Inactivated Viral Vaccine BBV87 Protects Against Chikungunya Virus Challenge in a Non-Human Primate Model

Abstract

Chikungunya virus (CHIKV) is an alphavirus transmitted by mosquitos that poses a threat to global public health and for which there is an urgent need for widespread access to globally licensed vaccines. Here, we demonstrate that an inactivated CHIKV vaccine (BBV87) protects against systemic infection with CHIKV in a non-human primate (NHP) challenge model. Groups of five cynomolgus macaques received two doses of 20 µg BBV87 vaccine or saline alone (28 days apart). Twenty-eight days after the second immunisation, all animals were challenged with CHIKV. All controls were productively infected with detectable viremia and pathological responses following challenge, including altered thermoregulation, haematological and cytokine changes. Critically, the histopathological analysis of finger joints identified areas of inflammation in the synovium. By contrast vaccinated macaques had no detectable viremia and none of the pathological changes were reported in control animals. This study demonstrates that a 20 µg dose of BBV87 vaccine confers robust protection in vivo, both on the acquisition of infection and pathology.

Keywords: chikungunya virus; immunity; non-human primate; pathogenesis; vaccine.

Figure 1

Study outline showing vaccination and bleed intervals for both vaccinated and control animals.

Figure 2

Anti-CHIKV antibody responses: (a) IgM antibody responses detected by ELISA following vaccination with BBV87 (blue) or control (red), and subsequent challenge with virus. The horizontal dotted lines denote the assay manufacturer’s interpretation of results criteria. Below the lower dotted line at Ratio 0.8 is considered negative, between the dotted lines (0.8–1.1 Ratio) is interpreted as equivocal, and >1.1 Ratio as positive. (b) IgG detected by ELISA following vaccination with BBV87 (blue) or control (red), and subsequent challenge with virus. The horizontal dotted lines denote the assay manufacturer’s interpretation of results criteria. Below the lower dotted line at 16 RU/mL is considered negative, between the dotted lines (16–22 RU/mL) is interpreted as equivocal, and >22 RU/mL positive. (c) In vitro neutralisation titres of vaccinated and control animals post-first and -second vaccination, and at time of challenge. (d) In vitro neutralisation of each vaccinated individual over time. LOD denotes limit of detection of neutralisation assay.

Figure 3

(a) CHIKV RNA as measured by RT-qPCR in plasma of macaques that had been immunised with BBV87 (blue) or saline prior to virus challenge (red). Lower limit of detection (LLOD) denoted by dotted line. (b) CHIKV infectious units/mL in serum of vaccinated and control animals two days post-challenge (mean ± SEM). Negative samples were assigned an arbitrary value of 2, nd = not detected. (c) CHIKV RNA in each individual animal in (left to right): left brachial lymph node (BLN(L)), right brachial lymph node (BLN(R)), mesenteric lymph node (MLN) and spleen expressed as CHIKV RNA International Units (IU)/100 ng total RNA.

Figure 4

Temperature profiles of BBV87-immunised (blue) and control (red) macaques before and after CHIKV challenge at time 0 (represented by dotted line). Lines represent LOWESS (Locally Weighted Scatterplot Smoothing) smoothed means of the groups, and points represent individual readings. Asterisk denotes time of significant increase in temperature in control group compared to vaccinated group from 24 to 84 h post-challenge (p < 0.05).

Figure 5

Haematological changes observed in BBV87-immunised (blue circles with dashed line) and controls (red squares with solid line) following challenge with CHIKV. Means ± SEM.

Figure 6

Representative images of pathology present within the finger joints of non-vaccinated (a–e) and vaccinated (f,g) cynomolgus macaques at termination (14–15 days post-challenge). (a) Lymphocytic and plasma cell infiltrate within synovium (scale bar = 200 µm), (b) higher magnification of boxed area of joint articulating surfaces with lymphocytes and plasma cells widely distributed within the synovium indicating early events in the development of an arthritic response (scale bar = 50 µm). (c–e) Lymphocytic and plasma cell inflammatory infiltrates present within skeletal muscle indicative of viral aetiology ((c): scale bar = 500 µm and boxed area shown in (d), scale bar = 50 µm, (e) scale bar = 500 µm). (f) Joint from vaccinated animal with no inflammatory pathology present (scale bar = 500 µm). (g) higher magnification of boxed areas of joint articulating surfaces showing a normal synovium (scale bar = 100 µm. (h) Points represent the scores for each individual animal; for each pathology parameter, lines represent mean ± SEM, (i) schematic representation (finger and location) of inflammatory changes in the right-hand knuckle or finger joints from vaccinated (s50, left hand image) and control animals (right hand image).

Figure 7

(a) IL-1ra, (b) MCP-1 and (c) CRP levels post-challenge in vaccinated (blue with dashed lines) and control (red with solid lines) animals plotted as mean ± SEM (left panels) and as individual plots (right panels). Statistical significance determined by Anova test with Post-hoc Bonferroni (*** p < 0.01, ** p < 0.05).