CHIKV viremia in blood peaks 1 to 2 days post infection of Rhesus macaques.

<p>CHIKV load in plasma and PBMC was quantified by qRT-PCR using virus specific primers and probes. A and C) Virus was detected in RNA prepared from 10 µl of plasma using ZR Viral RNA extraction kit (Zymol). B and D) Virus was detected in 0.1 µg of total RNA prepared with Trizol from 1×10⁶ PBMC.</p

Macrophage and dendritic cell population changes following CHIKV infection observed in adult animals are reduced in aged Rhesus macaques.

<p>Measurement of dendritic cell and monocyte/macrophage populations following CHIKV infection. PBMC were stained with antibodies directed against CD3, CD11c, CD14, CD20, CD123 and HLA-DR (shown in panel A) and subdivided into plasmacytoid DCs (B); myeloid DCs (C); non-P/non-M DC's (D); monocyte/macrophages (E). Fold increase in numbers of cells was calculated. N = 6 for adult and N = 2 for aged animals.</p

Aged Rhesus macaques have a delayed and lower B cell proliferative response following CHIKV infection.

<p>Measurement of B-cell proliferative burst following viral infection. PBMC were stained with antibodies directed against CD20, CD27, IgD and Ki67 (as shown in panel A) and subdivided into (B & C) Marginal Zone (MZ)-like B cells and (D & E) memory B cells. Fold increase in number of Ki67+ B cells was calculated at each time point. N = 6 for adult and N = 2 for aged animals.</p

Plasma from aged Rhesus macaques have lower levels of bioactive IFN compared to adult animals.

<p>Plasma samples from adult (Animal #22855, 21551, 20374) and aged (Animal #20969, 22163, 20994) RM at 3 days post infection with CHIKV were serially diluted and used to stimulate Rhesus fibroblasts for 24 hours. Recombinant universal Type-1 IFN stimulated cells (0.1, 1, 10 units/ml) were used as positive controls and untreated cells were used as a negative control. Then total RNA was prepared with Trizol and IFN stimulated genes Mx1 (A) and ISG56 (B) were quantified by qRT-PCR using gene-specific primers. Fold change is determined as the ratio of gene expression treated vs. untreated control samples.</p

Magnitude and breadth of anti-CHIKV T cell responses is reduced in aged Rhesus macaques.

<p>IFN-γ ELISPOT assays were used to quantify anti-CHIKV T cell responses in peripheral blood lymphocytes at 35 dpi in adult and aged animals (n = 4). In triplicate wells, PBMC (2×10⁵) were incubated overnight with overlapping peptides that corresponded to each of the 9 CHIKV proteins (NSP-1-4, Core, E1-3 and 6k). PMA/ionomycin stimulation was used as a positive control and medium plus DMSO was used as a negative control. A) Representative wells from IFN-γ ELISPOT assay performed with PBMC from adult and aged animals. B) Average cumulative anti-CHIKV responses to all viral proteins were compared for adult vs. aged Rhesus macaques (n = 4). C) Average response to individual CHIKV proteins (n = 4).</p

Therapeutic administration of a recombinant human monoclonal antibody reduces the severity of chikungunya virus disease in rhesus macaques

<div><p>Chikungunya virus (CHIKV) is a mosquito-borne virus that causes a febrile syndrome in humans associated with acute and chronic debilitating joint and muscle pain. Currently no licensed vaccines or therapeutics are available to prevent or treat CHIKV infections. We recently isolated a panel of potently neutralizing human monoclonal antibodies (mAbs), one (4N12) of which exhibited prophylactic and post-exposure therapeutic activity against CHIKV in immunocompromised mice. Here, we describe the development of an engineered CHIKV mAb, designated SVIR001, that has similar antigen binding and neutralization profiles to its parent, 4N12. Because therapeutic administration of SVIR001 in immunocompetent mice significantly reduced viral load in joint tissues, we evaluated its efficacy in a rhesus macaque model of CHIKV infection. Rhesus macaques that were treated after infection with SVIR001 showed rapid elimination of viremia and less severe joint infiltration and disease compared to animals treated with SVIR002, an isotype control mAb. SVIR001 reduced viral burden at the site of infection and at distant sites and also diminished the numbers of activated innate immune cells and levels of pro-inflammatory cytokines and chemokines. SVIR001 therapy; however, did not substantively reduce the induction of CHIKV-specific B or T cell responses. Collectively, these results show promising therapeutic activity of a human anti-CHIKV mAb in rhesus macaques and provide proof-of-principle for its possible use in humans to treat active CHIKV infections.</p></div