Heterologous vaccination with inactivated and mRNA vaccines increases B and T cell responses to SARS-CoV-2

Background There has been an unprecedented global effort to produce safe and effective vaccines against SARS-CoV-2. However, production challenges, supply shortages and unequal global reach, together with an increased number of breakthrough infections due to waning of immunity and the emergence of new variants of concern (VOC), have prolonged the pandemic. To boost the immune response, several heterologous vaccination regimes have been tested and have shown increased antibody responses compared to homologous vaccination. Here we evaluated the effect of mRNA vaccine booster on immunogenicity in individuals who had been vaccinated with two doses of inactivated vaccines. Methods The levels of specific antibodies against the receptor-binding domain (RBD) of the spike protein from wild-type virus and the Beta, Delta and Omicron variants were measured in healthy individuals who had received two doses of homologous inactivated (BBIBP-CorV or CoronoVac) or mRNA (BNT162b2 or mRNA-1273) vaccines, and in donors who were given an mRNA vaccine boost after two doses of either vaccine. Pre-vaccinated healthy donors, or individuals who had been infected and subsequently received the mRNA vaccine were also included as controls. In addition, specific memory B and T cell responses were measured in a subset of samples. Results A booster dose of an mRNA vaccine significantly increased the specific antibody response to the wild-type and VOCs including Omicron (by 14-fold), in individuals who had previously received two doses of inactivated vaccines. The levels of specific antibodies in the heterologous vaccination group were similar to those in individuals receiving a third dose of homologous mRNA vaccines or boosted with mRNA vaccine after natural infection. Furthermore, this heterologous vaccination regime significantly improved the specific memory B and T cell responses. Conclusions Heterologous prime-boost immunization with inactivated vaccine followed by an mRNA vaccine boost markedly increased the levels of specific antibodies and B and T cell responses and may thus increase protection against emerging SARS-CoV-2 variants including Omicron.

Evolution of protection after maternal immunization for respiratory syncytial virus in cotton rats

Maternal anti-respiratory syncytial virus (RSV) antibodies acquired by the fetus through the placenta protect neonates from RSV disease through the first weeks of life. In the cotton rat model of RSV infections, we previously reported that immunization of dams during pregnancy with virus-like particles assembled with mutation stabilized pre-fusion F protein as well as the wild type G protein resulted in robust protection of their offspring from RSV challenge. Here we describe the durability of those protective responses in dams, the durability of protection in offspring, and the transfer of that protection to offspring of two consecutive pregnancies without a second boost immunization. We report that four weeks after birth, offspring of the first pregnancy were significantly protected from RSV replication in both lungs and nasal tissues after RSV challenge, but protection was reduced in pups at 6 weeks after birth. However, the overall protection of offspring of the second pregnancy was considerably reduced, even at four weeks of age. This drop in protection occurred even though the levels of total anti-pre-F IgG and neutralizing antibody titers in dams remained at similar, high levels before and after the second pregnancy. The results are consistent with an evolution of antibody properties in dams to populations less efficiently transferred to offspring or the less efficient transfer of antibodies in elderly dams.

A vesicular stomatitis virus-based prime-boost vaccination strategy induces potent and protective neutralizing antibodies against SARS-CoV-2

The development of safe and effective vaccines to prevent SARS-CoV-2 infections remains an urgent priority worldwide. We have used a recombinant vesicular stomatitis virus (rVSV)-based prime-boost immunization strategy to develop an effective COVID-19 vaccine candidate. We have constructed VSV genomes carrying exogenous genes resulting in the production of avirulent rVSV carrying the full-length spike protein (SF), the S1 subunit, or the receptor-binding domain (RBD) plus envelope (E) protein of SARS-CoV-2. Adding the honeybee melittin signal peptide (msp) to the N-terminus enhanced the protein expression, and adding the VSV G protein transmembrane domain and the cytoplasmic tail (Gtc) enhanced protein incorporation into pseudotype VSV. All rVSVs expressed three different forms of SARS-CoV-2 spike proteins, but chimeras with VSV-Gtc demonstrated the highest rVSV-associated expression. In immunized mice, rVSV with chimeric S protein-Gtc derivatives induced the highest level of potent neutralizing antibodies and T cell responses, and rVSV harboring the full-length msp-SF-Gtc proved to be the superior immunogen. More importantly, rVSV-msp-SF-Gtc vaccinated animals were completely protected from a subsequent SARS-CoV-2 challenge. Overall, we have developed an efficient strategy to induce a protective response in SARS-CoV-2 challenged immunized mice. Vaccination with our rVSV-based vector may be an effective solution in the global fight against COVID-19.

Broad anti-SARS-CoV-2 antibody immunity induced by heterologous ChAdOx1/mRNA-1273 prime-boost vaccination

Heterologous prime-boost immunization strategies have the potential to augment COVID-19 vaccine efficacy and address ongoing vaccine supply challenges. Here, we longitudinally profiled SARS-CoV-2 spike (S)-specific serological and memory B cell (MBC) responses in individuals receiving either homologous (ChAdOx1:ChAdOx1) or heterologous (ChAdOx1:mRNA-1273) prime-boost vaccination. Heterologous mRNA booster immunization induced significantly higher serum neutralizing antibody and MBC responses compared to homologous ChAdOx1 boosting. Specificity mapping of circulating S-specific B cells revealed that mRNA-1273 booster immunization dramatically immunofocused ChAdOx1-primed responses onto epitopes expressed on prefusion-stabilized S. Monoclonal antibodies isolated from mRNA-1273-boosted participants displayed higher binding affinities and increased breadth of reactivity against variants of concern (VOCs) relative to those isolated from ChAdOx1-boosted participants. Overall, the results provide fundamental insights into the B cell response induced by ChAdOx1 and a molecular basis for the enhanced immunogenicity observed following heterologous mRNA booster vaccination.

BacMam virus-based surface display for HCV E2 glycoprotein induces strong cross-neutralizing antibodies and cellular immune responses in vaccinated mice

Background Despite recent advancements, limitations in the treatment and control of hepatitis C virus (HCV) infection reprioritized the studies for invention of an efficient HCV vaccine to elicit strong neutralizing antibodies (NAbs) and cellular responses. Methods Herein, we report molecular construction of a BacMam virus-based surface display for a subtype-1a HCV gpE2 (Bac-CMV-E2-gp64; Bac) that both expressed and displayed gpE2 in mammalian cells and bacouloviral envelope, respectively. Results Assessments by western blotting, Immunofluorescence and Immunogold-electron microscopy indicated the proper expression and incorporation in insect cell and baculovirus envelope, respectively. Mice immunized in three different prime-boost immunization groups of: Bac/Bac, Bac/Pro (bacoulovirus-derived gpE2) and Bac/DNA (plasmid DNA (pCDNA)-encoding gpE2) developed high levels of IgG and IFN-γ (highest for Bac/Bac group) indicating the induction of both humeral and cellular immune responses. Calculation of the IgG2a/IgG1 and IFN-γ/IL-4 ratios indicated a Th1 polarization of immune responses in the Bac/Bac and Bac/DNA groups but a balanced Th1-Th2 phenotype in the Bac/Pro group. Sera of the mice in the Bac/Bac group provided the highest percentage of cross-NAbs against a subtype-2a HCVcc (JFH1) compared to Bac/Pro and Bac/DNA groups (62% versus 41% and 6%). Conclusions Results indicated that BacMam virus-based surface display for gpE2 might act as both subunit and DNA vaccine and offers a promising strategy for development of HCV vaccine for concurrent induction of strong humoral and cellular immune responses.

Heterologous prime-boost immunizations with chimpanzee adenoviral vectors elicit potent and protective immunity against SARS-CoV-2 infection

A safe and effective vaccine for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is urgently needed to tackle the COVID-19 global pandemic. Here, we describe the development of chimpanzee adenovirus serotypes 6 and 68 (AdC6 and AdC68) vector-based vaccine candidates expressing the full-length transmembrane spike glycoprotein. We assessed the vaccine immunogenicity, protective efficacy, and immune cell profiles using single-cell RNA sequencing in mice. Mice were vaccinated via the intramuscular route with the two vaccine candidates using prime-only regimens or heterologous prime-boost regimens. Both chimpanzee adenovirus-based vaccines elicited strong and long-term antibody and T cell responses, balanced Th1/Th2 cell responses, robust germinal center responses, and provided effective protection against SARS-CoV-2 infection in mouse lungs. Strikingly, we found that heterologous prime-boost immunization induced higher titers of protective antibodies, and more spike-specific memory CD8+ T cells in mice. Potent neutralizing antibodies produced against the highly transmissible SARS-CoV-2 variants B.1.1.7 lineage (also known as N501Y.V1) and B.1.351 lineage (also known as N501Y.V2) were detectable in mouse sera over 6 months after prime immunization. Our results demonstrate that the heterologous prime-boost strategy with chimpanzee adenovirus-based vaccines is promising for further development to prevent SARS-CoV-2 infection.

Protective mucosal immunity against SARS-CoV-2 after heterologous systemic prime-mucosal boost immunization

Several effective SARS-CoV-2 vaccines are currently in use, but effective boosters are needed to maintain or increase immunity due to waning responses and the emergence of novel variants. Here we report that intranasal vaccinations with adenovirus 5 and 19a vectored vaccines following a systemic plasmid DNA or mRNA priming result in systemic and mucosal immunity in mice. In contrast to two intramuscular applications of an mRNA vaccine, intranasal boosts with adenoviral vectors induce high levels of mucosal IgA and lung-resident memory T cells (TRM); mucosal neutralization of virus variants of concern is also enhanced. The mRNA prime provokes a comprehensive T cell response consisting of circulating and lung TRM after the boost, while the plasmid DNA prime induces mostly mucosal T cells. Concomitantly, the intranasal boost strategies lead to complete protection against a SARS-CoV-2 infection in mice. Our data thus suggest that mucosal booster immunizations after mRNA priming is a promising approach to establish mucosal immunity in addition to systemic responses.

Recombinant BCG-Prime and DNA-Boost Immunization Confers Mice with Enhanced Protection against Mycobacterium kansasii

The incidence of infections with nontuberculous mycobacteria (NTM) has been increasing worldwide. The emergence of multidrug-resistant NTM is a serious clinical concern, and a vaccine for NTM has not yet been developed. We previously developed a new recombinant Bacillus Calmette–Guérin (rBCG) vaccine encoding the antigen 85B (Ag85B) protein of Mycobacterium kansasii—termed rBCG-Mkan85B—which was used together with a booster immunization with plasmid DNA expressing the same M. kansasii Ag85B gene (DNA-Mkan85B). We reported that rBCG-Mkan85B/DNA-Mkan85B prime–boost immunization elicited various NTM strain-specific CD4+ and CD8+ T cells and induced Mycobacterium tuberculosis-specific immunity. In this study, to investigate the protective effect against M. kansasii infection, we challenged mice vaccinated with a rBCG-Mkan85B or rBCG-Mkan85B/DNA-Mkan85B prime–boost strategy with virulent M. kansasii. Although BCG and rBCG-Mkan85B immunization each suppressed the growth of M. kansasii in the mouse lungs, the rBCG-Mkan85B/DNA-Mkan85B prime–boost vaccination reduced the bacterial burden more significantly. Moreover, the rBCG-Mkan85B/DNA-Mkan85B prime–boost vaccination induced antigen-specific CD4+ and CD8+ T cells. Our data suggest that rBCG-Mkan85B/DNA-Mkan85B prime–boost vaccination effectively enhances antigen-specific T cells. Our novel rBCG could be a potential alternative to clinical BCG for preventing various NTM infections.

Heterologous prime-boost immunization with CoronaVac and Convidecia

Background The safety and immunogenicity of heterologous prime-boost COVID-19 vaccine regimens with one shot of a recombinant adenovirus type-5-vectored COVID-19 vaccine Convidecia has not been reported. Methods We conducted a randomized, controlled, observer-blinded trial of heterologous prime-boost immunization with CoronaVac and Convidecia in healthy adults 18-59 years of age. Eligible participants who were primed with one or two doses of CoronaVac were randomly assigned at a 1:1 ratio to receive a booster dose of Convidecia or CoronaVac. Participants were masked to the vaccine received but not to the three-dose or two-dose regimen. The occurrences of adverse reactions within 28 days after the vaccination were documented. The geometric mean titers of neutralizing antibodies against live SARS-CoV-2 virus were measured at 14 and 28 days after the booster vaccination. Results Between May 25 and 26, 2021, a total of 300 participants were enrolled. Participants who received a booster shot with a heterologous dose of Convidecia reported increased frequencies of solicited injection-site reactions than did those received a homogeneous dose of CoronaVac, but frequencies of systemic reactions. The adverse reactions were generally mild to moderate. The heterologous immunization with Convidecia induced higher live viral neutralizing antibodies than did the homogeneous immunization with CoronaVac (197.4[167.7, 232.4] vs. 33.6[28.3, 39.8] and 54.4[37. 9, 78.0] vs. 12.8[9.3, 17.5]) at day 14 in the three- and two-dose regimen cohort, respectively. Conclusions The heterologous prime-boost regimen with Convidecia after the priming with CoronaVac was safe and significantly immunogenic than a homogeneous boost with CoronaVac (ClinicalTrials.gov, number NCT04892459).