus vaccines. Safe and effective COVID-19 vaccines must avoid VAH.

A Rewarding Career Unraveling the Pathogenesis of Viral Infections

My great-grandparents were immigrants from Sweden and settled as farmers in Iowa and Illinois. My father, the oldest of six children, was the first in his family to go to college and had careers as a petroleum geologist and an academic. My mother, the youngest of four children, had older siblings in education, and she focused on early childhood education. My childhood in Oklahoma with two younger sisters was happy and comfortable, and public school prepared me well. My career trajectory into virology did not involve much if any advance planning but was characterized by recognizing the fascinating puzzles of virus diseases, being in good places at the right time, taking advantage of opportunities as they presented themselves, and being surrounded by great mentors, colleagues, trainees, and family. Most of my career was spent studying two diseases caused by RNA viruses, alphavirus encephalomyelitis and measles, and was enriched with several leadership opportunities.

Edible Vaccines: Promises and Challenges

Vaccines are biological preparations that improve immunity to particular diseases and form an important innovation of 19th century research. It contains a protein that resembles a disease-causing microorganism and is often made from weak or killed forms of the microbe. Vaccines are agents that stimulate the body’s immune system to recognize the antigen. Now, a new form of vaccine was introduced which will have the power to mask the risk side of conventional vaccines. This type of vaccine was produced from plants which are genetically modified. In the production of edible vaccines, the gene-encoding bacterial or viral disease-causing agent can be incorporated in plants without losing its immunogenic property. The main mechanism of action of edible vaccines is to activate the systemic and mucosal immunity responses against a foreign disease-causing organism. Edible vaccines can be produced by incorporating transgene in to the selected plant cell. At present edible vaccine are developed for veterinary and human use. But the main challenge faced by edible vaccine is its acceptance by the population so that it is necessary to make aware the society about its use and benefits. When compared to other traditional vaccines, edible vaccines are cost effective, efficient and safe. It promises a better prevention option from diseases.

Measles virus persistence and its consequences

Clearance of measles virus is complex. Infectious virus is cleared by the adaptive immune response manifested by the characteristic maculopapular rash. CD8+ T cells are major effectors of infectious virus clearance, a process that may fail in individuals with compromised cellular immune responses leading to progressive giant cell pneumonia and/or measles inclusion body encephalitis. In contrast to the usual rapid clearance of infectious virus, clearance of viral RNA is slow with persistence in lymphoid tissue for many months. Persistence of MeV RNA may contribute to the late development of the slowly progressive disease subacute sclerosing panencephalitis in children infected at a young age and to measles-associated immune suppression but also to maturation of the immune response and development of life-long immunity.

Association of persistent wild-type measles virus RNA with long-term humoral immunity in rhesus macaques

Recovery from measles results in life-long protective immunity. To understand induction of long-term immunity, rhesus macaques were studied for 6 months after infection with wild-type measles virus (MeV). Infection caused viremia and rash, with clearance of infectious virus by day 14. MeV RNA persisted in PBMCs for 30-90 days and in lymphoid tissue for 6 months most often in B cells but was rarely detected in BM. Antibody with neutralizing activity and binding specificity for MeV nucleocapsid (N), hemagglutinin (H), and fusion proteins appeared with the rash and avidity matured over 3-4 months. Lymph nodes had increasing numbers of MeV-specific antibody-secreting cells (ASCs) and germinal centers with late hyalinization. ASCs appeared in circulation with the rash and continued to appear along with peripheral T follicular helper cells for the study duration. ASCs in lymph nodes and PBMCs produced antibody against both H and N, with more H-specific ASCs in BM. During days 14-21, 20- to 100-fold more total ASCs than MeV-specific ASCs appeared in circulation, suggesting mobilization of preexisting ASCs. Therefore, persistence of MeV RNA in lymphoid tissue was accompanied by continued germinal center formation, ASC production, avidity maturation, and accumulation of H-specific ASCs in BM to sustain neutralizing antibody and protective immunity.

Characterization of antibody response in patients with acute and chronic chikungunya virus disease

BACKGROUND

Chikungunya virus (CHIKV) is a re-emerging arbovirus capable of causing chronic arthralgia, which can last for months to years. Although neutralizing antibodies have been shown to be important for viral clearance, is it not clear whether the quantitative and qualitative nature of antibodies play a role in progression to chronic disease.

OBJECTIVES

To characterize and compare the antibody responses in acute and chronic patients in a prospective observational CHIKV study in Curaçao during the 2014-2015 outbreak.

STUDY DESIGN

We performed virus neutralization tests and ELISA on plasma samples collected from a prospective observational chikungunya study in Curaçao to compare the complement-dependent and -independent neutralization capacity, as well as the antibody avidity index of acute and chronic patients.

RESULTS

We found that there was no significant difference in the virus neutralization titers between patients with acute and chronic chikungunya infection. Furthermore, we found that complement increased the neutralization capacity when large amounts of virus was used. Moreover, we found that patients with acute chikungunya disease had a significantly higher antibody avidity index compared to those with chronic disease.

CONCLUSIONS

This study suggests that virus neutralization titers in late convalescent sera do not play a role in chronic chikungunya. However, the median antibody avidity was lower in these patients and may therefore suggest a role for antibody avidity in the development of chronic disease.

T Lymphocytes as Measurable Targets of Protection and Vaccination Against Viral Disorders

Continuous epidemiological surveillance of existing and emerging viruses and their associated disorders is gaining importance in light of their abilities to cause unpredictable outbreaks as a result of increased travel and vaccination choices by steadily growing and aging populations. Close surveillance of outbreaks and herd immunity are also at the forefront, even in industrialized countries, where previously eradicated viruses are now at risk of re-emergence due to instances of strain recombination, contractions in viral vector geographies, and from their potential use as agents of bioterrorism. There is a great need for the rational design of current and future vaccines targeting viruses, with a strong focus on vaccine targeting of adaptive immune effector memory T cells as the gold standard of immunity conferring long-lived protection against a wide variety of pathogens and malignancies. Here, we review viruses that have historically caused large outbreaks and severe lethal disorders, including respiratory, gastric, skin, hepatic, neurologic, and hemorrhagic fevers. To observe trends in vaccinology against these viral disorders, we describe viral genetic, replication, transmission, and tropism, host-immune evasion strategies, and the epidemiology and health risks of their associated syndromes. We focus on immunity generated against both natural infection and vaccination, where a steady shift in conferred vaccination immunogenicity is observed from quantifying activated and proliferating, long-lived effector memory T cell subsets, as the prominent biomarkers of long-term immunity against viruses and their associated disorders causing high morbidity and mortality rates.

High ratio of measles-specific IgG/IgM associated with nodular pneumonia in vaccinated individuals

BACKGROUND

Vaccinated individuals infected with measles can develop nodular pneumonia. These cases can be misdiagnosed due to the absence of specific IgM and typical symptoms. An effective diagnostic tool is needed.

METHODS

During March 2016, adult inpatients in Yucheng People's Hospital were enrolled prospectively and included in the study. Patients were included if samples were obtained ≤14 days from the onset of fever. Measles virus was detected by RT-PCR of the oropharyngeal swab sample. Chest computed tomography scans and medical records were obtained. Oropharyngeal swabs and blood samples were collected for IgM and IgG testing, RT-PCR, and gene sequencing.

RESULTS

Sixteen patients were enrolled. Ten were found to have nodular pneumonia and were defined as the nodular group. The remaining six patients were defined as the control group. Measles-specific IgG titers in the nodular group were high (3618.3-5000mIU/ml), while IgM titers were low (<25mIU/ml); IgG titers in the control group were low (241.4-2560.3mIU/ml), while IgM titers were high (137-5000mIU/ml). No obvious viral mutation was detected in the nodular group.

CONCLUSIONS

Measles-associated nodular pneumonia was only evident in those patients with an IgG/IgM ratio >20. In measles outbreaks, the IgG/IgM ratio may be useful to identify nodular pneumonia.

Measles virus: Background and oncolytic virotherapy

Measles is a highly transmissible disease caused by measles virus and remains a major cause of child mortality in developing countries. Measles virus nucleoprotein (N) encapsidates the RNA genome of the virus for providing protection from host cell endonucleases and for specific recognition of viral RNA as template for transcription and replication. This protein is over-expressed at the time of viral replication. The C-terminal of N protein is intrinsically disordered, which enables this protein to interact with several host cell proteins. It was previously proved in our laboratory that N expressing human cancerous cells undergo programmed cell death because of reactive oxygen species (ROS) generation as well as Caspase 3 activation. The phosphoprotein (P) along with N protein enclosed viral genomic RNA forming a ribonucleoprotein complex (RNP). It also establishes interaction with the large protein (L) i.e. viral RNA dependent RNA polymerase to ensure viral replication within host cells. The host cell receptors of this virus are CD46, SLAM/CD150 and PVRL4. Measles virus is latently oncotropic in nature and possesses oncolytic property by syncytia formation. We try to highlight the application of this property in developing a virotherapeutic vehicle.

Measles Vaccine

Measles remains an important cause of child morbidity and mortality worldwide despite the availability of a safe and efficacious vaccine. The current measles virus (MeV) vaccine was developed empirically by attenuation of wild-type (WT) MeV by in vitro passage in human and chicken cells and licensed in 1963. Additional passages led to further attenuation and the successful vaccine strains in widespread use today. Attenuation is associated with decreased replication in lymphoid tissue, but the molecular basis for this restriction has not been identified. The immune response is age dependent, inhibited by maternal antibody (Ab) and involves induction of both Ab and T cell responses that resemble the responses to WT MeV infection, but are lower in magnitude. Protective immunity is correlated with levels of neutralizing Ab, but the actual immunologic determinants of protection are not known. Because measles is highly transmissible, control requires high levels of population immunity. Delivery of the two doses of vaccine needed to achieve >90% immunity is accomplished by routine immunization of infants at 9-15 months of age followed by a second dose delivered before school entry or by periodic mass vaccination campaigns. Because delivery by injection creates hurdles to sustained high coverage, there are efforts to deliver MeV vaccine by inhalation. In addition, the safety record for the vaccine combined with advances in reverse genetics for negative strand viruses has expanded proposed uses for recombinant versions of measles vaccine as vectors for immunization against other infections and as oncolytic agents for a variety of tumors.

Evolution of T Cell Responses during Measles Virus Infection and RNA Clearance

Measles is an acute viral disease associated both with immune suppression and development of life-long immunity. Clearance of measles virus (MeV) involves rapid elimination of infectious virus during the rash followed by slow elimination of viral RNA. To characterize cellular immune responses during recovery, we analyzed the appearance, specificity and function of MeV-specific T cells for 6 months after respiratory infection of rhesus macaques with wild type MeV. IFN-γ and IL-17-producing cells specific for the hemagglutinin and nucleocapsid proteins appeared in circulation in multiple waves approximately 2-3, 8 and 18–24 weeks after infection. IFN-γ-secreting cells were most abundant early and IL-17-secreting cells late. Both CD4⁺ and CD8⁺ T cells were sources of IFN-γ and IL-17, and IL-17-producing cells expressed RORγt. Therefore, the cellular immune response evolves during MeV clearance to produce functionally distinct subsets of MeV-specific CD4⁺ and CD8⁺ T cells at different times after infection.

Perspective on Global Measles Epidemiology and Control and the Role of Novel Vaccination Strategies

Measles is a highly contagious, vaccine preventable disease. Measles results in a systemic illness which causes profound immunosuppression often leading to severe complications. In 2010, the World Health Assembly declared that measles can and should be eradicated. Measles has been eliminated in the Region of the Americas, and the remaining five regions of the World Health Organization (WHO) have adopted measles elimination goals. Significant progress has been made through increased global coverage of first and second doses of measles-containing vaccine, leading to a decrease in global incidence of measles, and through improved case based surveillance supported by the WHO Global Measles and Rubella Laboratory Network. Improved vaccine delivery methods will likely play an important role in achieving measles elimination goals as these delivery methods circumvent many of the logistic issues associated with subcutaneous injection. This review highlights the status of global measles epidemiology, novel measles vaccination strategies, and describes the pathway toward measles elimination.

The Immune Response in Measles: Virus Control, Clearance and Protective Immunity

Measles is an acute systemic viral infection with immune system interactions that play essential roles in multiple stages of infection and disease. Measles virus (MeV) infection does not induce type 1 interferons, but leads to production of cytokines and chemokines associated with nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) signaling and activation of the NACHT, LRR and PYD domains-containing protein (NLRP3) inflammasome. This restricted response allows extensive virus replication and spread during a clinically silent latent period of 10–14 days. The first appearance of the disease is a 2–3 day prodrome of fever, runny nose, cough, and conjunctivitis that is followed by a characteristic maculopapular rash that spreads from the face and trunk to the extremities. The rash is a manifestation of the MeV-specific type 1 CD4⁺ and CD8⁺ T cell adaptive immune response with lymphocyte infiltration into tissue sites of MeV replication and coincides with clearance of infectious virus. However, clearance of viral RNA from blood and tissues occurs over weeks to months after resolution of the rash and is associated with a period of immunosuppression. However, during viral RNA clearance, MeV-specific antibody also matures in type and avidity and T cell functions evolve from type 1 to type 2 and 17 responses that promote B cell development. Recovery is associated with sustained levels of neutralizing antibody and life-long protective immunity.

Relevance of the Measles Virus Expression in Cancer - an Update

Evidence of an association between classical Hodgkin lymphoma and the measles virus has previously been presented by our group. Arguments held against our thesis were reevaluated. Substantiation of a relationship between the measles virus and additional solid tumors was submitted. Moreover, a pathogenic pathway was suggested to support a possible contribution of the measles virus to the development of classical Hodgkin lymphoma. We have chosen to exclude a discussion of measles virotherapy, since this carries distinct implications. We now add new evidence regarding the expression of the measles virus phosphoprotein in a few cancers. We also suggest a role in this context for atypical measles syndrome in malignant tumors. Last, we propose a collaboration which may make the best, on the one hand of our cohort of classical Hodgkin lymphoma, half of which carry the measles virus expression in their tumor cells. The planned study will also look into the patients vaccination records and into a previous history of the measles disease. On the other hand, cohorts of patients diagnosed with late onset measles will be assessed for the eventual diagnosis of atypical measles syndrome and will be followed up for the subsequent development of a malignant tumor.

Brief History and Characterization of Enhanced Respiratory Syncytial Virus Disease

In 1967, infants and toddlers immunized with a formalin-inactivated vaccine against respiratory syncytial virus (RSV) experienced an enhanced form of RSV disease characterized by high fever, bronchopneumonia, and wheezing when they became infected with wild-type virus in the community. Hospitalizations were frequent, and two immunized toddlers died upon infection with wild-type RSV. The enhanced disease was initially characterized as a "peribronchiolar monocytic infiltration with some excess in eosinophils." Decades of research defined enhanced RSV disease (ERD) as the result of immunization with antigens not processed in the cytoplasm, resulting in a nonprotective antibody response and CD4(+) T helper priming in the absence of cytotoxic T lymphocytes. This response to vaccination led to a pathogenic Th2 memory response with eosinophil and immune complex deposition in the lungs after RSV infection. In recent years, the field of RSV experienced significant changes. Numerous vaccine candidates with novel designs and formulations are approaching clinical trials, defying our previous understanding of favorable parameters for ERD. This review provides a succinct analysis of these parameters and explores criteria for assessing the risk of ERD in new vaccine candidates.

Live attenuated vaccines: Historical successes and current challenges

Live attenuated vaccines against human viral diseases have been amongst the most successful cost effective interventions in medical history. Smallpox was declared eradicated in 1980; poliomyelitis is nearing global eradication and measles has been controlled in most parts of the world. Vaccines function well for acute diseases such as these but chronic infections such as HIV are more challenging for reasons of both likely safety and probable efficacy. The derivation of the vaccines used has in general not been purely rational except in the sense that it has involved careful clinical trials of candidates and subsequent careful follow up in clinical use; the identification of the candidates is reviewed.

Inactivated Viral Vaccines

Inactivated vaccines have been used for over a century to induce protection against viral pathogens. This established approach of vaccine production is relatively straightforward to achieve and there is an augmented safety profile as compared to their live counterparts. Today, there are six viral pathogens for which licensed inactivated vaccines are available with many more in development. Here, we describe the principles of viral inactivation and the application of these principles to vaccine development. Specifically emphasized are the manufacturing procedure and the accompanying assays, of which assays used for monitoring the inactivation process and preservation of neutralizing epitopes, are pivotal. Novel inactivated vaccines in development and the hurdles they face for licensure are also discussed as well as the (dis)advantages of inactivation over the other vaccine production methodologies.

Vaccine-induced measles virus-specific T cells do not prevent infection or disease but facilitate subsequent clearance of viral RNA

Infection with wild-type measles virus (MeV) induces lifelong protection from reinfection, and parenteral delivery of the live attenuated measles vaccine (LAV) also provides protection from measles. The level of neutralizing antibody is a good indicator of protection, but the independent roles of MeV-specific antibody and T cells have not been identified. In this study, macaques immunized with LAV through a nebulizer and a mouthpiece developed MeV-specific T-cell responses but not neutralizing antibodies. Upon challenge with wild-type MeV, these animals developed rashes and viremias similar to those in naive animals but cleared viral RNA from blood 25 to 40 days faster. The nebulizer-immunized animals also had more robust MeV-specific CD4⁺ and CD8⁺ T-cell responses than the naive animals after challenge, characterized by a higher number and better durability of gamma interferon (IFN-γ)-producing cells. Induction of MeV-specific circulating CD4⁺ and CD8⁺ T cells capable of producing multiple cytokines correlated with clearance of viral RNA in the nebulizer-immunized macaques. These studies demonstrated that MeV-specific T-cell immunity alone did not prevent measles, but T-cell priming enhanced the magnitude, durability, and polyfunctionality of MeV-specific T cells after challenge infection and correlated with more rapid clearance of MeV RNA.

The components of vaccine-induced immunity necessary for protection from infection and disease have not been clearly identified for most vaccines. Vaccine development usually focuses on induction of antibody, but T-cell-based vaccines are also under development. The live attenuated measles vaccine (LAV) given subcutaneously induces both T cells and neutralizing antibody and provides solid protection from infection. LAV delivered to the upper respiratory tract through a nebulizer and mouthpiece induced a T-cell response but no neutralizing antibody. These T-cell-primed macaques demonstrated no protection from rash or viremia when challenged with wild-type MeV, but viral RNA was cleared more rapidly than in unimmunized animals. Thus, T-cell immunity did not protect from infection or acute disease but facilitated virus clearance during recovery. These studies demonstrate the importance and independent roles of T cells and antibody in protection and recovery from measles.

T helper type 2 bias and type 17 suppression in primary dengue virus infection in infants and young children

BACKGROUND

The immune response to dengue virus (DENV) primary infection in infants and young children is not well characterized. In Northern Argentina, >90% of the population was DENV-naïve before the 2009 outbreak, allowing evaluation of age-dependent primary responses to infection.

METHODS

We conducted a comparative study of the immune response to DENV in 27 infected infants, young children and their mothers. Lymphocyte T helper (Th) 1, Th2, Th17 and inflammatory responses were assayed in blood during the 2009 DENV-1 epidemic.

RESULTS

The immune response to DENV-1 was significantly biased to Th2 in infected infants and young children, compared to infants with other febrile illnesses (for IL-4 p < 0.001) and to their infected mothers (for IL-4 p < 0.01). In addition, IL-17 suppression was observed in the memory response to DENV-1 in infected infants (p < 0.01 vs placebo).

CONCLUSION

Age-related differences in the primary response to DENV, characterized by an immature Th2 polarization and Th17 suppression in infants, should be studied further in order to expand our understanding of the mechanism of dengue pathogenesis.

Vaxfectin adjuvant improves antibody responses of juvenile rhesus macaques to a DNA vaccine encoding the measles virus hemagglutinin and fusion proteins

DNA vaccines formulated with the cationic lipid-based adjuvant Vaxfectin induce protective immunity in macaques after intradermal (i.d.) or intramuscular (i.m.) delivery of 0.5 to 1 mg of codon-optimized DNA encoding the hemagglutinin (H) and fusion (F) proteins of measles virus (MeV). To characterize the effect of Vaxfectin at lower doses of H+F DNA, rhesus macaques were vaccinated twice with 20 μg of DNA plus Vaxfectin i.d., 100 μg of DNA plus Vaxfectin i.d., 100 μg of DNA plus Vaxfectin i.m. or 100 μg of DNA plus phosphate-buffered saline (PBS) i.m. using a needleless Biojector device. The levels of neutralizing (P = 0.036) and binding (P = 0.0001) antibodies were higher after 20 or 100 μg of DNA plus Vaxfectin than after 100 μg of DNA plus PBS. Gamma interferon (IFN-γ)-producing T cells were induced more rapidly than antibody, but were not improved with Vaxfectin. At 18 months after vaccination, monkeys were challenged with wild-type MeV. None developed rash or viremia, but all showed evidence of infection. Antibody levels increased, and IFN-γ- and interleukin-17-producing T cells, including cells specific for the nucleoprotein absent from the vaccine, were induced. At 3 months after challenge, MeV RNA was detected in the leukocytes of two monkeys. The levels of antibody peaked 2 to 4 weeks after challenge and then declined in vaccinated animals reflecting low numbers of bone marrow-resident plasma cells. Therefore, Vaxfectin was dose sparing and substantially improved the antibody response to the H+F DNA vaccine. This immune response led to protection from disease (rash/viremia) but not from infection. Antibody responses after challenge were more transient in vaccinated animals than in an unvaccinated animal.

Poor immune responses of newborn rhesus macaques to measles virus DNA vaccines expressing the hemagglutinin and fusion glycoproteins

A vaccine that would protect young infants against measles could facilitate elimination efforts and decrease morbidity and mortality in developing countries. However, immaturity of the immune system is an important obstacle to the development of such a vaccine. In this study, DNA vaccines expressing the measles virus (MeV) hemagglutinin (H) protein or H and fusion (F) proteins, previously shown to protect juvenile macaques, were used to immunize groups of 4 newborn rhesus macaques. Monkeys were inoculated intradermally with 200 μg of each DNA at birth and at 10 months of age. As controls, 2 newborn macaques were similarly vaccinated with DNA encoding the influenza virus H5, and 4 received one dose of the current live attenuated MeV vaccine (LAV) intramuscularly. All monkeys were monitored for development of MeV-specific neutralizing and binding IgG antibody and cytotoxic T lymphocyte (CTL) responses. These responses were poor compared to the responses induced by LAV. At 18 months of age, all monkeys were challenged intratracheally with a wild-type strain of MeV. Monkeys that received the DNA vaccine encoding H and F, but not H alone, were primed for an MeV-specific CD8(+) CTL response but not for production of antibody. LAV-vaccinated monkeys were protected from rash and viremia, while DNA-vaccinated monkeys developed rashes, similar to control monkeys, but had 10-fold lower levels of viremia. We conclude that vaccination of infant macaques with DNA encoding MeV H and F provided only partial protection from MeV infection.

Measles virus, immune control, and persistence

Measles remains one of the most important causes of child morbidity and mortality worldwide with the greatest burden in the youngest children. Most acute measles deaths are owing to secondary infections that result from a poorly understood measles-induced suppression of immune responses. Young children are also vulnerable to late development of subacute sclerosing panencephalitis, a progressive, uniformly fatal neurologic disease caused by persistent measles virus (MeV) infection. During acute infection, the rash marks the appearance of the adaptive immune response and CD8(+) T cell-mediated clearance of infectious virus. However, after clearance of infectious virus, MeV RNA persists and can be detected in blood, respiratory secretions, urine, and lymphoid tissue for many weeks to months. This prolonged period of virus clearance may help to explain measles immunosuppression and the development of lifelong immunity to re-infection, as well as occasional infection of the nervous system. Once MeV infects neurons, the virus can spread trans-synaptically and the envelope proteins needed to form infectious virus are unnecessary, accumulate mutations, and can establish persistent infection. Identification of the immune mechanisms required for the clearance of MeV RNA from multiple sites will enlighten our understanding of the development of disease owing to persistent infection.

The recombinant globular head domain of the measles virus hemagglutinin protein as a subunit vaccine against measles

Despite the availability of live attenuated measles virus (MV) vaccines, a large number of measles-associated deaths occur among infants in developing countries. The development of a measles subunit vaccine may circumvent the limitations associated with the current live attenuated vaccines and eventually contribute to global measles eradication. Therefore, the goal of this study was to test the feasibility of producing the recombinant globular head domain of the MV hemagglutinin (H) protein by stably transfected human cells and to examine the ability of this recombinant protein to elicit MV-specific immune responses. The recombinant protein was purified from the culture supernatant of stably transfected HEK293T cells secreting a tagged version of the protein. Two subcutaneous immunizations with the purified recombinant protein alone resulted in the production of MV-specific serum IgG and neutralizing antibodies in mice. Formulation of the protein with adjuvants (polyphosphazene or alum) further enhanced the humoral immune response and in addition resulted in the induction of cell-mediated immunity as measured by the production of MV H-specific interferon gamma (IFN-γ) and interleukin 5 (IL-5) by in vitro re-stimulated splenocytes. Furthermore, the inclusion of polyphosphazene into the vaccine formulation induced a mixed Th1/Th2-type immune response. In addition, the purified recombinant protein retained its immunogenicity even after storage at 37°C for 2 weeks.

Independence of measles-specific humoral and cellular immune responses to vaccination

With a larger, independent cohort and more sophisticated measures, we sought to confirm our work that indicated independence of humoral and cellular immunity following measles vaccination. We recruited an age-stratified random cohort of 764 healthy subjects from all socioeconomic strata, all with medical-record documentation of 2 age-appropriate doses of measles-containing vaccine. We quantified measles-specific neutralizing antibody levels and assayed the interferon-γ (IFN-γ) enzyme-linked immunosorbent spot assay (ELISPOT) response to measles virus. We also measured secreted cytokines from the peripheral blood mononuclear cells (PBMCs) in response to measles virus by performing enzyme-linked immunosorbent assays as secondary measures of cellular immune status. The median antibody level and median IFN-γ ELISPOT response were 844 mIU/mL (interquartile range [IQR]: 418-1,752) and 36 (IQR: 13.00-69.00) spot-forming cells (per 2 × 10(5) PBMCs), respectively. We observed only a very weak and negative correlation (Spearman's r(s) or ρ of -0.090 [95% confidence interval: -0.162--0.018]). We observed a similar lack of quantitatively important correlations between the neutralizing antibody level and any of the secondary measures. Our data confirm the independence of humoral and cellular immune responses after the second dose of measles vaccination. As researchers pursue novel measles vaccine and measles vaccine delivery systems, they must not infer that humoral responses predict cellular responses.

Local innate and adaptive immune responses regulate inflammatory cell influx into the lungs after vaccination with formalin inactivated RSV

Inactivated respiratory syncytial virus (RSV) vaccines tend to predispose for immune mediated enhanced disease, characterized by Th2 responses and airway hypersensitivity reactions. We show in a C57BL/6 mouse model that the early innate response elicited by the challenge virus (RSV versus influenza virus) influences the outcome of the Th1/Th2 balance in the lung after intramuscular priming with inactivated vaccine. Priming of CD4(+)/IFN-γ(+) T cells by mature dendritic cells administered intravenously and/or priming of a virus specific CD8(+) T cell response ameliorated the Th2-mediated inflammatory response in the lung, suggesting that vaccination procedures are feasible that prevent vaccine induced immune pathology.

Role of nonhuman primates in the evaluation of candidate AIDS vaccines: an industry perspective

PURPOSE OF REVIEW

To consider how nonhuman primate (NHP) model systems can best contribute to HIV vaccine development.

RECENT FINDINGS

We review the traditional roles of NHP model systems in vaccine development and compare this with how NHP models have been used in HIV vaccine research and development. Comparisons of the immune responses elicited by cellular immune response-inducing vaccines in macaques and humans illustrate the value of primate studies for the relative ranking of HIV vaccine concepts for their likely immunogenicity in humans. The unusual structures (e.g. long complementarity-determining regions) of known broadly neutralizing HIV antibodies (bNAbs) suggest that it is critical to test candidate env immunogens in NHPs, whose germline antibody repertoires resemble those of humans. Recent clinical efficacy trial results question the utility of existing NHP challenge models in predicting HIV vaccine efficacy in humans, and highlight the need to further develop models in which acquisition of infection can be reliably evaluated. When evaluated in models using low virus dose challenges that better approximate human sexual exposure to HIV - some vaccine and passive NAb interventions appear to protect against acquisition of infection.

SUMMARY

NHP models have important roles in the preclinical evaluation, optimization, and ranking of novel HIV immunogens. The apparent vaccine efficacy observed using low virus dose challenge models provides an opportunity to investigate the correlates of protection.

How innate immune mechanisms contribute to antibody-enhanced viral infections

Preexisting antibodies may enhance viral infections. In dengue, nonneutralizing antibodies raised by natural infection with one of four dengue viruses (DENVs) may enhance infection with a different virus by a process we term "intrinsic antibody-dependent enhancement" (iADE). In addition, nonprotective antibodies raised by formalin-inactivated respiratory syncytial virus (RSV) and measles virus vaccines have led to enhanced disease during breakthrough infections. Infections under iADE conditions not only facilitate the process of viral entry into monocytes and macrophages but also modify innate and adaptive intracellular antiviral mechanisms, suppressing type 1 interferon (IFN) production and resulting in enhanced DENV replication. The suppression observed in vitro has been documented in patients with severe (dengue hemorrhagic fever [DHF]) but not in patient with mild (dengue fever [DF]) secondary dengue virus infections. Important veterinary viral infections also may exhibit iADE. It is thought that use of formalin deconforms viral epitopes of RSV, resulting in poor Toll-like receptor (TLR) stimulation; suboptimal maturation of dendritic cells with reduced production of activation factors CD40, CD80, and CD86; decreased germinal center formation in lymph nodes; and the production of nonprotective antibodies. These antibodies fail to neutralize RSV, allowing replication with secondary stimulation of RSV-primed Th2 cells producing more low-avidity antibody, resulting in immune complexes deposited into affected tissue. However, when formalin-inactivated RSV was administered with a TLR agonist to mice, they were protected against wild-type virus challenge. Safe and effective vaccines against RSV/measles virus and dengue virus may benefit from a better understanding of how innate immune responses can promote production of protective antibodies.

Comparison of the immune responses induced by chimeric alphavirus-vectored and formalin-inactivated alum-precipitated measles vaccines in mice

A variety of vaccine platforms are under study for development of new vaccines for measles. Problems with past measles vaccines are incompletely understood and underscore the need to understand the types of immune responses induced by different types of vaccines. Detailed immune response evaluation is most easily performed in mice. Although mice are not susceptible to infection with wild type or vaccine strains of measles virus, they can be used for comparative evaluation of the immune responses to measles vaccines of other types. In this study we compared the immune responses in mice to a new protective alphavirus replicon particle vaccine expressing the measles virus hemagglutinin (VEE/SIN-H) with a non-protective formalin-inactivated, alum-precipitated measles vaccine (FI-MV). MV-specific IgG levels were similar, but VEE/SIN-H antibody was high avidity IgG2a with neutralizing activity while FI-MV antibody was low-avidity IgG1 without neutralizing activity. FI-MV antibody was primarily against the nucleoprotein with no priming to H. Germinal centers appeared, peaked and resolved later for FI-MV. Lymph node MV antibody-secreting cells were more numerous after FI-MV than VEE/SIN-H, but were similar in the bone marrow. VEE/SIN-H-induced T cells produced IFN-gamma and IL-4 both spontaneously ex vivo and after stimulation, while FI-MV-induced T cells produced IL-4 only after stimulation. In summary, VEE/SIN-H induced a balanced T cell response and high avidity neutralizing IgG2a while FI-MV induced a type 2 T cell response, abundant plasmablasts, late germinal centers and low avidity non-neutralizing IgG1 against the nucleoprotein.

A chimeric alphavirus replicon particle vaccine expressing the hemagglutinin and fusion proteins protects juvenile and infant rhesus macaques from measles

Measles remains a major cause of child mortality, in part due to an inability to vaccinate young infants with the current live attenuated virus vaccine (LAV). To explore new approaches to infant vaccination, chimeric Venezuelan equine encephalitis/Sindbis virus (VEE/SIN) replicon particles were used to express the hemagglutinin (H) and fusion (F) proteins of measles virus (MV). Juvenile rhesus macaques vaccinated intradermally with a single dose of VEE/SIN expressing H or H and F proteins (VEE/SIN-H or VEE/SIN-H+F, respectively) developed high titers of MV-specific neutralizing antibody and gamma-interferon (IFN-gamma)-producing T cells. Infant macaques vaccinated with two doses of VEE/SIN-H+F also developed neutralizing antibody and IFN-gamma-producing T cells. Control animals were vaccinated with LAV or with a formalin-inactivated measles vaccine (FIMV). Neutralizing antibody remained above the protective level for more than 1 year after vaccination with VEE/SIN-H, VEE/SIN-H+F, or LAV. When challenged with wild-type MV 12 to 17 months after vaccination, all vaccinated juvenile and infant monkeys vaccinated with VEE/SIN-H, VEE/SIN-H+F, and LAV were protected from rash and viremia, while FIMV-vaccinated monkeys were not. Antibody was boosted by challenge in all groups. T-cell responses to challenge were biphasic, with peaks at 7 to 25 days and at 90 to 110 days in all groups, except for the LAV group. Recrudescent T-cell activity coincided with the presence of MV RNA in peripheral blood mononuclear cells. We conclude that VEE/SIN expressing H or H and F induces durable immune responses that protect from measles and offers a promising new approach for measles vaccination. The viral and immunological factors associated with long-term control of MV replication require further investigation.

SARS Coronavirus Pathogenesis and Therapeutic Treatment Design

Emerging pathogens are either new or newly recognized or those that are increasing in incidence and spread. Since the identity of emerging pathogens from animal reservoirs is difficult to predict, the development for pathogen-specific therapeutics and vaccines is problematic. The highly pathogenic SARS coronavirus (SARS-CoV) emerged from zoonotic pools in 2002 to cause a global epidemic of severe acute respiratory syndrome (SARS). Many patients with SARS-CoV experienced an exacerbated form of disease called acute respiratory distress syndrome (ARDS) requiring mechanical ventilation and supplemental oxygen and half of these patients died. Similar to other viral pathogens like influenza and West Nile Virus, the severity of SARS-CoV disease increased with age. Unfortunately, successful vaccination in the most vulnerable populations is a difficult task because of immunological deficiencies associated with aging (immune senescence). Due to the rapidity of virus emergence, technologies like synthetic biology can be harnessed to facilitate rapid recombinant virus construction for studying the novel virus biology, pathogenesis and the evaluation of therapeutic interventions. Since predicting the antigenic identity of future emergence is difficult, candidate vaccines and therapeutics should have a maximal breadth of cross-protection, and panels of antigenically divergent synthetically reconstructed viruses can be used as tools for this evaluation. We discuss how synthetic reconstruction of many animal and human SARS-CoV has provided a model to study the molecular mechanisms governing emergence and pathogenesis of viral diseases. In addition, we review the evolution, epidemiology, and pathogenesis of epidemic and zoonotic SARS-CoV with focus on the development of broadly reactive therapeutics and vaccines that protect aged populations from the zoonotic pool.

Pulmonary eosinophils and their role in immunopathologic responses to formalin-inactivated pneumonia virus of mice

Enhanced disease is the term used to describe the aberrant Th2-skewed responses to naturally acquired human respiratory syncytial virus (hRSV) infection observed in individuals vaccinated with formalin-inactivated viral Ags. Here we explore this paradigm with pneumonia virus of mice (PVM), a pathogen that faithfully reproduces features of severe hRSV infection in a rodent host. We demonstrate that PVM infection in mice vaccinated with formalin-inactivated Ags from PVM-infected cells (PVM Ags) yields Th2-skewed hypersensitivity, analogous to that observed in response to hRSV. Specifically, we detect elevated levels of IL-4, IL-5, IL-13, and eosinophils in bronchoalveolar lavage fluid of PVM-infected mice that were vaccinated with PVM Ags, but not among mice vaccinated with formalin-inactivated Ags from uninfected cells (control Ags). Interestingly, infection in PVM Ag-vaccinated mice was associated with a approximately 10-fold reduction in lung virus titer and protection against weight loss when compared with infected mice vaccinated with control Ags, despite the absence of serum-neutralizing Abs. Given recent findings documenting a role for eosinophils in promoting clearance of hRSV in vivo, we explored the role of eosinophils in altering the pathogenesis of disease with eosinophil-deficient mice. We found that eosinophil deficiency had no impact on virus titer in PVM Ag-vaccinated mice, nor on weight loss or levels of CCL11 (eotaxin-1), IFN-gamma, IL-5, or IL-13 in bronchoalveolar lavage fluid. However, levels of both IL-4 and CCL3 (macrophage inflammatory protein-1alpha) in bronchoalveolar lavage fluid were markedly diminished in PVM Ag-vaccinated, PVM-infected eosinophil-deficient mice when compared with wild-type controls.

Measles studies in the macaque model

Much of our current understanding of measles has come from experiments in non-human primates. In 1911, Goldberger and Anderson showed that macaques inoculated with filtered secretions from measles patients developed measles, thus demonstrating that the causative agent of this disease was a virus. Since then, different monkey species have been used for experimental measles virus infections. Moreover, infection studies in macaques demonstrated that serial passage of the virus in vivo and in vitro resulted in virus attenuation, providing the basis for all current live-attenuated measles vaccines. This chapter will review the macaque model for measles, with a focus on vaccination and immunopathogenesis studies conducted over the last 15 years. In addition, recent data are highlighted demonstrating that the application of a recombinant measles virus strain expressing enhanced green fluorescent protein dramatically increased the sensitivity of virus detection, both in living and sacrificed animals, allowing new approaches to old questions on measles vaccination and pathogenesis.

Lack of antibody affinity maturation due to poor Toll-like receptor stimulation leads to enhanced respiratory syncytial virus disease

Respiratory syncytial virus (RSV) is a leading cause of hospitalization in infants. A formalin-inactivated RSV vaccine was used to immunize children in 1966 and elicited non-protective, pathogenic antibody. Two immunized infants died and 80% were hospitalized after subsequent RSV exposure. No vaccine was licensed since.

A widely accepted hypothesis attributed vaccine failure to formalin disruption of protective antigens. Instead, we show that lack of protection was not due to alterations caused by formalin, but to low antibody avidity for protective epitopes. Lack of antibody affinity maturation followed poor Toll-like receptor stimulation. This study explains why the inactivated RSV vaccine failed to protect and consequently led to severe disease, hampering vaccine development for forty-two years. Also, it suggests that inactivated RSV vaccines may be rendered safe and effective by inclusion of TLR-agonists in their formulation. In addition, it identifies affinity maturation as a critical factor for the safe immunization of infants.

Measles vaccination: new strategies and formulations

Measles is a highly contagious viral disease. With 1 million deaths reported in 1996, measles was the leading cause of vaccine-preventable deaths. However, in recent years, significant progress has been made in measles control, reducing deaths attributed to measles to 454,000 in 2004 and 242,000 in 2006. The main strategy behind this reduction has been the improvement of vaccination coverage and implementation of a second opportunity for immunization with the live-attenuated measles vaccine. The Measles Initiative, a partnership between the American Red Cross, CDC, UNICEF, WHO and UN Foundation, has had a significant role in this achievement. Here, we provide an overview of old and new vaccination strategies, and discuss changes in the route of administration of the existing live-attenuated vaccine, the development of new-generation nonreplicating measles virus vaccine candidates and attempts to use recombinant measles virus as a vector for vaccination against other pathogens.

Measles: old vaccines, new vaccines

Isolation of measles virus in tissue culture by Enders and colleagues in the 1960s led to the development of the first measles vaccines. An inactivated vaccine provided only short-term protection and induced poor T cell responses and antibody that did not undergo affinity maturation. The response to this vaccine primed for atypical measles, a more severe form of measles, and was withdrawn. A live attenuated virus vaccine has been highly successful in protection from measles and in elimination of endemic measles virus transmission with the use of two doses. This vaccine is administered by injection between 9 and 15 months of age. Measles control would be facilitated if infants could be immunized at a younger age, if the vaccine were thermostable, and if delivery did not require a needle and syringe. To these ends, new vaccines are under development using macaques as an animal model and various combinations of the H, F, and N viral proteins. Promising studies have been reported using DNA vaccines, subunit vaccines, and virus-vectored vaccines.

The pathogenesis of measles revisited

Measles continues to be an important cause of childhood mortality in developing countries. The causative agent, measles virus (MV), is a member of the family Paramyxoviridae, genus Morbillivirus, and is spread via the respiratory route. MV was originally thought to enter the host by infecting epithelial cells of the respiratory tract, followed by viremia mediated by infected monocytes. However, neither of these cell types express signaling lymphocyte activation molecule (SLAM, CD150), which has been identified as the main receptor for wild-type MV. Measles has a relatively long incubation time, which makes it difficult to study the early stages of MV infection in humans. The animal models that best reflect the pathogenesis of measles are based on nonhuman primates. The use of recombinant MV strains expressing fluorescent proteins has greatly facilitated studies on viral tropism in macaques. These studies indicate that dendritic cells and lymphocytes expressing CD150 are the primary target cells for MV infection. At late stages of the infection MV also infects epithelial cells, despite the fact that these do not express CD150. Whether these cells express an as yet unidentified additional MV receptor remains unclear. On basis of these data it could be envisaged that dendritic cells are the first target cells for MV infection. These antigen-presenting cells may traffic the virus to the regional lymph nodes where they can transmit the virus to lymphocytes, which during viremia disseminate the virus throughout the body.

Macaque models of human infectious disease

Macaques have served as models for more than 70 human infectious diseases of diverse etiologies, including a multitude of agents—bacteria, viruses, fungi, parasites, prions. The remarkable diversity of human infectious diseases that have been modeled in the macaque includes global, childhood, and tropical diseases as well as newly emergent, sexually transmitted, oncogenic, degenerative neurologic, potential bioterrorism, and miscellaneous other diseases. Historically, macaques played a major role in establishing the etiology of yellow fever, polio, and prion diseases. With rare exceptions (Chagas disease, bartonellosis), all of the infectious diseases in this review are of Old World origin. Perhaps most surprising is the large number of tropical (16), newly emergent (7), and bioterrorism diseases (9) that have been modeled in macaques. Many of these human diseases (e.g., AIDS, hepatitis E, bartonellosis) are a consequence of zoonotic infection. However, infectious agents of certain diseases, including measles and tuberculosis, can sometimes go both ways, and thus several human pathogens are threats to nonhuman primates including macaques. Through experimental studies in macaques, researchers have gained insight into pathogenic mechanisms and novel treatment and vaccine approaches for many human infectious diseases, most notably acquired immunodeficiency syndrome (AIDS), which is caused by infection with human immunodeficiency virus (HIV). Other infectious agents for which macaques have been a uniquely valuable resource for biomedical research, and particularly vaccinology, include influenza virus, paramyxoviruses, flaviviruses, arenaviruses, hepatitis E virus, papillomavirus, smallpox virus, Mycobacteria, Bacillus anthracis, Helicobacter pylori, Yersinia pestis, and Plasmodium species. This review summarizes the extensive past and present research on macaque models of human infectious disease.