Cellular and humoral immunity following vaccination with two different PCV2 vaccines (containing PCV2a or PCV2a/PCV2b) and challenge with virulent PCV2d

Comparison of immune effects of porcine circovirus type 2d (PCV2d) capsid protein expressed by Escherichia coli and baculovirus-insect cells

Porcine circovirus type 2 (PCV2) is an important pathogen harmful to global pig production, which causes immunosuppression and serious economic losses. PCV2 capsid (Cap) protein expressed by E. coli or baculovirus-insect cells are often used in preparation of PCV2 subunit vaccines, but the latter is expensive to produce. It is therefore crucial to comparison of the immune effects of Cap protein expressed by the above two expression systems for reducing the production cost and guaranteeing PCV2 vaccine quality. In this study, the PCV2d-Cap protein lacking nuclear localization signal (NLS), designated as E. coli-Cap and Bac-Cap, was expressed by E. coli and baculovirus-Spodoptera frugiperda Sf9 (Bac-Sf9) cells, respectively. The expressed Cap proteins could self-assemble into virus-like particles (VLPs), but the Bac-Cap-assembled VLPs were more regular. The two system-expressed Cap proteins induced similar specific IgG responses in mice, but the neutralizing antibody levels of Bac-Cap-immunized mice was higher than those of E. coli-Cap. After PCV2 challenge, IL-10 in Bac-Cap immunized mice decreased significantly than that in E. coli-Cap. The lesions and PCV2 antigen positive cells in tissues of mice immunized with E. coli-Cap and Bac-Cap were significantly reduced, and Bac-Cap appeared mild lesions and fewer PCV2 antigen-positive cells compared with E. coli-Cap immunized mice. The study indicated that Cap proteins expressed by E. coli and Bac-Sf9 cells could induce specific protective immunity, but the latter induced more effective immunity, which provides valuable information for the research and development of PCV2 vaccine.

A porcine circovirus type 2d-based virus-like particle vaccine induces humoral and cellular immune responses and effectively protects pigs against PCV2d challenge

The pathogenic porcine circovirus type 2 (PCV2) leads to significant economic losses in pig production. PCV2d is currently the dominant genotype causing porcine circovirus-associated disease (PCVAD) worldwide. Therefore, development of a recombinant PCV2d-based vaccine is required to elicit complete protection against PCV2d infection. In this study, we generated virus-like particles of PCV2d-based capsid protein (Bac-2dCP) using a baculovirus expression system and evaluated its protective efficacy against PCV2d infection in specific pathogen-free (SPF) pigs. Three-week-old SPF miniature pigs were intramuscularly immunized with purified Bac-2dCP and intranasally challenged with PCV2d at 4 weeks post-vaccination. The Bac-2dCP group showed significantly higher IgG levels and neutralizing antibodies against PCV2b and PCV2d genotypes, as well as increased interferon-γ levels, and increased body weight and average daily weight gain compared with positive (challenged) and negative (unchallenged) controls. In particular, the Bac-2dCP group showed almost complete absence of PCV2d DNA in serum, nasal, and rectal swabs and in lung, lymph node, and kidney tissue samples. However, the positive control group exhibited low levels of neutralizing antibody, and high levels of PCV2 DNA in serum, swab, and tissue samples, resulting in PCV2-associated pathological lesions. The results of this study demonstrated that a recombinant Bac-2dCP vaccine conferred complete protection against a PCV2d challenge in SPF miniature pigs.

Safety of the Administration of an Inactivated PCV2a/PCV2b/Mycoplasma Hyopneumoniae Vaccine to Pregnant and Lactating Sows and Gilts

Porcine Circovirus type 2 (PCV2) vaccination of gilts during acclimation has become a routine practice in commercial pig farms to homogenize herd immunity to PCV2 and reduce the impact of diseases associated with PCV2 infection, namely reproductive, respiratory, systemic, and other PCV2-associated diseases. The periodic mass vaccination of sows, with the same objectives, is also common. To ensure mass vaccination is an appropriate health management tool, demonstrating that the vaccine is safe in different sow/gilt physiological stages is necessary. The objective of the present studies was to evaluate safety of a PCV2a/PCV2b/Mycoplasma hyopneumoniae (PCV2a2bMHP) killed vaccine in sows and gilts during gestation and lactation, under controlled experimental pen conditions, and during gestation, mimicking mass vaccination, under field conditions. Safety was assessed by monitoring for immediate adverse reactions after vaccination, rectal temperatures after vaccination (controlled experimental pen studies only), local and systemic reactions, and reproductive performance (studies conducted during pregnancy) or lactation performance (studies conducted during lactation). In total, 416 sows/gilts were enrolled, and more than 4000 piglets were observed during their first week of life, under field conditions. In both controlled experimental and field studies, no immediate anaphylactic type reactions were observed after vaccination and the incidence of adverse events, such as depression or decreased appetite, was acceptable for what is expected in a swine herd. In the studies conducted during gestation, vaccination did not significantly increase rectal temperature of the vaccinated animals. Sow reproductive outcomes were not affected by vaccination. The farrowing rate of animals participating in the field study was higher than the historic averages of the farms. In the laboratory studies conducted during the first and second half of gestation, no differences in reproductive outcome were observed between vaccinated and non-vaccinated animals. However, sows vaccinated during lactation experienced a transient hyperthermia which did not affect milk production since the piglets' average daily weight gain was not affected. The previously described results confirm that the administration of a PCV2a2bMHP vaccine was safe in the tested conditions. All the anticipated benefits of sow and gilt PCV2 vaccination, such as homogenization of PCV2 antibody titers or reduction in PCV2 circulation in the herd, would not be masked by potential adverse events due to herd vaccination. In conclusion, the administration of a PCV2a2bMHP vaccine to sows and gilts during different stages of gestation and during lactation is safe.

Laboratory safety evaluation of lokivetmab, a canine anti-interleukin-31 monoclonal antibody, in dogs

Lokivetmab (Cytopoint®, Zoetis) is a canine monoclonal antibody that specifically binds and neutralizes interleukin (IL)-31. Lokivetmab is approved for use in dogs for the treatment of atopic dermatitis (AD) and allergic dermatitis. The laboratory safety of lokivetmab was evaluated in 2 studies by adapting the science-based, case-by-case approach used for preclinical and early clinical safety evaluation of human biopharmaceuticals. The main objectives were to demonstrate the safety of lokivetmab in healthy laboratory Beagle dogs by using integrated clinical, morphologic, and functional evaluations. In Study 1, dogs were treated s.c. with saline or lokivetmab at 3.3 mg/kg (1X, label dose) or 10 mg/kg (3X intended dose) for 7 consecutive monthly doses, with terminal pathology and histology assessments. In Study 2, the functional immune response was demonstrated in naïve dogs using the T-cell dependent antibody response (TDAR) test with 2 different dose levels of unadjuvanted keyhole limpet hemocyanin (KLH) as the model immunogen. The primary endpoint was anti-KLH IgG antibody titer, and secondary endpoints were ex vivo IL-2 enzyme-linked immunospot (ELISpot) and peripheral blood mononuclear cell lymphoproliferation assays. Both studies included monitoring general health, periodic veterinary clinical evaluations, serial clinical pathology and toxicokinetics, and monitoring for anti-drug antibodies. In both studies, the health of dogs receiving lokivetmab was similar to controls, with no treatment-related changes uncovered. Extensive pathology evaluations of immune tissues (Study 1) revealed no lokivetmab-related morphologic changes, and in dogs treated at 10 mg/kg lokivetmab, immunization with the model antigen KLH did not impair the functional antibody or T-cell recall responses. There were no immunogenicity-related or hypersensitivity-related responses observed in either study. These studies in healthy laboratory dogs showed that lokivetmab was well-tolerated, did not produce any treatment-related effects, and had no effect on immune system morphology or its functional response. These studies also demonstrated the utility of a science-based case-by-case approach to the safety evaluation of a veterinary biopharmaceutical product.

Comparative Efficacy of Chimeric Porcine Circovirus (PCV) Vaccines against Experimental Heterologous PCV2d Challenges

The objective of this study was to evaluate the efficacy of two multivalent commercial porcine circovirus (PCV) vaccines against heterologous PCV2d challenges. A total of 24 crossbred male pigs aged 26 days selected from a specific pathogen-free herd were randomly divided into four groups (six pigs per group) and assigned as follows: negative control (unvaccinated/sham-challenge), vaccinated with chimeric PCV1-2a vaccine (PCV1-2a/PCV2d-challenge), vaccinated with chimeric PCV1-2a-2b vaccine (PCV1-2a-2b/PCV2d-challenge) and positive control (unvaccinated/PCV2d-challenge). At 21 days after vaccination, the pigs were intranasally and intramuscularly inoculated with either sham or field isolates of PCV2d (PCV2d/149/TH/2020). After being challenged, blood samples were obtained weekly and analyzed for levels of PCV2d viremia, neutralizing antibodies, and IgG against PCV2. At 30 days post-challenge (DPC), the pigs were euthanized and then subjected to pathological evaluations and molecular analysis. The results indicated that pigs in the PCV1-2a-2b/PCV2d-challenge and the PCV1-2a/PCV2d-challenge groups possessed significantly greater levels of PCV2d-neutralizing antibody titer when compared with the positive control group. Moreover, pigs in the PCV1-2a-2b/PCV2d-challenge group exhibited a lower degree of severity in terms of gross lesion scores and lower levels of PCV2 viremia when compared with the positive control group. This study demonstrated that vaccinating pigs with either the PCV1-2a or PCV1-2a-2b chimeric vaccines elicits a potent immune response against PCV2d infection and reduces viremia after PCV2d inoculation in pigs.

The Magic Staff: A Comprehensive Overview of Baculovirus-Based Technologies Applied to Human and Animal Health

Baculoviruses are enveloped, insect-specific viruses with large double-stranded DNA genomes. Among all the baculovirus species, Autographa californica multiple nucleopolyhedrovirus (AcMNPV) is the most studied. Due to its characteristics regarding biosafety, narrow host range and the availability of different platforms for modifying its genome, AcMNPV has become a powerful biotechnological tool. In this review, we will address the most widespread technological applications of baculoviruses. We will begin by summarizing their natural cycle both in larvae and in cell culture and how it can be exploited. Secondly, we will explore the different baculovirus-based protein expression systems (BEVS) and their multiple applications in the pharmaceutical and biotechnological industry. We will focus particularly on the production of vaccines, many of which are either currently commercialized or in advanced stages of development (e.g., Novavax, COVID-19 vaccine). In addition, recombinant baculoviruses can be used as efficient gene transduction and protein expression vectors in vertebrate cells (e.g., BacMam). Finally, we will extensively describe various gene therapy strategies based on baculoviruses applied to the treatment of different diseases. The main objective of this work is to provide an extensive up-to-date summary of the different biotechnological applications of baculoviruses, emphasizing the genetic modification strategies used in each field.

Development of gold Immunochromatographic assay strip based on specific polyclonal antibodies against capsid protein for rapid detection of porcine circovirus 2 in Zhejiang province, China

BACKGROUND

The existing detection methods for porcine circovirus type 2 (PCV2) specific antibodies in serum cannot determine the infection status, thus it is necessary to establish a method for detecting PCV2 antigen. The capsid protein (CAP) of PCV2, as a major structural protein that plays a significant role in viral replication and in inducing host's immune response, is an ideal target antigen to monitor PCV2 infection. Therefore, a gold immunochromatographic assay (GICA) for rapid detection of PCV2 antigen based on the polyclonal antibodies (PAbs) against PCV2-CAP will be developed.

RESULTS

The truncated CAP protein (dCAP) was used to immunize rabbits to generate anti-serum. After preliminary purification by caprylic acid/ammonium sulfate precipitation (CAAS), specific PAbs were purified by affinity chromatography column coupled with dCAP and its titer was about two-fold higher than preliminary purified PAbs. Colloidal gold-PAbs conjugate was synthesized under the optimum conditions. The specific anti-dCAP PAbs and goat anti-rabbit antibody (GAR) were then sprayed onto nitrocellulose (NC) membrane as a test line (TL) and a control line (CL), respectively. The visual limit detection (vLOD) of the GICA strips was 5 ng/mL. Specificity assay indicated that the GICA strips had specifically detected PCV2 and was not reactive for porcine epidemic diarrhea virus (PEDV), pseudorabies virus (PRV), porcine reproductive and respiratory syndrome virus (PRRSV) or classic swine fever virus (CSFV). A total of 36 porcine serum samples were detected by this GICA and commercial enzyme-linked immunosorbent assay (ELISA) Kit, 9 positive samples were found by the developed strip with the rate of 25.0% comparing with 11 positive samples detected by the commercially ELISA Kit which positive rate was 30.5%, and the receiver operating characteristic (ROC) curve revealed that the relative sensitivity and specificity of this GICA strip were 72.7 and 96.0%, respectively, with an area of 87.2%.

CONCLUSIONS

This study established an efficient detection method with high sensitivity and specificity for the clinical diagnosis of PCV2 antigen, that will facilitate a rapid and convenient way to evaluate the infection status of vaccinated pigs.

Recombinant vaccines in 2022: a perspective from the cell factory

The last big outbreaks of Ebola fever in Africa, the thousands of avian influenza outbreaks across Europe, Asia, North America and Africa, the emergence of monkeypox virus in Europe and specially the COVID-19 pandemics have globally stressed the need for efficient, cost-effective vaccines against infectious diseases. Ideally, they should be based on transversal technologies of wide applicability. In this context, and pushed by the above-mentioned epidemiological needs, new and highly sophisticated DNA-or RNA-based vaccination strategies have been recently developed and applied at large-scale. Being very promising and effective, they still need to be assessed regarding the level of conferred long-term protection. Despite these fast-developing approaches, subunit vaccines, based on recombinant proteins obtained by conventional genetic engineering, still show a wide spectrum of interesting potentialities and an important margin for further development. In the 80’s, the first vaccination attempts with recombinant vaccines consisted in single structural proteins from viral pathogens, administered as soluble plain versions. In contrast, more complex formulations of recombinant antigens with particular geometries are progressively generated and explored in an attempt to mimic the multifaceted set of stimuli offered to the immune system by replicating pathogens. The diversity of recombinant antimicrobial vaccines and vaccine prototypes is revised here considering the cell factory types, through relevant examples of prototypes under development as well as already approved products.

Surface Display of porcine circovirus type 2 antigen protein cap on the spores of bacillus subtilis 168: An effective mucosal vaccine candidate

The oral mucosal vaccine has great potential in preventing a series of diseases caused by porcine circovirus type 2 (PCV2) infection. This study constructed a recombinant Bacillus subtilis RB with PCV2 Capsid protein (Cap) on its spore surface and cotB as a fusion partner. The immune properties of the recombinant strain were evaluated in a mouse model. IgA in intestinal contents and IgG in serum were detected by enzyme-linked immunosorbent assay (ELISA). The results demonstrated that recombinant spores could activate strong specific mucosal and humoral immune responses. In addition, spores showed good mucosal immune adjuvant function, promoting the proliferation of CD3+, CD4+ and CD8+ T cells and other immune cells. We also found that the relative expression of inflammatory cytokines such as IL-1β, IL-6, IL-10, TNF-α and IFN in the small intestinal mucosa was significantly up-regulated under the stimulation of recombinant bacteriophage. These effects are important for the balance of Th1/Th2-like responses. In summary, our results suggest that recombinant B. subtilis RB as a feed additive provides a new strategy for the development of novel and safe PCV2 mucosal subunit vaccines.

Live attenuated Salmonella enterica serovar Choleraesuis vector delivering a virus-like particles induces a protective immune response against porcine circovirus type 2 in mice

The virus-like particles (VLPs) of porcine circovirus type 2 (PCV2) is an attractive vaccine candidate that retains the natural conformation of the virion but lacks the viral genome to replicate, thus balancing safety and immunogenicity. However, the assembly of VLPs requires cumbersome subsequent processes, hindering the development of related vaccines. In addition, as a subunit antigen, VLPs are defective in inducing cellular and mucosal immune responses. In this study, the capsid (Cap) protein of PCV2 was synthesized and self-assembled into VLPs in the recombinant attenuated S. Choleraesuis vector, rSC0016(pS-Cap). Furthermore, rSC0016(pS-Cap) induced a Cap-specific Th1-dominant immune response, mucosal immune responses, and neutralizing antibodies against PCV2. Finally, the virus genome copies in mice immunized with the rSC0016(pS-Cap) were significantly lower than those of the empty vector control group after challenge with PCV2. In conclusion, our study demonstrates the potential of using S. Choleraesuis vectors to delivery VLPs, providing new ideas for the development of PCV2 vaccines.

A bivalent porcine circovirus type 2 (PCV2), PCV2a-PCV2b, vaccine offers biologically superior protection compared to monovalent PCV2 vaccines

Recent publications suggest PCV2 vaccine-induced protection is superior when the vaccine and challenge are closely matched. PCV2's evolutionary rate, propensity for recombination, and genotype shifting, all provide rationale for modernizing PCV2 vaccines. One mechanism to increase a vaccine's epitope breadth is by designing a bivalent vaccine. The objective of these studies was to evaluate efficacy of a monovalent (PCV1-2 chimera, cPCV2a or cPCV2b) and bivalent (cPCV2a-cPCV2b) vaccine in terms of homologous and heterologous efficacy. In Study A, pigs were vaccinated with cPCV2a or saline and challenged with PCV2a or PCV2b. In Study B, pigs were vaccinated with cPCV2a, cPCV2a-cPCV2b bivalent, or saline, and challenged with PCV2a. In Study C, pigs were vaccinated with cPCV2b, cPCV2a-cPCV2b bivalent, or saline, and challenged with PCV2b. In all studies vaccines and saline were administered intramuscularly to pigs at three to four weeks of age. Virulent PCV2b or PCV2a was administered to all animals approximately three weeks post-vaccination. Both mono and bivalent vaccinated groups demonstrated significantly lower viremia, percent of animals ever viremic, percent of animals with lymphoid depletion and/or histiocytic replacement, and percent of animals with PCV2 colonization of lymphoid tissues compared to saline controls. In Study A, a biologically relevant, though not significantly different, improvement in homologous versus heterologous protection was observed. In Studies B and C, biologically superior efficacy of the bivalent cPCV2a-cPCV2b vaccine compared to either monovalent vaccine was demonstrated. Taken together, cross-protection among mismatched PCV2 vaccine and challenge genotypes is not 100%; a bivalent PCV2 vaccine may provide the best opportunity to broaden coverage to circulating strains of PCV2.