The lethal K18-hACE2 knock-in mouse model mimicking the severe pneumonia of COVID-19 is practicable for antiviral development.

Animal models of COVID-19 facilitate the development of vaccines and antivirals against SARS-CoV-2. The efficacy of antivirals or vaccines may differ in different animal models with varied degrees of disease. Here, we introduce a mouse model expressing human angiotensin-converting enzyme 2 (ACE2). In this model, ACE2 with the human cytokeratin 18 promoter was knocked into the Hipp11 locus of C57BL/6J mouse by CRISPR - Cas9 (K18-hACE2 KI). Upon intranasal inoculation with high (3 × 105 PFU) or low (2.5 × 102 PFU) dose of SARS-CoV-2 wildtype (WT), Delta, Omicron BA.1, or Omicron BA.2 variants, all mice showed obvious infection symptoms, including weight loss, high viral loads in the lung, and interstitial pneumonia. 100% lethality was observed in K18-hACE2 KI mice infected by variants with a delay of endpoint for Delta and BA.1, and a significantly attenuated pathogenicity was observed for BA.2. The pneumonia of infected mice was accompanied by the infiltration of neutrophils and pulmonary fibrosis in the lung. Compared with K18-hACE2 Tg mice and HFH4-hACE2 Tg mice, K18-hACE2 KI mice are more susceptible to SARS-CoV-2. In the antivirals test, REGN10933 and Remdesivir had limited antiviral efficacies in K18-hACE2 KI mice upon the challenge of SARS-CoV-2 infections, while Nirmatrelvir, monoclonal antibody 4G4, and mRNA vaccines potently protected the mice from death. Our results suggest that the K18-hACE2 KI mouse model is lethal and stable for SARS-CoV-2 infection, and is practicable and stringent to antiviral development.

CD4+ T cell depletion does not affect the level of viremia in chronically SHIVSF162P3N-infected Chinese cynomolgus monkeys.

Chronically SHIVSF162P3N-infected cynomolgus monkeys were used to determine the effects of the antibody-mediated acute CD4+ T cell depletion on viral load as well as on the immunological factors associated with disease progression. Compared with the control animals, CD4+ T cell-depleted animals with SHIV infection showed (i) little alteration in plasma viral load over the period of 22 weeks after the depletion; (ii) increased CD4+ T cell proliferation and turnover of macrophages at the early phase of the depletion, but subsequent decline to the basal levels; and (iii) little impact on the expression of the inflammatory cytokines and CC chemokines associated with disease progression. These findings indicate that the antibody-mediated acute CD4+ T cell depletion had minimal impact on plasma viral load and disease progression in chronically SHIVSF162P3N-infected cynomolgus monkeys. Future investigations are necessary to identify the key factor(s) related to the immune activation and macrophage infection during the CD4 deletion in chronic viral infection.

Mycobacterium tuberculosis Erdman infection of cynomolgus macaques of Chinese origin.

BACKGROUND: Nearly one-third of the population worldwide is estimated to have latent tuberculosis infection (LTBI), which represents a vast reservoir for a constant source of tuberculosis (TB) transmission. It has been suggested that cynomolgus macaques are less susceptible to Mycobacterium tuberculosis (M.tb) infection than rhesus macaques, we examined M.tb infection of Chinese cynomolgus macaques. METHODS: Eight Chinese cynomolgus macaques were infected with M.tb Erdman strain with a small [25 colony forming unit (CFU)] or large dose (500 CFU) via bronchoscopy. The infected animals were monitored for symptoms and examined by chest X-ray, computed tomography (CT), tuberculin skin test (TST), and enzyme-linked immunospot (ELISPOT). RESULTS: Based on TST conversion and the specific immune responses to M.tb antigens, all animals were successfully infected. Half of the animals developed active infection and died within 15 months postinfection. The other four animals were grouped with latent M.tb infection because of positive TST but few clinical signs and pathological changes of TB during the course of this study. Interestingly, a challenge with a large dose of M.tb also induced latent infection. Similar to the changes that occur with human TB patients, the animals with active infection exhibited weight loss, cough and typical TB pathological changes, including caseous granulomas, cavities, consolidation, lipid pneumonia, pleural effusion, lymphadenopathy and bacterial burden in lungs and other organs. CONCLUSIONS: The low dose of M.tb was sufficient to cause both active and latent M.tb infection in cynomolgus macaques of Chinese origin.

Comparative Analysis of Immune Activation Markers of CD8+ T Cells in Lymph Nodes of Different Origins in SIV-Infected Chinese Rhesus Macaques.

Altered T-cell homeostasis, such as expansion of CD8+ T cells to the secondary lymphatic compartments, has been suggested as a mechanism of HIV/simian immunodeficiency virus (SIV)-pathogenesis. However, the role of immune activation of CD8+ T cells in the CD4/CD8 turnover and viral replication in these tissues is not completely understood. In this study, we compared the expression of immune activation markers (CD69 and HLA-DR) on CD8+ T cells in the peripheral blood and lymph nodes (LNs) of SIV-infected/uninfected Chinese rhesus macaques. SIV-infected macaques had significantly higher percentages of CD8+CD69+ and CD8+HLA-DR+ T cells in all these anatomical compartments than uninfected macaques. LNs that located close to the gastrointestinal (GI) tract (colon, mesenteric, and iliac LNs) of SIV-infected macaques had profoundly lower numbers of CD4+ T cells, but no significant difference in expression of activation marker (CD8+CD69+ and CD8+HLA-DR+) as compared with the peripheral lymphatic tissues (axillary and inguinal LNs). The CD4/CD8 ratios were negatively correlated with the activation of CD8+ T cells in the overall LNs, with further associations with CD8+HLA-DR+ in GI LNs while CD8+CD69+ in peripheral LNs. These observations demonstrate that the increase of CD8+ T cell activation is a contributing factor for the decline of CD4/CD8 ratios in GI system.

SIV Infection Impairs the Central Nervous System in Chinese Rhesus Macaques.

The central nervous system (CNS) impairment is a consequence seen in SIV infection of rhesus macaques of Indian-origin, which is more common in infected macaques with rapid disease progression than in those with conventional disease progression. Here, we investigated the CNS damages in SIVmac239-infected Chinese rhesus macaques. We demonstrated that SIV infection of Chinese macaques could cause neuropathological impairments, which was evidenced by appearance of SIV-RNA positive cells, the infiltration of activated macrophages and abundant multinucleated giant cells (MNGCs) in the different regions of the brains. The animals with high viremia and short survival time (average of 16 weeks, rapid progression, RP) had severer neuropathological changes than those with conventional progression (CP). As compared with the RP animals, CP macaques had lower viremia and much longer survival time (average of 154 weeks). These findings indicate that SIVmac239 infection of Chinese rhesus macaque can be used as a suitable animal model and alternative resource for nueroAIDS research.

SIV Infection Facilitates Mycobacterium tuberculosis Infection of Rhesus Macaques.

Tuberculosis (TB) is a common opportunistic infection and the leading cause of death for human immunodeficiency virus (HIV)-infected patients. Thus, it is necessary to understand the pathogenetic interactions between M.tb and HIV infection. In this study, we examined M.tb and/or simian immunodeficiency virus (SIV) infection of Chinese rhesus macaques. While there was little evidence that M.tb enhanced SIV infection of macaques, SIV could facilitate M.tb infection as demonstrated by X-rays, pathological and microbiological findings. Chest X-rays showed that co-infected animals had disseminated lesions in both left and right lungs, while M.tb mono-infected animals displayed the lesions only in right lungs. Necropsy of co-infected animals revealed a disseminated M.tb infection not only in the lungs but also in the extrapulmonary organs including spleen, pancreas, liver, kidney, and heart. The bacterial counts in the lungs, the bronchial lymph nodes, and the extrapulmonary organs of co-infected animals were significantly higher than those of M.tb mono-infected animals. The mechanistic studies demonstrated that two of three co-infected animals had lower levels of M.tb specific IFN-γ and IL-22 in PBMCs than M.tb mono-infected animals. These findings suggest that Chinese rhesus macaque is a suitable and alternative non-human primate model for SIV/M.tb coinfection studies. The impairment of the specific anti-TB immunity is likely to be a contributor of SIV-mediated enhancement M.tb infection.

IL-28B down-regulates regulatory T cells but does not improve the protective immunity following tuberculosis subunit vaccine immunization.

Regulatory T cells (Tregs), which could be down-regulated by IL-28B, were reported to suppress T-cell-mediated immunity. The aim of this study was to investigate the role of IL-28B on the immune responses and protective efficacy of a tuberculosis (TB) subunit vaccine. First, a recombinant adenoviral vector expressing mouse IL-28B (rAd-mIL-28B) was constructed; then C57BL/6 mice were immunized with subunit vaccine ESAT6-Ag85B-Mpt64(190-198)-Mtb8.4-HspX (EAMMH) and rAd-mIL-28B together thrice or primed with Mycobacterium bovis bacillus Calmette-Gue'rin (BCG) and boosted by EAMMH and rAd-mIL-28B twice. At last the immune responses were evaluated, and the mice primed with BCG and boosted by subunit vaccines were challenged with virulent Mycobacterium tuberculosis H37Rv to evaluate the protective efficacy. The results showed that rAd-mIL-28B treatment significantly down-regulated the frequency of Tregs at 4 weeks after the last immunization but did not increase the Th1-type immune responses. Moreover, in the regimen of BCG priming and EAMMH boosting, rAd-mIL-28B treatment did not increase the antigen-specific cellular and humoral immune responses, and consequently did not reduce the bacteria load following H37Rv challenge. Instead, it induced more serious pathology reaction. In conclusion, IL-28B down-regulates Tregs following EAMMH vaccination but does not improve the protective immune responses.

Multi-Stage Tuberculosis Subunit Vaccine Candidate LT69 Provides High Protection against Mycobacterium tuberculosis Infection in Mice.

Effective tuberculosis (TB) vaccine should target tubercle bacilli with various metabolic states and confer long-term protective immunity. In this study, we constructed a novel multi-stage TB subunit vaccine based on fusion protein ESAT6-Ag85B-MPT64(190-198)-Mtb8.4-HspX (LT69 for short) which combined early expressed antigens and latency-associated antigen. The fusion protein was mixed with an adjuvant being composed of N, N'-dimethyl-N, N'-dioctadecylammonium bromide (DDA) and polyriboinosinic polyribocytidylic acid (PolyI:C) to construct subunit vaccine, whose immunogenicity and protective ability were evaluated in C57BL/6 mice. The results showed that LT69 had strong immunogenicity and high protective effect against Mycobacterium tuberculosis (M. tuberculosis) H37Rv aerosol challenge. Low-dose (2 µg) of LT69 generated long-term immune memory responses and provided effective protection, which was even higher than traditional vaccine BCG did at 30 weeks post the last vaccination. In conclusion, multistage subunit vaccine LT69 showed high and long-term protection against M. tuberculosis infection in mice, whose effect could be enhanced by using a relative low dosage of antigen.

Mycobacterium tuberculosis Erdman infection of rhesus macaques of Chinese origin.

Continuous high global tuberculosis (TB) mortality rates and variable vaccine efficacy of mycobacterium Bacille Calmette-Guérin (BCG) emphasize the need for improved vaccines and drugs against TB, which require clinically relevant animal models for evaluation. We infected a total of 24 Chinese rhesus macaques with varying doses (CFU of 25, 100 and 500) of Mycobacterium tuberculosis (M.tb) Erdman strain via bronchoscopy. Regardless of the M.tb doses, all animals were infected successfully with minor differences in clinical progression; as evidenced by clinical manifestations, laboratory analyses, bacterial burden in infected tissues and histopathology evaluations. Rhesus macaques of Chinese origin are highly susceptible to infection with M.tb Erdman strain and develop acute TB disease, which is similar to that in humans. Pathologically, Chinese rhesus macaques recapitulated the complete spectrum of granulomatous lesions seen in human TB disease. These data indicate that low-dose infection of rhesus macaques of Chinese origin is a suitable model for acute M.tb infection.

Subunit vaccine consisting of multi-stage antigens has high protective efficacy against Mycobacterium tuberculosis infection in mice.

To search for more effective tuberculosis (TB) subunit vaccines, antigens expressed in different growth stages of Mycobacterium tuberculosis (M. tuberculosis), such as RpfE (Rv2450c) produced in the stage of resuscitation, Mtb10.4 (Rv0288), Mtb8.4 (Rv1174c), ESAT6 (Rv3875), Ag85B (Rv1886c) mainly secreted by replicating bacilli, and HspX (Rv2031c) highly expressed in dormant bacilli, were selected to construct six fusion proteins: ESAT6-Ag85B-MPT64190-198-Mtb8.4 (EAMM), Mtb10.4-HspX (MH), ESAT6-Mtb8.4, Mtb10.4-Ag85B, ESAT6-Ag85B, and ESAT6-RpfE. The six fusion proteins were separately emulsified in an adjuvant composed of N,N'-dimethyl-N, N'-dioctadecylammonium bromide (DDA), polyribocytidylic acid (poly I:C) and gelatin to construct subunit vaccines, and their protective effects against M. tuberculosis infection were evaluated in C57BL/6 mice. Furthermore, the boosting effects of EAMM and MH in the adjuvant of DDA plus trehalose 6,6'-dimycolate (TDM) on BCG-induced immunity were also evaluated. It was found that the six proteins were stably produced in E. coli and successfully purified by chromatography. Among them, EAMM presented the most effective protection against M. tuberculosis. Interestingly, the mice that received EAMM+MH had significantly lower bacterial counts in the lungs and spleens than the single protein vaccinated groups, and had the same effect as those that received BCG. In addition, EAMM and MH could improve BCG-primed protective efficacy against M. tuberculosis infection in mice. In conclusion, the combination of EAMM and MH containing antigens from both replicating and dormant stages of the bacilli could induce robust immunity against M. tuberculosis infection in mice and may serve as promising subunit vaccine candidate.

Immunotherapy using IL-2 and GM-CSF is a potential treatment for multidrug-resistant Mycobacterium tuberculosis.

This study investigated the therapeutic effects of interleukin (IL)-2 and granulocyte-macrophage colony-stimulating factor (GM-CSF) co-administrated with antibacterial agents isoniazid (INH) and rifampin (RIF) to treat a mouse model of tuberculosis (TB) infection. A drug-susceptible TB strain, H37Rv was used to infect mice and the effectiveness of IL-2 and GM-CSF was initially evaluated based on survival rate, bacterial counts in lungs and spleens and the pathological condition of the lungs. Next, the therapeutic effect of the immunotherapy regimen was assessed in multidrug-resistant strain OB35-infected mice. In the H37Rv infection model, IL-2 and GM-CSF monotherapies reduced bacterial numbers in the lungs by 0.82 (P<0.01) and 0.58 (P<0.05) lg colony-forming units (CFU), respectively, and in the spleens by 1.42 (P<0.01) and 1.22 (P<0.01) lg CFU, respectively, compared with the untreated group. Mice receiving immunotherapy developed fewer lesions in the lungs compared with mice receiving antibacterial therapy alone. In the OB35 infection model, immunotherapy with either cytokine resulted in a significant reduction of bacterial load in the lungs and spleens and less severe lesions in the lungs compared with the untreated or antibacterial therapy treated mice. Notably, mice receiving immunotherapy with both cytokines had a 30% survival rate which was higher than that in other treated groups, and had significantly less CFUs in the lungs and spleens (1.02 and 1.34 lg CFU) compared with antibacterial therapy alone (P<0.01). This study demonstrated that immunotherapy with both IL-2 and GM-CSF may be useful to treat multidrug resistant tuberculosis (MDR-TB).

Azithromycin inhibits neutrophil accumulation in airways by affecting interleukin-17 downstream signals.

BACKGROUND: Azithromycin can reduce neutrophil accumulation in neutrophilic pulmonary diseases. However, the precise mechanism behind this action remains unknown. Our experiment assessed whether azithromycin inhibits neutrophil accumulation in the airways by affecting interleukin-17 (IL-17) downstream signals. METHODS: Mice were pretreated with azithromycin before murine IL-17A (mIL-17) stimulation. After the mIL-17 stimulation, the levels of six neutrophil-mobilizing cytokines were determined by enzyme-linked immunosorbent assay (ELISA) tests in bronchoalveolar lavage (BAL) fluid; IL-6, CXC chemokine ligand-1 (CXCL-1), CXCL-5, macrophage inflammatory protein-2 (MIP-2), granulocyte colony-stimulating factor (G-CSF), and granulocyte macrophage colony-stimulating factor (GM-CSF). The number of neutrophils in BAL fluid were evaluated by cytospin preparations. RESULTS: (1) Azithromycin pretreatment significantly inhibited both the release of three neutrophil-mobilizing cytokines (MIP-2, CXCL-5 and GM-CSF) and the accumulation of neutrophils in airways caused by mIL-17 stimulation. (2) The levels of three neutrophil-mobilizing cytokines (IL-6, MIP-2 and GM-CSF) were positively correlated with the numbers of neutrophil in BAL fluid. CONCLUSIONS: Azithromycin can inhibit neutrophil accumulation in the airways by affecting IL-17 downstream signals. This finding suggests that macrolide antibiotic application might be useful in prevention of neutrophilic pulmonary diseases characterized by high levels of IL-17.

Neonatal revaccination with Bacillus Calmette-Guérin elicits improved, early protection against Mycobacterium tuberculosis in mice.

The protective effect of revaccination with Mycobacterium bovis Bacillus Calmette-Guérin (BCG) against Mycobacterium tuberculosis in animals is controversial. To investigate whether revaccination of neonates with BCG could improve the protection against M. tuberculosis, C57BL/6 neonates were vaccinated with BCG on day 1, or on days 1, 7, and 14, and the mice at eight weeks of age were challenged with M. tuberculosis and monitored for survival. The M. tuberculosis burden in their livers and lungs, the pathological changes in the lungs, their splenic T cell responses and serum cytokines were examined longitudinally post-challenge. BCG vaccination significantly prevented the M. tuberculosis-related mouse death and reduced the burden of M. tuberculosis in the liver and lungs, and lung damage in the mice, particularly at early stage of the pathogenic process in the BCG-revaccinated mice. However, the BCG revaccination-induced protection waned over time. BCG vaccination did not significantly modulate the levels of serum IFN-γ and the frequency of splenic PPD-reactive IFN-γ-secreting T cells, but significantly decreased the levels of serum TNF-α and PPD-specific IL-4 responses at 3 weeks post challenge. Taken together, these data suggest that revaccination of neonates with BCG elicits improved, early protection against M. tuberculosis by modulating cytokine responses in adult mice.

[Establishment and evaluation of a Chinese rhesus model of tuberculosis].

OBJECTIVE: To establish and evaluate the Chinese rhesus model of tuberculosis. METHODS: Twelve Chinese rhesus macaques, randomly divided into 3 groups, were inoculated with 2 different doses of Mycobacterium tuberculosis H(37) Rv strain via both bronchoscopic and intratracheal instillation into the lungs. Clinical observation and laboratory examinations were performed, including erythrocyte sedimentation rate, C-reactive protein, tuberculin skin test and X-ray examination. Histopathological assessments were performed in the 24th week postinfection. Statistical analysis was performed by ANOVA in the 3 groups. RESULTS: After infection all the animals manifested fever, weight lose, lack of appetite, coughing and other symptoms of tuberculosis. The temperature gradually increased and reached a peak [(40.1 ± 0.2)°C] at the 8th week postinfection. The weight decreased significantly at 24th week postinfection (-5.5 ± 5.6)%. Erythrocyte sedimentation rate elevated significantly at the 6th to 8th week postinfection (36 ± 40) mm/1 h. C-reactive protein was significantly increased at the 6th to 24th week after infection (75.8 ± 49.8) mg/L. The positive rate of tuberculin skin test was 100%. In Group I (bronchoscopic instillation, 20 CFU) the disease developed slowly, and the main manifestation of chest X-ray was patchy shadows. In group II (bronchoscopic instillation, 100 CFU) and group III (intratracheal instillation, 100 CFU) the disease developed rapidly, and the main manifestation of chest X-ray was patchy and nodular lesions during the 4th to the 12th week postinfection, but became large patchy and consolidation lesions during the 12th to the 24th week postinfection. Tuberculosis granuloma and caseous necrosis, similar to the pathological changes of human tuberculosis, were found in the lungs, mediastinal lymph nodes, kidney and spleen. The results of acid-fast stain were positive. The most serious pathological manifestations were observed in group II, followed by group III and group I. The highest bacterial load of the right lung was seen in group II, followed by group I and group III. CONCLUSIONS: A chinese rhesus model of tuberculosis was successfully developed via both bronchoscopic and intratracheal instillation. Their clinical manifestations, disease progression and pathological changes were similar to human primary tuberculosis and hematogenous disseminated tuberculosis.

M. tuberculosis H37Rv infection of Chinese rhesus macaques.

Mycobacterium tuberculosis is the most common communicable infectious disease worldwide and the top killer of human immunodeficiency virus (HIV)-infected people. Because of common dual HIV and M. tuberculosis infections, the emergence of multidrug-resistant M. tuberculosis strains, the lack of effective vaccination, the morbidity, and the mortality of M. tuberculosis infection are increasing sharply. Therefore, there is an urgent need for vaccine and drug development against M. tuberculosis infection. These require appropriate animal models that closely resemble human disease. To this end, we infected Chinese rhesus macaques with the M. tuberculosis H37Rv strain. Bronchoscopy was used to inoculate nine monkeys with different doses of M. tuberculosis H37Rv strain. Regardless of the M. tuberculosis dose, all monkeys were infected successfully. This was shown by clinical, laboratory, and histopathology assessments. Among nine infected monkeys, six developed acute rapid progressive tuberculosis and the remaining animals mirrored early-stage chronic disease. These data, taken together, demonstrate that Chinese rhesus macaques are highly susceptible to M. tuberculosis infection and develop similar manifestations of disease that are seen in humans. This model affords new opportunities for studies of M. tuberculosis disease pathology and therapeutics.

In vitro and in vivo activities of a new lead compound I2906 against Mycobacterium tuberculosis.

BACKGROUND: Due to the long duration of treatment and the emergence of multidrug-resistant strains, new antitubercular agents are urgently needed. I2906, as a novel lead, was screened and tested for efficacy in vitro and in vivo. METHODS: To determine the efficacy of I2906,the minimum inhibitory concentrations against Mycobacterium tuberculosis and cytotoxicity were tested, and its in vivo activities were assessed by administering it to mice infected with M. tuberculosis H37Rv or multidrug-resistant strain. RESULTS: Under in vitro conditions, I2906 showed excellent antimycobacterial activities and low cytotoxicity. In a murine model infected with M. tuberculosis H37Rv, the reductions on bacterial loads of both lungs and spleen were statistically significant (p < 0.05) between I2906-treated mice and untreated controls after 4 weeks. Further, the colony-forming unit counts in the lungs were dramatically lower (p < 0.05) than that of isoniazid-treated mice by the addition of I2906 after 8 weeks. Moreover, survival rate was increased by I2906 treatment. For multidrug-resistant strain infection, bacterial counts were reduced significantly in the lungs and spleen due to I2906 treatment in comparison with data from untreated controls (p < 0.05). CONCLUSIONS: I2906 displayed potential antimicrobial activities against M. tuberculosis H37Rv and drug-resistant strains in vitro and in vivo, and could improve efficacy of isoniazid in vivo.

Fusion protein Ag85B-MPT64(190-198)-Mtb8.4 has higher immunogenicity than Ag85B with capacity to boost BCG-primed immunity against Mycobacterium tuberculosis in mice.

Tuberculosis (TB) remains a major infectious disease worldwide despite chemotherapy and BCG vaccine. The efficacy of the current TB vaccine BCG varies from 0 to 80%. New vaccines that have better protection than BCG or have the capability to boost BCG-primed immunity are urgently needed. We have previously constructed a fusion protein Ag85B-MPT64(190-198)-Mtb8.4 (AMM). In this study, we investigated the immunogenicity of the fusion protein AMM in a novel adjuvant of dimethyl-dioctyldecyl ammonium bromide and BCG polysaccharide nucleic acid (DDA-BCG PSN), and its capacity to boost BCG-primed immunity. The anti-Ag85B antibodies IgG1 and IgG2a were determined using ELISA and the number of spleen cells secreting IFN-gamma was determined by ELISPOT. In addition, the ability of the subunit vaccine AMM to boost BCG-primed immunity against Mycobacterium tuberculosis was analyzed. The fusion protein AMM induced more effective humoral and cell-mediated immune responses in mice than Ag85B alone. Mice primed with BCG vaccination followed by boosting with AMM produced a stronger immune response and afforded a better protection against M. tuberculosis infection than mice immunized with BCG alone or BCG priming followed by boosting with Ag85B. These findings suggest that AMM is a promising candidate subunit vaccine to enhance the protective efficiency of BCG.

Immunogenicity, safety, and protective efficacy of an inactivated SARS-associated coronavirus vaccine in rhesus monkeys.

An inactivated vaccine for severe acute respiratory syndrome (SARS)-associated coronavirus (SARS-CoV) was evaluated in rhesus monkeys. The monkeys were inoculated intramuscularly (i.m.) with 0.5, 5, 50, or 5000 microg of vaccine, or PBS as control, and boosted on day 7. After 3 weeks, they were challenged with the NS-1 strain of SARS-CoV. The humoral and mucosal immune responses, clinical signs, chemical indices and viremia were monitored following the immunization and challenge. The control animals who received PBS developed atypical SAR-CoV infection after viral challenge, according to clinical, virological and pathological findings. No systematic side effects were observed in vaccinated animals post-immunization, even in at the high dose of 5000 microg. The 50 microg dosage of vaccine elicited SARS-CoV specific immune responses against viral infection as compared to the partial immunity elicited by 0.5 and 5 microg doses. The results show that this inactivated vaccine can induce effective concomitant humoral and mucosal immunity against SARS-CoV infection, is safe in monkeys, and the vaccine maybe a good candidate for clinical trials.