Monoclonal antibodies to guinea pig interferon-gamma: tools for cytokine detection and neutralization

Animal models for COVID-19 and tuberculosis

Respiratory infections cause tremendous morbidity and mortality worldwide. Amongst these diseases, tuberculosis (TB), a bacterial illness caused by Mycobacterium tuberculosis which often affects the lung, and coronavirus disease 2019 (COVID-19) caused by the Severe Acute Respiratory Syndrome Coronavirus type 2 (SARS-CoV-2), stand out as major drivers of epidemics of global concern. Despite their unrelated etiology and distinct pathology, these infections affect the same vital organ and share immunopathogenesis traits and an imperative demand to model the diseases at their various progression stages and localizations. Due to the clinical spectrum and heterogeneity of both diseases experimental infections were pursued in a variety of animal models. We summarize mammalian models employed in TB and COVID-19 experimental investigations, highlighting the diversity of rodent models and species peculiarities for each infection. We discuss the utility of non-human primates for translational research and emphasize on the benefits of non-conventional experimental models such as livestock. We epitomize advances facilitated by animal models with regard to understanding disease pathophysiology and immune responses. Finally, we highlight research areas necessitating optimized models and advocate that research of pulmonary infectious diseases could benefit from cross-fertilization between studies of apparently unrelated diseases, such as TB and COVID-19.

Identification and primary application of hybridomas cell secreting monoclonal antibodies against mink (Neovison vison) interferon-gamma

Due to their susceptibility to several human viruses, the mink has been proposed as potential animal models for the study of human viral infections. However, there are no specific monoclonal antibody (mAbs) currently available for the detection of mink-specific interferon-gamma (miIFN-γ). The BALB/c mice were immunized intraperitoneally with purified recombinant miIFN-γ protein. The splenocytes were obtained and fused with murine myeloma cells. Five of 24 hybridoma clones were obtained to produce mAbs steadily with the strongest affinity to recombinant miIFN-γ protein. The isotype of the 31A, 31B and 31G were lgG 2b. The isotype of 44 and 46 were lgG 2a and 1. All five mAbs were κ light chains. Western blotting and indirect ELISA method showed that 5 mAbs were positive to miIFN-γ. Immunofluorescence showed that 2 mAbs (44 and 46) had a positive reaction to miIFN-γ. The hybridoma clone 46 had the highest sensitivity for the detection of miIFN-γ. Most importantly, our primary sandwich ELISA system (mAbs 46 and polyclonal antiserum) detected endogenous IFN-γ in mink lymphocytes infected with canine distemper virus (CDV). We have thus developed a novel mAbs could recognize miIFN-γ, and have demonstrated the first ELISA-based measurement of IFN-γ in lymphocyte of the mink.

Additive Protection against Congenital Cytomegalovirus Conferred by Combined Glycoprotein B/pp65 Vaccination Using a Lymphocytic Choriomeningitis Virus Vector

Subunit vaccines for prevention of congenital cytomegalovirus (CMV) infection based on glycoprotein B (gB) and pp65 are in clinical trials, but it is unclear whether simultaneous vaccination with both antigens enhances protection. We undertook evaluation of a novel bivalent vaccine based on nonreplicating lymphocytic choriomeningitis virus (rLCMV) vectors expressing a cytoplasmic tail-deleted gB [gB(dCt)] and full-length pp65 from human CMV in mice. Immunization with the gB(dCt) vector alone elicited a comparable gB-binding antibody response and a superior neutralizing response to that elicited by adjuvanted subunit gB. Immunization with the pp65 vector alone elicited robust T cell responses. Comparable immunogenicity of the combined gB(dCt) and pp65 vectors with the individual monovalent formulations was demonstrated. To demonstrate proof of principle for a bivalent rLCMV-based HCMV vaccine, the congenital guinea pig cytomegalovirus (GPCMV) infection model was used to compare rLCMV vectors encoding homologs of pp65 (GP83) and gB(dCt), alone and in combination versus Freund's adjuvanted recombinant gB. Both vectors elicited significant immune responses, and no loss of gB immunogenicity was noted with the bivalent formulation. Combined vaccination with rLCMV-vectored GPCMV gB(dCt) and pp65 (GP83) conferred better protection against maternal viremia than subunit or either monovalent rLCMV vaccine. The bivalent vaccine also was significantly more effective in reducing pup mortality than the monovalent vaccines. In summary, bivalent vaccines with rLCMV vectors expressing gB and pp65 elicited potent humoral and cellular responses and conferred protection in the GPCMV model. Further clinical trials of LCMV-vectored HCMV vaccines are warranted.

Characterization of guinea pig T cell responses elicited after EP-assisted delivery of DNA vaccines to the skin

The skin is an ideal target tissue for vaccine delivery for a number of reasons. It is highly accessible, and most importantly, enriched in professional antigen presenting cells. Possessing strong similarities to human skin physiology and displaying a defined epidermis, the guinea pig is an appropriate model to study epidermal delivery of vaccine. However, whilst we have characterized the humoral responses in the guinea pig associated with skin vaccine protocols we have yet to investigate the T cell responses. In response to this inadequacy, we developed an IFN-γ ELISpot assay to characterize the cellular immune response in the peripheral blood of guinea pigs. Using a nucleoprotein (NP) influenza pDNA vaccination regimen, we characterized host T cell responses. After delivery of the DNA vaccine to the guinea pig epidermis we detected robust and rapid T cell responses. The levels of IFN-γ spot-forming units averaged approximately 5000 per million cells after two immunizations. These responses were broad in that multiple regions across the NP antigen elicited a T cell response. Interestingly, we identified a number of NP immunodominant T cell epitopes to be conserved across an outbred guinea pig population, a phenomenon which was also observed after immunization with a RSV DNA vaccine. We believe this data enhances our understanding of the cellular immune response elicited to a vaccine in guinea pigs, and globally, will advance the use of this model for vaccine development, especially those targeting skin as a delivery site.

Detection of herpes simplex virus type 2 (HSV-2) -specific cell-mediated immune responses in guinea pigs during latent HSV-2 genital infection

Genital infections with herpes simplex virus type 2 (HSV-2) are a source of considerable morbidity and are a health concern for newborns exposed to virus during vaginal delivery. Additionally, HSV-2 infection diminishes the integrity of the vaginal epithelium resulting in increased susceptibility of individuals to infection with other sexually transmitted pathogens. Understanding immune protection against HSV-2 primary infection and immune modulation of virus shedding events following reactivation of the virus from latency is important for the development of effective prophylactic and therapeutic vaccines. Although the murine model of HSV-2 infection is useful for understanding immunity following immunization, it is limited by the lack of spontaneous reactivation of HSV-2 from latency. Genital infection of guinea pigs with HSV-2 accurately models the disease of humans including the spontaneous reactivation of HSV-2 from latency and provides a unique opportunity to examine virus-host interactions during latency. Although the guinea pig represents an accurate model of many human infections, relatively few reagents are available to study the immunological response to infection. To analyze the cell-mediated immune response of guinea pigs at extended periods of time after establishment of HSV-2 latency, we have modified flow-cytometry based proliferation assays and IFN-γ ELISPOT assays to detect and quantify HSV-specific cell-mediated responses during latent infection of guinea pigs. Here we demonstrate that a combination of proliferation and ELISPOT assays can be used to quantify and characterize effecter function of virus-specific immune memory responses during HSV-latency.

Virus-specific immune memory at peripheral sites of herpes simplex virus type 2 (HSV-2) infection in guinea pigs

Despite its importance in modulating HSV-2 pathogenesis, the nature of tissue-resident immune memory to HSV-2 is not completely understood. We used genital HSV-2 infection of guinea pigs to assess the type and location of HSV-specific memory cells at peripheral sites of HSV-2 infection. HSV-specific antibody-secreting cells were readily detected in the spleen, bone marrow, vagina/cervix, lumbosacral sensory ganglia, and spinal cord of previously-infected animals. Memory B cells were detected primarily in the spleen and to a lesser extent in bone marrow but not in the genital tract or neural tissues suggesting that the HSV-specific antibody-secreting cells present at peripheral sites of HSV-2 infection represented persisting populations of plasma cells. The antibody produced by these cells isolated from neural tissues of infected animals was functionally relevant and included antibodies specific for HSV-2 glycoproteins and HSV-2 neutralizing antibodies. A vigorous IFN-γ-secreting T cell response developed in the spleen as well as the sites of HSV-2 infection in the genital tract, lumbosacral ganglia and spinal cord following acute HSV-2 infection. Additionally, populations of HSV-specific tissue-resident memory T cells were maintained at these sites and were readily detected up to 150 days post HSV-2 infection. Unlike the persisting plasma cells, HSV-specific memory T cells were also detected in uterine tissue and cervicothoracic region of the spinal cord and at low levels in the cervicothoracic ganglia. Both HSV-specific CD4⁺ and CD8⁺ resident memory cell subsets were maintained long-term in the genital tract and sensory ganglia/spinal cord following HSV-2 infection. Together these data demonstrate the long-term maintenance of both humoral and cellular arms of the adaptive immune response at the sites of HSV-2 latency and virus shedding and highlight the utility of the guinea pig infection model to investigate tissue-resident memory in the setting of HSV-2 latency and spontaneous reactivation.

Development of a novel, guinea pig-specific IFN-γ ELISPOT assay and characterization of guinea pig cytomegalovirus GP83-specific cellular immune responses following immunization with a modified vaccinia virus Ankara (MVA)-vectored GP83 vaccine

The guinea pig (Cavia porcellus) provides a useful animal model for studying the pathogenesis of many infectious diseases, and for preclinical evaluation of vaccines. However, guinea pig models are limited by the lack of immunological reagents required for characterization and quantification of antigen-specific T cell responses. To address this deficiency, an enzyme-linked immunospot (ELISPOT) assay for guinea pig interferon (IFN)-γ was developed to measure antigen/epitope-specific T cell responses to guinea pig cytomegalovirus (GPCMV) vaccines. Using splenocytes harvested from animals vaccinated with a modified vaccinia virus Ankara (MVA) vector encoding the GPCMV GP83 (homolog of human CMV pp65 [gpUL83]) protein, we were able to enumerate and map antigen-specific responses, both in vaccinated as well as GPCMV-infected animals, using a panel of GP83-specific peptides. Several potential immunodominant GP83-specific peptides were identified, including one epitope, LGIVHFFDN, that was noted in all guinea pigs that had a detectable CD8+ response to GP83. Development of a guinea pig IFN-γ ELISPOT should be useful in characterization of additional T cell-specific responses to GPCMV, as well as other pathogens. This information in turn can help focus future experimental evaluation of immunization strategies, both for GPCMV as well as for other vaccine-preventable illnesses studied in the guinea pig model.

Temporal changes in the gene signatures of BCG-vaccinated guinea pigs in response to different mycobacterial antigens

Mycobacterium bovis BCG-vaccination in the guinea pig model of tuberculosis (TB) is sufficiently protective that candidate TB vaccines are judged against this. Little is understood about how the BCG vaccine works and, in the absence of a definitive correlate of protection, it is difficult to interpret the significance of novel vaccine induced host responses. Here an extended custom-made microarray (86 guinea pig genes) was used to dissect temporal changes in BCG-vaccine induced gene signatures to different mycobacterial antigens. Initially at 4h, pro-inflammatory genes such as IL-1α, IL-1β, IL-8 and GRO were up-regulated (P<0.001) and these were then superseded by IFN-γ and GM-CSF (at 12 and 20h) post-stimulation, ex vivo with PPD. Similar genes were seen following stimulation with viable BCG but with the addition of IL-23 (P<0.01) after 8h. Our results suggest that temporal changes in the up- and down-regulation of a variety of genes are required to trigger a successful protective response to TB in guinea pigs. This provides base-line information against which new TB vaccines can be compared.