HIV-specific immunity following immunization with HIV synthetic envelope peptides in asymptomatic HIV-infected patients

Evaluating influenza vaccines: progress and perspectives

Severe influenza infections are responsible for 3–5 million cases worldwide and 250,000–500,000 deaths per year. Although vaccination is the primary and most effective means of inducing protection against influenza viruses, it also presents limitations. This review outlines the promising steps that have been taken toward the development of a broadly protective influenza virus vaccine through the use of new technologies. The future challenge is to develop a broadly protective vaccine that is able to induce long-term protection against antigenically variant influenza viruses, regardless of antigenic shift and drift, and thus to protect against seasonal and pandemic influenza viruses.

Safety and tolerability evaluation of the use of Montanide ISA™51 as vaccine adjuvant: A systematic review

Montanide ISA™51 (ISA 51) is a vaccine adjuvant which has been tested in therapeutic and prophylactic vaccine trials. The aim of this review is to present a comprehensive examination of the safety and tolerability of ISA 51 containing vaccines. A systematic literature search was conducted in PubMed, EMBASE and clinicaltrials.gov . Eligible studies were categorized into: (A) uncontrolled studies with non-healthy subjects, (B) controlled studies with non-healthy subjects, and (C) controlled studies with healthy subjects. Reported adverse events (AEs) were assessed. 91 studies were included in our review. Generally observed AEs included injection site reaction; injection site pain; myalgia; headache; gastro-intestinal disorders; fatigue and fever - regardless of the administration route and subject characteristic. Specific AEs, e.g. injection site reactions and rash, were more frequently reported from subjects receiving ISA 51-adjuvanted vaccines than from subjects receiving antigen or ISA 51 only. The reported AEs were mainly mild to moderate in intensity. Serious AEs (SAEs) were reported in 27% of the uncontrolled trials and 2 trials conducted with healthy subjects. Notably, 2 other trials conducted with healthy subjects were stopped due to unacceptable AEs. Some studies indicate that the mixing procedure of antigen and adjuvant might influence the occurrence of AEs. Reports on SAEs and premature termination of 2 trials advise caution when using ISA 51. Yet, AEs might be preventable by proper mixing of vaccine and adjuvant to a stable emulsion. Trials including an active control group are needed for a fair evaluation of adjuvant safety.

Synthetic Influenza vaccine (FLU-v) stimulates cell mediated immunity in a double-blind, randomised, placebo-controlled Phase I trial

OBJECTIVES

Current Influenza vaccines elicit antibody mediated prophylactic immunity targeted to viral capsid antigens. Despite their global use these vaccines must be administered yearly to the population, cannot be manufactured until the circulating viral strain(s) have been identified and have limited efficacy. A need remains for Influenza vaccines addressing these issues and here we report the results of a Phase Ib trial of a novel synthetic Influenza vaccine (FLU-v) targeting T cell responses to NP, M1 and M2.

METHODS

Forty-eight healthy males aged 18-40 were recruited for this single-centre, randomised, double blind study. Volunteers received one single low (250 μg) or high (500 μg) dose of FLU-v, either alone or adjuvanted. Safety, tolerability and basic immunogenicity (IgG and IFN-γ responses) parameters were assessed pre-vaccination and for 21 days post-vaccination.

RESULTS

FLU-v was found to be safe and well tolerated with no vaccine associated severe adverse events. Dose-dependent IFN-γ responses >2-fold the pre-vaccination level were detected in 80% and 100% of volunteers receiving, respectively, the low and high dose adjuvanted FLU-v formulations. No formulation tested induced any significant FLU-v antibody response.

CONCLUSION

FLU-v is safe and induces a vaccine-specific cellular immunity. Cellular immune responses are historically known to control and mitigate infection and illness during natural infection.

Progress towards a universal influenza vaccine

Seasonal influenza is a common and highly transmissible disease, characterized by frequent and unpredictable mutations occurring in the viral envelope glycoproteins. Owing to this high variability, annual reformulation and immunization are required and still, the vaccine is not effective enough when there is an antigenic mismatch with circulating strains. A solution could come from the construction of a universal vaccine that would be based on highly conserved antigens and would be effective against many strains: some universal vaccine developers focus on the Matrix 2 protein, whereas others use additional conserved proteins, such as the nucleoprotein and Matrix 1, or even a range of peptides from these proteins and others to induce cross-strain immunity. This article aims to highlight recent significant advances in the development of a universal vaccine against influenza and focuses mainly on studies using the epitope-based approach that have also entered the clinical trial stage; it includes a brief summary of current vaccines against influenza as well as the ongoing efforts to develop a universal vaccine.

Protection against H1N1 influenza challenge by a DNA vaccine expressing H3/H1 subtype hemagglutinin combined with MHC class II-restricted epitopes

BACKGROUND

Multiple subtypes of avian influenza viruses have crossed the species barrier to infect humans and have the potential to cause a pandemic. Therefore, new influenza vaccines to prevent the co-existence of multiple subtypes within a host and cross-species transmission of influenza are urgently needed.

METHODS

Here we report a multi-epitope DNA vaccine targeted towards multiple subtypes of the influenza virus. The protective hemagglutinin (HA) antigens from H5/H7/H9 subtypes were screened for MHC II class-restricted epitopes overlapping with predicted B cell epitopes. We then constructed a DNA plasmid vaccine, pV-H3-EHA-H1, based on HA antigens from human influenza H3/H1 subtypes combined with the H5/H7/H9 subtype Th/B epitope box.

RESULTS

Epitope-specific IFN-γ ELISpot responses were significantly higher in the multi-epitope DNA group than in other vaccine and control groups (P < 0.05). The multi-epitope group significantly enhanced Th2 cell responses as determined by cytokine assays. The survival rate of mice given the multi-epitope vaccine was the highest among the vaccine groups, but it was not significantly different compared to those given single antigen expressing pV-H1HA1 vaccine and dual antigen expressing pV-H3-H1 vaccine (P > 0.05). No measurable virus titers were detected in the lungs of the multi-epitope immunized group. The unique multi-epitope DNA vaccine enhanced virus-specific antibody and cellular immunity as well as conferred complete protection against lethal challenge with A/New Caledonia/20/99 (H1N1) influenza strain in mice.

CONCLUSIONS

This approach may be a promising strategy for developing a universal influenza vaccine to prevent multiple subtypes of influenza virus and to induce long-term protective immune against cross-species transmission.

Immunization with cocktail of HIV-derived peptides in montanide ISA-51 is immunogenic, but causes sterile abscesses and unacceptable reactogenicity

Background

A peptide vaccine was produced containing B and T cell epitopes from the V3 and C4 Envelope domains of 4 subtype B HIV-1 isolates (MN, RF, CanO, & Ev91). The peptide mixture was formulated as an emulsion in incomplete Freund's adjuvant (IFA).

Methods

Low-risk, healthy adult subjects were enrolled in a randomized, placebo-controlled dose-escalation study, and selected using criteria specifying that 50% in each study group would be HLA-B7+. Immunizations were scheduled at 0, 1, and 6 months using a total peptide dose of 1 or 4 mg. Adaptive immune responses in16 vaccine recipients and two placebo recipients after the 2nd immunization were evaluated using neutralization assays of sera, as well as ELISpot and ICS assays of cryopreserved PBMCs to assess CD4 and CD8 T-cell responses. In addition, ⁵¹Cr release assays were performed on fresh PBMCs following 14-day stimulation with individual vaccine peptide antigens.

Results

24 subjects were enrolled; 18 completed 2 injections. The study was prematurely terminated because 4 vaccinees developed prolonged pain and sterile abscess formation at the injection site-2 after dose 1, and 2 after dose 2. Two other subjects experienced severe systemic reactions consisting of headache, chills, nausea, and myalgia. Both reactions occurred after the second 4 mg dose. The immunogenicity assessments showed that 6/8 vaccinees at each dose level had detectable MN-specific neutralizing (NT) activity, and 2/7 HLA-B7+ vaccinees had classical CD8 CTL activity detected. However, using both ELISpot and ICS, 8/16 vaccinees (5/7 HLA-B7+) and 0/2 controls had detectable vaccine-specific CD8 T-cell responses. Subjects with moderate or severe systemic or local reactions tended to have more frequent T cell responses and higher antibody responses than those with mild or no reactions.

Conclusions

The severity of local responses related to the formulation of these four peptides in IFA is clinically unacceptable for continued development. Both HIV-specific antibody and T cell responses were induced and the magnitude of response correlated with the severity of local and systemic reactions. If potent adjuvants are necessary for subunit vaccines to induce broad and durable immune responses, careful, incremental clinical evaluation is warranted to minimize the risk of adverse events.

Trial Registration

ClinicalTrials.gov NCT00000886

Expression, identification and biological effects of a novel VPAC2-specific agonist with high stability and bioactivity

The development of rBAY, a recombinant peptide with the similar sequence of synthetic BAY55-9837, as a potential peptide therapeutic for type 2 diabetes is still a challenge mainly because of its poor stability in aqueous solution. To improve the peptide stability and bioactivity and investigate its biological effects for VPAC2-specific activation, RBAYL with 31 aa was designed based on sequence alignments of pituitary adenylate cyclase-activating peptides (PACAPs), vasoactive intestinal peptide (VIP), and related analogs and generated through sitedirected mutagenesis. Stability analysis showed that the prepared RBAYL with three mutations (N9Q, V17L, and N28K) were much more stable than rBAY. rRBAYL (the recombinant RBAYL) was expressed and purified by gene-recombination technology via native thiol ligation on solid beads. As much as 27.7 mg rRBAYL peptide with purity over 98% was obtained from 1 L of LB medium without expensive high-performance liquid chromatography refinements. The bioactivity assay of rRBAYL showed that it displaced [(125)I]PACAP38 and [(125)I]VIP from VPAC2 with a half-maximal inhibitory concentration of 51+/-6 and 50+/-4 nM, respectively, which were similar to those of the chemically synthesized RBAYL (sRBAYL) and lower than those of Ro25-1553, an established VPAC2 agonist. rRBAYL enhances the cAMP accumulation in CHO cells expressing human VPAC2 with a half-maximal stimulatory concentration (EC50) of 0.91 nM, whereas the receptor potency of rRBAYL at human VPAC1 (EC50 of 719 nM) was only 1/790 of that at human VPAC2, and rRBAYL had no activity toward human PAC1 receptor. Western-blot assay for glucose transporter 4 (GLUT4) indicated that the rRBAYL could significantly induce GLUT4 expression more efficiently than rBAY or Ro25-1553 in adipocytes. Compared with rBAY, rRBAYL can more efficiently promote insulin release and decrease plasma glucose level in ICR mice. Our results suggested that rRBAYL is a novel recombinant VPAC2-specific agonist with high stability and bioactivity.

Peptide inhibition of HIV-1: current status and future potential

More than 2 decades of intensive research has focused on defining replication mechanisms of HIV type 1 (HIV-1), the etiologic agent of AIDS. The delineation of strategies for combating this viral infection has yielded many innovative approaches toward this end. HIV-1 is a lentivirus in the family retroviridae that is relatively small with regard to both structure and genome size, having a diploid RNA genome of approximately 9 kb, with only three major genes and several gene products resulting from alternate splicing and translational frameshifting. Most marketed drugs for treating AIDS are inhibitors of HIV-1 reverse transcriptase or protease enzymes, but new targets include the integrase enzyme, cell surface interactions that facilitate viral entry, and also virus particle maturation and assembly. The emergence of drug-resistant variants of HIV-1 has been the main impediment to successful treatment of AIDS. Thus, there is a pressing need to develop novel treatment strategies targeting multiple stages of the virus life-cycle. Research efforts aimed at developing successful means for combating HIV-1 infection have included development of peptide inhibitors of HIV-1. This article summarizes past and current endeavors in the development of peptides that inhibit replication of HIV-1 and the role of peptide inhibitors in the search for new anti-HIV drugs.

Clinical experience with therapeutic AIDS vaccines

Recently, there has been a renewed interest in therapeutic vaccination as an adjunct or alternative to current treatment options for HIV. The first immunotherapeutic trial relevant to this topic was published in 1983. Since then, several dozen therapeutic vaccine trials have been carried out. The results have consistently shown that although in vitro-measured HIV-specific immune responses were evident as a result of vaccination, clinical improvement has been seldom observed. The instances of apparent clinical benefit however, were invariably associated with the usage of vaccines that acted in accord with the principles of allo- or autoimmunization. The majority of these vaccines were derived from the blood of HIV carriers or a cell culture and therefore inherently contained host-cell antigens unrelated to HIV. These observations raise the issue of whether this clinically successful approach has been unduly neglected. Most commercial vaccines on the market today are made the old-fashioned way, but very little support or attention has been given to the development of such vaccines for AIDS therapy. The current strategy, biased toward vaccines which have shown little evidence of clinical efficacy, is shortsighted and needs to be revised.

Novel peptide-based HIV-1 immunotherapy

Therapeutic immunisation of human immunodeficiency virus type 1-infected individuals should be actively pursued in the first instance to augment highly active antiretroviral therapy regimens. Peptide-based immunotherapeutic strategies offer considerable advantages over conventional approaches, particularly regarding safety. Peptide design itself is becoming increasingly sophisticated, with the rapid evolution of bioinformatics tools that can analyse not only T cell epitopes, but also their potential for successful presentation on diverse human leukocyte antigen (HLA) class I or II following intracellular processing by antigen-presenting cells (APCs). By targeting conserved viral domains, peptides acquire improved reactivity to diverse viral strains. Dendritic cells represent a powerful route of administration, as they are the most potent APCs and can present exogenous peptides on both HLA class I and II through the process of cross-presentation. In this way, soluble peptides can thereby stimulate both CD4+ and CD8+ T cells.

Progress on new vaccine strategies against chronic viral infections

Among the most cost-effective strategies for preventing viral infections, vaccines have proven effective primarily against viruses causing acute, self-limited infections. For these it has been sufficient for the vaccine to mimic the natural virus. However, viruses causing chronic infection do not elicit an immune response sufficient to clear the infection and, as a result, vaccines for these viruses must elicit more effective responses--quantitative and qualitative--than does the natural virus. Here we examine the immunologic and virologic basis for vaccines against three such viruses, HIV, hepatitis C virus, and human papillomavirus, and review progress in clinical trials to date. We also explore novel strategies for increasing the immunogenicity and efficacy of vaccines.

Progress on new vaccine strategies against chronic viral infections

Among the most cost-effective strategies for preventing viral infections, vaccines have proven effective primarily against viruses causing acute, self-limited infections. For these it has been sufficient for the vaccine to mimic the natural virus. However, viruses causing chronic infection do not elicit an immune response sufficient to clear the infection and, as a result, vaccines for these viruses must elicit more effective responses--quantitative and qualitative--than does the natural virus. Here we examine the immunologic and virologic basis for vaccines against three such viruses, HIV, hepatitis C virus, and human papillomavirus, and review progress in clinical trials to date. We also explore novel strategies for increasing the immunogenicity and efficacy of vaccines.

Increase in plasmacytoid and myeloid dendritic cells by progenipoietin-1, a chimeric Flt-3 and G-CSF receptor agonist, in SIV-Infected rhesus macaques

As in HIV-1 infection in humans, SIVsm infection of rhesus macaques causes a slow progressive loss of CD4 T-cells followed by the onset of AIDS. In addition, there is a loss of dendritic cells (DC) in peripheral blood, peripheral lymphoid tissues, and the skin. Increasing the number of CD4 T cells and DC may be an important step in restoring immune competence and thus delay disease progression. Recently, progenipoietins (ProGP), a new family of chimeric Flt3 and G-CSF receptor agonists, were demonstrated to possess the capacity to mobilize hematopoietic progenitor cells in normal rhesus monkeys. In addition, these molecules induced increased numbers of myeloid cells, including dendritic cells, in the blood. Here we demonstrate that SIVsm-infected macaques, treated with ProGP-1, developed increased numbers of both plasmacytoid (CD123+, CD11c-) and myeloid (both CD11b+, CD11c+, and CD123-, CD11c+ subsets) DC and CD4 and CD8 T cells in peripheral blood. Importantly, during treatment, no changes in plasma virus load were observed. After 14 to 20 days of treatment, antibodies were formed against ProGP in all animals. As a consequence, white blood cell levels returned to baseline in several animals. In other animals values only returned to baseline after termination of ProGP treatment. In conclusion, ProGP-1 may be used to generate a transient increase in DC as well as CD4 T-cell numbers, thereby creating a window of opportunity for immunotherapeutic intervention.

Development of a DNA vaccine designed to induce cytotoxic T lymphocyte responses to multiple conserved epitopes in HIV-1

Epitope-based vaccines designed to induce CTL responses specific for HIV-1 are being developed as a means for addressing vaccine potency and viral heterogeneity. We identified a set of 21 HLA-A2, HLA-A3, and HLA-B7 restricted supertype epitopes from conserved regions of HIV-1 to develop such a vaccine. Based on peptide-binding studies and phenotypic frequencies of HLA-A2, HLA-A3, and HLA-B7 allelic variants, these epitopes are predicted to be immunogenic in greater than 85% of individuals. Immunological recognition of all but one of the vaccine candidate epitopes was demonstrated by IFN-gamma ELISPOT assays in PBMC from HIV-1-infected subjects. The HLA supertypes of the subjects was a very strong predictor of epitope-specific responses, but some subjects responded to epitopes outside of the predicted HLA type. A DNA plasmid vaccine, EP HIV-1090, was designed to express the 21 CTL epitopes as a single Ag and tested for immunogenicity using HLA transgenic mice. Immunization of HLA transgenic mice with this vaccine was sufficient to induce CTL responses to multiple HIV-1 epitopes, comparable in magnitude to those induced by immunization with peptides. The CTL induced by the vaccine recognized target cells pulsed with peptide or cells transfected with HIV-1 env or gag genes. There was no indication of immunodominance, as the vaccine induced CTL responses specific for multiple epitopes in individual mice. These data indicate that the EP HIV-1090 DNA vaccine may be suitable for inducing relevant HIV-1-specific CTL responses in humans.

Cross-reactive CD8+ T cell epitopes identified in US adolescent minorities

Vaccines designed to bring forth CD8+ T cell responses in different racial and ethnic groups will require inclusion of T cell epitopes presented by various MHC class I molecules. This study was designed to identify new CD8+ T cell epitopes in HIV-infected African American and Hispanic youth as well as to determine the frequency of responses to both novel and previously described HIV-1 epitopes in a cohort of racially and ethnically diverse individuals. We found 8 MHC class I-restricted CD8+ T cell epitopes that had not been previously described, another 8 epitopes that were restricted by class I alleles not previously associated with these epitopes, and 8 additional epitopes that have been described previously. In a larger cohort, we demonstrated that 11 (69%) of these 16 newly described immunogens were recognized by individuals of different race or ethnicity. Most HIV-1-specific CD8+ T cell epitopes identified were either novel or restricted by alternative MHC class I alleles. Frequent recognition of several of these CTL epitopes in persons of diverse racial backgrounds bodes well for the development of a broadly reactive HIV-1 vaccine.

Vaccines for viral diseases with dermatologic manifestations

Vaccines against infectious diseases have been available since the 1800s, when an immunization strategy against smallpox developed by Jenner gained wide acceptance. Until recently, the only vaccination strategies available involved the use of protein-based, whole killed, and attenuated live virus vaccines. These strategies have led to the development of effective vaccines against a variety of diseases with primary or prominent cutaneous manifestations. Effective and safe vaccines now used worldwide include those directed against measles and rubella (now commonly used together with a mumps vaccine as the trivalent MMR), chickenpox, and hepatitis B. The eradication of naturally occurring smallpox remains one of the greatest successes in the history of modern medicine, but stockpiles of live smallpox exist in the United States and Russia. Renewed interest in the smallpox vaccine reflects concerns about a possible bioterrorist threat using this virus. Yellow fever is a hemorrhagic virus endemic to tropical areas of South America and Africa. An effective vaccine for this virus has existed since 1937, and it is used widely in endemic areas of South America, and to a lesser extent in Africa. This vaccine is recommended once every 10 years for people who are traveling to endemic areas. Advances in immunology have led to a greater understanding of immune system function in viral diseases. Progress in genetics and molecular biology has allowed researchers to design vaccines with novel mechanisms of action (eg, DNA, vector, and VLP vaccines). Vaccines have also been designed to specifically target particular viral components, allowing for stimulation of various arms of the immune system as desired. Ongoing research shows promise in prophylactic and therapeutic vaccination for viral infections with cutaneous manifestations. Further studies are necessary before vaccines for HSV, HPV, and HIV become commercially available.

Vaccine development against HIV-1: current perspectives and future directions

The development of an efficacious vaccine against the human immunodeficiency virus (HIV) is of great urgency, because it is accepted that vaccination is the only means capable of controlling the AIDS pandemic. The foundation of HIV vaccine development is the analysis of immune responses during natural infection and the utilization of this knowledge for the development of protective immunization strategies. Initial vaccine development and experimentation are usually in animal models, including murine, feline, and nonhuman primates. Experimental vaccine candidates are closely studied for both efficacy and safety before proceeding to human clinical trials. There are a number of different therapeutic and prophylactic vaccine strategies currently being studied in human clinical trials. Vaccine strategies that are being tested, or have previously been tested, in humans include subunit, DNA plasmid, and viral vector, and combinations of these various strategies. Some of the results of these trials are promising, and additional research has focused on the development of appropriate chemical and genetic adjuvants as well as methods of vaccine delivery to improve the host immune response. This review summarizes the vaccine strategies that have been tested in both animal models and human clinical trials.

Immunological response of female macaques to the PH-20 sperm protein following injection of recombinant proteins or synthesized peptides

Because of its location on the sperm surface and its multiple functions during fertilization, the PH-20 protein is a potential target for contraceptive vaccines. Cynomolgus macaques were immunized using four different adjuvants together with synthesized peptides or recombinant proteins representing selected regions of macaque PH-20. The synthesized peptide (amino acids 387-412, designated Peptide 4) was used as a linear molecule in a 1:1 ratio with a peptide sequence of tetanus toxoid, as well as a multiple antigenic peptide (MAP) matrix held together by scaffolding lysine residues. In the MAP construct, the ratio of Peptide 4 to tetanus peptide was 4:1. To circumvent the poor production of recombinant PH-20 in bacterial cells, two truncated forms of the molecule were expressed in Escherichia coli, G18 (encoding amino acids 143-510) and E10 (encoding amino acids 291-510). The adjuvants were Montanide ISA 51, Titermax Gold, Syntex adjuvant formulation (SAF), and QS-21. All of the antigen/adjuvant combinations produced significant immune responses as measured by ELISA. The circulating antibodies from immunized animals recognized macaque sperm surface PH-20 on Western blots and were shown by indirect immunofluorescence to bind to the surface of macaque sperm. Montanide and Titermax were associated with higher titers of anti-PH-20 antibodies than QS-21 and SAF adjuvants. Immunization with Titermax, however, resulted in sterile abscesses in 4 of 8 animals injected. We conclude that antigens derived from synthesized peptides and recombinant proteins representing selected regions of the PH-20 molecule can be used as vaccine components in combination with the adjuvant Montanide to elicit a significant sperm-directed antibody response in immunized macaques.

Safety and efficacy of an oral HIV vaccine (V-1 Immunitor) in AIDS patients at various stages of the disease

PURPOSE

To evaluate the safety and efficacy of an orally available, therapeutic HIV vaccine (V-1 Immunitor) in patients who were not treated with antiviral drugs.

METHOD

All entrants who had been tested at least once at entry and at postimmunization were considered for analysis. Main endpoints were vaccine safety and differential effects on CD4 and CD8 cell counts, plasma HIV RNA levels, and body weight change. Forty patients, 21 females (52%) and 19 males (48%), aged 22-65 years (mean/median age, 35/32 years) with a mean 225/mm3 CD4 cells at baseline were retrospectively analyzed. Patients self-administered two 850-mg pills containing inactivated HIV-1 antigens b.i.d. for 27 weeks (median, 24 weeks).

RESULTS

The treatment was well tolerated without significant adverse effects. The mean body weight gain was 2.2 kg (p =.0004). The mean increase in absolute CD4 and CD8 cells was 51 (18%; p =.0088) and 172 (16%; p =.0199) cells/mm3. Viral load was measured by polymerase chain reaction (PCR) in 8 individuals; although overall decrease did not reach standard cut-off statistical significance (Friedman p =.0588), the trend in reduction of viremia attributable to vaccine administration was highly significant (Spearman correlation test: r = 0.96, p =.0005).

CONCLUSION

Mucosal delivery of HIV antigens provides compelling results and deserves further evaluation in placebo-controlled clinical trials.

The basis for HIV immunotherapeutic vaccines

The drug treatments introduced in recent years for HIV infection have enabled a marked reduction in morbidity and prolongation of life. These treatments, however, are often associated with acute and chronic toxicities, the development of resistant virus can limit their effectiveness, and they are too expensive and difficult to administer in most third world settings. A successful HIV immunotherapeutic vaccine has the potential to overcome these problems, and would be a valuable advance. The most promising approaches have induced the type of immune response found to correlate with reduced activity of HIV in man, especially cytotoxic T-cell responses, or have led to reduced HIV or SIV viral load and increased CD4 counts in non-human primates or man. The agents that have led to one or both of these effects have been selected for review, and include inactivated envelope depleted virus, recombinant envelope glycoprotein, DNA vaccines utilising HIV peptides or gene products, viral vectors, such as canarypox or attenuated vaccinia, with HIV core proteins. There are other approaches, such as alloimmunity, for which no candidate products yet exist, but which conceptually appear promising. Currently, however, only a few phase III studies of HIV therapeutic vaccines have been completed in man, and there has been a modest therapeutic effect. Further development of both existing and new candidates remains one of the key priorities in our fight against HIV.

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

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

Highly active antiretroviral therapy in human immunodeficiency virus type 1-infected children: analysis of cellular immune responses

The present study analyzes the effect of highly active antiretroviral therapy (HAART) on restoration of cellular immunity in human immunodeficiency virus (HIV)-infected children over a 24-week period following initiation of HAART with ritonavir, nevirapine, and stavudine. The immunological parameters evaluated at four time points (at enrollment and at 4, 12, and 24 weeks of therapy) included cytokine production by monocytes as well as T-cell proliferation in response to mitogen, alloantigen, and recall antigens including HIV type 1 envelope peptides. Circulating levels of interleukin-16 (IL-16) were measured, in addition to CD4+ T-cell counts, plasma HIV RNA levels, and the delayed-type hypersensitivity (DTH) response. At enrollment the children exhibited defects in several immune parameters measured. Therapy increased CD4+ T-cell counts and decreased viral loads significantly. By contrast, the only immunological parameter that was significantly increased was IL-12 p70 production by monocytes; the DTH response to Candida albicans also showed a strong increase in patients becoming positive. In conclusion, these results demonstrate that HAART in HIV-infected children affects the dynamics of HIV replication and the CD4+ T-cell count over 24 weeks, similar to the pattern seen in HIV-infected adults. Furthermore, these data indicate improvement in antigen-presenting cell immunological function in HIV-infected children induced by HAART.

Expression and immunogenicity of human immunodeficiency virus type 1 Gag expressed by a replication-competent rhabdovirus-based vaccine vector

A replication-competent rhabdovirus-based vector expressing human immunodeficiency virus type 1 (HIV-1) Gag protein was characterized on human cell lines and analyzed for the induction of a cellular immune response in mice. We previously described a rabies virus (RV) vaccine strain-based vector expressing HIV-1 gp160. The recombinant RV was able to induce strong humoral and cellular immune responses against the HIV-1 envelope protein in mice (M. J. Schnell et al., Proc. Natl. Acad. Sci. USA 97:3544-3549, 2000; J. P. McGettigan et al., J. Virol. 75:4430-4434, 2001). Recent research suggests that the HIV-1 Gag protein is another important target for cell-mediated host immune defense. Here we show that HIV-1 Gag can efficiently be expressed by RV on both human and nonhuman cell lines. Infection of HeLa cells with recombinant RV expressing HIV-1 Gag resulted in efficient expression of HIV-1 precursor protein p55 as indicated by both immunostaining and Western blotting. Moreover, HIV-1 p24 antigen capture enzyme-linked immunosorbent assay and electron microscopy showed efficient release of HIV-1 virus-like particles in addition to bullet-shaped RV particles in the supernatants of the infected cells. To initially screen the immunogenicity of this new vaccine vector, BALB/c mice received a single vaccination with the recombinant RV expressing HIV-1 Gag. Immunized mice developed a vigorous CD8(+) cytotoxic T-lymphocyte response against HIV-1 Gag. In addition, 26.8% of CD8(+) T cells from mice immunized with RV expressing HIV-1 Gag produced gamma interferon after challenge with a recombinant vaccinia virus expressing HIV-1 Gag. These results further confirm and extend the potency of RV-based vectors as a potential HIV-1 vaccine.

Selection of glutamate-rich protein long synthetic peptides for vaccine development: antigenicity and relationship with clinical protection and immunogenicity

Antibodies against three long synthetic peptides (LSPs) derived from the glutamate-rich protein (GLURP) of Plasmodium falciparum were analyzed in three cohorts from Liberia, Ghana, and Senegal. Two overlapping LSPs, LR67 and LR68, are derived from the relatively conserved N-terminal nonrepeat region (R0), and the third, LR70, is derived from the R2 repeat region. A high prevalence of antibody responses to each LSP was observed in all three areas of endemic infection. Levels of cytophilic immunoglobulin G (IgG) antibodies against both GLURP regions were significantly correlated with protection from clinical P. falciparum malaria. Protected children from the Ghana cohort possessed predominantly IgG1 antibodies against the nonrepeat epitope and IgG3 antibodies against the repeat epitope. T-cell proliferation responses, studied in the cohort from Senegal, revealed that T-helper-cell epitopes were confined to the nonrepeat region. When used as immunogens, the LR67 and LR68 peptides elicited strong IgG responses in outbred mice and LR67 also induced antibodies in mice of different H-2 haplotypes, confirming the presence of T-helper-cell epitopes in these constructs. Mouse antipeptide antisera recognized parasite proteins as determined by immunofluorescence and immunoblotting. This indicates that synthetic peptides derived from relatively conserved epitopes of GLURP might serve as useful immunogens for vaccination against P. falciparum malaria.

Tailoring cancer vaccines to the elderly: the importance of suitable mouse models

The incidence of cancer has increased over the last decade, mainly due to an increase in the elderly population. Vaccine therapy for cancer is potentially less toxic than chemotherapy or radiation and could, therefore, be especially effective in older, more frail cancer patients. However, it has been shown that older individuals do not respond to vaccine therapy as well as younger adults. This has been attributed to T cell unresponsiveness, a phenomenon also observed in cancer patients per se. Activation of tumor-specific T cells by cancer vaccines might be an approach, especially suitable for elderly patients, to eradicate or to prevent recurrence of tumors after primary treatment. To tailor pre-clinical testing of vaccine therapies to the elderly, it is important to have mouse models in which tumors develop at equivalent time points in their life span, as in humans. Such models are currently not available. This progress report first summarizes the current knowledge of tumor-immunological parameters potentially involved in T cell unresponsiveness in relation to aging in mice and humans. Secondly, it reviews those cancer vaccines that are known for their potential to induce tumor-specific T cell responses. Thirdly, it discusses the usefulness of currently available mouse models for pre-clinical testing of cancer vaccines applicable to the elderly population. Finally, experimental approaches are proposed, as to how to develop mouse models that allow the induction of specific tumors at will at different ages, expressing tumor-specific antigens in an 'immune competent' environment. These mouse models may teach us how to overcome immune deficits in the elderly, thereby facilitating the development of effective and safe cancer vaccines.

Rabies virus-based vectors expressing human immunodeficiency virus type 1 (HIV-1) envelope protein induce a strong, cross-reactive cytotoxic T-lymphocyte response against envelope proteins from different HIV-1 isolates

Novel viral vectors that are able to induce both strong and long-lasting immune responses may be required as effective vaccines for human immunodeficiency virus type 1 (HIV-1) infection. Our previous experiments with a replication-competent vaccine strain-based rabies virus (RV) expressing HIV-1 envelope protein from a laboratory-adapted HIV-1 strain (NL4-3) and a primary HIV-1 isolate (89.6) showed that RV-based vectors are excellent for B-cell priming. Here we report that cytotoxic T-lymphocyte (CTL) responses against HIV-1 gp160 are induced by recombinant RVs. Our results indicated that a single inoculation of mice with an RV expressing HIV-1 gp160 induced a solid and long-lasting memory CTL response specific for HIV-1 envelope protein. Moreover, CTLs from immunized mice were not restricted to the homologous HIV-1 envelope protein and were able to cross-kill target cells expressing HIV-1 gp160 from heterologous HIV-1 strains. These studies further suggest promise for RV-based vectors to elicit a persistent immune response against HIV-1 and their potential utility as efficacious anti-HIV-1 vaccines.

Identification of most frequent HLA class I antigen specificities in Botswana: relevance for HIV vaccine design

Since the mid-1990s, southern African countries have been experiencing an expansion of human immunodeficiency virus type 1 (HIV-1) infection caused by HIV-1 subtype C. To facilitate the design of an HLA-based HIV vaccine, we studied the distribution of the HLA class I antigen specificities in Botswana, a southern African country with a high prevalence of HIV infection. Botswana's highly efficient health care system and its central geographical location within southern Africa suggests that it might be an appropriate candidate site for future trials of an HLA-based HIV vaccine. Specificities of HLA class I genes have been investigated in DNA samples obtained from 161 persons of Botswana origin by polymerase chain reaction (PCR) with sequence-specific primers. We identified 4 HLA-A, 7 HLA-B, and 5 HLA-C specificities that were observed at high frequencies in the Botswana population: A30, A02, A23, A68, B58, B72, B42, B8, B18, B44, B45, Cw7, Cw2, Cw17, Cw6, and Cw4. HLA-A30, A02, A23, A68, B58, Cw2, Cw4, Cw6, Cw7, and Cw17 were observed at frequencies of more than 10%. The frequency of HLA-A30 was 27.3%. HLA-B58 (17.9%) was the most frequent generic HLA-B type. Other frequent antigen specificities detected for the HLA-B were B72 (9.6%), B42 (9.3%), B8 (7.4%), B18 (7.4%), B44 (7.4%), and B45 (6.4%). Analysis of haplotype frequencies revealed that haplotypes HLA-A30/HLA-B58 (6.7%), A30/B42 (6.1%), A30/B8 (4.1%), A30/B45 (3.2%), and A23/B58 (2.5%) were the most frequent among two-locus haplotypes. The comparison of HIV-positive patients and noninfected controls for HLA class I specificities confirmed the previously described association of A2/A6802 supertype with resistance to HIV. Our study suggested an increased resistance to HIV infection associated with A68 rather than A2. We also found that the generic HLA-B58 type was associated with increased susceptibility to HIV infection. Our findings suggest that the design of an HLA-based HIV vaccine that includes multiple CTL epitopes restricted by identified common HLA class I specificities might target up to 97.5% of the population in Botswana. The results of this study extend the HLA map to a southern African country that has high rates of HIV and also provide a database for the design of an HLA-based HIV vaccine.

Immune-based approaches for control of HIV infection and viral-induced immunopathogenesis

Due to the limited efficacy of the current antiretroviral drug regimens in completely eradicating HIV and reconstituting the immune system, AIDS research is turning toward immune-based therapy to complement highly active antiretroviral therapy. Here we review potential mechanisms of protective cellular immunity and current HIV-specific immune-based strategies and discuss the rationale for novel hypothetical immunologic approaches for modulation of host antiviral immunity. One of the mechanisms by which the immune system exerts antiviral effects is via leukocyte generation of anti-HIV factors. Recent observations in this area of research suggest that non-HIV antigens can stimulate the in vitro production of anti-HIV activity by leukocytes from healthy uninfected individuals and HIV-infected patients. These findings may provide insights for the design of novel therapeutic or prophylactic approaches, which might contribute to modulating immune system control of HIV infection.

In vivo antigen loading and activation of dendritic cells via a liposomal peptide vaccine mediates protective antiviral and anti-tumour immunity

Initiation of antiviral and anti-tumour T cell responses is probably achieved mainly by dendritic cells (DC) transporting antigen from the periphery into organised lymphoid tissues. To develop T cell vaccines it is, therefore, important to understand the accessibility of the antigen to DC in vivo and whether DC are activated by vaccination. Here we have evaluated the immunogenicity of a liposomal vaccine formulation with antigenic peptides derived from the glycoprotein of the lymphocytic choriomeningitis virus. Liposome-encapsulated peptides were highly immunogenic when administered intradermally and elicited protective antiviral immunity. After intradermal injection, liposomes formed antigen depots which facilitated long-lasting in vivo antigen loading of dendritic cells almost exclusively in the local draining lymph nodes. The immunogenicity of the liposomal peptide vaccine was further enhanced by incorporation of immunostimulatory oligonucleotides leading to activation of DC. This optimised liposomal peptide vaccine elicited also anti-tumour immunity and induced CTL responses comparable to adoptively transferred, peptide-presenting DC. Thus, our data show that liposomal formulations of peptide vaccines are highly effective at direct in vivo antigen loading and activation of DC leading to protective antiviral and anti-tumour immune responses.

Semi-allogeneic cell hybrids stimulate HIV-1 envelope-specific cytotoxic T lymphocytes

OBJECTIVE

The present study was designed to determine whether the HLA allogeneic T helper response stimulated by semi-allogeneic cell lines could be used as an in vitro model of immune-based therapy to stimulate HIV-specific cytotoxic T lymphocytes.

DESIGN AND METHODS

Semi-allogeneic cell hybrids were obtained by the fusion of peripheral blood mononuclear cells from HIV-infected patients with the allogeneic beta2-microglobulin-deficient FO1-12 melanoma cell line. These hybrids were used as antigen presenting cells for HIV envelope peptide (env)-specific cytotoxic assays.

RESULTS

The hybrid cell lines express HLA class I and II antigens from both parental cells, as well as the CD86 costimulatory molecule. HIV-specific cytotoxic T lymphocyte activity was obtained when patients' peripheral blood mononuclear cells were costimulated with env peptides plus semi-allogeneic hybrids, in contrast with stimulation with either env or hybrid cells alone. Thus, the semi-allogeneic hybrids enhanced HIV-specific killing of target cells.

CONCLUSIONS

Irradiated, semi-allogeneic cell hybrids engineered for individual AIDS patients provide efficient and simultaneous co-recognition of HLA allogeneic determinants and viral antigenic determinants presented by self-HLA molecules on the same antigen presenting cells and results in the generation of enhanced HIV-specific cytotoxic T lymphocyte activity.