In vitro model for the assessment of human immune responses to subunit RSV vaccines

Abstract

Respiratory syncytial virus (RSV) is the single most important cause of serious lower respiratory tract disease in infants and young children worldwide and a high priority for vaccine development. Despite over 50 years of research, however, no vaccine is yet available. One block to vaccine development is an incomplete understanding of the aberrant memory response to the formalin-inactivated RSV vaccine (FI-RSV) given to children in the 1960s. This vaccine caused enhanced respiratory disease (ERD) with later natural RSV infection. Concern that any non-live virus vaccine may also cause ERD has blocked development of subunit vaccines for young children. A number of animal FI-RSV studies suggest various immune mechanisms behind ERD. However, other than limited data from the original FI-RSV trial, there is no information on the human ERD-associated responses. An in vitro model with human blood specimens may shed light on the immune memory responses likely responsible for ERD. Memory T cell responses to an antigen are guided by the innate responses, particularly dendritic cells that present an antigen in conjunction with co-stimulatory molecules and cytokine signaling. Our in vitro model involves human monocyte derived dendritic cells (moDC) and allogenic T cell cultures to assess innate responses that direct T cell responses. Using this model, we evaluated human responses to live RSV, FI-RSV, and subunit RSV G vaccines (G-containing virus-like particles, G-VLP). Similar to findings in animal studies, FI-RSV induced prominent Th2/Th17-biased responses with deficient type-1 responses compared to live virus. Responses to G-VLPs were similar to live virus, i.e. biased towards a Th1 and not a Th2/Th17. Also mutating CX3C motif in G gave a more pronounced moDC responses associated with type-1 T cell responses. This in vitro model identifies human immune responses likely associated with ERD and provides another preclinical tool to assess the safety of RSV vaccines.

Functional Features of the Respiratory Syncytial Virus G Protein

“…In a study of human peripheral blood mononuclear cells exposed to RSV-infected A549 cells, the CX3C motif in G was implicated in the downregulation of the type I and III interferon responses in monocytes and plasmacytoid dendritic cells and interferon gamma in T cells [ 139 ]. In an in vitro model of the human response to RSV antigens, the Th1 directing dendritic cell response to RSV or G was increased when the CX3C motif was mutated to CX4C in the virus or in G expressed in VLPs, suggesting that this motif participates in inducing a more Th2-biased immune response, as reported in studies in mice [ 130 , 140 ]. The G protein has also been shown to inhibit the TLR3/TLR4 induction of INF-β in monocyte-derived dendritic cells [ 141 ].…”

Effect of Infant RSV Infection on Memory T Cell Responses at Age 2-3 Years

“…RSV A2001/3-12 (RSV 3-12) was propagated in HEp-2 cells and purified by ultracentrifugation through a 20% sucrose cushion as previously described ( 21 , 22 ). Briefly, HEp-2 cells were maintained in MEM media (Gibco, Thermo Fisher Scientific, Massachusetts, USA) with 5% FBS (HyClone, Thermo Fisher Scientific, Massachusetts, USA), and cells were infected with a low passage stock RSV 3-12 virus at multiplicity of infection (MOI) = 0.01 TCID 50 /ml.…”

Respiratory Viruses and Virus-like Particle Vaccine Development: How Far Have We Advanced?

“…When human monocyte-derived dendritic cells were stimulated with RSV G VLPs in vitro , Th1-dominant immunity was detected. Contrastingly, stimulating these cells with FI-RSV vaccines elicited a Th2/Th17-biased immune response with depreciated non-interferon antiviral immune responses [ 110 ]. Consistent with this notion, identical findings were reported in nasal wash samples of RSV-infected infants, which were characterized by Th2/Th17 dominance [ 111 ].…”