Ethical considerations related to the provision of care and treatment in vaccine trials

Ethical principles of beneficence and justice combined with international human rights norms and standards create certain obligations on researchers, sponsors and public health authorities. These include treatment provision for participants enrolled in clinical trials of vaccines, drugs and other new preventive and curative technologies and methods. However, these obligations are poorly defined in practical terms, inconsistently understood or inadequately applied. Vaccine clinical trial designs normally define standards of prevention applicable to the population where the trial is to take place. The present document addresses specifically the setting of standards applicable to care and treatment in vaccine trials. The lack of clear guidance on how to achieve the optimal synergy between the development of new health technologies, on the one hand, and the promotion and protection of ethical and human rights principles, on the other, is a barrier to the progress of health research and therefore to the advancement of public health. The World Health Organization and UNAIDS have engaged in a series of consultations in Africa, the Americas, Asia and Europe to reflect on how this aim could best be achieved. This document highlights the outcome of these consultations. It proposes a structured approach to consensual decision making in the context of the clinical trial of vaccines against such public health challenges as HIV and newly emerging or threatening epidemics. A structured approach involving investigators and sponsors in a consultative process with trial communities and other stakeholders in research will ensure that the needs and legitimate expectations of trial participants are appropriately met, obligations towards them are delivered and, as a result, ethical research is facilitated in the interest of public health.

Malaria Vaccine Development: Progress and Challenges

A safe and effective malaria vaccine would contribute greatly to the control and prevention of the disease. Although a review of global activity in malaria vaccine development does reflect significant activity, progress has remained slow. This article discusses the current vaccine candidates, with emphasis on those in the clinic, and explains the numerous challenges to making and evaluating malaria vaccines, which have resulted in only a few approaches being adopted and repeatedly evaluated. Against a parasite with more than 5200 genes, the lack of definitive knowledge regarding the nature of protective immunity and absence of reliable surrogates of protection are among the key challenges to a rational evaluation and prioritization of candidate vaccines. Pursuing the current R&D strategies may not result in the availability of a vaccine with characteristics suitable to impact significantly on disease morbidity in developing countries. Therefore, it is critical that the main challenges to malaria vaccine development be unambiguously identified and collectively addressed.

Review on flavivirus vaccine development. Proceedings of a meeting jointly organised by the World Health Organization and the Thai Ministry of Public Health, 26-27 April 2004, Bangkok, Thailand

In light of the continuous spread of human pathogenic flaviviruses, in particular the mosquito-transmitted species, vaccine development remains a high priority on the public health agenda. On 26-27 April 2004, a conference was held in Bangkok, Thailand, to review current status of flavivirus vaccine development and related issues, focussing on dengue (DEN) and Japanese encephalitis (JE). This event, co-sponsored by the World Health Organization (WHO) and the Thai Ministry of Public Health, reviewed the progress made with vaccine development, sero-epidemiological studies and other accompanying activities critical for vaccine development and vaccination. The considerable interest in and awareness of the flavivirus diseases and their prevention by public health decision makers, as well as the establishment of two dedicated programmes for dengue and Japanese encephalitis vaccine development raise hopes that new or improved vaccines will become available in the coming years.

HCV core, NS3, NS5A and NS5B proteins modulate cell proliferation independently from p53 expression in hepatocarcinoma cell lines

Several reports have shown that activity and/or expression of p53 can be modulated by Hepatitis C virus (HCV) proteins and may interfere with normal regulation of cell growth. In order to understand the relationship between p53 function and HCV proteins expression, we have investigated potential effects of the core, NS3, NS5A and NS5B proteins on Huh-7 (p53 +/+) and Hep3B (p53 -/-) cell proliferation. The effect of HCV proteins transiently expressed after recombinant-adenoviral infection was analyzed by Western blot, crystal violet and propidium iodide staining. Expression of the core, NS3, NS5A or NS5B proteins inhibited cell proliferation and blocked both cell lines in the G2/M phase of the cell cycle. c-myc and p53 expression were respectively induced and increased in Huh-7 cells only following expression of the Core protein. No expression of p21(waf1/cip1) could be detected and expression of cyclin A, cdk2 and p27(Kip1) were independent of HCV protein's expression. Our results show that the effect of core, NS3, NS5A and NS5B on cell proliferation is independent of p53 expression and that only the Core protein, induces the expression of both c-myc and p53.

Vaccines for parasitic diseases

Significant effort and progress has occurred over the last several years in the development of vaccines against three main tropical parasitic diseases (malaria, leishmaniases and schistosomiasis). However, an effective vaccine is not yet available. The difficulties in developing a vaccine against parasitic disease are complicated not only by the necessity to identify (and produce) appropriate, protective antigens but also a lack of complete understanding of the types of immune responses needed for protection. Despite these hurdles, several candidate vaccines are under development for each disease; at least one promising vaccine candidate exists that is in late stage clinical testing.

Recombinant vaccinia viruses expressing immunoglobulin variable regions efficiently and selectively protect mice against tumoral B-cell growth

The variable regions of the immunoglobulin (Ig) expressed on the surface of a malignant B cell can be considered tumor-specific antigens and, as such, could be targets for immunotherapeutic approaches. However, because until now the immunization procedures have been complex and have given only partial protection, it was necessary to find new methods of immunotherapy. Here, we present a successful method of vaccination against B-cell tumors in a murine model. We produced recombinant vaccinia viruses (rVV) expressing the heavy and the light chain of surface Ig of a patient's malignant B cells and we tested the ability of these rVV to protect immunized mice against tumor growth of transfectomas producing the same human Ig. The protection of the mice was complete and specific to the variable region of the immunizing heavy chain although specific lymphoproliferative and cytotoxic responses were not detectable in vitro. The protection was strictly dependent on the presence of CD4 T cells and asialo GM1+ cells. Furthermore, tumor protection clearly required gamma-interferon and was partially inhibited by blocking the Fas-Fas ligand interaction. We also show, in a murine syngeneic model, that rVV expressing a poorly mutated Ig protects against the growth of Ig-producing tumor.

Persistence of pathogenic challenge virus in macaques protected by simian immunodeficiency virus SIVmacDeltanef

Live attenuated simian immunodeficiency virus (SIV) is the most efficient vaccine yet developed in monkey models of human immunodeficiency virus infection. In all successful vaccine trials, attenuation was achieved by inactivating at least the nef gene. We investigated some virological and immunological characteristics of five rhesus macaques immunized with a nef-inactivated SIVmac251 molecular clone (SIVmac251Deltanef) and challenged 15 months later with the pathogenic SIVmac251 isolate. Three animals were killed 2 weeks postchallenge (p.c.) to search for the challenge virus and to assess immunological changes in various organs. The other two animals have been monitored up for 7 years p.c., with clinical and nef gene changes being noted. The animals killed showed no increase in viral load and no sign of a secondary immune response, although the challenged virus was occasionally detected by PCR. In one of the monkeys being monitored, the vaccine virus persisted and an additional deletion occurred in nef. In the other monkey that was monitored, the challenge and the vaccine (Deltanef) viruses were both detected by PCR until a virus with a hybrid nef allele was isolated 48 months p.c. This nef hybrid encodes a 245-amino-acid protein. Thus, our results show (i) that monkeys were not totally protected against homologous virus challenge but controlled the challenge very efficiently in the absence of a secondary immune response, and (ii) that the challenge and vaccine viruses may persist in a replication-competent form for long periods after the challenge, possibly resulting in recombination between the two viruses.

Recombinant vaccinia virus encoding human MUC1 and IL2 as immunotherapy in patients with breast cancer

Polymorphic epithelial mucin, encoded by the MUC1 gene, is present at the apical surface of glandular epithelial cells. It is over-expressed and aberrantly glycosylated in most breast tumors, resulting in an antigenically distinct molecule and a potential target for immunotherapy. This transmembrane protein, when produced by tumor cells, is often cleaved into the circulation, where it is detectable as a tumor marker (CA 15.3) by various antibodies, allowing for early detection of recurrences and evaluation of treatment efficacy. The objective of the current study was to examine the clinical and environmental safety and immunogenicity of a live recombinant vaccinia virus expressing the human MUC1 and IL2 genes (VV TG5058), referred to here as TG1031. The study was an open-label phase 1 and 2 trial in nine patients with advanced inoperable breast cancer recurrences to the chest wall. The patients were vaccinated intramuscularly with a single dose of TG1031; three patients were treated at each of three progressive dose levels ranging from 5x10(5) to 5x10(7) plaque-forming units. A boost injection at their original dose level was administered in patients responding immunologically, clinically, or both. Vaccination resulted in no significant clinical adverse effects, and there was no environmental contamination by live TG1031. All patients had been vaccinated as children, and patients treated at the highest dose level mounted a significant anti-vaccinia antibody response. None of the nine patients had a significant increase in MUC1-specific antibody titers after one single injection, whereas five patients had a detectable increase in vaccinia virus antibody titers. Peripheral blood mononuclear cells of one patient at the intermediate dose level showed a proliferative response to in vitro culture with vaccinia virus, with a stimulation index of 6. A second patient treated at the intermediate dose level had a stimulation index of 7 to MUC1 peptide and of 14 after a boost injection. This patient had a concomitant decrease in carcinoembryonic antigen serum levels and remained clinically stable for 10 weeks. Evidence of MUC1-specific cytotoxic T lymphocytes was detected in two patients. Immunohistochemical analysis revealed an increase in T memory cells (CD45RO) in tumor biopsies after vaccination. The absence of serious adverse events, together with the documentation of immune stimulations in vivo, warrant the further use of TG1031 in immunotherapy trials of breast cancer.

An anti-human immunodeficiency virus multiple antigen peptide encompassing the cleavage region of the env precursor interferes with membrane fusion at a post-CD4 binding step

CLIV is a multiple antigen peptide ([PTKAKRRVVQREKR](4)-K(2)-K-betaA) that encompasses the cleavage region of the human immunodeficiency virus type 1 (HIV-1) envelope precursor. It displays an antiviral activity against HIV-1 and HIV-2 and inhibits HIV-1 Env-mediated cell-to-cell fusion. This effect has previously been attributed to interference with Env processing, resulting in the expression of a nonfusogenic envelope [Virology (1998) 247, 137]. However, we show here that CLIV does not alter the status of Env cleavage at steady state. Using various aggregation/syncytium assays that allow us to discriminate between gp120/CD4 binding and binding followed by gp41-mediated fusion, we demonstrate that CLIV inhibits a step of the cell-to-cell fusion process after CD4 binding. We demonstrate also that CLIV binds at 37 degrees C to a single class of protein present at the CD4(+) cell surface (Scatchard analysis: K(d) = 8 nM; B(max) = 10(4) sites/cell) and that the fusion inhibition activity seems to correlate with binding to this proteic component. In contrast, CLIV interacts with neither membrane-inserted nor CD4-associated Env. We therefore propose that CLIV interferes after Env/CD4 binding with a step of the membrane fusion process that may involve the C-terminal domain of gp120.

Targeted macrophage cytotoxicity using a nonreplicative live vector expressing a tumor-specific single-chain variable region fragment

Antigen-specific recognition and subsequent destruction of tumor cells is the goal of vaccine-based immunotherapy of cancer. Often, however, tumor antigen-specific cytotoxic T lymphocytes (CTLs) are either not available or in a state of anergy. In addition, MHCI expression on tumor cells is often downregulated. Either or both of these situations can allow tumor growth to proceed unchecked by CTL control. We have shown previously that tumor antigen-specific monoclonal antibodies can be expressed in vaccinia virus and that activated macrophages infected with this virus acquire the ability to kill tumor cells expressing that antigen. Here we show that a membrane-anchored form of the scFv portion of the MUC1 tumor antigen-specific monoclonal antibody, SM3, can be expressed on activated macrophages with the highly attenuated poxvirus, modified vaccinia Ankara (MVA), as a gene transfer vector. Cells infected with the MVA-scFv construct were shown to express the membrane-bound scFv by Western blot and FACS analysis. That cells expressing the membrane-anchored scFv specifically bind antigen was shown by FACS and by BIAcore analysis. GM-CSF-activated macrophages were infected with the construct and shown to recognize specifically MUC1-expressing tumor cells as measured by IL-12 release. Furthermore, activated macrophages expressing the membrane-bound scFv specifically lyse target cells expressing the MUC1 antigen but not cells that do not express MUC1.

Redirected cellular cytotoxicity by infection of effector cells with a recombinant vaccinia virus encoding a tumor-specific monoclonal antibody

Cytotoxicity is an important function of the immune system that results in the destruction of cellular targets by humoral and/or cellular mechanisms. We wanted to assess the possibility of targeting the lytic function of immune cells toward cancer cells, which express the gene coding for a known tumor antigen (Ag) (GA733-2/epithelial cell adhesion molecule), using a viral vector encoding a monoclonal antibody (mAb) specific for said tumor Ag (CO17-1A). To this end, we have constructed recombinant vaccinia viruses expressing the sequences corresponding to mAb CO17-1A, which recognizes a specific Ag (GA733-2) that is present on the surface of most gastrointestinal carcinomas. The recombinant vectors encoding either a secreted or membrane-anchored form of CO17-1A mAb were used to infect effector cells, which were subsequently assessed for their cytotoxic activity. The recombinant viruses were able to infect both granulocyte-macrophage colony-stimulating factor-activated human macrophages and Ag-stimulated murine cytotoxic T lymphocytes. Infected granulocyte-macrophage colony-stimulating factor-activated macrophages were found to be able to kill GA733-2-expressing tumor cells. Likewise, infected cytotoxic T lymphocytes, although conserving their original alloreactivity, gained the capability of killing GA733-2-expressing cancer cells.

Mucosal immunity and tolerance: relevance to vaccine development

The mucosal immune system of mammals consists of an integrated network of lymphoid cells which work in concert with innate host factors to promote host defense. Major mucosal effector immune mechanisms include secretory antibodies, largely of immunoglobulin A (IgA) isotype, cytotoxic T cells, as well as cytokines, chemokines and their receptors. Immunologic unresponsiveness (tolerance) is a key feature of the mucosal immune system, and deliberate vaccination or natural immunization by a mucosal route can effectively induce immune suppression. The diverse compartments located in the aerodigestive and genitourinary tracts and exocrine glands communicate via preferential homing of lymphocytes and antigen-presenting cells. Mucosal administration of antigens may result in the concomitant expression of secretory immunoglobulin A (S-IgA) antibody responses in various mucosal tissues and secretions, and under certain conditions, in the suppression of immune responses. Thus, developing formulations based on efficient delivery of selected antigens/tolerogens, cytokines and adjuvants may impact on the design of future vaccines and of specific immunotherapeutic approaches against diseases associated with untoward immune responses, such as autoimmune disorders, allergic reactions, and tissue-damaging inflammatory reactions triggered by persistent microorganisms.

Lack of evidence for an immunosuppressive role for MUC1

The in vitro anti-proliferative properties of various supernatants from MUC1-expressing cell lines and of purified preparations of MUC1 were evaluated. We have observed that supernatants from the MUC1-and MUC3-positive cell line T47D, but not from the MUC1- and MUC4-positive cell line MCF7, were able to inhibit proliferation of cells from various haematopoietic cell lines. Although the activity of T47D supernatants could be abrogated by immunodepletion of MUC1, immunopurified MUC1 from T47D was unable to inhibit cell proliferation. Significantly, supernatants from mouse 3T3 cells transfected with a secreted form of MUC1 or from BHK-21 cells infected with a recombinant vaccinia virus coding for the secreted form of MUC1, as well as preparations of purified MUC1 from bile or urine, were likewise unable to inhibit T cell proliferation. Surprisingly, a crude mixture of bile mucins had a suppressive effect on T cell growth. Our results suggest that other molecules, such as amino sugars or other mucins, which can associate with MUC1, are likely to be responsible for the observed anti-proliferative effects of T47D cells.

Production of cholera toxin B subunit in Lactobacillus

The intracellular expression of the B subunit of cholera toxin (CTB) was first achieved in Lactobacillus paracasei LbTGS1.4 with an expression cassette including the P25 promoter of Streptococcus thermophilus combined with the translation initiation region from the strongly expressed L. pentosus D-lactate dehydrogenase gene (ldhD). Secretion of CTB was next attempted in L. paracasei LbTGS1.4 and L. plantarum NCIMB8826 with four different signal sequences from exported proteins of lactic acid bacteria (Lactococcus lactis Usp45 and PrtP, Enterococcus faecalis unknown protein and S. pyogenes M6 protein). Host-dependent secretion of CTB was clearly observed: whereas none of the secretion cassettes led to detectable CTB in the extracellular fraction of L. paracasei LbTGS1.4, secretion of CTB molecules was clearly achieved with three of the selected signal sequences in L. plantarum NCIMB8826.

Restricted specificity of anti-V3 antibodies induced in humans by HIV candidate vaccines

We analyzed the fine specificity of anti-V3 antibodies elicited in three different species (human, guinea pig, and macaque) by various HIV candidate vaccines. Following immunization with recombinant canarypox virus expressing gp160MN or with recombinant gp160MN/LAI, this antibody response was shown to be directed against the NH2-terminal region of the V3 loop. Although this response was increased by a prime-boost regimen using immunization with canarypox expressing gp160 followed by an rgp160 boost, its specificity remained restricted mainly to the recognition of this region of the V3 loop. Pepscan analysis of sera confirmed the results obtained by ELISA and allowed the definition of an immunodominant common binding site for these sera located within the sequence NKRKRIHIGPGR. In contrast to these results, a boost with the V3 peptide was shown to broaden the antibody response and pepscan analysis showed that sera from individuals boosted with the V3 synthetic peptide recognize determinants all along the V3 loop. Similar fine specificity of anti-V3 antibodies was obtained in human, guinea pig, and macaque following immunization by a prime-boost regimen using canarypox recombinants expressing gp160 or gp120 and purified rgp160. In contrast, a V3 synthetic peptide boost stimulated the production of antibodies that recognize multiple epitopes within the V3 loop. Because the induction of antibodies that recognize multiple sites in the V3 loop could be of major importance to neutralize different HIV isolates, these results may have implications for the design and selection of HIV candidate vaccines.

Protection of SIVmac-infected macaque monkeys against superinfection by a simian immunodeficiency virus expressing envelope glycoproteins of HIV type 1

The infection of macaque monkeys by attenuated simian immunodeficiency virus can vaccinate against pathogenic molecular clones and isolates of the same virus. The correlates of this potent protective immunity are not fully understood but may be the key to an effective AIDS vaccine for humans. Aiming to determine whether host immune responses to envelope glycoprotein are an essential component of the immunity to primate lentiviruses, we have tried to superinfect SIVmac-infected macaque monkeys with SHIVsbg, a chimeric primate lentivirus constructed from the SIVmac239 genome with the env, rev, tat, and vpu genes from HIV-1 Lai. After inoculation of a large dose of SHIVsbg, the chimeric virus was isolated by coculture of mononuclear blood cells from four of five SIV-infected monkeys, but three animals were protected from extracellular SHIV viremia and did not seroconvert to HIV-1 glycoproteins. In the two SIV-infected monkeys that did develop SHIV viremia, cell-associated viral load was reduced at least 100-fold. These data indicate that an antiviral response capable of effectively controlling primate lentivirus replication might not necessarily involve the envelope glycoprotein.

Cyp7b, a novel brain cytochrome P450, catalyzes the synthesis of neurosteroids 7alpha-hydroxy dehydroepiandrosterone and 7alpha-hydroxy pregnenolone

Steroids produced locally in brain (neurosteroids), including dehydroepiandrosterone (DHEA), influence cognition and behavior. We previously described a novel cytochrome P450, Cyp7b, strongly expressed in rat and mouse brain, particularly in hippocampus. Cyp7b is most similar to steroidogenic P450s and potentially could play a role in neurosteroid metabolism. To examine the catalytic activity of the enzyme mouse Cyp7b cDNA was introduced into a vaccinia virus vector. Extracts from cells infected with the recombinant showed NADPH-dependent conversion of DHEA (Km, 13.6 microM) and pregnenolone (Km, 4.0 microM) to slower migrating forms on thin layer chromatography. The expressed enzyme was less active against 25-hydroxycholesterol, 17beta-estradiol and 5alpha-androstane-3beta,17beta-diol, with low to undetectable activity against progesterone, corticosterone, and testosterone. On gas chromatography and mass spectrometry of the Cyp7b metabolite of DHEA the retention time and fragmentation patterns were identical to those obtained with authentic 7alpha-hydroxy DHEA. The reaction product also comigrated on thin layer chromatography with 7alpha-hydroxy DHEA but not with 7beta-hydroxy DHEA; when [7alpha-3H]pregnenolone was incubated with Cyp7b extracts the extent of release of radioactivity into the medium suggested that hydroxylation was preferentially at the 7alpha position. Brain extracts also efficiently liberated tritium from [7alpha-3H]pregnenolone and converted DHEA to a product with a chromatographic mobility indistinguishable from 7alpha-hydroxy DHEA. We conclude that Cyp7b is a 7alpha-hydroxylase participating in the synthesis, in brain, of neurosteroids 7alpha-hydroxy DHEA, and 7alpha-hydroxy pregnenolone.

Immunogenicity of HIV-1LAI gp160 and env peptides in squirrel monkey Saimiri sciureus using alumine and experimental adjuvants

Since the identification of the HIV virus, important advances have been achieved in the definition of potential subunit vaccines. We investigated the immunogenicity of a recombinant gp160 antigen and of two gp41 peptides from HIV-1LAI associated with seven different adjuvant formulations in squirrel monkeys. All animals were immunized twice with gp160 and then with a gp41 peptide using the same formulation. All adjuvants used led to a subsequent antibody response against gp160, and 55% of the animals immunized developed anti-gp160 antibodies that could neutralize the virus in vitro. Specific anti-gp41 antibody response was also observed. Results obtained underlined the key role of the adjuvant formulation in the antibody response against a given part of the immunogen, and indicate that such immunogenicity-related investigation can be carried out conveniently in the squirrel monkey Saimiri sciureus.

Memory cytotoxic T lymphocyte responses in human immunodeficiency virus type 1 (HIV-1)-negative volunteers immunized with a recombinant canarypox expressing gp 160 of HIV-1 and boosted with a recombinant gp160

A vaccine against human immunodeficiency virus (HIV) should induce virus-specific cytotoxic T lymphocyte (CTL) activity. Immunization of uninfected volunteers with a canarypox virus expressing HIV envelope was carried out in a phase I trial. Two injections of canarypox expressing HIV-1MN gp 160 (months 0 and 1) were followed by two boosts of recombinant envelope protein (months 3 and 6). HIV envelope-specific CTL were detected in peripheral blood mononuclear cells stimulated with autologous HIV-1-infected blast cells. T cell lines were obtained from 18 of 20 donors: CTL were detected at least once following immunization in 7 (39%) of these 18. This activity was mediated by major histocompatibility complex class I-restricted CD3+CD8+ T cells. For two subjects, this activity was still present 2 years after the initial immunization. The CTL responses with this prime-boost regimen are the best observed with any HIV vaccine tested in humans.

High viral load and CD4 lymphopenia in rhesus and cynomolgus macaques infected by a chimeric primate lentivirus constructed using the env, rev, tat, and vpu genes from HIV-1 Lai

Chimeric primate lentiviruses composed of SIV and HIV genes may allow the analysis of the role of these discrete HIV genes in viral pathogenesis in macaque monkeys. We have constructed a chimeric virus in which the env, rev, tat, and vpu genes of HIV-1 Lai replace the env, rev, and tat genes of the SIVmac239 genome. This virus, SHIVsbg, replicates efficiently in rhesus (Indian and Chinese subspecies) and cynomolgus monkeys with viral loads in PBMC and lymph nodes of up to one infected cell per 30 cells during the acute phase of the infection. Sera from all monkeys recognize specific HIV-1 glycoproteins. The onset of lymphadenopathy in all animals was concurrent with a depletion of CD4 lymphocytes in peripheral blood. The virulence of this SHIV for rhesus and cynomolgus monkeys therefore closely parallels that of HIV-1 for human in the acute phase of the infection. Changes in the env and vpu genes of a molecular clone of HIV-1 can now be analyzed after passage in nonhuman primate species as the SHIVsbg replicates efficiently. The SHIVsbg-macaque model is an important step in the development of a readily available animal model for HIV-1 vaccine studies.

Diversity of the envelope glycoprotein among human immunodeficiency virus type 1 isolates of clade E from Asia and Africa

Human immunodeficiency virus type 1 isolates of clade E, known to be largely responsible for the fulminating epidemic in Southeast Asia, have been derived exclusively from Asia and Africa. Here we provide full or partial sequences of the envelope glycoprotein gene from 13 additional clade E isolates from Asia representing patients in both early and late stages of disease. More extensive comparison of isolates within clade E by geographic locale, stage of disease, and year of isolation is now possible. The genetic diversity of clade E isolates from Asia, particularly among those derived from early-stage patients, is restricted compared with African isolates (mean interisolate distances in gp120, 5.4 and 20.2%, respectively). However, patients hospitalized with AIDS-related illnesses in Thailand harbored clade E isolates exhibiting broader interisolate diversity and with highly heterogeneous third hypervariable loop sequences. An additional pair of cysteine residues, predicting a novel disulfide bridge and present in 80% of clade E isolates from Asia, was uniformly absent from six African isolates. Clade E isolates in Thailand from early-stage subjects continue to be genetically similar to potential vaccine prototype strains, providing a favorable environment for the evaluation of genotype E candidate vaccines. However, evidence of increasing interisolate diversity is appearing among late-stage patients in Asia. This diversification of the clade E virus, if sustained, may impact preventive vaccine development strategies.

Safety and immunogenicity of a recombinant HIV type 1 glycoprotein 160 boosted by a V3 synthetic peptide in HIV-negative volunteers

The safety and the immunogenicity of a recombinant hybrid envelope glycoprotein MN/LAI (rgp160) followed by booster injections of a V3 (MN) linear peptide were evaluated in HIV-negative adults at low risk for HIV infection. Volunteers received either rgp160 in alum at 0, 1, and 6 months (group A), rgp160 at 0 and 1 months followed by V3 at 3 and 6 months formulated in alum (group B), or in Freund's incomplete adjuvant (FIA) (group C). Local and systemic reactions were mild to moderate and resolved within the first 72 hr after immunization. No significant biological changes (routine tests and autoantibodies) were observed. One month after the last injection in either group, neutralizing antibodies (NAs) against the HIV-1 MN isolate were detected in 4 of 5 (A), 7 of 10 (B), and 10 of 10 (C) subjects with significantly higher geometric mean titers in the latter group. Four of nine sera with the highest NA titers against MN weakly cross-neutralized the HIV-1 SF2 isolate; none had NA against the HIV-1 LAI strain or against a North American primary isolate. Specific lymphocyte T cell proliferation to rgp160 was detected in 92% of the subjects after the second injection of rgp160 and in 80% of them 12 months after the first injection. A weak and short-lived envelope-specific CD(4+)-mediated cytotoxic lymphocyte activity was detected at certain time points in few subjects. This prime-boost vaccine approach using rgp160 followed by a V3 peptide was safe in humans, and was able to elicit high levels of neutralizing antibodies and a strong and persistent T cell lymphoproliferative response to rgp160 and to V3. However, the neutralization response was restricted to the homologous HIV-1 strain and little env-specific cytotoxic activity was induced.

Vaccine-induced protection of chimpanzees against infection by a heterologous human immunodeficiency virus type 1

The extraordinary genetic diversity of human immunodeficiency virus type 1 (HIV-1) is a major problem to overcome in the development of an effective vaccine. In the most reliable animal model of HIV-1 infection, chimpanzees were immunized with various combinations of HIV-1 antigens, which were derived primarily from the surface glycoprotein, gp160, of HIV-1 strains LAI and MN. The immunogens also included a live recombinant canarypox virus expressing a gp160-MN protein. In one experiment, two chimpanzees were immunized multiple times; one animal received antigens derived only from HIV-1LAI, and the second animal received antigens from both HIV-1LAI and HIV-1MN. In another experiment, four chimpanzees were immunized in parallel a total of five times over 18 months; two animals received purified gp160 and V3-MN peptides, whereas the other two animals received the recombinant canarypox virus and gp160. At 3 months after the final booster, all immunized and naive control chimpanzees were challenged by intravenous inoculation of HIV-1SF2; therefore, the study represented an intrasubtype B heterologous virus challenge. Virologic and serologic follow-up showed that the controls and the two chimpanzees immunized with the live recombinant canarypox virus became infected, whereas the other animals that were immunized with gp160 and V3-MN peptides were protected from infection. Evaluation of both cellular and humoral HIV-specific immune responses at the time of infectious HIV-1 challenge identified the following as possible correlates of protection: antibody titers to the V3 loop of MN and neutralizing antibody titers to HIV-1MN or HIV-1LAI, but not to HIV-1SF2. The results of this study indicate that vaccine-mediated protection against intravenous infection with heterologous HIV-1 strains of the same subtype is possible with some immunogens.

Single peptide and anti-idiotype based immunizations can broaden the antibody response against the variable V3 domain of HIV-1 in mice

The third variable (V3) domain of the human immunodeficiency virus type 1 (HIV-1) external envelope glycoprotein gp120 is a major target of neutralizing antibodies in infected persons and in experimental immunized animals. Given the high degree of sequence variability of V3, the humoral response toward this region is very type-specific. In the present study, we evaluated the potential of a single peptide and an anti-idiotypic antibody to broaden the anti-V3 antibody specificity in BALB/c mice. We show that a synthetic peptide derived from the V3 determinant of HIV-1 MN isolate (V3MN), when used as an immunogen, was able to induce an antibody response to multiple (up to six) HIV-1 strains. The extent of this cross-reactivity, which tended to enlarge as the injections increased, appeared to be inversely correlated with the binding affinity to V3MN peptide. These data thus present evidence that, despite its great sequence heterogeneity, the V3 loop encompasses conserved amino-acid positions and/or stretches which may be less immunogenic than their variable counterparts. We additionally demonstrate that a rabbit anti-idiotype (Ab2), recognizing a binding site related idiotype on a V3-specific mouse monoclonal antibody (Ab1), could mount a broadened humoral response (Ab3) in mice. Unlike nominal antibody Ab1 which strictly reacted with the European HIV-1 LAI isolate, elicited Ab3 recognized the two divergent HIV-1 strains SF2 and 1286, originating respectively from North America and Central Africa, in addition to LAI. The reasons accounting for this Ab2-induced enlargement of the V3 antibody response are discussed. Our findings suggest that single peptide and anti-idiotype based immunizations may provide viable approaches to overcome, at least in part, HIV epitope variability.

Cloned antigens and antiidiotypes

Both monoclonal and polyclonal antiidiotypic antibodies mimicking the human colorectal carcinoma (CRC) associated antigen CO17-1A/GA733 have induced antigen-specific humoral and cellular immunity in CRC patients. The immune responses may underlie the clinical responses observed in some of the treated patients. Recently, the CO17-1A/GA733 antigen has been molecularly cloned and expressed in baculo-, adeno-, and vaccinia viruses. In preclinical studies, these recombinant antigen preparations elicited specific humoral immunity (cytotoxic antibodies) and cellular immunity (DTH-reactive and proliferative T cells). Antibody titers elicited in animals by recombinant antigen were significantly higher than those elicited by antiidiotypes. The recombinant antigen has a potential as a vaccine for CRC patients.

HIV-1 recombinant poxvirus vaccine induces cross-protection against HIV-2 challenge in rhesus macaques

Rhesus macaques were immunized with attenuated vaccinia or canarypox human immunodeficiency virus type 1 (HIV-1) recombinants and boosted with HIV-1 protein subunits formulated in alum. Following challenge with HIV-2SBL6669, three out of eight immunized macaques resisted infection for six months and another exhibited significantly delayed infection, whereas all three naive controls became infected. Immunizations elicited both humoral and cellular immune responses; however, no clear correlates of protection were discerned. Although more extensive studies are now called for, this first demonstration of cross-protection between HIV-1 and -2 suggests that viral variability may not be an insurmountable problem in the design of a global AIDS vaccine.

A prime-boost approach to HIV preventive vaccine using a recombinant canarypox virus expressing glycoprotein 160 (MN) followed by a recombinant glycoprotein 160 (MN/LAI). The AGIS Group, and l'Agence Nationale de Recherche sur le SIDA

The safety and the immunogenicity of a recombinant canarypox live vector expressing the human immunodeficiency virus type 1 (HIV-1) gp160 gene from the MN isolate, ALVAC-HIV (vCP125), followed by booster injections of a soluble recombinant hybrid envelope glycoprotein MN/LAI (rgp160), were evaluated in vaccinia-immune, healthy adults at low risk for acquiring HIV-1 infection. Volunteers (n = 20) received vCP125 (10(6) TCID50) at 0 and 1 month, followed randomly by rgp160 formulated in alum or in Freund's incomplete adjuvant (FIA) at 3 and 6 months. Local and systemic reactions were mild or moderate and resolved within the first 72 hr after immunization. No significant biological changes in routine tests were observed in any volunteer. Two injections of vCP125 did not elicit antibodies. Neutralizing antibodies (NA) against the HIV-1 MN isolate were detected in 65 and 90% of the subjects after the first and the second rgp 160 booster injections, respectively. Six months after the last boost, only 55% were still positive. Seven of 14 sera with the highest NA titers against MN weakly cross-neutralized the HIV-1 SF2 isolate; none had NA against the HIV-1 LAI or against a North American primary isolate. Specific lymphocyte T cell proliferation to rgp 160 was detected in 25% of the subjects after vCP125 and in all subjects after the first booster injection and 12 months after the first injection. An envelope-specific cytotoxic lymphocyte activity was found in 39% of the volunteers and characterized for some of them as CD3+, CD8+, MHC class I restricted. The adjuvant formulation did not influence significantly the immune responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Heterologous HIV-2 challenge of rhesus monkeys immunized with recombinant vaccinia viruses and purified recombinant HIV-2 proteins

In an attempt to analyse the role of anti-envelope immunity in the protection of rhesus monkeys against an HIV-2 intravenous challenge, rhesus macaques were immunized twice with recombinant HIV-2 ROD vaccinia viruses (10(8) p.f.u. each) at days 0 and 30, followed by booster injections of purified HIV-2 proteins at months 8, 9, 15 and 27. One group of five macaques was immunized with the Gag, Pol, Vif and Nef antigens, whereas a second group received the same antigens with the addition of HIV-2 Env protein. Eight months after the last boost, the animals were challenged by intravenous injection of 100 AID50 of a monkey PBMC-grown stock of HIV-2 SBL. None of the animals was protected in spite of high humoral immune responses on day of challenge as determined by ELISA and Western Blot assays.

Kex2p: a model for cellular endoprotease processing human immunodeficiency virus type 1 envelope glycoprotein precursor

The endoproteolytic cleavage of the envelope glycoprotein precursor (gp160) of the human immunodeficiency virus type 1 (HIV-1) by a cellular protease is required for full activation of the virus. In this study, processing of gp160 was analyzed in vitro using the Kex2p endoprotease from the yeast Saccharomyces cerevisiae as a processing enzyme model. Endoproteolytic processing was examined using a synthetic peptide that mimics the cleavage site of HIV-1 glycoprotein, and a recombinant gp160 bearing the entire sequence of the env gene product, including the conserved cleavage site Arg508-Glu-Lys-Arg511. Coexpression in BHK-21 of Kex2p and gp160 by recombinant vaccinia viruses demonstrates that Kex2p can correctly process the HIV-1 glycoprotein to gp120 and gp41. Furthermore, recombinant gp160 and peptide were used as substrates and subjected to proteolysis with purified membranes from an S. cerevisiae strain overproducing the Kex2p endoprotease. Treatment of recombinant gp160, which has an apparent molecular mass of 127 kDa, with Kex2p and Western blot analysis showed that the precursor was cleaved into two products of about 101 and 34 kDa apparent molecular mass. Amino acid sequencing of the NH2-terminus of the 34-kDa product showed that the cleavage site of recombinant gp160 was between Arg511 and Ala512. Recombinant gp160 mutated at the sequence coding for the potential cleavage site, and mature recombinant gp120, however, were not cleaved when treated with Kex2p. In summary, our results show that Kex2p cleaves both the HIV-1 envelope glycoprotein precursor and a synthetic peptide mimicking the cleavage site of HIV-1 gp160 at the dibasic site, suggesting functional analogy between yeast Kex2p and the cellular protease responsible for the maturation of HIV-1 envelope glycoproteins in infected human cells.

Recombinant cholera toxin B subunit in Escherichia coli: high-level secretion, purification, and characterization

The gene coding for cholera toxin subunit B (CT-B) was fused to a modified ompA signal sequence and subsequently cloned into a high expression vector based on the regulatory signals of the arabinose operon of Salmonella typhimurium. Upon induction of gene expression in Escherichia coli, a product of the expected size for CT-B monomer was detected at a level of approximately 60% of total periplasmic protein. At pilot scale, batch cultivation in a 20-liter bioreactor allowed a production level of 1 g/liter of recombinant CT-B (rCT-B), the majority of which was released into the culture medium. The latter phenomenon was dependent on the medium selected for cultivation. A simple and inexpensive purification scheme was developed which enabled the recovery of 81% of rCT-B from the culture supernatant. Comparing amino acid composition, amino-terminal sequence, mass spectrum, pentamerisation, and GM1-binding, rCT-B is indistinguishable from natural CT-B produced by Vibrio cholerae. This rCT-B overproducing E. coli strain represents an interesting alternative to overexpressing systems developed in V. cholerae.

Alteration of V3 loop context within the envelope of human immunodeficiency virus type 1 enhances neutralization

Neutralization of a chimeric human immunodeficiency virus (HIV) type 1, containing the V3 loop of the MN isolate substituted within the HXB2 envelope, was enhanced up to 20-fold compared with the HXB2 or MN parental isolates by human HIV-positive sera. MN V3 loop-specific monoclonal antibodies were better able to recognize the chimeric virus compared with MN, staining a greater percentage of infected cells and exhibiting slight increases in relative affinity with a concomitant increase in neutralization titer. Competition analysis revealed that enhanced neutralization by human HIV-positive sera of the chimera was attributable in some cases to better reactivity with the linear V3 loop epitope but in others to conformational loop epitopes or previously cryptic or poorly recognized epitopes outside the loop region. Mice primed with a vaccinia virus-chimeric envelope recombinant and boosted with gp160 developed a spectrum of antibodies different from that of mice similarly immunized with HXB2 or MN recombinants or that of naturally infected humans. The chimeric envelope elicited antibodies with enhanced binding to the native MN V3 loop; however, the sites seen by the BALB/c mice were not neutralizing epitopes. Nevertheless, similar to the observations made with use of human sera, the chimeric virus was more readily neutralized by all of the immune mouse sera, an effect apparently mediated by non-V3 loop epitopes. These studies illustrate that not only the V3 loop sequence and conformation but also its context within the viral envelope influence neutralization.

Immunomodulatory activity of monoclonal anti-idiotypic antibody to anti-colorectal carcinoma antibody CO17-1A in animals and patients

Monoclonal anti-idiotypic antibody (Ab2) VF2 was derived from rats immunized with anti-colorectal carcinoma (anti-CRC) monoclonal antibody (Ab1) CO17-1A. In rabbits the Ab2 induced anti anti-idiotypic antibodies (Ab3) that shared idiotopes with the Ab1, bound to the same epitope on CRC cells as Ab1, and bound to the isolated CO17-1A antigen. Monoclonal Ab2 VF2 was superior to the previously described polyclonal goat Ab2 against Ab1 CO17-1A in its capacity to elicit humoral immunity in animals. Ab2 VF2 also induced a specific delayed-type hypersensitivity (DTH) response to challenge with irradiated CO17-1A antigen-positive human CRC cells in mice. Of nine CRC patients immunized with aluminum hydroxide-precipitated Ab2 VF2, six developed antibodies that bound to Ab2, but only three patients developed Ab3 that bound to idiotypic determinants on Ab2. However, the Ab3 did not bind to CO17-1A antigen-positive CRC cells. In contrast, in a previously described trial with polyclonal goat Ab2 to Ab1 CO17-1A, most of the patients developed anti-CRC antibodies. Four of the nine patients immunized with Ab2 VF2 developed DTH responses to intradermal challenge with the Ab2, and in one patient DTH was both Ab2- and antigen-specific. Peripheral blood mononu-clear cells of the four DTH-reactive patients did not proliferate in response to in vitro stimulation with either Ab2 or antigen. These studies demonstrate that the immunomodulatory activity of monoclonal Ab2 VF2 in animals is only in part predictive of its activity in patients.

Strain specificity of cell-mediated cytotoxic responses specific for the human immunodeficiency virus type 1 (HIV-1) envelope protein in seropositive donors: HIV-1Lai is more commonly recognized than HIV-1MN

Cell-mediated cytotoxic (CMC) responses were measured in a group of human immunodeficiency virus type 1 (HIV-1)-seropositive donors against target cells expressing the envelope protein of either the HIV-1 strain Lai or strain MN. In primary CMC assays using freshly isolated peripheral blood mononuclear cells, seropositive individuals more commonly had CMC responses against HIV-1Lai than HIV-1MN. Moreover, each of the responders to HIV-1MN envelope also had primary CMC responses against HIV-1Lai envelope. Cytotoxic T cells generated by nonspecific in vitro stimulation recognized both strains at a similar frequency. These results may indicate the existence of multiple effector populations or that the cellular immune response is directed at regions of the envelope outside the V3 loop. By contrast, serologic studies done on similar populations have shown that most persons have antibodies capable of recognizing the V3 loop of HIV-1MN but rarely that of HIV-1Lai.

Directed cytokine expression in tumour cells in vivo using recombinant vaccinia virus

Athymic (Swiss nude) and euthymic (DBA) tumour-bearing mice were injected intravenously with various vaccinia virus (Copenhagen strain) recombinants. Several days after inoculation, tumour cells were found to be well infected with infective vaccinia particles, while organs such as liver, spleen, brain and bone marrow showed barely detectable levels or no signs at all of virus infection. Injection of tumour bearing mice with recombinant VV harbouring the cDNA for either huIL-2 or muIL-6 resulted in detectable lymphokine in the sera of injected animals. Injection of tumour-bearing nude mice with VV-IL-6, but not with VV-IL-2, resulted in significant reduction in growth rate of the tumour, and in some cases, complete rejection of the tumour. Tumour-bearing euthymic mice responded differently. Intravenous injection of VV-IL-2, but not VV-IL-6 resulted in reduced growth rate of 50% of tumours and complete rejection of 17% of tumours.

Anti-idiotype and recombinant antigen in immunotherapy of colorectal cancer

The CO17-1A/GA733 antigen (Ag), bound by monoclonal antibodies (MAb) CO17-1A and GA733 that define two different epitopes on the Ag, has proven a useful target in passive and active immunotherapy of colorectal carcinoma (CRC). Previous studies suggest that the antitumor effects demonstrated in MAb-treated patients may be mediated by idiotypic cascades. In approaches to active immunotherapy against the Ag, polyclonal goat and monoclonal rat anti-idiotypic antibodies (Ab2) directed against MAb CO17-1A or GA733 (Ab1) were administered as alum precipitates to 54 patients with CRC (stage Dukes' B, C, and D). The majority of the patients treated with the various Ab2 preparations developed anti-anti-idiotypic antibodies (Ab3) that specifically bound to the CO17-1A or GA733 epitope and shared idiotopes with the corresponding Ab1. Approximately 30% of the patients tested developed specific cellular immunity, i.e., Ag-specific T-cells mediating delayed-type hypersensitivity (DTH) reaction in vivo or proliferating on stimulation with the Ag in vitro. The humoral and cellular immune responses may underlie the clinical responses observed in some of the treated patients. Recently, the CO17-1A/GA733 Ag has been molecularly cloned and expressed in baculo-, adeno-, and vaccinia viruses. In preclinical studies, these recombinant Ag preparations elicited specific humoral immunity (cytotoxic antibodies) and cellular immunity (DTH-reactive and proliferative T-cells), similar to the native Ag. Antibody titers elicited in experimental animals by recombinant Ag were significantly higher than those elicited by Ab2, presumably because Ag expresses numerous epitopes, whereas Ab2 mimics a single epitope. Recombinant CO17-1A/GA733 Ag has potential as a vaccine for CRC patients.

Diversity of V3 region sequences of human immunodeficiency viruses type 1 from the central African Republic

Nucleotide sequences of the central portion of gp120, including the third hypervariable (V3) loop, were obtained from lymphocytes cocultivated with SupT1 cells from 29 AIDS patients in Bangui, Central African Republic. These sequences displayed significantly greater diversity (average distance, 23%) than has been previously observed in isolates from comparably restricted geographical areas. Isolates belonging to four major subtypes of HIV-1 were found; the only subtype not represented was the North American/European subtype B. Unlike the situation in Zaire and Uganda, where subtypes A and D account equally for virtually all isolates of HIV-1, the predominant subtypes in the Central African Republic, accounting for two-thirds of the isolates, were subtypes A (10 isolates) and E (9 isolates). Subtype E represents a group of variants that have previously been found only in Thailand. Only one isolate belonging to subtype D was found. Also recovered were two isolates of subtype C, a subtype associated with southern African and Indian isolates but not previously detected in central Africa. These isolates, although clearly clustering with subtype C, formed a distinct subset, differing from one another by 8.8% and from the Indian and South African subtype C isolates by an average of 22.5%. High interpatient, intrasubtype variation was also seen among the CAR subtype A (average pairwise difference, 19.3%) and subtype E (10.9%) isolates. The diversity of V3 sequences in this set has implications for immunization protocols that rely on the recognition of V3. This study underscores the necessity of basing intervention strategies on knowledge of the particular sequences present in the target population or geographical area.

Cytotoxic T cells in HIV2 seropositive Gambians. Identification of a virus-specific MHC-restricted peptide epitope

A preliminary study of gag-specific, MHC-restricted CD8+ CTL has been performed in nine Gambian patients infected with HIV2. Such CTL were present in at least 55% of patients in fresh peripheral blood mononuclear cells without the requirement for in vitro restimulation. We have identified a nonamer peptide from HIV2 gag that is recognized by CD8+ HLA-B53 CTL using an amino acid sequence motif predicted from analysis of endogenous peptides eluted from HLA-B53 molecules. This peptide, from an HIV2/SIV conserved sequence, has previously been reported to be recognized by CTL from non-human primates vaccinated with recombinant vaccinia virus expressing the gag protein of SIV or infected with SIV virus. HLA-B53-restricted, HIV2 gag-specific CTL did not recognize target cells expressing HIV1 gag proteins, indicating that no cellular cross protection to HIV1 could be expected in this case.

Cytotoxic T cells in HIV2 seropositive Gambians. Identification of a virus-specific MHC-restricted peptide epitope

A preliminary study of gag-specific, MHC-restricted CD8+ CTL has been performed in nine Gambian patients infected with HIV2. Such CTL were present in at least 55% of patients in fresh peripheral blood mononuclear cells without the requirement for in vitro restimulation. We have identified a nonamer peptide from HIV2 gag that is recognized by CD8+ HLA-B53 CTL using an amino acid sequence motif predicted from analysis of endogenous peptides eluted from HLA-B53 molecules. This peptide, from an HIV2/SIV conserved sequence, has previously been reported to be recognized by CTL from non-human primates vaccinated with recombinant vaccinia virus expressing the gag protein of SIV or infected with SIV virus. HLA-B53-restricted, HIV2 gag-specific CTL did not recognize target cells expressing HIV1 gag proteins, indicating that no cellular cross protection to HIV1 could be expected in this case.

Immunogenicity of HILDA/LIF either in a soluble or in a membrane anchored form expressed in vivo by recombinant vaccinia viruses

Insertion of various cDNAs in the genome of the vaccinia virus (VV) enables the in vivo and in vitro study of the functional role and/or the immunogenicity of the virally encoded recombinant proteins. We have prepared a recombinant VV expressing the cDNA of the human cytokine HILDA/LIF (human interleukin for DA cells/leukaemia inhibitory factor), and used this virus to immunize mice against this protein, which is very homologous to its murine counterpart (approximately 80% homology). We also constructed and expressed by the same system a chimeric gene encoding the HILDA/LIF protein fused to the 37 COOH-terminal amino-acids of the human decay accelerating factor (DAF). This sequence proved to be sufficient for the targeting of the fusion protein to the cell membrane, where it is linked to the phosphatidylinositols. Both recombinant VVs induced cytokine-specific antibodies in mice as analysed with an ELISA where the recombinant HILDA/LIF was plastic-coated and a cytofluorometric assay where the LIF-DAF molecule was present at the cell surface of stably transfected P815. In the latter case HILDA/LIF remained biologically active suggesting that it was expressed in its native form. The LIF-DAF fusion protein was found to exhibit a better capacity to elicit an antibody response against the native form of the cytokine as detected in cytofluorometric assays. Whatever the recombinant virus used to immunize the mice, the MoAbs obtained were positive either in the ELISA or in the cytofluorometric assays but one, which suggested that the plastic coating induced a conformational change of HILDA/LIF.

Vaccinia virus MUC1 immunization of mice: immune response and protection against the growth of murine tumors bearing the MUC1 antigen

MUC1 is a mucin found on the apical surfaces of some normal mammalian mucin-secreting cells. It is characterized by heavy glycosylation and a 20-amino-acid tandem repeat segment. In most cases of human breast adenocarcinoma, this antigen is overexpressed. Moreover, abnormal glycosylation exposes a novel peptide epitope within the tandem repeat, such that antibodies to this epitope can distinguish normal from malignant adenocarcinomatous breast tissue. We have constructed a vaccinia virus (VV) that carries the cDNA for the MUC1 antigen. Murine and human cells infected with this virus express the MUC1 molecule, with three to four tandem repeats per molecule and with the tumor-associated epitopes exposed. Mice immunized with this virus produce antibodies that recognize MUC1 outside the tandem repeat, within the tandem repeat, and within the tumor-associated protein core epitope. Tumorigenic P815 (DBA) and 3T3 (BALB/c) cells have been transfected with MUC1. Thirty percent of DBA mice immunized with VV-MUC1 are protected from growth of P815-MUC1 tumors when implanted with 10(5) cells. Immunized BALB/c mice show a late development of transfected 3T3 tumor cells. Immunized mice show a moderate MUC1-specific IgG titer, but it cannot be correlated with subsequent tumor rejection. No evidence for a MUC1-specific cytotoxic T lymphocyte response has been found after immunization with VV-MUC1.

Membrane expression of HIV envelope glycoproteins triggers apoptosis in CD4 cells

The cytopathic effect of HIV-1 and HIV-2 in CD4+ lymphocytes has been shown to be associated with apoptosis or programmed cell death. Using different experimental conditions, we demonstrate here that apoptosis is triggered by cell membrane expression of the mature HIV envelope glycoproteins, gp120-gp41 complex, and their interaction with CD4 receptor molecules. Viral entry alone did not induce apoptosis but virus replication was required in order to produce the gp120-gp41 complex. Indeed, expression of the HIV env gene alone in the CD4+ T cell line (CEM) was sufficient for the induction of apoptosis. In general, syncytium formation and apoptosis induction were closely associated as both events require functional envelope glycoproteins and CD4 molecules. Nevertheless, apoptosis but not syncytium formation was suppressed by a monoclonal antibody against CD4 that does not affect gp120 binding. Furthermore, single-cell killing by apoptosis was observed in infected cell cultures treated with a monoclonal antibody against gp41, which completely abolishes the formation of syncytia. These results indicate that apoptosis is not the consequence of toxic effects induced by the formation of syncytia but is triggered by the HIV envelope glycoproteins. Therefore, cell death during HIV infection in CD4+ lymphocyte cultures is due to a specific event triggered by the gp120-gp41 heterodimer complex programming death in metabolically active cells.

Functional role of the glycan cluster of the human immunodeficiency virus type 1 transmembrane glycoprotein (gp41) ectodomain

To examine the role of the glycans of human immunodeficiency virus type 1 transmembrane glycoprotein gp41, conserved glycosylation sites within the env sequence (Asn-621, Asn-630, and Asn-642) were mutated to Gln. The mutated and control wild-type env genes were introduced into recombinant vaccinia virus and used to infect BHK-21 or CD4+ CEM cells. Mutated gp41 appeared as a 35-kDa band in a Western blot (immunoblot), and it comigrated with the deglycosylated form of wild-type gp41. Proteolytic cleavage of the recombinant wild-type and mutant forms of the gp160 envelope glycoprotein precursor was analyzed by pulse-chase experiments and enzyme-linked immunosorbent assay: gp160 synthesis was similar whether cells were infected with control or mutated env-expressing recombinant vaccinia virus, but about 10-fold less cleaved gp120 and gp41 was produced by the mutated construct than the control construct. The rates of gp120-gp41 cleavage at each of the two potential sites appeared to be comparable in the two constructs. By using a panel of antibodies specific for gp41 and gp120 epitopes, it was shown that the overall immunoreactivities of control and mutated gp41 proteins were similar but that reactivity to epitopes at the C and N termini of gp120, as present on gp160 produced by the mutated construct, was enhanced. This was no longer observed for cleaved gp120 in supernatants. Both gp120 proteins, from control and mutated env, were expressed on the cell surface under a cleaved form and could bind to membrane CD4, as determined by quantitative immunofluorescence assay. In contrast, and despite sufficient expression of env products at the cell membrane, gp41 produced by the mutated construct was unable to induce membrane fusion. Therefore, while contradictory results reported in the literature suggest that gp41 individual glycosylation sites are dispensable for the bioactivity and conformation of env products, it appears that such is not the case when the whole gp41 glycan cluster is removed.

A novel transgenic mouse model for the in vivo evaluation of anti-human immunodeficiency virus type 1 drugs

We have developed a binary transgenic mouse system that allows easy in vivo evaluation of new anti-human immunodeficiency virus type 1 (HIV-1) drugs or therapies specifically designed to target the viral transactivator protein (TAT) or long terminal repeat (LTR) functions. This approach consists of a simple genetic cross between an "activator" transgenic mouse expressing the HIV-1-tat gene exclusively to T lymphocytes and a "target" transgenic mouse bearing a silent reporter gene whose expression is under the control of the HIV-1-LTR. As expected, most of the target transgenic animals did not express the reporter gene; on the contrary, all the double-transgenic mice bearing both the activator and target transgenes strongly expressed the TAT-induced reporter gene. The choice of a secreted human alpha 1-antitrypsin variant (alpha 1-AT) as reporter gene readily permits in a single animal the quantitative determination of the plasma level of alpha 1-AT protein before and after anti-LTR or anti-TAT treatments. Such mice may be valuable as new laboratory models for the in vivo evaluation of agents with potential anti-HIV-1 activity.

Vaccine protection of chimpanzees against challenge with HIV-1-infected peripheral blood mononuclear cells

Because human immunodeficiency virus (HIV) can be transmitted as cell-free virus or as infected cells (cell-associated virus), vaccines must protect against infection by both viral forms. Vaccine-mediated protection of nonhuman primates against low doses of cell-free HIV-1, HIV-2, or simian immunodeficiency virus (SIV) has been demonstrated. It is now shown that multiple immunizations of chimpanzees with HIV-1 antigens protected against infection with cell-associated virus. Protection can persist for extended periods (one animal had not been exposed to viral antigens for 1 year before challenge). These results show that it is possible to elicit long-lasting protective immunity against cell-associated HIV-1.

[Experimental vaccination against HIV-1 protects the chimpanzee against challenge with injections of infected lymphocytes]

Two chimpanzees were immunized against HIV-1 : C-339, using whole inactivated HIV-1 followed by purified recombinant gp160 and a KLH-V3 peptide conjugate; and, C-499, using purified recombinant gp160 and p18gag followed by a mixture of uncoupled V3 peptides. The antigens were emulsified prior to use with one volume Syntex adjuvant SAF-1 containing 1 mg/ml Threonyl-MDP. The animals were challenged twice one year apart by the intravenous route, the first time with cell-free virus, using 40 chimpanzee infectious units (100 TCID50) of the titrated HTLV-IIIB virus stock from the National Cancer Institute, Frederick, MD; and the second time with cell-associated virus, using 6 x 10(5) viable peripheral blood mononuclear cells (PBMC) from a naive chimpanzee which had been injected 3 months earlier with cell-free virus and had become virus-positive within a few weeks. From end-point titration of C-087 PBMC on indicator human PBMC, using a reverse transcriptase assay, this represented the equivalent of at least 15 infected cells. A 3rd chimpanzee, C-435, a näive animal, was also injected with 6 x 10(5) PBMC from C-087 to serve as a positive control. The PMBC of the animals were co-cultivated with fresh human PBMC and assayed for reverse transcriptase on a regular basis. In parallel, ELISA and Western blot analyses were carried out. Virus was detected in the PBMC from C-435 beginning at 4 weeks after challenge. This was followed by seroconversion of the animal to the Env and Gag antigens. By contrast, no virus could be detected in the PBMC from chimpanzees C-499 and C-339 during 7 and 12 months, respectively. Lymph node biopsies and bone marrow aspirates from these animals remained virus-negative upon co-cultivation with human PBMC. PBMC, bone marrow aspirates and lymph node biopsies also scored HIV-negative by polymerase chain reaction. Finally, no anamnestic antibody response of the animals could be detected by ELISA, and no modification of their western blot profiles that could have signed HIV-infection were observed during the follow-up period. C-499 accidentally developed an infectious endocarditis with congestive liver and kidney failure and had to be euthanized at 7 months post-challenge. Specimens from its brain, kidneys, liver, mesenteric nodes, pancreas, salivary glands, and spleen were processed for co-cultivation with human PBMC. No evidence for the presence of virus could be detected by reverse transcriptase assays in any of these co-cultures.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of a neutralizing domain in the external envelope glycoprotein of simian immunodeficiency virus

Two murine monoclonal antibodies (MAbs), designated MATG2014 and MATG2033, were generated. They are reactive with the external envelope glycoprotein gp130 of the simian immunodeficiency virus of macaque monkey (SIVmac251), and display a cell-free virus neutralizing activity in vitro. In addition, MATG2014 cross-reacts with HIV-2Rod gp140. Epitope mapping of these MAbs was performed by screening and SIVmac peptide library expressed in yeast and confirmed using synthetic peptides. MATG2014 and MATG2033 recognize two overlapping epitopes localized in an 18 residue domain between amino acid 171 and 188 of the SIVmac251 gp130. Sera from experimentally SIV-infected macaques are immunoreactive with this neutralizing domain. Sequence comparison with related SIV and HIV-2 viral strains indicates a low variability of this region, consistent with the cross-reactivity of MATG2014 with HIV-2Rod gp140. This domain should then be considered in designing experimental vaccines.