Steven L. Wechsler

Lipopeptide vaccines—yesterday, today, and tomorrow

Peptide-based vaccines offer several potential advantages over the conventional whole proteins (or whole gene, in the case of genetic immunisation) in terms of purity and a high specificity in eliciting immune responses. However, concerns about toxic adjuvants, which are critical for immunogenicity of synthetic peptides, still remain. Lipopeptides, a form of peptide vaccine, discovered more then a decade ago, are currently under intensive investigation because they can generate comprehensive immune responses, without the use of adjuvants. In this review, we address the past of lipopeptide vaccines, highlight the progress made toward their optimisation, and stress future challenges and issues related to their synthesis, formulation, and delivery. In particular, the recent development of mucosal application of lipopeptide vaccines may present an ideal strategy against many pathogens that infect mucosal surfaces.

Region of Herpes Simplex Virus Type 1 Latency-Associated Transcript Sufficient for Wild-Type Spontaneous Reactivation Promotes Cell Survival in Tissue Culture

ABSTRACT The latency-associated transcript (LAT) is the only abundant herpes simplex virus type 1 (HSV-1) transcript expressed during latency. In the rabbit eye model, LAT null mutants do not reactivate efficiently from latency. We recently demonstrated that the LAT null mutantdLAT2903 induces increased levels of apoptosis in trigeminal ganglia of infected rabbits compared to LAT+strains (G.-C. Perng, C. Jones, J. Ciacci-Zarella, M. Stone, G. Henderson, A. Yokht, S. M. Slanina, F. M. Hoffman, H. Ghiasi, A. B. Nesburn, and C. S. Wechsler, Science 287:1500–1503, 2000).The same study also demonstrated that a plasmid expressing LAT nucleotides 301 to 2659 enhanced cell survival of transfected cells after induction of apoptosis. Consequently, we hypothesized that LAT enhances spontaneous reactivation in part, because it promotes survival of infected neurons. Here we report on the ability of plasmids expressing different portions of the 5′ end of LAT to promote cell survival after induction of apoptosis. A plasmid expressing the first 1.5 kb of LAT (LAT nucleotides 1 to 1499) promoted cell survival in neuro-2A (mouse neuronal) and CV-1 (monkey fibroblast) cells. A plasmid expressing just the first 811 nucleotides of LAT promoted cell survival less efficiently. Plasmids expressing the first 661 nucleotides or less of LAT did not promote cell survival. We previously showed that a mutant expressing just the first 1.5 kb of LAT has wild-type spontaneous reactivation in rabbits, and a mutant expressing just the first 811 nucleotides of LAT has a reactivation frequency higher than that of dLAT2903 but lower than that of wild-type virus. In addition, mutants reported here for the first time, expressing just the first 661 or 76 nucleotides of LAT, had spontaneous reactivation indistinguishable from that of the LAT null mutantdLAT2903. In summary, these studies provide evidence that there is a functional relationship between the ability of LAT to promote cell survival and its ability to enhance spontaneous reactivation.

Molecular cloning and sequence analysis of the human parainfluenza 3 virus gene encoding the matrix protein

The sequence of the matrix (M) protein gene and contiguous intergenic regions of the human parainfluenza 3 virus (PF3) was determined by molecular cloning. The encoded M protein contains 354 amino acids and has a predicted mol wt of 39,506. The M protein amino acid sequence was compared to the homologous proteins from other members of the Paramyxoviridae family. The PF3 protein shared 61% homology with the Sendai virus protein and approximately 35% homology with measles and canine distemper virus proteins. Little homology was observed with respiratory syncytial virus. The M protein appears to be the most highly conserved among the Paramyxoviridae proteins.

The Latency-Associated Transcript Gene Enhances Establishment of Herpes Simplex Virus Type 1 Latency in Rabbits

ABSTRACT The latency-associated transcript (LAT) gene the only herpes simplex virus type 1 (HSV-1) gene abundantly transcribed during neuronal latency, is essential for efficient in vivo reactivation. Whether LAT increases reactivation by a direct effect on the reactivation process or whether it does so by increasing the establishment of latency, thereby making more latently infected neurons available for reactivation, is unclear. In mice, LAT-negative mutants appear to establish latency in fewer neurons than does wild-type HSV-1. However, this has not been confirmed in the rabbit, and the role of LAT in the establishment of latency remains controversial. To pursue this question, we inserted the gene for the enhanced green fluorescent protein (EGFP) under control of the LAT promoter in a LAT-negative virus (ΔLAT-EGFP) and in a LAT-positive virus (LAT-EGFP). Sixty days after ocular infection, trigeminal ganglia (TG) were removed from the latently infected rabbits, sectioned, and examined by fluorescence microscopy. EGFP was detected in significantly more LAT-EGFP-infected neurons than ΔLAT-EGFP-infected neurons (4.9% versus 2%, P < 0.0001). The percentages of EGFP-positive neurons per TG ranged from 0 to 4.6 for ΔLAT-EGFP and from 2.5 to 11.1 for LAT-EGFP (P = 0.003). Thus, LAT appeared to increase neuronal latency in rabbit TG by an average of two- to threefold. These results suggest that LAT enhances the establishment of latency in rabbits and that this may be one of the mechanisms by which LAT enhances spontaneous reactivation. These results do not rule out additional LAT functions that may be involved in maintenance of latency and/or reactivation from latency.

A genital tract peptide epitope vaccine targeting TLR-2 efficiently induces local and systemic CD8 + T cells and protects against herpes simplex virus type 2 challenge

The next generation of needle-free mucosal vaccines is being rationally designed according to rules that govern the way in which the epitopes are recognized by and stimulate the genital mucosal immune system. We hypothesized that synthetic peptide epitopes extended with an agonist of Toll-like receptor 2 (TLR-2), that are abundantly expressed by dendritic and epithelial cells of the vaginal mucosa, would lead to induction of protective immunity against genital herpes. To test this hypothesis, we intravaginally (IVAG) immunized wild-type B6, TLR-2 (TLR2−/−) or myeloid differentiation factor 88 deficient (MyD88−/−) mice with a herpes simplex virus type 2 (HSV-2) CD8+ T-cell peptide epitope extended by a palmitic acid moiety (a TLR-2 agonist). IVAG delivery of the lipopeptide generated HSV-2-specific memory CD8+ cytotoxic T cells both locally in the genital tract draining lymph nodes and systemically in the spleen. Moreover, lipopeptide-immunized TLR2−/− and MyD88−/− mice developed significantly less HSV-specific CD8+ T-cell response, earlier death, faster disease progression, and higher vaginal HSV-2 titers compared to lipopeptide-immunized wild-type B6 mice. IVAG immunization with self-adjuvanting lipid-tailed peptides appears to be a novel mucosal vaccine approach, which has attractive practical and immunological features.

A Gene Capable of Blocking Apoptosis Can Substitute for the Herpes Simplex Virus Type 1 Latency-Associated Transcript Gene and Restore Wild-Type Reactivation Levels

ABSTRACT After ocular herpes simplex virus type 1 (HSV-1) infection, the virus travels up axons and establishes a lifelong latent infection in neurons of the trigeminal ganglia. LAT (latency-associated transcript), the only known viral gene abundantly transcribed during HSV-1 neuronal latency, is required for high levels of reactivation. The LAT function responsible for this reactivation phenotype is not known. Recently, we showed that LAT can block programmed cell death (apoptosis) in neurons of the trigeminal ganglion in vivo and in tissue culture cells in vitro (G.-C. Perng et al., Science 287:1500–1503, 2000; M. Inman et al., J. Virol. 75:3636–3646, 2001). Consequently, we proposed that this antiapoptosis function may be a key to the mechanism by which LAT enhances reactivation. To study this further, we constructed a recombinant HSV-1 virus in which the HSV-1 LAT gene was replaced by an alternate antiapoptosis gene. We used the bovine herpes virus 1 (BHV-1) latency-related (LR) gene, which was previously shown to have antiapoptosis activity, for this purpose. The resulting chimeric virus, designated CJLAT, contains two complete copies of the BHV-1 LR gene (one in each viral long repeat) in place of the normal two copies of the HSV-1 LAT, on an otherwise wild-type HSV-1 strain McKrae genomic background. We report here that in both rabbits and mice reactivation of CJLAT was significantly greater than the LAT null mutant dLAT2903 (P < 0.0004 and P = 0.001, respectively) and was at least as efficient as wild-type McKrae. This strongly suggests that a BHV-1 LR gene function was able to efficiently substitute for an HSV-1 LAT gene function involved in reactivation. Although replication of CJLAT in rabbits and mice was similar to that of wild-type McKrae, CJLAT killed more mice during acute infection and caused more corneal scarring in latently infected rabbits. This suggested that the BHV-1 LR gene and the HSV-1 LAT gene are not functionally identical. However, LR and LAT both have antiapoptosis activity. These studies therefore strongly support the hypothesis that replacing LAT with an antiapoptosis gene restores the wild-type reactivation phenotype to a LAT null mutant of HSV-1 McKrae.

Identification of novel immunodominant CD4+ Th1-type T-cell peptide epitopes from herpes simplex virus glycoprotein D that confer protective immunity.

ABSTRACT The molecular characterization of the epitope repertoire on herpes simplex virus (HSV) antigens would greatly expand our knowledge of HSV immunity and improve immune interventions against herpesvirus infections. HSV glycoprotein D (gD) is an immunodominant viral coat protein and is considered an excellent vaccine candidate antigen. By using the TEPITOPE prediction algorithm, we have identified and characterized a total of 12 regions within the HSV type 1 (HSV-1) gD bearing potential CD4+ T-cell epitopes, each 27 to 34 amino acids in length. Immunogenicity studies of the corresponding medium-sized peptides confirmed all previously known gD epitopes and additionally revealed four new immunodominant regions (gD49-82, gD146-179, gD228-257, and gD332-358), each containing naturally processed epitopes. These epitopes elicited potent T-cell responses in mice of diverse major histocompatibility complex backgrounds. Each of the four new immunodominant peptide epitopes generated strong CD4+ Th1 T cells that were biologically active against HSV-1-infected bone marrow-derived dendritic cells. Importantly, immunization of H-2d mice with the four newly identified CD4+ Th1 peptide epitopes but not with four CD4+ Th2 peptide epitopes induced a robust protective immunity against lethal ocular HSV-1 challenge. These peptide epitopes may prove to be important components of an effective immunoprophylactic strategy against herpes.

HLA-A*0201-Restricted CD8+ Cytotoxic T Lymphocyte Epitopes Identified from Herpes Simplex Virus Glycoprotein D

Evidence obtained from both animal models and humans suggests that T cells specific for HSV-1 and HSV-2 glycoprotein D (gD) contribute to protective immunity against herpes infection. However, knowledge of gD-specific human T cell responses is limited to CD4+ T cell epitopes, with no CD8+ T cell epitopes identified to date. In this study, we screened the HSV-1 gD amino acid sequence for HLA-A*0201-restricted epitopes using several predictive computational algorithms and identified 10 high probability CD8+ T cell epitopes. Synthetic peptides corresponding to four of these epitopes, each nine to 10 amino acids in length, exhibited high-affinity binding in vitro to purified human HLA-A*0201 molecules. Three of these four peptide epitopes, gD53–61, gD70–78, and gD278–286, significantly stabilized HLA-A*0201 molecules on T2 cell lines and are highly conserved among and between HSV-1 and HSV-2 strains. Consistent with this, in 33 sequentially studied HLA-A*0201-positive, HSV-1-seropositive, and/or HSV-2-seropositive healthy individuals, the most frequent and robust CD8+ T cell responses, assessed by IFN-γ ELISPOT, CD107a/b cytotoxic degranulation, and tetramer assays, were directed mainly against gD53–61, gD70–78, and gD278–286 epitopes. In addition, CD8+ T cell lines generated by gD53–61, gD70–78, and gD278–286 peptides recognized infected target cells expressing native gD. Lastly, CD8+ T cell responses specific to gD53–61, gD70–78, and gD278–286 epitopes were induced in HLA-A*0201 transgenic mice following ocular or genital infection with either HSV-1 or HSV-2. The functional gD CD8+ T cell epitopes described herein are potentially important components of clinical immunotherapeutic and immunoprophylactic herpes vaccines.

Identification of a major regulatory sequence in the latency associated transcript (LAT) promoter of herpes simplex virus type 1 (HSV-1)

The latency associated transcript (LAT) gene is the only viral genomic region that is abundantly transcribed during herpes simplex virus type 1 (HSV-1) neuronal latency. As such, it may play an important role in HSV-1 latency and/or reactivation. The regulation of the LAT gene is complex and appears to include a combination of positive and negative functional elements in and near the LAT promoter. In this study, transient CAT assays were used to map the minimal promoter necessary for constitutive activity in neuronal and nonneuronal cells to between nucleotide positions -161 and -2 (relative to the start of LAT transcription). The region from -283 to -161 was able to slightly increase promoter activity of the minimal promoter and appeared to have a larger effect in neuronal derived cells. Gel-shift experiments using nuclear extracts from neuronal and nonneuronal derived cells detected a major factor that bound specifically to the -161 to -2 probe. We designated this factor LAT promoter binding factor (LPBF). Two additional minor factors also bound specifically to the minimal promoter. DNase I footprint analysis and gel-shift competition experiments demonstrated that LPBF bound to a region that includes the palindromic sequence CCACGTGG located at nucleotides -72 to -65. Deletion of this palindrome resulted in a loss of binding of LPBF from the minimal promoter region and an 8- to 30-fold reduction in promoter activity in both neuronal and nonneuronal cells. Thus, LPBF appears to play a major role in LAT promoter regulation.

Regulation of caspase 8- and caspase 9-induced apoptosis by the herpes simplex virus type 1 latency-associated transcript.

The latency-associated transcript (LAT) is the only herpes simplex virus type 1 (HSV-1) gene that is abundantly transcribed during latency. Plasmids expressing LAT inhibit apoptosis induced by etoposide and ceramide in transiently transfected cells. LAT also inhibits apoptosis in trigeminal ganglia of rabbits and promotes spontaneous reactivation, suggesting these events are coupled. In this study, we compared caspase cleavage (activation) in cells infected with dLAT2903 (LAT-null mutant) versus wild-type McKrae or the rescued LAT-null mutant (dLAT2903R). Neuro-2A cells (mouse neuroblastoma), but not NIH3T3 cells infected with dLAT2903, contained higher levels of cleaved caspase 9 compared to cells infected with McKrae. Cleaved caspase 9 was also readily detected in neuro-2A cells, but not NIH3T3 cells, after ultraviolet (UV) light treatment, suggesting that the ability of cells to process caspases and undergo apoptosis influences the antiapoptotic properties of LAT. HSV-1 expresses numerous genes in addition to LAT that can block apoptosis during productive infection of cultured cells. Because these genes may mask the effects of LAT on apoptosis, transient transfection assays were performed to test whether LAT can inhibit caspase 8- and caspase 9-induced apoptosis. A plasmid expressing nucleotides 1 to 4658 of LAT efficiently inhibited caspase 8- and caspase 9-induced apoptosis in transiently transfected neuro-2A cells. These studies indicate that LAT has the potential to inhibit the two major pathways of apoptosis in the absence of other viral genes. Furthermore, these studies support a role for the antiapoptotic properties of LAT in the latency-reactivation cycle.