Translational Mini-Review Series on Vaccines for HIV: T lymphocyte trafficking and vaccine-elicited mucosal immunity

What is the influence of vaccination's routes on the regression of tumors located at mucosal sites?

Tumor-regressions following tumor-associated-antigen vaccination in animal models contrast with the limited clinical outcomes in cancer patients. Most animal studies however used subcutaneous-tumor-models and questions arise as whether these are relevant for tumors growing in mucosae; whether specific mucosal-homing instructions are required; and how this may be influenced by the tumor.

Conjugated anionic PEG-citrate G2 dendrimer with multi-epitopic HIV-1 vaccine candidate enhance the cellular immune responses in mice

Multi-epitope vaccines might cause immunity against multiple antigenic targets. Four immunodominant epitopes of HIV-1 genome were used to construct a polytope vaccine, formulated by dendrimer. Two regimens of polytopes mixture with dendrimer were utilized to immunize BALB/c mice. Adjuvants were also used to boost immune responses. The conjugated polytope could arouse significant cellular immune responses (P < 0.05) and Th1 response showed higher intensity compared to Th2 (P < 0.05). Our study depicted that conjugated dendrimer with multi-epitopic rHIVtop4 would efficiently induce cell-mediated immune responses and might be considered as promising delivery system for vaccines formulation.

Identification of biomarkers to measure HIV-specific mucosal and systemic CD8(+) T-cell immunity using single cell Fluidigm 48.48 Dynamic arrays

Thirty genes composed of cytokines, chemokines, granzymes, perforin and integrins were evaluated in gut and splenic K(d)Gag197-205-specific single CD8(+) T cells using Fluidigm 48.48 Dynamic arrays, with the aim of identifying biomarkers to predict effective mucosal and systemic vaccine efficacy. The mRNA expression profiles were analyzed in three ways: (i) the "number" of K(d)Gag197-205-specific CD8(+) T cells expressing the biomarker, (ii) "level" of mRNA expression using principal component analysis (PCA) and (iii) poly-functionality in relation to RANTES expression. In total, 21 genes were found to be differentially expressed between the vaccine groups and the immune compartments tested. Overall, the PCA indicated that IL-13Rα2 or IL-4R antagonist adjuvanted vaccines that previously induced high-avidity mucosal/systemic CD8(+) T cells with better protective efficacy, the "level" of mRNA expression, specifically RANTES, MIP-1β, and integrin α4 in gut K(d)Gag197-205-specific single CD8(+) T cells, were significantly elevated compared to unadjuvanted vaccine. Furthermore, significantly elevated granzymes/perforin levels were detected in IL-13(-/-) mice given the unadjuvanted vaccine, indicating that the degree of IL-13 inhibition (total, transient or no inhibition) can considerably alter the level of T-cell activity/poly-functionality. When splenic- and gut-K(d)Gag197-205-specific CD8(+) T cells were compared, PC1 vs. PC2 scores revealed that not only RANTES, MIP-1β, and integrin α4 mRNA, but also perforin, granzymes A/B, and integrins β1 and β2 mRNA were elevated in spleen. Collectively, data suggest that RANTES, MIP-1β, perforin, and integrins α4, β1 and β7 mRNA in single HIV-specific CD8(+) T cells could be used as a measure of effective mucosal and systemic vaccine efficacy.

Natural killer T cell and TLR9 agonists as mucosal adjuvants for sublingual vaccination with clade C HIV-1 envelope protein

The vast majority of HIV-1 infections occur at mucosa during sexual contact. It may therefore be advantageous to provide mucosal barrier protection against this entry by mucosal vaccination. While a number of mucosal routes of vaccination are possible, many like enteric oral vaccines or intranasal vaccines have significant impediments that limit vaccine efficacy or pose safety risks. In contrast, immunogens applied to the sublingual region of the mouth could provide a simple route for mucosal vaccination. While sublingual immunization is appealing, this site does not always drive strong immune responses, particularly when using protein antigens. To address this issue, we have tested the ability of two mucosal adjuvants: alpha-galactosylceramide (αGalCer) that is a potent stimulator of natural killer T cells and CpG-oligodeoxynucleotide (CpG-ODN) a TLR9 agonist for their ability to amplify immune responses against clade C gp140 HIV-1 envelope protein antigen. Immunization with envelope protein alone resulted in a weak T cell and antibody responses. In contrast, CD4(+) and CD8(+) T cells responses in systemic and mucosal tissues were significantly higher in mice immunized with gp140 in the presence of either αGalCer or CpG-ODN and these responses were further augmented when the two adjuvants were used together. While both the adjuvants effectively increased gp140-specific serum IgG and vaginal IgA antibody levels, combining both significantly improved these responses. Memory T cell responses 60 days after immunization revealed αGalCer to be more potent than CpG-ODN and the combination of the αGalCer and CpG-ODN adjuvants was more effective than either alone. Serum and vaginal washes collected 60 days after immunization with gp140 with both αGalCer and CpG-ODN adjuvants had significant neutralization activity against Tier 1 and Tier 2 SHIVs. These data support the utility of the sublingual route for mucosal vaccination particularly in combination with αGalCer and CpG-ODN adjuvants.

Current and novel approaches to vaccine development against tuberculosis

Antibiotics and vaccines are the two most successful medical countermeasures that humans have created against a number of pathogens. However a select few e.g., Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB) have evaded eradication by vaccines and therapeutic approaches. TB is a global public health problem that kills 1.4 million people per year. The past decade has seen significant progress in developing new vaccine candidates, but the most fundamental questions in understanding disease progression and protective host responses that are responsible for controlling Mtb infection still remain poorly resolved. Current TB treatment requires intense chemotherapy with several antimicrobials, while the only approved vaccine is the classical viable whole-cell based Bacille-Calmette-Guerin (BCG) that protects children from severe forms of TB, but fails to protect adults. Taken together, there is a growing need to conduct basic and applied research to develop novel vaccine strategies against TB. This review is focused on the discussion surrounding current strategies and innovations being explored to discover new protective antigens, adjuvants, and delivery systems in the hopes of creating an efficacious TB vaccine.

Evidence for cyclic diguanylate as a vaccine adjuvant with novel immunostimulatory activities

Cyclic diguanylate (c-di-GMP), a bacterial signaling molecule, possesses protective immunostimulatory activity in bacterial challenge models. This study explored the potential of c-di-GMP as a vaccine adjuvant comparing it with LPS, CpG oligonucleotides, and a conventional aluminum salt based adjuvant. In this evaluation, c-di-GMP was a more potent activator of both humoral and Th1-like immune responses as evidenced by the robust IgG2a antibody response it induced in mice and the strong IFN-γ, TNF-α and IP-10 responses, it elicited in mice and in vitro in non-human primate peripheral blood mononuclear cells. Further, compared to LPS or CpG, c-di-GMP demonstrated a more pronounced ability to induce germinal center formation, a hallmark of long-term memory, in immunized mice. Together, these data add to the growing body of evidence supporting the utility of c-di-GMP as an adjuvant in vaccination for sustained and robust immune responses and provide a rationale for further evaluation in appropriate models of immunization.

Parenteral is more efficient than mucosal immunization to induce regression of human papillomavirus-associated genital tumors

Cervical cancer is a public health concern as it represents the second cause of cancer death in women worldwide. High-risk human papillomaviruses (HPV) are the etiologic agents, and HPV E6 and/or E7 oncogene-specific therapeutic vaccines are under development to treat HPV-related lesions in women. Whether the use of mucosal routes of immunization may be preferable for inducing cell-mediated immune responses able to eradicate genital tumors is still debated because of the uniqueness of the female genital mucosa (GM) and the limited experimentation. Here, we compared the protective activity resulting from immunization of mice via intranasal (i.n.), intravaginal (IVAG) or subcutaneous (s.c.) routes with an adjuvanted HPV type 16 E7 polypeptide vaccine. Our data show that s.c. and i.n. immunizations elicited similar frequencies and avidity of TetE71CD81 and E7-specific Interferon-gamma-secreting cells in the GM, whereas slightly lower immune responses were induced by IVAG immunization. In a novel orthotopic murine model, both s.c. and i.n. immunizations allowed for complete long-term protection against genital E7-expressing tumor challenge. However, only s.c. immunization induced complete regression of already established genital tumors. This suggests that the higher E7-specific systemic response observed after s.c. immunization may contribute to the regression of growing genital tumors, whereas local immune responses may be sufficient to impede genital challenges. Thus, our data show that for an efficiently adjuvanted protein-based vaccine, parenteral vaccination route is superior to mucosal vaccination route for inducing regression of established genital tumors in a murine model of HPV-associated genital cancer.

Distribution of primed T cells and antigen-loaded antigen presenting cells following intranasal immunization in mice

Priming of T cells is a key event in vaccination, since it bears a decisive influence on the type and magnitude of the immune response. T-cell priming after mucosal immunization via the nasal route was studied by investigating the distribution of antigen-loaded antigen presenting cells (APCs) and primed antigen-specific T cells. Nasal immunization studies were conducted using the model protein antigen ovalbumin (OVA) plus CpG oligodeoxynucleotide adjuvant. Trafficking of antigen-specific primed T cells was analyzed in vivo after adoptive transfer of OVA-specific transgenic T cells in the presence or absence of fingolimod, a drug that causes lymphocytes sequestration within lymph nodes. Antigen-loaded APCs were observed in mediastinal lymph nodes, draining the respiratory tract, but not in distal lymph nodes. Antigen-specific proliferating T cells were first observed within draining lymph nodes, and later in distal iliac and mesenteric lymph nodes and in the spleen. The presence at distal sites was due to migration of locally primed T cells as shown by fingolimod treatment that caused a drastic reduction of proliferated T cells in non-draining lymph nodes and an accumulation of extensively divided T cells within draining lymph nodes. Homing of nasally primed T cells in distal iliac lymph nodes was CD62L-dependent, while entry into mesenteric lymph nodes depended on both CD62L and α4β7, as shown by in vivo antibody-mediated inhibition of T-cell trafficking. These data, elucidating the trafficking of antigen-specific primed T cells to non-draining peripheral and mucosa-associated lymph nodes following nasal immunization, provide relevant insights for the design of vaccination strategies based on mucosal priming.

Update on mucosal HIV vaccine vectors

PURPOSE OF REVIEW

HIV's primary site of infection is at mucosal surfaces. To successfully defend against sexually transmitted diseases (STDs), including HIV, protection may need to be specifically elicited at the mucosal interface, where the organism enters the host. Recent advances in measuring adaptive responses at mucosal sites and optimization of techniques for low-dose repeated mucosal challenge in nonhuman primate animal models allow more in depth studies of mucosal vaccine vectors.

RECENT FINDINGS

Although parenterally administered vaccines can elicit responses at mucosal sites, vaccination of mucosal sites is being explored in an attempt to increase the frequency, strength and distribution of the adaptive mucosal response. Recent studies in nonhuman primates involve vaccination of the gastrointestinal tract and rectum, as well as the nose, oropharynx or respiratory tree in an attempt to elicit responses at the distal mucosal sites where HIV transmission occurs, the rectum and genital tract.

SUMMARY

Recent experiments in nonhuman primates indicate that vaccination at mucosal sites can elicit robust responses in the periphery and at mucosal sites, although the response pattern varies widely by route and regimen used. For most regimens, disease course after challenge did not differ by route of vaccination.

Current progress in the development of a prophylactic vaccine for HIV-1

Since its discovery and characterization in the early 1980s as a virus that attacks the immune system, there has been some success for the treatment of human immunodeficiency virus-1 (HIV-1) infection. However, due to the overwhelming public health impact of this virus, a vaccine is needed urgently. Despite the tireless efforts of scientist and clinicians, there is still no safe and effective vaccine that provides sterilizing immunity. A vaccine that provides sterilizing immunity against HIV infection remains elusive in part due to the following reasons: 1) degree of diversity of the virus, 2) ability of the virus to evade the hosts' immunity, and 3) lack of appropriate animal models in which to test vaccine candidates. There have been several attempts to stimulate the immune system to provide protection against HIV-infection. Here, we will discuss attempts that have been made to induce sterilizing immunity, including traditional vaccination attempts, induction of broadly neutralizing antibody production, DNA vaccines, and use of viral vectors. Some of these attempts show promise pending continued research efforts.

Blocking of α4β7 gut-homing integrin during acute infection leads to decreased plasma and gastrointestinal tissue viral loads in simian immunodeficiency virus-infected rhesus macaques

Intravenous administration of a novel recombinant rhesus mAb against the α4β7 gut-homing integrin (mAb) into rhesus macaques just prior to and during acute SIV infection resulted in significant decrease in plasma and gastrointestinal (GI) tissue viral load and a marked reduction in GI tissue proviral DNA load as compared with control SIV-infected rhesus macaques. This mAb administration was associated with increases in peripheral blood naive and central memory CD4(+) T cells and maintenance of a high frequency of CCR5(+)CD4(+) T cells. Additionally, such mAb administration inhibited the mobilization of NK cells and plasmacytoid dendritic cells characteristically seen in the control animals during acute infection accompanied by the inhibition of the synthesis of MIP-3α by the gut tissues. These data in concert suggest that blocking of GI trafficking CD4(+) T cells and inhibiting the mobilization of cell lineages of the innate immune system may be a powerful new tool to protect GI tissues and modulate acute lentiviral infection.

Educating CD4 T cells with vaccine adjuvants: lessons from lipopolysaccharide

Toll-like receptor (TLR) adjuvants are capable of driving T cell immunity. The TLR4 agonist LPS activates antigen-presenting cells through myeloid differentiation primary response gene 88 (MyD88) and TIR domain-containing adaptor inducing interferon-beta (TRIF)-dependent signaling pathways, initiating CD4 T helper cell clonal expansion and differentiation. Lipopolysaccharide (LPS) supports the development of diverse T helper (Th) lineages depending on the tissue microenvironment. For instance, peripheral immunization with LPS drives Th1 priming in lymphoid tissue and Th17 priming in the gut. This could be due to commensal bacteria inducing Th17-stabilizing cytokines within the intestinal lamina propria. Here, we detail how the response to LPS stimulates CD4 T cell priming in lymphoid tissue and the intestinal mucosa. How this knowledge might be exploited to target specific features of T cell immunity by vaccine adjuvants is also considered.