Chikungunya Virus Strains Show Lineage-Specific Variations in Virulence and Cross-Protective Ability in Murine and Nonhuman Primate Models

Chikungunya virus (CHIKV) is a reemerging arbovirus capable of causing explosive outbreaks of febrile illness, polyarthritis, and polyarthralgia, inflicting severe morbidity on affected populations. CHIKV can be genetically classified into 3 major lineages: West African (WA); East, Central, and South African (ECSA); Indian Ocean (IOL); and Asian. Additionally, the Indian Ocean (IOL) sublineage emerged within the ECSA clade and the Asian/American sublineage emerged within the Asian clade. While differences in epidemiological and pathological characteristics among outbreaks involving different CHIKV lineages and sublineages have been suggested, few targeted investigations comparing lineage virulence levels have been reported. We compared the virulence levels of CHIKV isolates representing all major lineages and sublineages in the type I interferon receptor-knockout A129 mouse model and found lineage-specific differences in virulence. We also evaluated the cross-protective efficacy of the IOL-derived, live-attenuated vaccine strain CHIKV/IRESv1 against the Asian/American CHIKV isolate YO123223 in both murine and nonhuman primate models, as well as the WA strain SH2830 in a murine model. The CHIKV/IRES vaccine provided protection both in mice and in nonhuman primate cohorts against Caribbean strain challenge and protected mice against WA challenge. Taken together, our data suggest that Asian/American CHIKV strains are less virulent than those in the Asian, ECSA, and WA lineages and that despite differences in virulence, IOL-based vaccine strains offer robust cross-protection against strains from other lineages. Further research is needed to elucidate the genetic basis for variation in CHIKV virulence in the A129 mouse model and to corroborate this variation with human pathogenicity

Immunologic Characterization of a Rhesus Macaque H1N1 Challenge Model for Candidate Influenza Virus Vaccine Assessment

Despite the availability of annually formulated vaccines, influenza virus infection remains a worldwide public health burden. Therefore, it is important to develop preclinical challenge models that enable the evaluation of vaccine candidates while elucidating mechanisms of protection. Here, we report that naive rhesus macaques challenged with 2009 pandemic H1N1 (pH1N1) influenza virus do not develop observable clinical symptoms of disease but develop a subclinical biphasic fever on days 1 and 5 to 6 postchallenge. Whole blood microarray analysis further revealed that interferon activity was associated with fever. We then tested whether type I interferon activity in the blood is a correlate of vaccine efficacy. The animals immunized with candidate vaccines carrying hemagglutinin (HA) or nucleoprotein (NP) exhibited significantly reduced interferon activity on days 5 to 6 postchallenge. Supported by cellular and serological data, we conclude that blood interferon activity is a prominent marker that provides a convenient metric of influenza virus vaccine efficacy in the subclinical rhesus macaque model

Core body temperature in vaccinated and unvaccinated primates after VEEV challenge.

<p>Physiological response of vaccinated cynomolgus macaques to VEEV challenge measured as changes in core body temperature for animals vaccinated with saline (red) or 68U201/IRESv1 (blue). Data were time-matched to pre-exposure values from each animal for derivation of relative changes. Significant changes in individual values were identified by divergence of more than 1.5 standard deviations from the pre-exposure value collected from the individual animal. Inset graph shows the difference in fever intensity among vaccination groups. Analysis (t-test) of vaccination group differences in fever intensity (mean ± SD) showed significant differences: saline (2.420 ± 1.143°C) and 68U201/IRESv1 (0.813 ± 0.348°C) with P = 0.012.</p

Viremia following aerosol exposure in vaccinated primates.

<p>Sera were titrated on Vero cells to determine levels of viremia for 3 days after 68U201 VEEV exposure. Individual points are shown for each vaccinated (triangle, n = 6) or unvaccinated (square, n = 4) NHP. The limit of detection was 10 pfu/ml. Serum samples with undetectable viremia are shown below this limit.</p

Neutralizing antibody titers in response to vaccination and challenge.

<p>Individual sera was tested for their ability to neutralize strain 68U201 VEEV at the indicated timepoints. Average PRNT₈₀ values are shown. Values less than 20 are considered negative. Bars denote standard error.</p