Identification of an immunodominant cytotoxic T-lymphocyte recognition site in glycoprotein B of herpes simplex virus by using recombinant adenovirus vectors and synthetic peptides

Adenovirus Transcriptome in Human Cells Infected with ChAdOx1-Vectored Candidate HIV-1 Vaccine Is Dominated by High Levels of Correctly Spliced HIVconsv1&62 Transgene RNA

We develop candidate HIV-1 vaccines, of which two components, ChAdOx1.tHIVconsv1 (C1) and ChAdOx1.HIVconsv62 (C62), are delivered by the simian adenovirus-derived vaccine vector ChAdOx1. Aberrant adenovirus RNA splicing involving transgene(s) coding for the SARS-CoV-2 spike was suggested as an aetiology of rare adverse events temporarily associated with the initial deployment of adenovirus-vectored vaccines during the COVID-19 pandemic. Here, to eliminate this theoretically plausible splicing phenomenon from the list of possible pathomechanisms for our HIV-1 vaccine candidates, we directly sequenced mRNAs in C1- and C62-infected nonpermissive MRC-5 and A549 and permissive HEK293 human cell lines. Our two main observations in nonpermissive human cells, which are most similar to those which become infected after the intramuscular administration of vaccines into human volunteers, were that (i) the dominant adenovirus vector-derived mRNAs were the expected transcripts coding for the HIVconsvX immunogens and (ii) atypical splicing events within the synthetic open reading frame of the two transgenes are rare. We conclude that inadvertent RNA splicing is not a safety concern for the two tested candidate HIV-1 vaccines.

Adenovirus DNA Polymerase Loses Fidelity on a Stretch of Eleven Homocytidines during Pre-GMP Vaccine Preparation

In this study, we invented and construct novel candidate HIV-1 vaccines. Through genetic and protein engineering, we unknowingly constructed an HIV-1-derived transgene with a homopolymeric run of 11 cytidines, which was inserted into an adenovirus vaccine vector. Here, we describe the virus rescue, three rounds of clonal purification and preparation of good manufacturing practise (GMP) starting material assessed for genetic stability in five additional virus passages. Throughout these steps, quality control assays indicated the presence of the transgene in the virus genome, expression of the correct transgene product and immunogenicity in mice. However, DNA sequencing of the transgene revealed additional cytidines inserted into the original 11-cytidine region, and the GMP manufacture had to be aborted. Subsequent analyses indicated that as little as 1/25th of the virus dose used for confirmation of protein expression (10⁶ cells at a multiplicity of infection of 10) and murine immunogenicity (10⁸ infectious units per animal) met the quality acceptance criteria. Similar frameshifts in the expressed proteins were reproduced in a one-reaction in vitro transcription/translation employing phage T7 polymerase and E. coli ribosomes. Thus, the most likely mechanism for addition of extra cytidines into the ChAdOx1.tHIVconsv6 genome is that the adenovirus DNA polymerase lost its fidelity on a stretch of 11 cytidines, which informs future adenovirus vaccine designs.

Expression of Murine CD80 by Herpes Simplex Virus 1 in Place of Latency-Associated Transcript (LAT) Can Compensate for Latency Reactivation and Anti-apoptotic Functions of LAT

High rates of wild-type (WT) herpes simplex virus 1 (HSV-1) latency reactivation depend on the anti-apoptotic activities of latency-associated transcript (LAT). Replacing LAT with the baculovirus inhibitor of apoptosis protein (cpIAP) or cellular FLIP (FLICE-like inhibitory protein) gene restored the WT latency reactivation phenotype to that of a LAT-minus [LAT(-)] virus, while similar recombinant viruses expressing interleukin-4 (IL-4) or interferon gamma (IFN-γ) did not. However, HSV-1 recombinant virus expressing cpIAP did not restore all LAT functions. Recently, we reported that a similar recombinant virus expressing CD80 in place of LAT had higher latency reactivation than a LAT-null virus. The present study was designed to determine if this CD80-expressing recombinant virus can restore all LAT functions as observed with WT virus. Our results suggest that overexpression of CD80 fully rescues LAT function in latency reactivation, apoptosis, and immune exhaustion, suggesting that LAT and CD80 have multiple overlapping functions.IMPORTANCE Recurring ocular infections caused by HSV-1 can cause corneal scarring and blindness. A major function of the HSV-1 latency-associated transcript (LAT) is to establish high levels of latency and reactivation, thus contributing to the development of eye disease. Here, we show that the host CD80 T cell costimulatory molecule functions similarly to LAT and can restore the ability of LAT to establish latency, reactivation, and immune exhaustion as well as induce the expression of caspase 3, caspase 8, caspase 9, and Bcl2. Our results suggest that, in contrast to several other previously tested genes, CD80-expressing virus can completely compensate for all known and tested LAT functions.

Attenuated Herpes Simplex Virus 1 (HSV-1) Expressing a Mutant Form of ICP6 Stimulates a Strong Immune Response That Protects Mice against HSV-1-Induced Corneal Disease

We previously isolated a herpes simplex virus 1 (HSV-1) mutant, KOS-NA, that carries two nonsynonymous mutations in UL39, resulting in L393P and R950H amino acid substitutions in infected cell protein 6 (ICP6). Our published data studying KOS-NA pathogenesis strongly suggest that one of these ICP6 substitutions expressed from KOS-NA, R950H, severely impaired acute viral replication in the eyes and trigeminal ganglia of mice after inoculation onto the cornea and consequently impaired establishment and reactivation from latency. Because of its significant neuroattenuation, we tested KOS-NA as a potential prophylactic vaccine against HSV-1 in a mouse model of corneal infection. KOS-NA stimulated stronger antibody and T cell responses than a replication-competent ICP0-null mutant and a replication-incompetent ICP8-null mutant optimized for immunogenicity. Immunizations with the ICP0^-, ICP8^-, and KOS-NA viruses all reduced replication of wild-type HSV-1 challenge virus in the corneal epithelium to similar extents. Low immunizing doses of KOS-NA and the ICP8^- virus, but not the ICP0^- virus, protected mice against eyelid disease (blepharitis). Notably, only KOS-NA protected almost completely against corneal disease (keratitis) and greatly reduced latent infection by challenge virus. Thus, vaccination of mice with KOS-NA prior to corneal challenge provides significant protection against HSV-1-mediated disease of the eye, even at a very low immunizing dose. These results suggest that KOS-NA may be the foundation of an effective prophylactic vaccine to prevent or limit HSV-1 ocular diseases.IMPORTANCE HSV-1 is a ubiquitous human pathogen that infects the majority of the world's population. Although most infections are asymptomatic, HSV-1 establishes lifelong latency in infected sensory neurons, from which it can reactivate to cause deadly encephalitis or potentially blinding eye disease. No clinically effective vaccine is available. In this study, we tested the protective potential of a neuroattenuated HSV-1 mutant (KOS-NA) as a vaccine in mice. We compared the effects of immunization with KOS-NA to those of two other attenuated viruses, a replication-competent (ICP0^-) virus and a replication-incompetent (ICP8^-) virus. Our data show that KOS-NA proved superior to the ICP0- and ICP8-null mutants in protecting mice from corneal disease and latent infection. With its significant neuroattenuation, severe impairment in establishing latency, and excellent protective effect, KOS-NA represents a significant discovery in the field of HSV-1 vaccine development.

Hexokinase II may be dispensable for CD4 T cell responses against a virus infection

Activation of CD4 T cells leads to their metabolic reprogramming which includes enhanced glycolysis, catalyzed through hexokinase enzymes. Studies in some systems indicate that the HK2 isoform is the most up regulated isoform in activated T cells and in this report the relevance of this finding is evaluated in an infectious disease model. Genetic ablation of HK2 was achieved in only T cells and the outcome was evaluated by measures of T cell function. Our results show that CD4 T cells from both HK2 depleted and WT animals displayed similar responses to in vitro stimulation and yielded similar levels of Th1, Treg or Th17 subsets when differentiated in vitro. A modest increase in the levels of proliferation was observed in CD4 T cells lacking HK2. Deletion of HK2 led to enhanced levels of HK1 indicative of a compensatory mechanism. Finally, CD4 T cell mediated immuno-inflammatory responses to a virus infection were similar between WT and HK2 KO animals. The observations that the expression of HK2 appears non-essential for CD4 T cell responses against virus infections is of interest since it suggests that targeting HK2 for cancer therapy may not have untoward effects on CD4 T cell mediated immune response against virus infections.

Lytic Promoters Express Protein during Herpes Simplex Virus Latency

Herpes simplex virus (HSV) has provided the prototype for viral latency with previously well-defined acute or lytic and latent phases. More recently, the deep quiescence of HSV latency has been questioned with evidence that lytic genes can be transcribed in this state. However, to date the only evidence that these transcripts might be translated has come from immunological studies that show activated T cells persist in the nervous system during latency. Here we use a highly sensitive Cre-marking model to show that lytic and latent phases are less clearly defined in two significant ways. First, around half of the HSV spread leading to latently infected sites occurred beyond the initial acute infection and second, we show direct evidence that lytic promoters can drive protein expression during latency.

Herpes simplex virus, which causes cold sores and genital herpes, has active and inactive (or latent) phases of infection that have been considered to be distinct. In this study we found that the active phase of infection, including spread in the nervous system, continues longer than has been previously appreciated. We also show evidence that virus genes previously only associated with active infection are turned on during latency. These genes are of particular interest because other work has found that they are targets of the immune response to HSV. The extent and nature of residual viral activity during latency is important to understand because it may suggest therapeutic targets to reduce recurrent HSV disease.

Antibodies Are Required for Complete Vaccine-Induced Protection against Herpes Simplex Virus 2

Herpes simplex virus 2 (HSV-2) 0ΔNLS is a live HSV-2 ICP0- mutant vaccine strain that is profoundly attenuated in vivo due to its interferon-hypersensitivity. Recipients of the HSV-2 0ΔNLS vaccine are resistant to high-dose HSV-2 challenge as evidenced by profound reductions in challenge virus spread, shedding, disease and mortality. In the current study, we investigated the requirements for HSV-2 0ΔNLS vaccine-induced protection. Studies using (UV)-inactivated HSV-2 0ΔNLS revealed that self-limited replication of the attenuated virus was required for effective protection from vaginal or ocular HSV-2 challenge. Diminished antibody responses in recipients of the UV-killed HSV-2 vaccine suggested that antibodies might be playing a critical role in early protection. This hypothesis was investigated in B-cell-deficient μMT mice. Vaccination with live HSV-2 0ΔNLS induced equivalent CD8+ T cell responses in wild-type and μMT mice. Vaccinated μMT mice shed ~40-fold more infectious HSV-2 at 24 hours post-challenge relative to vaccinated wild-type (B-cell+) mice, and most vaccinated μMT mice eventually succumbed to a slowly progressing HSV-2 challenge. Importantly, passive transfer of HSV-2 antiserum restored full protection to HSV-2 0ΔNLS-vaccinated μMT mice. The results demonstrate that B cells are required for complete vaccine-induced protection against HSV-2, and indicate that virus-specific antibodies are the dominant mediators of early vaccine-induced protection against HSV-2.

Topical herpes simplex virus 2 (HSV-2) vaccination with human papillomavirus vectors expressing gB/gD ectodomains induces genital-tissue-resident memory CD8+ T cells and reduces genital disease and viral shedding after HSV-2 challenge

No herpes simplex virus 2 (HSV-2) vaccine has been licensed for use in humans. HSV-2 glycoproteins B (gB) and D (gD) are targets of neutralizing antibodies and T cells, but clinical trials involving intramuscular (i.m.) injection of HSV-2 gB and gD in adjuvants have not been effective. Here we evaluated intravaginal (ivag) genetic immunization of C57BL/6 mice with a replication-defective human papillomavirus pseudovirus (HPV PsV) expressing HSV-2 gB (HPV-gB) or gD (HPV-gD) constructs to target different subcellular compartments. HPV PsV expressing a secreted ectodomain of gB (gBsec) or gD (gDsec), but not PsV expressing a cytoplasmic or membrane-bound form, induced circulating and intravaginal-tissue-resident memory CD8(+) T cells that were able to secrete gamma interferon (IFN-γ) and tumor necrosis factor alpha (TNF-α) as well as moderate levels of serum HSV neutralizing antibodies. Combined immunization with HPV-gBsec and HPV-gDsec (HPV-gBsec/gDsec) vaccines conferred longer survival after vaginal challenge with HSV-2 than immunization with HPV-gBsec or HPV-gDsec alone. HPV-gBsec/gDsec ivag vaccination was associated with a reduced severity of genital lesions and lower levels of viral shedding in the genital tract after HSV-2 challenge. In contrast, intramuscular vaccination with a soluble truncated gD protein (gD2t) in alum and monophosphoryl lipid A (MPL) elicited high neutralizing antibody titers and improved survival but did not reduce genital lesions and viral shedding. Vaccination combining ivag HPV-gBsec/gDsec and i.m. gD2t-alum-MPL improved survival and reduced genital lesions and viral shedding. Finally, high levels of circulating HSV-2-specific CD8(+) T cells, but not serum antibodies, correlated with reduced viral shedding. Taken together, our data underscore the potential of HPV PsV as a platform for a topical mucosal vaccine to control local manifestations of primary HSV-2 infection.

IMPORTANCE

Genital herpes is a highly prevalent chronic disease caused by HSV infection. To date, there is no licensed vaccine against HSV infection. This study describes intravaginal vaccination with a nonreplicating HPV-based vector expressing HSV glycoprotein antigens. The data presented in this study underscore the potential of HPV-based vectors as a platform for the induction of genital-tissue-resident memory T cell responses and the control of local manifestations of primary HSV infection.

Us3 kinase encoded by herpes simplex virus 1 mediates downregulation of cell surface major histocompatibility complex class I and evasion of CD8+ T cells

Detection and elimination of virus-infected cells by CD8⁺ cytotoxic T lymphocytes (CTLs) depends on recognition of virus-derived peptides presented by major histocompatibility complex class I (MHC-I) molecules on the surface of infected cells. In the present study, we showed that inactivation of the activity of viral kinase Us3 encoded by herpes simplex virus 1 (HSV-1), the etiologic agent of several human diseases and a member of the alphaherpesvirinae, significantly increased cell surface expression of MHC-I, thereby augmenting CTL recognition of infected cells in vitro. Overexpression of Us3 by itself had no effect on cell surface expression of MHC-I and Us3 was not able to phosphorylate MHC-I in vitro, suggesting that Us3 indirectly downregulated cell surface expression of MHC-I in infected cells. We also showed that inactivation of Us3 kinase activity induced significantly more HSV-1-specific CD8⁺ T cells in mice. Interestingly, depletion of CD8⁺ T cells in mice significantly increased replication of a recombinant virus encoding a kinase-dead mutant of Us3, but had no effect on replication of a recombinant virus in which the kinase-dead mutation was repaired. These results indicated that Us3 kinase activity is required for efficient downregulation of cell surface expression of MHC-I and mediates evasion of HSV-1-specific CD8⁺ T cells. Our results also raised the possibility that evasion of HSV-1-specific CD8⁺ T cells by HSV-1 Us3-mediated inhibition of MHC-I antigen presentation might in part contribute to viral replication in vivo.

Pathways of antigen processing

T cell recognition of antigen-presenting cells depends on their expression of a spectrum of peptides bound to major histocompatibility complex class I (MHC-I) and class II (MHC-II) molecules. Conversion of antigens from pathogens or transformed cells into MHC-I- and MHC-II-bound peptides is critical for mounting protective T cell responses, and similar processing of self proteins is necessary to establish and maintain tolerance. Cells use a variety of mechanisms to acquire protein antigens, from translation in the cytosol to variations on the theme of endocytosis, and to degrade them once acquired. In this review, we highlight the aspects of MHC-I and MHC-II biosynthesis and assembly that have evolved to intersect these pathways and sample the peptides that are produced.

Recognition of the nonclassical MHC class I molecule H2-M3 by the receptor Ly49A regulates the licensing and activation of NK cells

The development and function of natural killer (NK) cells is regulated by the interaction of inhibitory receptors of the Ly49 family with distinct peptide-laden major histocompatibility complex (MHC) class I molecules, although whether the Ly49 family is able bind to other MHC class I-like molecules is unclear. Here we found that the prototypic inhibitory receptor Ly49A bound the highly conserved nonclassical MHC class I molecule H2-M3 with an affinity similar to its affinity for H-2D(d). The specific recognition of H2-M3 by Ly49A regulated the 'licensing' of NK cells and mediated 'missing-self' recognition of H2-M3-deficient bone marrow. Host peptide-H2-M3 was required for optimal NK cell activity against experimental metastases and carcinogenesis. Thus, nonclassical MHC class I molecules can act as cognate ligands for Ly49 molecules. Our results provide insight into the various mechanisms that lead to NK cell tolerance.

Dendritic cell activation and memory cell development are impaired among mice administered medroxyprogesterone acetate prior to mucosal herpes simplex virus type 1 infection

Epidemiological studies indicate that the exogenous sex steroid medroxyprogesterone acetate (MPA) can impair cell-mediated immunity, but mechanisms responsible for this observation are not well defined. In this study, MPA administered to mice 1 wk prior to HSV type 1 (HSV-1) infection of their corneal mucosa impaired initial expansion of viral-specific effector and memory precursor T cells and reduced the number of viral-specific memory T cells found in latently infected mice. MPA treatment also dampened expression of the costimulatory molecules CD40, CD70, and CD80 by dendritic cells (DC) in lymph nodes draining acute infection, whereas coculture of such DC with T cells from uninfected mice dramatically impaired ex vivo T cell proliferation compared with the use of DC from mice that did not receive MPA prior to HSV-1 infection. In addition, T cell expansion was comparable to that seen in untreated controls if MPA-treated mice were administered recombinant soluble CD154 (CD40L) concomitant with their mucosal infection. In contrast, the immunomodulatory effects of MPA were infection site dependent, because MPA-treated mice exhibited normal expansion of virus-specific T cells when infection was systemic rather than mucosal. Taken together, our results reveal that the administration of MPA prior to viral infection of mucosal tissue impairs DC activation, virus-specific T cell expansion, and development of virus-specific immunological memory.

A lentiviral vector-based, herpes simplex virus 1 (HSV-1) glycoprotein B vaccine affords cross-protection against HSV-1 and HSV-2 genital infections

Genital herpes is caused by herpes simplex virus 1 (HSV-1) and HSV-2, and its incidence is constantly increasing in the human population. Regardless of the clinical manifestation, HSV-1 and HSV-2 infections are highly transmissible to sexual partners and enhance susceptibility to other sexually transmitted infections. An effective vaccine is not yet available. Here, HSV-1 glycoprotein B (gB1) was delivered by a feline immunodeficiency virus (FIV) vector and tested against HSV-1 and HSV-2 vaginal challenges in C57BL/6 mice. The gB1 vaccine elicited cross-neutralizing antibodies and cell-mediated responses that protected 100 and 75% animals from HSV-1- and HSV-2-associated severe disease, respectively. Two of the eight fully protected vaccinees underwent subclinical HSV-2 infection, as demonstrated by deep immunosuppression and other analyses. Finally, vaccination prevented death in 83% of the animals challenged with a HSV-2 dose that killed 78 and 100% naive and mock-vaccinated controls, respectively. Since this FIV vector can accommodate two or more HSV immunogens, this vaccine has ample potential for improvement and may become a candidate for the development of a truly effective vaccine against genital herpes.

Use of PCR-based assays for the detection of the adventitious agent porcine circovirus type 1 (PCV1) in vaccines, and for confirming the identity of cell substrates and viruses used in vaccine production

Safety and quality are important issues for vaccines. Whereas reversion to virulence poses a safety risk with live attenuated vaccines, the potential for the presence of adventitious agents is also an issue of vaccine quality. The recent detection or porcine circovirus type 1 (PCV1) in human vaccines has further highlighted the importance of quality control in vaccine production. The purpose of this study was to use a novel conventional PCR to detect PCV1, and subsequently screen materials used in the manufacture of vaccines at Bharat Biotech International Limited, India. The genome or gene fragments of PCV1 were not detected in any of the vaccines and materials tested, including the live attenuated rotavirus vaccine candidate ROTAVAC(®). Further, the identity of the cells and the viruses used as starting materials in the manufacture of these vaccines was confirmed by species-specific PCR or virus-specific RT-PCR, and no cross-contamination was detected in any case. The methods can be applied for regular in-house quality control screening of raw materials and seeds/banks, as well as formulated vaccines.

B7 costimulation molecules encoded by replication-defective, vhs-deficient HSV-1 improve vaccine-induced protection against corneal disease

Herpes simplex virus 1 (HSV-1) causes herpes stromal keratitis (HSK), a sight-threatening disease of the cornea for which no vaccine exists. A replication-defective, HSV-1 prototype vaccine bearing deletions in the genes encoding ICP8 and the virion host shutoff (vhs) protein reduces HSV-1 replication and disease in a mouse model of HSK. Here we demonstrate that combining deletion of ICP8 and vhs with virus-based expression of B7 costimulation molecules created a vaccine strain that enhanced T cell responses to HSV-1 compared with the ICP8⁻vhs⁻ parental strain, and reduced the incidence of keratitis and acute infection of the nervous system after corneal challenge. Post-challenge T cell infiltration of the trigeminal ganglia and antigen-specific recall responses in local lymph nodes correlated with protection. Thus, B7 costimulation molecules expressed from the genome of a replication-defective, ICP8⁻vhs⁻ virus enhance vaccine efficacy by further reducing HSK.

CXCL10 expressing hematopoietic-derived cells are requisite in defense against HSV-1 infection in the nervous system of CXCL10 deficient mice

The chemokine CXCL10 is crucial for the control of viral replication through the regulation of mobilization of antigen-specific T cells to sites of infection. CXCL10 is highly expressed both at sites of inflammation as well as constitutively within lymphoid organs by both bone marrow (BM)-derived and non-BM-derived cells. However, the relative immunologic importance of CXCL10 expressed by these divergent sources relative to HSV-1 infection is unknown. Using mouse chimeras reconstituted with either wild type or CXCL10 deficient mouse BM, we show BM-derived, radiation-sensitive cells from wild type mice were solely responsible for resistance to HSV-1 in the trigeminal ganglia and brain stem. The resistance was not reflected by a deficiency in the recruitment of effector cells to sites of inflammation or expression of chemokines or IFN-gamma and likely results from additional, yet-to-be-determined factors emanating from wild type, BM-derived cells.

Defective cross-presentation of viral antigens in GILT-free mice

Gamma-interferon-inducible lysosomal thiolreductase (GILT) promotes major histocompatibility complex (MHC) class II-restricted presentation of exogenous antigens containing disulfide bonds. Here, we show that GILT also facilitates MHC class I-restricted recognition of such antigens by CD8+ T cells, or cross-presentation. GILT is essential for cross-presentation of a CD8+ T cell epitope of glycoprotein B (gB) from herpes simplex virus 1 (HSV-1) but not for its presentation by infected cells. Initiation of the gB-specific CD8+ T cell response during HSV-1 infection, or cross-priming, is highly GILT-dependent, as is initiation of the response to the envelope glycoproteins of influenza A virus. Efficient cross-presentation of disulfide-rich antigens requires a complex pathway involving GILT-mediated reduction, unfolding, and partial proteolysis, followed by translocation into the cytosol for proteasomal processing.

Inflation and long-term maintenance of CD8 T cells responding to a latent herpesvirus depend upon establishment of latency and presence of viral antigens

Following the priming and contraction phases of the T cell response, latent persistent herpesviruses lead to an accumulation of large pools of virus-specific CD8 T cells, also known as memory inflation (MI). The mechanism of this inflation is incompletely understood, largely because the molecular reactivation of these viruses in vivo and its impact upon T cell biology have not been resolved in mice, and because the relevant observations in humans remain, by necessity, correlative. Understanding these processes is essential from the standpoint of the proposed critical role for latent herpesviruses in aging of the immune system. We studied the causes of memory CD8 T cell accumulation following systemic HSV-1 administration as a model of widespread latent viral infection in humans. A direct role of viral latency and Ag-specific restimulation in driving the accumulation and maintenance of inflated CD8 T cells and a strongly suggested role of viral reactivation in that process were shown by the following: 1) lack of MI in the absence of established latency; 2) prevention or delay of MI with drugs that curtail viral replication; and 3) abrogation of MI by the transfer of inflated T cells into a virus-free environment. These results strongly suggest that periodic, subclinical reactivations of a latent persistent virus cause dysregulation of memory CD8 T cell homeostasis, similar to the one in humans. Moreover, results with antiviral drugs suggest that this approach could be considered as a treatment modality for maintaining T cell diversity and/or function in old age.

Herpesvirus gB-induced fusion between the virion envelope and outer nuclear membrane during virus egress is regulated by the viral US3 kinase

Herpesvirus capsids collect along the inner surface of the nuclear envelope and bud into the perinuclear space. Enveloped virions then fuse with the outer nuclear membrane (NM). We previously showed that herpes simplex virus (HSV) glycoproteins gB and gH act in a redundant fashion to promote fusion between the virion envelope and the outer NM. HSV mutants lacking both gB and gH accumulate enveloped virions in herniations, vesicles that bulge into the nucleoplasm. Earlier studies had shown that HSV mutants lacking the viral serine/threonine kinase US3 also accumulate herniations. Here, we demonstrate that HSV gB is phosphorylated in a US3-dependent manner in HSV-infected cells, especially in a crude nuclear fraction. Moreover, US3 directly phosphorylated the gB cytoplasmic (CT) domain in in vitro assays. Deletion of gB in the context of a US3-null virus did not add substantially to defects in nuclear egress. The majority of the US3-dependent phosphorylation of gB involved the CT domain and amino acid T887, a residue present in a motif similar to that recognized by US3 in other proteins. HSV recombinants lacking gH and expressing either gB substitution mutation T887A or a gB truncated at residue 886 displayed substantial defects in nuclear egress. We concluded that phosphorylation of the gB CT domain is important for gB-mediated fusion with the outer NM. This suggested a model in which the US3 kinase is incorporated into the tegument layer (between the capsid and envelope) in HSV virions present in the perinuclear space. By this packaging, US3 might be brought close to the gB CT tail, leading to phosphorylation and triggering fusion between the virion envelope and the outer NM.

Dysregulation of CXCR3 signaling due to CXCL10 deficiency impairs the antiviral response to herpes simplex virus 1 infection

The chemokine, CXCL10, chemotactic for NK cells, activated T cells, and dendritic cells is highly expressed during viral infections, including HSV-1. The importance of this chemokine to the control of HSV-1 infection was tested using mice deficient in CXCL10 (CXCL10(-/-)). Following corneal infection, HSV-1 viral titers were elevated in the nervous system of CXCL10(-/-) mice, which correlated with defects in leukocyte recruitment including dendritic cells, NK cells, and HSV-1-specific CD8(+) T cells to the brain stem. In the absence of NK cells and HSV-1-specific CD8(+) T cells in wild-type (WT) or CXCL10(-/-) mice, similar levels of virus were recovered in the nervous system, suggesting these cells are responsible for the observed defects in the control of viral replication in CXCL10(-/-) mice. Leukocyte mobilization was also compared between WT, CXCL10(-/-), and mice deficient in the only known receptor for CXCL10, CXCR3 (CXCR3 (-/-)). NK cell mobilization was comparably reduced in both CXCL10(-/-) and CXCR3(-/-) mice relative to WT animals. However, the reduction in mobilization of HSV-1-specific CD8(+) T cells in CXCL10(-/-) was not observed in CXCR3(-/-) mice following HSV-1 infection. The defect was not the result of an alternative receptor for CXCL10, as Ag-specific CD8(+) T cell recruitment was not reduced in mice which were deficient in both CXCL10 and CXCR3. Thus, CXCL10 deficiency results in reduced mobilization of HSV-1-specific CD8(+) T cells as a result of dysregulation of CXCR3 signaling.

Psychological stress exacerbates primary vaginal herpes simplex virus type 1 (HSV-1) infection by impairing both innate and adaptive immune responses

Chronic psychological stress is generally immunosuppressive and contributes to an increase in herpes simplex virus (HSV) pathogenicity. We have previously shown that mice experiencing stress at the time of intranasal HSV infection have increased levels of infectious virus in their nasal cavity, as compared to control mice that were not subjected to stress. We have extended our studies to determine the effects of stress at another clinically-relevant mucosal site by examining the immune response to and pathogenesis of vaginal HSV infection. Mice experiencing psychological stress during vaginal HSV infection exhibited an increase in both vaginal viral titers and the pathology associated with this HSV infection. We demonstrate that these observations result from the failure of both the innate and HSV-specific adaptive immune responses. At 2 days post-infection, NK cell numbers were significantly decreased in mice experiencing restraint stress. Studies examining the adaptive immune response revealed a decrease in the number of HSV-specific CD8(+) T cells in not only the vaginal tissue itself but also the draining iliac lymph nodes (ILN). Furthermore, the number of functional cells, in terms of both their degranulation and interferon-gamma production, in the ILN of stressed mice was decreased as compared to non-stressed mice. We conclude that psychological stress, through its suppression of both innate and adaptive immune responses, may be an important factor in the ability to control vaginal HSV infection.

Psychological stress impairs the local CD8+ T cell response to mucosal HSV-1 infection and allows for increased pathogenicity via a glucocorticoid receptor-mediated mechanism

Psychological stress and its associated increases in corticosterone are generally immunosuppressive and contribute to increased herpes simplex virus (HSV)-associated pathogenicity. However, the impact of stress on local control of the initial mucosal-based HSV infection has not been elucidated, nor have the ramifications of such failures of the immune response in terms of viral spread. To address these gaps in knowledge, the studies described herein sought to determine how psychological stress and associated increases in corticosterone may increase susceptibility to HSV encephalitis by allowing for increased viral titers at the site of initial infection. We have shown that in mice intranasally infected with HSV-1, a cell-mediated immune response occurs in the nasopharyngeal-associated lymphoid tissue (NALT), mediastinal lymph nodes (MLN), and superficial cervical lymph nodes (CLN). However, psychological stress induced by restraint decreased the number of lymphocytes in these tissues in HSV-infected mice. Surprisingly, the effects of this restraint stress on HSV-specific CTL function varied by immune tissue. Increased viral titers were found in the nasal cavity of stressed mice, an observation which correlated with an increased CD8+ cell response in the CLN. These findings led us to extend our studies to also determine the ramifications of decreased numbers of locally derived lymphocytes on viral titers following infection. Using an approach in which the NALT was surgically removed prior to infection, we confirmed that decreased numbers of NALT-derived lymphocytes at the time of infection allows for increased viral replication. We conclude that the increased viral titers observed in mice experiencing psychological stress are the consequence of a glucocorticoid-mediated reduction in the numbers of lymphocytes responsible for resolving the initial infection.

Age-related dysregulation of CD8+ T cell memory specific for a persistent virus is independent of viral replication

The immune system devotes substantial resources to the lifelong control of persistent pathogens, which were hypothesized to play an important role in immune aging. Specifically, the presence of latent herpesviruses has been correlated with immune exhaustion and shorter lifespan in octogenarians. But neither the causality nor the mechanistic link(s) were established, and the relative roles of persistent antigenic stimulation and of virus-independent homeostatic disturbances in T cell aging remain unresolved. We longitudinally analyzed expansion, contraction, and long-term maintenance of CD8(+) T cells responding to localized infection with a latent virus, HSV-1. Young mice exhibited the expected expansion and contraction of HSV-1-specific cells and the stable maintenance of memory T cells into advanced adulthood. However, upon entry into senescence, many (>40%) animals exhibited an accumulation in Ag-specific cells (memory inflation) which in some animals was comparable to that observed in acute infection. Inflation occurred to the same extent in control mice and mice continuously treated with the anti-HSV drug famciclovir, which inhibits viral replication and was able to reduce expression of the glycoprotein B. Age-related inflation was also found long after infection with an acute virus. The inflating cells largely maintained Ag-specific function, and exhibited typical central memory phenotype, with no signs of Ag-specific activation. They exhibited increased expression of CD122 and CD127, akin to the Ag-independent T cell clonal expansions found in old specific pathogen-free laboratory mice. This collectively suggests that, in this model, the inflating cells may be selected for high responsiveness to environmental cytokines largely in an Ag-independent manner.

The role of chemokines during herpes simplex virus-1 infection

Herpes simplex virus-type 1 is among the most prevalent and successful humans pathogens. Although infection is largely uncomplicated in the immunocompetent human host, HSV-1 infection can cause blinding corneal disease, and individuals with defects in innate or adaptive immunity are susceptible to herpes simplex encephalitis. Chemokines regulate leukocyte trafficking to inflamed tissues and play a crucial role in orchestrating the immune response to HSV-1 infection. In this review we will focus on the pathways that induce chemokine expression during HSV-1 infection and the implications of chemokine signaling on control of viral replication.

Adaptive immune responses fail to provide protection against genital HSV-2 infection in the absence of IL-15

IL-15 plays a crucial role in innate defense against viral infections. The role of IL-15 in the generation and function of adaptive immunity, following mucosal immunization, against genital HSV-2 has not been studied. Here, we report that immunized IL-15(-/-) mice were able to generate antibody and T cell-mediated immune responses against HSV-2, comparable to those seen in immunized B6 mice. However, immunized IL-15(-/-) mice were not protected against subsequent HSV-2 challenge, compared to B6 immunized mice, even with a ten times lower challenge dose. We then examined if the adaptive immune responses generated in the absence of IL-15 could provide protection against HSV-2 in an IL-15-positive environment. Adoptive transfer of lymphocytes from immunized IL-15(-/-) to naive mice were able to provide protection against HSV-2 challenge similar to protection with immunized cells from control mice. This suggests that the adaptive immune responses raised in the absence of IL-15 are functional in vivo. Reconstitution of the innate components, particularly IL-15, NK cells and NK cell-derived IFN-gamma, in immunized IL-15(-/-) mice restored their protective adaptive immunity against subsequent genital HSV-2 challenge. Our results clearly suggest that innate antiviral activity of IL-15 is necessary for protective adaptive immunity against genital HSV-2 infection.

The cycle of human herpes simplex virus infection: virus transport and immune control

After infection of skin or mucosa, herpes simplex virus enters the sensory nerve endings and is conveyed by retrograde axonal transport to the dorsal root ganglion, where the virus develops lifelong latency. Intermittent reactivation, which is spontaneous in humans, leads to anterograde transport of virus particles and proteins to the skin or mucosa, where the virus is shed and/or causes disease. Immune control of viral infection and replication occurs at the level of skin or mucosa during initial or recurrent infection and also within the dorsal root ganglion, where immune mechanisms control latency and reactivation. This article examines current views on the mechanisms of retrograde and anterograde transport of the virus in axons and the mechanisms of innate and adaptive immunity that control infection in the skin or mucosa and in the dorsal root ganglion--in particular, the role of interferons, myeloid and plasmacytoid dendritic cells, CD4(+) and CD8(+) T cells, and interferon- gamma and other cytokines, including their significance in the development of vaccines for genital herpes.

Bone marrow-derived cells expand memory CD8+ T cells in response to viral infections of the lung and skin

While naive CD8(+) T cells have been shown to require bone marrow-derived dendritic cells (DC) to initiate immunity, such a requirement for memory CD8(+) T cells has had limited assessment. By generating bone marrow chimeras that express the appropriate antigen-presenting molecules on either radiation-sensitive bone marrow-derived or radiation-resistant non-bone marrow-derived compartments, we showed that both primary and secondary immune responses to influenza virus infection of the lung were initiated in the draining LN. This required cells of bone marrow origin, most likely DC, for optimal expansion within the secondary lymphoid compartment. This was similarly the case with HSV-1 infection of the skin. As Langerhans cells are radioresistant, unlike other DC populations, these studies also demonstrate that the radiosensitive DC responsible for secondary expansion of HSV-specific memory are not Langerhans cells.

Th-cytotoxic T-lymphocyte chimeric epitopes extended by Nepsilon-palmitoyl lysines induce herpes simplex virus type 1-specific effector CD8+ Tc1 responses and protect against ocular infection

Molecularly defined vaccine formulations capable of inducing antiviral CD8+ T-cell-specific immunity in a manner compatible with human delivery are limited. Few molecules achieve this target without the support of an appropriate immunological adjuvant. In this study, we investigate the potential of totally synthetic palmitoyl-tailed helper-cytotoxic-T-lymphocyte chimeric epitopes (Th-CTL chimeric lipopeptides) to induce herpes simplex virus type 1 (HSV-1)-specific CD8+ T-cell responses. As a model antigen, the HSV-1 glycoprotein B498-505 (gB498-505) CD8+ CTL epitope was synthesized in line with the Pan DR peptide (PADRE), a universal CD4+ Th epitope. The peptide backbone, composed solely of both epitopes, was extended by N-terminal attachment of one (PAM-Th-CTL), two [(PAM)2-Th-CTL], or three [(PAM)3-Th-CTL] palmitoyl lysines and delivered to H2b mice in adjuvant-free saline. Potent HSV-1 gB498-505-specific antiviral CD8+ T-cell effector type 1 responses were induced by each of the palmitoyl-tailed Th-CTL chimeric epitopes, irrespective of the number of lipid moieties. The palmitoyl-tailed Th-CTL chimeric epitopes provoked cell surface expression of major histocompatibility complex and costimulatory molecules and production of interleukin-12 and tumor necrosis factor alpha proinflammatory cytokines by immature dendritic cells. Following ocular HSV-1 challenge, palmitoyl-tailed Th-CTL-immunized mice exhibited a decrease of virus replication in the eye and in the local trigeminal ganglion and reduced herpetic blepharitis and corneal scarring. The rational of the molecularly defined vaccine approach presented in this study may be applied to ocular herpes and other viral infections in humans, providing steps are taken to include appropriate Th and CTL epitopes and lipid groups.

Latent infection with herpes simplex virus is associated with ongoing CD8+ T-cell stimulation by parenchymal cells within sensory ganglia

CD8+ T-cell persistence can be seen in ganglia harboring latent herpes simplex virus (HSV) infection. While there is some evidence that these cells suppress virus reactivation, this view remains controversial. Given that maintenance of latency by CD8+ T cells would necessitate ongoing exposure to antigen within this site, we sought evidence for such chronic stimulation. Initial experiments showed infiltration by activated but not naïve CD8+ T cells into ganglia harboring latent HSV infection. While such infiltration was independent of T-cell specificity, once recruited, only virus-specific T cells expressed high levels of preformed granzyme B, a marker of ongoing activation. Moreover, bone marrow replacement chimeras showed that these elevated granzyme levels were totally dependent on presentation by parenchymal cells within the ganglia. Overall, this study argues that activated CD8+ T cells are nonspecifically recruited into latently infected ganglia, and in this site they are exposed to ongoing antigen stimulation, most likely by infected neuronal cells.

NKT cells are not critical for HSV‐1 disease resolution

NKT cells are a minor subset of T cells that have important roles in controlling immune responses in disease states including cancer, autoimmunity and pathogenic infections. In contrast to conventional T cells, NKT cells express an invariant TCR and respond to glycolipids presented by CD1d. In this study, we sought to investigate the role of NKT cells in regulating the response to infection with HSV-1, and the mechanism involved, in well-established mouse models. Previous studies of HSV-1 disease in mice have shown clear roles for CD4+ and CD8+ T cells. The role of NKT cells in the resolution of HSV-1 (KOS strain) infection was investigated through flank zosteriform or footpad infection in wild-type versus CD1d-deficient mice, by measurement of viral plaque-forming units at different sites after infection, lesion severity and HSV-1-specific T-cell responses. In contrast to a previous study using a more virulent strain of HSV-1 (SC16 strain), no differences were observed in disease magnitude or resolution, and furthermore, the T-cell response to HSV-1 (KOS strain) was unaltered in the absence of NKT cells. In conclusion, this study shows that NKT cells do not play a general role in controlling the resolution or severity of HSV-1 infection. Instead, the resolution or severity of the infection may depend on the HSV-1 strain under investigation.

Treatment of mice with anti-CD86 mAb reduces CD8+ T cell-mediated CTL activity and enhances ocular viral replication in HSV-1-infected mice

PURPOSE

To determine the relative impact of the CD86 (B7-2) costimulatory molecule in protection against ocular HSV-1 infection.

METHODS

BALB/c mice were depleted of CD86 by antibody and depleted mice were examined for their ability to withstand HSV-1 ocular infection. Depleted mice were tested for the presence of virus replication, T-cell activation, survival, and eye disease.

RESULTS

Mice that had been depleted of CD86 had significantly higher titers of HSV-1 in their eyes compared to mock-depleted infected mice. However, the levels of corneal scarring between the two groups of mice were similar. Following ocular infection, the levels of class I MHC-restricted cytotoxic T lymphocytes (CTL) were significantly higher in mock-depleted mice than in CD86-depleted mice. Finally, adoptive transfer of primed CD8(+) T cells but not CD4(+) T cells to CD86-depleted mice resulted in a decrease in peak virus titers in the eyes, such that HSV-1 titers were similar to that of their mock-depleted counterparts.

CONCLUSIONS

These data demonstrate an important role for CD86 in the development of CTL and reduction of virus replication in the eyes of HSV-1-infected mice.

A soluble divalent class I MHC/IgG1 fusion protein activates CD8+ T cells in vivo

CD8+ T lymphocytes recognize tumor and viral antigens bound to class I major histocompatibility complexes (MHC). Tumors and viruses may evade detection by preventing antigen presentation. The present study was designed to determine whether a soluble divalent fusion protein, containing the extracellular domains of a class I MHC molecule fused to beta2-microglobulin and the constant domains of IgG1, could induce an immune response in vivo. Administration to mice of the fusion protein loaded with a tumor peptide induced peptide-specific T cell activation and retarded tumor growth. Administration of the fusion protein loaded with a glycoprotein B (gB) peptide derived from herpes simplex virus type 1 (HSV-1) induced gB-specific cytotoxic T lymphocytes and protected mice from a lethal HSV-1 challenge. These data suggest that antigen-loaded MHC/IgG fusion proteins may enhance T cell immunity in conditions where antigen presentation is altered.

Adenoviral Vectors for Mucosal Vaccination Against Infectious Diseases

Adenoviral vector has been extensively studied as a vaccine platform because of its ability to induce potent cellular and humoral immunity. One main advantage of adenoviral vectors is their natural tropism for mucosal surfaces, which makes them ideal for the purpose of mucosal vaccination against pathogens that preferentially initiate infection at the mucosal site. The current understanding of mucosal immunity suggests that mucosal vaccination is far superior to parenteral vaccination in protecting mucosal surfaces. Mucosal vaccination is particularly relevant to those infections for which parenteral immunization strategies have failed to confer protection. This review examines the use of adenoviral vector at mucosal sites for infectious disease against which the current vaccination strategies have been unsuccessful in eliciting protection. Data from animal models have suggested that adenoviral vectors are effective in protecting against infections caused by HIV, herpes simplex virus and Mycobacterium tuberculosis. We believe that these encouraging results will lead to further evaluation in clinical trials in the near future.

Development and migration of protective CD8+ T cells into the nervous system following ocular herpes simplex virus-1 infection

After infection of epithelial surfaces, HSV-1 elicits a multifaceted antiviral response that controls the virus and limits it to latency in sensory ganglia. That response encompasses the CD8(+) T cells, whose precise role(s) is still being defined; immune surveillance in the ganglia and control of viral spread to the brain were proposed as the key roles. We tracked the kinetics of the CD8(+) T cell response across lymphoid and extralymphoid tissues after ocular infection. HSV-1-specific CD8(+) T cells first appeared in the draining (submandibular) lymph node on day 5 and were detectable in both nondraining lymphoid and extralymphoid tissues starting on day 6. However, although lymphoid organs contained both resting (CD43(low)CFSE(high)) and virus-specific cells at different stages of proliferation and activation, extralymphoid sites (eye, trigeminal ganglion, and brain) contained only activated cells that underwent more than eight proliferations (CD43(high)CFSE(neg)) and promptly secreted IFN-gamma upon contact with viral Ags. Regardless of the state of activation, these cells appeared too late to prevent HSV-1 spread, which was seen in the eye (from day 1), trigeminal ganglia (from day 2), and brain (from day 3) well before the onset of a detectable CD8(+) T cell response. However, CD8(+) T cells were critical in reducing viral replication starting on day 6 and for its abrogation between days 8 and 10; CD8-deficient animals failed to control the virus, exhibited persisting high viral titers in the brain after day 6, and died of viral encephalitis between days 7 and 12. Thus, CD8(+) T cells do not control HSV-1 spread from primary to tertiary tissues, but, rather, attack the virus in infected organs and control its replication in situ.

Redistribution of cellular and herpes simplex virus proteins from the trans-golgi network to cell junctions without enveloped capsids

Herpes simplex virus (HSV) and other alphaherpesviruses assemble enveloped virions in the trans-Golgi network (TGN) or endosomes. Enveloped particles are formed when capsids bud into TGN/endosomes and virus particles are subsequently ferried to the plasma membrane in TGN-derived vesicles. Little is known about the last stages of virus egress from the TGN/endosomes to cell surfaces except that the HSV directs transport of nascent virions to specific cell surface domains, i.e., epithelial cell junctions. Previously, we showed that HSV glycoprotein gE/gI accumulates extensively in the TGN at early times after infection and also when expressed without other viral proteins. At late times of infection, gE/gI and a cellular membrane protein, TGN46, were redistributed from the TGN to epithelial cell junctions. We show here that gE/gI and a second glycoprotein, gB, TGN46, and another cellular protein, carboxypeptidase D, all moved to cell junctions after infection with an HSV mutant unable to produce cytoplasmic capsids. This redistribution did not involve L particles. In contrast to TGN membrane proteins, several cellular proteins that normally adhere to the cytoplasmic face of TGN, Golgi, and endosomal membranes remained primarily dispersed throughout the cytoplasm. Therefore, cellular and viral membrane TGN proteins move to cell junctions at late times of HSV infection when the production of enveloped particles is blocked. This is consistent with the hypothesis that there are late HSV proteins that reorganize or redistribute TGN/endosomal compartments to promote virus egress and cell-to-cell spread.

Effects of mutations in the cytoplasmic domain of herpes simplex virus type 1 glycoprotein B on intracellular transport and infectivity

Herpes simplex virus type 1 (HSV-1) is a human pathogen of the alphaherpesvirus family which infects and spreads in the nervous system. Glycoproteins play a key role in the process of assembly and maturation of herpesviruses, which is essential for neuroinvasion and transneuronal spread. Glycoprotein B (gB) is a main component of the HSV-1 envelope and is necessary for the production of infectious particles. The cytoplasmic domain of gB, the longest one among HSV-1 glycoproteins, contains several highly conserved peptide sequences homologous to motifs involved in intracellular sorting. To determine the specific roles of these motifs in processing, subcellular localization, and the capacity of HSV-1 gB to complement a gB-null virus, we generated truncated or point mutated forms of a green fluorescent protein (GFP)-tagged gB. GFP-gB with a deletion in the acidic cluster DGDADEDDL (amino acids [aa] 896 to 904) behaved the same as the parental form. Deletion or disruption of the YTQV motif (aa 889 to 892) abolished internalization and reduced complementation by 60%. Disruption of the LL motif (aa 871 to 872) impaired the return of the protein to the trans-Golgi network (TGN) while enhancing its recycling to the plasma membrane. Truncations from residue E 857 abolished transport and processing of the truncated proteins, which had null complementation activity, through the Golgi complex. Altogether, our results favor a model in which HSV-1 gets its final envelope in the TGN, and they suggest that endocytosis, albeit not necessary, might play a role in infectivity.

Intravascular naked DNA vaccine encoding glycoprotein B induces protective humoral and cellular immunity against herpes simplex virus type 1 infection in mice

Naked plasmid DNA (pDNA) vaccine expressing herpes simplex virus type 1 (HSV-1) glycoprotein B (gB) was tested for protective activity against acute HSV-1 infection in mice. The pDNA was intravenously injected into Balb/c mice via their tail vein under high pressure, and the vaccination was performed two times at an interval of 7 days. The gB gene vaccination significantly protected the mice from subsequent intraperitoneal challenge with a lethal dose of HSV-1, which killed all the animals given control plasmid or saline. The protective activity was correlated with the dose of the plasmid inoculated, the survival rate reaching 83% in mice vaccinated with 5 microg of pDNA. The vaccinated mice were also protected from latent HSV infection. The immunized mice showed significant elevation in neutralizing antibody against HSV-1 as well as serum levels of interleukin-12 (IL-12) and interferon-gamma (IFN-gamma). When mice were immunized with 5 microg of an Epstein-Barr virus (EBV)-based plasmid vector harboring the gB, the cytotoxic T lymphocytes (CTLs) activity and proliferative response for HSV-1 were also induced. The results strongly suggest that intravenous immunization of naked pDNA may induce humoral and cellular immune responses against the virus, leading to a significant prophylactic outcome against HSV-1 infection in mice.

Immunological properties of a DNA plasmid encoding a chimeric protein of herpes simplex virus type 2 glycoprotein B and glycoprotein D

A DNA plasmid containing a chimeric sequence encoding both herpes simplex virus type 2 (HSV-2) glycoprotein B (gB) and glycoprotein D (gD) external domains (pcgDB) was used to immunize BALB/c mice against genital HSV-2 infection. To determine the efficacy of this vaccine, groups of mice immunized with the pcgDB plasmid were compared with animals immunized with plasmids corresponding to the individual proteins (pcgBt or pcgDt), administered separately or in combination (pcgBt + pcgDt). We studied the response of the different mouse groups to viral challenge by analyzing clinical disease (vaginitis), serum antibody levels, as well as lymphoproliferative responses and cytokine production by spleen cells. Increased IFN-gamma levels correlated with prolonged survival in mice immunized with the plasmid pcgDB, relative to mice immunized with plasmids coding for the individual proteins alone or in combination. Our results show that immunization with the plasmid encoding the chimeric protein is advantageous over separate proteins. These findings may have important implications for the development of multivalent DNA vaccines against HSV and other complex pathogens.

Cutting edge: conventional CD8 alpha+ dendritic cells are preferentially involved in CTL priming after footpad infection with herpes simplex virus-1

CTL play a major role in immunity to HSV type 1, but little is known about the priming process. In this study, we have examined the class I-restricted presentation of an immunodominant determinant from HSV-1 glycoprotein B after footpad infection. We have found that the only cell types capable of presenting this determinant in draining popliteal lymph nodes within the first 3 days after infection are the CD11c(+)CD8alpha(+)CD45RA(-) dendritic cells. Given that such class I-restricted presentation is essential for CTL priming, this implies that these conventional CD8alpha(+) dendritic cells are the key subset involved in CTL immunity to this virus.

The early expression of glycoprotein B from herpes simplex virus can be detected by antigen-specific CD8+ T cells

The immune response to cutaneous herpes simplex virus type 1 (HSV-1) infection begins with remarkable rapidity. Activation of specific cytotoxic T lymphocytes (CTL) begins within hours of infection, even though the response within the draining lymph nodes peaks nearly 5 days later. HSV gene products are classified into three main groups, alpha, beta, and gamma, based on their kinetics and requirements for expression. In C57BL/6 mice, the immunodominant epitope from HSV is derived from glycoprotein B (gB(498-505)). While gB is considered a gamma or "late" gene product, previous reports have indicated that some level of gene expression may occur soon after infection. Using brefeldin A as a specific inhibitor of viral antigen presentation to major histocompatibility complex class I-restricted CTL, we have formally addressed the timing of gB peptide expression in an immunologically relevant manner following infection. Presentation of gB peptide detected by T-cell activation was first observed within 2 h of infection. Comparison with another viral epitope expressed early during infection, HSV-1 ribonucleotide reductase, demonstrated that gB is presented with the same kinetics as this classical early-gene product. Moreover, this rapidity of gB expression was further illustrated via rapid priming of naïve transgenic CD8(+) T cells in vivo after HSV-1 infection of mice. These results establish that gB is expressed rapidly following HSV-1 infection, at levels capable of effectively stimulating CD8(+) T cells.

Quantitative assessment of antigen-specific CD8+ T cells in the mouse: application to vaccine research

An effective HIV vaccine will likely need to induce potent and broad-based immunity, including CD8+ T cell responses. Hence, a quantitative assay to measure such responses in animal models will be important in the evaluation of candidate HIV vaccines. We show here that a single immunization with HIV DNA vaccines, followed by challenge with recombinant vaccinia virus expressing the relevant HIV antigen, allows quantitative assessment of CD8+ T cell responses. These responses can be profound (>30% of total CD8+ T cells) and directly reflect the level of memory CD8+ T cells at the time of challenge. Therefore, this assay will facilitate the selection of promising HIV vaccine candidates for further evaluation.

Direct link between mhc polymorphism, T cell avidity, and diversity in immune defense

Major histocompatibility complex (mhc)-encoded molecules govern immune responses by presenting antigenic peptides to T cells. The extensive polymorphism of genes encoding these molecules is believed to enhance immune defense by broadening the array of antigenic peptides available for T cell recognition, but direct evidence supporting the importance of this mechanism in combating pathogens is limited. Here we link mhc polymorphism-driven diversification of the cytotoxic T lymphocyte (CTL) repertoire to the generation of high-avidity, protective antiviral T cells and to superior antiviral defense. Thus, much of the beneficial effect of the mhc polymorphism in immune defense may be due to its critical influence on the properties of the selected CTL repertoire.

Multiple proteases process viral antigens for presentation by MHC class I molecules to CD8(+) T lymphocytes

Recognition by CD8(+) cytotoxic T lymphocytes of any intracellular viral protein requires its initial cytosolic proteolytic processing, the translocation of processed peptides to the endoplasmic reticulum via the transporters associated with antigen processing, and their binding to nascent major histocompatibility complex (MHC) class I molecules that then present the antigenic peptides at the infected cell surface. From initial assumptions that the multicatalytic and ubiquitous proteasome is the only protease capable of fully generating peptide ligands for MHC class I molecules, the last few years have seen the identification of a number of alternative proteases that contribute to endogenous antigen processing. Trimming by non-proteasomal proteases of precursor peptides produced by proteasomes is now a well-established fact. In addition, proteases that can process antigens in a fully proteasome-independent fashion have also been identified. The final level of presentation of many viral epitopes is probably the result of interplay between different proteolytic activities. This expands the number of tissues and physiological and pathological situations compatible with antigen presentation, as well as the universe of pathogen-derived sequences available for recognition by CD8(+) T lymphocytes.

Immunization with combined HSV-2 glycoproteins B2 : D2 gene DNAs: protection against lethal intravaginal challenges in mice

The immunity of a combined DNA vaccine of HSV-2 glycoproteins B2 (gB2) and D2 (gD2) genes in comparison to individual vaccines was studied with regard to protecting against the HSV infection. Two recombinant DNA vaccines of the pHS2-gB2 or pHS2-gD2 were constructed and formulated. The neutralizing antibody titers appeared higher in the B2 : D2 gene cocktail-vaccinated mice than that of the individual B2 or D2 gene-vaccinated group alone, and the positive KOS control induced higher titer of the neutralizing antibody than combined or individual gene vaccines. The mock-immunized mice failed to induce enough. The ranks for the CTL activity and the protection rates against the lethal intravaginal challenge were shown as KOS > B2:D2 cocktail > D2 > B2 gene vaccines. The vaginal external diseases in the B2 : D2 or D-vaccinated mice were significantly reduced against the challenging dosages. The virus titers in the vaginal secretions of the vaccinated mice significantly reduced with time, and the B2 : D2 gene vaccine decreased more than each individual vaccine alone. It can be concluded that the cocktailed vaccines are more effective in the humoral and cellular immune responses in the mice, and in the protection of the mice against the intravaginal challenging dosages when compared with individual gene vaccines. All the DNA vaccines failed to block the latent infection in sensory nerves.

Induction of cross clade reactive specific antibodies in mice by conjugates of HGP-30 (peptide analog of HIV-1(SF2) p17) and peptide segments of human beta-2-microglobulin or MHC II beta chain

HGP-30, a 30 amino acid synthetic peptide homologous to a conserved region of HIV-1(SF2) p17 (aa86-115), has previously been shown to elicit both cellular and humoral immune responses when conjugated to KLH and adsorbed to alum. However, the free HGP-30 peptide is not immunogenic in animals. In order to improve the immunogenicity of HGP-30, peptide conjugates consisting of a modified HGP-30 sequence (m-HGP-30/aa82-111) and a peptide segment, residues 38-50, of the MHC I accessory molecule, human beta-2-microglobulin (beta-2-M), referred to as Peptide J, or a peptide from the MHC II beta chain (peptide G) were evaluated in mice. The effects of carriers and adjuvants on serum antibody titers, specificities to various HIV-1 clade peptides similar to HGP-30 and isotype patterns were examined. Peptides J or especially G conjugated to modified-HGP-30 (LEAPS 102 and LEAPS 101, respectively) generated comparable or better immune responses to modified HGP-30 than KLH conjugates as judged by the induction of: (1) similar antibody titers; (2) broader HIV clade antigen binding; and (3) antibody isotype response patterns indicative of a TH1 pathway (i.e. increased amounts of IgG2a and IgG2b antibodies). The ISA 51 and MPL(R)-SE adjuvants induced higher antibody responses than alum, with the ISA 51 being more potent. Immune responses to LEAPS 102, as compared to LEAPS 101, were weaker and slower to develop as determined by antibody titers and cross clade reactivity of the antibodies induced. Compared to KLH conjugates which induced significant anti-KLH antibody titers, minimal antibody responses were observed to peptide G, the more immunogenic conjugate, and peptide J. These results suggest that modified HGP-30 L.E.A.P.S. constructs may be useful as HIV vaccine candidates for preferential induction of TH1 directed cell mediated immune responses.

Induction of herpes simplex virus gB-specific cytotoxic T lymphocytes in TAP1-deficient mice by genetic immunization but not HSV infection

Loading of most endogenous peptides on major histocompatibility complex class I molecules is conditional on their transport into the endoplasmic reticulum (ER) by the peptide transporter TAP. We describe an HSV-2/1 cross-reactive cytotoxic T-cell (CTL) epitope that is processed in a TAP1-independent manner in vivo following immunization of TAP1-/- mice with naked DNA or a recombinant vaccinia virus. These data indicated that TAP1-independent processing of endogenous proteins is sufficient to prime CTLs in vivo. TAP1-independent processing of this epitope was not due to ER targeting by signal sequences and exogenous loading of MHC-I molecules and was not influenced by the amino acids flanking this epitope. In contrast, TAP1-/- mice infected with HSV-2 or HSV-2 mutants did not mount a CTL response against this epitope.

Reverse immunogenetic and polyepitopic approaches for the induction of cell-mediated immunity against bovine viral pathogens

The control of several infectious diseases of animals by vaccination is perhaps the most outstanding accomplishment of veterinary medicine in the last century. Even the eradication of some pathogens is in sight, at least in some parts of the world. However, infectious diseases continue to cost millions of dollars to the livestock industry. One of the reasons for the failure to control certain pathogens is the limited emphasis placed on cell-mediated immunity (CMI) in the design of vaccines against these pathogens. Traditionally, vaccine-induced immunity has been studied in relation to antibody-mediated protection. More recent studies, however, have focused on understanding CMI and developing means of inducing CMI. This review focuses on recent advances made in the study of CMI in general and of cytotoxic T lymphocytes in particular. Parallels from studies in human and mouse immunology are drawn in order to point out implications to bovine immunology, specifically for immunity against bovine herpesvirus 1.

Induction of mucosal homing virus-specific CD8(+) T lymphocytes by attenuated simian immunodeficiency virus

Induction of virus-specific T-cell responses in mucosal as well as systemic compartments of the immune system is likely to be a critical feature of an effective AIDS vaccine. We investigated whether virus-specific CD8(+) lymphocytes induced in rhesus macaques by immunization with attenuated simian immunodeficiency virus (SIV), an approach that is highly effective in eliciting protection against mucosal challenge, express the mucosa-homing receptor alpha4beta7 and traffic to the intestinal mucosa. SIV-specific CD8(+) T cells expressing alpha4beta7 were detected in peripheral blood and intestine of macaques infected with attenuated SIV. In contrast, virus-specific T cells in blood of animals immunized cutaneously by a combined DNA-modified vaccinia virus Ankara regimen did not express alpha4beta7. These results demonstrate the selective induction of SIV-specific CD8(+) T lymphocytes expressing alpha4beta7 by a vaccine approach that replicates in mucosal tissue and suggest that induction of virus-specific lymphocytes that are able to home to mucosal sites may be an important characteristic of a successful AIDS vaccine.

Expression of intracellular IFN-gamma in HSV-1-specific CD8+ T cells identifies distinct responding subpopulations during the primary response to infection

Cutaneous infection in the footpads of C57BL/6 mice with HSV-1 results in an accumulation of activated (CD44high CD25+) CD8+ T cells within the draining popliteal lymph node (PLN). These studies were undertaken to evaluate the frequency and phenotype of the CD8+ T cell population within the PLN, recognizing the single immunodominant HSV-1 epitope derived from the viral envelope glycoprotein, glycoprotein B (gB), using an intracellular IFN-gamma-staining assay. It revealed that approximately 6% of the CD8+ T cells were specific for the gB epitope. Phenotypic analysis of the IFN-gamma-producing gB-specific CD8+ T cells generated in the PLN during the course of the acute infection expressed the CD44high CD25+ phenotype on days 3-5 postinfection. Surprisingly, IFN-gamma-producing CD8+ T cells expressed the CD44high CD25- phenotype on days 5-8 postinfection, in contrast to expectations for a CD8+ effector T cell. IFN-gamma-producing CD25- CD8+ T cells were detected in the PLN on day 21 postinfection, long after infectious virus had been cleared. Throughout the response, the spleen was found to be the major reservoir of gB-specific CD8+ T cells, even during the peak of the response. In contrast to the gB-specific CD8+ T cell population within the PLN, the entire gB-specific CD8+ T cell population within the spleen was CD25-. Collectively, these results suggest the generation of subpopulations of virus-specific CD8+ T cells, distinguished by the expression of CD25, during the acute phase of the primary response to a localized viral infection.