Peroxicretion: a novel secretion pathway in the eukaryotic cell.

BACKGROUND: Enzyme production in microbial cells has been limited to secreted enzymes or intracellular enzymes followed by expensive down stream processing. Extracellular enzymes consists mainly of hydrolases while intracellular enzymes exhibit a much broader diversity. If these intracellular enzymes could be secreted by the cell the potential of industrial applications of enzymes would be enlarged. Therefore a novel secretion pathway for intracellular proteins was developed, using peroxisomes as secretion vesicles. RESULTS: Peroxisomes were decorated with a Golgi derived v-SNARE using a peroxisomal membrane protein as an anchor. This allowed the peroxisomes to fuse with the plasma membrane. Intracellular proteins were transported into the peroxisomes by adding a peroxisomal import signal (SKL tag). The proteins which were imported in the peroxisomes, were released into the extra-cellular space through this artificial secretion pathway which was designated peroxicretion. This concept was supported by electron microscopy studies. CONCLUSION: Our results demonstrate that it is possible to reroute the intracellular trafficking of vesicles by changing the localisation of SNARE molecules, this approach can be used in in vivo biological studies to clarify the different control mechanisms regulating intracellular membrane trafficking. In addition we demonstrate peroxicretion of a diverse set of intracellular proteins. Therefore, we anticipate that the concept of peroxicretion may revolutionize the production of intracellular proteins from fungi and other microbial cells, as well as from mammalian cells.

Therapeutic immunization with Modified Vaccinia Virus Ankara (MVA) vaccines in SIV-infected rhesus monkeys undergoing antiretroviral therapy.

BACKGROUND: The long-term benefits of highly active antiretroviral therapy in HIV-infected patients are limited by emergence of drug-resistant variants and side effects. Therefore, we studied the concept of therapeutic immunization in 18 rhesus monkeys infected with a highly pathogenic simian immunodeficiency virus (SIV) swarm. METHODS: Monkeys were treated with the reverse transcriptase inhibitor (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA) for 19 weeks starting 10 days after infection. After suppression of viremia, one group of monkeys was immunized with recombinant modified vaccinia virus Ankara (MVA) vectors expressing gag-pol and env. A second group received MVA vectors expressing the regulatory genes tat, rev and nef, while a third group was not immunized. RESULTS: Immunization with gag-pol and env expressing MVA enhanced SIV antibody titers. Following discontinuation of PMPA treatment, a rebound in viral load was observed. However, in three of six monkeys immunized with MVA gag-pol and MVA env, and two of six monkeys immunized MVA expressing regulatory genes set point RNA levels were below or close to a threshold level of 10(4) RNA copies/ml, while only one of six unvaccinated monkeys maintained such low RNA levels. CONCLUSIONS: Although a subset of animals seem to benefit from therapeutic immunization with MVA vectors, the difference in set point RNA levels between the groups did not reach statistical significance.

Transmission of simian immunodeficiency virus SIVcpz and the evolution of infection in the presence and absence of concurrent human immunodeficiency virus type 1 infection in chimpanzees.

Current data suggest that the human immunodeficiency virus type 1 (HIV-1) epidemic arose by transmission of simian immunodeficiency virus (SIV) SIVcpz from a subspecies of common chimpanzees (Pan troglodytes troglodytes) to humans. SIVcpz of chimpanzees is itself a molecular chimera of SIVs from two or more different monkey species, suggesting that recombination was made possible by coinfection of one individual animal with different lentiviruses. However, very little is known about SIVcpz transmission and the susceptibility to lentivirus coinfection of its natural host, the chimpanzee. Here, it is revealed that either infected plasma or peripheral blood mononuclear cells readily confer infection when exposure occurs by the intravenous or mucosal route. Importantly, the presence of preexisting HIV-1 infection did not modify the kinetics of SIVcpz infection once it was established by different routes. Although humoral responses appeared as early as 4 weeks postinfection, neutralization to SIVcpz-ANT varied markedly between animals. Analysis of the SIVcpz env sequence over time revealed the emergence of genetic viral variants and persistent SIVcpz RNA levels of between 10(4) and 10(5) copies/ml plasma regardless of the presence or absence of concurrent HIV-1 infection. These unique data provide important insight into possible routes of transmission, the kinetics of acute SIVcpz infection, and how readily coinfection with SIVcpz and other lentiviruses may be established as necessary preconditions for potential recombination.

Importance of the N-distal AP-2 binding element in Nef for simian immunodeficiency virus replication and pathogenicity in rhesus macaques.

Point mutations in SIVmac239 Nef disrupting CD4 downmodulation and enhancement of virion infectivity attenuate viral replication in acutely infected rhesus macaques, but changes selected later in infection fully restore Nef function (A. J. Iafrate et al., J. Virol. 74:9836-9844, 2000). To further evaluate the relevance of these Nef functions for viral persistence and disease progression, we analyzed an SIVmac239 Nef mutant containing a deletion of amino acids Q64 to N67 (delta64-67Nef). This mutation inactivates the N-distal AP-2 clathrin adaptor binding element and disrupts the abilities of Nef to downregulate CD4, CD28 and CXCR4 and to stimulate viral replication in vitro. However, it does not impair the downmodulation of CD3 and class I major histocompatibility complex (MHC-I) or MHC-II and the upregulation of the MHC-II-associated invariant chain, and it has only a moderate effect on the enhancement of virion infectivity. Replication of the delta64-67Nef variant in acutely infected macaques was intermediate between grossly nef-deleted and wild-type SIVmac239. Subsequently, three of six macaques developed moderate to high viral loads and developed disease, whereas the remaining animals efficiently controlled SIV replication and showed a more attenuated clinical course of infection. Sequence analysis revealed that the deletion in nef was not repaired in any of these animals. However, some changes that slightly enhanced the ability of Nef to downmodulate CD4 and moderately increased Nef-mediated enhancement of viral replication and infectivity in vitro were observed in macaques developing high viral loads. Our results imply that both the Nef functions that were disrupted by the delta64-67 mutation and the activities that remained intact contribute to viral pathogenicity.

Direct inoculation of simian immunodeficiency virus from sooty mangabeys in black mangabeys (Lophocebus aterrimus): first evidence of AIDS in a heterologous African species and different pathologic outcomes of experimental infection.

A unique opportunity for the study of the role of serial passage and cross-species transmission was offered by a series of experiments carried out at the Tulane National Primate Research Center in 1990. To develop an animal model for leprosy, three black mangabeys (BkMs) (Lophocebus aterrimus) were inoculated with lepromatous tissue that had been serially passaged in four sooty mangabeys (SMs) (Cercocebus atys). All three BkMs became infected with simian immunodeficiency virus from SMs (SIVsm) by day 30 postinoculation (p.i.) with lepromatous tissue. One (BkMG140) died 2 years p.i. from causes unrelated to SIV, one (BkMG139) survived for 10 years, whereas the third (BkMG138) was euthanized with AIDS after 5 years. Histopathology revealed a high number of giant cells in tissues from BkMG138, but no SIV-related lesions were found in the remaining two BkMs. Four-color immunofluorescence revealed high levels of SIVsm associated with both giant cells and T lymphocytes in BkMG138 and no detectable SIV in the remaining two. Serum viral load (VL) showed a significant increase (>1 log) during the late stage of the disease in BkMG138, as opposed to a continuous decline in VL in the remaining two BkMs. With the progression to AIDS, neopterin levels increased in BkMG138. This study took on new significance when phylogenetic analysis unexpectedly showed that all four serially inoculated SMs were infected with different SIVsm lineages prior to the beginning of the experiment. Furthermore, the strain infecting the BkMs originated from the last SM in the series. Therefore, the virus infecting BkMs has not been serially passaged. In conclusion, we present the first compelling evidence that direct cross-species transmission of SIV may induce AIDS in heterologous African nonhuman primate (NHP) species. The results showed that cross-species-transmitted SIVsm was well controlled in two of three BkMs for 2 and 10 years, respectively. Finally, this case of AIDS in an African monkey suggests that the dogma of SIV nonpathogenicity in African NHP hosts should be reconsidered.

Long-term protection against SHIV89.6P replication in HIV-1 Tat vaccinated cynomolgus monkeys.

Vaccination with a biologically active Tat protein or tat DNA contained infection with the highly pathogenic SHIV89.6P virus, preventing CD4 T-cell decline and disease onset. Here we show that protection was prolonged, since neither CD4 T-cell decline nor active virus replication was observed in all vaccinated animals that controlled virus replication up to week 104 after the challenge. In contrast, virus persisted and replicated in peripheral blood mononuclear cells and lymph nodes of infected animals, two of which died. Tat-specific antibody, CD4 and CD8 T-cell responses were high and stable only in the animals controlling the infection. In contrast, Gag-specific antibody production and CD4 and CD8 T-cell responses were consistently and persistently positive only in the monkeys that did not control primary virus replication. These results indicate that vaccination with Tat protein or DNA induced long-term memory Tat-specific immune responses and controlled primary infection at its early stages allowing a long-term containment of virus replication and spread in blood and tissues.

A novel HIV-CCR5 receptor vaccine strategy in the control of mucosal SIV/HIV infection.

OBJECTIVE: To develop a novel SIV-CCR5 receptor vaccine strategy that will protect macaques from SHIV infection by the vaginal mucosal route. DESIGN: The rationale for this strategy is that humans who express the homozygous delta32 CCR5 mutation and the associated upregulation of CC chemokines, the down-modulation of cell-surface expression of CCR5 and antibodies to CCR5 are protected against HIV infection. METHODS: A vaccine was prepared consisting of three extracellular peptides of CCR5, an N-terminal HIV gp120 fragment generated in transgenic plants and recombinant SIV p27. These were linked to the 70 000 Mr microbial heat shock protein (HSP70) carrier. The vaccine was administered (x3) either by the vaginal mucosal route or by targeting the proximity of the draining iliac lymph nodes. RESULTS: Serum and vaginal fluid IgG and IgA antibodies, IL-2 and IFN-gamma-producing cells, and macrophage-inflammatory protein (MIP) 1beta and MIP-1alpha (CCL4 and CCL3) were significantly raised in immunized macaques (P = 0.01-0.05). Vaginal challenge with SHIV(89.6P) infected all macaques, but sequential analysis over 24 weeks showed a significant variation in viral loads between the animals (P = 0.05). Whereas SHIV(89.6P) persisted in the four unimmunized macaques, in five of the eight immunized macaques the virus was cleared or became undetectable by reverse transcriptase-polymerase chain reaction. The CD4 cell counts in the immunized macaques were significantly higher than those in unimmunized animals (P < 0.05). CONCLUSION: An immunization strategy that targets both the virus and its CCR5 receptor has significantly inhibited SHIV(89.6P) infection and may serve as a novel strategy in the prevention of HIV transmission.

Qualitative T-helper responses to multiple viral antigens correlate with vaccine-induced immunity to simian/human immunodeficiency virus infection.

Evidence is accumulating that CD4(+) T-helper (Th) responses play a critical role in facilitating effector responses which are capable of controlling and even preventing human immunodeficiency virus (HIV) infection. The present work was undertaken to determine whether immunization with multiple antigens influenced individual Th responses and increased protection relative to a single antigen. Rhesus macaques were primed with DNA and boosted (immune-stimulating complex-formulated protein) with a combination of regulatory and structural antigens (Tat-Env-Gag) or with Tat alone. Immunization with combined antigens reduced the magnitude of the responses to Tat compared to the single-antigen immunization. Interestingly, the Th immune responses to the individual antigens were noticeably different. To determine whether the qualitative differences in vaccine-induced Th responses correlated with vaccine efficacy, animals were challenged intravenously with simian/human immunodeficiency virus (strain SHIV(89.6p)) 2 months following the final immunization. Animals that developed combined Th1- and Th2-like responses to Gag and Th2 dominant Env-specific responses were protected from disease progression. Interestingly, one animal that was completely protected from infection had the strongest IFN-gamma and interleukin-2 (IL-2) responses prior to challenge, in addition to very strong IL-4 responses to Gag and Env. In contrast, animals with only a marked vaccine-induced Tat-specific Th2 response (no IFN-gamma) were not protected from infection or disease. These data support the rationale that effective HIV vaccine-induced immunity requires a combination of potent Th1- and Th2-like responses best directed to multiple antigens.

Single-cycle immunodeficiency viruses provide strategies for uncoupling in vivo expression levels from viral replicative capacity and for mimicking live-attenuated SIV vaccines.

To reduce the risks associated with live-attenuated immunodeficiency virus vaccines, single-cycle immunodeficiency viruses (SCIVs) were developed by primer complementation and production of the vaccine in the absence of vif in a vif-independent cell line. After a single intravenous injection of SCIVs into rhesus monkeys, peak viral RNA levels of 10(3) to 10(4) copies/ml plasma were observed, indicating efficient expression of SCIV in the vaccinee. After booster immunizations with SCIVs, SIV-specific humoral and cellular immune responses were observed. Although the vaccine doses used in this pilot study could not protect vaccinees from subsequent intravenous challenge with pathogenic SIVmac239, our results demonstrate that the novel SCIV approach allows us to uncouple in vivo expression levels from the viral replicative capacity facilitating the analysis of the relationship between viral expression levels or viral genes and immune responses induced by SIV.

Replication, immunogenicity, and protective properties of live-attenuated simian immunodeficiency viruses expressing interleukin-4 or interferon-gamma.

Nef deletion mutants of SIV-expressing interleukin-4 (SIV-IL4) or interferon-gamma (SIV-IFN) were constructed to study the effect of interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) on viral load, immunogenicity, and protective properties. Four rhesus monkeys were infected with SIV-IL4 and four were infected with SIV-IFN. During the acute phase of infection, the cell-associated viral load, but not the plasma viral RNA load, was approximately 10-fold lower in SIV-IFN-infected macaques than in SIV-IL4-infected rhesus monkeys. The viral load declined to hardly detectable levels 4 months postinfection in all animals. SIV antibody titers and the affinity of these antibodies were higher in SIV-IL4-infected macaques than in SIV-IFN-infected animals, consistent with a stimulation of T helper cell type 2 immune responses by IL-4. At peak viremia, there was a trend to higher interleukin-12 and perforin mRNA levels of the lymph nodes in the SIV-IFN-infected macaques than in the SIV-IL4-infected monkeys. Deletion of the viral IFN gene, but not the viral IL-4 gene, after the development of antiviral immune responses suggests a repressive effect of IFN, but not IL-4, on virus spread in vivo. A trend to higher set point viral RNA levels in SIV-IL4-infected monkeys in comparison to monkeys infected with the parental nef deletion mutant and similar viral RNA levels during the acute phase of infection suggest that IL-4 expression leads to a slight reduction in the control of virus replication by host immune responses. However, SIV-IL4 and SIV-IFN induced protection against a homologous challenge virus. Subsequent challenge with an SIV-HIV-1 hybrid virus (SHIV) also revealed protection in the absence of neutralizing antibodies.

T-cell receptor:CD3 down-regulation is a selected in vivo function of simian immunodeficiency virus Nef but is not sufficient for effective viral replication in rhesus macaques.

We investigated the function of severely truncated simian immunodeficiency virus (SIV) Nef proteins (tNef) in vitro and in vivo. These variants emerged in rhesus monkeys infected with SIVmac239 containing a 152-bp deletion in the nef-unique region and have been suggested to enhance SIV virulence (E. T. Sawai, M. S. Hamza, M. Ye, K. E. Shaw, and P. A. Luciw, J. Virol. 74:2038-2045, 2000). We found that the tNef proteins were unable to down-regulate the cell surface expression of major histocompatibility complex class I proteins, CD4, and CD28 and neither stimulated SIV replication nor enhanced virion infectivity. The tNef proteins did efficiently down-regulate T-cell receptor (TCR):CD3 cell surface expression. Nevertheless, the SIVmac239 tnef variants were strongly attenuated in six infected juvenile rhesus macaques. Thus, while the ability of SIV Nef to down-modulate TCR:CD3 cell surface expression apparently confers a selective advantage in vivo, it is insufficient for efficient viral replication in infected macaques. Additional mutations elsewhere in SIVmac239 tnef genomes are required for a virulent phenotype.

HIV-1 Tat-based vaccines: from basic science to clinical trials.

Vaccination against human immunodeficiency virus (HIV)-1 infection requires candidate antigen(s) (Ag) capable of inducing an effective, broad, and long-lasting immune response against HIV-1 despite mutation events leading to differences in virus clades. The HIV-1 Tat protein is more conserved than envelope proteins, is essential in the virus life cycle and is expressed very early upon virus entry. In addition, both humoral and cellular responses to Tat have been reported to correlate with a delayed progression to disease in both humans and monkeys. This suggested that Tat is an optimal target for vaccine development aimed at controlling virus replication and blocking disease onset. Here are reviewed the results of our studies including the effects of the Tat protein on monocyte-derived dendritic cells (MDDCs) that are key antigen-presenting cells (APCs), and the results from vaccination trials with both the Tat protein or tat DNA in monkeys. We provide evidence that the HIV-1 Tat protein is very efficiently taken up by MDDCs and promotes T helper (Th)-1 type immune responses against itself as well as other Ag. In addition, a Tat-based vaccine elicits an immune response capable of controlling primary infection of monkeys with the pathogenic SHIV89.6P at its early stages allowing the containment of virus spread. Based on these results and on data of Tat conservation and immune cross-recognition in field isolates from different clades, phase I clinical trials are being initiated in Italy for both preventive and therapeutic vaccination.

MHC class I alleles influence set-point viral load and survival time in simian immunodeficiency virus-infected rhesus monkeys.

In HIV-infected humans and SIV-infected rhesus macaques, host genes influence viral containment and hence the duration of the disease-free latency period. Our knowledge of the rhesus monkey immunogenetics, however, is limited. In this study, we describe partial cDNA sequences of five newly discovered rhesus macaque (Mamu) class I alleles and PCR-based typing techniques for the novel and previously published Mhc class I alleles. Using 15 primer pairs for PCR-based typing and DNA sequence analysis, we identified at least 21 Mhc class I alleles in a cohort of 91 SIV-infected macaques. The results confirm the presence of multiple class I genes in rhesus macaques. Of these alleles, Mamu-A*01 was significantly associated with lower set-point viral load and prolonged survival time. Mamu-A*1303 was associated with longer survival and a "novel" Mhc class I allele with lower set-point viral load. The alleles are frequent in rhesus macaques of Indian origin (12-22%). In addition, survival probability of individual SIV-infected rhesus monkeys increased with their number of alleles considered to be associated with longer survival. The results contribute to improve the interpretation and quality of preclinical studies in rhesus monkeys.

Immunization with recombinant modified vaccinia virus Ankara can modify mucosal simian immunodeficiency virus infection and delay disease progression in macaques.

In the present study, the immunogenicity and protective efficacy of a recombinant vaccinia virus-based simian immunodeficiency virus (SIV) vaccine, given alone or in combination with a protein boost, were investigated. Cynomolgus macaques were immunized intramuscularly with modified vaccinia virus Ankara (MVA) expressing the SIVsm env and gag-pol genes (MVA-SIVsm) at 0 and 3 months (n=4), at 0, 3 and 8 months (n=4) or at 0 and 3 months followed by purified native SIVsm gp148 and recombinant SIVmac p27 in immunostimulatory complexes at 8 months (n=4). One month after the last immunization, the vaccinees, together with four naive control monkeys and four monkeys immunized with wild-type MVA, were challenged intrarectally with 10 MID50 SIVsm. At the time of challenge, antibody titres to SIV Env and lymphocyte proliferation responses to whole viral antigen were highest in vaccinees receiving MVA-SIVsm in combination with protein immunizations. Following rectal challenge, one of these vaccinees was completely protected. A prolonged survival time was observed in two of four monkeys in each of the groups immunized with MVA-SIVsm, in two monkeys given MVA-SIVsm followed by protein and in three of four monkeys given wild-type MVA, compared with naive controls. In conclusion, one monkey given the combined vaccine was protected completely against SIVsm infection. Furthermore, immunization with MVA-SIVsm, as well as wild-type MVA alone, seemed to delay disease progression after mucosal SIV infection in a proportion of the monkeys.

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

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

Cross-protection against mucosal simian immunodeficiency virus (SIVsm) challenge in human immunodeficiency virus type 2-vaccinated cynomolgus monkeys.

In this study we compared the efficacy of live attenuated human immunodeficiency virus type 2 (HIV-2) vaccine alone versus boosting with live non-pathogenic HIV-2 following priming with ALVAC HIV-2 (recombinant canarypox virus expressing HIV-2 env, gag and pol). Six monkeys were first inoculated intravenously with live HIV-2(SBL-6669) and 7 to 10 months later were challenged intrarectally with 10 MID(50) of cell-free simian immunodeficiency virus (SIV) strain SIVsm. One monkey was completely protected against SIV infection and all five monkeys that became SIV-infected showed a lower virus replication and an initial lower virus load as compared with a parallel group of six control animals. In another experiment five monkeys were immunized either three times with ALVAC HIV-2 alone or twice with ALVAC HIV-2 and once with purified native HIV-2 gp125. The monkeys were then challenged with HIV-2 given intravenously and finally with pathogenic SIVsm given intrarectally. After challenge with SIVsm, three of five monkeys were completely protected against SIVsm infection whereas the remaining two macaques became SIV-infected but with limited virus replication. In conclusion, vaccination with an ALVAC HIV-2 vaccine followed by exposure to live HIV-2 could induce cross-protection against mucosal infection with SIVsm and seemed to be more efficient than immunization with a live HIV-2 vaccine only.

Specific passage of simian immunodeficiency virus from end-stage disease results in accelerated progression to AIDS in rhesus macaques.

To determine whether passage of late-stage variants of simian immunodeficiency virus (SIV) would lead to a more virulent infection and rapid disease progression, a study was designed to examine the effects of selective transmission of SIV from late-stage cases of AIDS in Macaca mulatta. In a uniform group of 10 age-matched animals from the same genetic breeding stock infected with SIV(B670), it took 7 months before one of the ten animals developed AIDS. Passage of virus taken from this animal immediately prior to death resulted in death of the recipient due to AIDS within 4 months. Again, subsequent passage of virus taken late in disease resulted in an accelerated disease course, with AIDS developing within 2.5 and 1.8 months in two recipients. The fourth passage of virus taken late in disease from the most rapid progressor (1.8 months) resulted in AIDS developing in this recipient within 1 month of infection. During each consecutive passage in vivo, the loss of memory T cells became more acute. Evidence that the virus became more virulent with selective passage of late-stage variants was provided by the markedly increased levels of both plasma antigen and viral RNA. Subsequent in vivo passage from end-stage AIDS selected for a strain of SIV capable of causing the acute development of AIDS as rapidly as 1 month post-infection. The pathology of acute AIDS in these cases closely resembled that seen after a chronic disease course.