Evaluation of a prime-boost vaccine schedule with distinct adenovirus vectors against malaria in rhesus monkeys

A vaccine that elicits both specific antibodies and IFN-γ-producing T cells is required to protect against pre-erythrocytic malaria. Among the most promising approaches to induce such complex immunity are heterologous prime-boost vaccination regimens, in particular ones containing live viral vector. We have demonstrated previously that adenovectors serotype 35 (Ads35) encoding the circumsporozoite (CS) antigen or liver-stage antigen-1 (LSA-1) are highly effective in improving the T-cell responses induced by immunizations with protein-based vaccines in a heterologous prime-boost schedule. Here we evaluated the potential of a heterologous prime-boost vaccination that combines the Ad35.CS vector with the serologically distinct adenovector Ad5.CS, in rhesus macaques, after establishing the potency in mice. We show that the heterologous Ad35.CS/Ad5.CS prime-boost regimen elicits both antibody responses and robust IFN-γ-producing CD8⁺ T-cell responses against the CS antigen. Analysis of the quality of the antibody responses in rhesus macaques, using indirect immunofluorescence assay (IFA) with Plasmodium falciparum-coated slides, demonstrated that this heterologous prime-boost regimen elicits a high titer of antibodies that are able to bind to P. falciparum sporozoites. Level of the IFA response was superior to the response measured with sera of an adult human population living in endemic malaria region. In conclusion, the combination of Ad35.CS, a vaccine based on a rare serotype adenovirus, with Ad5.CS or possibly another adenovector of a distinct serotype, induces a complex immune response that is required for protection against malaria, and is thus a highly promising approach for pediatric vaccination.     

Evaluation of recombinant adenovirus vectors and adjuvanted protein as a heterologous prime-boost strategy using HER2 as a model antigen

Induction of strong antigen-specific cell-mediated and humoral responses are critical to developing a successful therapeutic vaccine. Herein, using HER2 as a model antigen, we aim to evaluate a therapeutic vaccine protocol that elicits anti-tumor antibody and cytotoxic T cells to HER2/neu antigen. Replication-competent (ΔPS AdV) and non-replicating recombinant adenoviral vectors (AdV) expressing a rat HER2/neu (ErbB2) oncogene, were generated and compared for four different doses and over four time points for their ability to induce antigen-specific T and B cell responses in mice. Although ΔPS AdV:Her2 vector was shown to induce more durable antigen-specific CD8⁺ T cell responses, overall, the AdV:Her2 vector induced broader T and B cell responses. Hence the AdV:Her2 vector was used to evaluate a heterologous prime-boost vaccination regimen using rat HER2 protein encapsulated in archaeosomes composed of a semi-synthetic glycolipid (sulfated S-lactosylarchaeol, SLA; and lactosylarchaeol, LA) (SLA/LA:HER2enc) or admixed with archaeosomes composed of SLA alone (SLA:HER2adm). We first tested AdV:Her2 using a prime-boost approach with SLA/LA:HER2enc, and thereafter evaluated a sub-optimal AdV:Her2 dose in a heterologous prime-boost approach with SLA:HER2adm. A single administration of AdV:Her2 alone induced strong cell-mediated immune responses, whereas SLA/LA:HER2enc alone induced strong antigen-specific IgG titers. In mice primed with a suboptimal dose of AdV:Her2, strong CD8⁺ T-cell responses were observed after a single dose which were not further augmented by protein boost. AdV:Her2 induced CD4⁺ specific T-cell responses were augmented by SLA:HER2adm. Homologous vaccination using SLA:HER2adm induced strong antigen-specific antibody responses. However, the overall magnitude of the responses was similar with three doses of SLA:HER2adm or Ad:HER2 prime followed by two doses of SLA:HER2adm.We demonstrate that AdV:Her2 is capable of inducing strong antigen-specific CD8⁺ T cell responses, even at a low dose, and that these responses can be broadened to include antigen-specific antibody responses by boosting with SLA adjuvanted proteins without compromising CD8 T cell responses elicited by AdV priming.     

Combination recombinant simian or chimpanzee adenoviral vectors for vaccine development

Recombinant adenoviral vector (rAd)-based vaccines are currently being developed for several infectious diseases and cancer therapy, but pre-existing seroprevalence to such vectors may prevent their use in broad human populations. In this study, we investigated the potential of low seroprevalence non-human primate rAd vectors to stimulate cellular and humoral responses using HIV/SIV Env glycoprotein (gp) as the representative antigen. Mice were immunized with novel simian or chimpanzee rAd (rSAV or rChAd) vectors encoding HIV gp or SIV gp by single immunization or in heterologous prime/boost combinations (DNA/rAd; rAd/rAd; rAd/NYVAC or rAd/rLCM), and adaptive immunity was assessed. Among the rSAV and rChAd tested, rSAV16 or rChAd3 vector alone generated the most potent immune responses. The DNA/rSAV regimen also generated immune responses similar to the DNA/rAd5 regimen. rChAd63/rChAd3 and rChAd3 /NYVAC induced similar or even higher levels of CD4+ and CD8+ T-cell and IgG responses as compared to rAd28/rAd5, one of the most potent combinations of human rAds. The optimized vaccine regimen stimulated improved cellular immune responses and neutralizing antibodies against HIV compared to the DNA/rAd5 regimen. Based on these results, this type of novel rAd vector and its prime/boost combination regimens represent promising candidates for vaccine development.     

AIDSVAX protein boost improves breadth and magnitude of vaccine-induced HIV-1 envelope-specific responses after a 7-year rest period

BackgroundEliciting durable humoral immunity with sufficient breadth and magnitude is important for HIV-1 vaccine design. The HVTN 114 vaccine trial evaluated different boost regimens administered after a 7-year rest period in participants previously enrolled in HVTN 205, who received either three MVA/HIV62B (MMM) or two DNA and two MVA/HIV62B (DDMM) injections; both vaccines expressed multiple HIV-1 antigens in non-infectious virus-like-particles. The primary objective of HVTN 114 was to assess the impact of a heterologous gp120 protein AIDSVAX B/E boost on the magnitude, breadth and durability of vaccine-induced immune responses.MethodsWe enrolled 27 participants from HVTN 205 into five groups. Eight participants who previously received MMM were randomized and boosted with either MVA/HIV62B alone (T1; n = 4) or MVA/HIV62B and AIDSVAX B/E (T2; n = 4). Nineteen participants who received DDMM were randomized and boosted with MVA/HIV62B alone (T3; n = 6), MVA/HIV62B and AIDSVAX B/E (T4; n = 6), or AIDSVAX B/E alone (T5; n = 7). Boosts were at months 0 and 4. Participants were followed for safety and immunogenicity for 10 months and were pooled for analysis based on the regimen: MVA-only (T1 + T3), MVA + AIDSVAX (T2 + T4), and AIDSVAX-only (T5).ResultsAll regimens were safe and well-tolerated. Prior to the boost vaccination, binding antibody and CD4+T-cell responses were observed 7 years after HVTN 205 vaccinations. Late boosting with AIDSVAX, with or without MVA, resulted in high binding antibody responses to gp120 and V1V2 epitopes, with increased magnitude and breadth compared to those observed in HVTN 205. Late boosting with MVA, with or without AIDSVAX, resulted in increased gp140 and gp41 antibody responses and higher CD4+T-cell responses to Env and Gag.ConclusionsLate boosting with AIDSVAX, alone or in combination with MVA, can broaden binding antibody responses and increase T-cell responses even years following the original MVA/HIV62B with or without DNA-priming vaccine.     

Heterologous prime-boost immunizations with different Salmonella serovars for enhanced antigen-specific CD8 T-cell induction

Pre-existing anti-vector immunity can severely compromise the ability of Salmonella enterica serovar Typhimurium live vaccines to induce protective CD8 T-cell frequencies after type III secretion system-mediated heterologous protein translocation in orally immunized mice. In the present study, we demonstrate that heterologous prime-boost immunizations using attenuated serovar Typhimurium and serovar Dublin strains for foreign antigen delivery can be employed to bypass anti-Salmonella immunity resulting in enhanced antigen-specific CD8 T-cell induction. This desirable effect can be explained by the fact that, in contrast to homologous prime-boost immunizations, vaccination with different Salmonella serovars is characterized by long-lasting colonization of mice by both live carrier vaccines.     

A comparative analysis of HIV-specific mucosal/systemic T cell immunity and avidity following rDNA/rFPV and poxvirus-poxvirus prime boost immunisations

In this study we have firstly compared a range of recombinant DNA poxvirus prime-boost immunisation strategies and shown that combined intramuscular (i.m.) 2× DNA-HIV/intranasal (i.n.) 2× FPV-HIV prime-boost immunisation can generate high-level of HIV-specific systemic (spleen) and mucosal (genito-rectal nodes, vaginal tissues and lung tissues) T cell responses and HIV-1 p24 Gag-specific serum IgG1, IgG2a and mucosal IgG, SIgA responses in vaginal secretions in BALB/c mice. Data indicate that following rDNA priming, two rFPV booster immunisations were necessary to generate good antibody and mucosal T cell immunity. This data also revealed that mucosal uptake of recombinant fowl pox (rFPV) was far superior to plasmid DNA. To further evaluate CD8+ T cell immunity, i.m. 2× DNA-HIV/i.n. 1× FPV-HIV immunisation strategy was directly compared with single shot poxvirus/poxvirus, i.n. FPV-HIV/i.m. VV-HIV immunisation. Results indicate that the latter strategy was able to generate strong sustained HIV-specific CD8+ T cells with higher avidity, broader cytokine/chemokine profiles and better protection following influenza-K^dGag_197-205 challenge compared to rDNA poxvirus prime-boost strategy. Our findings further substantiate the importance of vector selection/combination, order and route of delivery when designing effective vaccines for HIV-1.     

Prime-boost vaccine strategy against viral infections: Mechanisms and benefits

The essential goal of vaccination is to generate potent and long-term protection against diseases. Among different vaccine modalities, prime-boost vaccine strategies could enhance cellular and also humoral immunity in several animal models. These strategies have been applied for the development of vaccines against important infectious diseases such as HIV, SIV, HCV, HSV, and HBV indicating promising results even in clinical trials. Several factors including selection of antigen, type of vector, delivery route, dose, adjuvant, boosting regimen, the order of vector injection, and the intervals between different vaccinations influence the outcome of prime-boost immunization approaches. The reported data suggest that the prime-boost strategy as a combination of vaccines (i.e., heterologous prime-boost) may be better than a single vaccine for protection against infectious diseases. Indeed, in many cases, heterologous prime-boost can be more immunogenic than homologous prime-boost strategy. This review discusses the recent advances in prime-boost immunization strategies as well as their benefits and mechanisms of action.     

Recombinant rubella vectors elicit SIV Gag-specific T cell responses with cytotoxic potential in rhesus macaques

Live-attenuated rubella vaccine strain RA27/3 has been demonstrated to be safe and immunogenic in millions of children. The vaccine strain was used to insert SIV gag sequences and the resulting rubella vectors were tested in rhesus macaques alone and together with SIV gag DNA in different vaccine prime-boost combinations. We previously reported that such rubella vectors induce robust and durable SIV-specific humoral immune responses in macaques. Here, we report that recombinant rubella vectors elicit robust de novo SIV-specific cellular immune responses detectable for >10 months even after a single vaccination. The antigen-specific responses induced by the rubella vector include central and effector memory CD4⁺ and CD8⁺ T cells with cytotoxic potential. Rubella vectors can be administered repeatedly even after vaccination with the rubella vaccine strain RA27/3. Vaccine regimens including rubella vector and SIV gag DNA in different prime-boost combinations resulted in robust long-lasting cellular responses with significant increase of cellular responses upon boost. Rubella vectors provide a potent platform for inducing HIV-specific immunity that can be combined with DNA in a prime-boost regimen to elicit durable cellular immunity.     

Comparison of immune responses and protective efficacy of intranasal prime-boost immunization regimens using adenovirus-based and CpG/HH2 adjuvanted-subunit vaccines against genital Chlamydia muridarum infection

An efficacious Chlamydia vaccine is urgently needed to control Chlamydia infections. Heterologous prime-boost vaccination regimens are emerging as a promising strategy for preventing intracellular viral and bacterial infections. However, it remains to be determined if this regimen would be a feasible and effective approach for Chlamydia infection. In this study, we examined the immune response and the protective efficacy induced by various vaccination regimens using a recombinant adenovirus vector expressing the Chlamydia antigen CPAF (AdCPAF) and recombinant CPAF (rCPAF) subunit vaccines formulated with CpG oligodeoxynucleotides and/or a synthetic immunomodulatory peptide HH2 as adjuvants. A single dose of AdCPAF stimulated potent antibody production but weak cellular immune responses in mice. A booster rCPAF vaccine formulated with both CpG and HH2, but not CpG alone or HH2 alone, showed robust adjuvant effects on induction of Th1-biased cellular immune responses in mice primed with AdCPAF. In contrast, a homologous regimen using rCPAF/CpG/HH2 subunit vaccine for both priming and boosting induced a weak antibody response, but potent cellular immunity with a mixed Th1/Th17 profile. Despite the disparities observed in humoral and cellular immune responses, both the heterologous and homologous prime-boost regimens conferred significant immune protection against genital Chlamydia muridarum challenge in C3H/HeN and BALB/c mice.     

A heterologous AZD1222 priming and BNT162b2 boosting regimen more efficiently elicits neutralizing antibodies,but not memory T cells,than the homologous BNT162b2 regimen

BackgroundComparative analyses of SARS-CoV-2-specific immune responses elicited by diverse prime-boost regimens are required to establish efficient regimens for the control of COVID-19.MethodIn this prospective observational cohort study, spike-specific immunoglobulin G (IgG) and neutralizing antibodies (nAbs) alongside spike-specific T-cell responses in age-matched groups of homologous BNT162b2/BNT162b2 or AZD1222/AZD1222 vaccination, heterologous AZD1222/BNT162b2 vaccination, and prior wild-type SARS-CoV-2 infection/vaccination were evaluated.ResultsPeak immune responses were achieved after the second vaccine dose in the naïve vaccinated groups and after the first dose in the prior infection/vaccination group. Peak titers of anti-spike IgG and nAb were significantly higher in the AZD1222/BNT162b2 vaccination and prior infection/vaccination groups than in the BNT162b2/BNT162b2 or AZD1222/AZD1222 groups. However, the frequency of interferon-γ-producing CD4⁺ T cells was highest in the BNT162b2/BNT162b2 vaccination group. Similar results were observed in the analysis of polyfunctional T cells. When nAb and CD4⁺ T-cell responses against the Delta variant were analyzed, the prior infection/vaccination group exhibited higher responses than the groups of other homologous or heterologous vaccination regimens.ConclusionnAbs are efficiently elicited by heterologous AZD1222/BNT162b2 vaccination, as well as prior infection/vaccination, whereas spike-specific CD4⁺ T-cell responses are efficiently elicited by homologous BNT162b2 vaccination. Variant-recognizing immunity is more efficiently generated by prior infection/vaccination than the other homologous or heterologous vaccination regimens.     

SIV antigen-specific effects on immune responses induced by vaccination with DNA electroporation and plasmid IL-12

Molecular adjuvants are important for augmenting or modulating immune responses induced by DNA vaccination. Promising results have been obtained using IL-12 expression plasmids in a variety of disease models including the SIV model of HIV infection. We used a mouse model to evaluate plasmid IL-12 (pIL-12) in a DNA prime, recombinant adenovirus serotype 5 (rAd5) boost regimen specifically to evaluate the effect of IL-12 expression on cellular and humoral immunity induced against both SIVmac239 Gag and Env antigens. Priming with electroporated (EP) DNA + pIL-12 resulted in a 2–4-fold enhanced frequency of Gag-specific CD4 T cells which was maintained through the end of the study irrespective of the pIL-12 dose, while memory Env-specific CD4 + T cells were maintained only at the low dose of pIL-12. There was little positive effect of pIL-12 on the humoral response to Env, and in fact, high dose pIL-12 dramatically reduced SIV Env-specific IgG. Additionally, both doses of pIL-12 diminished the frequency of CD8 T-cells after DNA prime, although a rAd5 boost recovered CD8 responses regardless of the pIL-12 dose. In this prime-boost regimen, we have shown that a high dose pIL-12 can systemically reduce Env-specific humoral responses and CD4T cell frequency, but not Gag-specific CD4+ T cells. These data indicate that it is important to independently characterize individual SIV or HIV antigen immunogenicity in multi-antigenic vaccines as a function of adjuvant dose.     

Enhanced simian immunodeficiency virus-specific immune responses in macaques induced by priming with recombinant Semliki Forest virus and boosting with modified vaccinia virus Ankara

The immunogenicity of two vector-based vaccines, either given alone or in a prime-boost regimen, was investigated. Cynomolgus macaques were immunised with modified vaccinia virus Ankara (MVA) expressing simian immunodeficiency virus (SIV)macJ5 env, gag-pol, nef, rev, and tat genes (MVA-SIVmac) or primed with a Semliki forest virus (SFV) vaccine expressing the same genes (SFV-SIVmac) and boosted with MVA-SIVmac. Generally, antibody responses, T-cell proliferative responses and cytotoxic T-cell responses remained low or undetectable in vaccinees receiving MVA-SIVmac or SFV-SIVmac alone. In contrast, monkeys who first received SFV-SIVmac twice and then were boosted with MVA-SIVmac showed increased antibody responses as well as high T-cell proliferative responses. Three of these vaccinees had cytotoxic T-lymphocytes directed against three or four of the gene products. No evidence of protection was seen against an intrarectal heterologous SIVsm challenge given 3 months after the last immunisation. The study demonstrates a prime-boost strategy that efficiently induces both humoral and cellular immune responses.     

Evaluation of the Friend Virus model for the development of improved adenovirus-vectored anti-retroviral vaccination strategies

We evaluated the suitability of the Friend Virus (FV) model for the development of improved adenovirus vectors for anti-retroviral vaccination using two types of adenovirus vectors, encoding F-MuLV Env and Gag, which differed only in their fiber genes (Ad5 and Ad5F35). Genetically FV-resistant C57BL/6 mice and highly susceptible CB6F1 hybrid mice were vaccinated by either homologous or heterologous prime-boost regimen. After FV challenge, viral loads in the spleens of C57BL/6 mice were reduced approximately 250-fold and were below the detection threshold in >50% of the mice. Vaccination outcome was critically influenced by the route of vector administration. In CB6F1 mice, vaccination resulted in reduced viremia, delayed onset of splenomegaly, and induction of FV-specific T cells as assessed by tetramer staining. Heterologous prime-boost vaccination resulted in significantly higher neutralizing antibody titers, translating into improved immune protection, in contrast to coexpression of cytokines. Our results suggest that the FV model can provide insight into the development of improved adenovirus vectors for HIV-1 vaccination.     

Enhanced cellular immune responses to SIV Gag by immunization with influenza and vaccinia virus recombinants

An effective vaccination strategy against human immunodeficiency virus type 1 (HIV-1) should include the induction of potent cellular immune responses against conserved HIV-1 antigens. We have generated five replication competent recombinant influenza viruses (rFlu/SIV Gag nos. 1-5) expressing different portions of Gag of simian immunodeficiency virus (SIV). Single intranasal immunizations in mice with each rFlu/SIV Gag viruses resulted in different degrees of protection against a challenge with recombinant vaccinia virus expressing SIV Gag. Immunized BALB/c mice had detectable CD8+ T cell responses specific for Gag peptide 185-199 when mice were vaccinated with rFlu/SIV Gag no. 3 virus, and for Gag peptides 281-295 and 285-299 when vaccinated with rFlu/SIV Gag no. 4 virus. Cellular immune responses against SIV Gag were further enhanced by a booster with a recombinant vaccinia virus expressing SIV Gag in both the spleen and local lymph node tissues, resulting in the induction of robust Gag-specific CD8+ T cell responses at both systemic and mucosal levels. We suggest that a prime-boost immunization regimen using recombinant influenza and vaccinia viruses expressing HIV Gag might represent an effective means to induce potent HIV-specific, protective CD8+ T cell responses.     

Therapeutic vaccination with MVA-HIV-1 nef elicits Nef-specific T-helper cell responses in chronically HIV-1 infected individuals

Vaccination is currently considered as an additional therapeutic approach to stimulate HIV-specific immune response in subjects that could not naturally control HIV. Ten chronically HIV infected individuals have been vaccinated with a modified vaccinia Ankara (MVA)-HIV-1(LAI)-nef vector in order to assess safety and immunogenicity. No significant adverse effects were observed during the course of vaccination indicating for the first time that the highly attenuated vaccinia-virus vector MVA is safe in HIV-1 infected individuals. We observed a CD4 T-cell response to Nef in the majority of vaccinated chronically HIV infected individuals. In two subjects CD4 T-cell response was directed to previously unidentified Nef epitopes. The strong Nef-specific CD4 T-cell response elicited by MVA-nef vaccination provides a rationale for immunotherapeutic interventions in HIV infected individuals with suppressed CD4 T-cell responses. Moreover, the CD4 T-cell response elicited was comparable with that usually detected in long-term non-progressor (LTNP) suggesting an improvement in the immunological status of the vaccinated subjects. Furthermore, the new putative CD4 epitopes described here hold promise as important tools for epitope-based vaccination.     

Heterologous prime-boost regimen adenovector 35-circumsporozoite protein vaccine/recombinant Bacillus Calmette-Guérin expressing the Plasmodium falciparum circumsporozoite induces enhanced long-term memory immunity in BALB/c mice

Background

Sustained antibody levels are a hallmark of immunity against many pathogens, and induction of long-term durable antibody titers is an essential feature of effective vaccines. Heterologous prime-boost approaches with vectors are optimal strategies to improve a broad and prolonged immunogenicity of malaria vaccines.

Results

In this study, we demonstrate that the heterologous prime-boost regimen Ad35-CS/BCG-CS induces stronger immune responses by enhancing type 1 cellular producing-cells with high levels of CSp-specific IFN-γ and cytophilic IgG2a antibodies as compared to a homologous BCG-CS and a heterologous BCG-CS/CSp prime-boost regimen. Moreover, the heterologous prime-boost regimen elicits the highest level of LLPC-mediated immune responses.

Conclusion

The increased IFN-γ-producing cell responses induced by the combination of Ad35-CS/BCG-CS and sustained type 1 antibody profile together with high levels of LLPCs may be essential for the development of long-term protective immunity against liver-stage parasites.     

Novel HIV IL-4R antagonist vaccine strategy can induce both high avidity CD8 T and B cell immunity with greater protective efficacy

We have established that the efficacy of a heterologous poxvirus vectored HIV vaccine, fowlpox virus (FPV)-HIV gag/pol prime followed by attenuated vaccinia virus (VV)-HIV gag/pol booster immunisation, is strongly influenced by the cytokine milieu at the priming vaccination site, with endogenous IL-13 detrimental to the quality of the HIV specific CD8+ T cell response induced. We have now developed a novel HIV vaccine that co-expresses a C-terminal deletion mutant of the mouse IL-4, deleted for the essential tyrosine (Y119) required for signalling. In our vaccine system, the mutant IL-4C118 can bind to IL-4 type I and II receptors with high affinity, and transiently prevent the signalling of both IL-4 and IL-13 at the vaccination site. When this IL-4C118 adjuvanted vaccine was used in an intranasal rFPV/intramuscular rVV prime-boost immunisation strategy, greatly enhanced mucosal/systemic HIV specific CD8+ T cells with higher functional avidity, expressing IFN-γ, TNF-α and IL-2 and greater protective efficacy were detected. Surprisingly, the IL-4C118 adjuvanted vaccines also induced robust long-lived HIV gag-specific serum antibody responses, specifically IgG1 and IgG2a. The p55-gag IgG2a responses induced were of a higher magnitude relative to the IL-13Rα2 adjuvant vaccine. More interestingly, our recently tested IL-13Rα2 adjuvanted vaccine which only inhibited IL-13 activity, even though induced excellent high avidity HIV-specific CD8+ T cells, had a detrimental impact on the induction of gag-specific IgG2a antibody immunity. Our observations suggest that (i) IL-4 cell-signalling in the absence of IL-13 retarded gag-specific antibody isotype class switching, or (ii) IL-13Rα2 signalling was involved in inducing good gag-specific B cell immunity. Thus, we believe our novel IL-4R antagonist adjuvant strategy offers great promise not only for HIV-1 vaccines, but also against a range of chronic infections where sustained high quality mucosal and systemic T and B cell immunity are required for protection.     

CD8+ T cells induced by adenovirus-vectored vaccine are capable of preventing establishment of latent murine γ-herpesvirus 68 infection

CD8+ T cells are known to control infections, but their role in preventing latent infection from establishing has not been thoroughly investigated.We hypothesized that a potent CD8+ T cell response patrolling the mucosal viral entry points could kill the first infected cells and thereby abrogate the infection before latency is established.To investigate this, replication deficient adenovirus serotype 5 vectors encoding murine γ-herpesvirus-68 CD8+ T cell epitopes linked to the T cell adjuvant Invariant chain, were developed. We show that intranasal vaccination of mice reduces the risk of establishment of latent infection from multiple intranasal ID50 challenges with murine γ-herpesvirus-68 by 81% per exposure at 14 days post vaccination. Protection waned over time, but immune responses were extended by heterologous prime-boost vaccination applied simultaneously intramuscularly and intranasally, and animals vaccinated 66 days prior to challenge showed a strong trend of long-term protection.Our data provides evidence that CD8+ T cells are able to protect against establishment of latent infection. Although the protective efficacy is difficult to maintain over time, this proof-of-concept study suggests a role for a CD8+ T cell arm in future vaccine strategies against latent human viral infections caused by pathogens such as HIV and multiple herpes virus.     

Vaccine strategies against Babesia bovis based on prime-boost immunizations in mice with modified vaccinia Ankara vector and recombinant proteins

In this study, a recombinant modified vaccinia virus Ankara vector expressing a chimeric multi-antigen was obtained and evaluated as a candidate vaccine in homologous and heterologous prime-boost immunizations with a recombinant protein cocktail. The chimeric multi-antigen comprises immunodominant B and T cell regions of three Babesia bovis proteins. Humoral and cellular immune responses were evaluated in mice to compare the immunogenicity induced by different immunization schemes. The best vaccination scheme was achieved with a prime of protein cocktail and a boost with the recombinant virus. This scheme induced high level of specific IgG antibodies and secreted IFN and a high degree of activation of IFNγ⁺ CD4⁺ and CD8⁺ specific T cells. This is the first report in which a novel vaccine candidate was constructed based on a rationally designed multi-antigen and evaluated in a prime-boost regime, optimizing the immune response necessary for protection against bovine babesiosis.     

Safety, tolerability, and antibody responses in humans after sequential immunization with a PfCSP DNA vaccine followed by the recombinant protein vaccine RTS,S/AS02A

Optimal protection against malaria may require induction of high levels of protective antibody and CD8(+) and CD4(+) T cell responses. In humans, malaria DNA vaccines elicit CD8(+) cytotoxic T cells (CTL) and IFNgamma responses as measured by short-term (ex vivo) ELISPOT assays, and recombinant proteins elicit antibodies and excellent T cell responses, but no CD8(+) CTL or CD8(+) IFNgamma-producing cells as measured by ex vivo ELISPOT. Priming with DNA and boosting with recombinant pox virus elicits much better T cell responses than DNA alone, but not antibody responses. In an attempt to elicit antibodies and enhanced T cell responses, we administered RTS,S/AS02A, a partially protective Plasmodium falciparum recombinant circumsporozoite protein (CSP) vaccine in adjuvant, to volunteers previously immunized with a P. falciparum CSP DNA vaccine (VCL-2510) and to na?ve volunteers. This vaccine regimen was well tolerated and safe. The volunteers who received RTS,S/AS02A alone had, as expected, antibody and CD4(+) T cell responses, but no CD8(+) T cell responses. Volunteers who received PfCSP DNA followed by RTS,S/AS02A had antibody and CD8(+) and CD4(+) T cell responses (Wang et al., submitted). Sequential immunization with DNA and recombinant protein, also called heterologous prime-boost, led to enhanced immune responses as compared to DNA or recombinant protein alone, suggesting that it might provide enhanced protective immunity.