Involvement of an ATP-dependent peptide chaperone in cross-presentation after DNA immunization

Chaperone protein HSC70 regulates intercellular transfer of Y chromosome antigen DBY

Recent studies have demonstrated that CD4+ T cells can efficiently reject MHC-II-negative tumors. This requires indirect presentation of tumor-associated antigens on surrounding antigen-presenting cells. We hypothesized that intercellular transfer of proteins is not the sole consequence of cell death-mediated protein release, but depends on heat-shock cognate protein 70 (HSC70) and its KFERQ-like binding motif on substrate proteins. Using human Y chromosome antigen DBY, we showed that mutation of one of its 2 putative binding motifs markedly diminished T cell activation after indirect presentation and reduced protein-protein interaction with HSC70. Intercellular antigen transfer was shown to be independent of cell-cell contact, but relied on engulfment within secreted microvesicles. In vivo, alterations of the homologous KFERQ-like motif in murine DBY hampered tumor rejection, T cell activation, and migration into the tumor and substantially impaired survival. Collectively, we show that intercellular antigen transfer of DBY is tightly regulated via binding to HSC70 and that this mechanism influences recognition and rejection of MHC-II-negative tumors in vivo.

Enzymatic status of blood lymphocytes in young children with Epstein-Barr virus infection

Activities of NAD(PH)-dependent dehydrogenases in peripheral blood lymphocytes were studied in children aged 1-3 years in the dynamics of the disease caused by Epstein-Barr virus. A relationship between changes in activities of the studied enzymes and disease period was revealed. The disorders of blood lymphocyte enzymatic status persisted during convalescence.

RhoH regulates subcellular localization of ZAP-70 and Lck in T cell receptor signaling

RhoH is an hematopoietic-specific, GTPase-deficient Rho GTPase that plays a role in T development. We investigated the mechanisms of RhoH function in TCR signaling. We found that the association between Lck and CD3ζ was impaired in RhoH-deficient T cells, due to defective translocation of both Lck and ZAP-70 to the immunological synapse. RhoH with Lck and ZAP-70 localizes in the detergent-soluble membrane fraction where the complex is associated with CD3ζ phosphorylation. To determine if impaired translocation of ZAP-70 was a major determinant of defective T cell development, Rhoh(-/-) bone marrow cells were transduced with a chimeric myristoylation-tagged ZAP-70. Myr-ZAP-70 transduced cells partially reversed the in vivo defects of RhoH-associated thymic development and TCR signaling. Together, our results suggest that RhoH regulates TCR signaling via recruitment of ZAP-70 and Lck to CD3ζ in the immunological synapse. Thus, we define a new function for a RhoH GTPase as an adaptor molecule in TCR signaling pathway.

[Genetic immunization: new ways for protective and therapeutic vaccines against allergic diseases]

Gene vaccines have proven to be a powerful tool to induce anti-allergic immune responses. Their underlying functional principle is based on the recruitment of allergen-specific Th1 cells and the establishment of a Th1 cytokine milieu, which protects against the development of a Th2-biased response and balances an already ongoing Th2-type response. Genetic immunization also offers novel approaches to the major problems associated with protein immunization, such as crosslinking of preexisting IgE on mast cells/basophils or induction of de novo synthesis of IgE by the protein immunization itself. In addition to the description of the principles of gene vaccination, this review gives a short overview of recently developed anti-allergic gene vaccines with an optimized efficacy and safety profile.

RhoH GTPase recruits and activates Zap70 required for T cell receptor signaling and thymocyte development

RhoH is a hematopoietic-specific, GTPase-deficient member of the Rho GTPase family with unknown physiological function. Here we demonstrate that Rhoh-/- mice have impaired T cell receptor (TCR)-mediated thymocyte selection and maturation, resulting in T cell deficiency. RhoH deficiency resulted in defective CD3zeta phosphorylation, impaired translocation of the signaling molecule Zap70 to the immunological synapse and reduced activation of Zap70-mediated signaling in thymic and peripheral T cells. Proteomic analyses demonstrated that RhoH is a component of TCR signaling and is required for recruitment of Zap70 to the TCR through interaction with RhoH noncanonical immunoreceptor tyrosine-based activation motifs (ITAMs). In vivo reconstitution studies also demonstrated that RhoH function depends on phosphorylation of the RhoH ITAMs. These findings suggest that RhoH is a critical regulator of thymocyte development and TCR signaling by mediating recruitment and activation of Zap70.

Generation of anti-tumor immunity using mammalian heat shock protein 70 DNA vaccines for cancer immunotherapy

In this study, we explored the protective anti-tumor potency of mouse (self) Hsp70 or Hsp110-based DNA vaccination approach targeting a tumor-associated antigen, human papilloma virus (HPV) type 16 E7 protein. Linkage of E7 to the N-terminus of the mouse Hsp70 not only elicits an E7-specific cytotoxic T cell (CTL) response, but also protects mice against challenge with E7 expressing tumors. CD8+ T-cells are crucial in both priming and effector phases for the induction of tumor immunity, whereas CD4+ T-cells and NK cells do not appear to play a major role. Furthermore, the ATP-binding domain deletion mutant Hsp70(382-641), when fused to E7, was immunologically effective, suggesting that the peptide-binding region, not the ATPase domain of Hsp70, is required for the vaccine activity of the E7-Hsp70 DNA. This study demonstrates that autologous Hsp70 is highly potent in enhancing antigen-specific immune responses. Functional domain mapping and orientation of the E7 and Hsp70 in the fusion gene may have clinical implications for the design and optimization of Hsp70-based DNA vaccines.

Current developments in viral DNA vaccines: shall they solve the unsolved?

This review describes the mechanisms of immune response following DNA vaccination. The efficacy of DNA vaccines in animal models is highlighted, especially in viral diseases against which no widely accepted vaccination is currently available. Emphasis is given to possible therapeutic vaccination in chronic infections due to persisting virus genomes, such as recurrent herpes (HSV-1 and HSV-2), pre-AIDS (HIV-1) and/or chronic hepatitis B (HBV). In these, the problem of introducing foreign viral DNA may not be of crucial importance, since the immunised subject is already a viral DNA (or provirus) carrier. The DNA-based immunisation strategies may overcome several problems of classical viral vaccines. Novel DNA vaccines could induce immunity against multiple viral epitopes including the conservative type common ones, which do not undergo antigenic drifts. Within the immunised host, they mimic the effect of live attenuated viral vaccines when continuously expressing the polypeptide in question. For this reason they directly stimulate the antigen-presenting cells, especially dendritic cells. The antigen encoded by plasmid elicits T helper cell activity (Th1 and Th2 type responses), primes the cytotoxic T cell memory and may induce a satisfactory humoral response. The efficacy of DNA vaccines can be improved by adding plasmids encoding immunomodulatory cytokines and/or their co-receptors.

MyD88 expression is required for efficient cross-presentation of viral antigens from infected cells

While virus-infected dendritic cells (DCs) in certain instances have the capacity to activate naive T cells by direct priming, cross-priming by DCs via the uptake of antigens from infected cells has lately been recognized as another important pathway for the induction of antiviral immunity. During cross-priming, danger and stranger signals play important roles in modulating immune responses. Analogous to what has been shown for other microbial infections, virally infected cells may contain several pathogen-associated molecular patterns that are recognized by Toll-like receptors (TLRs). We analyzed whether the efficient presentation of antigens derived from infected cells requires the usage of MyD88, which is a common adaptor molecule used by all TLRs. For this study, we used murine DCs that were wild type or deficient in MyD88 expression and fibroblasts that were infected with an alphavirus replicon to answer this question. Our results show that when DCs are directly infected, they are able to activate antigen-specific CD8(+) T cells in a MyD88-independent manner. In contrast, a strict requirement of MyD88 for cross-priming was observed when virally infected cells were used as a source of antigen in vitro and in vivo. This indicates that the effects of innate immunity stimulation via the MyD88 pathway control the efficiency of cross-presentation, but not direct presentation or DC maturation, and have important implications in the development of cytotoxic T lymphocyte responses against alphaviral replicon infections.

Human Clinical Trials of Plasmid DNA Vaccines

This article gives an overview of DNA vaccines with specific emphasis on the development of DNA vaccines for clinical trials and an overview of those trials. It describes the preclinical research that demonstrated the efficacy of DNA vaccines as well as an explication of the immunologic mechanisms of action. These include the induction of cognate immune responses, such as the generation of cytolytic T lymphocytes (CTL) as well as the effect of the plasmid DNA upon the innate immune system. Specific issues related to the development of DNA as a product candidate are then discussed, including the manufacture of plasmid, the qualification of the plasmid DNA product, and the safety testing necessary for initiating clinical trials. Various human clinical trials for infectious diseases and cancer have been initiated or completed, and an overview of these trials is given. Finally, because the early clinical trials have shown less than optimal immunogenicity, methods to increase the potency of the vaccines are described.

The processing of antigens delivered as DNA vaccines

The ability of DNA vaccines to provide effective immunological protection against infection and tumors depends on their ability to generate good CD4+ and CD8+ T-cell responses. Priming of these responses is a property of dendritic cells (DCs), and so the efficacy of DNA-encoded vaccines is likely to depend on the way in which the antigens they encode are processed by DCs. This processing could either be via the synthesis of the vaccine-encoded antigen by the DCs themselves or via its uptake by DCs following its synthesis in bystander cells that are unable to prime T cells. These different sources of antigen are likely to engage different antigen-processing pathways, which are the subject of this review. Understanding how to access different processing pathways in DCs may ultimately aid the rational development of plasmid-based vaccines to pathogens and to cancer.

DNA vaccines for allergy treatment

In the past 10 years, a great number of studies have demonstrated that injection of plasmid DNA coding for certain genes results in the induction of humoral and cellular immune responses against the respective gene product. This vaccination approach covers a broad range of possible applications, including the induction of protective immunity against viral, bacterial, and parasitic infections, and it opens new perspectives for treatment of cancer. Surprisingly, DNA immunization also turned out as a promising novel type of immunotherapy against allergy. In this paper, we describe the construction of DNA vaccines for application in allergy models. Beyond, we offer a palette of recently developed modulations to optimize DNA vaccines for allergy treatment by increasing their immunogenicity and minimizing their anaphylactic potential.

Secretory heat-shock protein as a dendritic cell-targeting molecule: a new strategy to enhance the potency of genetic vaccines

DNA vaccines are an appealing strategy for inducing cytotoxic T-lymphocyte and antibody responses against tumor cells as well as infectious agents. Dendritic cells (DCs) play a critical role in inducing immune responses, but their potential is not fully utilized in the DNA vaccine setting since they take up only a minor fraction of the injected DNA. Here we describe a novel DNA vaccination strategy based on the targeting of a modified tumor-associated antigen, the human papilloma virus (HPV) type 16 E7 protein, to DCs by a heat-shock protein (HSP) to enhance antigen presentation and immune responses. Specifically, a chimerical HPV-E7 and HSP70 fusion gene preceded with a leader sequence was constructed. When mice were immunized with this construct, the DNA is taken up by various types of cells, which then produce and secrete an HPV-E7-HSP70 fusion protein that is targeted to DCs by the HSP70 portion of the chimerical molecule for antigen presentation. In studies to test the efficacy of this strategy, we demonstrated that DNA vaccination with this secretory HPV-E7-HSP70 construct strongly enhanced an antigen-specific CD8+ T-cell response as well as a specific B-cell response in mice. Furthermore, this immunization approach not only protected mice against lethal challenge with an HPV E7-expressing tumor line (TC-1), but also showed a therapeutic effect against established tumors. The results of this study indicate that secretory HSPs can be broadly used to target tumor-associated antigens to DCs to enhance antigen-specific immune responses.

DNA vaccines expressing antigens with a stress protein-capturing domain display enhanced immunogenicity

An expression system for DNA vaccines is described, in which a fusion protein with an N-terminal, viral J-domain that captures heat-shock proteins (Hsps) is translated in-frame with C-terminal antigen-encoding sequences (of various lengths and origins). The system supports enhanced expression of chimeric antigens (of >800 residues in length) with an extended half life (>8 h). When used as a DNA vaccine, it delivers antigen together with the intrinsic adjuvant activity provided by bound Hsps. We describe the design of vectors for DNA vaccination that support the expression of different immunogenic domains of different origins as large, Hsp-capturing chimeric fusion antigens. The immunogenicity of the antigens produced by this expression system (when it is built into DNA vaccines) has been characterized in detail, with particular emphasis on priming CD8+ T-cell responses. We also discuss areas of vaccine research to which the new technology may provide useful contributions.

Antigenic peptides complexed to phylogenically diverse Hsp70s induce differential immune responses

The Hsp70 class of heat shock proteins (Hsps) has been implicated at multiple points in the immune response, including initiation of proinflammatory cytokine production, antigen recognition and processing, and phenotypic maturation of antigen-presenting cells (APCs). This class of chaperones is highly conserved in both sequence and structure, from prokaryotes to higher eukaryotes. In all cases, these chaperones function to bind short segments of either peptides or proteins through an adenosine triphosphate-dependent process. In addition to a possible role in antigen presentation, these chaperones have also been proposed to function as a potent adjuvant. We compared 4 evolutionary diverse Hsp70s, E. coli DnaK, wheat cytosolic Hsc70, plant chloroplastic CCS1, and human Hsp70, for their ability to prime and augment a primary immune response against herpes simplex virus-1 (HSV1). We discovered that all 4 Hsp70s were highly effective as adjuvants displaying similar ability to lipopolysaccharides in upregulating cytokine gene expression. In addition, they were all capable of inducing phenotypic maturation of APCs, as measured by the display of various costimulatory molecules. However, only the human Hsp70 was able to mediate sufficient cross-priming activity to afford a protective immune response to HSV1, as judged by protection from a lethal viral challenge, in vitro proliferation, cytotoxicity, and intracellular interferon-gamma production. The difference in immune response generated by the various Hsp70s could possibly be due to their differential ability to interact productively with other coreceptors and different regulatory cochaperones.

Enhanced priming of multispecific, murine CD8+ T cell responses by DNA vaccines expressing stress protein-binding polytope peptides

A polytope DNA vaccine (pCI/pt10) was used that encodes within a 106-residue sequence 10-well characterized epitopes binding MHC class I molecules encoded by the K, D, or L locus (of H-2(d), H-2(b), and H-2(k) haplotype mice). The pCI/pt10 DNA vaccine efficiently primed all four K(b)/D(b)-restricted CD8(+) T cell responses in H-2(b) mice, but was deficient in stimulating most CD8(+) T cell responses in H-2(d) mice. Comparing CD8(+) T cell responses elicited with the pCI/pt10 DNA vaccine in L(d+) BALB/c and L(d-) BALB/c(dm2) (dm2) mice revealed that L(d)-restricted CD8(+) T cell responses down-regulated copriming of CD8(+) T cell responses to other epitopes regardless of their restriction or epitope specificity. Although the pt10 vaccine could thus efficiently co prime multispecific CD8(+) T cell responses, this priming was impaired by copriming L(d)-restricted CD8(+) T cell responses. When the pt10 sequence was fused to a 77-residue DnaJ-homologous, heat shock protein 73-binding domain (to generate a 183-residue cT(77)-pt10 fusion protein), expression and immunogenicity (for CD8(+) T cells) of the chimeric Ag were greatly enhanced. Furthermore, priming of multispecific CD8(+) T cell responses was readily elicited even under conditions in which the suppressive, L(d)-dependent immunodominance operated. The expression of polytope vaccines as chimeric peptides that endogenously capture stress proteins during in situ production thus facilitates copriming of CD8(+) T cell populations with a diverse repertoire.

The heat-shock protein receptor CD91 is up-regulated in monocytes of HIV-1-infected "true" long-term nonprogressors

A small proportion of patients with human immunodeficiency virus type 1 (HIV-1) remains asymptomatic for a long period after infection. It is thought that a vigorous immune response may contribute to long-term nonprogression, though studies are confounded by heterogeneity among patients. We studied the levels of HIV-1 receptors, costimulatory T-cell molecules, and dendritic cell (DC) numbers in 18 patients with long-term infection, CD4 counts greater than 400 cells/mm(3), and HIV-1 viral loads lower than 50 copies/mL. These patients were further differentiated through the presence or absence of 2-LTR DNA circles, a possible marker for residual ongoing HIV-1 replication. A statistically significant increase in levels of CD91, the heat-shock protein (HSP) receptor, was observed in therapy-naive patients who had no evidence of ongoing viral replication (P =.01). This difference was most notable on their monocytes. High levels of CD91 may be a host factor that contributes to the maintenance of long-term nonprogression. The ability of CD91 to internalize alpha-defensins and to cross-present exogenous antigen to cytotoxic T lymphocytes through major histocompatibility complex (MHC) class 1 may maintain CD8(+) responses in these patients.

Toll-like receptor ligand links innate and adaptive immune responses by the production of heat-shock proteins

The report shows that CpG can exert additional adjuvant effects by inducing cells that are normally inferior antigen (Ag)-presenting cells to participate in immune induction by cross-priming. Macrophages (Mphi) exposed to protein Ag in the presence of bioactive CpG DNA released material that induced primary CD8(+) T cell responses in DC-naïve T cell cultures. This cross-priming event was accompanied by up-regulation of the stress protein response as well as inflammatory cytokine expression in treated Mphi. The material released was indicated to contain inducible heat shock protein-70 and epitope peptide, which in turn, were presented by dendritic cells (DCs) to responder T cells. Such an adjuvant effect by CpG may serve to salvage immunogenic material from otherwise inert depot cellular sites and additionally stimulate DCs to effectively cross-prime. The cross-priming, shown also to occur in vivo, may be particularly useful when Ag doses are low and have minimal opportunity for delivery to DCs for consequent direct priming.

Indirect activation of naïve CD4+ T cells by dendritic cell-derived exosomes

Dendritic cells (DCs) secrete vesicles of endosomal origin, called exosomes, that bear major histocompatibility complex (MHC) and T cell costimulatory molecules. Here, we found that injection of antigen- or peptide-bearing exosomes induced antigen-specific naïve CD4+ T cell activation in vivo. In vitro, exosomes did not induce antigen-dependent T cell stimulation unless mature CD8alpha- DCs were also present in the cultures. These mature DCs could be MHC class II-negative, but had to bear CD80 and CD86. Therefore, in addition to carrying antigen, exosomes promote the exchange of functional peptide-MHC complexes between DCs. Such a mechanism may increase the number of DCs bearing a particular peptide, thus amplifying the initiation of primary adaptive immune responses.

Efficient priming of CD4+ and CD8+ T cells by DNA vaccination depends on appropriate targeting of sufficient levels of immunologically relevant antigen to appropriate processing pathways

The initial cellular events and interactions that occur following DNA immunization are likely to be key to determining the character and magnitude of the resulting immune response, and as such, a better understanding of these events could ultimately lead to the design of more effective pathogen-appropriate DNA vaccines. Therefore, we have used a variety of sensitive cell-based techniques to study the induction of adaptive immunity in vivo. We examined the efficacy of induction of Ag-specific CD4(+) and CD8(+) T cell responses in vivo by the adoptive transfer of fluorescently labeled Ag-specific TCR transgenic T cells and have demonstrated how such approaches can be used to study the effect of simple DNA construct manipulations on immunological priming. OVA-specific CD8(+) and CD4(+) T cells were activated and divided in vivo following immunization with DNA constructs that targeted OVA expression to different subcellular locations; however, the kinetics and degree of cell proliferation were dependent on the cellular location of the expressed protein. DNA vectors encoding cell-associated OVA resulted in greater CD8(+) T cell division compared with other forms of OVA. In contrast, soluble secreted OVA targeted to the classical secretory pathway enhanced division of CD4(+) T cells. Furthermore, the inclusion of mammalian introns to enhance protein expression increased the ability of poorly immunogenic forms of Ag to activate naive T cells, indicating that not only the location, but also the amount of Ag expression, is important for efficient T cell priming following DNA injection.

Noncovalent association with stress protein facilitates cross-priming of CD8+ T cells to tumor cell antigens by dendritic cells

A viral oncogene carrying well-defined K(b)/D(b)-restricted epitopes was expressed in a heat shock protein (hsp)-associated or nonassociated form in the murine tumor cells P815 and Meth-A. Wild-type SV40 large T-Ag (wtT-Ag) is expressed without stable hsp association; mutant (cytoplasmic cT-Ag) or chimeric (cT272-green fluorescent fusion protein) T-Ag is expressed in stable association with the constitutively expressed, cytosolic hsp73 (hsc70) protein. In vitro, remnants from apoptotic wtT-Ag- or cT-Ag-expressing tumor cells are taken up and processed by immature dendritic cells (DC), and the K(b)/D(b)-binding epitopes T1, T2/3, and T4 of the T-Ag are cross-presented to CTL in a TAP-independent way. DC pulsed with remnants of transfected, apoptotic tumor cells cross-presented the three T-Ag epitopes more efficiently when they processed ATP-sensitive hsp73/cT-Ag complexes than when they processed hsp-nonassociated (native) T-Ag. In vivo, more IFN-gamma-producing CD8+ T cells were elicited by a DNA vaccine that encoded hsp73-binding mutant T-Ag than by a DNA vaccine that encoded native, non-hsp-binding T-Ag. Three- to 5-fold higher numbers of T-Ag (T1-, T2/3-, or T4-) specific, D(b)/K(b)-restricted IFN-gamma-producing CD8+ T cells were primed during the growth of transfected H-2(d) Meth-A/cT tumors than during the growth of transfected Meth-A/T tumors in F(1)(b x d) hosts. Hence, the association of an oncogene with constitutively expressed, cytosolic hsp73 facilitates cross-priming in vitro and in vivo of CTL by DC that process material from apoptotic cells.

DNA vaccines: future strategies and relevance to intracellular pathogens

Increasing awareness of microbial threat has rekindled interest in the great potential of vaccines for controlling infectious diseases. The fact that diseases caused by intracellular pathogens cannot be overcome by chemotherapy alone has increased our interest in the generation of highly efficacious novel vaccines. Vaccines have proven their efficacy, as the immunoprotection they induce appears to be mediated by long-lived humoral immune responses. However, there are no consistently effective vaccines available against diseases such as tuberculosis and HIV, and other infections caused by intracellular pathogens, which are predominantly controlled by T lymphocytes. This review describes the T-cell populations and the type of immunity that should be activated by successful DNA vaccines against intracellular pathogens. It further discusses the parameters that need to be fulfilled by protective T-cell Ag. We then discuss future approaches for DNA vaccination against diseases in which cell-mediated immune responses are essential for providing protection.

Cross-priming as a predominant mechanism for inducing CD8(+) T cell responses in gene gun DNA immunization

DNA immunization induces CD8(+) CTL responses by bone marrow-derived APCs, which are directly transfected with a plasmid DNA and/or acquire Ags from DNA-transfected non-APCs. To investigate the relative contribution of DNA-transfected APCs vs non-APCs to the initiation of CD8(+) T cell responses, we used tissue-specific promoter-directed gene expression and adoptive transfer systems in gene gun DNA immunization. In this study, we demonstrated that non-APC-specific gene expressions induced significant CD8(+) CTL and IFN-gamma-producing cells and Ab responses, whereas APC-specific gene expressions led to moderate CTL and IFN-gamma-producers, but no Ab responses. Interestingly, mice immunized with a non-APC-specific plasmid induced more rapid, vigorous, and prolonged proliferation of adoptively transferred Ag-specific CD8(+) T cells than APC-specific plasmid-immunized mice. In addition, the in vivo proliferative responses elicited by a non-APC-specific plasmid administration were dependent on TAP, but were independent of CD4(+) T cell help. Collectively, our results suggest that cross-priming, in which Ags expressed in non-APCs are taken up, processed, and presented by APCs, plays an important role in the initiation, magnitude, and maintenance of CD8(+) T cell responses in gene gun DNA immunization.

Plasmid DNA encoding CCR7 ligands compensate for dysfunctional CD8+ T cell responses by effects on dendritic cells

Lymphotoxin alpha-deficient (LTalpha-/-) mice, which lack lymph nodes and possess a disorganized spleen, develop dysfunctional CD8+ T cells upon HSV infection and readily succumb to herpes encephalitis. Such mice do develop apparently normal peptide-specific CD8+ T cell responses, as measured by MHC class I tetramer staining, but the majority of cells fail to become cytotoxic or express peptide-induced IFN-gamma production. In the present study, we demonstrate that functional defects of CD8+ T cells in LTalpha-/- mice can be largely rectified by the administration of plasmid DNA encoding CCR7 ligands before HSV infection. Treated mutant mice developed increased peptide-specific cytotoxic responses, enhanced numbers of CD8+ T cells capable of producing IFN-gamma, as well as improved resistance to HSV challenge. The corrective effect of chemokine treatment appeared to result from improved dendritic cell-mediated Ag presentation. Thus, a major consequence of the treatment was an increase in splenic dendritic cell number in CCR7 ligand-treated LTalpha-/- mice with such splenocyte populations showing improved APC activity in vitro. Our results document that functional defects of CD8+ T cells can be corrected, and indicate the value of plasmid vector encoding appropriate chemokines to achieve such immunotherapy.

Immunopotentiation of DNA vaccine against herpes simplex virus via co-delivery of plasmid DNA expressing CCR7 ligands

The CCR7 ligands, secondary lymphoid tissue chemokine (SLC) and Epstein-Barr virus-induced molecule 1 ligand chemokine (ELC), were recently recognized as key molecules in establishing functional microenvironments for the initiation of immune responses in secondary lymphoid tissue. Here, we investigated the effect of CCR7 ligands-DNA administration on systemic and mucosal immune responses to plasmid DNA encoding gB of herpes simplex virus (HSV). Systemic co-transfer of both CCR7 ligands enhanced serum gB-specific IgG Ab but failed to elicit enhancement of distal mucosal IgA responses. In contrast, mucosal co-transfer provided significant increases of distal mucosal IgA responses. CCR7 ligands also enhanced T cell-mediated immunity as measured by CD4+ T helper cell proliferation and CD8+ T cell-mediated CTL activity. Of particular interest, is the observation that SLC significantly increased the production of Th1-type cytokines (IL-2 and IFN-gamma) (P<0.05), whereas ELC increased the production of both Th1-type and Th2-type (IL-4) cytokines (P<0.05). Moreover, co-vaccination of CCR7 ligands increased the number of dendritic cells in secondary lymphoid tissue. These data indicate that CCR7 ligands may prove to be useful adjuvants for genetic vaccination against intracellular infection as well as cancer.

Prime-boost immunization with DNA vaccine: mucosal route of administration changes the rules

In this study we assessed prime-boost immunization strategies with a DNA vaccine (gB DNA) and attenuated recombinant vaccinia virus vector (rvacgB), both encoding the gB protein of HSV, for their effectiveness at inducing mucosal as well as systemic immunity to HSV. Confirming the reports of others, systemic priming with gB DNA and systemic boosting with rvacgB were the most effective means of inducing serum Ab and splenic T cell responses. Nevertheless, the systemic prime-boost approach failed to induce detectable humoral or T cell responses at mucosal sites. However, such responses, at both proximal and distal locations, were induced if immunizations, especially the priming dose, were administered mucosally. Curiously, whereas optimal immunity with systemic priming and boosting occurred when gB DNA was used to prime and rvacgB was used as a boost, mucosal responses were optimal when animals were mucosally primed with rvacgB and boosted with gB DNA given mucosally. Furthermore, notable mucosal responses also occurred in animals mucosally primed with rvacgB and subsequently boosted systemically with gB DNA. Because the mucosal prime-boost immunization protocol also induced excellent systemic immune responses, the approach should be useful to vaccinate against agents for which both mucosal and systemic immunity are important for protection.

Optimisation of DNA vaccines for the prophylaxis and modulation of herpes simplex virus infections

Herpes simplex virus (HSV) lacks an effective vaccine. Despite its prevalence and importance HSV infection is not controlled with an acceptable vaccine. Perhaps the best candidate and so far untested approach is the use of plasmid DNA encoding viral proteins. Immunomodulators are also holding some hope as a potential therapeutic. In this review various DNA vaccine approaches used in animal model systems to prevent HSV infections are discussed. Judgements are made as to which of these may prove effective for prophylactic or therapeutic vaccines in humans.

Lymphotoxin alpha-/- mice develop functionally impaired CD8+ T cell responses and fail to contain virus infection of the central nervous system

Recent observations have indicated that viral persistence and tumor spreading could occur because of effector function-defective CD8(+) T cells. Although chronic exposure to Ag, lack of CD4 help, and epitope dominance are suggested to interfere with CTL differentiation, mechanisms underlying the defective effector function remain obscure. We demonstrate in this report that lymphotoxin alpha-deficient mice develop CD8(+) T cells at normal frequencies when infected with HSV or immunized with OVA Ag but show impaired cytotoxic and cytokine-mediated effector functions resulting in enhanced susceptibility to HSV-induced encephalitis. Although these cells display near normal levels of perforin and Fas ligand, they remain largely at a naive state as judged by high expression of CD62 ligand and failure to up-regulate activation or memory markers. In particular, these CD8(+) T cells revealed inadequate expression of the IL-12 receptor, thus establishing a link between CTL differentiation and LTalpha possibly through regulation of IL-12 receptor. Viruses and tumors could evade immunity by targeting the same pathway.

Modulation of immunity against herpes simplex virus infection via mucosal genetic transfer of plasmid DNA encoding chemokines

In this study, we examined the effects of murine chemokine DNA, as genetic adjuvants given mucosally, on the systemic and distal mucosal immune responses to plasmid DNA encoding gB of herpes simplex virus (HSV) by using the mouse model. The CC chemokines macrophage inflammatory protein 1beta (MIP-1beta) and monocyte chemotactic protein 1 (MCP-1) biased the immunity to the Th2-type pattern as judged by the ratio of immunoglobulin isotypes and interleukin-4 cytokine levels produced by CD4(+) T cells. The CXC chemokine MIP-2 and the CC chemokine MIP-1alpha, however, mounted immune responses of the Th1-type pattern, and such a response rendered recipients more resistant to HSV vaginal infection. In addition, MIP-1alpha appeared to act via the upregulation of antigen-presenting cell (APC) function and the expression of costimulatory molecules (B7-1 and B7-2), whereas MIP-2 enhanced Th1-type CD4(+) T-cell-mediated adaptive immunity by increasing gamma interferon secretion from activated NK cells. Our results emphasize the value of using the mucosal route to administer DNA modulators such as chemokines that function as adjuvants by regulating the activity of innate immunity. Our findings provide new insight into the value of CXC and CC chemokines, which act on different innate cellular components as the linkage signals between innate and adaptive immunity in mucosal DNA vaccination.