Th1 memory: implications for vaccine development

Host immunity in the protective response to nasal immunization with a pneumococcal antigen associated to live and heat-killed Lactobacillus casei

Background

At present, available pneumococcal vaccines have failed to eradicate infections caused by S. pneumoniae. Search for effective vaccine continues and some serotype independent pneumococcal proteins are considered as candidates for the design of new vaccines, especially a mucosal vaccine, since pneumococci enter the body through mucosal surfaces. Selection of the appropriate adjuvant is important for mucosal vaccines, and lactic acid bacteria (LAB) with immunostimulant properties are promissory candidates. In this work, we assessed the adjuvant effect of a probiotic strain, Lactobacillus casei (L. casei), when nasally administered with a pneumococcal antigen (pneumococcal protective protein A: PppA) for the prevention of pneumococcal infection. Adjuvanticity of both live (LcV) and heat-killed (LcM) was evaluated and humoral and cellular antigen-specific immune response was assessed in mucosal and systemic compartments. The potential mechanisms induced by nasal immunization were discussed.

Results

Nasal immunization of young mice with PppA+LcV and PppA+LcM induced anti-PppA IgA and IgG antibodies in mucosal and systemic compartments and levels of these specific antibodies remained high even at day 45 after the 3rd Immunization (3rd I). These results were correlated with IL-4 induction by the mixture of antigen plus LcV and LcM. Also, PppA+Lc (V and M) induced stimulation of Th1 and Th17 cells involved in the defence against pneumococci. The protection against pneumococcal respiratory challenge at day 30 after the 3rd I showed that PppA+LcV and PppA+LcM immunizations significantly reduced pathogen counts in nasal lavages while prventing their passage into lung and blood. Survival of mice immunized with the co-application of PppA plus LcV and LcM was significantly higher than in mice immunized with PppA alone and control mice when intraperitoneal challenge was performed. No significant differences between the treatments involving LcV and LcM were found.

Conclusions

Live and heat-killed L. casei enhanced the antigen-specific immune response when administered nasally with a pneumococcal antigen. Considering the potential risk associated with live bacteria, the design of a nasal vaccine based on pneumococcal antigens and heat-killed L. casei emerges as a safe and effective strategy for the prevention of pneumococcal infections and opens new possibilities of application of dead LAB as adjuvants in vaccine formulations against other pathogens.

Dendritic cells exposed to MVA-based HIV-1 vaccine induce highly functional HIV-1-specific CD8(+) T cell responses in HIV-1-infected individuals

Currently, MVA virus vectors carrying HIV-1 genes are being developed as HIV-1/AIDS prophylactic/therapeutic vaccines. Nevertheless, little is known about the impact of these vectors on human dendritic cells (DC) and their capacity to present HIV-1 antigens to human HIV-specific T cells. This study aimed to characterize the interaction of MVA and MVA expressing the HIV-1 genes Env-Gag-Pol-Nef of clade B (referred to as MVA-B) in human monocyte-derived dendritic cells (MDDC) and the subsequent processes of HIV-1 antigen presentation and activation of memory HIV-1-specific T lymphocytes. For these purposes, we performed ex vivo assays with MDDC and autologous lymphocytes from asymptomatic HIV-infected patients. Infection of MDDC with MVA-B or MVA, at the optimal dose of 0.3 PFU/MDDC, induced by itself a moderate degree of maturation of MDDC, involving secretion of cytokines and chemokines (IL1-ra, IL-7, TNF-α, IL-6, IL-12, IL-15, IL-8, MCP-1, MIP-1α, MIP-1β, RANTES, IP-10, MIG, and IFN-α). MDDC infected with MVA or MVA-B and following a period of 48 h or 72 h of maturation were able to migrate toward CCL19 or CCL21 chemokine gradients. MVA-B infection induced apoptosis of the infected cells and the resulting apoptotic bodies were engulfed by the uninfected MDDC, which cross-presented HIV-1 antigens to autologous CD8⁺ T lymphocytes. MVA-B-infected MDDC co-cultured with autologous T lymphocytes induced a highly functional HIV-specific CD8⁺ T cell response including proliferation, secretion of IFN-γ, IL-2, TNF-α, MIP-1β, MIP-1α, RANTES and IL-6, and strong cytotoxic activity against autologous HIV-1-infected CD4⁺ T lymphocytes. These results evidence the adjuvant role of the vector itself (MVA) and support the clinical development of prophylactic and therapeutic anti-HIV vaccines based on MVA-B.

T-cell activation differentially mediates the host response to sepsis

Survival during sepsis requires both swift control of infectious organisms and tight regulation of the associated inflammatory response. As the role of T cells in sepsis is somewhat controversial, we examined the impact of increasing antigen-dependent activation of CD4 T cells in a murine model of cecal ligation and puncture using T-cell receptor transgenic II (OT-II) mice that are specific for chicken ovalbumin (OVA) in the context of major histocompatibility complex II. Here, we injected OT-II mice with 0, 1, or 100 μg of OVA and demonstrate that increased antigen treatment resulted in increased numbers of activated splenic CD4 T cells. Vehicle-treated, septic OT-II mice had decreased survival, increased bacterial load, and increased levels of IL-6. Interestingly, this decrease in survival was abrogated when OT-II mice were injected with 1 μg OVA, which was correlated with normalized bacterial load and levels of IL-6. However, when OT-II mice were injected with 100 μg OVA, decreased survival was restored but, in contrast to vehicle-treated OT-II mice, had decreased bacterial load and enhanced IL-6 levels. We also observed that neutrophil oxidative burst and phagocytosis were dependent on CD4 T-cell activation. Further, at extreme levels of T-cell activation, intestinal permeability was significantly increased. Altogether, we conclude that too little CD4 T-cell activation produces dysfunctional neutrophils leading to decreased bacteria clearance and survival, whereas too much CD4 T-cell activation produces a neutrophil phenotype that leads to efficient bacterial clearance but with increased tissue damage and mortality.

Future vaccination strategies against tuberculosis: thinking outside the box

With almost a dozen vaccine candidates in clinical trials, tuberculosis (TB) research and development is finally reaping the first fruits of its labors. Vaccine candidates in clinical trials may prevent TB disease reactivation by efficiently containing the pathogen Mycobacterium tuberculosis (Mtb). Future research should target vaccines that achieve sterile eradication of Mtb or even prevent stable infection. These are ambitious goals that can be reached only by highly cooperative engagement of basic immunologists, vaccinologists, and clinical researchers--or in other words, by translation from basic immunology to vaccine research and development, as well as reverse translation of insights from clinical trials back to hypothesis-driven research in the basic laboratory. Here, we review current and future strategies toward the rational design of novel vaccines against TB, as well as the progress made thus far, and the hurdles that need to be overcome in the near and distant future.

Baculovirus as an avian influenza vaccine vector: differential immune responses elicited by different vector forms

Baculovirus is an enveloped virus that infects insects in nature and has emerged as a novel vaccine vector. We previously constructed a recombinant baculovirus displaying the hemagglutinin protein (HA) of avian influenza virus (AIV) on the viral envelope (Bac-HA64), and demonstrated the induction of humoral responses in immunized mice. To improve the vector design and explore how the vector forms influence the vaccine efficacy, we constructed two more baculoviruses Bac-CHA and Bac-CHA/HA64. Bac-CHA expressed HA after transducing the host cells while Bac-CHA/HA64 not only expressed HA but also displayed HA on the envelope. After administration into BALB/c mice, all three vectors elicited HA-specific humoral (IgG1, IgG2a and hemagglutination inhibition titers), mucosal (IgA titers) and cellular (interferon (IFN)-γ and IL-4 producing T cells and IFN-γ(+)/CD8(+) T cells) immune responses. Intriguingly, the magnitudes and types of responses hinged on the vaccine form and administration route. Via intranasal (i.n.) and subcutaneous (s.c.) inoculation, the HA-displaying vectors Bac-HA64 and Bac-CHA/HA64 triggered stronger humoral and mucosal responses than Bac-CHA, but upon intramuscular (i.m.) injection the HA-expressing vectors (Bac-CHA and Bac-CHA/2HA64) elicited more robust humoral and cellular responses than Bac-HA64. Via either administration route, the dual form vaccine Bac-CHA/HA64 gave rise to superior or at least comparable HA-specific immune responses than the other two vaccine forms, implicating the potential of Bac-CHA/HA64 as a vaccine candidate against AIV infection.

Genetically modified Bifidobacterium displaying Salmonella-antigen protects mice from lethal challenge of Salmonella Typhimurium in a murine typhoid fever model

We developed a novel vaccine platform utilizing Bifidobacterium as an antigen delivery vehicle for mucosal immunization. Genetically modified Bifidobacterium longum displaying Salmonella-flagellin on the cell surface was constructed for the oral typhoid vaccine. The efficiency of this vaccine was evaluated in a murine model of typhoid fever. We then orally administered 2.5 × 10(7) CFU of the recombinant Bifidobacterium longum (vaccine) or parental Bifidobacterium longum, or PBS to BALB/C mice every other day for 2 weeks. After the administration, a total of 42 mice (14 mice in each group) were challenged with Salmonella Typhimurium (1.0 × 10(7) CFU/mouse). While 12 mice in the PBS group, and 9 in the parental Bifidobacterium longum group died (median survival: 14 and 25 days), only two in the vaccine group died. These data support that our genetically modified Bifidobacterium antigen delivery system offers a promising vaccine platform for inducing efficient mucosal immunity.

New vaccines for tuberculosis

New vaccines are urgently needed if we want to reach the goal of substantially reducing the incidence of tuberculosis by 2050. Despite a steady increase in funding over the past decade, there is still a striking financial shortfall for vaccine research and development for tuberculosis. Yet, around ten vaccine candidates have left the laboratory stage and entered clinical trials. These vaccines are either aimed at replacing the present vaccine, BCG, or at enhancing immunity induced by BCG. However, these pre-exposure candidates are designed for prevention of disease and will therefore neither eradicate the pathogen, nor prevent stable infection. Long-term vaccination strategies need to target these more ambitious goals. Even though vaccine development will have a price, the return of investment will greatly exceed original costs.

Human Th1 cells that express CD300a are polyfunctional and after stimulation up-regulate the T-box transcription factor eomesodermin

Human naïve CD4 T cells express low levels of the immunomodulatory receptor CD300a, whereas effector/memory CD4 cells can be either CD300a⁺ or CD300a⁻. This suggested that CD300a expression could define a specific subset within the effector/memory CD4 T cell subpopulations. In fact, ex vivo analysis of the IFN-γ producing CD4 T cells showed that they are enriched in the CD300a⁺ subset. Moreover, stimulated CD4 T cells producing TNF-α and IL-2 besides IFN-γ (polyfunctional) are predominantly CD300a⁺. In addition to producing markedly higher levels of Th1-associated cytokines, the stimulated CD300a⁺ CD4 T cells are distinguished by a striking up-regulation of the T-box transcription factor eomesodermin (Eomes), whereas T-bet is up-regulated in both CD300a⁺ and CD300a⁻ activated CD4 T cells to similar levels. The pleiotropic cytokine TGF-β1 has a determinant role in dictating the development of this Th1 subset, as its presence inhibits the expression of CD300a and down-regulates the expression of Eomes and IFN-γ. We conclude that CD300a⁺ human Th1 cells tend to be polyfunctional and after stimulation up-regulate Eomes.

Novel tuberculosis vaccination strategies based on understanding the immune response

The current tuberculosis (TB) vaccine bacillus Calmette-Guérin (BCG) fails to protect against adult pulmonary TB. Yet, its capacity to control miliary TB in newborn infants forms the basis for development of novel vaccine candidates. These either exploit genetic modification of BCG to create a viable replacement vaccine or use BCG to prime the immune response followed by boost with a novel subunit vaccine. This could ultimately result in a combination vaccination schedule comprising a prime with a live BCG replacement followed by a subunit vaccine boost. Ultimately, vaccination strategies that achieve sterile eradication of, or prevent infection with, tubercle bacilli would be an ambitious highly promising goal.

Persistent gamma-herpesvirus infection induces a CD4 T cell response containing functionally distinct effector populations

The direct effector mechanisms of CD4 T cells during gamma-herpesvirus 68 (gammaHV68)-persistent infection are less well understood than those of their CD8 T cell counterparts, although there is substantial evidence that CD4 T cells are critical for the control of persistent gamma-herpesvirus infection. Our results show that in gammaHV68-persistently infected mice, CD4 T cells are not cytokine polyfunctional, but there is a division of labor in the CD4 T cell compartment in which CD4 T cells polarize toward two distinct populations with different effector functions: IFN-gamma producers and CD107(+) cytolytic effectors. These two CD4 T cell effector populations degranulate and produce IFN-gamma during steady state without need for exogenous antigenic restimulation, which is fundamentally different from that observed with gammaHV68-specific CD8 T cells. By using anti-IFN-gamma Ab depletions and IFN-gamma-deficient mice, we show that CD4 T cell-mediated cytotoxicity in vivo is not dependent on IFN-gamma activity. In addition, our data show that purified CD4 T cells isolated from gammaHV68-latently infected mice have the capacity to inhibit gammaHV68 reactivation from latency. Our results support the concept that CD4 T cells are critical effectors for the control of gamma-herpesvirus latent infection, and they mediate this effect by two independent mechanisms: IFN-gamma production and cytotoxicity.

Aqueous extract of Carica papaya leaves exhibits anti-tumor activity and immunomodulatory effects

AIM OF THE STUDY

Various parts of Carica papaya Linn. (CP) have been traditionally used as ethnomedicine for a number of disorders, including cancer. There have been anecdotes of patients with advanced cancers achieving remission following consumption of tea extract made from CP leaves. However, the precise cellular mechanism of action of CP tea extracts remains unclear. The aim of the present study is to examine the effect of aqueous-extracted CP leaf fraction on the growth of various tumor cell lines and on the anti-tumor effect of human lymphocytes. In addition, we attempted to identify the functional molecular weight fraction in the CP leaf extract.

MATERIALS AND METHODS

The effect of CP extract on the proliferative responses of tumor cell lines and human peripheral blood mononuclear cells (PBMC), and cytotoxic activities of PBMC were assessed by [(3)H]-thymidine incorporation. Flow cytometric analysis and measurement of caspase-3/7 activities were performed to confirm the induction of apoptosis on tumor cells. Cytokine productions by PBMC were measured by ELISA. Gene profiling of the effect of CP extract treatment was performed by microarray analysis and real-time RT-PCR.

RESULTS

We observed significant growth inhibitory activity of the CP extract on tumor cell lines. In PBMC, the production of IL-2 and IL-4 was reduced following the addition of CP extract, whereas that of IL-12p40, IL-12p70, IFN-gamma and TNF-alpha was enhanced without growth inhibition. In addition, cytotoxicity of activated PBMC against K562 was enhanced by the addition of CP extract. Moreover, microarray analyses showed that the expression of 23 immunomodulatory genes, classified by gene ontology analysis, was enhanced by the addition of CP extract. In this regard, CCL2, CCL7, CCL8 and SERPINB2 were representative of these upregulated genes, and thus may serve as index markers of the immunomodulatory effects of CP extract. Finally, we identified the active components of CP extract, which inhibits tumor cell growth and stimulates anti-tumor effects, to be the fraction with M.W. less than 1000.

CONCLUSION

Since Carica papaya leaf extract can mediate a Th1 type shift in human immune system, our results suggest that the CP leaf extract may potentially provide the means for the treatment and prevention of selected human diseases such as cancer, various allergic disorders, and may also serve as immunoadjuvant for vaccine therapy.

A whole genome transcriptional analysis of the early immune response induced by live attenuated and inactivated influenza vaccines in young children

The protective mechanisms of influenza vaccines in young children are not completely understood. A phase 2 clinical study was conducted in 85 children 12-35 months of age to describe and compare the immune responses to live attenuated influenza vaccine (LAIV) with trivalent inactivated influenza vaccine (TIV). To better understand the biology of vaccine effects, oligonucleotide microarrays were employed to measure the genome-wide changes in transcript profiles in whole blood at approximately 7 days after 1 dose of LAIV or TIV. Of the total 265 differentially expressed genes identified in this study, 6 clusters of genes were identified to be tightly coexpressed, many of which are likely modulated by cytokines including type 1 interferons (IFNs) and granulocyte-macrophage colony-stimulating factor. Additional functional analyses revealed that the type 1 IFN pathway and cell cycle regulation-related genes are enriched in the 6 coexpressed gene sets. Promoter characterization of these coexpressed genes also supported this conclusion. Moreover, it is suggested that the IFN-stimulated response element is likely to be a potential bidirectional promoter, and the CCAAT/enhancer-binding protein might cooperate with the E2F transcription factor family in the regulation of the cell cycle in the early immune response induced by the influenza vaccine. Overall, our study clearly indicates that the expression profile changes induced by LAIV are significantly different from those induced by TIV. These results suggest that the pattern of overexpression of type 1 IFN-stimulated genes can potentially be used as a biomarker to identify the early vaccination response of LAIV and may also explain, to a certain extent, previous clinical study observations of LAIV-induced protection against influenza-like illness in the first 2 weeks after administration.

Immune impairment in patients with terminal cancers: influence of cancer treatments and cytomegalovirus infection

Although immunodeficiency is usually considered a prerequisite of oncogenesis, a detailed immune pro- file in cancer has not yet been described. Without such profiling, it is not surprising that there is a vast discrepancy in the responses of cancer patients to immunotherapy. Our results show that the integrity of the immune system deteriorates with cancer progression by displaying a trend toward decreasing levels of functional T cells, including CD4, naïve, and central memory T cells, and an expansion of hyporesponsive populations such as CD28⁻ and CMV-specific T cells. One hundred and one patients constitute the study group for the observational study reported in this paper. Forty-eight patients with newly diagnosed stages III and IV and 53 patients with extensively treated stage IV disease. The costimulatory molecules CD27 and CD28 were downregulated in all patients. Among the proinflammatory cytokines (IL-6, TNF-α, IFN-γ), only IL-6 differed significantly among the groups, increasing as the cancer stage progressed. Plasma IL-7 did not diVer among the participants. The relative deficits of naïve T cells in cancer patients may be associated with the downregulation of IL-7Rα expression rather than changes in the circulating levels of IL-7. The downregulation of IL-7Rα expression was shown to be associated with increased levels of intracellular CMV. The present study suggests that the immune impairment in patients with cancer is associated with multiple factors, such as the stage of cancer, consequence of CMV infection and impact of treatment.

Divergent adaptive and innate immunological responses are observed in humans following blunt trauma

BACKGROUND

The immune response to trauma has traditionally been modeled to consist of the systemic inflammatory response syndrome (SIRS) followed by the compensatory anti-inflammatory response syndrome (CARS). We investigated these responses in a homogenous cohort of male, severe blunt trauma patients admitted to a University Hospital surgical intensive care unit (SICU). After obtaining consent, peripheral blood was drawn up to 96 hours following injury. The enumeration and functionality of both myeloid and lymphocyte cell populations were determined.

RESULTS

Neutrophil numbers were observed to be elevated in trauma patients as compared to healthy controls. Further, neutrophils isolated from trauma patients had increased raft formation and phospho-Akt. Consistent with this, the neutrophils had increased oxidative burst compared to healthy controls. In direct contrast, blood from trauma patients contained decreased naïve T cell numbers. Upon activation with a T cell specific mitogen, trauma patient T cells produced less IFN-gamma as compared to those from healthy controls. Consistent with these results, upon activation, trauma patient T cells were observed to have decreased T cell receptor mediated signaling.

CONCLUSIONS

These results suggest that following trauma, there are concurrent and divergent immunological responses. These consist of a hyper-inflammatory response by the innate arm of the immune system concurrent with a hypo-inflammatory response by the adaptive arm.

Administration of a probiotic associated with nasal vaccination with inactivated Lactococcus lactis-PppA induces effective protection against pneumoccocal infection in young mice

Streptococcus pneumoniae is a serious public health problem, especially in developing countries, where available vaccines are not part of the vaccination calendar. We evaluated different respiratory mucosa immunization protocols that included the nasal administration of Lactococcus lactis-pneumococcal protective protein A (PppA) live, inactivated, and in association with a probiotic (Lc) to young mice. The animals that received Lc by the oral and nasal route presented the highest levels of immunoglobulin (Ig)A and IgG anti-PppA antibodies in bronchoalveolar lavages (BAL) and IgG in serum, which no doubt contributed to the protection against infection. However, only the groups that received the live and inactivated vaccine associated with the oral administration of the probiotic were able to prevent lung colonization by S. pneumoniae serotypes 3 and 14 in a respiratory infection model. This would be related to a preferential stimulation of the T helper type 1 (Th1) cells at local and systemic levels and with a moderate Th2 and Th17 response, shown by the cytokine profile induced in BAL and by the results of the IgG1/IgG2a ratio at local and systemic levels. Nasal immunization with the inactivated recombinant strain associated with oral Lc administration was able to stimulate the specific cellular and humoral immune response and afford protection against the challenge with the two S. pneumoniae serotypes. The results obtained show the probiotic-inactivated vaccine association as a valuable alternative for application to human health, especially in at-risk populations, and are the first report of a safe and effective immunization strategy using an inactivated recombinant strain.

Adenosine deaminase enhances T-cell response elicited by dendritic cells loaded with inactivated HIV

As host immunological defenses are impaired during HIV infection, it is difficult to elicit good responses when attempting to develop therapeutic vaccines against HIV. To try to solve this situation, adjuvants, particularly cytokines, are currently under evaluation. Owing to the fact that adenosine deaminase (ADA) is a member of the family of growth factor with deaminase activity, we tested whether it could improve immune responses in the development of HIV dendritic-cell-based therapeutic vaccines. A co-culture model approach has been used to test the usefulness of ADA as adjuvant. Monocyte-derived dendritic cells from HIV-infected patients were pulsed with inactivated HIV, matured and co-cultured with autologous T cells. Addition of ADA to the co-cultures resulted in enhanced CD4(+) and CD8(+) T-cell proliferation and robust ADA-induced increase in cytokine production (IFN-gamma, TNF-alpha and IL-6). As IFN-gamma, TNF-alpha and IL-6 promote the Th1 versus Th2 phenotype and improve T helper proliferation responses and antigen-specific CTL responses ADA may be considered a promising candidate for therapeutic vaccine adjuvant.

Vaccination with an attenuated strain of Francisella novicida prevents T-cell depletion and protects mice infected with the wild-type strain from severe sepsis

Francisella tularensis is the causative agent of zoonotic tularemia, a severe pneumonia in humans, and Francisella novicida causes a similarly severe tularemia in mice upon inhalation. The correlates of protective immunity, as well as the virulence mechanisms of this deadly pathogen, are not well understood. In the present study, we compared the host immune responses of lethally infected and vaccinated mice to highlight the host determinants of protection from this disease. Intranasal infection with an attenuated mutant (Mut) of F. novicida lacking a 58-kDa hypothetical protein protected C57BL/6 mice from a subsequent challenge with the fully virulent wild-type strain U112 via the same route. The protection conferred by Mut vaccination was associated with reduced bacterial burdens in systemic organs, as well as the absence of bacteremia. Also, there was reduced lung pathology and associated cell death in the lungs of vaccinated mice. Both vaccinated and nonvaccinated mice displayed an initial 2-day delay in upregulation of signature inflammatory mediators after challenge. Whereas the nonvaccinated mice developed severe sepsis characterized by hypercytokinemia and T-cell depletion, the vaccinated mice displayed moderated cytokine induction and contained increased numbers of alphabeta T cells. The recall response in vaccinated mice consisted of a characteristic Th1-type response in terms of cytokines, as well as antibody isotypes. Our results show that a regulated Th1 type of cell-mediated and humoral immunity in the absence of severe sepsis is associated with protection from respiratory tularemia, whereas a deregulated host response leading to severe sepsis contributes to mortality.

Interferon gamma enhances clonal expansion and survival of CD4+ T cells

Interferon-gamma (IFN-gamma) serves numerous functions in the regulation of the immune response. During the early phase of the immune response IFN-gamma is produced by natural killer and natural killer T cells. Although the effects of this cytokine on antigen presenting cells and other cell types are known, its direct role on CD4(+) T cells remains unclear. We demonstrate that CD4(+) T cells exposed to IFN-gamma proliferate more vigorously than the controls in response to signals through the antigen receptor. The increased proliferation of IFN-gamma-treated CD4(+) T cells is not due to enhanced signaling through the antigen receptor, but is accounted for by their increased survival. Our data suggest that enhanced survival of IFN-gamma-treated CD4(+)T cells is independent of signal transducer and activator of transcription 1 (STAT 1), a transcription factor that controls the expression of a variety of IFN-gamma-targeted genes. In addition, we demonstrate that independent of STAT 1, IFN-gamma treatment increases the expression of double-stranded RNA-dependent protein kinase, a kinase involved in regulating protein synthesis. Taken together, our findings suggest a direct role of IFN-gamma on unstimulated CD4(+) T cells that is likely to enhance the advent of adaptive immunity by augmenting their survival during the initiation of the immune response.

Coadministration of the fungal immunomodulatory protein FIP-Fve and a tumour-associated antigen enhanced antitumour immunity

Fve is a fungal protein isolated from the golden needle mushroom Flammulina velutipes and has previously been reported to trigger immunological responses in both mouse and human lymphocytes. In this study, we evaluated the potential application of Fve as an adjuvant for tumour immunotherapy and examined the underlying mechanism(s). When the human papillomavirus (HPV)-16 E7 oncoprotein was used as a model antigen, mice coimmunized with HPV-16 E7 and Fve showed enhanced production of HPV-16 E7-specific antibodies as well as expansion of HPV-16 E7-specific interferon (IFN)-gamma-producing CD4(+) and CD8(+) T cells as compared with mice immunized with HPV-16 E7 alone. Tumour protection assays showed that 60% of mice coimmunized with HPV-16 E7 plus Fve, as compared with 20% of those immunized only with HPV-16 E7, remained tumour-free for up to 167 days after challenge with the tumour cells. Tumour therapeutic assays showed that HPV-16 E7 plus Fve treatment significantly prolonged the survival of tumour-bearing mice as compared with those treated only with HPV-16 E7. In vivo cell depletion and adoptive T-cell transfer assays showed that CD4(+) and CD8(+) T cells and IFN-gamma played critical roles in conferring the antitumour effects. Interestingly, Fve could stimulate the maturation of splenic dendritic cells in vivo and induce antigen-specific CD8(+) T-cell immune responses. In summary, Fve has potent adjuvant properties that enhance T helper type 1 antigen-specific humoral and cellular immune responses which confer strong antitumour effects. The use of Fve as an adjuvant could be an attractive alternative to the current vaccination strategy for cancer immunotherapy.

Enhanced in vivo immunogenicity of SIV vaccine candidates with cationic liposome-DNA complexes in a rhesus macaque pilot study

This pilot study tested the immunogenicity of a novel cationic liposome-DNA complex (CLDC) immunomodulatory vaccine adjuvant. Combined with a specific antigen, CLDC enhanced anti-SIV immune responses induced by various SIV vaccine candidates. Rhesus macaques immunized in the presence of CLDC developed stronger SIV-specific T and B cell responses compared to animals immunized without CLDC. These differences persisted and resulted in better memory responses after an in vivo boost of the animals several months later with whole AT-2 inactivated SIVmac239. Thus, CLDC should be explored further as a potential immunomodulatory adjuvant in HIV vaccine design.

Immunity to malaria: more questions than answers

Malaria is one of the main health problems facing developing countries today. At present, preventative and treatment strategies are continuously hampered by the issues of the ever-emerging parasite resistance to newly introduced drugs, considerable costs and logistical problems. The main hope for changing this situation would be the development of effective malaria vaccines. An important part of this process is understanding the mechanisms of naturally acquired immunity to malaria. This review will highlight key aspects of immunity to malaria, about which surprisingly little is known and which will prove critical in the search for effective malaria vaccines.

A DNA adjuvant encoding a fusion protein between anti-CD3 single-chain Fv and AIMP1 enhances T helper type 1 cell-mediated immune responses in antigen-sensitized mice

T helper type 1 (Th1) cell-mediated immune responses contribute to host defences against intracellular pathogen infections and cancer. Previously, we found that aminoacyl tRNA synthetase-interacting multifunctional protein 1 (AIMP1) activated macrophages and dendritic cells to enhance Th1 responses. Herein, we manipulated this property to improve Th1 immune responses in vivo by constructing a mammalian expression plasmid (pAnti-CD3sFv/AIMP1) encoding AIMP1 fused to the anti-CD3 single-chain Fv (sFv), the smallest unit of the antibody that interacts with the CD3epsilon region of the T-cell receptor. Intramuscular injection of ovalbumin (OVA)-sensitized BALB/c mice with pAnti-CD3sFv/AIMP1 DNA adjuvant increased the OVA-specific, interferon-gamma production by their CD4(+) T cells and the levels of anti-OVA immunoglobulin G2a (IgG2a) isotype in their sera. Furthermore, the pAnti-CD3sFv/AIMP1 DNA adjuvant decreased interleukin-4 production and anti-OVA IgE levels in the OVA-injected mice. Importantly, the pAnti-CD3sFv/AIMP1 was more efficient than a mixture of pAnti-CD3sFv and pAIMP1 in inducing OVA-specific Th1 immune responses and also in inhibiting OVA-specific Th2 responses during antigen priming. These studies indicated that the pAnti-CD3sFv/AIMP1 fusion DNA adjuvant enhanced Th1 immune responses in antigen-sensitized mice.

CD4-expressing cells are early mediators of the innate immune system during sepsis

It is well established that the immune response to sepsis is mediated by leukocytes associated with the innate immune system. However, there is an emerging view that T lymphocytes can also mediate this response. Here, we observed a significant depletion of both CD4 and CD8 T cells in human patients after blunt trauma. To determine what effect the loss of these cells may have during a subsequent infection, we obtained CD4- and CD8-deficient mice and subjected them to cecal ligation and puncture (CLP). We observed that CD4 knockout (KO) mice showed increased CLP-induced mortality compared with CD8-deficient and wild-type (WT) mice especially within the first 30 h of injury. CD4 KO mice also exhibited significantly increased IL-6 concentrations after the CLP. The CD4 KO mice had an increased concentration of bacteremia as compared with WT mice. Antibiotic treatment decreased mortality in the CD4 KO mice as compared with no changes in the wild mice after CLP. Neutrophils isolated from septic CD4 KO mice showed decreased spontaneous oxidative burst compared with neutrophils taken from septic controls. We examined the role of IFN-gamma by using mice deficient in this cytokine and found these mice to have significantly higher mortality as compared with WT mice. Finally, we detected a 2-fold increase in CD11b+ cells that exhibited intracellular IFN-gamma staining in the peritoneum of WT mice after CLP. The data suggest that CD4+ cells may facilitate the early clearance of bacteria by regulating neutrophils function possibly through an IFN-gamma-dependent mechanism.

Confronting the scientific obstacles to global control of tuberculosis

Tuberculosis (TB) is a major threat to global health, recently exacerbated by the emergence of highly drug-resistant forms of the disease-causing pathogen and synergy with HIV/AIDS. In 2006, the Stop TB Partnership published "The global plan to stop TB: 2006--2015," which set out a vision of halving the prevalence of and mortality caused by the disease by 2015, followed by eliminating the disease as a public health problem by 2050. This vision depends on the development of improved diagnostics, simpler treatment, and more effective vaccination. Recently, active translational research pipelines directed toward each of these goals have been established, but improved understanding of the fundamental biology of this complex disease will prove to be the key to radical advances in TB control.

NK cells lyse T regulatory cells that expand in response to an intracellular pathogen

We evaluated the capacity of NK cells to influence expansion of CD4(+)CD25(+)FoxP3(+) regulatory T cells (Tregs) in response to microbial Ags, using Mycobacterium tuberculosis as a model. We previously found that Tregs expand when CD4(+) cells and monocytes are exposed to M. tuberculosis. Addition of NK cells that were activated by monokines (IL-12, IL-15, and IL-18) or by exposure to M. tuberculosis-stimulated monocytes reduced Treg expansion in response to M. tuberculosis. NK cell inhibition of Treg expansion was not mediated through IFN-gamma. Activated NK cells lysed expanded, but not freshly isolated Tregs. Although monokines increased NK cell expression of the activating receptors NKp46, NKG2D, 2B4, CD16, and DNAM-1, only anti-NKG2D and anti-NKp46 inhibited NK cell lysis of expanded Tregs. Of five NKG2D ligands, only UL16-binding protein 1 (ULBP1) was up-regulated on M. tuberculosis-expanded Tregs, and anti-ULBP1 inhibited NK cell lysis of expanded Tregs. M. tuberculosis-stimulated monocytes activated NK cells to lyse expanded Tregs, and this was also inhibited by anti-NKG2D and anti-ULBP1, confirming the physiological relevance of this effect. Our study identifies a potential new role for NK cells in maintaining the delicate balance between the regulatory and effector arms of the immune response.

Fine-tuning CD4+ central memory T cell heterogeneity by strength of stimulation

The memory T cell pool serves as a relatively long-lived heterogeneous repository of antigen-experienced T cells that "remember" previous encounters with antigen. While heterogeneity in the memory T cell pool is now well established, signals regulating the generation of this memory T cell heterogeneity are not fully understood. Two articles in this issue of the European Journal of Immunology highlight the importance of the strength of antigenic stimulation in regulating the generation of phenotypically and functionally distinct CD4(+) T cell memory subsets. New insights are also provided into key molecular players that likely mediate differences in homeostatic and secondary expansion between the memory subsets.

Memory CD4 T cells emerge from effector T-cell progenitors

A hallmark of adaptive immunity is the generation of memory T cells that confer long-lived, antigen-specific protection against repeat challenges by pathogens. Understanding the mechanisms by which memory T cells arise is important for rational vaccination strategies and improved therapeutic interventions for chronic infections and autoimmune disorders. The large clonal expansion of CD8 T cells in response to some infections has made the development of CD8 T-cell memory more amenable to study, giving rise to a model of memory cell differentiation in which a fraction of fully competent effector T cells transition into long-lived memory T cells. Delineation of CD4 T-cell memory development has proved more difficult as a result of limitations on tracking the smaller populations of CD4 effector T cells generated during a pathogenic challenge, complicating efforts to determine whether CD4 memory T cells are direct descendants of effector T cells or whether they develop by alternative pathways. Here, using two complementary cytokine reporter mouse models to identify interferon (IFN)-gamma-positive effector T cells and track their fate, we show that the lineage relationship between effector and memory CD4 T cells resembles that for CD8 T cells responding to the same pathogen. We find that, in parallel with effector CD8 T cells, IFN-gamma-positive effector CD4 T cells give rise to long-lived memory T cells capable of anamnestic responses to antigenic rechallenge.

Functional and genomic profiling of effector CD8 T cell subsets with distinct memory fates

An important question in memory development is understanding the differences between effector CD8 T cells that die versus effector cells that survive and give rise to memory cells. In this study, we provide a comprehensive phenotypic, functional, and genomic profiling of terminal effectors and memory precursors. Using killer cell lectin-like receptor G1 as a marker to distinguish these effector subsets, we found that despite their diverse cell fates, both subsets possessed remarkably similar gene expression profiles and functioned as equally potent killer cells. However, only the memory precursors were capable of making interleukin (IL) 2, thus defining a novel effector cell that was cytotoxic, expressed granzyme B, and produced inflammatory cytokines in addition to IL-2. This effector population then differentiated into long-lived protective memory T cells capable of self-renewal and rapid recall responses. Experiments to understand the signals that regulate the generation of terminal effectors versus memory precursors showed that cells that continued to receive antigenic stimulation during the later stages of infection were more likely to become terminal effectors. Importantly, curtailing antigenic stimulation toward the tail end of the acute infection enhanced the generation of memory cells. These studies support the decreasing potential model of memory differentiation and show that the duration of antigenic stimulation is a critical regulator of memory formation.

How do adjuvants work? Important considerations for new generation adjuvants

In this Commentary, McKee et al. highlight the properties of extrinsic vaccine adjuvants that must be considered to achieve the most protective immune response, as occurs naturally with many intrinsic pathogen-derived adjuvants.

IFN-gamma mediates the death of Th1 cells in a paracrine manner

Th1 cells have different capacities to develop into memory cells based on their production of IFN-gamma. In this study, the mechanism by which a homogenous population of IFN-gamma-producing CD4 T cells was eliminated in vivo was assessed. When such cells were transferred into naive mice and activated with Ag, a striking decrease in the frequency of cells in the spleen and lung was observed. However, administration of neutralizing anti-IFN-gamma Ab at the time of Ag challenge largely prevented the elimination of such cells. To determine whether IFN-gamma was mediating its effects directly and/or indirectly, the ability of IFN-gamma to effectively signal in such cells was assessed in vitro. Indeed, there was reduced phosphorylation of STAT1 in response to IFN-gamma as well as markedly reduced expression of the IFN-gammaR beta-chain. Furthermore, transfer of such cells into IFN-gammaR-deficient mice limited their death following activation with Ag. Together, these data suggest that IFN-gamma acts in a paracrine manner to mediate the death of activated IFN-gamma-producing Th1 cells. In contrast to Ag stimulation, administration of CpG alone resulted in the elimination of Th1 cells in IFN-gammaR-/- mice. These results show that in response to Ag stimulation, the death of IFN-gamma-producing effector Th1 cells is controlled in an IFN-gamma-dependent manner, whereas in response to innate activation, the death of IFN-gamma-producing Th1 cells can occur through an IFN-gamma-independent pathway. Collectively, these data show the multiple mechanisms by which Th1 effector cells are efficiently eliminated in vivo.

Immunogenicity and safety of combined intradermal recombinant Hepatitis B with BCG vaccines at birth

This randomized, prospective, non-inferiority study aimed to quantify anti-HBs titers induced by recombinant Hepatitis B vaccine from healthy infants vaccinated with combined Hepatitis B and Bacillus Calmette-Guérin (BCG) vaccines (HbsAg 10 microg plus BCG suspension 0.1mg) and compare them to titers obtained with separated vaccines. Infants were immunized at birth either with combined intradermal (ID) BCG and Hepatitis B or ID BCG alone and intramuscular (IM) Hepatitis B. Both groups received IM Hepatitis B at 1 and 6 months of age. After the third dose anti-HBs titers > or =10 IU/mL were observed in 99% of vaccinees and > or =1000 IU/mL in 71%. There were no adverse events in both groups. Combination of HbsAg with BCG as first dose did not modify the profile of the humoral immune response for Hepatitis B indicating safety and immunogenicity of this vaccine in newborn.

The contribution of immunology to the rational design of novel antibacterial vaccines

In most cases, a successful vaccine must induce an immune response that is better than the response invoked by natural infection. Vaccines are still unavailable for several bacterial infections and vaccines to prevent such infections will be best developed on the basis of our increasing insights into the immune response. Knowledge of the signals that determine the best possible acquired immune response against a given pathogen - comprising a profound T- and B-cell memory response as well as long-lived plasma cells - will provide the scientific framework for the rational design of novel antibacterial vaccines.

Poor correlation between BCG vaccination-induced T cell responses and protection against tuberculosis

Mycobacterium bovis bacille Calmette-Guérin (BCG) is the most widely used live bacterial vaccine. However, limited information is available correlating route and dose of vaccination and induction of specific T cell responses with protection against tuberculosis. We compared efficacy of oral and systemic vaccination and correlated vaccine-induced T cell responses with protection in experimental tuberculosis of mice. After oral and systemic vaccination, we observed profound differences in persistence and dissemination of BCG and frequencies and location of specific IFN-gamma-secreting CD4(+) and CD8(+) T cells. Yet, both vaccination routes caused comparable levels of protection against aerosol challenge with Mycobacterium tuberculosis. Protection correlated best with rapid accumulation of specific CD8(+) T cells in infected tissues of challenged mice. In contrast, specific IFN-gamma production by CD4(+) T cells reflected the load of M. tuberculosis rather than the strength of protection. Our data question the measurement of IFN-gamma secretion by CD4(+) T cells and emphasize the need for new biomarkers for evaluation of tuberculosis vaccine efficacies.