Plasmid-encoded hygromycin B resistance: the sequence of hygromycin B phosphotransferase gene and its expression in Escherichia coli and Saccharomyces cerevisiae

The plasmid-borne gene hph coding for hygromycin B phosphotransferase (HPH) in Escherichia coli has been identified and its nucleotide sequence determined. The hph gene is 1026 nucleotides long, coding for a protein with a predicted Mr of 39 000. The hph gene was placed in a shuttle plasmid vector, downstream from the promoter region of the cyc 1 gene of Saccharomyces cerevisiae, and an hph construction containing a single AUG in the 5' noncoding region allowed direct selection following transformation in yeast and in E. coli. Thus the hph gene can be used in cloning vectors for both pro- and eukaryotes.

A recombinant vaccinia virus expressing human prostate-specific antigen (PSA): safety and immunogenicity in a non-human primate

Prostate-specific antigen (PSA) is a serine protease secreted by prostatic epithelial cells and is widely used as a marker for prostate cancer. The tissue specificity of PSA makes it a potential target for active specific immunotherapy, especially in prostate cancer patients who have undergone prostatectomy and in whom the only PSA-expressing tissue in the body resides in metastatic deposits. We report here the cloning, construction and immunological consequences of immunization of rhesus monkeys with a recombinant vaccinia virus expressing human PSA (designated rV-PSA). The prostate gland of the rhesus is structurally and functionally similar to the human prostate. While rodent and other mammalian species do not share homology with human PSA, there is 94% homology between the amino acid sequences of rhesus and human PSA. Immunization of rhesus monkeys with wild-type vaccinia virus or rV-PSA elicited the usual low-grade constitutional symptoms of vaccinia virus infection. There was no evidence of any adverse effects in any immunized monkeys. A short-lived PSA-specific IgM antibody response was noted in all rV-PSA immunized monkeys regardless of dose level. All monkeys receiving the 10(8)pfu dose of rV-PSA demonstrated PSA-specific T-cell responses that were maintained up to 270 days. No differences in anti-PSA immune responses or toxicity were observed in animals that received prostatectomy prior to immunization. Our results thus demonstrate the safety and immunogenicity of rV-PSA in a non-human primate and have implications for potential specific immunotherapy protocols using PSA as a target.

Enhanced activation of T cells by dendritic cells engineered to hyperexpress a triad of costimulatory molecules

BACKGROUND

Activation and proliferation of T cells are essential for a successful cellular immune response to an antigen. Antigen-presenting cells (APCs) activate T cells through a two-signal mechanism. The first signal is antigen specific and causes T cells to enter the cell cycle. The second signal involves a costimulatory molecule that interacts with a ligand on the T-cell surface and leads to T-cell cytokine production and their proliferation. Dendritic cells express several costimulatory molecules and are believed to be the most potent APCs. Two recombinant poxvirus vectors (replication-defective avipox [fowlpox; rF] and a replication-competent vaccinia [rV]) have been engineered to express a triad of costimulatory molecules (B7-1, intercellular adhesion molecule-1, and leukocyte function-associated antigen-3; designated TRICOM). This study was designed to determine if dendritic cells infected with these vectors would have an enhanced capacity to stimulate T-cell responses.

METHODS

Murine dendritic cells (of both intermediate maturity and full maturity) were infected with rF-TRICOM or rV-TRICOM and were used in vitro to stimulate naive T cells with the use of a pharmacologic agent as signal 1, to stimulate T cells in allospecific mixed lymphocyte cultures, and to stimulate CD8(+) T cells specific for a peptide from the ovalbumin (OVA) protein. In addition, dendritic cells infected with TRICOM vectors were pulsed with OVA peptide and used to vaccinate mice to examine T-cell responses in vivo. All statistical tests were two-sided.

RESULTS

Dendritic cells infected with either rF-TRICOM or rV-TRICOM were found to greatly enhance naive T-cell activation (P<.001), allogeneic responses of T cells (P<.001), and peptide-specific T-cell stimulation in vitro (P<.001). Peptide-pulsed dendritic cells infected with rF-TRICOM or rV-TRICOM induced cytotoxic T-lymphocyte activity in vivo to a markedly greater extent than peptide-pulsed dendritic cells (P =.001 in both).

CONCLUSIONS

The ability of dendritic cells to activate both naive and effector T cells in vitro and in vivo can be enhanced with the use of poxvirus vectors that potentiate the hyperexpression of a triad of costimulatory molecules. Use of either rF-TRICOM or rV-TRICOM vectors significantly improved the efficacy of dendritic cells in priming specific immune responses. These studies have implications in vaccine strategies for both cancer and infectious diseases.

Production and of monoclonal antibodies to simian immunodeficiency virus envelope glycoproteins

Eighteen monoclonal antibodies (MAb) to simian immunodeficiency virus (SIV) envelope have been characterized. All MAb were shown to bind to viral antigens on the surface of unfixed SIV-infected cells and to precipitate surface glycoproteins of SIVmac251. In Western blot 11 MAb bound to gp160 and gp120, five bound to gp160 and the transmembrane protein gp41 and two MAb did not react with denatured antigen. Preliminary competition assays identified the existence of six competition groups; two groups were within gp41 and four were within gp120. Of the latter four groups, three contained MAb with neutralizing activity. Two of the neutralizing MAb (KK5 and KK9) did not react with denatured antigen in Western blot suggesting that they may recognize conformational epitopes. Enzyme-linked immunosorbent-assay titres of MAb against SIVmac251 ranged from 10(2.4) to 10(5.6) and although similar titres were obtained with some MAb against other SIV and HIV antigens, the presence of isolate specific and shared group epitopes was demonstrated.

Effect of RP51 gene dosage alterations on ribosome synthesis in Saccharomyces cerevisiae

The Saccharomyces cerevisiae ribosomal protein rp51 is encoded by two interchangeable genes, RP51A and RP51B. We altered the RP51 gene dose by creating deletions of the RP51A or RP51B genes or both. Deletions of both genes led to spore inviability, indicating that rp51 is an essential ribosomal protein. From single deletion studies in haploid cells, we concluded that there was no intergenic dosage compensation at the level of mRNA abundance or mRNA utilization (translational efficiency), although phenotypic analysis had previously indicated a small compensation effect on growth rate. Similarly, deletions in diploid strains indicated that no strong mechanisms exist for intragenic dosage compensation; in all cases, a decreased dose of RP51 genes was characterized by a slow growth phenotype. A decreased dose of RP51 genes also led to insufficient amounts of 40S ribosomal subunits, as evidenced by a dramatic accumulation of excess 60S ribosomal subunits. We conclude that inhibition of 40S synthesis had little or no effect on the synthesis of the 60S subunit components. Addition of extra copies of rp51 genes led to extra rp51 protein synthesis. The additional rp51 protein was rapidly degraded. We propose that rp51 and perhaps many ribosomal proteins are normally oversynthesized, but the unassembled excess is degraded, and that the apparent compensation seen in haploids, i.e., the fact that the growth rate of mutant strains is less depressed than the actual reduction in mRNA, is a consequence of this excess which is spared from proteolysis under this circumstance.

Therapeutic antitumor response after immunization with an admixture of recombinant vaccinia viruses expressing a modified MUC1 gene and the murine T-cell costimulatory molecule B7

Tumor-associated antigens have considerable promise not only as diagnostic or prognostic markers but also as targets for active or passive immunotherapy. DF3/MUC1 is a tumor-associated antigen that is overexpressed with an abnormal glycosylation pattern in breast, ovarian, lung, and pancreatic cancers. The major extracellular portion of MUC1 is composed of tandem repeat units of 20 amino acids. Recombinant vaccinia viruses encoding mucin molecules have been constructed by several groups. However, these recombinants have met with limited success in protecting animals from MUC1-expressing tumors because of the vaccinia genome being subject to high-frequency homologous recombination, therefore being unstable in expression of the tandem repeats. In light of these studies, two concurrent strategies were used to improve immune responses to MUC1: a recombinant vaccinia virus was constructed containing a modified "mini" MUC1 gene containing only 10 tandem repeat sequences to minimize vaccinia-mediated rearrangement (designated rV-MUC1); and an admixture was used containing rV-MUC1 and a recombinant vaccinia virus containing the gene for the murine T-cell costimulatory molecule B7-1 (rV-B7). The rV-MUC1 gene product maintained a consistent molecular weight throughout several passages, indicating stability of the inserted gene. Mice inoculated with rV-MUC1 demonstrated MUC1-specific cytolytic responses that were further enhanced by admixture with rV-B7. In a MUC1-expressing pulmonary metastases prevention model, mice inoculated two times with rV-MUC1 were protected from the establishment of metastases. No additive effect on antitumor immunity (> 90% with rV-MUC1 alone) was observed in mice primed with an admixture of rV-MUC1 and rV-B7 and boosted with rV-MUC1. When rV-MUC1 was used to treat established MUC1 positive metastases, however, three administrations of rV-MUC1 were not sufficient to confer antitumor effects. In contrast, when tumor-bearing mice were primed with an admixture of rV-MUC1 and rV-B7, followed by two boosts with rV-MUC1, there was a significant reduction in pulmonary metastases (p = < 0.0001), which correlated to 100% survival. Coexpression of the B7 molecule, although not necessary for the induction of an immune response of sufficient magnitude to prevent MUC1 tumors, was thus essential in a treatment setting.

Formation of lentivirus particles by mammalian cells infected with recombinant fowlpox virus

Recombinant fowlpox viruses (FPV) containing the env or gag-pol genes of simian immunodeficiency virus from macaques (SIVmac) were constructed. The env, gag, and pol-encoded polypeptides were efficiently expressed and processed in avian cells productively infected with FPV as well as in mammalian cells, in which FPV infection is abortive. In addition, the recombinant FPV expressing the gag-pol genes directed the formation of defective, lentivirus-like particles which were released into the culture medium of infected cells. Coinfection of cells with the env and gag-pol recombinant viruses resulted in the generation of particles containing SIVmac envelope glycoprotein. The applications of this system to vaccine development are discussed.

Evaluation of prime/boost regimens using recombinant poxvirus/tyrosinase vaccines for the treatment of patients with metastatic melanoma

PURPOSE

Two clinical trials were conducted to evaluate the clinical efficacy and immunologic impact of vaccination against the tyrosinase protein plus systemic interleukin 2 (IL-2) administration in patients with advanced metastatic melanoma.

EXPERIMENTAL DESIGN

Full-length tyrosinase was employed as an immunogen to induce diverse immunologic responses against a commonly expressed melanoma antigen. Heterologous prime/boost vaccination with recombinant vaccinia and fowlpox vectors encoding tyrosinase was first explored in a randomized three-arm phase II trial, in which vaccines were administered alone or concurrently with low-dose or high-dose IL-2. In a subsequent single cohort phase II trial, all patients received the same vaccines and high-dose IL-2 sequentially rather than concurrently.

RESULTS

Among a total of 64 patients treated on these trials, 8 objective partial responses (12.5%) were observed, all in patients receiving high-dose IL-2. Additional patients showed evidence of lesional regression (mixed tumor response) or overall regression that did not achieve partial response status (minor response). In vitro evidence of enhanced immunity against tyrosinase following protocol treatments was documented in 3 of 49 (6%) patients tested serologically, 3 of 23 (13%) patients tested for T-cell recognition of individual tyrosinase peptides, and 4 of 16 (25%) patients tested for T-cell recognition of full-length tyrosinase protein with real-time reverse transcription-PCR techniques.

CONCLUSIONS

Whereas prime/boost immunization with recombinant vaccinia and fowlpox viruses enhanced antityrosinase immunity in some patients with metastatic melanoma, it was ineffective alone in mediating clinical benefit, and in combination with IL-2 did not mediate clinical benefit significantly different from that expected from treatment with IL-2 alone.

Analyses of recombinant vaccinia and fowlpox vaccine vectors expressing transgenes for two human tumor antigens and three human costimulatory molecules

PURPOSE

The poor immunogenicity of tumor antigens and the antigenic heterogeneity of tumors call for vaccine strategies to enhance T-cell responses to multiple antigens. Two antigens expressed noncoordinately on most human carcinomas are carcinoembryonic antigen (CEA) and MUC-1. We report here the construction and characterization of two viral vector vaccines to address these issues.

EXPERIMENTAL DESIGN

The two viral vectors analyzed are the replication-competent recombinant vaccinia virus (rV-) and the avipox vector, fowlpox (rF-), which is replication incompetent in mammalian cells. Each vector encodes the transgenes for three human costimulatory molecules (B7-1, ICAM-1, and LFA-3, designated TRICOM) and the CEA and MUC-1 transgenes (which also contain agonist epitopes). The vectors are designated rV-CEA/MUC/TRICOM and rF-CEA/MUC/TRICOM.

RESULTS

Each of the vectors is shown to be capable of faithfully expressing all five transgenes in human dendritic cells (DC). DCs infected with either vector are shown to activate both CEA- and MUC-1-specific T-cell lines to the same level as DCs infected with CEA-TRICOM or MUC-1-TRICOM vectors. Thus, no evidence of antigenic competition between CEA and MUC-1 was observed. Human DCs infected with rV-CEA/MUC/TRICOM or rF-CEA/MUC/TRICOM are also shown to be capable of generating both MUC-1- and CEA-specific T-cell lines; these T-cell lines are in turn shown to be capable of lysing targets pulsed with MUC-1 or CEA peptides as well as human tumor cells endogenously expressing MUC-1 and/or CEA.

CONCLUSION

These studies provide the rationale for the clinical evaluation of these multigene vectors in patients with a range of carcinomas expressing MUC-1 and/or CEA.

The use of combination vaccinia vaccines and dual-gene vaccinia vaccines to enhance antigen-specific T-cell immunity via T-cell costimulation

Several recombinant vaccinia viruses are currently being evaluated to induce antigen-specific immunity to a variety of infectious disease agents and tumor associated antigens. T-cell costimulation is extremely important in enhancing T-cell responses, and recombinant vaccines have now been shown to be effective vectors to express a range of these molecules. Both combination vaccines (an admixture of a recombinant vaccinia virus expressing a specific target antigen and a recombinant vaccinia virus expressing a costimulatory molecule) and dual-gene vaccines expressing both transgenes on the same vector have been shown capable of effectively enhancing antigen-specific responses via T-cell costimulation. In this report, we compare for the first time the use of both types of approaches to enhance antigen-specific T-cell responses, and we demonstrate the importance of route of vaccine administration and vaccine dose in attaining optimal T-cell responses. These studies should have direct bearing on the design of vaccine clinical trials for infectious agents and/or tumor associated antigens, in which T-cell costimulatory molecules will be employed to enhance antigen-specific T-cell responses via the use of either combination or dual-gene vaccinia vaccines.

Generation of hybrid genes and proteins by vaccinia virus-mediated recombination: application to human immunodeficiency virus type 1 env

The ability of poxviruses to undergo intramolecular recombination within tandemly arranged homologous sequences can be used to generate chimeric genes and proteins. Genes containing regions of nucleotide homology will recombine to yield a single sequence composed of portions of both original genes. A recombinant virus containing two genes with a number of conserved regions will yield a population of recombinant viruses containing a spectrum of hybrid sequences derived by recombination between the original genes. This scheme has been used to generate hybrid human immunodeficiency virus type 1 env genes. Recombinant vaccinia viruses that contain two divergent env genes in tandem array have been constructed. In the absence of selective pressure to maintain both genes, recombination between conserved homologous regions in these genes generated a wide range of progeny, each of which expressed a novel variant polypeptide encoded by the newly created hybrid env gene. Poxvirus-mediated recombination may be applied to map type-specific epitopes, to create novel pharmaceuticals such as hybrid interferons, to study receptor-binding or enzyme substrate specificities, or to mimic the antigenic diversity found in numerous pathogens.

Role of genes that modulate host immune responses in the immunogenicity and pathogenicity of vaccinia virus

Poxvirus vaccine vectors, although capable of eliciting potent immune responses, pose serious health risks in immunosuppressed individuals. We therefore constructed five novel recombinant vaccinia virus vectors which contained overlapping deletions of coding regions for the B5R, B8R, B12R, B13R, B14R, B16R, B18R, and B19R immunomodulatory gene products and assessed them for both immunogenicity and pathogenicity. All five of these novel vectors elicited both cellular and humoral immunity to the inserted HIV-BH10 env comparable to that induced by the parental Wyeth strain vaccinia virus. However, deletion of these immunomodulatory genes did not increase the immunogenicity of these vectors compared with the parental vaccinia virus. Furthermore, four of these vectors were slightly less virulent and one was slightly more virulent than the Wyeth strain virus in neonatal mice. Attenuated poxviruses have potential use as safer alternatives to current replication-competent vaccinia virus. Improved vaccinia virus vectors can be generated by deleting additional genes to achieve a more significant viral attenuation.

Use of recombinant poxviruses to stimulate anti-melanoma T cell reactivity

BACKGROUND

Dendritic cells (DC) are potent professional antigen-presenting cells that can activate naive T lymphocytes and initiate cellular immune responses. As adjuvants, DC may be useful for enhancing immunogenicity and mediating tumor regression. Endogenous expression of antigen by DC could offer the potential advantage of allowing prolonged constitutive presentation of endogenously processed epitopes and exploitation of multiple restriction elements for the presentation of the same antigen.

METHODS

DC were prepared from the peripheral blood of HLA A*0201 patients with metastatic melanoma in the presence of IL-4 (1000 IU/mL) and GMCSF (1000 IU/mL). Recombinant vaccinia and fowlpox viruses encoding the hMART-1 gene were constructed and used to infect DC. The efficiency of infection and expression of the MART-1 antigen were assessed by immunohistochemistry and intracellular FACS analyses. Cytotoxic lymphocytes (CTL) were generated by the stimulation of CD8+ T cells, with DC expressing the recombinant gene. Reactivity of the CTL was determined at weeks 1 and 2 by the amount of IFN-gamma released.

RESULTS

DC were infected with recombinant poxviruses and demonstrated specific melanoma antigen expression by immunohistochemistry, immunofluorescence, and intracellular FACS analysis. The expression by DC of MART-1 MAA after viral infection was sufficient to generate CD8+ T lymphocytes that recognized naturally processed epitopes on tumor cells in 10 of 11 patients.

CONCLUSIONS

Human DC are receptive to infection by recombinant poxviruses encoding MAA genes and are capable of efficiently processing and presenting these MAA to cytotoxic T cells. The potential advantage of this approach is the ability to present specific antigen independent of the identification of the epitope or the MHC restriction element. This strategy may be useful for the identification of relevant epitopes for a diverse number of HLA alleles and for active immunization in patients.

Identification of multiple simian immunodeficiency virus (SIV)-specific CTL epitopes in sooty mangabeys with natural and experimentally acquired SIV infection

Host immune responses to SIV infection in sooty mangabeys are likely to be an important determinant of how such nonhuman primate species maintain asymptomatic lentivirus infection. We have previously described two patterns of asymptomatic SIV infection in sooty mangabeys: low viral loads with vigorous SIV-specific CTL activity in SIVmac239-infected sooty mangabeys, and high viral loads with generally weak or absent SIV-specific CTL activity in naturally infected sooty mangabeys. To define the specificity of the CTL response in SIV-infected mangabeys, we characterized CTL epitopes in two naturally infected and three SIVmac239-infected sooty mangabeys. Compared with that in SIVmac239-infected mangabeys, the yield of SIV-specific CTL clones was significantly lower in naturally infected sooty mangabeys. All CTL clones were phenotypically CD3+ CD8+, and lysis was MHC restricted. Seven SIV CTL epitopes were identified in five sooty mangabeys: one in Gag and three each in Nef and Envelope (Env). The CTL epitopes mapped to conserved regions in the SIV genome and were immunodominant. Several similar or identical CTL epitopes were recognized by both naturally infected and SIVmac239-infected mangabeys that shared class I MHC alleles. To our knowledge, this is the first report of SIV-specific CTL epitopes in sooty mangabeys. Longitudinal studies of viral load and sequence variation in CTL epitopes may provide useful information on the role of CTL in control or persistence of SIV infection in sooty mangabeys.

A recombinant vector expressing transgenes for four T-cell costimulatory molecules (OX40L, B7-1, ICAM-1, LFA-3) induces sustained CD4+ and CD8+ T-cell activation, protection from apoptosis, and enhanced cytokine production

The role of OX40L on the activation of T cells was investigated using poxvirus vectors expressing OX40L alone or in combination with three other T-cell costimulatory molecules: B7-1, ICAM-1, and LFA-3. Poxvirus vector-infected cells were used to stimulate nai;ve or activated CD4(+) and CD8(+) T cells. These studies demonstrate that (a) OX40L plays a role in sustaining the long-term proliferation of CD8(+) T cells in addition to the known effect on CD4(+) T cells following activation, (b) OX40L enhances the production of Th1 cytokines (IL-2, IFN-gamma, and TNF-alpha) from both CD4(+) and CD8(+) while no change in IL-4 expression was observed, and (c) the anti-apoptotic effect of OX40L on T cells is likely the result of sustained expression of anti-apoptotic genes while genes involved in apoptosis are inhibited. In addition, these are the first studies to demonstrate that the combined use of a vector driving the expression of OX40L with three other costimulatory molecules (B7-1, ICAM-1, and LFA-3) both enhances initial activation and then further potentiates sustained activation of nai;ve and effector T cells.

Analysis of cytotoxic T lymphocyte responses to SIV proteins in SIV-infected macaques using antigen-specific stimulation with recombinant vaccinia and fowl poxviruses

Methods to analyze CD8+ CTL responses to simian immunodeficiency virus (SIV)-encoded proteins are essential to understand lentivirus immunopathogenesis and protective immune responses. Recombinant infectious shuttle vectors are useful for analyzing CTL responses to many viruses, including HIV. Therefore, CTL responses in SIV-infected Macaca fascicularis to SIV env and SIV gag/pol were evaluated using specific antigen stimulation with recombinant vaccinia (rVV) and fowl poxviruses (rFPV) containing SIV genes. Peripheral blood mononuclear cells from SIV-infected animals were stimulated with autologous cells infected with rVV expressing SIV env/gag/pol, and CTLs specific for SIV env and for SIV gag/pol were detected by testing for lytic activity in target cells expressing these genes separately. Lymphocyte subset purifications from the effector population demonstrated that the CTL response was mediated by CD8+ cells, and the use of brefeldin A to selectively block antigen presentation in association with MHC class I products affirmed this cytolytic activity was class I restricted. The use of rVV to analyze responses to SIV genes is potentially problematic in hosts immunized to vaccinia. Fowl poxvirus is an alternative virus that has many of the molecular advantages of vaccinia virus but is genomically distinct. Therefore, the ability of rFPV to expand and detect SIV-specific CTLs was evaluated. Although there was no cytopathic effect following infection with rFPV, macaque cells infected with this vector did express rFPV gene products, and could be used as stimulator and target cells to detect SIV-specific CD8+ CTLs. The results suggest that these recombinant viral vectors can be used to specifically stimulate CD8+, MHC class I-restricted CTLs reactive to SIV proteins, and should facilitate evaluating CTL responses in both SIV-infected animals and animals vaccinated against SIV.

Gender differences in human immunodeficiency virus type 1-specific CD8 responses in the reproductive tract and colon following nasal peptide priming and modified vaccinia virus Ankara boosting

Induction of mucosal anti-human immunodeficiency virus type 1 (HIV-1) T-cell responses in males and females will be important for the development of a successful HIV-1 vaccine. An HIV-1 envelope peptide, DNA plasmid, and recombinant modified vaccinia virus Ankara (rMVA) expressing the H-2D(d)-restricted cytotoxic T lymphocyte P18 epitope were used as immunogens to test for their ability to prime and boost anti-HIV-1 T-cell responses at mucosal and systemic sites in BALB/c mice. We found of all prime-boost combinations tested, an HIV-1 Env peptide subunit mucosal prime followed by systemic (intradermal) boosting with rMVA yielded the maximal induction of gamma interferon (IFN-gamma) spot-forming cells in the female genital tract and colon. However, this mucosal prime-systemic rMVA boost regimen was minimally immunogenic for the induction of genital, colon, or lung anti-HIV-1 T-cell responses in male mice. We determined that a mucosal Env subunit immunization could optimally prime an rMVA boost in female but not male mice, as determined by the magnitude of antigen-specific IFN-gamma responses in the reproductive tracts, colon, and lung. Defective mucosal priming in male mice could not be overcome by multiple mucosal immunizations. However, rMVA priming followed by an rMVA boost was the optimal prime-boost strategy for male mice as determined by the magnitude of antigen-specific IFN-gamma responses in the reproductive tract and lung. Thus, prime-boost immunization strategies able to induce mucosal antigen-specific IFN-gamma responses were identified for male and female mice. Understanding the cellular and molecular basis of gender-determined immune responses will be important for optimizing induction of anti-HIV-1 mucosal immune responses in both males and females.

Posttranscriptional regulation and assembly into ribosomes of a Saccharomyces cerevisiae ribosomal protein-beta-galactosidase fusion

To study the regulation of ribosomal protein genes, we constructed a 'lacZ fusion of the Saccharomyces cerevisiae RP51A gene, containing the first 64 codons of RP51A. In a strain lacking an intact RP51A gene (cells are viable due to the presence of an active RP51B gene), beta-galactosidase activity is 10-fold greater than in a strain containing RP51A. RP51A-lacZ mRNA levels are equal in the two strains, indicating that regulation is posttranscriptional. In the absence of the RP51A gene, the fusion protein is predominantly cytoplasmic and associated with polysomes, whereas in the presence of RP51A, the fusion protein is predominantly nuclear, and none is associated with polysomes. Deletions were made in the RP51A-coding portion of the fusion gene. The most extensively deleted gene, containing only the first seven RP51A codons fused to lacZ, produced a high level of beta-galactosidase activity in both the presence and the absence of the RP51A gene. In both cases, little or none of this shorter fusion protein was found associated with polysomes. Thus, a regulatory site (or sites) lies in the protein-coding region of RP51A. We suggest that posttranscriptional regulation of the rp51 fusion protein is related to assembly of the protein into ribosomes.

Inhibition of allergic encephalomyelitis in marmosets by vaccination with recombinant vaccinia virus encoding for myelin basic protein

A primary demyelinating form of experimental allergic encephalomyelitis (EAE) resembling human multiple sclerosis (MS) occurs in Callithrix jacchus marmosets following immunization with human white matter. Participation of a T-cell immune response against myelin basic protein (MBP) in this disease model is supported by observations of increased reactivity against MBP in PBMC and of adoptive transfer of an inflammatory form of EAE by MBP-reactive T-cells. To evaluate the effects of ectopic presentation of MBP on marmoset EAE, animals were vaccinated prior to induction of EAE by subcutaneous injection of attenuated strains of vaccinia virus genetically engineered to contain either the entire coding sequence for human MBP (vT15) or the equine herpes virus glycoprotein gH gene (vAbT249). Vaccination with vT15 was followed by transient cytoplasmic and surface membrane expression of MBP in circulating PBMC (15-45 days). The onset of clinical EAE after immunization (pi) was markedly delayed in vT15-vaccinated animals (37-97 days pi, n = 4) compared to vAbT249-vaccinated controls (14-18 days pi, n = 3). Proliferative responses against MBP but not against vaccinia antigens or phytohemagglutinin were suppressed in protected animals. Thus, development of attenuated live viruses carrying genes for myelin antigens could be useful for induction of immunologic tolerance and for modulation of autoimmune demyelination.

Futility rules for telaprevir combination treatment for patients with hepatitis C virus infection

For patients treated with telaprevir, peginterferon, and ribavirin, futility rules have been developed to prevent needless drug exposure and minimize development of drug-resistant variants for patients who have little or no chance of achieving a sustained virologic response. We performed retrospective analyses of data from phase 3 trials and validated the current futility rule. All therapy should be stopped for treatment-naive and treatment-experienced patients if hepatitis C virus RNA levels are greater than 1000 IU/mL at weeks 4 or 12, or if hepatitis C virus RNA is detectable at week 24.

Active immunotherapy of cancer with a nonreplicating recombinant fowlpox virus encoding a model tumor-associated antigen

Some tumor cells express Ags that are potentially recognizable by T lymphocytes and yet do not elicit significant immune responses. To explore new immunotherapeutic strategies aimed at enhancing the recognition of these tumor-associated Ags (TAA), we developed an experimental mouse model consisting of a lethal clone of the BALB/c tumor line CT26 designated CT26.WT, which was transduced with the lacZ gene encoding beta-galactosidase, to create CT26.CL25. The growth rate and lethality of CT26.CL25 and CT26.WT were virtually identical despite the expression by CT26.CL25 of the model tumor Ag in vivo. A recombinant fowlpox virus (rFPV), which is replication incompetent in mammalian cells, was constructed that expressed the model TAA, beta-galactosidase, under the influence of the 40-kDa vaccinia virus early/late promoter. This recombinant, FPV.bg40k, functioned effectively in vivo as an immunogen, eliciting CD8+ T cells that could effectively lyse CT26.CL25 in vitro. FPV.bg40k protected mice from both subcutaneous and intravenous tumor challenge by CT26.CL25, and most surprisingly, mice bearing established 3-day pulmonary metastasis were found to have significant, Ag-specific decreases in tumor burden and prolonged survival after treatment with the rFPV. These observations constitute the first reported use of rFPV in the prevention and treatment of an experimental cancer and suggest that changing the context in which the immune system encounters a TAA can significantly and therapeutically alter the host immune response against cancer.

Recombinant fowlpox viruses encoding the anchor-modified gp100 melanoma antigen can generate antitumor immune responses in patients with metastatic melanoma

PURPOSE

The purpose of this study was to evaluate the immunological responses and therapeutic effectiveness of immunization with fowlpox vaccines encoding the gp100 melanoma antigen in patients with metastatic melanoma.

EXPERIMENTAL DESIGN

In three consecutive clinical trials, patients were immunized with recombinant fowlpox viruses encoding three different forms of the melanoma/melanocyte-associated antigen gp100: (a) the native, full-length gp100 molecule; (b) the gp100 molecule with two amino acids modified to increase binding to HLA-A*0201 molecules; and (c) a "minigene" construct encoding a single, modified epitope gp100:209-217(210M) targeted to the endoplasmic reticulum. The immunogenicity of these constructs was studied using peripheral blood mononuclear cells to measure epitope-specific release of IFN-gamma.

RESULTS

Reactivity against gp100 was not seen in any patient before receiving fowlpox immunization. Whereas just one of seven patients developed reactivity after receiving fowlpox encoding native gp100, 10 of 14 patients who received fowlpox encoding the anchor modified full-length gp100 exhibited reactivity against the native gp100 molecule, and 12 of 16 patients were successfully immunized after inoculation with the modified minigene construct (p2 = 0.02). There was no difference in the latter group between those randomized to vaccination by i.v. or i.m. routes. There was one partial cancer regression in the group of 46 patients receiving virus in the absence of interleukin (IL)-2. Once patients showed evidence of progressive disease, they were eligible for "cross-over" treatment to IL-2 alone or with the fowlpox virus. None of the 13 patients receiving the full-length or modified full-length forms of gp100 responded when receiving IL-2, whereas 6 of 12 patients who received the fowlpox containing the minigene construct and then received IL-2 showed objective cancer regressions, including three patients with complete regression.

CONCLUSIONS

These data underscore the importance of modifying anchor residues of nonmutated self-antigen peptides to generate cellular immune responses after immunization and support the further investigation of recombinant fowlpox viruses encoding modified epitopes administered in combination with IL-2.

Active immunotherapy of cancer with a nonreplicating recombinant fowlpox virus encoding a model tumor-associated antigen

Some tumor cells express Ags that are potentially recognizable by T lymphocytes and yet do not elicit significant immune responses. To explore new immunotherapeutic strategies aimed at enhancing the recognition of these tumor-associated Ags (TAA), we developed an experimental mouse model consisting of a lethal clone of the BALB/c tumor line CT26 designated CT26.WT, which was transduced with the lacZ gene encoding beta-galactosidase, to create CT26.CL25. The growth rate and lethality of CT26.CL25 and CT26.WT were virtually identical despite the expression by CT26.CL25 of the model tumor Ag in vivo. A recombinant fowlpox virus (rFPV), which is replication incompetent in mammalian cells, was constructed that expressed the model TAA, beta-galactosidase, under the influence of the 40-kDa vaccinia virus early/late promoter. This recombinant, FPV.bg40k, functioned effectively in vivo as an immunogen, eliciting CD8+ T cells that could effectively lyse CT26.CL25 in vitro. FPV.bg40k protected mice from both subcutaneous and intravenous tumor challenge by CT26.CL25, and most surprisingly, mice bearing established 3-day pulmonary metastasis were found to have significant, Ag-specific decreases in tumor burden and prolonged survival after treatment with the rFPV. These observations constitute the first reported use of rFPV in the prevention and treatment of an experimental cancer and suggest that changing the context in which the immune system encounters a TAA can significantly and therapeutically alter the host immune response against cancer.