Annulling a dangerous liaison: vaccination strategies against AIDS and tuberculosis

Tuberculosis subunit vaccine design: the conflict of antigenicity and immunogenicity

The attempts to find an effective antituberculous subunit vaccine are based on the assumption that it must drive a Th1 response. In the absence of effective correlates of protection, a vast array of mycobacterial components are being evaluated worldwide either on the basis of their ability to be recognized by T lymphocytes in in vitro assays during early stage of animal or human infection (antigenicity) or their capacity to induce T cell response following immunization in animal models (immunogenicity). The putative vaccine candidates selected using either of these strategies are then subjected to challenge studies in different animal models to evaluate the protective efficacy. Here we review the outcome of this current scheme of selection of vaccine candidates using an 'antigenicity' or 'immunogenicity' criterion on the actual protective efficacy observed in experimental animal models. The possible implications for the success of some of the leading vaccine candidates in clinical trials will also be discussed.

Immunostimulatory activity of recombinant Mycobacterium bovis BCG that secretes major membrane protein II of Mycobacterium leprae

We previously demonstrated that major membrane protein II (MMP-II) is one of the immunodominant antigens (Ags) of Mycobacterium leprae capable of activating T cells through Toll-like receptor 2. Based on the observation that Mycobacterium bovis BCG secreting a 30-kDa protein offered better protection against tuberculosis, we constructed a recombinant BCG strain (BCG-SM) that secretes MMP-II to improve the potency of BCG against leprosy. The secreted MMP-II protein from BCG-SM stimulated monocyte-derived dendritic cells (DC) to produce interleukin-12. DC infected with BCG-SM expressed MMP-II on their surfaces, and MMP-II expression was suppressed by the pretreatment of DC with chloroquine. These results indicated that secreted MMP-II was processed by DC for higher expression levels on their surfaces. In addition, BCG-SM phenotypically activated DC and induced higher expression levels of major histocompatibility complex, CD86, and CD83 Ags on DC than did vector control BCG (BCG-pMV). The DC infected with BCG-SM more efficiently stimulated naïve and memory CD4+ T cells and memory CD8+ T cells to produce gamma interferon than did those infected with BCG-pMV. However, naïve CD8+ T cells were significantly activated only when they were stimulated with BCG-SM-infected DC. When CD8+ T cells were cocultured with BCG-SM-infected DC, the proportion of perforin-producing T cells was significantly higher than that in cells cocultured with BCG-pMV-infected DC. Moreover, MMP-II-specific memory T cells were more efficiently produced in mice inoculated with BCG-SM than in mice inoculated with BCG-pMV. Taken together, these results indicate that BCG capable of secreting the immunodominant Ag is more potent in the stimulation of T cells.

Evaluation of a Self-Inactivating Lentiviral Vector Expressing Simian Immunodeficiency Virus Gag for Induction of Specific Immune Responsesin Vitroandin Vivo

Humoral and cellular immune responses have been shown to play a fundamental role in controlling simian and/or simian-human immunodeficiency virus (SIV-SHIV) replication in infected macaques. Therefore, the appropriate induction of both compartments of the immune system should be elicited after immunization. In this context, viral vectors have been proven effective in inducing both humoral and cellular immune responses during immunization protocols after direct injection in vivo. Among them, recombinant self-inactivating lentiviral vectors represent a useful strategy for vaccine development because they efficiently transduce and express foreign genes into a wide variety of mammalian cells. Here we report on the development and evaluation of a self-inactivating HIV-based lentiviral vector expressing a codon-optimized SIV Gag sequence (TY2-SIVGagDX), which when used to transduce dendritic cells mediated in vitro expansion of Gag-specific T cells derived from an SHIV-infected cynomolgus monkey, as measured by interferon (IFN)-gamma enzyme-linked immunospot (ELISPOT) and (51)Cr release standard assays. To evaluate the ability to elicit specific immune responses in vivo, TY2-SIVGagDX was also employed in a vaccination protocol after a single intramuscular injection in BALB/c mice. Results indicated that the vector was able to efficiently induce both cellular and humoral responses, as measured by IFN-gamma ELISPOT assay and antibody production. These data further confirm that lentiviral vectors encoding viral genes represent an advantageous delivery system for vaccine development.

Envisioning future strategies for vaccination against tuberculosis

The design of tuberculosis vaccines has entered a new era. Although several new vaccine candidates will pass Phase I clinical trials within the next year, I believe that the most effective vaccination strategy will be to combine different vaccine candidates and to use a prime-boost approach. This strategy, however, would require several years of iterative vaccine trials, unless the process is expedited by the identification of reliable biomarkers for assessing vaccine efficacy. In this Essay, I briefly summarize past and present attempts to develop a vaccine against tuberculosis, and I describe, using imagined scenarios, the tuberculosis vaccination schemes that might become available from a large repertoire of candidate schemes in the near and distant future.

The promise and challenge of anti-HIV cellular immunity

PURPOSE OF REVIEW

We discuss recent studies giving insight into the promise of cell-mediated immunity for prophylactic HIV vaccine strategies, and challenges to be overcome for this approach to succeed.

RECENT FINDINGS

Advances in understanding of events in very early HIV infection and their importance in viral pathogenesis emphasize the rapidity with which vaccine-induced T-cell responses must act to modulate CD4 cell destruction, but also reveal an early window of opportunity when foci of infection are limited and could potentially be eliminated. Super-infection with diverse HIV strains is now appreciated to be relatively common, indicating that cell-mediated responses in most infected individuals do not confer protection. Recent studies suggest that T-cell correlates of good control of HIV replication may be a consequence rather than a cause of containment of viraemia. Analysis of features of HIV-specific T-cell responses restricted by human leukocyte antigen alleles associated with differential prognosis of infection is giving insight into correlates of protection. The importance of efficacious responses, escape from which incurs high fitness costs, is increasingly appreciated.

SUMMARY

There are many challenges to be overcome before the promise of cell-mediated immunity for HIV vaccines is realized.

Vaccinia virus K1L protein supports viral replication in human and rabbit cells through a cell-type-specific set of its ankyrin repeat residues that are distinct from its binding site for ACAP2

Vaccinia virus (VV) K1L is a host-range gene and encodes a protein comprised of six ankyrin repeats (ANKs). We showed here that a large portion of the K1L protein, except ankyrin repeat 1 (ANK1) and C-terminal halves of ANK2 and ANK3, can be deleted or substituted with an unrelated ANK with no adverse effect on VV replication in human HeLa cells. In contrast, only ANK4 and ANK6 can be mutated without impairing VV replication in rabbit RK13 cells. The growth rate of VV in HeLa cells was reduced differentially by substituting phenylalanine 82 or serine 83 of ANK2 and abolished completely by substituting both residues. These substitutions, however, did not affect K1L's ability to bind ACAP2, a GTPase-activating protein for ARF6. Our data support the hypothesis that surface residues of a few consecutive K1L ANKs mediate the host-range function by interacting with protein factors that are distinct from ACAP2.

Bacterial resistance: a sensitive issue complexity of the challenge and containment strategy in Europe

The development of antimicrobial agents has been a key achievement of modern medicine. However, their overuse has led to an increasing incidence of infections due to antibiotic-resistant microorganisms. Quantitative figures on the current economic and health impact of antimicrobial resistance are scant, but it is clearly a growing challenge that requires timely action. That action should be at the educational, ethical, economic and political level. An important first step would be to increase public awareness and willingness to take the necessary measures to curb resistance. Hence, studies are needed that would provide solid, quantitative data on the societal impact of antibiotic resistance. This review discusses the complexity of resistance, identifies its main drivers and proposes measures to contain it on a European scale.

Advances in tuberculosis vaccine strategies

Tuberculosis (TB), an ancient human scourge, is a growing health problem in the developing world. Approximately two million deaths each year are caused by TB, which is the leading cause of death in HIV-infected individuals. Clearly, an improved TB vaccine is desperately needed. Heterologous prime-boost regimens probably represent the best hope for an improved vaccine regimen to prevent TB. This first generation of new vaccines might also complement drug treatment regimens and be effective against reactivation of TB from the latent state, which would significantly enhance their usefulness.

Tuberculosis vaccines: past, present and future

PURPOSE OF REVIEW

The current vaccine against tuberculosis protects against severe forms of the disease in children but confers variable effectiveness against pulmonary disease. With tuberculosis eradication on the horizon new vaccines with better protection than Mycobacterium bovis bacillus Calmette-Guérin (BCG) are needed. This review will outline the most promising tuberculosis vaccine candidates from selected publications.

RECENT FINDINGS

The enormous effort of the scientific community in the last 10 years has generated hundreds of tuberculosis vaccine candidates. These include sub-unit vaccines and live vaccines such as recombinant BCG and other attenuated live vaccines. Some of these are being included for the first time in phase I clinical trials.

SUMMARY

For more than 80 years now no new tuberculosis vaccine has successfully been developed. There is now renewed optimism that vaccines superior to BCG can be developed in the coming years. The goal is to obtain a new generation of vaccines effective against more transmissible forms of tuberculosis. As a first step, good candidate vaccines able to boost BCG and improve BCG protection could be a reality in the near future. Tuberculosis vaccine candidates, able to replace the currently used BCG and make the eradication of tuberculosis feasible, can be expected in the mid-term, and live vaccines are reliable and promising candidates.

Progress in tuberculosis vaccine development

The first tuberculosis vaccine candidates have reached clinical testing. Novel subunit vaccine candidates aimed at boosting previous BCG-prime vaccination and novel viable attenuated vaccine candidates aimed at substituting BCG have both completed the preclinical stage. Despite these achievements, rational vaccine design against tuberculosis has not come to an end. Novel findings in basic immunology and microbiology will advance further improvements in vaccine development. These include the potential role of crosspriming to induce more potent T-cell responses, the role of memory T cells and regulatory T cells in sustaining or curtailing optimal immune responses, respectively, as well as the involvement of cytokines in T-cell migration to nonimmunologic tissue sites and in the generation of memory. Knowledge about basic mechanisms underlying optimum protection will not only have a direct impact on future vaccine design against tuberculosis but also help in the formulation of a set of biomarkers with predictive value for vaccine efficacy assessment.

The Mycobacterium tuberculosis LipB enzyme functions as a cysteine/lysine dyad acyltransferase

Lipoic acid is essential for the activation of a number of protein complexes involved in key metabolic processes. Growth of Mycobacterium tuberculosis relies on a pathway in which the lipoate attachment group is synthesized from an endogenously produced octanoic acid moiety. In patients with multiple-drug-resistant M. tuberculosis, expression of one gene from this pathway, lipB, encoding for octanoyl-[acyl carrier protein]-protein acyltransferase is considerably up-regulated, thus making it a potential target in the search for novel antiinfectives against tuberculosis. Here we present the crystal structure of the M. tuberculosis LipB protein at atomic resolution, showing an unexpected thioether-linked active-site complex with decanoic acid. We provide evidence that the transferase functions as a cysteine/lysine dyad acyltransferase, in which two invariant residues (Lys-142 and Cys-176) are likely to function as acid/base catalysts. Analysis by MS reveals that the LipB catalytic reaction proceeds by means of an internal thioesteracyl intermediate. Structural comparison of LipB with lipoate protein ligase A indicates that, despite conserved structural and sequence active-site features in the two enzymes, 4'-phosphopantetheine-bound octanoic acid recognition is a specific property of LipB.

Tuberculosis: back on the immunologists' agenda

Although tuberculosis research was instrumental in the birth of immunology, the two disciplines soon separated. The time is ripe for a reunion. Immunology has much to offer for rational intervention measures toward tuberculosis control.

The hbhA gene of Mycobacterium tuberculosis is specifically upregulated in the lungs but not in the spleens of aerogenically infected mice

We report that hbhA is differentially regulated during Mycobacterium tuberculosis infection. Upregulation was observed in epithelial cell infection but not in macrophage infection and in the lungs but not in the spleens of infected mice, and it was greater during the early steps of infection, when bacilli disseminate from the site of primary infection.

Deletion of gene A41L enhances vaccinia virus immunogenicity and vaccine efficacy

Vaccinia virus (VACV) is the vaccine that was used to eradicate smallpox and is being developed as a recombinant vaccine for other pathogens. Removal of genes encoding immunomodulatory proteins expressed by VACV may enhance virus immunogenicity and improve its potential as a vaccine. Protein A41 is a candidate for removal, having sequence similarity to the VACV chemokine-binding protein, vCKBP, and an association with reduced inflammation during dermal infection. Here, it is shown that, at low doses, VACV strain Western Reserve (WR) lacking A41L (vDeltaA41L) was slightly more virulent than wild-type and revertant controls after intranasal infection of BALB/c mice. The primary immune response to vDeltaA41L was marked by an increase in the percentage of VACV-specific gamma interferon-producing CD8(+) T cells and enhancement of cytotoxic T-cell responses in the spleen. However, this augmentation of cellular response was not seen in lung infiltrates. Splenic CD8(+) T-cell responses were also enhanced when VACV strain modified vaccinia virus Ankara (MVA) lacking A41L was used to immunize mice. Lastly, immunization with VACV MVA lacking A41L provided better protection than control viruses to subsequent challenge with a 300 LD(50) dose of VACV WR. This study provides insight into the immunomodulatory role of A41 and suggests that MVA lacking A41 may represent a more efficacious vaccine.

The rational design of vaccines

This review provides an insight into the various opportunities for vaccine intervention, analysis of strategies for vaccine development, vaccine ability to modulate immune responses and resultant rational vaccine design. In addition, wider aspects are considered, such as biotechnological advances, advances in immunological understanding and host–pathogen interactions. The key question addressed here is, with all our research and understanding, have we reached a new echelon in vaccine development, that of rational design?

New insights into the function of granulomas in human tuberculosis

The human tuberculous granuloma provides the morphological framework for local immune processes central to the outcome of tuberculosis. This review article describes investigations on human lung granulomas aimed at better understanding the regional host response and counter-measures to Mycobacterium tuberculosis. These findings lead to a revised view of the regional immune response in human tuberculosis. Novel insights into this dynamic cross-talk form the basis of novel intervention strategies.

Immune systems in developed and developing countries; implications for the design of vaccines that will work where BCG does not

New vaccine candidates for tuberculosis are beginning to enter clinical trials. In this review we discuss issues surrounding the design of these candidates, and the way they were screened in animal models. First, screening vaccines for their ability to attenuate inevitably fatal tuberculosis in immunologically naïve mice might be leading to the selection of inappropriate candidates. We need to screen vaccines for their ability to stop the development of progressive disease, since this is what they must achieve in man. A solution to this problem is proposed. Secondly, we point out that some mouse models of tuberculosis in laboratories in developing countries, where exposure to environmental mycobacteria is large, mimic neglected aspects of human disease more closely than do low-dose infections in hyper-susceptible immunologically naïve mice in the USA or Europe. We need to think more about geographical differences in immunological experience, and these mouse models can help us. Thirdly, we conclude that in developing countries where BCG fails this is not because there is too little Th1 response, but rather because the Th1 response is rendered ineffective and immunopathological by other subversive mechanisms, including IL-4 responses and inappropriate regulatory T cell function. Therefore, we suggest that vaccines that will work in those countries might need to have immunoregulatory properties that can switch off pre-existing subversive mechanisms, and block their development in the future. The development of such vaccines, that might work where BCG does not, will require a greater understanding of the roles of the many types of regulatory T cell in tuberculosis.

Apoptotic vesicles crossprime CD8 T cells and protect against tuberculosis

CD8 T lymphocytes are important effectors in protective immunity against Mycobacterium tuberculosis. We recently characterized the detour pathway of CD8 T cell activation in tuberculosis mediated by apoptotic vesicles from infected cells that transport mycobacterial antigens to dendritic cells (DCs). Here we demonstrate that apoptotic vesicles from mycobacteria-infected macrophages stimulate CD8 T cells in vivo. Homing of DCs to draining lymph nodes was critically required for effective crosspriming. Subsequent fate of vesicle-associated antigens in recipient DCs was characterized by endosomal mechanisms predominating over proteasomal processing. In addition, vesicle processing depended on the presence of saposins to disintegrate apoptotic membranes. Apoptotic vesicles displayed potent adjuvant activity by stimulating through Toll-like receptors (TLR). Ultimately, vaccination with vesicles from infected cells induced protection against M. tuberculosis infection. Taken together, we propose the detour pathway to represent a genuine immunological mechanism mediating crosspriming of CD8 T cells in vivo and protection against tuberculosis.

Progress in the development of tuberculosis vaccines for cattle and wildlife

Vaccination against bovine tuberculosis is likely to become an important disease control strategy in developing countries, which cannot afford a test and slaughter control programme, or in countries which have a wildlife reservoir of Mycobacterium bovis infection. In the past decade, considerable progress has been made in the development and evaluation of tuberculosis vaccines for cattle and for a range of wildlife maintenance hosts including possums, badgers, deer and African buffaloes. Experimental challenge systems have been established for the different target species and the resulting disease process has mimicked that seen in the field. In cattle, neonatal vaccination with BCG appeared to be more effective than vaccination of 6-month-old calves and in most situations no other vaccine has been shown to be better than BCG. However, prime-boost strategies involving combinations of BCG with a protein or DNA vaccine, to improve on BCG vaccination alone, have produced very encouraging results. Differential diagnostic tests have been developed using mycobacterial antigens that are only present in virulent M. bovis to differentiate between BCG-vaccinated and M. bovis-infected cattle. BCG vaccine has been shown to reduce the spread of tuberculous lesions in a range of wildlife species and a prototype oral bait delivery system has been developed. Prospects for the development of improved vaccines against bovine tuberculosis are promising and vaccination approaches could become very valuable in the control and eradication of bovine tuberculosis.

100th anniversary of Robert Koch's Nobel Prize for the discovery of the tubercle bacillus

The year 2005 marks the 100th anniversary of Robert Koch's Nobel Prize. Here, we describe the scientific career of Robert Koch, the discoverer of the etiologic agent of tuberculosis but also of those of anthrax, cholera and wound infections. Equally important, Koch developed the methodologies and concepts that made medical microbiology a scientific discipline. Despite great efforts, however, Koch failed to conquer tuberculosis, which still causes enormous health problems worldwide 100 years after his Nobel award.

Recent findings in immunology give tuberculosis vaccines a new boost

Tuberculosis remains a major health threat, solved by neither chemotherapy nor the current vaccine, BCG. Although a new generation of vaccine candidates is ready for field trials, further improvements will be required. A successful vaccination regime must stimulate memory T cells and, at the same time, avoid exhaustion of memory and suppression by regulatory mechanisms. The most probable scenario is priming with one vaccine candidate followed by boosting with a another vaccine candidate. For clinical trials, biomarkers need to be defined with T cells alternating between lung and periphery as prime indicator cells.

Increased vaccine efficacy against tuberculosis of recombinant Mycobacterium bovis bacille Calmette-Guérin mutants that secrete listeriolysin

The tuberculosis vaccine Mycobacterium bovis bacille Calmette-Guérin (BCG) was equipped with the membrane-perforating listeriolysin (Hly) of Listeria monocytogenes, which was shown to improve protection against Mycobacterium tuberculosis. Following aerosol challenge, the Hly-secreting recombinant BCG (hly+ rBCG) vaccine was shown to protect significantly better against aerosol infection with M. tuberculosis than did the parental BCG strain. The isogenic, urease C-deficient hly+ rBCG (DeltaureC hly+ rBCG) vaccine, providing an intraphagosomal pH closer to the acidic pH optimum for Hly activity, exhibited still higher vaccine efficacy than parental BCG. DeltaureC hly+ rBCG also induced profound protection against a member of the M. tuberculosis Beijing/W genotype family while parental BCG failed to do so consistently. Hly not only promoted antigen translocation into the cytoplasm but also apoptosis of infected macrophages. We concluded that superior vaccine efficacy of DeltaureC hly+ rBCG as compared with parental BCG is primarily based on improved cross-priming, which causes enhanced T cell-mediated immunity.

Can successful vaccines teach us how to induce efficient protective immune responses?

Some recently introduced vaccines that have excellent efficacy records have been developed without a clear understanding of their mechanism of protection. In fact, successful vaccines have often emerged out of empirical observations and have only rarely been the result of a rational use of the continuously increasing immunological knowledge available to scientists. However, a posteriori deciphering of the biological bases for the efficacy of successful vaccines should be an essential component of research efforts directed at the development of new vaccines for the most challenging infectious diseases.