Role of CD8(+) lymphocytes in control and clearance of measles virus infection of rhesus monkeys

The contributions of T cell-mediated immunity to protection from vaccine-preventable diseases: A primer

In the face of the ever-present burden of emerging and reemerging infectious diseases, there is a growing need to comprehensively assess individual- and population-level immunity to vaccine-preventable diseases (VPDs). Many of these efforts, however, focus exclusively on antibody-mediated immunity, ignoring the role of T cells. Aimed at clinicians, public health practioners, and others who play central roles in human vaccine research but do not have formal training in immunology, we review how vaccines against infectious diseases elicit T cell responses, what types of vaccines elicit T cell responses, and how T cell responses are measured. We then use examples to demonstrate six ways that T cells contribute to protection from VPD, including directly mediating protection, enabling antibody responses, reducing disease severity, increasing cross-reactivity, improving durability, and protecting special populations. We conclude with a discussion of challenges and solutions to more widespread consideration of T cell responses in clinical vaccinology.

Comparative Efficacy of Parenteral and Mucosal Recombinant Probiotic Vaccines Against SARS-CoV-2 and S. pneumoniae Infections in Animal Models

BACKGROUND

The accumulation of specific IgG antibodies in blood serum is considered a key criterion for the effectiveness of vaccination. For several vaccine-preventable infections, quantitative indicators of the humoral response have been established, which, when reached, provide a high probability of protection against infection. The presence of such a formal correlate of vaccine effectiveness is crucial, for example, in organizing preventive measures and validating newly developed vaccines. However, can effective protection against infection occur when the level of serum antibodies is lower than that provided by parenteral vaccination? Will protection be sufficient if the same vaccine antigen is administered via mucosal membranes without achieving high levels of specific IgG circulating in the blood?

METHODS

In this study, we compared the immunogenicity and protective efficacy of parenteral and mucosal forms of vaccines in experimental animals, targeting infections caused by the SARS-CoV-2 coronavirus and Streptococcus pneumoniae. We investigated the protective properties of a fragment of the coronavirus S1 protein administered intramuscularly with an adjuvant and orally as part of the probiotic strain Enterococcus faecium L3 in a Syrian hamster model. A comparative assessment of the immunogenicity and protective efficacy of a recombinant tandem (PSP) of immunogenic peptides from S. pneumoniae surface proteins, administered either parenterally or orally, was performed in a Balb/c mouse model.

RESULTS

Both models demonstrated significant differences in the immunogenicity of parenteral and oral vaccine antigens, but comparable protective efficacy.

What's going on with measles?

Measles is a highly transmissible systemic viral infection associated with substantial mortality primarily due to secondary infections. Measles induces lifelong immunity to reinfection but loss of immunity to other pathogens. An attenuated live virus vaccine is highly effective, but lapses in delivery have resulted in increasing cases worldwide. Although the primary cause of failure to control measles is failure to vaccinate, waning vaccine-induced immunity and the possible emergence of more virulent virus strains may also contribute.

Immunogenicity of a peptide-based vaccine for measles: a pilot evaluation in a mouse model

Although neutralizing antibody is an established correlate of protection for measles, T cell-mediated responses play at least two critical roles in immunity to measles: first, through provision of 'help' enabling robust humoral immune responses; and second, through clearance of measles virus-infected cells. Previously, we identified 13 measles-derived peptides that bound to human leukocyte antigen (HLA) molecules in Priess cells infected with measles virus. In this study, we evaluated the immunogenicity of these peptides in a transgenic mouse model. Our results demonstrated that these peptides induced Th1-biased immune responses at varying levels. Of the 13 peptides, the top four immunogenic peptides were further selected for a viral challenge study in mice. A vaccine based on a combination of these four peptides reduced morbidity and weight loss after viral challenge compared to placebo. Our results emphasize the potential of T cell-mediated, peptide-based vaccines against measles.

Measles Infection Dose Responses: Insights from Mathematical Modeling

How viral infections develop can change based on the number of viruses initially entering the body. The understanding of the impacts of infection doses remains incomplete, in part due to challenging constraints, and a lack of research. Gaining more insights is crucial regarding the measles virus (MV). The higher the MV infection dose, the earlier the peak of acute viremia, but the magnitude of the peak viremia remains almost constant. Measles is highly contagious, causes immunosuppression such as lymphopenia, and contributes substantially to childhood morbidity and mortality. This work investigated mechanisms underlying the observed wild-type measles infection dose responses in cynomolgus monkeys. We fitted longitudinal data on viremia using maximum likelihood estimation, and used the Akaike Information Criterion (AIC) to evaluate relevant biological hypotheses and their respective model parameterizations. The lowest AIC indicates a linear relationship between the infection dose, the initial viral load, and the initial number of activated MV-specific T cells. Early peak viremia is associated with high initial number of activated MV-specific T cells. Thus, when MV infection dose increases, the initial viremia and associated immune cell stimulation increase, and reduce the time it takes for T cell killing to be sufficient, thereby allowing dose-independent peaks for viremia, MV-specific T cells, and lymphocyte depletion. Together, these results suggest that the development of measles depends on virus-host interactions at the start and the efficiency of viral control by cellular immunity. These relationships are additional motivations for prevention, vaccination, and early treatment for measles.

Immune response elicited in the tumor microenvironment upon rMV-SLAMblind cancer virotherapy

Oncolytic virotherapy is a promising therapy for cancer. We previously established a recombinant measles virus (rMV-SLAMblind) that targets NECTIN4-expressing cancer cells and demonstrated its antitumor effects using a xenograft model in an immunodeficient mouse. In the current study, to investigate the immune response after rMV-SLAMblind therapy, we developed an immunocompetent cancer mouse model by introducing the NECTIN4 gene into mouse cancer cell lines. NECTIN4-expressing mouse cancer cells were successfully killed by rMV-SLAMblind in vitro. After transplantation of the NECTIN4-expressing tumor cells, rMV-SLAMblind significantly suppressed tumor growth in immunocompetent mice. Thus, this immunocompetent mouse cancer model could be a powerful tool in which to study the effect of rMV-SLAMblind therapy on the immune response. Using this model we found that rMV-SLAMblind elicited significant activation of natural killer cells, type 1 helper T cells and the tumor-specific CD8⁺ T-cell response in the tumor microenvironment. Immune cell depletion study revealed that CD8⁺ cells particularly played significant roles in the therapeutic efficacy of rMV-SLAMblind. Thus, rMV-SLAMblind exerts a therapeutic effect, not only directly by tumor cell killing, but also indirectly by efficient induction of antitumor immunity.

Prolonged persistence of canine distemper virus RNA, and virus isolation in naturally infected shelter dogs

Canine distemper virus remains an important source of morbidity and mortality in animal shelters. RT-PCR is commonly used to aid diagnosis and has been used to monitor dogs testing positive over time to gauge the end of infectious potential. Many dogs excrete viral RNA for prolonged periods which has complicated disease management. The goal of this retrospective study was to describe the duration and characteristics of viral RNA excretion in shelter dogs with naturally occurring CDV and investigate the relationship between that viral RNA excretion and infectious potential using virus isolation data. Records from 98 different humane organizations with suspect CDV were reviewed. A total of 5,920 dogs were tested with 1,393; 4,452; and 75 found to be positive, negative, or suspect on RT-PCR respectively. The median duration of a positive test was 34 days (n = 325), and 25% (82/325) of the dogs still excreting viral RNA after 62 days of monitoring. Virus isolation was performed in six dogs who were RT-PCR positive for > 60 days. Infectious virus was isolated only within the first two weeks of monitoring at or around the peak viral RNA excretion (as detected by the lowest cycle threshold) reported for each dog. Our findings suggest that peak viral RNA excretion and the days surrounding it might be used as a functional marker to gauge the end of infectious risk. Clarifying the earliest point in time when dogs testing positive for canine distemper by RT-PCR can be considered non-contagious will improve welfare and lifesaving potential of shelters by enabling recovered dogs to be cleared more quickly for live release outcomes.

Measles Virus-Induced Host Immunity and Mechanisms of Viral Evasion

The immune system deploys a complex network of cells and signaling pathways to protect host integrity against exogenous threats, including measles virus (MeV). However, throughout its evolutionary path, MeV developed various mechanisms to disrupt and evade immune responses. Despite an available vaccine, MeV remains an important re-emerging pathogen with a continuous increase in prevalence worldwide during the last decade. Considerable knowledge has been accumulated regarding MeV interactions with the innate immune system through two antagonistic aspects: recognition of the virus by cellular sensors and viral ability to inhibit the induction of the interferon cascade. Indeed, while the host could use several innate adaptors to sense MeV infection, the virus is adapted to unsettle defenses by obstructing host cell signaling pathways. Recent works have highlighted a novel aspect of innate immune response directed against MeV unexpectedly involving DNA-related sensing through activation of the cGAS/STING axis, even in the absence of any viral DNA intermediate. In addition, while MeV infection most often causes a mild disease and triggers a lifelong immunity, its tropism for invariant T-cells and memory T and B-cells provokes the elimination of one primary shield and the pre-existing immunity against previously encountered pathogens, known as "immune amnesia".

Repurposing live attenuated trivalent MMR vaccine as cost-effective cancer immunotherapy

It has long been known that oncolytic viruses wield their therapeutic capability by priming an inflammatory state within the tumor and activating the tumor immune microenvironment, resulting in a multifaceted antitumor immune response. Vaccine-derived viruses, such as measles and mumps, have demonstrated promising potential for treating human cancer in animal models and clinical trials. However, the extensive cost of manufacturing current oncolytic viral products makes them far out of reach for most patients. Here by analyzing the impact of intratumoral (IT) administrations of the trivalent live attenuated measles, mumps, and rubella viruses (MMR) vaccine, we unveil the cellular and molecular basis of MMR-induced anti-cancer activity. Strikingly, we found that IT delivery of low doses of MMR correlates with tumor control and improved survival in murine hepatocellular cancer and colorectal cancer models via increased tumor infiltration of CD8+ granzyme B+ T-cells and decreased macrophages. Moreover, our data indicate that MMR activates key cellular effectors of the host's innate and adaptive antitumor immunity, culminating in an immunologically coordinated cancer cell death. These findings warrant further work on the potential for MMR to be repurposed as safe and cost-effective cancer immunotherapy to impact cancer patients globally.

Study protocol for a phase 1/2, single-centre, double-blind, double-dummy, randomized, active-controlled, age de-escalation trial to assess the safety, tolerability and immunogenicity of a measles and rubella vaccine delivered by a microneedle patch in healthy adults (18 to 40 years), measles and rubella vaccine-primed toddlers (15 to 18 months) and measles and rubella vaccine-naïve infants (9 to 10 months) in The Gambia [Measles and Rubella Vaccine Microneedle Patch Phase 1/2 Age De-escalation Trial]

BACKGROUND

New strategies to increase measles and rubella vaccine coverage, particularly in low- and middle-income countries, are needed if elimination goals are to be achieved. With this regard, measles and rubella vaccine microneedle patches (MRV-MNP), in which the vaccine is embedded in dissolving microneedles, offer several potential advantages over subcutaneous delivery. These include ease of administration, increased thermostability, an absence of sharps waste, reduced overall costs and pain-free administration. This trial will provide the first clinical trial data on MRV-MNP use and the first clinical vaccine trial of MNP technology in children and infants.

METHODS

This is a phase 1/2, randomized, active-controlled, double-blind, double-dummy, age de-escalation trial. Based on the defined eligibility criteria for the trial, including screening laboratory investigations, 45 adults [18-40 years] followed by 120 toddlers [15-18 months] and 120 infants [9-10 months] will be enrolled in series. To allow double-blinding, participants will receive either the MRV-MNP and a placebo (0.9% sodium chloride) subcutaneous (SC) injection or a placebo MNP and the MRV by SC injection (MRV-SC). Local and systemic adverse event data will be collected for 14 days following study product administration. Safety laboratories will be repeated on day 7 and, in the adult cohort alone, on day 14. Unsolicited adverse events including serious adverse events will be collected until the final study visit for each participant on day 180. Measles and rubella serum neutralizing antibodies will be measured at baseline, on day 42 and on day 180. Cohort progression will be dependent on review of the unblinded safety data by an independent data monitoring committee.

DISCUSSION

This trial will provide the first clinical data on the use of a MNP to deliver the MRV and the first data on the use of MNPs in a paediatric population. It will guide future product development decisions for what may be a key technology for future measles and rubella elimination.

TRIAL REGISTRATION

Pan-African Clinical Trials Registry 202008836432905 .

CLINICALTRIALS

gov NCT04394689.

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.

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.

Human Paramyxovirus Infections Induce T Cells That Cross-React with Zoonotic Henipaviruses

Humans are infected with paramyxoviruses of different genera early in life, which induce cytotoxic T cells that may recognize conserved epitopes. This raises the question of whether cross-reactive T cells induced by antecedent paramyxovirus infections provide partial protection against highly lethal zoonotic Nipah virus infections. By characterizing a measles virus-specific but paramyxovirus cross-reactive human T cell clone, we discovered a highly conserved HLA-B*1501-restricted T cell epitope in the fusion protein. Using peptides, tetramers, and single cell sorting, we isolated a parainfluenza virus-specific T cell clone from a healthy adult and showed that both clones cleared Nipah virus-infected cells. We identified multiple conserved hot spots in paramyxovirus proteomes that contain other potentially cross-reactive epitopes. Our data suggest that, depending on HLA haplotype and history of paramyxovirus exposures, humans may have cross-reactive T cells that provide protection against Nipah virus. The effect of preferential boosting of these cross-reactive epitopes needs to be further studied in light of paramyxovirus vaccination studies.IMPORTANCE Humans encounter multiple paramyxoviruses early in life. This study shows that infection with common paramyxoviruses can induce T cells cross-reactive with the highly pathogenic Nipah virus. This demonstrates that the combination of paramyxovirus infection history and HLA haplotype affects immunity to phylogenetically related zoonotic paramyxoviruses.

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.

Modeling the measles paradox reveals the importance of cellular immunity in regulating viral clearance

Measles virus (MV) is a highly contagious member of the Morbillivirus genus that remains a major cause of childhood mortality worldwide. Although infection induces a strong MV-specific immune response that clears viral load and confers lifelong immunity, transient immunosuppression can also occur, leaving the host vulnerable to colonization from secondary pathogens. This apparent contradiction of viral clearance in the face of immunosuppression underlies what is often referred to as the 'measles paradox', and remains poorly understood. To explore the mechanistic basis underlying the measles paradox, and identify key factors driving viral clearance, we return to a previously published dataset of MV infection in rhesus macaques. These data include virological and immunological information that enable us to fit a mathematical model describing how the virus interacts with the host immune system. In particular, our model incorporates target cell depletion through infection of host immune cells-a hallmark of MV pathology that has been neglected from previous models. We find the model captures the data well, and that both target cell depletion and immune activation are required to explain the overall dynamics. Furthermore, by simulating conditions of increased target cell availability and suppressed cellular immunity, we show that the latter causes greater increases in viral load and delays to MV clearance. Overall, this signals a more dominant role for cellular immunity in resolving acute MV infection. Interestingly, we find contrasting dynamics dominated by target cell depletion when viral fitness is increased. This may have wider implications for animal morbilliviruses, such as canine distemper virus (CDV), that cause fatal target cell depletion in their natural hosts. To our knowledge this work represents the first fully calibrated within-host model of MV dynamics and, more broadly, provides a new platform from which to explore the complex mechanisms underlying Morbillivirus infection.

Fatal Measles Virus Infection After Rituximab-Containing Chemotherapy in a Previously Vaccinated Patient

We report the case of a young patient treated with rituximab-containing chemotherapy who was infected with measles despite previous vaccination. Treatment with vitamin A, ribavirin, and immunoglobulins was started; nevertheless he developed severe pneumonitis and deceased. Broad vaccination coverage is crucial in protecting vulnerable subjects.

Understanding the causes and consequences of measles virus persistence

Measles is an acute systemic viral disease with initial amplification of infection in lymphoid tissue and subsequent spread over 10–14 days to multiple organs. Failure of the innate response to control initial measles virus (MeV) replication is associated with the ability of MeV to inhibit the induction of type I interferon and interferon-stimulated antiviral genes. Rather, the innate response is characterized by the expression of proteins regulated by nuclear factor kappa B and the inflammasome. With eventual development of the adaptive response, the rash appears with immune cell infiltration into sites of virus replication to initiate the clearance of infectious virus. However, MeV RNA is cleared much more slowly than recoverable infectious virus and remains present in lymphoid tissue for at least 6 months after infection. Persistence of viral RNA and protein suggests persistent low-level replication in lymphoid tissue that may facilitate maturation of the immune response, resulting in lifelong protection from reinfection, while persistence in other tissues (for example, the nervous system) may predispose to development of late disease such as subacute sclerosing panencephalitis. Further studies are needed to identify mechanisms of viral clearance and to understand the relationship between persistence and development of lifelong immunity.

Measles

Measles is a highly contagious disease that results from infection with measles virus and is still responsible for more than 100 000 deaths every year, down from more than 2 million deaths annually before the introduction and widespread use of measles vaccine. Measles virus is transmitted by the respiratory route and illness begins with fever, cough, coryza, and conjunctivitis followed by a characteristic rash. Complications of measles affect most organ systems, with pneumonia accounting for most measles-associated morbidity and mortality. The management of patients with measles includes provision of vitamin A. Measles is best prevented through vaccination, and the major reductions in measles incidence and mortality have renewed interest in regional elimination and global eradication. However, urgent efforts are needed to increase stagnating global coverage with two doses of measles vaccine through advocacy, education, and the strengthening of routine immunisation systems. Use of combined measles-rubella vaccines provides an opportunity to eliminate rubella and congenital rubella syndrome. Ongoing research efforts, including the development of point-of-care diagnostics and microneedle patches, will facilitate progress towards measles elimination and eradication.

Vaccination with recombinant adenovirus expressing peste des petits ruminants virus-F or -H proteins elicits T cell responses to epitopes that arises during PPRV infection

Peste des petits ruminants virus (PPRV) causes an economically important disease that limits productivity in small domestic ruminants and often affects the livestock of the poorest populations in developing countries. Animals that survive PPRV develop strong cellular and humoral responses, which are probably necessary for protection. Vaccination should thus aim at mimicking these natural responses. Immunization strategies against this morbillivirus using recombinant adenoviruses expressing PPRV-F or -H proteins can protect PPRV-challenged animals and permit differentiation of infected from vaccinated animals. Little is known of the T cell repertoire these recombinant vaccines induce. In the present work, we identified several CD4⁺ and CD8⁺ T cell epitopes in sheep infected with PPRV. We also show that recombinant adenovirus vaccination induced T cell responses to the same epitopes, and led to memory T cell differentiation. T cells primed by these recombinant adenovirus vaccines expanded after PPRV challenge and probably contributed to protection. These data validate the use of recombinant adenovirus expressing PPRV genes as DIVA strategies to control this highly contagious disease.

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.

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.

Development of new therapy for canine mammary cancer with recombinant measles virus

Oncolytic virotherapy is a promising treatment strategy for cancer. We previously generated a recombinant measles virus (rMV-SLAMblind) that selectively uses a poliovirus receptor-related 4 (PVRL4/Nectin4) receptor, but not signaling lymphocyte activation molecule (SLAM). We demonstrated that the virus exerts therapeutic effects against human breast cancer cells. Here, we examined the applicability of rMV-SLAMblind to treating canine mammary cancers (CMCs). We found that the susceptibilities of host cells to rMV-SLAMblind were dependent on canine Nectin-4 expression. Nectin-4 was detected in four of nine CMC cell lines. The rMV-SLAMblind efficiently infected those four Nectin-4-positive cell lines and was cytotoxic for three of them (CF33, CHMm, and CTBm). In vivo experiment showed that the administration of rMV-SLAMblind greatly suppressed the progression of tumors in mice xenografted with a CMC cell line (CF33). Immunohistochemistry revealed that canine Nectin-4 was expressed in 45% of canine mammary tumors, and the tumor cells derived from one clinical specimen were efficiently infected with rMV-SLAMblind. These results suggest that rMV-SLAMblind infects CMC cells and displays antitumor activity in vitro, in xenografts, and ex vivo. Therefore, oncolytic virotherapy with rMV-SLAMblind can be a novel method for treating CMCs.

Neonatal Vaccination: Challenges and Intervention Strategies

BACKGROUND

While vaccines have been tremendously successful in reducing the incidence of serious infectious diseases, newborns remain particularly vulnerable in the first few months of their life to life-threatening infections. A number of challenges exist to neonatal vaccination. However, recent advances in the understanding of neonatal immunology offer insights to overcome many of those challenges.

OBJECTIVE

This review will present an overview of the features of neonatal immunity which make vaccination difficult, survey the mechanisms of action of available vaccine adjuvants with respect to the unique features of neonatal immunity, and propose a possible mechanism contributing to the inability of neonates to generate protective immune responses to vaccines.

METHODS

We surveyed recent published findings on the challenges to neonatal vaccination and possible intervention strategies including the use of novel vaccine adjuvants to develop efficacious neonatal vaccines.

RESULTS

Challenges in the vaccination of neonates include interference from maternal antibody and excessive skewing towards Th2 immunity, which can be counteracted by the use of proper adjuvants.

CONCLUSION

Synergistic stimulation of multiple Toll-like receptors by incorporating well-defined agonist-adjuvant combinations to vaccines is a promising strategy to ensure a protective vaccine response in neonates.

Understanding respiratory syncytial virus (RSV) vaccine development and aspects of disease pathogenesis

Respiratory syncytial virus (RSV) is the most important cause of lower respiratory tract infections causing bronchiolitis and some mortality in young children and the elderly. Despite decades of research there is no licensed RSV vaccine. Although significant advances have been made in understanding the immune factors responsible for inducing vaccine-enhanced disease in animal models, less information is available for humans. In this review, we discuss the different types of RSV vaccines and their target population, the need for establishing immune correlates for vaccine efficacy, and how the use of different animal models can help predict vaccine efficacy and clinical outcomes in humans.

Maternal antibodies: clinical significance, mechanism of interference with immune responses, and possible vaccination strategies

Neonates have an immature immune system, which cannot adequately protect against infectious diseases. Early in life, immune protection is accomplished by maternal antibodies transferred from mother to offspring. However, decaying maternal antibodies inhibit vaccination as is exemplified by the inhibition of seroconversion after measles vaccination. This phenomenon has been described in both human and veterinary medicine and is independent of the type of vaccine being used. This review will discuss the use of animal models for vaccine research. I will review clinical solutions for inhibition of vaccination by maternal antibodies, and the testing and development of potentially effective vaccines. These are based on new mechanistic insight about the inhibitory mechanism of maternal antibodies. Maternal antibodies inhibit the generation of antibodies whereas the T cell response is usually unaffected. B cell inhibition is mediated through a cross-link between B cell receptor (BCR) with the Fcγ-receptor IIB by a vaccine-antibody complex. In animal experiments, this inhibition can be partially overcome by injection of a vaccine-specific monoclonal IgM antibody. IgM stimulates the B cell directly through cross-linking the BCR via complement protein C3d and antigen to the complement receptor 2 (CR2) signaling complex. In addition, it was shown that interferon alpha binds to the CD21 chain of CR2 as well as the interferon receptor and that this dual receptor usage drives B cell responses in the presence of maternal antibodies. In lieu of immunizing the infant, the concept of maternal immunization as a strategy to protect neonates has been proposed. This approach would still not solve the question of how to immunize in the presence of maternal antibodies but would defer the time of infection to an age where infection might not have such a detrimental outcome as in neonates. I will review successful examples and potential challenges of implementing this concept.

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.

Two replication-defective adenoviral vaccine vectors for the induction of immune responses to PPRV

Peste des petits ruminants is a highly contagious disease of small ruminants caused by a Morbillivirus, peste des petits ruminants virus (PPRV). Two recombinant replication-defective human adenovirus serotype 5 (Ad5) containing the highly immunogenic fusion protein (F) and hemaglutinine protein (H) genes from PPRV were constructed. HEK293A cells infected with either virus (Ad5-PPRV-F or -H) express F and H proteins respectively. These viruses were used to vaccinate mice by intramuscular inoculation. Both viruses elicited PPRV-specific B- and T-cell responses. Thus, after two immunizations, sera from immunized mice elicited neutralizing antibody response, indicating that this approach has the potential to confer protective immunity. In addition, we detected a significant antigen specific CD4(+) and CD8(+) T-cell response in mice vaccinated with either virus. These results indicate that these adenovirus constructs offer a promising alternative to current vaccine strategies for the development of PPRV DIVA vaccines.

Molecular Localization Techniques in the Diagnosis and Characterization of Nonhuman Primate Infectious Diseases

Molecular localization techniques remain important diagnostic and research tools for the pathologist evaluating nonhuman primate tissues. In situ hybridization and immunohistochemistry protocols have been developed for many important pathogens of nonhuman primates, including RNA and DNA viruses, prions, and bacterial, protozoal, and fungal pathogens. Such techniques will remain critical in defining the impact and relevance of novel agents on animal health and disease. A comparative pathology perspective often provides valuable insight to the best strategy for reagent development and can also facilitate interpretation of molecular localization patterns. Such a perspective is grounded in a firm understanding of microbe-host pathobiology. This review summarizes current molecular localization protocols used in the diagnosis of selected primate infectious diseases.

Synergistic induction of interferon α through TLR-3 and TLR-9 agonists identifies CD21 as interferon α receptor for the B cell response

Maternal antibodies inhibit seroconversion and the generation of measles virus (MeV)-specific antibodies (both neutralizing and non-neutralizing antibodies) after vaccination whereas T cell responses are usually unaffected. The lack of seroconversion leaves individuals susceptible to vaccine-preventable infections. Inhibition of antibody secretion is due to the inhibition of B cells through a cross-link of the B cell receptor with the inhibitory FcγIIB receptor (CD32) by maternal antibody/vaccine complexes. Here, we demonstrate that a combination of TLR-3 and TLR-9 agonists induces synergistically higher levels of type I interferon in vitro and in vivo than either agonist alone. The synergistic action of TLR-3 and TLR-9 agonists is based on a feedback loop through the interferon receptor. Finally, we have identified CD21 as a potential receptor for interferon α on B cells which contributes to interferon α-mediated activation of B cells in the presence of maternal antibodies. The combination leads to complete restoration of B cell and antibody responses after immunization in the presence of inhibitory MeV-specific IgG. The strong stimulatory action of type I interferon is due to the fact that type I interferon uses not only the interferon receptor but also CD21 as a functional receptor for B cell activation.

Maternal antibodies provide protection against infection with pathogens early in life but also interfere with vaccination. This interference is caused by a vaccine/maternal antibody complex which links the B cell receptor to the inhibitory CD32 molecule. Here, we show that this cross-link results in impaired B cell activation and proliferation which is correlated with diminished antibody responses. We also found that induction of large amounts of type I interferon restores the neutralizing antibody response in the presence of maternal antibodies. The best induction of type I interferon was accomplished by a combination of known activators of interferon secretion (a combination of TLR-3 and TLR-9 agonists). The strong stimulation by interferon is due to the previously unappreciated role of CD21 as functional receptor for interferon alpha. Our findings demonstrate that the dual receptor usage of type I interferon receptor and CD21 is crucial for B cell activation in the presence of maternal antibodies. This study suggests that measles vaccine, and potentially other vaccines, may induce optimal antibody responses when they are reconstituted with TLR-3 and TLR-9 agonists and thus these agonists may have great potential for clinical use.

Measles humoral and cell-mediated immunity in children aged 5-10 years after primary measles immunization administered at 6 or 9 months of age

BACKGROUND

Given the high infant measles mortality rate, there is interest in whether a measles immunization regimen beginning at <12 months of age provides lasting immunity.

METHODS

Measles-specific immune responses were evaluated in 70 children aged 5-10 years after primary measles vaccine administered at 6, 9, or 12 months.

RESULTS

At 5-10 years of age, the stimulation index for measles T-cell proliferation was 11.4 (SE, 1.3), 10.9 (SE, 1.5), and 14.4 (SE 2.1) when the first measles dose was given at 6, 9, or 12 months, respectively. Neutralizing antibody concentration (geometric mean titer [GMT]) in those immunized at 6 months of age was 125 mIU/mL (95% confidence interval [CI], 42-377) in the presence of passive antibodies (PAs) and 335 mIU/mL (95% CI, 211-531) in those without PAs; in those immunized at 9 months, GMTs were 186 mIU/mL (95% CI, 103-335) and 1080 mIU/mL (95% CI, 642-1827) in the presence and absence of PAs, respectively. The GMT was 707 mIU/mL (95% CI, 456-1095) when vaccine was administered at 12 months (P ≤ .04).

CONCLUSIONS

Measles-specific T-cell responses were sustained at 5-10 years of age regardless of age at time of primary measles immunization. Neutralizing antibody concentrations were lower in cohorts given the first vaccine dose at 6 months of age and in the presence of PAs; however, responses could be boosted by subsequent doses. Starting measles vaccination at <12 months of age may be beneficial during measles outbreaks or in endemic areas.

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.

Toll-like receptor 7 suppresses virus replication in neurons but does not affect viral pathogenesis in a mouse model of Langat virus infection

Toll-like receptor 7 (TLR7) recognizes guanidine-rich viral ssRNA and is an important mediator of peripheral immune responses to several ssRNA viruses. However, the role that TLR7 plays in regulating the innate immune response to ssRNA virus infections in specific organs such as the central nervous system (CNS) is not as clear. This study examined the influence of TLR7 on the neurovirulence of Langat virus (LGTV), a ssRNA tick-borne flavivirus. TLR7 deficiency did not substantially alter the onset or incidence of LGTV-induced clinical disease; however, it did significantly affect virus levels in the CNS with a log(10) increase in virus titres in brain tissue from TLR7-deficient mice. This difference in virus load was also observed following intracranial inoculation, indicating a direct effect of TLR7 deficiency on regulating virus replication in the brain. LGTV-induced type I interferon responses in the CNS were not dependent on TLR7, being higher in TLR7-deficient mice compared with wild-type controls. In contrast, induction of pro-inflammatory cytokines including tumour necrosis factor, CCL3, CCL4 and CXCL13 were dependent on TLR7. Thus, although TLR7 is not essential in controlling LGTV pathogenesis, it is important in controlling virus infection in neurons in the CNS, possibly by regulating neuroinflammatory responses.

Evaluating measles vaccines: can we assess cellular immunity?

Measles remains an important cause of childhood mortality, and global eradication of the disease is being seriously considered. Because of limitations of the current live-attenuated vaccines, new vaccines and routes of administration are being investigated. In the article under review, the authors have measured measles-specific humoral and cellular immune responses after two doses of live-attenuated measles vaccine and found limited correlation between the two. This study highlights an important issue, namely that we cannot assume humoral and cellular immune responses to go hand in hand. However, it remains to be determined if assays with peripheral blood lymphocytes can be used as a correlate of protection from disease.

Toxicology, biodistribution and shedding profile of a recombinant measles vaccine vector expressing HIV-1 antigens, in cynomolgus macaques

As a new human immunodeficiency virus type 1 (HIV-1) vaccine approach, the live-attenuated measles virus (MV) Schwarz vaccine strain was genetically engineered to express the F4 antigen (MV1-F4). F4 is a fusion protein comprising HIV-1 antigens p17 and p24, reverse transcriptase and Nef. This study assessed the toxicity, biodistribution and shedding profiles of MV1-F4. Cynomolgus macaques were intramuscularly immunized one or three times with the highest dose of MV1-F4 intended for clinical use, the reference (Schwarz) measles vaccine or saline, and monitored clinically for 11 or 85 days. Toxicological parameters included local and systemic clinical signs, organ weights, haematology, clinical and gross pathology and histopathology. Both vaccines were well tolerated, with no morbidity, clinical signs or gross pathological findings observed. Mean spleen weights were increased after three doses of either vaccine, which corresponded with increased numbers and/or sizes of germinal centers. This was likely a result of the immune response to the vaccines. Either vaccine virus replicated preferentially in secondary lymphoid organs and to a lesser extent in epithelium-rich tissues (e.g., intestine, urinary bladder and trachea) and the liver. At the expected peak of viremia, viral RNA was detected in some biological fluid samples from few animals immunized with either vaccine, but none of these samples contained infectious virus. In conclusion, no shedding of infectious viral particles was identified in cynomolgus monkeys after injection of MV1-F4 or Schwarz measles vaccines. Furthermore, no toxic effect in relation to the MV vaccination was found with these vaccines in this study.

Prolonged persistence of measles virus RNA is characteristic of primary infection dynamics

Measles virus (MeV) is the poster child for acute infection followed by lifelong immunity. However, recent work shows the presence of MeV RNA in multiple sites for up to 3 mo after infection in a proportion of infected children. Here, we use experimental infection of rhesus macaques to show that prolonged RNA presence is characteristic of primary infection. We found that viral RNA persisted in the blood, respiratory tract, or lymph nodes four to five times longer than the infectious virus and that the clearance of MeV RNA from blood happened in three phases: rapid decline coincident with clearance of infectious virus, a rebound phase with increases up to 10-fold, and a phase of slow decrease to undetectable levels. To examine the effect of individual host immune factors on MeV load dynamics further, we developed a mathematical model that expressed viral replication and elimination in terms of the strength of MeV-specific T-cell responses, antibody responses, target cell limitations, and immunosuppressive activity of regulatory T cells. Based on the model, we demonstrate that viral dynamics, although initially regulated by T cells, require antibody to eliminate viral RNA. These results have profound consequences for our view of acute viral infections, the development of prolonged immunity, and, potentially, viral evolution.

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.

The association of CD46, SLAM and CD209 cellular receptor gene SNPs with variations in measles vaccine-induced immune responses: a replication study and examination of novel polymorphisms

BACKGROUND

The measles virus (MV) interacts with two known cellular receptors: CD46 and SLAM. The transmembrane receptor CD209 interacts with MV and augments dendritic cell infection.

METHODS

764 subjects previously immunized with measles-mumps-rubella vaccine were genotyped for 66 candidate SNPs in the CD46, SLAM and CD209 genes as part of a larger study.

RESULTS

A previously detected association of the CD46 SNP rs2724384 with measles-specific antibodies was successfully replicated in this study. Increased representation of the minor allele G for an intronic CD46 SNP was associated with an allele dose-related decrease (978 vs. 522 mIU/ml, p = 0.0007) in antibody levels. This polymorphism rs2724384 also demonstrated associations with IL-6 (p = 0.02), IFN-α (p = 0.007) and TNF-α (p = 0.0007) responses. Two polymorphisms (coding rs164288 and intronic rs11265452) in the SLAM gene that were associated with measles antibody levels in our previous study were associated with IFN-γ Elispot (p = 0.04) and IL-10 responses (p = 0.0008), respectively, in this study. We found associations between haplotypes, AACGGAATGGAAAG (p = 0.009) and GGCCGAGAGGAGAG (p < 0.001), in the CD46 gene and TNF-α secretion.

CONCLUSION

Understanding the functional and mechanistic consequences of these genetic polymorphisms on immune response variations could assist in directing new measles and potentially other viral vaccine design, and in better understanding measles immunogenetics.

Biological feasibility of measles eradication

Recent progress in reducing global measles mortality has renewed interest in measles eradication. Three biological criteria are deemed important for disease eradication: (1) humans are the sole pathogen reservoir; (2) accurate diagnostic tests exist; and (3) an effective, practical intervention is available at reasonable cost. Interruption of transmission in large geographical areas for prolonged periods further supports the feasibility of eradication. Measles is thought by many experts to meet these criteria: no nonhuman reservoir is known to exist, accurate diagnostic tests are available, and attenuated measles vaccines are effective and immunogenic. Measles has been eliminated in large geographical areas, including the Americas. Measles eradication is biologically feasible. The challenges for measles eradication will be logistical, political, and financial.

Successful respiratory immunization with dry powder live-attenuated measles virus vaccine in rhesus macaques

Measles remains an important cause of childhood mortality worldwide. Sustained high vaccination coverage is the key to preventing measles deaths. Because measles vaccine is delivered by injection, hurdles to high coverage include the need for trained medical personnel and a cold chain, waste of vaccine in multidose vials and risks associated with needle use and disposal. Respiratory vaccine delivery could lower these barriers and facilitate sustained high coverage. We developed a novel single unit dose, dry powder live-attenuated measles vaccine (MVDP) for respiratory delivery without reconstitution. We tested the immunogenicity and protective efficacy in rhesus macaques of one dose of MVDP delivered either with a mask or directly intranasal with two dry powder inhalers, PuffHaler and BD Solovent. MVDP induced robust measles virus (MeV)-specific humoral and T-cell responses, without adverse effects, which completely protected the macaques from infection with wild-type MeV more than one year later. Respiratory delivery of MVDP was safe and effective and could aid in measles control.

Measles virus-induced suppression of immune responses

Measles is an important cause of child mortality that has a seemingly paradoxical interaction with the immune system. In most individuals, the immune response is successful in eventually clearing measles virus (MV) infection and in establishing life-long immunity. However, infection is also associated with persistence of viral RNA and several weeks of immune suppression, including loss of delayed type hypersensitivity responses and increased susceptibility to secondary infections. The initial T-cell response includes CD8+ and T-helper 1 CD4+ T cells important for control of infectious virus. As viral RNA persists, there is a shift to a T-helper 2 CD4+ T-cell response that likely promotes B-cell maturation and durable antibody responses but may suppress macrophage activation and T-helper 1 responses to new infections. Suppression of mitogen-induced lymphocyte proliferation can be induced by lymphocyte infection with MV or by lymphocyte exposure to a complex of the hemagglutinin and fusion surface glycoproteins without infection. Dendritic cells (DCs) are susceptible to infection and can transmit infection to lymphocytes. MV-infected DCs are unable to stimulate a mixed lymphocyte reaction and can induce lymphocyte unresponsiveness through expression of MV glycoproteins. Thus, multiple factors may contribute both to measles-induced immune suppression and to the establishment of durable protective immunity.

Induction of type I interferon secretion through recombinant Newcastle disease virus expressing measles virus hemagglutinin stimulates antibody secretion in the presence of maternal antibodies

Measles virus (MV) vaccine effectively protects seronegative individuals against infection. However, inhibition of vaccine-induced seroconversion by maternal antibodies after vaccination remains a problem, as it leaves infants susceptible to MV infection. In cotton rats, passive transfer of MV-specific IgG mimics maternal antibodies and inhibits vaccine-induced seroconversion. Here, we report that immunization in the presence of passively transferred IgG inhibits the secretion of neutralizing antibodies but not the generation of MV-specific B cells. This finding suggested that MV-specific B cells require an additional stimulus to mature into antibody-secreting plasma cells. In order to provide such a stimulus, we generated a recombinant Newcastle disease virus (NDV) expressing the MV hemagglutinin (NDV-H). In contrast to MV, NDV-H induced high levels of type I interferon in plasmacytoid dendritic cells and in lung tissue. In cotton rats immunized with NDV-H, neutralizing antibodies were also generated in the presence of passively transferred antibodies. In the latter case, however, the level and kinetics of antibody generation were reduced. In vitro, alpha interferon stimulated the activation of MV-specific B cells from MV-immune spleen cells. NDV infection (which induces alpha interferon) had the same effect, and stimulation could be abrogated by antibodies neutralizing alpha interferon, but not interleukin 6 (IL-6). In vivo, coapplication of UV-inactivated MV with NDV led to increased MV-specific antibody production in the presence and absence of passively transferred antibodies. These data indicate that MV-specific B cells are being generated after immunization in the presence of maternal antibodies and that the provision of alpha interferon as an additional signal leads to antibody secretion.

Effect of maternal HIV infection on measles susceptibility during early infancy: implications for optimizing protection of the infant

The measles virus was first isolated as the causative pathogen of measles approximately 50 years ago by John Enders and Thomas Peebles. Despite a safe and effective vaccine extant for nearly the same amount of time, control of measles nevertheless remains a challenge in developing countries. This article investigates the possible contribution of maternal HIV infection on measles susceptibility in infants. The current WHO position on measles vaccination in HIV-infected children recommends vaccinating asymptomatic HIV-infected infants as early as 6 months of age, followed with two additional doses at 9 and 18 months. This is rarely implemented due to logistical constraints related to early HIV diagnosis in infants and access to vaccines in low-resource settings. In addition, measles vaccine safety and immunogenicity in HIV-infected children are based on very low levels of scientific evidence. There are no specific recommendations for measles immunization of HIV-uninfected children born to HIV-infected mothers. We reviewed the available data on transplacental transfer of measles antibody and the influence of HIV, the findings of which suggest that consideration should be given to extending early measles immunization to all infants born to HIV-infected women.