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

Effects of prime-boost strategies on the protective efficacy and immunogenicity of a PLGA (85:15)-encapsulated Chlamydia recombinant MOMP nanovaccine

To begin to optimize the immunization routes for our reported PLGA-rMOMP nanovaccine [PLGA-encapsulated Chlamydia muridarum (Cm) recombinant major outer membrane protein (rMOMP)], we compared two prime-boost immunization strategies [subcutaneous (SC) and intramuscular (IM-p) prime routes followed by two SC-boosts)] to evaluate the nanovaccine-induced protective efficacy and immunogenicity in female BALB/c mice. Our results showed that mice immunized via the SC and IM-p routes were protected against a Cm genital challenge by a reduction in bacterial burden and with fewer bacteria in the SC mice. Protection of mice correlated with rMOMP-specific Th1 (IL-2 and IFN-γ) and not Th2 (IL-4, IL-9, and IL-13) cytokines, and CD4+ memory (CD44highCD62Lhigh) T-cells, especially in the SC mice. We also observed higher levels of IL-1α, IL-6, IL-17, CCL-2, and G-CSF in SC-immunized mice. Notably, an increase of cytokines/chemokines was seen after the challenge in the SC, IM-p, and control mice (rMOMP and PBS), suggesting a Cm stimulation. In parallel, rMOMP-specific Th1 (IgG2a and IgG2b) and Th2 (IgG1) serum, mucosal, serum avidity, and neutralizing antibodies were more elevated in SC than in IM-p mice. Overall, the homologous SC prime-boost immunization of mice induced enhanced cellular and antibody responses with better protection against a genital challenge compared to the heterologous IM-p.

HIV specific Th1 responses are altered in Ugandans with HIV and Schistosoma mansoni coinfection

BACKGROUND

Fishing communities surrounding Lake Victoria in Uganda have HIV prevalence of 28% and incidence rates of 5 per 100 person years. More than 50% of the local fishermen are infected with Schistosoma mansoni (S. mansoni). We investigated the role of S. mansoni coinfection as a possible modifier of immune responses against HIV. Using polychromatic flow cytometry and Gran-ToxiLux assays, HIV specific responses, T cell phenotypes, antibody-dependent cell-mediated cytotoxic (ADCC) potency and titres were compared between participants with HIV-S. mansoni coinfection and participants with HIV infection alone.

RESULTS

S. mansoni coinfection was associated with a modified pattern of anti-HIV responses, including lower frequency of bifunctional (IFNγ + IL-2 - TNF-α+) CD4 T cells, higher overall CD4 T cell activation and lower HIV ADCC antibody titres, compared to participants with HIV alone.

CONCLUSIONS

These results support the hypothesis that S. mansoni infection affects T cell and antibody responses to HIV in coinfected individuals.

The Influence of Sex, Body Mass Index, and Age on Cellular and Humoral Immune Responses Against Measles After a Third Dose of Measles-Mumps-Rubella Vaccine

BACKGROUND

A third dose of measles-mumps-rubella vaccine (MMR3) is recommended in mumps outbreak scenarios, but the immune response and the need for widespread use of MMR3 remain uncertain. Herein, we characterized measles-specific immune responses to MMR3 in a cohort of 232 healthy subjects.

METHODS

Serum and peripheral blood mononuclear cells (PBMCs) were sampled at day 0 and day 28 after MMR3. Measles-specific binding and neutralizing antibodies were quantified in sera by enzyme-linked immunosorbent assay and a microneutralization assay, respectively. PBMCs were stimulated with inactivated measles virus, and the release of cytokines/chemokines was assessed by a multiplex assay. Demographic variables of subjects were examined for potential correlations with immune outcomes.

RESULTS

Of the study participants, 95.69% and 100% were seropositive at day 0 and day 28, respectively. Antibody avidity significantly increased from 38.08% at day 0 to 42.8% at day 28 (P = .00026). Neutralizing antibodies were significantly enhanced, from 928.7 at day 0 to 1289.64 mIU/mL at day 28 (P = .0001). Meanwhile, cytokine/chemokine responses remained largely unchanged. Body mass index was significantly correlated with the levels of inflammatory cytokines/chemokines.

CONCLUSIONS

Measles-specific humoral immune responses, but not cellular responses, were enhanced after MMR3 receipt, extending current understanding of immune responses to MMR3 and supporting MMR3 administration to seronegative or high-risk individuals.

Seroprevalence of Measles Antibodies in a Highly MMR-Vaccinated Population

As an extremely contagious pathogen, a high rate of vaccine coverage and the durability of vaccine-induced immunity are key factors to control and eliminate measles. Herein, we assessed the seroprevalence of antibodies specific to measles in a cohort of 1393 adults (20-44 years old). ELISA results showed a nontrivial proportion of 37.6% study subjects being negative for measles immunoglobulin G (IgG). We also found significant influences of sex and age of the study cohort on the IgG level. Our findings suggest that even within a highly vaccinated population, a subset of individuals may still have sub-optimal immunity against measles and potentially be susceptible during any future measles outbreaks.

Breakthrough Infections: A Challenge towards Measles Elimination?

Measles is one of the most contagious diseases known to man. Despite the existence of a safe and effective live attenuated vaccine, measles can appear in vaccinated individuals. Paradoxically, breakthrough cases increase as vaccination coverage in the general population rises. In measles endemic areas, breakthrough cases represent less than 10% of total infections, while in areas with high vaccination coverage these are over 10% of the total. Two different vaccination failures have been described: primary vaccination failure, which consists in the complete absence of humoral response and occurs in around 5% of vaccinated individuals; and secondary vaccination failure is due to waning immunity or incomplete immunity and occurs in 2–10% of vaccinees. Vaccination failures are generally associated with lower viral loads and milder disease (modified measles) since vaccination limits the risk of complicated disease. Vaccination failure seems to occur between six and twenty-six years after the last vaccine dose administration. This review summarizes the literature about clinical, serological, epidemiological, and molecular characteristics of measles breakthrough cases and their contribution to virus transmission. In view of the measles elimination goal, the assessment of the potential decline in antibody protection and the targeted implementation of catch-up vaccination are essential.

Systematic Determination of TCR–Antigen and Peptide–MHC Binding Kinetics among Field Variants of a Theileria parva Polymorphic CTL Epitope

Positions 1–3 in the Tp9 CTL epitope are required for binding to BoLA-1*023:01.

Positions 5–8 in the Tp9 epitope are required for TCR recognition in diverse CTLs.

Tp9-specific CTLs from Muguga-immunized animals can cross-react with variants 4 and 7.

CTLs are known to contribute to immunity toward Theileria parva, the causative agent of East Coast fever. The Tp9_67–75 CTL epitope from the Muguga strain of T. parva is polymorphic in other parasite strains. Identifying the amino acids important for MHC class I binding, as well as TCR recognition of epitopes, can allow the strategic selection of Ags to induce cellular immunity toward T. parva. In this study, we characterized the amino acids important for MHC class I binding and TCR recognition in the Tp9_67–75 epitope using alanine scanning and a series of variant peptide sequences to probe these interactions. In a peptide–MHC class I binding assay, we found that the amino acids at positions 1, 2, and 3 were critical for binding to its restricting MHC class I molecule BoLA-1*023:01. With IFN-γ ELISPOT and peptide–MHC class I Tet staining assays on two parasite-specific bovine CTL lines, we showed that amino acids at positions 5–8 in the epitope were required for TCR recognition. Only two of eight naturally occurring polymorphic Tp9 epitopes were recognized by both CTLs. Finally, using a TCR avidity assay, we found that a higher TCR avidity was associated with a stronger functional response toward one of two variants recognized by the CTL. These data add to the growing knowledge on the cross-reactivity of epitope-specific CTLs and specificities that may be required in the selection of Ags in the design of a wide-spectrum vaccine for East Coast fever.

Recommendations for Vaccination in Children with Atopic Dermatitis Treated with Dupilumab: A Consensus Meeting, 2020

Dupilumab is the only biologic therapy currently approved in Europe and the United States for severe atopic dermatitis in patients 6 years of age or older. Off-label use is rationalized in younger children with severe atopic dermatitis. Decisions about vaccination for children on dupilumab are complex and depend on both the child’s current treatment and the type of vaccination required. To achieve consensus on recommendations for vaccination of pediatric patients with atopic dermatitis treated with or planning to start dupilumab, a review of the literature and a modified-Delphi process was conducted by a working group of 5 panelists with expertise in dermatology, immunology, infectious diseases and vaccination. Here, we provide seven recommendations for vaccination of pediatric patients with atopic dermatitis treated with or planning to start dupilumab. These recommendations serve to guide physicians’ decisions about vaccination in children with atopic dermatitis treated with dupilumab. Furthermore, we highlight an unmet need for research to determine how significantly dupilumab affects cellular and humoral immune responses to vaccination with live attenuated and inactivated vaccines.

A durable protective immune response to wild-type measles virus infection of macaques is due to viral replication and spread in lymphoid tissues

Infection with wild-type (WT) measles virus (MeV) is an important cause of childhood mortality that leads to lifelong protective immunity in survivors. WT MeV and the live-attenuated MeV used in the measles vaccine (LAMV) are antigenically similar, but the determinants of attenuation are unknown, and protective immunity induced by LAMV is less robust than that induced by WT MeV. To identify factors that contribute to these differences, we compared virologic and immunologic responses after respiratory infection of rhesus macaques with WT MeV or LAMV. In infected macaques, WT MeV replicated efficiently in B and T lymphocytes with spreading throughout lymphoid tissues resulting in prolonged persistence of viral RNA. In contrast, LAMV replicated efficiently in the respiratory tract but displayed limited spread to lymphoid tissue or peripheral blood mononuclear cells. In vitro, WT MeV and LAMV replicated similarly in macaque primary respiratory epithelial cells and human lymphocytes, but LAMV-infected lymphocytes produced little virus. Plasma concentrations of interleukin-1β (IL-1β), IL-12, interferon-γ (IFN-γ), CCL2, CCL11, CXCL9, and CXCL11 increased in macaques after WT MeV but not LAMV infection. WT MeV infection induced more protective neutralizing, hemagglutinin-specific antibodies and bone marrow plasma cells than did LAMV infection, although numbers of MeV-specific IFN-γ- and IL-4-producing T cells were comparable. Therefore, MeV attenuation may involve altered viral replication in lymphoid tissue that limited spread and decreased the host antibody response, suggesting a link between lifelong protective immunity and the ability of WT MeV, but not LAMV, to spread in lymphocytes.

Serotypic evolution of measles virus is constrained by multiple co-dominant B cell epitopes on its surface glycoproteins

After centuries of pestilence and decades of global vaccination, measles virus (MeV) genotypes capable of evading vaccine-induced immunity have not emerged. Here, by systematically building mutations into the hemagglutinin (H) glycoprotein of an attenuated measles virus strain and assaying for serum neutralization, we show that virus evolution is severely constrained by the existence of numerous co-dominant H glycoprotein antigenic sites, some critical for binding to the pathogenicity receptors SLAMF1 and nectin-4. We further demonstrate the existence in serum of protective neutralizing antibodies targeting co-dominant fusion (F) glycoprotein epitopes. Lack of a substantial reduction in serum neutralization of mutant measles viruses that retain even one of the co-dominant antigenic sites makes evolution of pathogenic measles viruses capable of escaping serum neutralization in vaccinated individuals extremely unlikely.

MeV-Stealth: A CD46-specific oncolytic measles virus resistant to neutralization by measles-immune human serum

The frequent overexpression of CD46 in malignant tumors has provided a basis to use vaccine-lineage measles virus (MeV) as an oncolytic virotherapy platform. However, widespread measles seropositivity limits the systemic deployment of oncolytic MeV for the treatment of metastatic neoplasia. Here, we report the development of MeV-Stealth, a modified vaccine MeV strain that exhibits oncolytic properties and escapes antimeasles antibodies in vivo. We engineered this virus using homologous envelope glycoproteins from the closely-related but serologically non-cross reactive canine distemper virus (CDV). By fusing a high-affinity CD46 specific single-chain antibody fragment (scFv) to the CDV-Hemagglutinin (H), ablating its tropism for human nectin-4 and modifying the CDV-Fusion (F) signal peptide we achieved efficient retargeting to CD46. A receptor binding affinity of ~20 nM was required to trigger CD46-dependent intercellular fusion at levels comparable to the original MeV H/F complex and to achieve similar antitumor efficacy in myeloma and ovarian tumor-bearing mice models. In mice passively immunized with measles-immune serum, treatment of ovarian tumors with MeV-Stealth significantly increased overall survival compared with treatment with vaccine-lineage MeV. Our results show that MeV-Stealth effectively targets and lyses CD46-expressing cancer cells in mouse models of ovarian cancer and myeloma, and evades inhibition by human measles-immune serum. MeV-Stealth could therefore represent a strong alternative to current oncolytic MeV strains for treatment of measles-immune cancer patients.

Vaccine strains of the measles virus (MeV) have been shown to be promising anti-cancer agents because of the frequent overexpression of the host-cell receptor CD46 in human malignancies. However, anti-MeV antibodies in the human population severely restrict the use of MeV as an oncolytic agent. Here, we engineered a neutralization-resistant MeV vaccine, MeV-Stealth, by replacing its envelope glycoproteins with receptor-targeted glycoproteins from wild-type canine distemper virus. By fully-retargeting the new envelope to the receptor CD46, we found that in mouse models of ovarian cancer and myeloma MeV-Stealth displayed oncolytic properties similar to the parental MeV vaccine. Furthermore, we found that passive immunization with measles-immune human serum did not eliminate the oncolytic potency of the MeV-Stealth, whereas it did destroy the potency of the parental MeV strain. The virus we here report may be considered a suitable oncolytic agent for the treatment of MeV-immune patients.

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.

Depletion of CD8+ T cells from vaccinated goats does not affect protection from challenge with wild-type peste des petits ruminants virus

Peste des petits ruminants (PPR) is a severe disease of goats and sheep that is widespread in Africa, the Middle East and Asia. The disease is caused by peste des petits ruminants virus (PPRV); cell culture-attenuated strains of PPRV have been shown, both experimentally and by extensive use in the field, to be effective vaccines and are widely used. We have previously demonstrated that these vaccines elicit both serological (PPRV-specific antibody) and cell-based (PPRV-specific CD4⁺ and CD8⁺ T cells) immune responses. However, it is not known which of these responses are required for protection from PPRV, information that would be useful in the evaluation of new vaccines that are being developed to provide the capability to differentiate infected and vaccinated animals (DIVA capability). To begin to address this issue, we have used a complement-fixing monoclonal antibody recognizing caprine CD8 to deplete >99.9% of circulating CD8⁺ T cells from vaccinated goats. Animals were then infected with wild-type PPRV. Despite the absence of the CD8⁺ T-cell component of the vaccine-induced immune response, the vaccinated animals were almost fully protected, showing no pyrexia or viraemia, and almost no clinical signs. These data suggest that a virus-specific CD8⁺ T-cell response is not critical for protection against PPRV and that virus-specific antibody and/or CD4⁺ T cells are the main mediators of protection. We have also shown that the leucopenia caused by infection with wild-type PPRV affects all major classes of circulating leucocytes.

Effects of Social Housing Changes on Immunity and Vaccine-Specific Immune Responses in Adolescent Male Rhesus Macaques

Nonhuman primates (NHPs) in research institutions may be housed in a variety of social settings, such as group housing, pair housing or single housing based on the needs of studies. Furthermore, housing may change over the course of studies. The effects of housing and changes in housing on cell activation and vaccine mediated immune responses are not well documented. We hypothesized that animals moved indoors from group to single housing (GH-SH) would experience more stress than those separated from groups into pair housing (GH-PH), or those placed briefly into pair housing and separated 5 weeks later into single housing (GH-PH-SH). We also compared the effects of separation from group to pair housing with the separation from pair to single housing. Eighteen male rhesus macaques were followed over the course of changes in housing condition over 10–14 weeks, as well as prior to and after primary vaccination with a commercially available measles vaccine. We identified two phenotypic biomarkers, namely total CD8 population and proliferating B cells, that differed significantly across treatment groups over time. At 10 weeks post-separation, levels of proliferating B cells were higher in GH-SH subjects compared to GH-PH subjects, and in the latter, levels were lower at 10 weeks than prior to removal from group housing. At 2 weeks post-separation from group to single housing, the frequency of CD8+ T cells was higher in GH-SH subjects compared to one week post separation from pair into single housing in the GH-PH-SH subjects. Comparing the same elapsed time since the most recent separation activated CD20 populations were persistently higher in the GH-SH animals than the GH-PH-SH animals. Housing configuration did not influence vaccine-mediated responses. Overall, our study found benefits of pair housing over single housing, suggesting that perturbations in immune function will be more severe following separation from group to single housing than from pair to single housing, and supporting the use of short-duration pair housing even when animals must subsequently be separated. These findings are useful for planning the housing configurations of research NHPs used for vaccine studies and other studies where immune response is being assessed.

Measles pathogenesis, immune suppression and animal models

Measles virus causes a disease with seemingly innocent symptoms, such as fever and rash. However, measles immune suppression causes increased susceptibility to opportunistic infections that are responsible for the majority of over 100000 yearly fatalities. The pathogenesis of measles is complex, because measles virus uses multiple receptors to infect different cell types in different phases of the disease. Experimental morbillivirus infections with wild-type viruses in natural host species have demonstrated that direct infection and depletion of memory immune cells causes immune amnesia. This was confirmed in studies of a measles outbreak in unvaccinated children and provides an explanation for epidemiological observations of long-term increases in morbidity and mortality after measles.

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.

Probing Morbillivirus Antisera Neutralization Using Functional Chimerism between Measles Virus and Canine Distemper Virus Envelope Glycoproteins

Measles virus (MeV) is monotypic. Live virus challenge provokes a broadly protective humoral immune response that neutralizes all known measles genotypes. The two surface glycoproteins, H and F, mediate virus attachment and entry, respectively, and neutralizing antibodies to H are considered the main correlate of protection. Herein, we made improvements to the MeV reverse genetics system and generated a panel of recombinant MeVs in which the globular head domain or stalk region of the H glycoprotein or the entire F protein, or both, were substituted with the corresponding protein domains from canine distemper virus (CDV), a closely related morbillivirus that resists neutralization by measles-immune sera. The viruses were tested for sensitivity to human or guinea pig neutralizing anti-MeV antisera and to ferret anti-CDV antisera. Virus neutralization was mediated by antibodies to both H and F proteins, with H being immunodominant in the case of MeV and F being so in the case of CDV. Additionally, the globular head domains of both MeV and CDV H proteins were immunodominant over their stalk regions. These data shed further light on the factors constraining the evolution of new morbillivirus serotypes.

Effects of pre-existing orthopoxvirus-specific immunity on the performance of Modified Vaccinia virus Ankara-based influenza vaccines

The replication-deficient orthopoxvirus modified vaccinia virus Ankara (MVA) is a promising vaccine vector against various pathogens and has an excellent safety record. However, pre-existing vector-specific immunity is frequently suggested to be a drawback of MVA-based vaccines. To address this issue, mice were vaccinated with MVA-based influenza vaccines in the presence or absence of orthopoxvirus-specific immunity. Importantly, protective efficacy of an MVA-based influenza vaccine against a homologous challenge was not impaired in the presence of orthopoxvirus-specific pre-existing immunity. Nonetheless, orthopoxvirus-specific pre-existing immunity reduced the induction of antigen-specific antibodies under specific conditions and completely prevented induction of antigen-specific T cell responses by rMVA-based vaccination. Notably, antibodies induced by vaccinia virus vaccination, both in mice and humans, were not capable of neutralizing MVA. Thus, when using rMVA-based vaccines it is important to consider the main correlate of protection induced by the vaccine, the vaccine dose and the orthopoxvirus immune status of vaccine recipients.

Beyond vaccine dosage, genetic modifications to the current measles vaccine to overcome maternal passive immunity

Pediatric measles infections still cause an unacceptable rate of childhood mortality. Despite the availability of an efficient preventative vaccine, measles virus can spread among the population of even developed countries. The availability of a reverse genetic system for measles, based on recombinant virus recovery from cDNA, allows application of the principles of intelligent vaccine design. Using this system, we recently demonstrated that a version of the current attenuated measles virus strain genetically modified to express higher levels of the viral hemagglutinin protein, the major target of neutralizing antibodies, is more immunogenic and resists passive immunity with a better immunogenicity profile in a mouse model than the current measles vaccine. The significance and practicality of this development are discussed.

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.

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.

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.

Achieving safe, effective, and durable Zika virus vaccines: lessons from dengue

Newly proposed candidate Zika virus vaccines might or might not succeed in raising safe, effective, and durable protection against human Zika virus infections or syndromes. Analyses of a clinically tested and licensed dengue vaccine that failed to protect seronegative individuals from breakthrough or enhanced dengue infections suggest that poor T-cell immunity might have contributed to protection failure. Because of the similarity of Zika and dengue viruses, an analogous unwanted outcome might occur with some Zika virus vaccine designs. A successful Zika virus vaccine requires challenge experiments that are done at long intervals after immunisation and that identify protection as the absence of viraemia and the absence of an anamnestic antibody response. T-cell immunity might be an essential component of safe, efficacious, and durable Zika virus vaccines.

Antigenic Drift Defines a New D4 Subgenotype of Measles Virus

The measles virus hemagglutinin (MeV-H) protein is the main target of protective neutralizing antibodies. Using a panel of monoclonal antibodies (MAbs) that recognize known major antigenic sites in MeV-H, we identified a D4 genotype variant that escapes neutralization by MAbs targeting the neutralizing epitope (NE) antigenic site. By site-directed mutagenesis, L249P was identified as the critical mutation disrupting the NE in this genotype D4 variant. Forty-two available D4 genotype gene sequences were subsequently analyzed and divided into 2 groups according to the presence or absence of the L249P MeV-H mutation. Further analysis of the MeV-N gene sequences of these 2 groups confirmed that they represent clearly definable, sequence-divergent D4 subgenotypes, which we named subgenotypes D4.1 and D4.2. The subgenotype D4.1 MeVs were isolated predominantly in Kenya and Ethiopia, whereas the MAb-resistant subgenotype D4.2 MeVs were isolated predominantly in France and Great Britain, countries with higher vaccine coverage rates. Interestingly, D4.2 subgenotype viruses showed a trend toward diminished susceptibility to neutralization by human sera pooled from approximately 60 to 80 North American donors. Escape from MAb neutralization may be a powerful epidemiological surveillance tool to monitor the evolution of new MeV subgenotypes.IMPORTANCE Measles virus is a paradigmatic RNA virus, as the antigenic composition of the vaccination has not needed to be updated since its discovery. The vaccine confers protection by inducing neutralizing antibodies that interfere with the function of the hemagglutinin protein. Viral strains are indistinguishable serologically, although characteristic nucleotide sequences differentiate 24 genotypes. In this work, we describe a distant evolutionary branch within genotype D4. Designated subgenotype D4.2, this virus is distinguishable by neutralization with vaccine-induced monoclonal antibodies that target the neutralizing epitope (NE). The subgenotype D4.2 viruses have a higher predominance in countries with intermediary levels of vaccine coverage. Our studies demonstrate that subgenotype D4.2 lacks epitopes associated with half of the known antigenic sites, which significantly impacts our understanding of measles virus evolution.

The Predominant CD4+ Th1 Cytokine Elicited to Chlamydia trachomatis Infection in Women Is Tumor Necrosis Factor Alpha and Not Interferon Gamma

Chlamydia trachomatis infection is the most prevalent bacterial sexually transmitted infection and can cause significant reproductive morbidity in women. There is insufficient knowledge of C. trachomatis-specific immune responses in humans, which could be important in guiding vaccine development efforts. In contrast, murine models have clearly demonstrated the essential role of T helper type 1 (Th1) cells, especially interferon gamma (IFN-γ)-producing CD4⁺ T cells, in protective immunity to chlamydia. To determine the frequency and magnitude of Th1 cytokine responses elicited to C. trachomatis infection in humans, we stimulated peripheral blood mononuclear cells from 90 chlamydia-infected women with C. trachomatis elementary bodies, Pgp3, and major outer membrane protein and measured IFN-γ-, tumor necrosis factor alpha (TNF-α)-, and interleukin-2 (IL-2)-producing CD4⁺ and CD8⁺ T-cell responses using intracellular cytokine staining. The majority of chlamydia-infected women elicited CD4⁺ TNF-α responses, with frequency and magnitude varying significantly depending on the C. trachomatis antigen used. CD4⁺ IFN-γ and IL-2 responses occurred infrequently, as did production of any of the three cytokines by CD8⁺ T cells. About one-third of TNF-α-producing CD4⁺ T cells coproduced IFN-γ or IL-2. In summary, the predominant Th1 cytokine response elicited to C. trachomatis infection in women was a CD4⁺ TNF-α response, not CD4⁺ IFN-γ, and a subset of the CD4⁺ TNF-α-positive cells produced a second Th1 cytokine.

A large population-based association study between HLA and KIR genotypes and measles vaccine antibody responses

Human antibody response to measles vaccine is highly variable in the population. Host genes contribute to inter-individual antibody response variation. The killer cell immunoglobulin-like receptors (KIR) are recognized to interact with HLA molecules and possibly influence humoral immune response to viral antigens. To expand on and improve our previous work with HLA genes, and to explore the genetic contribution of KIR genes to the inter-individual variability in measles vaccine-induced antibody responses, we performed a large population-based study in 2,506 healthy immunized subjects (ages 11 to 41 years) to identify HLA and KIR associations with measles vaccine-induced neutralizing antibodies. After correcting for the large number of statistical tests of allele effects on measles-specific neutralizing antibody titers, no statistically significant associations were found for either HLA or KIR loci. However, suggestive associations worthy of follow-up in other cohorts include B*57:01, DQB1*06:02, and DRB1*15:05 alleles. Specifically, the B*57:01 allele (1,040 mIU/mL; p = 0.0002) was suggestive of an association with lower measles antibody titer. In contrast, the DQB1*06:02 (1,349 mIU/mL; p = 0.0004) and DRB1*15:05 (2,547 mIU/mL; p = 0.0004) alleles were suggestive of an association with higher measles antibodies. Notably, the associations with KIR genotypes were strongly nonsignificant, suggesting that KIR loci in terms of copy number and haplotypes are not likely to play a major role in antibody response to measles vaccination. These findings refine our knowledge of the role of HLA and KIR alleles in measles vaccine-induced immunity.

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.

Dengue vaccine: hypotheses to understand CYD-TDV-induced protection

Dengue virus (DENV) is a human pathogen with a large impact on public health. Although no vaccine against DENV is currently licensed, a recombinant vaccine - chimeric yellow fever virus-DENV tetravalent dengue vaccine (CYD-TDV) - has shown efficacy against symptomatic dengue disease in two recent Phase III clinical trials. Safety observations were also recently reported for these trials. In this Opinion article, we review the data from recent vaccine clinical trials and discuss the putative mechanisms behind the observed efficacy of the vaccine against different forms of the disease, focusing on the interactions between the infecting virus, pre-existing host immunity and vaccine-induced immune responses.