Cytotoxic T-lymphocytes against malaria and tuberculosis: from natural immunity to vaccine design

Immunological Characterization of Proteins Expressed by Genes Located in Mycobacterium tuberculosis-Specific Genomic Regions Encoding the ESAT6-like Proteins

The 6 kDa early secreted antigen target (ESAT6) is a low molecular weight and highly immunogenic protein of Mycobacterium tuberculosis with relevance in the diagnosis of tuberculosis and subunit vaccine development. The gene encoding the ESAT6 protein is located in the M. tuberculosis-specific genomic region known as the region of difference (RD)1. There are 11 M. tuberculosis-specific RDs absent in all of the vaccine strains of BCG, and three of them (RD1, RD7, and RD9) encode immunodominant proteins. Each of these RDs has genes for a pair of ESAT6-like proteins. The immunological characterizations of all the possible proteins encoded by genes in RD1, RD7 and RD9 have shown that, besides ESAT-6 like proteins, several other proteins are major antigens useful for the development of subunit vaccines to substitute or supplement BCG. Furthermore, some of these proteins may replace the purified protein derivative of M. tuberculosis in the specific diagnosis of tuberculosis by using interferon-gamma release assays and/or tuberculin-type skin tests. At least three subunit vaccine candidates containing ESAT6-like proteins as antigen components of multimeric proteins have shown efficacy in phase 1 and phase II clinical trials in humans.

Distinct Treatment Outcomes of Antiparasitic Therapy in Trypanosoma cruzi-Infected Children Is Associated With Early Changes in Cytokines, Chemokines, and T-Cell Phenotypes

Background: In contrast to adults, Trypanosoma cruzi-infected children have more broadly functional Trypanosoma cruzi-specific T cells, and the total T-cell compartment exhibits fewer signs of immune exhaustion. However, not much is known about the link between immunocompetence and the treatment efficacy for human Chagas disease.

Methods: Using cytokine enzyme-linked immunosorbent spot (ELISPOT) polychromatic flow cytometry, cytometric bead assay, multiplex serological assays and quantitative PCR, we evaluated T. cruzi-specific T-cell and antibody immune responses, T-cell phenotypes and parasitemia in children in the early chronic phase of Chagas disease undergoing anti-Trypanosoma cruzi treatment.

Results: Treatment with benznidazole or nifurtimox induced a decline in T. cruzi-specific IFN-γ- and IL-2-producing cells and proinflammatory cytokines and chemokines. T-cell responses became detectable after therapy in children bearing T-cell responses under background levels prior to treatment. The total frequencies of effector, activated and antigen-experienced T cells also decreased following anti-T. cruzi therapy, along with an increase in T cells expressing the receptor of the homeostatic cytokine IL-7. Posttreatment changes in several of these markers distinguished children with a declining serologic response suggestive of successful treatment from those with sustained serological responses in a 5-year follow-up study. A multivariate analysis demonstrated that lower frequency of CD4⁺CD45RA⁻CCR7⁻CD62L⁻ T cells prior to drug therapy was an independent indicator of successful treatment.

Conclusions: These findings further validate the usefulness of alternative metrics to monitor treatment outcomes. Distinct qualitative and quantitative characteristics of T cells prior to drug therapy may be linked to treatment efficacy.

The Significance of Discordant Serology in Chagas Disease: Enhanced T-Cell Immunity to Trypanosoma cruzi in Serodiscordant Subjects

Background

Subjects are considered infected with Trypanosoma cruzi when tested positive by at least two out of three serological tests, whereas a positive result in only one of up to three tests is termed “serodiscordant” (SD). Assessment of parasite-specific T-cell responses may help discriminate the uninfected from infected individuals among SD subjects.

Methods

Peripheral blood mononuclear cells from SD and seropositive (SP) subjects, who were born in areas endemic for T. cruzi infection but living in Buenos Aires city, Argentina, at the time of the study, and seronegative unexposed subjects were included for analysis. The function and phenotype of T cells were assessed by interferon-γ (IFN-γ) and interleukin (IL)-2 enzyme-linked immunospot assay and multiparameter flow cytometry. T. cruzi-specific antibodies were quantified by conventional serology and a multiplex assay format.

Results

SD subjects exhibited immunity cell responses to T. cruzi but in contrast to SP subjects, T cells in SD subjects more often display the simultaneous production of IFN-γ and IL-2 in response to T. cruzi antigens and have a resting phenotype. SD individuals also have higher IFN-γ spot counts, polyfunctional CD4⁺ T-cells enriched in IL-2 secreting cells and low levels of antibodies specific for a set of T. cruzi-derived recombinant proteins compared with the SP group. Long-term follow-up of SD individuals confirmed that humoral and T-cell responses fluctuate but are sustained over time in these subjects. T cells in SD subjects for T. cruzi infection did not recognize Leishmania antigens.

Conclusion

Both T-cell and humoral responses in most subjects assessed by conventional tests as SD for T. cruzi infection indicate prior exposure to infection and the establishment of immunological memory suggestive of a resolved infection.

Development of novel plant-based adjuvant formulation against rubella and hepatitis B vaccine antigen

Introduction: Numerous metabolites present in the aqueous extract from plants are responsible for inducing adjuvant activity against rubella and hepatitis B vaccine antigen (HBsAg). One of the medicinal plants, Adhatoda vasica has been pointed out with great potential of vaccine adjuvant property.

Objective: The objective of our study is to evaluate the adjuvant potential of aqueous leaves extract of Adhatoda vasica against rubella and hepatitis B vaccine antigen (HBsAg).

Methods: For these studies, our group evaluated the antibody (IgG) titre of HBsAg and rubella vaccine antigen using variable doses (0.625–5 mg) of aqueous leaves extract of Adhatoda vasica and also determined the lymphocyte (splenocyte) proliferation assay (0.625–5 mg; 50 μl) in mice model studies ex vivo (i.e. immunized with HBsAg subcutaneously).

Results: The results showed that aqueous leaves extract showed anti-HBsAg and anti-rubella titre and also enhanced the lymphocyte proliferation assay at higher doses (5 mg) as compared to control.

Conclusion: Aqueous leaves extract of Adhatoda vasica showed adjuvant activity against HBsAg and rubella vaccine antigen.

Changes in Trypanosoma cruzi-specific immune responses after treatment: surrogate markers of treatment efficacy

BACKGROUND

As many as 20 million people are living with Trypanosoma cruzi infection in Latin American, yet few receive any treatment. The major limitation in developing and evaluating potential new drugs for their efficacy is the lack of reliable tests to assess parasite burden and elimination.

METHODS

Adults volunteers with chronic T. cruzi infection were evaluated clinically and stratified according to the Kuschnir classification. Individuals with group 0 and group 1 clinical status were treated with benznidazole (5 mg/kg per day for 30 days). The changes in T. cruzi-specific T cell and antibody responses, as well as in clinical status, were measured periodically over the 3-5-year follow-up period and were compared with pretreatment conditions and with values in an untreated control group.

RESULTS

The frequency of peripheral interferon (IFN)-gamma-producing T cells specific for T. cruzi declined as early as 12 months after benznidazole treatment and subsequently became undetectable in a substantial proportion of treated subjects. In addition, decreases in antibody responses to a pool of recombinant T. cruzi proteins also decreased in many of these same subjects. The shift to negative IFN-gamma T cell responses was highly associated with an early increase in IFN-gamma-producing T cells with phenotypic features of effector/effector memory cells in a subset of subjects. Benznidazole treatment also resulted in an increase in naive and early differentiated memory-like CD8(+) T cells in a majority of subjects.

CONCLUSIONS

Benznidazole treatment during chronic Chagas disease has a substantial impact on parasite-specific immune response that is likely indicative of treatment efficacy and cure.

Immunological mechanisms underlying protection mediated by RTS,S: a review of the available data

The RTS,S/AS candidate malaria vaccine has demonstrated efficacy against a variety of endpoints in Phase IIa and Phase IIb trials over more than a decade. A multi-country phase III trial of RTS,S/AS01 is now underway with submission as early as 2012, if vaccine safety and efficacy are confirmed. The immunologic basis for how the vaccine protects against both infection and disease remains uncertain. It is, therefore, timely to review the information currently available about the vaccine with regard to how it impacts the human-Plasmodium falciparum host-pathogen relationship. In this article, what is known about mechanisms involved in partial protection against malaria induced by RTS,S is reviewed.

HLA Class I-T cell epitopes from trans-sialidase proteins reveal functionally distinct subsets of CD8+ T cells in chronic Chagas disease

Background

Previously, we identified a set of HLA-A020.1-restricted trans-sialidase peptides as targets of CD8⁺ T cell responses in HLA-A0201⁺ individuals chronically infected by T. cruzi.

Methods and Findings

Herein, we report the identification of peptides encoded by the same trans-sialidase gene family that bind alleles representative of the 6 most common class I HLA-supertypes. Based on a combination of bioinformatic predictions and HLA-supertype considerations, a total of 1001 epitopes predicted to bind to HLA A01, A02, A03, A24, B7 and B44 supertypes was selected. Ninety-six supertype-binder epitopes encoded by multiple trans-sialidase genes were tested for the ability to stimulate a recall CD8⁺ T cell response in the peripheral blood from subjects with chronic T. cruzi infection regardless the HLA haplotype. An overall hierarchy of antigenicity was apparent, with the A02 supertype peptides being the most frequently recognized in the Chagas disease population followed by the A03 and the A24 supertype epitopes. CD8⁺ T cell responses to promiscuous epitopes revealed that the CD8⁺ T cell compartment specific for T. cruzi displays a functional profile with T cells secreting interferon-γ alone as the predominant pattern and very low prevalence of single IL-2-secreting or dual IFN-γ/IL-2 secreting T cells denoting a lack of polyfunctional cytokine responses in chronic T. cruzi infection.

Conclusions

This study identifies a set of T. cruzi peptides that should prove useful for monitoring immune competence and changes in infection and disease status in individuals with chronic Chagas disease.

At present, 16–20 million people in Central and South America are infected with Trypanosoma cruzi, the causative agent of Chagas disease in humans. The primary clinical consequence of the infection is a cardiomyopathy, which manifests in approximately 30% of infected individuals, many years after the initial infection. Our work in Chagas disease patients began as an effort to assess the range and specificity of antigens that were recognized by T cells, in particular CD8⁺ T cells, in individuals with long-term infections with Trypanosoma cruzi. Trans-sialidase proteins from T. cruzi are major surface and released proteins that are targets of humoral and cellular immune responses. We previously, identified a set of trans-sialidase peptides that were recognized by a very low frequency of chronically T. cruzi-infected subjects. Based on bioinformatic predictions, herein we report the identification of new trans-sialidase epitopes that are recognized by a higher proportion of T. cruzi-infected people. The functional profile of T cells specific for these peptides is characteristic of an infection with long term stimulation of the immune system, with high levels of IFN-γ-secreting T cells and low levels of IL-2 production. This set of T. cruzi peptides should prove useful for monitoring immune competence and changes in infection and disease status in individuals with chronic Chagas disease.

An adaptation of recombinant vaccinia-based ELISPOT and intracellular cytokine staining for a comparative measurement of cellular immune responses in HIV-1 and HIV-2 infections in West Africa

An efficient and quantitative tool for rapid assessment of human immunodeficiency virus (HIV)-induced cellular immune responses is important for resource-limited settings, such as in sub-Saharan Africa. Modifications are required to previously reported methods for evaluating ex-vivo antigen-specific cellular responses based on direct recombinant vaccinia virus (rVV) stimulation of peripheral blood mononuclear cells (PBMCs) by enzyme linked immunosorbent assay (ELISPOT) and by flow cytometry intracellular cytokine assay (ICA). We made such modifications in order to detect specific responses and compared quantitative cellular immune responses in HIV-1 and HIV-2 infected Gambians. The sensitivity of the rVV-based ELISPOT assay was on average 1.25 interferon (IFN)-gamma spot forming cells (SFC) per 50 000 PBMCs specific for either infection, and 5 IFN-gamma-secreting CD8+ T cells/50 000 in the ICA. The level of IFN-gamma SFC detected by ELISPOT and by ICA were correlated (P < 0.02). ICA detected pol-specific responses in 88% and 67% of HIV-1 and HIV-2 subjects, respectively, and gag-specific responses in more than 80% of both infections. Lower proportions of responders were obtained with ELISPOT, for which pol responses were present in 60% of HIV-1 and 46% of HIV-2 infected patients, and gag responses in 55% and 69%, respectively. The assays did not show any significant difference in cellular immune responses between HIV-1 and HIV-2 infected subjects with CD4% >or= 20%. These outcomes are comparable with results obtained using standard techniques and thus this method is a suitable, rapid and less expensive assessment of cellular immunity.

Does malaria suffer from lack of memory?

It is widely perceived that immunity to malaria is, to an extent, defective and that one component of this defective immune response is the inability to induce or maintain long-term memory responses. If true, this is likely to pose problems for development of an effective vaccine against malaria. In this article, we critically review and challenge this interpretation of the epidemiological and experimental evidence. While evasion and modulation of host immune responses clearly occurs and naturally acquired immunity is far from optimal, mechanisms to control blood-stage parasites are acquired and maintained by individuals living in endemic areas, allowing parasite density to be kept below the threshold for induction of acute disease. Furthermore, protective immunity to severe pathology is achieved relatively rapidly and is maintained in the absence of boosting by re-infection. Nevertheless, there are significant challenges to overcome. The need for multiple infections to acquire immunity means that young children remain at risk of infection for far too long. Persistent or frequent exposure to antigen seems to be required to maintain anti-parasite immunity (premunition). Lastly, pre-erythrocytic and sexual stages of the life cycle are poorly immunogenic, and there is little evidence of effective pre-erythrocytic or transmission-blocking immunity at the population level. While these problems might theoretically be due to defective immunological memory, we suggest alternative explanations. Moreover, we question the extent to which these problems are malaria-specific rather than generic (i.e. result from inherent limitations of the vertebrate immune system).

Long-term multiepitopic cytotoxic-T-lymphocyte responses induced in chimpanzees by combinations of Plasmodium falciparum liver-stage peptides and lipopeptides

Preclinical immunogenicity studies of 12 malaria peptides, selected from four Plasmodium falciparum antigens (Ags), namely, LSA1, LSA3, SALSA, and STARP, that are expressed at the pre-erythrocytic (sporozoite and liver) stages of the human parasite were carried out in chimpanzees. To strengthen their immunogenicity, six of these synthetic peptides were modified by the C-terminal addition of a single palmitoyl chain (lipopeptides) and delivered without adjuvant, whereas the remaining six unmodified peptides were emulsified and delivered by using Montanide ISA51 adjuvant. We have previously reported that these peptides and lipopeptides induce high B-cell and CD4(+)-T-helper responses in chimpanzees. In this report, we show their ability to induce multiepitopic and long-lasting antigen-specific CD8(+) cytotoxic-T-lymphocyte (CTL) responses. The magnitude, consistency, and memory of CTL responses generated by LSA3 peptides point to the strong immunogenicity of this liver-stage Ag. These findings support the screening strategy used to select the four P. falciparum pre-erythrocytic Ags and emphasize their valuable immunogenic properties. The successful immunization of nonhuman primates with combinations of corresponding peptides in a mineral oil emulsion (ISA51) and lipopeptides in saline provide a vaccine formulation that can be tested in humans.

Generation of PSA-reactive effector cells after vaccination with a PSA-based vaccine in patients with prostate cancer

BACKGROUND

JBT 1001 is a vaccine used for therapy of prostate cancer (CA), which consists of recombinant prostate-specific antigen (PSA) with lipid A formulated in liposomes. Patients with prostate CA were vaccinated with JBT 1001 emulsified in mineral oil (n = 5) or with the vaccine in combination with granulocyte-macrophage colony-stimulating factor (GM-CSF) administered locally at the site of vaccination (n = 5). Frequency of PSA-reactive T cells was measured in peripheral blood mononuclear cells (PBMC) before and after immunization, using an interferon-gamma (IFN-gamma) enzyme-linked immunospot (ELISPOT) assay with autologous dendritic cells (DC) as antigen-presenting cells. The hypothesis tested was that PSA-based vaccines induce T cell responses to human PSA.

METHODS

In order to expand precursor cells, in vitro sensitization (IVS) was performed. Microcultures of peripheral blood lymphocytes (PBL) (1 x 10(5)/well) in medium supplemented with interleukin-2 (IL-2) (10 IU/ml) and interleukin-7 (IL-7) (10 ng/ml) were stimulated twice (day 0 and day 7) with monocyte-derived autologous DC, generated by culture with interleukin-4 (IL-4) and GM-CSF and pulsed with PSA (10 microg/ml) at an effector to stimulator ratio of 10:1. ELISPOT assays were performed on day 14 of culture. In addition, PBMC were separated on immunobeads into CD4(+) and CD8(+) subsets for ELISPOT assays performed without IVS.

RESULTS

Two patients had PSA-reactive responses before vaccination (frequency range, 1/700-1/4,400). After vaccination, 8/10 patients had measurable PSA-reactive T-cell frequencies, ranging from 1/200-1/1900, using IVS. In contrast, without IVS, but after immunoselection to enrich in CD8(+) and CD4(+) T cells, only 2/10 patients had detectable PSA-reactive T cells after vaccination, at a frequency ranging from 1/2,600-1/4,000.

CONCLUSIONS

Vaccination with PSA formulated into liposomes induced T-cell responses in 8/10 patients with prostate carcinoma. The frequency of PSA-reactive precursor T cells was relatively low in the blood of these patients, and IVS, leading to amplification of the precursor cells prior to ELISPOT, was necessary for quantification of the PSA-responding T cells. Cellular responses to PSA were predominantly mediated by CD4(+) T lymphocytes.