Presentation of SIVgag to monkey T cells using dendritic cells transfected with a recombinant adenovirus

Prolonged expression of MHC class I - peptide expression in bone marrow derived retrovirus transfected matured dendritic cells by continuous centrifugation in the presence of IL-4

Background & objectives:

Dendritic cells (DCs) are potent antigen presenting cells which proceed from immature to a mature stage during their differentiation. There are several methods of obtaining long lasting mature antigen expressing DCs and different methods show different levels of antigen expressions. We investigated bone marrow derived DCs for the degree of maturation and genetically engineered antigen presentation in the presence of interleukin-4 (IL-4) as a maturity enhancer.

Methods:

DCs and transfected retrovirus were cultured together in the presence of granulocyte-macrophage colony stimulating factor (GMCSF)-IL4, GMCSF +IL4, lipopolysaccharide (LPS). B 7.1, B7.2 and CD11c were measured by the degree of immune fluorescence using enhanced green fluorescent protein (EGFP) shuttled retrovirus transfected antigen. Degree of MHC class I molecule with antigen presentation of antigen was also evaluated by fluorescence activated cell sorting. The antigen presenting capacity of transfected DCs was investigated. Bone marrow DCs were generated in the presence of GMCSF and IL-4 in vitro. Dividing bone marrow cells were infected with EGFP shuttled retrovirus expressing SSP2 by prolonged centrifugation for three consecutive days from day 5, 6 and 7 and continued to culture in the presence of GMSCF and IL-4 until day 8.

Results:

IL-4 as a cytokine increased the maturation of retrovirus transfected DCs by high expression of B 7-1 and B 7-2. Also, IL-4 induced DC enhanced by the prolonged centrifugation and it was shown by increased antigen presentation of these dendric cells as antigen presenting cell (APC). Cytolytic effects were significantly higher in cytotoxic T cell response (CTLs) mixed with transfected DCs than CTLs mixed with pulsed DCs.

Interpretation & conclusions:

There was an enhanced antigen presentation by prolonged expression of antigen loaded MHC class I receptors in DCs in the presence of IL-4 by prolonged centrifugation.

Dendritic cells (DCs) transfected with a recombinant adenovirus carrying chlamydial major outer membrane protein antigen elicit protective immune responses against genital tract challenge infection

Chlamydia trachomatis, an obligate intracellular bacterial pathogen, is the major cause of sexually transmitted diseases worldwide. Although a variety of strategies have been taken to promote the development of a protective vaccine, no ideal vaccine has been generated so far. In this study, we transfected dendritic cells (DCs) with recombinant adenovirus carrying C. trachomatis serovar E major outer membrane protein gene (Ad-MOMP), and investigated their ability to induce specific protection against genital tract chlamydial challenge infection. The results showed that when DCs were transfected with Ad-MOMP in vitro, the DCs exhibited increased expression of CD80 and MHC-II molecules as well as enhanced IL-12 secretion and were able to stimulate T-cell proliferation. The level of IFN-gamma secreted by stimulated T cells was also up-regulated significantly. When the Ad-MOMP transfected DCs were adoptively transferred intravenously to naive mice, they generated Th1-biased cytokine production and mucosal IgA responses specific for C. trachomatis. More importantly, the mice immunized with Ad-MOMP-DC mounted protection against genital tract challenge infection, shown by lower body mass loss, lower chlamydial loads, and less severe pathological changes. In conclusion, Ad-MOMP transfected DCs are capable of inducing effective protective immune responses against C. trachomatis genital infection.

Induction of protective immunity to anthrax lethal toxin with a nonhuman primate adenovirus-based vaccine in the presence of preexisting anti-human adenovirus immunity

Prevention or therapy for bioterrorism-associated anthrax infections requires rapidly acting effective vaccines. We recently demonstrated (Y. Tan, N. R. Hackett, J. L. Boyer, and R. G. Crystal, Hum. Gene Ther. 14:1673-1682, 2003) that a single administration of a recombinant serotype 5 adenovirus (Ad) vector expressing anthrax protective antigen (PA) provides rapid protection against anthrax lethal toxin challenge. However, approximately 35 to 50% of humans have preexisting neutralizing antibodies against Ad5. This study assesses the hypothesis that a recombinant adenovirus vaccine based on the nonhuman primate-derived serotype AdC7, against which humans do not have immunity, expressing PA (AdC7PA) will protect against anthrax lethal toxin even in the presence of preexisting anti-Ad5 immunity. Naive and Ad5-immunized BALB/c mice received (intramuscularly) 10(8) to 10(11) particle units (PU) of AdC7PA, Ad5PA (a human serotype Ad5-based vector expressing a secreted form of PA), or AdNull (an Ad5 vector with no transgene). Robust anti-PA immunoglobulin G and neutralizing antibodies were detected by 2 to 4 weeks following administration of AdC7PA to naive or Ad5 preimmunized mice, whereas low anti-PA titers were detected in Ad5-preimmunized mice following administration of Ad5PA. To assess protection in vivo, naive or mice previously immunized against Ad5 were immunized with AdC7PA or Ad5PA and then challenged with a lethal intravenous dose of Bacillus anthracis lethal toxin. Whereas Ad5PA protected naive mice against challenge with B. anthracis lethal toxin, Ad5PA was ineffective in mice that were previously immunized against Ad5. In contrast, AdC7PA functioned effectively not only to protect naive mice but also to protect Ad5-preimmunized mice, with 100% survival after lethal toxin challenge. These data suggest the nonhuman-based vector AdC7PA is an effective vaccine for the development of protective immunity against B. anthracis and importantly functions as a "sero-switch" base for an adenovirus vaccine to function in the context of preexisting anti-Ad immunity.

Replicating rather than nonreplicating adenovirus-human immunodeficiency virus recombinant vaccines are better at eliciting potent cellular immunity and priming high-titer antibodies

A major challenge in combating the human immunodeficiency virus (HIV) epidemic is the development of vaccines capable of inducing potent, persistent cellular immunity and broadly reactive neutralizing antibody responses to HIV type 1 (HIV-1). We report here the results of a preclinical trial using the chimpanzee model to investigate a combination vaccine strategy involving sequential priming immunizations with different serotypes of adenovirus (Ad)/HIV-1(MN)env/rev recombinants and boosting with an HIV envelope subunit protein, oligomeric HIV(SF162) gp140deltaV2. The immunogenicities of replicating and nonreplicating Ad/HIV-1(MN)env/rev recombinants were compared. Replicating Ad/HIV recombinants were better at eliciting HIV-specific cellular immune responses and better at priming humoral immunity against HIV than nonreplicating Ad-HIV recombinants carrying the same gene insert. Enhanced cellular immunity was manifested by a greater frequency of HIV envelope-specific gamma interferon-secreting peripheral blood lymphocytes and better priming of T-cell proliferative responses. Enhanced humoral immunity was seen in higher anti-envelope binding and neutralizing antibody titers and better induction of antibody-dependent cellular cytotoxicity. More animals primed with replicating Ad recombinants mounted neutralizing antibodies against heterologous R5 viruses after one or two booster immunizations with the mismatched oligomeric HIV-1(SF162) gp140deltaV2 protein. These results support continued development of the replicating Ad-HIV recombinant vaccine approach and suggest that the use of replicating vectors for other vaccines may prove fruitful.

The functional consequences of delivery of HIV-1 Nef to dendritic cells using an adenoviral vector

The Nef gene is a major determinant of HIV-1 pathogenicity. Several immunomodulatory functions have been reported for Nef, including down-regulation of CD4 and class I MHC in T-lymphocytes, and the ability to enhance viral transmission from macrophages and dendritic cells (DC) to T-lymphocytes. In this study, HIV-1 (SF2 strain) Nef was expressed in human monocyte-derived dendritic cells, using an adenovirus based delivery system. Nef expression resulted in decreased CD4 levels, but no change to class I MHC, and no impairment in the ability of DC to stimulate recall PPD responses, mixed leukocyte responses, or hepatitis B-specific CD8 responses. The adenovirus vector itself stimulated a strong recall CD4 response in all individuals tested, and also induced up-regulation of class I MHC, CD86 and CD40 on the dendritic cell surface. The study provides no evidence that HIV Nef impairs the function of human dendritic cells, and suggests that delivery of Nef to dendritic cells may be one strategy with which to stimulate an HIV-1 immune response.

Early protection against pathogenic virus infection at a mucosal challenge site after vaccination with attenuated simian immunodeficiency virus

Atraumatic application of attenuated SIVmac239 Delta nef vaccine to the tonsils of rhesus macaques provided protection against challenge 26 weeks later with infectious SIVmac251 applied through this route. Early events at the mucosal portal of entry of challenge virus were followed. Wild-type virus was detected in nonvaccinated controls by day 4, and then simian immunodeficiency virus (SIV) replicated vigorously at days 7 and 14. In contrast, a challenge of 10 of 10 vaccinees with SIV did not significantly raise RNA levels in the plasma or increase infected cells in lymphoid tissues, as assessed by single-cell labeling for viral RNA and nef protein. Vaccine virus was found in the tonsils of all vaccinees, but challenge virus was only detected at this portal of entry in 4 of 10 monkeys. In the tonsil, the challenge virus did not induce an expansion of perforin(+) killer cells. However, there was a significant increase in gamma delta T cells and mature dendritic cells relative to unvaccinated controls. Therefore, during tonsillar SIV Delta nef vaccination, infection is blocked early at the entry portal, which we propose is due in part to innate functions of gamma delta T and dendritic cells.

Adenovirus-Transduced Dendritic Cells Injected into Skin or Lymph Node Prime Potent Simian Immunodeficiency Virus-Specific T Cell Immunity in Monkeys

Adenoviral vectors can be used to deliver complex Ag to dendritic cells (DC), and thus may be ideal for stimulating broad T cell responses to viral pathogens and tumors. To test this hypothesis in a relevant primate model, we used recombinant adenovirus serotype 5 vectors expressing SIV Gag Ag to transduce monocyte-derived DC from rhesus macaques, and then immunized donor animals either by intradermal or intranodal injections. T cell responses were evaluated by ELISPOT assay using previously frozen PBMC pulsed with pools of 15-mer peptides representing the Gag sequence. Immunization resulted in rapid and potent induction of T cell responses to multiple regions of Gag, with frequencies approaching 1 Gag-specific T cell per 500 uncultured PBMC. Surprisingly, intradermal and intranodal injections generated a similar intensity and breadth of response, indicating that administration of Ag-expressing DC by either route may be equally effective at inducing immune responses. Detailed analysis of two monkeys revealed CD8(+) T cell responses to several peptide epitopes of Gag not previously described, at least two of which are restricted by MHC class I alleles not currently identified. Repeated vaccination did not induce T cell responses to the adenoviral vector and did not prevent Ag-expressing DC injected under the capsule of the lymph node from migrating to the paracortex and interposing between T cells. However, boost injections of adenovirus-transduced DC were generally limited in efficacy. These findings support the use of adenovirus-transduced DC in the therapy of HIV infection and cancer.

Prime-boost vaccination with HIV-1 Gag protein and cytosine phosphate guanosine oligodeoxynucleotide, followed by adenovirus, induces sustained and robust humoral and cellular immune responses

A prophylactic vaccine for HIV-1 will probably require the induction and maintenance of both humoral and cellular immunity. One current strategy to achieve such long term immune responses is a prime-boost vaccination approach using a DNA priming inoculation, followed by recombinant viral boost. In this report we use a novel prime-boost approach in which the priming injections consist of recombinant HIV-1 Gag protein mixed with cytosine phosphate guanosine oligodeoxynucleotide (CpG ODN), followed by recombinant adenoviral boost expressing HIV-1 Gag. Analysis of the immune responses indicates that HIV-1 Gag protein plus CpG ODN immunization alone induces potent humoral as well as Th1 and CD8+ T cell responses. Boosting with recombinant adenovirus strikingly enhances CD8+, but not Th1, T cell responses, resulting in CD8+ T cell responses far greater in magnitude than Th1 responses. Furthermore, the Th1 and CD8+ T cell responses following prime-boost immunization were seen in both lymphoid and peripheral mucosal organs and were sustained over several months. Together, these data suggest a new immunization approach for elicitation of long term humoral and cellular immune responses.

Improved protection of rhesus macaques against intrarectal simian immunodeficiency virus SIV(mac251) challenge by a replication-competent Ad5hr-SIVenv/rev and Ad5hr-SIVgag recombinant priming/gp120 boosting regimen

In this study we investigated the ability of a replication-competent Ad5hr-SIVenv/rev and Ad5hr-SIVgag recombinant priming/gp120 boosting regimen to induce protective immunity in rhesus macaques against pathogenic simian immunodeficiency virus(mac251). Immunization of macaques by two sequential administrations of the same recombinants by the same route resulted in boosting and persistence of SIV-specific cellular immune responses for 42 weeks past the initial immunization. Anti-SIV gp120 immunoglobulin G (IgG) and IgA antibodies were induced in secretory fluids, and all macaques exhibited serum neutralizing antibody activity. After intrarectal SIV(mac251) challenge, all of the macaques became infected. However, relative protection, as assessed by statistically significant lower SIV viral loads in plasma at both acute infection and set point, was observed in 8 out of 12 immunized non-Mamu-A(*)01 animals. Elevated mean cellular immune responses to Gag and Env, neutralizing antibody activity, and IgG and IgA binding antibody levels were observed in the eight protected macaques. Statistically significant correlations with protective outcome were observed for cellular immune responses to SIV Env and Gag and for SIV gp120-specific IgG antibodies in nasal and vaginal fluids. Two macaques that exhibited the greatest and most persistent viremia control also exhibited strong CD8(+) T-cell antiviral activity. The results suggest that a spectrum of immune responses may be necessary for adequate control of viral replication and disease progression and highlight a potential role for nonneutralizing antibodies at mucosal sites.

Lentivirally transduced dendritic cells as a tool for cancer immunotherapy

BACKGROUND

Dendritic cells (DC) are the professional antigen-presenting cells of the immune system, fully equipped to prime naive T cells and thus essential components for cancer immunotherapy.

METHODS

We tested the influence of several elements (cPPT, trip, WPRE, SIN) on the transduction efficiency of human DC. Human and murine DC were transduced with tNGFR-encoding lentiviruses to assess the effect of transduction on phenotype and function. Human DC were transduced with lentiviruses encoding huIi80MAGE-A3 and murine DC with huIi80tOVA to test antigen presentation.

RESULTS

A self-inactivating (SIN) lentiviral vector containing the trip element was most efficient in transducing human DC. The transduction of DC with trip/SIN tNGFR encoding lentiviral vectors at MOI 15 resulted in stable gene expression in up to 94.6% (murine) and 88.2% (human) of the mature DC, without perturbing viability, phenotype and function. Human huIi80MAGE-A3-transduced DC were able to stimulate MAGE-A3-specific CD4(+) and CD8(+) T cell clones and could prime both MAGE-A3-specific CD4(+) and CD8(+) T cells in vitro. Murine huIi80tOVA-transduced DC were able to present OVA peptides in the context of MHC class I and class II in vitro and induced a strong OVA-specific cytotoxic T lymphocyte response in vivo, that was protective against subsequent challenge with OVA-expressing tumor cells.

CONCLUSIONS

We show that, using lentiviral vectors, efficient gene transfer in human and murine DC can be obtained and that these DC can elicit antigen-specific immune responses in vitro and in vivo. The composition of the transfer vector has a major impact on the transduction efficiency.

The interaction of immunodeficiency viruses with dendritic cells

Dendritic cells (DCs) can influence HIV-1 and SIV pathogenesis and protective mechanisms at several levels. First, HIV-1 productively infects select populations of DCs in culture, particularly immature DCs derived from blood monocytes and skin (Langerhans cells). However, there exist only a few instances in which HIV-1- or SIV-infected DCs have been identified in vivo in tissue sections. Second, different types of DCs reliably sequester and transmit infectious HIV-1 and SIV in culture, setting up a productive infection in T cells interacting with the DCs. This stimulation of infection in T cells may explain the observation that CD4+ T lymphocytes are the principal cell type observed to be infected with HIV-1 in lymphoid tissues in vivo. DCs express a C-type lectin, DC-SIGN/CD209, that functions to bind HIV-1 (and other infectious agents) and transmit virus to T cells. When transfected into the THP-1 cell line, the cytosolic domain of DC-SIGN is needed for HIV-1 sequestration and transmission. However, DCs lacking DC-SIGN (Langerhans cells) or expressing very low levels of DC-SIGN (rhesus macaque monocyte-derived DCs) may use additional molecules to bind and transmit immunodeficiency viruses to T cells. Third, DCs are efficient antigen-presenting cells for HIV-1 and SIV antigens. Infection with several recombinant viral vectors as well as attenuated virus is followed by antigen presentation to CD4+ and CD8+ T cells. An intriguing pathway that is well developed in DCs is the exogenous pathway for nonreplicating viral antigens to be presented on class I MHC products. This should allow DCs to stimulate CD8+ T cells after uptake of antibody-coated HIV-1 and dying infected T cells. It has been proposed that DCs, in addition to expanding effector helper and killer T cells, induce tolerance through T cell deletion and suppressor T cell formation, but this must be evaluated directly. Fourth, DCs are likely to be valuable in improving vaccine design. Increasing DC uptake of a vaccine, as well as increasing their numbers and maturation, should enhance efficacy. However, DCs can also capture antigens from other cells that are initially transduced with a DNA vaccine or a recombinant viral vector. The interaction of HIV-1 and SIV with DCs is therefore intricate but pertinent to understanding how these viruses disrupt immune function and elicit immune responses.

Converting nonhuman primate dendritic cells into potent antigen-specific cellular immunosuppressants by genetic modification

T cell depletion plus donor bone marrow cell (BMC) infusion induces long-term kidney allograft survival in a limited number of rhesus macaque recipients. Therefore, there is a need to enhance the tolerogenic activity of donor BMCs. The tolerogenic effect of donor BMCs is ascribed to a veto activity, mediated by a CD8+ subset that upregulates immunoregulatory effector molecules, transforming growth factor-beta1 (TGF-beta), and FasL, after interaction with donor-reactive cytotoxic T lymphocyte precursors (CTLp), leading to clonal inactivation/deletion of donor-reactive CTLp. Of note, the receptors for TGF-beta1- and FasL-induced signal transduction are upregulated in activated T cells. Since mature dendritic cells (DCs) are exceptionally efficient activators of T cells, we postulated that mature DCs modified to overexpress TGF-beta1 and FasL might exert potent veto (i.e., inactivating/deleting) activity independent of CD8 expression. A fusion protein comprising antihuman CD40 single-chain antibody and soluble coxsackie-adenovirus receptor enabled high-efficiency transduction of rhesus monocyte-derived DCs (Rh MDDCs) by recombinant adenovirus (Ad). Mature Rh MDDCs transduced with Ad encoding active TGF-beta1 retained a mature phenotype yet exhibited potent alloantigen-specific cellular immunosuppression. Such modified MDDCs have the potential to promote tolerance induction to allografts in vivo.

Efficient transduction of human monocyte-derived dendritic cells by chimpanzee-derived adenoviral vector

Using recombinant adenoviruses (Ads) to target host dendritic cells (DCs) presents an attractive prospect for immunization. The efficacy of commonly used human Ad-derived gene transfer vectors for antigen delivery in humans is often compromised by preexisting anti-Ad immunity, acquired by the majority of human population as a result of frequent naturally occurring virus infections. As an alternative vector we propose chimpanzee-derived recombinant adenoviruses, which are poorly neutralized by human sera. In the present study we examine the ability of one such vector, AdC68, to transduce and activate human monocyte-derived DCs in culture. We found that AdC68 could efficiently transduce both immature and mature DCs at levels similar to those by the human serotype 5 Ad recombinant. Exposure of immature DCs to AdC68 did not alter the expression of activation and maturation marker molecules on the cell surface. Nevertheless, the transduction induced DCs to secrete interferon alpha and interleukin (IL)-6, but not IL-12 or tumor necrosis factor alpha. In addition, AdC68-transduced immature DCs could stimulate proliferation of autologous T lymphocytes. This is the first report describing a chimpanzee-derived recombinant Ad as a vector for transduction of human DCs.

Nucleoporation of dendritic cells: efficient gene transfer by electroporation into human monocyte-derived dendritic cells

Dendritic cells (DCs) are ideal accessory cells in the developing field of gene therapy. Although viral transfection of DCs has become widespread, non-viral transfection of DCs has shown disappointing results. Recently, a new technique for transfecting primary cells has become available -- the Amaxa Nucleofector. Here, we describe the use of this device in the successful non-viral transfection of human monocyte-derived DCs. Using enhanced green fluorescent protein as a reporter gene DCs were transfectable with efficiencies approaching 60%, remaining responsive to lipopolysaccharide-stimulated cytokine production in short-term experiments (though long-term functional assays were hampered by loss of viability). Although these data demonstrate the ease and efficiency with which human monocyte-derived DCs can now be non-virally transfected, they also suggest the limitations of this technology due to the gradual loss of cell viability. The potential use of this system in the development of DC-based cell and gene therapies will be hampered until cell viability can be maintained.

T helper cell-independent antibody responses to the transgene product of an e1-deleted adenoviral vaccine require NK1.1 T cells

Mice lacking CD4(+) T cells due to a knock-out mutation respond to vaccination with a replication-defective adenoviral recombinant expressing the glycoprotein of rabies virus with a long-lasting virus-neutralizing antibody response. The vaccine-induced B cells secrete antibodies that are mainly of IgG isotypes. The response can be enhanced upon booster immunization, indicating the induction of B cell memory in the absence of CD4(+) T cells. The antibody response is independent of CD8(+) T cells but requires the presence of CD3(+) cells carrying the NK1.1 markers.

Quantitative analysis of the antigen-specific IFNgamma+ T cell-mediated immune response in conventional outbred pigs: kinetics and duration of the DNA-induced IFNgamma+ CD8+ T cell response

It is now well established that antigen-specific CD8(+) T cells play a major role in vaccine-induced immunity against intracellular pathogens and tumor cells. The detection of these immune cells in outbred animals has been hampered mainly by the need to generate individual autologous antigen-presenting cells (APCs) due to the high degree of polymorphism of the major histocompatibility complex (MHC) Class I loci. We used individually derived immature porcine dendritic cells infected with a pox-based recombinant viral vector to ex vivo stimulate PBMCs from vaccinated conventional pigs. The frequencies of antigen-specific T cells was determined by the number of IFNgamma-secreting cells in a quantitative enzyme-linked immune spot (ELISPOT) assay. Using this approach we were able to rank different pseudorabies virus (PRV) vaccines strategies for their ability to prime viral-specific IFNgamma(+) T cells. Plasmid DNA has recently emerged as a promising tool with multiple applications in the field of infectious diseases, allergy and cancer. We showed for the first time in this study that DNA immunization induced a long-lived antigen-specific IFNgamma(+) T cells response in conventional pigs. Additional studies allowed us to show that these virus-specific IFNgamma(+) responding cells detected in this ELISPOT assay were MHC-restricted and comprised in the CD8alpha(bright) pig T cell subset. These new data confirm the usefulness of DNA vaccines to control diseases requiring cellular immunity in pigs.

Endogenously expressed nef uncouples cytokine and chemokine production from membrane phenotypic maturation in dendritic cells

Immature dendritic cells (DCs), unlike mature DCs, require the viral determinant nef to drive immunodeficiency virus (SIV and HIV) replication in coculture with CD4(+) T cells. Since immature DCs may capture and get infected by virus during mucosal transmission, we hypothesized that Nef associated with the virus or produced during early replication might modulate DCs to augment virus dissemination. Adenovirus vectors expressing nef were used to introduce nef into DCs in the absence of other immunodeficiency virus determinants to examine Nef-induced changes that might activate immature DCs to acquire properties of mature DCs and drive virus replication. Nef expression by immature human and macaque DCs triggered IL-6, IL-12, TNF-alpha, CXCL8, CCL3, and CCL4 release, but without up-regulating costimulatory and other molecules characteristic of mature DCs. Coincident with this, nef-expressing immature DCs stimulated stronger autologous CD4(+) T cell responses. Both SIV and HIV nef-expressing DCs complemented defective SIVmac239 delta nef, driving replication in autologous immature DC-T cell cultures. In contrast, if DCs were activated after capturing delta nef, virus growth was not exacerbated. This highlights one way in which nef-defective virus-bearing immature DCs that mature while migrating to draining lymph nodes could induce stronger immune responses in the absence of overwhelming productive infection (unlike nef-containing wild-type virus). Therefore, Nef expressed in immature DCs signals a distinct activation program that promotes virus replication and T cell recruitment but without complete DC maturation, thereby lessening the likelihood that wild-type virus-infected immature DCs would activate virus-specific immunity, but facilitating virus dissemination.

Human immunodeficiency virus type 1 Nef mediates activation of STAT3 in immature dendritic cells

Replication of immunodeficiency viruses (HIV-1 and SIV) in immature dendritic cell (DC)-T cell cocultures is dependent on Nef. In contrast, mature DCs promote the replication of wild-type and nef-defective SIV in concert with CD4(+) T cells. Transcription factor activation occurs on DC maturation and this study aimed to investigate whether Nef triggers similar events in immature DCs, rendering them more like mature DCs. Recombinant HIV nef-expressing adenovirus was used to selectively introduce nef into immature human or macaque DCs. These data provide the first evidence that the expression of HIV nef in immature DCs induced selective activation of STAT3 and, to a lesser extent, NF-kappaB. This highlights how Nef can signal primary immature DCs, suggesting one way in which Nef may modulate immature DCs to drive virus replication in the DC-T cell milieu.

Rhesus monocyte-derived dendritic cells modified to over-express TGF-beta1 exhibit potent veto activity

BACKGROUND

The tolerogenic activity of allogeneic bone marrow cells (BMCs) associates with functional inactivation of alloreactive T cells and has been attributed to a veto effect. Studies in mice and rhesus monkeys indicated that the CD8alpha molecule expressed on a subpopulation of allogeneic BMCs is necessary to induce signal transduction within the BMCs to increase veto effector molecules such as transforming growth factor (TGF)-beta1. In vitro activation of alloreactive cytotoxic T-lymphocyte precursor enhances their susceptibility to veto-mediated functional inactivation by specific alloantigen-bearing BMCs. Accordingly, we examined a hypothesis that mature rhesus monkey (Rh) monocyte-derived dendritic cells (MDDCs) modified by gene transfer to over-express active TGF-beta1 might mediate veto activity without the need to express CD8alpha.

METHODS

Rh MDDCs were modified by recombinant adenovirus (Ad) transduction and characterized by phenotype and functional studies.

RESULTS

Rh MDDC transduction with Ad vectors using conventional methods was remarkably inefficient. However, a single-chain anti-CD40/soluble Coxsackie and adenovirus receptor-fusion protein (G28/sCAR) permitted high-efficiency transduction of Rh MDDCs by retargeting Ad to Rh MDDC CD40. Mature Rh MDDCs that were transduced to overexpress active TGF-beta1 (AdTGF-beta1 Rh MDDC) significantly suppressed alloimmune responses in [ H]thymidine uptake mixed leukocyte reaction assays. We showed by the carboxyfluorescein succinimidyl ester dilution method that allogeneic mature AdTGF-beta1 Rh MDDCs inhibited proliferation of CD4 and CD8 responder T cells. Notably, AdTGF-beta1 Rh MDDC abrogated alloimmune responses induced by control AdGFP Rh MDDC in an antigen-specific manner.

CONCLUSIONS

These results suggest that nonhuman primate mature MDDCs can be genetically engineered to function as alloantigen-specific cellular immunosuppressants, an approach that has potential to facilitate induction of allograft tolerance in vivo.

New hope for an AIDS vaccine

The twenty-first century has begun with considerable success for new AIDS vaccines in macaque models. A common feature of these vaccines is their ability to induce high-frequency CD8+ T-cell responses that control, rather than prevent, infection with HIV. The new vaccines, which include DNA vaccines and live viral vectors, are based on technologies that have been developed since the start of the AIDS epidemic. The ultimate promise of these vaccines will be realized only when efficacy trials in humans are conducted.

Novel, chimpanzee serotype 68-based adenoviral vaccine carrier for induction of antibodies to a transgene product

An E1-deletion-containing adenoviral recombinant based on the chimpanzee serotype 68 (AdC68) was developed to express the rabies virus glycoprotein. Mice immunized with this construct (AdC68rab.gp) developed antibodies to rabies virus and remained resistant to challenge with an otherwise lethal dose of rabies virus. In naïve mice immunized intranasally, the rabies virus-specific antibody responses elicited by AdC68rab.gp were comparable with regard to both titers and isotype profiles to those induced by an adenoviral recombinant based on human serotype 5 (Adhu5) expressing the same transgene product. In contrast, subcutaneous immunization with the AdC68rab.gp vaccine resulted in markedly lower antibody responses to the rabies virus glycoprotein than the corresponding Adhu5 vaccine. Antibodies from AdC68rab.gp-immunized mice were strongly biased towards the immunoglobulin G2a isotype. The antibody response to the rabies virus glycoprotein presented by Adhu5rab.gp was severely compromised in animals preexposed to the homologous adenovirus. In contrast, the rabies virus-specific antibody response to the AdC68rab.gp vaccine was at most marginally affected by preexisting immunity to common human adenovirus serotypes, such as 2, 4, 5, 7, and 12. This novel vaccine carrier thus offers a distinct advantage over adenoviral vaccines based on common human serotypes.

The simian immunodeficiency virus deltaNef vaccine, after application to the tonsils of Rhesus macaques, replicates primarily within CD4(+) T cells and elicits a local perforin-positive CD8(+) T-cell response

Deletion of the nef gene from simian immunodeficiency virus (SIV) strain SIVmac239 yields a virus that undergoes attenuated growth in rhesus macaques and offers substantial protection against a subsequent challenge with some SIV wild-type viruses. We used a recently described model to identify sites in which the SIVDeltanef vaccine strain replicates and elicits immunity in vivo. A high dose of SIVDeltanef was applied to the palatine and lingual tonsils, where it replicated vigorously in this portal of entry at 7 days. Within 2 weeks, the virus had spread and was replicating actively in axillary lymph nodes, primarily in extrafollicular T-cell-rich regions but also in germinal centers. At this time, large numbers of perforin-positive cells, both CD8(+) T cells and CD3-negative presumptive natural killer cells, were found in the tonsil and axillary lymph nodes. The number of infected cells and perforin-positive cells then fell. When autopsy studies were carried out at 26 weeks, only 1 to 3 cells hybridized for viral RNA per section of lymphoid tissue. Nevertheless, infected cells were detected chronically in most lymphoid organs, where the titers of infectious virus could exceed by a log or more the titers in blood. Immunocytochemical labeling at the early active stages of infection showed that cells expressing SIVDeltanef RNA were CD4(+) T lymphocytes. A majority of infected cells were not in the active cell cycle, since 60 to 70% of the RNA-positive cells in tissue sections lacked the Ki-67 cell cycle antigen, and both Ki-67-positive and -negative cells had similar grain counts for viral RNA. Macrophages and dendritic cells, identified with a panel of monoclonal antibodies to these cells, were rarely infected. We conclude that the attenuated growth and protection observed with the SIVDeltanef vaccine strain does not require that the virus shift its characteristic site of replication, the CD4(+) T lymphocyte. In fact, this immunodeficiency virus can replicate actively in CD4(+) T cells prior to being contained by the host, at least in part by a strong killer cell response that is generated acutely in the infected lymph nodes.

Dendritic cell vaccination induces cross-reactive cytotoxic T lymphocytes specific for wild-type and natural variant human immunodeficiency virus type 1 epitopes in HLA-A*0201/Kb transgenic mice

Dendritic cells (DC) are highly efficient at inducing primary T cell responses. Consequently, DC are being investigated for their potential to prevent and/or treat human immunodeficiency virus type 1 (HIV-1) infection. In the current study, we examined the capacity of DC to elicit CD8+ cytotoxic T lymphocyte (CTL) reactivity against an HLA-A*0201-restricted HIV-1 reverse transcriptase (pol) epitope (residues 476-484) and two naturally occurring variants. Previous work demonstrated that the wild-type pol epitope is recognized by CTLs from HIV-1-infected individuals, whereas the variant pol epitopes are not, despite binding to HLA-A*0201. In agreement with these observations, parenteral administration of wild-type pol peptide induced HLA-A*0201-restricted CTL activity in A2Kb transgenic mice. In contrast, similar treatment with the two variant pol peptides failed to stimulate CTL reactivity, and this lack of immunogenicity correlated with reduced peptide:HLA-A*0201 complex stability. However, CTL responses were induced in A2Kb transgenic mice upon adoptive transfer of syngeneic bone marrow DC pulsed with the variant pol peptides. Furthermore, DC pulsed with the wild-type pol peptide elicited CTLs that cross-reacted with the variant pol epitopes. These results demonstrate that DC effectively expand the T cell repertoire of a given epitope to include cross-reactive T cell clonotypes. Accordingly, DC vaccination may aid in immune recognition of HIV-1 escape variants by broadening the T cell response.

Dendritic cells transduced with HIV Nef express normal levels of HLA-A and HLA-B class I molecules

HIV Nef protein is important for viral pathogenesis and disease progression. Nef downregulates CD4 and major histocompatibility antigens on the surface of HIV-infected T cells. HIV also infects dendritic cells. We wanted to determine if Nef had a similar function in professional antigen-presenting cells, where downregulation of Class I could have important effects on the initiation of HIV specific cytolytic T cell responses. We infected human dendritic cells with adenovirus expressing Nef. In contrast to T cells and Hela cells, HLA-A and HLA-B molecules are not downregulated nor are other class I molecules increased. We show that, in dendritic cells, HIV Nef has little effect on CD4 or Class I expression.

Vaccines for the prevention of HIV-1 disease

Clinical investigation in humans and experimental lentivirus infection in nonhuman primates have advanced our understanding of immune responses that control HIV-1 disease. Recently, immunization approaches in macaques have shown that the immune response can control viremia and improve clinical outcome. When such vaccine strategies are formulated to be similarly immunogenic in humans, they could form the basis for the development of candidate AIDS vaccines that would prevent infection, suppress progression to disease or reduce HIV-1 transmission in humans.