Mucosal AIDS vaccines

Innate and Adaptive Mucosal Immunity in Protection against HIV Infection

The appalling toll on the populations of developing countries as a result of the HIV epidemic shows no signs of abatement. While costly drug therapies are effective in developed nations, the sheer scale of the epidemic elsewhere makes the need for a vaccine an ever more urgent goal. The prevalent DNA prime-viral boost strategy aims to elicit cytotoxic lymphocytes (CTL) against HIV, but this approach is undermined by the rapid mutation of HIV, which thereby escapes CTL control. Alloimmunity has been found to be protective in vertical transmission from infected mothers to their babies, in alloimmunization of women with their partners’ mononuclear cells, and in monkeys immunized with SIV grown in human T-cells. Vaginal mucosal immunization, as a result of unprotected sex with a regular partner, induced in vitro protection against HIV infection, and this was confirmed in macaques. The second type of natural protection is found in persons with the homozygous Δ32 CCR5 mutation, a 32-base-pair deletion of the CCR5 gene, which results in a lack of cell-surface expression of CCR5, which is associated with an increase in CC chemokines and the development of CCR5 antibodies. These two ‘experiments of nature’ have been used to develop vaccine strategies—first, in vaginal immunization of macaques with CCR5 peptides, in addition to HIV envelope (env) and SIV core (gag) antigens, all of which were linked to the 70-kD heat-shock protein (HSP70); and second, in mucosal allo-immunization of macaques, which also gave rise to in vitro protection from infection. Immunization with this vaccine elicited serum and vaginal IgG and IgA antibodies, IFNγ- and IL-12-producing cells, and increased concentrations of CCL-3 and CCL-4. Vaginal challenge with a simian immunodeficiency virus engineered to carry a human envelope protein (SHIV 89.6) showed significant clearance of SHIV in the immunized macaques. This platform strategy will now be developed to activate the co-stimulatory pathways with the aim of enhancing the primary allogeneic and CCR5-directed responses which are involved in natural protection against HIV infection. Abbreviations: IFN-γ, gamma interferon; IL-12, interleukin 12; MIP-1 α,β, Macrophage inflammatory protein-1; RANTES, Regulated on activation normal T-cell expressed and secreted; SDF-1, stromal-derived factor 1; SIV, simian immunodeficiency virus; and SHIV, engineered SIV carrying a human envelope protein.

Prospects for oral replicating adenovirus-vectored vaccines

Orally delivered replicating adenovirus (Ad) vaccines have been used for decades to prevent adenovirus serotype 4 and 7 respiratory illness in military recruits, demonstrating exemplary safety and high efficacy. That experience suggests that oral administration of live recombinant Ads (rAds) holds promise for immunization against other infectious diseases, including those that have been refractory to traditional vaccination methods. Live rAds can express intact antigens from free-standing transgenes during replication in infected cells. Alternatively, antigenic epitopes can be displayed on the rAd capsid itself, allowing presentation of the epitope to the immune system both prior to and during replication of the virus. Such capsid-display rAds offer a novel vaccine approach that could be used either independently of or in combination with transgene expression strategies to provide a new tool in the search for protection from infectious disease.

Natural anti-CCR5 antibodies in HIV-infection and -exposure

Natural antibodies constitute a first-line of defence against pathogens; they may also play other roles in immune regulation and homeostasis, through their ability to bind host antigens, surface molecules and receptors. Natural anti-CCR5 antibodies can be decisive in preventing HIV infection in mucosal tissues and offer prompt and effective protection just at major sites of virus entry. Among natural anti-CCR5 antibodies, IgG and IgA to the ECL1 domain have been shown to block HIV effectively and durably without causing harm to the host. Their biological properties and their uncommon generation in subsets of HIV-infected and HIV-exposed individuals (so called ESN) will be introduced and discussed, with the aim at exploiting their potential in therapy and prevention.

CCR5: From Natural Resistance to a New Anti-HIV Strategy

The C-C chemokine receptor type 5 (CCR5) is a key player in HIV infection due to its major involvement in the infection process. Investigations into the role of the CCR5 coreceptor first focused on its binding to the virus and the molecular mechanisms leading to the entry and spread of HIV. The identification of naturally occurring CCR5 mutations has allowed scientists to address the CCR5 molecule as a promising target to prevent or limit HIV infection in vivo. Naturally occurring CCR5-specific antibodies have been found in exposed but uninfected people, and in a subset of HIV seropositive people who show long-term control of the infection. This suggests that natural autoimmunity to the CCR5 coreceptor exists and may play a role in HIV control. Such natural immunity has prompted strategies aimed at achieving anti-HIV humoral responses through CCR5 targeting, which will be described here.

The development of an AIDS mucosal vaccine

It is well known that mucosal tissues contain the largest surface area of the human body and are the front line of natural host defense against various pathogens. In fact, more than 80% of infectious disease pathogens probably gain entry into the susceptible human hosts through open mucosal surfaces. Human immunodeficiency virus type one (HIV-1), a mainly sexually transmitted virus, also primarily targets the vaginal and gastrointestinal mucosa as entry sites for viral transmission, seeding, replication and amplification. Since HIV-1 establishes its early replication in vaginal or rectal mucosal tissues, the induction of sufficient mucosal immunity at the initial site of HIV-1 transmission becomes essential for a protective vaccine. However, despite the fact that current conventional vaccine strategies have remained unsuccessful in preventing HIV-1 infection, sufficient financial support and resources have yet to be given to develop a vaccine able to elicit protective mucosal immunity against sexual transmissions. Interestingly, Chinese ancestors invented variolation through intranasal administration about one thousand years ago, which led to the discovery of a successful smallpox vaccine and the final eradication of the disease. It is the hope for all mankind that the development of a mucosal AIDS vaccine will ultimately help control the AIDS pandemic. In order to discover an effective mucosal AIDS vaccine, it is necessary to have a deep understanding of mucosal immunology and to test various mucosal vaccination strategies.

Oral vaccination: where we are?

As early as 900 years ago, the Bedouins of the Negev desert were reported to kill a rabid dog, roast its liver and feed it to a dog-bitten person for three to five days according to the size and number of bites [1] . In sixteenth century China, physicians routinely prescribed pills made from the fleas collected from sick cows, which purportedly prevented smallpox. One may dismiss the wisdom of the Bedouins or Chinese but the Nobel laureate, Charles Richet, demonstrated in 1900 that feeding raw meat can cure tuberculous dogs - an approach he termed zomotherapy. Despite historical clues indicating the feasibility of oral vaccination, this particular field is notoriously infamous for the abundance of dead-end leads. Today, most commercial vaccines are delivered by injection, which has the principal limitation that recipients do not like needles. In the last few years, there has been a sharp increase in interest in needle-free vaccine delivery; new data emerges almost daily in the literature. So far, there are very few licensed oral vaccines, but many more vaccine candidates are in development. Vaccines delivered orally have the potential to take immunization to a fundamentally new level. In this review, the authors summarize the recent progress in the area of oral vaccines.

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.

Production of a Short Recombinant C4V3 HIV-1 Immunogen That Induces Strong Anti-HIV Responses by Systemic and Mucosal Routes Without the Need of Adjuvants

Synthetic peptides have been shown to evoke neutralizing and cytotoxic protective anti-HIV responses in mice and other animal models. Recent data support that C4V3 peptides can induce anti- V3 antibodies that neutralize primary isolates. Critical to the success of peptide-based vaccines is the development of strategies to augment their immunogenicity while reducing their large-scale production costs. Therefore, finding efficient and economical alternatives for the production of epitopic vaccines could have an impact on researches using such immunogens. Herein, we report the recombinant production and immunological characterization of a short polypeptide which carries the three relevant epitopes contained in a C4V3 peptide. This polypeptide, named rC4V3, was efficiently produced in E. coli, yielding more than 75 mg per culture liter. No major difficulties were found in the recovery, refolding and purification of this peptide; the latter facilitated by C-terminal inclusion of a histidine tag. The immunogenicity of this protein was studied by administering it intramuscularly or intranasally to mice and it demonstrated to be a strong elicitor of anti-HIV antibodies at systemic and mucosal compartments. Remarkably, such responses were attained with rC4V3 even without the need of adjuvants. We can conclude that this protein might be a promising tool for studies using epitope-based vaccine designs.

Enhanced mucosal and systemic immune response with intranasal immunization of mice with HIV peptides entrapped in PLG microparticles in combination with Ulex Europaeus-I lectin as M cell target

The predominant route of HIV infection is through the sexual transmission via M cells. Most of the peptide and protein vaccines show poor transport across the epithelial barrier and are commonly administered by parenteral route. In the present study four HIV peptides from envelope (gp 41-LZ (leucine zipper), gp 41-FD (fusion domain) and gp120-C2) and regulatory (Nef) region in poly lactic-co-glycolide (PLG) micro-particle delivery were evaluated in mice of outbred and with different genetic background to compare immune response versus MHC restriction. Out of the combinational and single routes of immunization attempted, the single route maintained the IgG, IgA and sIgA in sera and washes for longer duration as compared to combinational routes in which the response was declined. The study demonstrated that single intranasal immunization offered significantly higher immune response (p<0.05) over oral and rectal mucosal routes in terms of inducing systemic as well as mucosal response. Also, the specific activity measurement of IgA and IgG in sera and sIgA in washes were correlating to the antibody titers. However, the intramuscular route of immunization generated systemic response only. The entrapment of plant lectin UEA-1 a ligand specific for M cells in micro-particle further enhanced the immune response in all the mucosal routes. The IgG isotypes generated were of IgG1 and IgG2a/2b in sera for all the peptides. The T cell proliferation response study with and without UEA-1 lectin in micro-particles showed significantly high (p<0.05) stimulation index (SI) with intranasal immunization for all the peptides from cells collected from spleen (SP), peyer's patches (PP) and lamina propria (LP) with SI in the order LP cells>PP>or=SP. The cytokine measurement profile of IL-2, IFN-gamma and IL-6 and low levels of IL-4 in the cultural supernatants of SP, PP and LP showed mixed CD4(+) Th1 and Th2 immune response. The p24 assay showed high percent inhibition of HIV-IIIB virus with sera and washes obtained from intranasal route. Thus, overall the study highlighted the combination of UEA-1 lectin with HIV peptides in micro-particles through intranasal immunization generated systemic as well as mucosal immune response.

Phase II placebo-controlled study of V-1 Immunitor as a therapeutic modality for treatment of HIV

BACKGROUND

V-1 Immunitor (V1) is an oral AIDS vaccine containing heat- and chemically-inactivated viral antigens derived from pooled blood of HIV-positive donors. V1 has a pending status as an investigational drug but is currently marketed as a dietary supplement. Earlier published, uncontrolled studies of V1 demonstrated body weight gain, increase in T-lymphocyte numbers, decrease in viral load, and improved survival of end-stage AIDS patients.

OBJECTIVES AND STUDY DESIGN

In order to substantiate prior observations we have undertaken a placebo-controlled phase II clinical trial involving 47 antiviral therapy naive, asymptomatic individuals who had over 350 mm(3) CD4 T-cells (mean/median 538/480) at study entry. Both placebo and treatment arms were identical demographically and by every clinical parameter measured at baseline.

RESULTS AND CONCLUSIONS

At the end of 6-month follow-up 29 volunteers who received V1 b.i.d. had gained on average 43 CD4 T-cells (540 versus 583). This gain was statistically significant (p=0.01) while changes in T-cell numbers in placebo group failed to reach the significance threshold (p=0.33). The clinical potential of V1 is further supported by an elevation in CD4/CD8 ratio among V1 recipients and decline in CD4/CD8 ratio in patients on placebo (0.575 versus 0.524; p=0.02). The average weight gain among patients on V1 was 1.8 kg while placebo group lost 0.5 kg. These results suggest that V1 may delay or reverse the disease progression without any concurrent toxicity and support our prior open-label studies indicating that V1 confers clinical benefit. A phase III clinical study is required to confirm these findings and to allow us to seek license for V1 as a therapeutic AIDS vaccine.