Heterologous Prime-boost Vaccination Strategy Research Articles

A superior heterologous prime-boost vaccination strategy against COVID-19: A bivalent vaccine based on yeast-derived RBD proteins followed by a heterologous vaccine.

Various vaccines have been challenged by SARS-CoV-2 variants. Here, we reported a yeast-derived recombinant bivalent vaccine (Bivalent wild-type [Wt]+De) based on the wtand Delta receptor-binding domain (RBD). Yeast derived RBD proteins based on the wtand Delta mutant were used as the prime vaccine. It was found that, in the presence of aluminium hydroxide (Alum) and unmethylated CpG-oligodeoxynucleotides (CpG) adjuvants, more cross-protective immunity against SARS-CoV-2 prototype and variants were elicited by bivalent vaccine than monovalent wtRBD or Delta RBD. Furthermore, a heterologous boosting strategy consisting of two doses of bivalent vaccines followed by one dose adenovirus vectored vaccine exhibited cross-neutralization capacity and specific T cell responses against Delta and Omicron (BA.1 and BA.4/5) variants in mice, superior to a homologous vaccination strategy. This study suggested that heterologous prime-boost vaccination with yeast-derived bivalent protein vaccine could be a potential approach to address the challenge of emerging variants.

Intravenous heterologous prime-boost vaccination activates innate and adaptive immunity to promote tumor regression

Therapeutic neoantigen cancer vaccines have limited clinical efficacy to date. Here, we identify a heterologous prime-boost vaccination strategy using a self-assembling peptide nanoparticle TLR-7/8 agonist (SNP) vaccine prime and a chimp adenovirus (ChAdOx1) vaccine boost that elicits potent CD8 Tcells and tumor regression. ChAdOx1 administered intravenously (i.v.) had 4-fold higher antigen-specific CD8 Tcell responses than mice boosted by the intramuscular (i.m.) route. In the therapeutic MC38 tumor model, i.v. heterologous prime-boost vaccination enhances regression compared with ChAdOx1 alone. Remarkably, i.v. boosting with a ChAdOx1 vector encoding an irrelevant antigen also mediates tumor regression, which is dependent on type I IFN signaling. Single-cell RNA sequencing of the tumor myeloid compartment shows that i.v. ChAdOx1 reduces the frequency of immunosuppressive Chil3 monocytes and activates cross-presenting type 1 conventional dendritic cells (cDC1s). The dual effect of i.v. ChAdOx1 vaccination enhancing CD8 Tcells and modulating the TME represents a translatable paradigm for enhancing anti-tumor immunity in humans.

Safety and efficacy of COVID-19 prime-boost vaccinations: Homologous BBIBP-CorV versus heterologous BNT162b2 boosters in BBIBP-CorV-primed individuals.

Booster vaccine doses against SARS-CoV-2 have been advocated to address evidence of waning immunity, breakthrough infection, and the emergence of immune-evasive variants. A heterologous prime-boost vaccine strategy may offer advantages over a homologous approach, but the safety and efficacy of this approach with the mRNA vaccine BNT162b2 (BNT: Pfizer) and inactivated BBIBP-CorV (BBIBT: Sinopharm) vaccines have not been studied. We conducted a non-randomized, non-blinded phase II observational community trial acrossBahrain, investigating the reactogenic and immunogenic responseof participants who had previously received two doses of BBIBP, followed by a third booster dose of either BBIBP (homologous booster) or BNT (heterologous booster). Immunogenicity through serological statuswas determined at baseline and on the following 8thweek. Reactogenicity data (safety and adverse events) were collected throughout study period, in addition to participant-led electronic journaling. 305 participants (152 BBIBP and 153 BNT booster) were enrolled in the study,with 246 (127 BBIBP and 119 BNT booster) included in the final analysis. There was a significant increase in anti-SARS-CoV-2 antibody levels post booster administration in both groups; however, the heterologous BNT arm demonstrated a significantly larger mean increase in the level of spike (S) antigen-specific antibodies (32.7-fold increase versus 2.6, p<0.0001) and sVNT neutralising antibodies (3.4-fold increase versus 1.8, p<0.0001), whereas the homologous arm demonstrated a significant increase in the levels of nucleocapsid (N) antigen-specific antibodies (3.8-fold increase versus none). Non-serious adverse events (injection site pain, fever, and fatigue) were more commonly reported in the heterologous arm, but no serious adverse events occurred. Heterologous prime-boost vaccination with the mRNA BNT162b2 (Pfizer) vaccine in those who had received two doses of inactivated virus BBIBP-CorV (Sinopharm) vaccine demonstrated a more robust immune response against SARS-CoV-2 than the homologous BBIBP booster and appears safe and well tolerated. Clinical Trial Registry Number (ClinicalTrials.gov): NCT04993560.

A randomized controlled trial of heterologous ChAdOx1 nCoV-19 and recombinant subunit vaccine MVC-COV1901 against COVID-19

Heterologous prime-boost COVID-19 vaccine strategy may facilitate mass COVID-19 immunization. We reported early immunogenicity and safety outcomes of heterologous immunization with a viral vector vaccine (ChAdOx1) and a spike-2P subunit vaccine (MVC-COV1901) in a participant-blinded, randomized, non-inferiority trial (NCT05054621). A total of 100 healthy adults aged 20–70 years having the first dose of ChAdOx1 were 1:1 randomly assigned to receive a booster dose either with ChAdOx1 (n = 50) or MVC-COV1901 (n = 50) at an interval of 4–6 or 8–10 weeks. At day 28 post-boosting, the neutralizing antibody geometric mean titer against wild-type SARS-CoV-2 in MVC-COV1901 recipients (236 IU/mL) was superior to that in ChAdOx1 recipients (115 IU/mL), with a GMT ratio of 2.1 (95% CI, 1.4 to 2.9). Superiority in the neutralizing antibody titer against Delta variant was also found for heterologous MVC-COV1901 immunization with a GMT ratio of 2.6 (95% CI, 1.8 to 3.8). Both spike-specific antibody-secreting B and T cell responses were substantially enhanced by the heterologous schedule. Heterologous boosting was particularly prominent at a short prime-boost interval. No serious adverse events occurred across all groups. The findings support the use of heterologous prime-boost with ChAdOx1 and protein-based subunit vaccines.

CD4+ T-cell epitope-based heterologous prime-boost vaccination potentiates anti-tumor immunity and PD-1/PD-L1 immunotherapy

BackgroundAntitumor therapeutic vaccines are generally based on antigenic epitopes presented by major histocompatibility complex (MHC-I) molecules to induce tumor-specific CD8+ T cells. Paradoxically, continuous T cell receptor (TCR) stimulation from...

Efficacy of the NS1-truncated live attenuated influenza virus vaccine for swine against infection with viruses of major North American and European H3N2 lineages

Control of swine influenza A virus (swIAV) in North America and Europe is complicated because multiple antigenically distinct swIAV strains co-circulate in the field, and no vaccine is available that can provide broad cross-protection against all these swIAVs. In 2017, the first live attenuated influenza vaccine (LAIV) for swine was licensed in the US. The non-structural protein 1 (NS1)-truncated cluster I H3N2 strain A/swine/Texas/4199-2/98 NS1del126 (TX98 LAIV) in this vaccine provides partial cross-protection against heterologous North American cluster II and IV H3N2 swIAV strains. Its efficacy against European or more recent North American H3N2 lineages remains to be investigated. In this study, we evaluated the level of cross-protection against heterologous IAVs representative of the major H3N2 swIAV lineages in Europe and North America. TX98 LAIV prevented both nasal shedding and replication in the lungs of a North American cluster IV H3N2 swIAV for 2/4 pigs, prevented considerable nasal shedding of a North American novel human-like H3N2 swIAV for 2/4 pigs, and reduced replication of a European H3N2 swIAV in the lower respiratory tract to minimal titers for 1/3 pigs. Although TX98 LAIV elicited neutralizing antibodies against the homologous virus in serum and to a lesser extent in nose and lungs, no significant cross-reactive antibody titers against the heterologous swIAVs were detected. Partial cross-protection therefore likely relies on cellular and mucosal immune responses against conserved parts of the swIAV proteins. Since TX98 LAIV can offer partial protection against a broad range of H3N2 swIAVs, it might be a suitable priming vaccine for use in a heterologous prime-boost vaccination strategy.

Antibody Response of Combination of BNT162b2 and CoronaVac Platforms of COVID-19 Vaccines against Omicron Variant.

By vaccinating SARS-CoV-2 naïve individuals who have already received two doses of COVID-19 vaccines, we aimed to investigate whether a heterologous prime-boost strategy, using vaccines of different platforms as the booster dose, can enhance the immune response against SARS-CoV-2 virus variants. Participants were assigned into four groups, each receiving different combination of vaccinations: two doses of BNT162b2 followed by one dose of BNT162b2 booster (B-B-B); Combination of BNT162b2 (first dose) and CoronaVac (second dose) followed by one dose of BNT162b2 booster (B-C-B); two doses of CoronaVac followed by one dose of CoronaVac booster (C-C-C); two doses of CoronaVac followed by one dose of BNT162b2 booster (C-C-B). The neutralizing antibody in sera against the virus was determined with live virus microneutralization assay (vMN). The B-B-B group and C-C-B group demonstrated significantly higher immunogenicity against SARS-CoV-2 Wild type (WT), Beta variant (BV) and Delta variant (DV). In addition, the B-B-B group and C-C-B group showed reduced but existing protection against Omicron variant (OV). Moreover, A persistent rise in vMN titre against OV was observed 3 days after booster dose. Regarding safety, a heterologous prime-boost vaccine strategy is well tolerated. In this study, it was demonstrated that using vaccines of different platforms as booster dose can enhance protection against SARS-CoV-2 variants, offering potent neutralizing activity against wild-type virus (WT), Beta variant (BV), Delta variant (DV) and some protection against the Omicron variant (OV). In addition, a booster mRNA vaccine results in a more potent immune response than inactivated vaccine regardless of which platform was used for prime doses.

Antibody response induced by the boost overdose during COVID-19 heterologous prime-boost vaccination strategy

BackgroundMeasurement of anti-SARS-CoV-2 RBD Ig G antibody response is very important to define the dynamics of immunization in vaccine COVID-19 recipients. Materials and methodsSera from four BNT162b2 vaccine recipients who erroneously received vaccine overdose were analyzed at different time-points. ResultsAt 6 days the serum increase of antibodies was analogous for the three SARS-CoV-2 naïve recipients. At 14 days the antibody level increased and reached a peak, though showing a different pattern among the three recipients. At 21 days the serum antibody level started to decrease from its maximum value. The data for the previously infected recipient were in agreement with values found in COVID-19 positive receivers. Thus, the prime-dose of vaccine was enough to elicit a significant antibody response. ConclusionsIn spite of the overdosage, this study confirms the efficiency of the BNT162b vaccine in eliciting a sustained antibody response as heterologous boost-vaccine in previously Oxford/AstraZeneca vaccinated recipients, as well as, prime-vaccine in COVID-19 infected receivers. Importantly, the humoral immune response of recipients was not proportional to the vaccine overdose. Nonetheless, we cannot portray a univocal effect of vaccine overdose concerning anti-SARS-CoV-2 antibody response because the values found were highly heterogeneous.

Vaccination with a DNA and MVA ‘Prime-Boost’ Regimen Induces Strong CD8+ T-Cell Responses Against the Immunodominant Minor Histocompatibility Antigen, HA-1: Results of a First-in-Man Phase I Clinical Trial

INTRODUCTIONThe Graft- versus -Leukemia (G v L) effect in allogeneic stem cell transplantation (allo-SCT) is thought to be mediated largely by alloreactive T-cells which recognise minor histocompatibility antigens (mHAg). HA-1 is a potent, immunodominant mHAg which is presented by HLA-A2 and expressed selectively by hematopoietic cells. We hypothesized that immunization of HA-1- stem cell donors with an HA-1 vaccine prior to lymphocyte donation would generate HA-1-specific cytotoxic T lymphocytes (CTL) which, after adoptive transfer to the transplant recipient as donor lymphocyte infusions (DLI), may provide a potent anti-leukemia effect in HA-1+ leukemia patients without increasing the risk of Graft- versus -Host disease. Furthermore, this may allow HA-1-specific T cells to be selected and purified for targeted immunotherapy. Having previously shown that the vaccination of HLA-A2+ transgenic mice with the DNA construct (pDOM-HA-1) encoding the HLA-A2-restricted CTL-epitope, VLHDDLLEA (VLH) from HA-1, induces functional T cell responses to HA-1, we conducted a first-in-man Phase I dose-escalation trial in healthy immunocompetent HLA-A2+ and HA-1- males using the pDOM-HA-1 vaccine and subsequently boosting with a modified vaccinia Ankara virus (MVA) encoding the VLH epitope (MVA-HA-1).PARTICIPANTS AND METHODSThe primary endpoint was vaccine safety and establishment of an optimal dose for phase II evaluation. Secondary outcomes included assessments of the kinetics and magnitude of HA-1-specific T-cell responses which were assessed weekly up to 3 months and then at months 6 and 12. 86 healthy male volunteers were screened for the trial, 20 of whom were the correct genotype. 9 participants were enrolled, median age being 45 years (range 27 - 69). Participants were to receive escalated doses of the vaccine regimen (1mg pDOM-HA-1 x 2 cycles + MVA boost (cohort 1); 1mg pDOM-HA-1 x 3 cycles + MVA boost (cohort 2), (2mg pDOM-HA-1 x 2 cycles + MVA boost (cohort 3); 2mg pDOM-HA-1 x 3 cycles + MVA boost (cohort 4). Vaccines were administered every 3 weeks. Participants were assessed for dose-limiting-toxicity (DLT) using the Toxicity Grading Scale for Healthy Volunteers Enrolled in Vaccine Trials.RESULTS3 participants completed the first vaccine schedule in Cohort 1 with 2 grade 2 DLTs (myalgia and headache observed in 1 participant). The observed events were not considered to be of clinical significance and the definition of a DLT was amended prior to further participants being recruited. Cohort 1 was expanded to recruit an additional 3 participants with no further DLTs observed. 3 participants received Cohort 2 with no DLTs observed. No serious adverse events were observed in any participants. The most common non-hematological toxicities were hypertension, hypermagnesemia, and injection site reactions. The most common hematological toxicities were increased monocytes, neutropenia and leucopenia. All adverse events resolved shortly after vaccine administration. The trial experienced recruitment challenges and was closed to recruitment after the completion of Cohort 2.HA-1 specific CD8+ T cell responses were detectable by MHC-I multimer staining in 78% (7/9) of vaccinated individuals (Figure 1). Functional ex vivo responses to HA-1 peptide were confirmed byIFNγ ELISPOT assay. HA-1-specific responses were first detected between week 1 and 3 following MVA administration and displayed an effector memory (TEM) phenotype at the peak of the response, which transitioned to a more terminally differentiated TEMRA phenotype during 12 month follow-up. HA-1 specific CD8+ T cell clones analysed from 3 vaccinated individuals displayed polyfunctional cytokine profiles and cytotoxicity against HA-1 peptide-loaded targets.CONCLUSIONWe demonstrate that a heterologous prime-boost DNA-MVA vaccination strategy in HA1- healthy volunteers is tolerable and safe and elicits a detectable and sustained HA1-specific CD8+ T-cell response. 3 doses of 1mg pDOM-HA-1 with 1 dose of MVA-HA-1 boost is identified as the combination for evaluation in future Phase II studies. This demonstration of a vaccine-induced CD8+ T-cell response against an immunodominant mHAg provides the basis for trials to investigate the adoptive transfer of HA-1-specific CD8+ T-cells to recipients of allo-SCT as “vaccine-augmented DLI.” [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Exploring heterologous prime-boost vaccination approaches to enhance influenza control in pigs

Influenza A viruses evolve rapidly to escape host immunity. In swine, this viral evolution has resulted in the emergence of multiple H1 and H3 influenza A virus (IAV) lineages in the United States (US) pig populations. The heterologous prime-boost vaccination strategy is a promising way to deal with diverse IAV infection in multiple animal models. However, whether or not this vaccination strategy is applicable to US swine to impart immunity against infection from North American strains of IAV is still unknown. We performed a vaccination-challenge study to evaluate the protective efficacy of using multivalent inactivated vaccine and/or a live attenuated IAV vaccine (LAIV) in pigs following multiple prime-boost vaccination protocols against a simultaneous H1N1 and H3N2 IAV infection. Our data show that pigs in the heterologous prime-boost vaccination group had more favorable outcomes consistent with a better response against virus challenge than non-vaccinated pigs. Additionally, delivering a multivalent heterologous inactivated vaccine boost to pigs following a single LAIV administration was also beneficial. We concluded the heterologous prime boost vaccination strategy may potentiate responses to suboptimal immunogens and holds the potential applicability to control IAV in the North American swine industry. However, more studies are needed to validate the application of this vaccination approach under field conditions.

Heterologous prime-boost vaccination against tuberculosis with recombinant Sendai virus and DNA vaccines.

In an earlier study, a novel Sendai virus-vectored anti-tuberculosis vaccine encoding Ag85A and Ag85B (SeV85AB) was constructed and shown to elicit antigen-specific T cell responses and protection against Mycobacterium tuberculosis (Mtb) infection in a murine model. In this study, we evaluate whether the immune responses induced by this novel vaccine might be elevated by a recombinant DNA vaccine expressing the same antigen in a heterologous prime-boost vaccination strategy. The results showed that both SeV85AB prime-DNA boost (SeV85AB-DNA) and DNA prime-SeV85AB boost (DNA-SeV85AB) vaccination strategies significantly enhanced the antigen-specific T cell responses induced by the separate vaccines. The SeV85AB-DNA immunization regimen induced higher levels of recall T cell responses after Mtb infection and conferred better immune protection compared with DNA-SeV85AB or a single immunization. Collectively, our study lends strong evidence that a DNA vaccine boost might be included in a novel SeV85AB immunization strategy designed to enhance the immune protection against Mtb. KEY MESSAGES: A heterologous prime-boost regimen with a novel recombinant SeV85AB and a DNA vaccine increase the T cell responses above those from a single vaccine. The heterologous prime-boost regimen provided protection against Mtb infection. The DNA vaccine might be included in a novel SeV85AB immunization strategy designed to enhance the immune protection against Mtb.

Interleukin-21 enhances the antibody avidity elicited by DNA prime and MVA boost vaccine

Enhancement of the magnitude or affinity of protective antibodies (Abs) induced by vaccine adjuvant is highly desirable to prevent challenging pathogens such as HIV-1. IL-21 plays a crucial role in germinal center reactions during humoral immune responses. However, the effect of IL-21 as a vaccine adjuvant on the quantity and quality of antigen-specific Abs elicited by DNA prime and MVA boost vaccine, a commonly used vaccine strategy, remains unknown. To close this knowledge gap, female adult B6N mice were primed with DNA vaccine twice (days 0, 14, 100 µg, I.M.) and boosted with MVA vaccine (day 28, 2 × 107 pfu, I.M.) with or without an IL-21 DNA adjuvant (days 3, 17, 31, 40 µg, I.M.), in which HIV-1 gag was expressed as a model antigen. With the addition of an IL-21 adjuvant, we found significantly increased avidity of antigen-specific Abs at multiple time points in a longitudinal follow up. Collectively, our results suggest that an IL-21 immune adjuvant can significantly increase Ab quality induced by heterologous DNA-MVA prime-boost vaccine strategy.

Are we there yet? The never-ending quest for an Epstein-Barr virus vaccine.

The Epstein-Barr virus (EBV) is estimated to infect a large part of the population and is associated with a variety of human tumors; therefore, EBV is an important target for vaccine development. In this issue of the JCI, Rühl et al. developed a promising heterologous prime-boost vaccination strategy for EBV-associated malignancies and symptomatic primary infection. The authors show that two prime-boost regimens, using either dendritic cells or an adenovirus approach targeting nuclear antigen EBNA1 followed by a modified vaccinia virus Ankara (MVA) booster, induced significant T cell-mediated, EBV-specific immune control and Ab production. These findings suggest that administration of heterologous prime-boost vaccinations targeting EBNA1 may result in potent CD4+ and CD8+ T cell-mediated EBV immune control and may be a promising clinical approach.

Immunization of Experimental Dogs With Salivary Proteins From Lutzomyia longipalpis, Using DNA and Recombinant Canarypox Virus Induces Immune Responses Consistent With Protection Against Leishmania infantum.

Metacyclic Leishmania promastigotes are transmitted by sand flies that inject parasites and saliva into the host's skin. Previous studies have demonstrated that DNA plasmids encoding Lutzomyia longipalpis salivary proteins LJM17 and LJL143, when used to immunize dogs, resulted in a systemic and local Th1 cell-mediated immunity that interfered in parasite survival in vitro. Here we evaluated the ability of these same salivary antigens to induce anti-Leishmania immunity and to confer protection by immunizing dogs using a novel vaccination strategy more suitable for use in the field. The strategy consisted of a single dose of plasmid followed by two doses of recombinant Canarypoxvirus (rCanarypoxvirus) expressing L. longipalpis salivary proteins (LJM17 or LJL143). Thirty days after the final immunization, dogs were intradermally challenged with 107 Leishmania infantum promastigotes in the presence of L. longipalpis saliva. We followed the experimentally infected dogs for 10 months to characterize clinical, parasitological, and immunological parameters. Upon vaccination, all immunized dogs presented strong and specific humoral responses with increased serum concentrations of IFN-γ, TNF, IL-7, and IL-15. The serum of dogs immunized with LJM17 also exhibited high levels of IL-2, IL-6, and IL-18. L. infantum infection was established in all experimental groups as evidenced by the presence of anti-Leishmania IgG, and by parasite detection in the spleen and skin. Dogs immunized with LJM17-based vaccines presented higher circulating levels of IFN-γ, IL-2, IL-6, IL-7, IL-15, IL-18, TNF, CXCL10, and GM-CSF post-infection when compared with controls. Results demonstrated that relevant Leishmania-specific immune responses were induced following vaccination of dogs with L. longipalpis salivary antigen LJM17 administered in a single priming dose of plasmid DNA, followed by two booster doses of recombinant Canarypox vector. Importantly, a significant increase in pro-inflammatory cytokines and chemokines known to be relevant for protection against leishmaniasis was evidenced after challenging LJM17-vaccinated dogs as compared to controls. Although similar results were observed following immunization with LJL143, the pro-inflammatory response observed after immunization was attenuated following infection. Collectively, these data suggest that the LJM17-based vaccine induced an immune profile consistent with the expected protective immunity against canine leishmaniosis. These results clearly support the need for further evaluation of the LJM17 antigen, using a heterologous prime-boost vaccination strategy against canine visceral leishmaniosis (CVL).

Heterologous prime–boost vaccination with adenoviral vector and protein nanoparticles induces both Th1 and Th2 responses against Middle East respiratory syndrome coronavirus

The Middle East respiratory syndrome coronavirus (MERS-CoV) is a highly pathogenic and zoonotic virus with a fatality rate in humans of over 35%. Although several vaccine candidates have been developed, there is still no clinically available vaccine for MERS-CoV. In this study, we developed two types of MERS-CoV vaccines: a recombinant adenovirus serotype 5 encoding the MERS-CoV spike gene (Ad5/MERS) and spike protein nanoparticles formulated with aluminum (alum) adjuvant. Next, we tested a heterologous prime–boost vaccine strategy, which compared priming with Ad5/MERS and boosting with spike protein nanoparticles and vice versa, with homologous prime–boost vaccination comprising priming and boosting with either spike protein nanoparticles or Ad5/MERS. Although both types of vaccine could induce specific immunoglobulin G against MERS-CoV, neutralizing antibodies against MERS-CoV were induced only by heterologous prime–boost immunization and homologous immunization with spike protein nanoparticles. Interestingly, Th1 cell activation was induced by immunization schedules including Ad5/MERS, but not by those including only spike protein nanoparticles. Heterologous prime–boost vaccination regimens including Ad5/MERS elicited simultaneous Th1 and Th2 responses, but homologous prime–boost regimens did not. Thus, heterologous prime–boost may induce longer-lasting immune responses against MERS-CoV because of an appropriate balance of Th1/Th2 responses. However, both heterologous prime–boost and homologous spike protein nanoparticles vaccinations could provide protection from MERS-CoV challenge in mice. Our results demonstrate that heterologous immunization by priming with Ad5/MERS and boosting with spike protein nanoparticles could be an efficient prophylactic strategy against MERS-CoV infection.

Development of a Live Recombinant BCG Expressing Human Immunodeficiency Virus Type 1 (HIV-1) Gag Using a pMyong2 Vector System: Potential Use As a Novel HIV-1 Vaccine.

Even though the rate of new human immunodeficiency virus type 1 (HIV-1) infections is gradually decreasing worldwide, an effective preventive vaccine for HIV-1 is still urgently needed. The recombinant Mycobacterium bovis BCG (rBCG) is promising for the development of an HIV-1 vaccine. Recently, we showed that a recombinant Mycobacterium smegmatis expressing HIV-1 gag in a pMyong2 vector system (rSmeg-pMyong2-p24) increased the efficacy of a vaccine against HIV-1 in mice. Here, we evaluated the potential of an rBCG expressing HIV-1 p24 antigen Gag in pMyong2 (rBCG-pMyong2-p24) in a vaccine application for HIV-1 infection. We found that rBCG-pMyong2-p24 elicited an enhanced HIV-1 p24 Gag expression in rBCG and infected antigen-presenting cells. We also found that compared to rBCG-pAL-p24 in a pAL5000 derived vector system, rBCG-pMyong2-p24 elicited enhanced p24-specific immune responses in vaccinated mice as evidenced by higher levels of HIV-1 Gag-specific CD4 and CD8 T lymphocyte proliferation, gamma interferon ELISPOT cell induction, antibody production, and cytotoxic T lymphocytes (CTL) responses. Furthermore, rBCG-pMyong2-p24 showed a higher level of p24-specific Ab production than rSmeg-pMyong2-p24 in the same pMyong2 vector system. In conclusion, our data indicated that a live recombinant BCG expressing HIV-1 Gag using a pMyong2 vector system, rBCG-pMyong2-p24 elicited an enhanced immune response against HIV-1 infections in a mouse model system. So, rBCG-pMyong2-p24 may have the potential as a prime vaccine in a heterologous prime-boost vaccine strategy for HIV-1 infection.

New adenovirus-based vaccine vectors targeting Pfs25 elicit antibodies that inhibit Plasmodium falciparum transmission

BackgroundAn effective malaria transmission-blocking vaccine (TBV) would be a major advance in the current efforts to eliminate and, ultimately, eradicate malaria. Antibodies against Plasmodium falciparum surface protein, Pfs25, are known to block parasite development in the mosquito vector. However, in initial clinical trials the limited immunogenicity of recombinant Pfs25 protein-in-adjuvant vaccines has been a challenge.MethodsNovel human adenovirus type 5 (Ad5) vectors were used in heterologous prime boost vaccination strategies to augment the immune response against Pfs25. Specifically, an Ad5 vector that directs expression of full-length, membrane-bound Pfs25 was used as a priming immunization followed by a boost with Ad5 viral particles displaying only the Pfs25 epitope targeted by transmission-blocking antibodies 4B7 and 1D2 (Pfs25 aa 122–134) in hypervariable region 5 of the hexon capsid protein.ResultsThis heterologous prime-boost vaccine strategy induced antibodies that significantly inhibit P. falciparum transmission to mosquitoes in a standard membrane-feeding assay. Further, immunized mice generated a robust anti-Pfs25 antibody response characterized by higher titer, higher relative avidity and a broader IgG subclass profile than observed with a homologous prime-boost with recombinant Pfs25/alum.ConclusionThe data suggest that focusing the immune response against defined epitopes displayed on the viral capsid is an effective strategy for transmission-blocking vaccine development.

Efficient control of chronic LCMV infection by CD4 T cell epitope-based heterologous prime-boost vaccination in a murine model

Abstract CD4+ T cells are essential for sustaining CD8+ T cell responses during chronic infection. The adoptive transfer of virus-specific CD4+ T cells has been shown to efficiently rescue exhausted CD8+ T cells. However, the question of whether endogenous virus-specific CD4+ T cell responses can be enhanced by certain vaccination strategies and subsequently reinvigorate exhausted CD8+ T cells remains unexplored. In this study, we developed a CD4+ T cell epitope-based heterologous prime-boost immunization strategy and examined the efficacy of this strategy using a mouse model of chronic lymphocytic choriomeningitis virus (LCMV) infection. We primed chronically LCMV-infected mice with the Listeria monocytogenes vector expressing the LCMV glycoprotein-specific I-Ab-restricted CD4+ T cell epitope GP61-80 (LM-GP61) and subsequently boosted the primed mice with an influenza virus A (PR8 strain) vector expressing the same CD4+ T cell epitope (IAV-GP61). This heterologous prime-boost vaccination strategy elicited strong anti-viral CD4+ T cell responses, which further improved both the quantity and quality of the virus-specific CD8+ T cells and led to better control of viral loads. The combination of this strategy and the blockade of the programmed cell death-1 (PD-1) inhibitory pathway further enhanced anti-viral CD8+ T cell responses and viral clearance. Therefore, heterologous prime-boost immunization that selectively induces virus-specific CD4+ T cell responses in conjunction with inhibitory pathway blockade may represent a promising therapeutic approach to treating patients with chronic viral infection.

A Bivalent Heterologous DNA Virus-Like-Particle Prime-Boost Vaccine Elicits Broad Protection against both Group 1 and 2 Influenza A Viruses.

Current seasonal influenza vaccines are efficacious when vaccine strains are matched with circulating strains. However, they do not protect antigenic variants and newly emerging pandemic and outbreak strains. Thus, there is a critical need for developing so-called "universal" vaccines that protect against all influenza viruses. In the present study, we developed a bivalent heterologous DNA virus-like particle prime-boost vaccine strategy. We show that mice immunized with this vaccine were broadly protected against lethal challenge from group 1 (H1, H5, and H9) and group 2 (H3 and H7) viruses, with 94% aggregate survival. To determine the immune correlates of protection, we performed passive immunizations and in vitro assays. We show that this vaccine elicited antibody responses that bound HA from group 1 (H1, H2, H5, H6, H8, H9, H11, and H12) and group 2 (H3, H4, H7, H10, H14, and H15) and neutralized homologous and intrasubtypic H5 and H7 and heterosubtypic H1 viruses and hemagglutinin-specific CD4 and CD8 T cell responses. As a result, passive immunization with immune sera fully protected mice against H5, H7, and H1 challenge, whereas with both immune sera and T cells the mice survived heterosubtypic H3 and H9 challenge. Thus, it appears that (i) neutralizing antibodies alone fully protect against homologous and intrasubtypic H5 and H7 and (ii) neutralizing and binding antibodies are sufficient to protect against heterosubtypic H1, (iii) but against heterosubtypic H3 and H9, binding antibodies and T cells are required for complete survival. We believe that this vaccine regimen could potentially be a candidate for a "universal" influenza vaccine.IMPORTANCE Influenza virus infection is global health problem. Current seasonal influenza vaccines are efficacious only when vaccine strains are matched with circulating strains. However, these vaccines do not protect antigenic variants and newly emerging pandemic and outbreak strains. Because of this, there is an urgent need to develop so-called "universal" influenza vaccines that can protect against both current and future influenza strains. In the present study, we developed a bivalent heterologous prime-boost vaccine strategy. We show that a bivalent vaccine regimen elicited broad binding and neutralizing antibody and T cell responses that conferred broad protection against diverse challenge viruses in mice, suggesting that this bivalent prime-boost strategy could practically be a candidate for a "universal" influenza vaccine.

Microspheres-prime/rMVA-boost vaccination enhances humoral and cellular immune response in IFNAR(−/−) mice conferring protection against serotypes 1 and 4 of bluetongue virus

Bluetongue virus (BTV) is the causative agent of bluetongue disease (BT), which affects domestic and wild ruminants. At the present, 27 different serotypes have been documented. Vaccination has been demonstrated as one of the most effective methods to avoid viral dissemination. To overcome the drawbacks associated with the use of inactivated and attenuated vaccines we engineered a new recombinant BTV vaccine candidate based on proteins VP2, VP7, and NS1 of BTV-4 that were incorporated into avian reovirus muNS-Mi microspheres (MS-VP2/VP7/NS1) and recombinant modified vaccinia virus Ankara (rMVA). The combination of these two antigen delivery systems in a heterologous prime-boost vaccination strategy generated significant levels of neutralizing antibodies in IFNAR(−/−) mice. Furthermore, this immunization strategy increased the ratio of IgG2a/IgG1 in sera, indicating an induction of a Th1 response, and elicited a CD8 T cell response. Immunized mice were protected against lethal challenges with the homologous serotype 4 and the heterologous serotype 1 of BTV. All these results support the strategy based on microspheres in combination with rMVAs as a promising multiserotype vaccine candidate against BTV.