The quest for an AIDS vaccine: is the CD8+ T-cell approach feasible?

Exploring HIV Vaccine Progress in the Pre-Clinical and Clinical Setting: From History to Future Prospects

The human immunodeficiency virus (HIV) continues to pose a significant global health challenge, with millions of people affected and new cases emerging each year. While various treatment and prevention methods exist, including antiretroviral therapy and non-vaccine approaches, developing an effective vaccine remains the most crucial and cost-effective solution to combating the HIV epidemic. Despite significant advancements in HIV research, the HIV vaccine field has faced numerous challenges, and only one clinical trial has demonstrated a modest level of efficacy. This review delves into the history of HIV vaccines and the current efforts in HIV prevention, emphasizing pre-clinical vaccine development using the non-human primate model (NHP) of HIV infection. NHP models offer valuable insights into potential preventive strategies for combating HIV, and they play a vital role in informing and guiding the development of novel vaccine candidates before they can proceed to human clinical trials.

Preventive HIV Vaccines-Leveraging on Lessons from the Past to Pave the Way Forward

Almost four decades on, since the 1980’s, with hundreds of HIV vaccine candidates tested in both non-human primates and humans, and several HIV vaccines trials later, an efficacious HIV vaccine continues to evade us. The enormous worldwide genetic diversity of HIV, combined with HIV’s inherent recombination and high mutation rates, has hampered the development of an effective vaccine. Despite the advent of antiretrovirals as pre-exposure prophylaxis and preventative treatment, which have shown to be effective, HIV infections continue to proliferate, highlighting the great need for a vaccine. Here, we provide a brief history for the HIV vaccine field, with the most recent disappointments and advancements. We also provide an update on current passive immunity trials, testing proof of the concept of the most clinically advanced broadly neutralizing monoclonal antibodies for HIV prevention. Finally, we include mucosal immunity, the importance of vaccine-elicited immune responses and the challenges thereof in the most vulnerable environment–the female genital tract and the rectal surfaces of the gastrointestinal tract for heterosexual and men who have sex with men transmissions, respectively.

New insights into pathogenesis point to HIV-1 Tat as a key vaccine target

Despite over 30 years of enormous effort and progress in the field, no preventative and/or therapeutic vaccines against human immunodeficiency virus (HIV) are available. Here, we briefly summarize the vaccine strategies and vaccine candidates that in recent years advanced to efficacy trials with mostly unsatisfactory results. Next, we discuss a novel and somewhat contrarian approach based on biological and epidemiological evidence, which led us to choose the HIV protein Tat for the development of preventive and therapeutic HIV vaccines. Toward this goal, we review here the role of Tat in the virus life cycle as well as experimental and epidemiological evidence supporting its key role in the natural history of HIV infection and comorbidities. We then discuss the preclinical and clinical development of a Tat therapeutic vaccine, which, by improving the functionality and homeostasis of the immune system and by reducing the viral reservoir in virologically suppressed vaccinees, helps to establish key determinants for intensification of combination antiretroviral therapy (cART) and a functional cure. Future developments and potential applications of the Tat therapeutic vaccine are also discussed, as well as the rationale for its use in preventative strategies. We hope this contribution will lead to a reconsideration of the current paradigms for the development of HIV/AIDS vaccines, with a focus on targeting of viral proteins with key roles in HIV pathogenesis.

Major Scientific Hurdles in HIV Vaccine Development: Historical Perspective and Future Directions

Following the discovery of HIV as a causative agent of AIDS, the expectation was to rapidly develop a vaccine; but thirty years later, we still do not have a licensed vaccine. Progress has been hindered by the extensive genetic variability of HIV and our limited understanding of immune responses required to protect against HIV acquisition. Nonetheless, valuable knowledge accrued from numerous basic and translational science research studies and vaccine trials has provided insight into the structural biology of the virus, immunogen design and novel vaccine delivery systems that will likely constitute an effective vaccine. Furthermore, stakeholders now appreciate the daunting scientific challenges of developing an effective HIV vaccine, hence the increased advocacy for collaborative efforts among academic research scientists, governments, pharmaceutical industry, philanthropy, and regulatory entities. In this review, we highlight the history of HIV vaccine development efforts, highlighting major challenges and future directions.

Antigenic variability: Obstacles on the road to vaccines against traditionally difficult targets

Despite the impressive impact of vaccines on public health, the success of vaccines targeting many important pathogens and cancers has to date been limited. The burden of infectious diseases today is mainly caused by antigenically variable pathogens (AVPs), which escape immune responses induced by prior infection or vaccination through changes in molecular structures recognized by antibodies or T cells. Extensive genetic and antigenic variability is the major obstacle for the development of new or improved vaccines against "difficult" targets. Alternative, qualitatively new approaches leading to the generation of disease- and patient-specific vaccine immunogens that incorporate complex permanently changing epitope landscapes of intended targets accompanied by appropriate immunomodulators are urgently needed. In this review, we highlight some of the most critical common issues related to the development of vaccines against many pathogens and cancers that escape protective immune responses owing to antigenic variation, and discuss recent efforts to overcome the obstacles by applying alternative approaches for the rational design of new types of immunogens.

Pooled-Peptide Epitope Mapping Strategies Are Efficient and Highly Sensitive: An Evaluation of Methods for Identifying Human T Cell Epitope Specificities in Large-Scale HIV Vaccine Efficacy Trials

The interferon gamma, enzyme-linked immunospot (IFN-γ ELISpot) assay is widely used to identify viral antigen-specific T cells is frequently employed to quantify T cell responses in HIV vaccine studies. It can be used to define T cell epitope specificities using panels of peptide antigens, but with sample and cost constraints there is a critical need to improve the efficiency of epitope mapping for large and variable pathogens. We evaluated two epitope mapping strategies, based on group testing, for their ability to identify vaccine-induced T-cells from participants in the Step HIV-1 vaccine efficacy trial, and compared the findings to an approach of assaying each peptide individually. The group testing strategies reduced the number of assays required by >7-fold without significantly altering the accuracy of T-cell breadth estimates. Assays of small pools containing 7–30 peptides were highly sensitive and effective at detecting single positive peptides as well as summating responses to multiple peptides. Also, assays with a single 15-mer peptide, containing an identified epitope, did not always elicit a response providing validation that 15-mer peptides are not optimal antigens for detecting CD8+ T cells. Our findings further validate pooling-based epitope mapping strategies, which are critical for characterizing vaccine-induced T-cell responses and more broadly for informing iterative vaccine design. We also show ways to improve their application with computational peptide:MHC binding predictors that can accurately identify the optimal epitope within a 15-mer peptide and within a pool of 15-mer peptides.

Transgenic 4-1BBL-engineered vaccine stimulates potent Gag-specific therapeutic and long-term immunity via increased priming of CD44(+)CD62L(high) IL-7R(+) CTLs with up- and downregulation of anti- and pro-apoptosis genes

Human immunodeficiency virus type-1 (HIV-1)-specific dendritic cell (DC) vaccines have been used in clinical trials. However, they have been found to only induce some degree of immune responses in these studies. We previously demonstrated that the HIV-1 Gag-specific Gag-Texo vaccine stimulated Gag-specific effector CD8(+) cytotoxic T lymphocyte (CTL) responses, leading to completely protective, but very limited, therapeutic immunity. In this study, we constructed a recombinant adenoviral vector, adenovirus (AdV)4-1BBL, which expressed mouse 4-1BB ligand (4-1BBL), and generated transgenic 4-1BBL-engineered OVA-Texo/4-1BBL and Gag-Texo/4-1BBL vaccines by transfecting ovalbumin (OVA)-Texo and Gag-Texo cells with AdV4-1BBL, respectively. We demonstrate that the OVA-specific OVA-Texo/4-1BBL vaccine stimulates more efficient OVA-specific CTL responses (3.26%) compared to OVA-Texo-activated responses (1.98%) in wild-type C57BL/6 mice and the control OVA-Texo/Null vaccine without transgenic 4-1BBL expression, leading to enhanced therapeutic immunity against 6-day established OVA-expressing B16 melanoma BL6-10OVA cells. OVA-Texo/4-1BBL-stimulated CTLs, which have a CD44(+)CD62L(high) IL-7R(+) phenotype, are likely memory CTL precursors, demonstrating prolonged survival and enhanced differentiation into memory CTLs with functional recall responses and long-term immunity against BL6-10OVA melanoma. In addition, we demonstrate that OVA-Texo/4-1BBL-stimulated CTLs up- and downregulate the expression of anti-apoptosis (Bcl2l10, Naip1, Nol3, Pak7 and Tnfrsf11b) and pro-apoptosis (Casp12, Trp63 and Trp73) genes, respectively, by RT(2) Profiler PCR array analysis. Importantly, the Gag-specific Gag-Texo/4-1BBL vaccine also stimulates more efficient Gag-specific therapeutic and long-term immunity against HLA-A2/Gag-expressing B16 melanoma BL6-10Gag/A2 cells than the control Gag-Texo/Null vaccine in transgenic HLA-A2 mice. Taken together, our novel Gag-Texo/4-1BBL vaccine, which is capable of stimulating potent Gag-specific therapeutic and long-term immunity, may represent a new immunotherapeutic vaccine for controlling HIV-1 infection.

Recent progress in HIV vaccines inducing mucosal immune responses

In spite of several attempts over many years at developing a HIV vaccine based on classical strategies, none has convincingly succeeded to date. As HIV is transmitted primarily by the mucosal route, particularly through sexual intercourse, understanding antiviral immunity at mucosal sites is of major importance. An ideal vaccine should elicit HIV-specific antibodies and mucosal CD8⁺ cytotoxic T-lymphocyte (CTL) as a first line of defense at a very early stage of HIV infection, before the virus can disseminate into the secondary lymphoid organs in mucosal and systemic tissues. A primary focus of HIV preventive vaccine research is therefore the induction of protective immune responses in these crucial early stages of HIV infection. Numerous approaches are being studied in the field, including building upon the recent RV144 clinical trial. In this article, we will review current strategies and briefly discuss the use of adjuvants in designing HIV vaccines that induce mucosal immune responses.

Preventive and therapeutic applications of neutralizing antibodies to Human Immunodeficiency Virus Type 1 (HIV-1)

The development of a preventive vaccine to neutralize the highly variable and antigenically diverse human immunodeficiency virus type 1 (HIV-1) has been an indomitable goal. The recent discovery of a number of cross-neutralizing and potent monoclonal antibodies from elite neutralizers has provided important insights in this field. Neutralizing antibodies (NAbs) are useful in identifying neutralizing epitopes of vaccine utility and for understanding the mechanism of potent and broad cross-neutralization thus providing a modality of preventive and therapeutic value. In this article we review the current understanding on the potential use of broadly neutralizing antibodies (bNAbs) in their full-length IgG structure, engineered domain antibody or bispecific versions towards preventive and therapeutic applications. The potential implications of NAbs are discussed in the light of the recent developments as key components in vaccination against HIV-1. The development of a vaccine immunogen which elicits bNAbs and confers protective immunity remains a real challenge.

Broadly neutralizing antibodies and the search for an HIV-1 vaccine: the end of the beginning

The field of HIV-1 vaccine research has seen a renaissance with the identification of antibodies that neutralize most circulating HIV-1 strains. An understanding of the structural mode of target recognition that these antibodies use and the immune pathways that lead to their development is emerging. This knowledge has provided fundamental insights into the pathways that elicit broadly neutralizing antibodies and provides a foundation for active and passive immunization strategies to prevent HIV-1 infection.

What Has 30 Years of HIV Vaccine Research Taught Us?

When HIV was discovered and established as the cause of AIDS in 1983-1984, many people believed that a vaccine would be rapidly developed. However, 30 years have passed and we are still struggling to develop an elusive vaccine. In trying to achieve that goal, different scientific paradigms have been explored. Although major progress has been made in understanding the scientific basis for HIV vaccine development, efficacy trials have been critical in moving the field forward. Major lessons learned are: the development of an HIV vaccine is an extremely difficult challenge; the temptation of just following the fashion should be avoided; clinical trials are critical, especially large-scale efficacy trials; HIV vaccine research will require long-term commitment; and sustainable collaborations are needed to accelerate the development of an HIV vaccine. Concrete actions must be implemented with the sense of urgency imposed by the severity of the AIDS epidemic.

A brief history of the global effort to develop a preventive HIV vaccine

Soon after HIV was discovered as the cause of AIDS in 1983-1984, there was an expectation that a preventive vaccine would be rapidly developed. In trying to achieve that goal, three successive scientific paradigms have been explored: induction of neutralizing antibodies, induction of cell mediated immunity, and exploration of combination approaches and novel concepts. Although major progress has been made in understanding the scientific basis for HIV vaccine development, efficacy trials have been critical in moving the field forward. In 2009, the field was reinvigorated with the modest results obtained from the RV144 trial conducted in Thailand. Here, we review those vaccine development efforts, with an emphasis on events that occurred during the earlier years. The goal is to provide younger generations of scientists with information and inspiration to continue the search for an HIV vaccine.

Pharmacogenomics of Viral Diseases

Viral diseases are leading cause of deaths worldwide as WHO report suggests that hepatitis A virus (HAV) infects more than 80 % of the population of many developing countries. Viral hepatitis B (HBV) affects an estimated 360 million people, whereas hepatitis C affects 123 million people worldwide, and last but not least, at current, India has an HIV/AIDS population of approximately 2.4 million people and more than 30 million in whole world and now it has become a reason for 1.8 million death globally; thus, millions of people still struggle for their lives.

The progress in medical science has made it possible in overcoming the various fatal diseases such as small pox, chicken pox, dengue, etc., but human immunodeficiency viruses, influenza, and hepatitis virus have renewed challenge surprisingly. The obstacles and challenges in therapy include existence of antibiotic resistance strains of common organisms due to overuse of antibiotics, lack of vaccines, adverse drug reaction, and last but not least the susceptibility concerns. Emergence of pharmacogenomics and pharmacogenetics has shown some promises to take challenges. The discovery of human genome project has opened new vistas to understand the behaviors of genetic makeup in development and progression of diseases and treatment in various viral diseases. Current and previous decade have been engaged in making repositories of polymorphisms (SNPs) of various genes including drug-metabolizing enzymes, receptors, inflammatory cells related with immunity, and antigen-presenting cells, along with the prediction of risks. The genetic makeup alone is most likely an adequate way to handle the therapeutic decision-making process for previous regimen failure. With the introduction of new antiviral therapeutic agents, a significant improvement in progression and overall survival has been achieved, but these drugs have shown several adverse responses in some individuals, so the success is not up to the expectations. Research and acquisition of new knowledge of pharmacogenomics may help in overcoming the prevailing burden of viral diseases. So it will definitely help in selecting the most effective therapeutic agents, effective doses, and drug response for the individuals. Thus, it will be able to transform the laboratory research into the clinical bench side and will also help in understanding the pathogenesis of viral diseases with drug action, so the patients will be managed more properly and finally become able to fulfill the promise of the future.

Soluble proteins induce strong CD8+ T cell and antibody responses through electrostatic association with simple cationic or anionic lipopeptides that target TLR2

The low immunogenicity exhibited by most soluble proteins is generally due to the absence of molecular signatures that are recognized by the immune system as dangerous. In this study, we show that electrostatic binding of synthetic branched cationic or anionic lipopeptides that contain the TLR-2 agonist Pam(2)Cys markedly enhance a protein's immunogenicity. Binding of a charged lipopeptide to oppositely charged protein Ags resulted in the formation of stable complexes and occurs at physiologic pH and salt concentrations. The induction of cell-mediated responses is dependent on the electrostatic binding of lipopeptide to the protein, with no CD8(+) T cells being elicited when protein and lipopeptide possessed the same electrical charge. The CD8(+) T cells elicited after vaccination with lipopeptide-protein Ag complexes produced proinflammatory cytokines, exhibited in vivo lytic activity, and protected mice from challenge with an infectious chimeric influenza virus containing a single OVA epitope as part of the influenza neuraminidase protein. Induction of a CD8(+) T cell response correlated with the ability of lipopeptide to facilitate Ag uptake by DCs followed by trafficking of Ag-bearing cells into draining lymph nodes. Oppositely charged but not similarly charged lipopeptides were more effective in DC uptake and trafficking. Very high protein-specific Ab titers were also achieved by vaccination with complexes composed of oppositely charged lipopeptide and protein, whereas vaccination with similarly charged constituents resulted in significant but lower Ab titers. Regardless of whether similarly or oppositely charged lipopeptides were used in the induction of Ab, vaccination generated dominant IgG1 isotype Abs rather than IgG2a.

Immunogenicity of a novel engineered HIV-1 clade C synthetic consensus-based envelope DNA vaccine

DNA vaccines require significant engineering in order to generate strong CTL responses in both non-human primates and humans. In this study, we designed a clade C env gene (EY3E1-C) to decrease the genetic distances of virus isolates within clade C and focus the induced T cell responses to conserved clade C epitopes. After generating a consensus sequence by analyzing full-length clade C env early transmitter sequences, several modifications were performed to increase the expression of the EY3E1-C, including codon/RNA optimization, addition of Kozak sequence and addition of an IgE leader sequence. We also shortened the V1 and V2 loops to approximate early transmitter isolate sequences and the cytoplasmic tail was truncated to prevent envelope recycling. When studied as a DNA vaccine in Balb/c mice, compared to a primary codon-optimized clade C envelope DNA vaccine (p96ZM651gp140-CD5), this novel construct is up to three times more potent in driving CTL responses. Importantly this construct not only induces stronger cross-reactive cellular responses within clade C, it also induces stronger immune responses against clade B and group M envelope peptide pools than p96ZM651gp140-CD5. Epitope mapping demonstrated that EY3E1-C was able to induce clade C envelope-specific immune responses against 15 peptide pools, clade B envelope-specific immune responses against 19 peptide pools and group M envelope-specific immune responses against 16 peptide pools out of 29, respectively, indicating that a significant increase in the breadth of induced immune responses. The analysis of antibody responses suggested that vaccination of pEY3E1-C could induce a clade C envelope-specific antibody response. The cellular immune responses of pEY3E1-C could be further enhanced when the DNA was delivered by using electroporation (EP). Thus, the synthetic engineered consensus EY3E1-C gene is capable of eliciting stronger and broader CTL responses than primary clade C envelopes. This finding suggests that such synthetic immunogens could be important for examination of their potential as part of an efficient HIV DNA vaccine.

B-cell depletion reveals a role for antibodies in the control of chronic HIV-1 infection

HIV can be partially contained by host immunity and understanding the basis of this may inform vaccine design. The importance of B-cell function in long-term control is poorly understood. One method of investigating this is in vivo cellular depletion. In this study, we take advantage of a unique opportunity to investigate the role of B cells in an HIV-infected patient. The HIV-1(+) patient studied here was not taking antiretroviral drugs and was treated for pre-existing low-grade lymphoplasmacytoid lymphoma by depletion of CD20+ B cells using rituximab. We demonstrate that B-cell depletion results in a decline in autologous neutralizing antibody (NAb) responses and a 1.7 log(10) rise in HIV-1 plasma viral load (pVL). The recovery of NAbs results in a decline in pVL. The HIV-1 sequences diversify and NAb-resistant mutants are subsequently selected. These data suggest that B-cell function can contribute to the long-term control of pVL, and that NAbs may be more important in controlling chronic HIV-1 infection than previously suspected.

CD8+ T cells as a source of IFN-γ production in human cutaneous leishmaniasis

Background

In human leishmaniasis Th1/Th2 dichotomy similar to murine model is not clearly defined and surrogate marker(s) of protection is not yet known. In this study, Th1/Th2 cytokines (IL-5, IL-10, IL-13 and IFN-γ) profile induced by purified CD4⁺/CD8⁺ T cells in response to Leishmania antigens were assessed at transcript and protein levels in 14 volunteers with a history of self-healing cutaneous leishmaniasis (HCL) and compared with 18 healthy control volunteers.

Methodology/Principal Findings

CD4⁺/CD8⁺/CD14⁺ cells were purified from peripheral blood using magnetic beads; CD4⁺/CD8⁺ T cells were co-cultured with autologous CD14⁺ monocytes in the presence of soluble Leishmania antigens (SLA). Stimulation of either CD4⁺ T cells or CD8⁺ T cells of HCL volunteers with SLA induced a significantly (P<0.05) higher IFN-γ production compared with the cells of controls. Upregulation of IFN-γ gene expression in CD4⁺ cells (P<0.001) and CD8⁺ cells (P = 0.006) of HCL volunteers was significantly more than that of controls. Significantly (P<0.05) higher fold-expression of IFN-γ gene was seen in CD4⁺ cells than in CD8⁺ cells. In HCL volunteers a significantly (P = 0.014) higher number of CD4⁺ cells were positive for intracellular IFN-γ production than CD8⁺ cells.

Conclusions/Significance

Collectively, the volunteers have shown maintenance of specific long-term immune responses characterized by a strong reaction to leishmanin skin test and IFN-γ production. The dominant IFN-γ response was the result of expansion of both CD4⁺ and CD8⁺ T cells. The results suggested that immune response in protected individuals with a history of zoonotic cutaneous leishmaniasis (ZCL) due to L. major is mediated not only through the expansion of antigen-specific IFN-γ producing CD4⁺ Th1 cells, but also through IFN-γ producing CD8⁺ T cells.

Cutaneous leishmaniasis (CL) is usually a self-healing skin lesion caused by different species of Leishmania parasite. Resistance and susceptibility of mice to Leishmania major infection is associated with two types of CD4+ T lymphocytes development: Th1 type response with production of cytokine IFN-γ is associated with resistance, whereas Th2 type response with production of cytokines IL-4 and IL-5 is associated with susceptibility. A clear Th1/Th2 dichotomy similar to murine model is not defined in human leishmaniasis and we need as much information as possible to define marker(s) of protection. We purified CD4⁺/CD8⁺ T cells, stimulated them with Leishmania antigens and analysed gene and protein expression of Th1/Th2 cytokines in volunteers with a history of self-healing CL who are presumed to be protected against further Leishmania infection. We have seen significant upregulation of IFN-γ gene expression and high IFN-γ production in the Leishmania stimulated CD4⁺ T cells and CD8⁺ T cells. We concluded that both antigen-specific IFN-γ producing CD4⁺ Th1 cells and IFN-γ producing CD8⁺ T cells contribute to the long term protection in individuals with a history of CL. This proves the importance of CD8+ T cells as a source of IFN-γ in Th1-like immune responses.

Innovative approaches to develop prophylactic and therapeutic vaccines against HIV/AIDS

The acquired immunodeficiency syndrome (AIDS) emerged in the human population in the summer of 1981. According to the latest United Nations estimates, worldwide over 33 million people are infected with human immunodeficiency virus (HIV) and the prevalence rates continue to rise globally. To control the alarming spread of HIV, an urgent need exists for developing a safe and effective vaccine that prevents individuals from becoming infected or progressing to disease. To be effective, an HIV/AIDS vaccine should induce broad and long-lasting humoral and cellular immune responses, at both mucosal and systemic level. However, the nature of protective immune responses remains largely elusive and this represents one of the major roadblocks preventing the development of an effective vaccine. Here we summarize our present understanding of the factors responsible for resistance to infection or control of progression to disease in human and monkey that may be relevant to vaccine development and briefly review recent approaches which are currently being tested in clinical trials. Finally, the rationale and the current status of novel strategies based on nonstructural HIV-1 proteins, such as Tat, Nef and Rev, used alone or in combination with modified structural HIV-1 Env proteins are discussed.

The role of antibodies in HIV vaccines

Licensed vaccines against viral diseases generate antibodies that neutralize the infecting virus and protect against infection or disease. Similarly, an effective vaccine against HIV-1 will likely need to induce antibodies that prevent initial infection of host cells or that limit early events of viral dissemination. Such antibodies must target the surface envelope glycoproteins of HIV-1, which are highly variable in sequence and structure. The first subunit vaccines to enter clinical trails were safe and immunogenic but unable to elicit antibodies that neutralized most circulating strains of HIV-1. However, potent virus neutralizing antibodies (NAbs) can develop during the course of HIV-1 infection, and this is the type of antibody response that researchers seek to generate with a vaccine. Thus, current vaccine design efforts have focused on a more detailed understanding of these broadly neutralizing antibodies and their epitopes to inform the design of improved vaccines.

IFN-gamma expressed by T cells regulates the persistence of antigen presentation by limiting the survival of dendritic cells

Ag presentation to T cells orchestrates the development of acquired immune response. Although it is considered that Ag presentation may persist at high levels during chronic infections, we have previously reported that in mice infected with bacillus Calmette-Guérin, Ag presentation gets drastically curtailed during the chronic stage of infection despite antigenic persistence. In this report we evaluated the mechanism of this curtailment. Ag presentation declined precipitously as the T cell response developed, and Ag presentation was not curtailed in mice that were deficient in CD8(+) T cells or MHC class II, suggesting that T cells regulate Ag presentation. Curtailment of Ag presentation was reduced in IFN-gamma-deficient mice, but not in mice with a deficiency/mutation in inducible NOS2, perforin, or Fas ligand. In hosts with no T cells (Rag1(-/-)), Ag presentation was not curtailed during the chronic stage of infection. However, adoptive transfer of wild-type, but not IFN-gamma(-/-), CD4(+) and CD8(+) T cells into Rag1-deficient hosts strongly curtailed Ag presentation. Increased persistence of Ag presentation in IFN-gamma-deficient hosts correlated to increased survival of dendritic cells, but not of macrophages, and was not due to increased stimulatory capacity of IFN-gamma-deficient dendritic cells. These results reveal a novel mechanism indicating how IFN-gamma prevents the persistence of Ag presentation, thereby preventing memory T cells from going into exhaustion.

Variable epitope library-based vaccines: shooting moving targets

While the antigenic variability is the major obstacle for developing vaccines against antigenically variable pathogens (AVPs) and cancer, this issue is not addressed adequately in current vaccine efforts. We developed a novel variable epitope library (VEL)-based vaccine strategy using immunogens carrying a mixture of thousands of variants of a single epitope. In this proof-of-concept study, we used an immunodominant HIV-1-derived CD8+ cytotoxic T-lymphocyte (CTL) epitope as a model antigen to construct immunogens in the form of plasmid DNA and recombinant M13 bacteriophages. We generated combinatorial libraries expressing epitope variants with random amino acid substitutions at 2-5 amino acid positions within the epitope. Mice immunized with these immunogens developed epitope-specific CD8+ IFN-gamma+ T-cell responses that recognized more than 50% of heavily mutated variants of wild-type epitope, as demonstrated in T-cell proliferation assays and FACS analysis. Strikingly, these potent and broad epitope-specific immune responses were long lasting: after 12 months of priming, epitope variants were recognized by CD8+ cells and effector memory T cells were induced. In addition, we showed, for the first time, the inhibition of T-cell responses at the molecular level by immune interference: the mice primed with wild-type epitope and 8 or 12 months later immunized with VELs, were not able to recognize variant epitopes efficiently. These data may give a mechanistic explanation for the failure of recent HIV vaccine trials as well as highlight specific hurdles in current molecular vaccine efforts targeting other important antigenically variable pathogens and diseases. These findings suggest that the VEL-based strategy for immunogen construction can be used as a reliable technological platform for the generation of vaccines against AVPs and cancer, and contribute to better understanding complex host-pathogen interactions.

Antigen sensitivity is a major determinant of CD8+ T-cell polyfunctionality and HIV-suppressive activity

CD8(+) T cells are major players in the immune response against HIV. However, recent failures in the development of T cell-based vaccines against HIV-1 have emphasized the need to reassess our basic knowledge of T cell-mediated efficacy. CD8(+) T cells from HIV-1-infected patients with slow disease progression exhibit potent polyfunctionality and HIV-suppressive activity, yet the factors that unify these properties are incompletely understood. We performed a detailed study of the interplay between T-cell functional attributes using a bank of HIV-specific CD8(+) T-cell clones isolated in vitro; this approach enabled us to overcome inherent difficulties related to the in vivo heterogeneity of T-cell populations and address the underlying determinants that synthesize the qualities required for antiviral efficacy. Conclusions were supported by ex vivo analysis of HIV-specific CD8(+) T cells from infected donors. We report that attributes of CD8(+) T-cell efficacy against HIV are linked at the level of antigen sensitivity. Highly sensitive CD8(+) T cells display polyfunctional profiles and potent HIV-suppressive activity. These data provide new insights into the mechanisms underlying CD8(+) T-cell efficacy against HIV, and indicate that vaccine strategies should focus on the induction of HIV-specific T cells with high levels of antigen sensitivity to elicit potent antiviral efficacy.

MHC class I characterization of Indonesian cynomolgus macaques

Cynomolgus macaques (Macaca fascicularis) are quickly becoming a useful model for infectious disease and transplantation research. Even though cynomolgus macaques from different geographic regions are used for these studies, there has been limited characterization of full-length major histocompatibility complex (MHC) class I immunogenetics of distinct geographic populations. Here, we identified 48 MHC class I cDNA nucleotide sequences in eleven Indonesian cynomolgus macaques, including 41 novel Mafa-A and Mafa-B sequences. We found seven MHC class I sequences in Indonesian macaques that were identical to MHC class I sequences identified in Malaysian or Mauritian macaques. Sharing of nucleotide sequences between these geographically distinct populations is also consistent with the hypothesis that Indonesia was a source of the Mauritian macaque population. In addition, we found that the Indonesian cDNA sequence Mafa-B*7601 is identical throughout its peptide binding domain to Mamu-B*03, an allele that has been associated with control of Simian immunodeficiency virus (SIV) viremia in Indian rhesus macaques. Overall, a better understanding of the MHC class I alleles present in Indonesian cynomolgus macaques improves their value as a model for disease research, and it better defines the biogeography of cynomolgus macaques throughout Southeast Asia.

A promising balanced Th1 and Th2 directing immunological adjuvant, saponins from the root of Platycodon grandiflorum

The haemolytic activities and adjuvant potentials of Platycodon grandiflorum saponin (PGS) and its fractions on the cellular and humoral immune responses of ICR mice against ovalbumin (OVA) were evaluated. PGS was subjected to silica gel column chromatography to afford four fractions, and two fractions PGSC and PGSD selected for testing for activities because of containing dominant saponin peaks. PGS, PGSC, and PGSD showed a slight haemolytic effect, with their HD50 value being 37.91+/-2.24, 21.30+/-1.22, 37.58+/-1.86 microg/ml against 0.5% rabbit red blood cell, respectively. ICR mice were immunized subcutaneously with OVA 100 microg alone or with OVA 100 microg dissolved in saline containing Alum (200 microg), Quil A (10 microg), PGS (50, 100 or 200 microg), PGSC, or PGSD (25, 50 or 100 microg) on days 1 and 15. Two weeks later (day 28), concanavalin A (Con A)-, pokeweed (PWM)-, and OVA-stimulated splenocyte proliferation and OVA-specific antibodies in serum were measured. PGS and PGSC significantly enhanced the Con A-, PWM-, and OVA-induced splenocyte proliferation in OVA-immunized mice at three doses (P<0.01 or P<0.001). However, no significant differences (P>0.05) were observed among the OVA group, OVA/Alum group and OVA/PGSD group. OVA-specific IgG, IgG1, and IgG2b antibody levels in serum were significantly enhanced by PGS, PGSC, and PGSD compared with OVA control group (P<0.05, P<0.01, or P<0.001). Moreover, the adjuvant effects of PGSC (50 or 100 microg) on the OVA-specific IgG, IgG1, and IgG2b antibody responses to OVA in mice were more significant than those of Alum. In conclusion, PGS seem to be a promising balanced Th1 and Th2 directing immunological adjuvants which can enhance the immunogenicity of vaccine.

Efficient peptide-MHC-I binding prediction for alleles with few known binders

MOTIVATION

In silico methods for the prediction of antigenic peptides binding to MHC class I molecules play an increasingly important role in the identification of T-cell epitopes. Statistical and machine learning methods in particular are widely used to score candidate binders based on their similarity with known binders and non-binders. The genes coding for the MHC molecules, however, are highly polymorphic, and statistical methods have difficulties building models for alleles with few known binders. In this context, recent work has demonstrated the utility of leveraging information across alleles to improve the performance of the prediction.

RESULTS

We design a support vector machine algorithm that is able to learn peptide-MHC-I binding models for many alleles simultaneously, by sharing binding information across alleles. The sharing of information is controlled by a user-defined measure of similarity between alleles. We show that this similarity can be defined in terms of supertypes, or more directly by comparing key residues known to play a role in the peptide-MHC binding. We illustrate the potential of this approach on various benchmark experiments where it outperforms other state-of-the-art methods.

AVAILABILITY

The method is implemented on a web server: http://cbio.ensmp.fr/kiss. All data and codes are freely and publicly available from the authors.

A statistical framework for modeling HLA-dependent T cell response data

The identification of T cell epitopes and their HLA (human leukocyte antigen) restrictions is important for applications such as the design of cellular vaccines for HIV. Traditional methods for such identification are costly and time-consuming. Recently, a more expeditious laboratory technique using ELISpot assays has been developed that allows for rapid screening of specific responses. However, this assay does not directly provide information concerning the HLA restriction of a response, a critical piece of information for vaccine design. Thus, we introduce, apply, and validate a statistical model for identifying HLA-restricted epitopes from ELISpot data. By looking at patterns across a broad range of donors, in conjunction with our statistical model, we can determine (probabilistically) which of the HLA alleles are likely to be responsible for the observed reactivities. Additionally, we can provide a good estimate of the number of false positives generated by our analysis (i.e., the false discovery rate). This model allows us to learn about new HLA-restricted epitopes from ELISpot data in an efficient, cost-effective, and high-throughput manner. We applied our approach to data from donors infected with HIV and identified many potential new HLA restrictions. Among 134 such predictions, six were confirmed in the lab and the remainder could not be ruled as invalid. These results shed light on the extent of HLA class I promiscuity, which has significant implications for the understanding of HLA class I antigen presentation and vaccine development.

At the core of the human adaptive immune response is the train-to-kill mechanism in which specialized immune cells are sensitized to recognize small peptides from foreign pathogens (e.g., HIV virus). Following this sensitization, these cells are then activated to kill other cells that display this same peptide (and that are infected by this same pathogen). However, for sensitization and killing to occur, the pathogen peptide must be “paired up” with one of the infected person's other specialized immune molecules—an HLA (human leukocyte antigen) molecule. The way in which pathogen peptides interact with these HLA molecules defines if and how an immune response will be generated, which has implications for vaccine design where one may artificially introduce select peptides to pre-train the immune system. Furthermore, there is a huge repertoire of such HLA molecules, with almost no two people having the same set. We introduce a statistical approach for identifying which HLA molecules interact with which pathogen peptides, given a particular kind of laboratory data. Our approach takes as input, data that tells us only which pathogen peptides generate a response, but not which HLA molecules support the response. Our statistical approach fills in this missing information.

Role of alpha3 domain of class I MHC molecules in the activation of high- and low-avidity CD8+ CTLs

CD8 can serve as a co-receptor or accessory molecule on the surface of CTL. As a co-receptor, CD8 can bind to the alpha3 domain of the same MHC class I molecules as the TCR to facilitate TCR signaling. To evaluate the role of the MHC class I molecule alpha3 domain in the activation of CD8(+) CTL, we have produced a soluble 227 mutant of H-2D(d), with a point mutation in the alpha3 domain (Glu227 --> Lys). 227 mutant class I-peptide complexes were not able to effectively activate H-2D(d)-restricted CD8 T cells in vitro, as measured by IFN-gamma production by an epitope-specific CD8(+) CTL line. However, the 227 mutant class I-peptide complexes in the presence of another MHC class I molecule (H-2K(b)) (that cannot present the peptide) with a normal alpha3 domain can induce the activation of CD8(+) CTL. Therefore, in order to activate CD8(+) CTL, the alpha3 domain of MHC class I does not have to be located on the same molecule with the alpha1 and alpha2 domains of MHC class I. A low-avidity CD8(+) CTL line was significantly less sensitive to stimulation by the 227 mutant class I-peptide complexes in the presence of the H-2K(b) molecule. Thus, low-avidity CTL may not be able to take advantage of the interaction between CD8 and the alpha3 domain of non-presenting class I MHC molecules, perhaps because of a shorter dwell time for the TCR-MHC interaction.

Clonal focusing of epitope-specific CD8+ T lymphocytes in rhesus monkeys following vaccination and simian-human immunodeficiency virus challenge

To afford the greatest possible immune protection, candidate human immunodeficiency virus (HIV) vaccines must generate diverse and long-lasting CD8(+) T lymphocyte responses. In the present study, we evaluate T-cell receptor Vbeta (variable region beta) gene usage and a CDR3 (complementarity-determining region 3) sequence to assess the clonality of epitope-specific CD8(+) T lymphocytes generated in rhesus monkeys following vaccination and simian-human immunodeficiency virus (SHIV) challenge. We found that vaccine-elicited epitope-specific CD8(+) T lymphocytes have a clonal diversity comparable to those cells generated in response to SHIV infection. Moreover, we show that the clonal diversity of vaccine-elicited CD8(+) T-lymphocyte responses is dictated by the epitope sequence and is not affected by the mode of antigen delivery to the immune system. Clonal CD8(+) T-lymphocyte populations persisted following boosting with different vectors, and these clonal cell populations could be detected for as long as 4 years after SHIV challenge. Finally, we show that the breadth of these epitope-specific T lymphocytes transiently focuses in response to intense SHIV replication. These observations demonstrate the importance of the initial immune response to SHIV, induced by vaccination or generated during primary infection, in determining the clonal diversity of cell-mediated immune responses and highlight the focusing of this clonal diversity in the setting of high viral loads. Circumventing this restricted CD8(+) T-lymphocyte clonal diversity may present a significant challenge in the development of an effective HIV vaccine strategy.

Immunodominant Francisella tularensis antigens identified using proteome microarray

Stimulation of protective immune responses against intracellular pathogens is difficult to achieve using non-replicating vaccines. BALB/c mice immunized by intramuscular injection with killed Francisella tularensis (live vaccine strain) adjuvanted with preformed immune stimulating complexes admixed with CpG, were protected when systemically challenged with a highly virulent strain of F. tularensis (Schu S4). Serum from immunized mice was used to probe a whole proteome microarray in order to identify immunodominant antigens. Eleven out of the top 12 immunodominant antigens have been previously described as immunoreactive in F. tularensis. However, 31 previously unreported immunoreactive antigens were revealed using this approach. Twenty four (50%) of the ORFs on the immunodominant hit list belonged to the category of surface or membrane associated proteins compared to only 22% of the entire proteome. There were eight hypothetical protein hits and eight hits from proteins associated with different aspects of metabolism. The chip also allowed us to readily determine the IgG subclass bias, towards individual or multiple antigens, in protected and unprotected animals. These data give insight into the protective immune response and have potentially important implications for the rational design of non-living vaccines for tularemia and other intracellular pathogens.

HIV-1 Subtype C gag-specific T-cell responses in relation to human leukocyte antigens in a diverse population of HIV-infected Ethiopians

Knowledge of the most dominant T-cell epitopes in the context of the local human leukocyte antigen (HLA) background is a prerequisite for the development of an effective HIV vaccine. In 100 Ethiopian subjects, 16 different HLA-A, 23 HLA-B, and 12 HLA-C specificities were observed. Ninety-four percent of the population carried at least 1 of the 5 most common HLA-A and/or HLA-B specificities. HIV-specific T-cell responses were measured in 48 HIV-infected Ethiopian subjects representing a wide range of ethnicities in Ethiopia using the interferon (IFN)-gamma enzyme-linked immunospot (Elispot) assay and 49 clade C-specific synthetic Gag peptides. Fifty-eight percent of the HIV-positive study subjects showed T-cell responses directed to 1 or more HIV Gag peptides. Most Gag-specific responses were directed against the subset of peptides spanning Gag p24. The breadth of response ranged from 1 to 9 peptides, with most (78%) individuals showing detectable responses to <3 Gag peptides. The magnitude of HIV-specific T-cell responses was not associated with HIV viral load but correlated positively with CD4 T-cell counts. The most frequently targeted Gag peptides overlapped with those previously described for HIV-1 subtype C-infected southern Africans, and therefore can be used in a multiethnic vaccine.

Progress towards an AIDS mucosal vaccine: An overview

The mucosal immune system acts as a first line of defense against infection caused by luminal pathogens. Because HIV is transmitted primarily via mucosal-associated tissues, particularly with sexual transmission, understanding antiviral immunity present at these sites is important. HIV infection results in depletion of gut-associated lymphoid tissue (GALT) and in this sense can be considered to be a disease of the mucosal immune system. A stumbling block for efforts to develop a vaccine against this disease has been the escape of vaccine-induced neutralizing antibodies and cytotoxic T lymphocytes (CTLs) at mucosal compartments and the resulting viral spread. To avoid these problems, the ideal mucosal vaccine would induce HIV-specific secretory IgA (S-IgA) and mucosal CD8(+) CTL as a first line of defense at a very early stage of HIV infection, before the virus can seed into the secondary lymphoid organs in mucosal and systemic tissues. In this review, we provide an overview of mucosal vaccine concepts and vaccination strategies that have been proposed for the development of an HIV mucosal vaccine, including live recombinant vaccines, peptide-based vaccines, virus-like particles (VLP), subunit vaccines and DNA vaccines.

Enhanced cellular immune responses elicited by an engineered HIV-1 subtype B consensus-based envelope DNA vaccine

An important goal for human immunodeficiency virus (HIV) vaccines is to develop immunogens that induce broader and more potent cellular immune responses. In this study of DNA vaccine potency, we constructed a novel subtype B env gene (EY2E1-B) with the goal of increasing vaccine antigen immune potency. The vaccine cassette was designed based on subtype B-specific consensus sequence with several modifications, including codon optimization, RNA optimization, the addition of a Kozak sequence, and a substituted immunoglobulin E leader sequence. The V1 and V2 loops were shortened and the cytoplasmic tail was truncated to prevent envelope recycling. Three different strains of mice (BALB/c, C57BL/6, and HLA-A2 transgenic mice) were immunized three times with pEY2E1-B or the primary DNA immunogen pEK2P-B alone. The analysis of specific antibody responses suggested that EY2E1-B could induce a moderate subtype B-specific antibody response. Moreover, this construct was up to four times more potent at driving cellular immune responses. Epitope mapping results indicated that there is an increase in the breadth and magnitude of cross-reactive cellular responses induced by the EY2E1-B immunogen. These properties suggest that such a synthetic immunogen deserves further examination for its potential to serve as a component antigen in an HIV vaccine cocktail.

Evaluation of aldrithiol-2-inactivated preparations of HIV type 1 subtypes A, B, and D as reagents to monitor T cell responses

The development of HIV vaccines is an urgent priority and there is need to generate reagents representing multiple subtypes that can be used to screen HIV-1-specific responses. We used Aldrithiol-2 (AT-2), a mild oxidizing reagent, to eliminate the infectivity of HIV while maintaining its structure and ability to be processed for presentation to T cells. Inactivated subtype A, B, and D viruses were evaluated for their ability to stimulate T cell responses in PBMC samples from 18 U.S. subjects infected with HIV-1 subtype B and 32 Ugandan subjects infected with subtypes A and D or recombinants AC and AD. Five HIV-1-negative samples were also analyzed. T cell responses to AT-2-inactivated viral isolates were monitored by interferon-gamma (IFN-gamma) intracellular cytokine secretion (ICS) analysis; matched microvesicle preparations served as negative controls. Among the 18 subtype B infected subjects, 39% had CD3(+) CD4 (+) IFN-gamma responses and 67% had CD3(+) CD8(+) IFN-gamma responses. Of the 32 Ugandan subjects, 34% demonstrated CD3(+) CD4(+) IFN-gamma responses and 78% demonstrated CD3(+) CD8(+) IFN-gamma responses. Both subtype-specific and cross-reactive responses were observed. Responses to the AT-2 viruses tended to be lower in magnitude than those detected by a set of overlapping gag peptides. Robust lymphoproliferative responses to AT-2 viruses were seen in a subset of subjects. In conclusion, AT-2-inactivated HIV-1 virions stimulated both CD4 and CD8 HIV-1-specific responses and may provide an additional reagent for screening HIV-1-specific responses in HIV seropositives and vaccinees.

Virus-like particles: designing an effective AIDS vaccine

Viruses that infect eukaryotic organisms have the unique characteristic of self-assembling into particles. The mammalian immune system is highly attuned to recognizing and attacking these viral particles following infection. The use of particle-based immunogens, often delivered as live-attenuated viruses, has been an effective vaccination strategy for a variety of viruses. The development of an effective vaccine against the human immunodeficiency virus (HIV) has proven to be a challenge, since HIV infects cells of the immune system causing severe immunodeficiency resulting in the syndrome known as AIDS. In addition, the ability of the virus to adapt to immune pressure and reside in an integrated form in host cells presents hurdles for vaccinologists to overcome. A particle-based vaccine strategy has promise for eliciting high titer, long-lived, immune responses to a diverse number of viral epitopes against different HIV antigens. Live-attenuated viruses are effective at generating both cellular and humoral immune responses. However, while these vaccines stimulate immunity, challenged animals rarely clear the viral infection and the degree of attenuation directly correlates with protection from disease. Further, a live-attenuated vaccine has the potential to revert to a pathogenic form. Alternatively, virus-like particles (VLPs) mimic the viral particle without causing an immunodeficiency disease. VLPs are self-assembling, non-replicating, non-pathogenic particles that are similar in size and conformation to intact virions. A variety of VLPs for lentiviruses are currently in preclinical and clinical trials. This review focuses on our current status of VLP-based AIDS vaccines, regarding issues of purification and immune design for animal and clinical trials.

Identification of a novel HIV type 1 CRF01_AE cytotoxic T lymphocyte (CTL) epitope restricted by an HLA-Cw0602 allele and a novel HLA-A0206/peptide restriction

This report describes specific T cell responses to HIV-1 CRF01_AE Env and A Gag peptides in 20 HIV-1 CRF01_AE-infected Thai individuals using an interferon-gamma (IFN-gamma) enzyme-linked immunospot (ELISpot) assay. Twenty-six potentially novel HLA class I-restricted CD8+ T cell epitopes were identified in 14/20 subjects. Fine mapping analysis using the chromium release cytotoxic T lymphocyte (CTL) assay revealed a novel HLA-Cw0602 restricted epitope of HIV-1 CRF01_AE Env (NAKTIIVHL) and a previously identified HIV-1 A Gag epitope (ATLEEMMTA) with a novel HLA-A0206 restriction.

Induction of long-lasting multi-specific CD8+T cells by a four-component DNA-MVA/HIVA-RENTA candidate HIV-1 vaccine in rhesus macaques

As a part of a long-term effort to develop vaccine against HIV-1 clade A inducing protective T cell responses in humans, we run mutually complementing studies in humans and non-human primates (NHP) with the aim to maximize vaccine immunogenicity. The candidate vaccine under development has four components, pTHr.HIVA and pTH.RENTA DNA, and modified vaccinia virus Ankara (MVA).HIVA and MVA.RENTA, delivered in a heterologous DNA prime-MVA boost regimen. While the HIVA (Gag/epitopes) components have been tested in NHP and over 300 human subjects, we plan to test in humans the RENTA (reverse transcriptase, gp41, Nef, Tat) vaccines designed to broaden HIVA-induced responses in year 2007. Here, we investigated the four-component vaccine long-term immunogenicity in Mamu-A*01-positive rhesus macaques and demonstrated that the vaccine-induced T cells were multi-specific, multi-functional, readily proliferated to recall peptides and were circulating in the peripheral blood of vaccine recipients over 1 year after vaccine administration. The consensus clade A-elicited T cells recognized 50% of tested epitope variants from other HIV-1 clades. Thus, the DNA-MVA/HIVA-RENTA vaccine induced memory T cells of desirable characteristics and similarities to those induced in humans by HIVA vaccines alone; however, single-clade vaccines may not elicit sufficiently cross-reactive responses.

Decreased specific CD8+ T cell cross-reactivity of antigen recognition following vaccination with Melan-A peptide

The aim of T cell vaccines is the expansion of antigen-specific T cells able to confer immune protection against pathogens or tumors. Although increase in absolute cell numbers, effector functions and TCR repertoire of vaccine-induced T cells are often evaluated, their reactivity for the cognate antigen versus their cross-reactive potential is rarely considered. In fact, little information is available regarding the influence of vaccines on T cell fine specificity of antigen recognition despite the impact that this feature may have in protective immunity. To shed light on the cross-reactive potential of vaccine-induced cells, we analyzed the reactivity of CD8(+) T cells following vaccination of HLA-A2(+) melanoma patients with Melan-A peptide, incomplete Freund's adjuvant and CpG-oligodeoxynucleotide adjuvant, which was shown to induce strong expansion of Melan-A-reactive CD8(+) T cells in vivo. A collection of predicted Melan-A cross-reactive peptides, identified from a combinatorial peptide library, was used to probe functional antigen recognition of PBMC ex vivo and Melan-A-reactive CD8(+) T cell clones. While Melan-A-reactive CD8(+) T cells prior to vaccination are usually constituted of widely cross-reactive naive cells, we show that peptide vaccination resulted in expansion of memory T cells displaying a reactivity predominantly restricted to the antigen of interest. Importantly, these cells are tumor-reactive.

A single administration of lentiviral vectors expressing either full-length human immunodeficiency virus 1 (HIV-1)HXB2 Rev/Env or codon-optimized HIV-1JR-FL gp120 generates durable immune responses in mice

Genetic immunization using viral vectors provides an effective means to elicit antigen-specific cellular immune responses. Several viral vectors have proven efficacious in inducing immune responses after direct injection in vivo. Among them, recombinant, self-inactivating lentiviral vectors are very attractive delivery systems, as they are able to efficiently transduce into and express foreign genes in a wide variety of mammalian cells. A self-inactivating lentiviral vector was evaluated for the delivery of human immunodeficiency virus 1 (HIV-1) envelope sequences in mice in order to elicit specific immune responses. With this aim, BALB/c mice were immunized with a single injection of self-inactivating lentiviral vectors carrying either the full-length HIV-1HXB2 Rev/Env (TY2-IIIBEnv) or the codon-optimized HIV-1JR-FL gp120 (TY2-JREnv) coding sequence. Both vectors were able to elicit specific cellular responses efficiently, as measured by gamma interferon ELISPOT and chromium-release assays, upon in vitro stimulation of splenocytes from BALB/c immunized mice. However, only the TY2-JREnv-immunized mice were able to elicit specific humoral responses, measured as anti-gp120 antibody production. These data provide the first evidence that a single, direct, in vivo administration of a lentiviral vector encoding a viral gene might represent a useful strategy for vaccine development.

Cellular immunotherapy for cytomegalovirus and HIV-1 infection

Current antiviral drugs do not fully reconstitute the specific antiviral immune control in chronically human immunodeficiency virus (HIV)-1-infected patients or in cytomegalovirus (CMV)-infected patients after hematopoietic stem cell transplantation. Therefore, immunotherapy in which the patient's immune system is manipulated to enhance antiviral immune responses has become a promising area of viral immunology research. In this review, an overview is provided on the cellular immunotherapy strategies that have been developed for HIV infection and CMV reactivation in immunocompromised patients. As an introduction, the mechanisms behind the cellular immune system and their importance for the development of a workable immunotherapy approach are discussed. Next, the focus is shifted to the immunopathogenesis of CMV and HIV-1 infections to correlate these findings with the concepts and ideas behind the viral-specific immunotherapies discussed. Current and future perspectives of active and passive cellular immunotherapy for the treatment of CMV and HIV-1 infections are reviewed. Finally, pitfalls and key issues with regard to the development of immunotherapy protocols that can be applied in a clinical setting are addressed.

Impact of vaccine-induced mucosal high-avidity CD8+ CTLs in delay of AIDS viral dissemination from mucosa

Natural HIV transmission occurs through mucosa, but it is debated whether mucosal cytotoxic T lymphocytes (CTLs) can prevent or reduce dissemination from the initial mucosal site to the systemic circulation. Also, the role of CTL avidity in mucosal AIDS viral transmission is unknown. To address these questions, we used delay in acute-phase peak viremia after intrarectal challenge as an indicator of systemic dissemination. We found that a peptide-prime/poxviral boost vaccine inducing high levels of high-avidity mucosal CTLs can have an impact on dissemination of intrarectally administered pathogenic SHIV-ku2 in macaques and that such protection correlates better with mucosal than with systemic CTLs and particularly with levels of high-avidity mucosal CTLs.

Genetic fusion of proteins to the SIV Tat protein enhances their immunogenicity

The potential of genetically fusing recombinant proteins to the simian immunodeficiency virus (SIV) Tat protein has been investigated. The recombinant SIV Tat protein was initially expressed in very low amounts in E. coli, but optimization of the coding sequence for translation in the bacterial host significantly improved protein expression. Whilst fusion of SIV Tat to an experimental antigen (GST) facilitated the binding of the antigen to cell surfaces it did not appear to facilitate the transport of the protein into the cytosol. The immunogenicity of GST was significantly enhanced, in the absence of adjuvants, when fused to SIV Tat, with the induction of IgG1 and IgG2a antibodies indicative of a Th1 response being induced. However, no evidence was obtained that such an immunization scheme efficiently induced a CTL response.

Induction of human immunodeficiency virus type 1-specific T cells by a bluetongue virus tubule-vectored vaccine prime-recombinant modified virus Ankara boost regimen

In the absence of strategies for reliable induction of antibodies broadly neutralizing human immunodeficiency virus type 1 (HIV-1), vaccine efforts have shifted toward the induction of cell-mediated immunity. Here we describe the construction and immunogenicity of novel T-cell vaccine NS1.HIVA, which delivers the HIV-1 clade A consensus-derived immunogen HIVA on the surface of tubular structures spontaneously formed by protein NS1 of bluetongue virus. We demonstrated that NS1 tubules can accommodate a protein as large as 527 amino acids without losing their self-assembly capability. When injected into BALB/c mice by several routes, chimeric NS1.HIVA tubules induced HIV-1-specific major histocompatibility complex class I-restricted T cells. These could be boosted by modified virus Ankara expressing the same immunogen and generate a memory capable of gamma interferon (IFN-gamma) production, proliferation, and lysis of sensitized target cells. Induced memory T cells readily produced IFN-gamma 230 days postimmunization, and upon a surrogate virus challenge, NS1.HIVA vaccine alone decreased the vaccinia virus vv.HIVA load in ovaries by 2 orders of magnitude 280 days after immunization. Thus, because of its T-cell immunogenicity and antigenic simplicity, the NS1 delivery system could serve as a priming agent for heterologous prime-boost vaccination regimens. Its usefulness in primates, including humans, remains to be determined.

Development of a synthetic consensus sequence scrambled antigen HIV-1 vaccine designed for global use

Induction of high levels of broadly reactive cytotoxic T lymphocytes (CTL) remains a promising approach for an effective HIV-1 vaccine. We have developed a novel genetic-based vaccine strategy that encodes consensus overlapping peptide sets from all HIV-1 proteins scrambled together. This synthetic scrambled antigen vaccine (SAVINE) strategy has significant advantages, e.g. capacity to encode more antigens safely and is very flexible compared to traditional isolate-based strategies. The SAVINE vaccine strategy is clearly immunogenic, being able to restimulate a range of human HIV-1 specific responses in vitro and induce HIV-1 specific immunity in vivo in mice. Interestingly, different in vivo delivery strategies affected the resulting immunity and immunodominance pattern in mice. This platform strategy could be used for other infections and cancers where T cell responses are important for protection.

Two sides of a cellular coin: CD4(+)CD3- cells regulate memory responses and lymph-node organization

We propose that CD4(+)CD3(-) cells have two functions: a well-established role in organizing lymphoid tissue during development, and a newly discovered role in supporting T-cell help for B cells both during affinity maturation in germinal centres and for memory antibody responses. As CD4(+)CD3(-) cells express the HIV co-receptors CD4 and CXC-chemokine receptor 4, we think that infection of these cells by HIV, and their subsequent destruction by the host immune system, could help to explain the loss of memory antibody responses and the destruction of lymphoid architecture that occur during disease progression to AIDS.

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