Viral vector vaccine Mechanism of action Flashcards
What is the route of administration for an rVSV vaccine and which cells are primarily infected at the injection site?
The rVSV vaccine is typically administered intramuscularly. At the injection site, both myocytes and resident antigen‐presenting cells (APCs) — including dendritic cells (DCs) and macrophages — are initially infected.
How does the modified rVSV vaccine particle enter host cells, and what role does the inserted antigen spike play?
The vaccine particle enters cells via receptor‐mediated endocytosis. The inserted antigen spike protein, displayed on the viral envelope, may interact with its cognate receptor (e.g., ACE2 in the context of SARS‑CoV‑2), facilitating viral entry and ensuring robust antigen expression.
Describe the replication cycle of the rVSV vaccine and how it contributes to antigen expression.
Once inside the cytoplasm, the attenuated rVSV replicates using its RNA-dependent RNA polymerase. The inserted spike gene is transcribed under native VSV promoters, resulting in high levels of spike protein synthesis. This protein is incorporated into new virions and expressed on the plasma membrane of infected cells, thereby amplifying the antigen load.
How is the replication of the rVSV vaccine controlled to ensure safety while still achieving an effective immune response?
The virus is attenuated through targeted mutations (for instance, in the matrix protein) which reduce pathogenicity while allowing controlled replication. This balance enables sufficient antigen production without causing disease.
What pathogen-associated molecular patterns (PAMPs) are generated during rVSV replication, and which cellular receptors recognize these patterns?
Viral replication generates PAMPs such as single-stranded RNA (ssRNA) and double-stranded RNA (dsRNA) intermediates. These are recognized by endosomal Toll-like receptors (TLR7 for ssRNA and TLR3 for dsRNA) and cytosolic sensors like RIG-I and MDA5.
Explain the intracellular signaling cascades initiated by PRR engagement upon rVSV infection.
TLR7 engagement activates the MyD88-dependent pathway, leading to IRAK kinase activation and NF-κB translocation. Simultaneously, RIG-I/MDA5 activation recruits MAVS, which via TBK1 and IKKε leads to phosphorylation of IRF3. These cascades culminate in the production of type I interferons (IFN‑α and IFN‑β) and pro-inflammatory cytokines (IL‑6, TNF‑α, IL‑1β).
Which cytokines are secreted early during the innate immune response to an rVSV vaccine, and what are their roles?
Type I interferons (IFN‑α, IFN‑β) are secreted to establish an antiviral state and enhance antigen presentation. Additionally, pro-inflammatory cytokines such as IL‑6, TNF‑α, and IL‑1β are released, along with chemokines like CXCL10, which recruit immune cells to the site of vaccination.
How do dendritic cells (DCs) process antigens from the rVSV vaccine, and what are the key changes they undergo upon maturation?
DCs endocytose viral particles and soluble spike proteins. Inside the endosomes, the spike protein is degraded into peptide fragments. PRR engagement and cytokine signals (e.g., type I IFNs, IL‑12) induce DC maturation, which is characterized by upregulation of MHC class II and costimulatory molecules (CD80, CD86, CD40), as well as migration to draining lymph nodes.
In what ways do dendritic cells prime T cells following rVSV vaccination?
In the draining lymph nodes, mature DCs present spike-derived peptides on MHC class II to CD4+ helper T cells and, via cross-presentation on MHC class I, to CD8+ cytotoxic T cells. Costimulatory signals (e.g., CD80/CD86 binding CD28, and CD40 binding CD40L) further facilitate robust T cell activation.
What cytokines and receptor interactions are critical for T cell activation and differentiation in response to the rVSV vaccine?
IL‑12 promotes Th1 differentiation, while type I IFNs and IL‑2 support CTL activation and proliferation. Additionally, costimulatory interactions—CD80/CD86 on APCs with CD28 on T cells and CD40 on APCs with CD40L on T cells—are essential for full T cell activation. T cell receptors (TCRs) recognize peptide-MHC complexes, triggering specific T cell responses.
How are B cells activated following rVSV vaccination, and what processes lead to the production of high-affinity antibodies?
B cells bind the native conformation of the spike protein via their B cell receptor (BCR), internalize and process the antigen, and present peptides on MHC class II. Interaction with T follicular helper (Tfh) cells (via IL‑21, IL‑4, and CD40L–CD40 interaction) in germinal centers drives B cell proliferation, somatic hypermutation, and class-switch recombination, resulting in the generation of plasma cells that secrete high-affinity neutralizing antibodies (IgG, and IgA in mucosal sites).
What role does cross-presentation play in the immune response elicited by an rVSV vaccine?
Cross-presentation by certain dendritic cell subsets enables extracellular spike antigens to be presented on MHC class I molecules, thereby priming CD8+ cytotoxic T lymphocytes (CTLs) that are crucial for targeting and lysing infected cells.
How is long-term immunity established following rVSV vaccination?
Long-term immunity is achieved through the formation of memory T and B cells. Memory CD4+ and CD8+ T cells, along with memory B cells, persist and allow for rapid, robust responses upon subsequent exposure to the pathogen, ensuring durable protection.
Summarize the key cytokines involved in the rVSV vaccine response and their immunological roles.
Type I Interferons (IFN‑α, IFN‑β): Establish an antiviral state and enhance antigen presentation. IL‑12: Drives Th1 differentiation and supports CTL activation. IL‑6, TNF‑α, IL‑1β: Mediate local inflammation and immune cell recruitment. IL‑2 and IFN‑γ: Promote T cell proliferation and reinforce cytotoxic functions. IL‑21: Essential for B cell maturation and the affinity maturation of antibodies.
Identify the receptor molecules and costimulatory interactions essential for initiating the immune response to the rVSV vaccine.
Pattern Recognition Receptors: Endosomal TLR3 and TLR7 detect viral RNA, while cytosolic receptors RIG-I and MDA5 sense viral RNA in the cytoplasm. Costimulatory Molecules: CD80/CD86 on APCs engage CD28 on T cells, and CD40 on APCs interacts with CD40L on T cells, ensuring full T cell activation. Antigen Recognition Receptors: T cell receptors (TCRs) and B cell receptors (BCRs) mediate specific recognition of antigenic peptides and native protein structures, respectively.
How does the replicative nature of the rVSV vaccine enhance immune responses while maintaining a favorable safety profile?
The replicative nature allows for amplification of the antigen load, leading to robust innate and adaptive immune activation. However, attenuation through specific mutations (e.g., in the matrix protein) limits pathogenicity, ensuring that viral replication is sufficient for immunogenicity but not for causing disease.
What is the significance of the local inflammatory environment generated by the rVSV vaccine?
The local inflammatory milieu, created by the secretion of cytokines and chemokines (e.g., type I IFNs, IL‑6, TNF‑α, CXCL10), promotes the recruitment of innate immune cells such as NK cells, monocytes, and additional dendritic cells, thereby enhancing antigen uptake, processing, and subsequent adaptive immune activation.
Describe the role of pattern recognition receptors (PRRs) in the immunogenicity of the rVSV vaccine.
PRRs such as TLR7 (detecting ssRNA) and TLR3 (sensing dsRNA) in endosomal compartments, along with cytosolic receptors like RIG-I and MDA5, detect viral RNA produced during replication. Their activation initiates MyD88- and MAVS-dependent signaling cascades that lead to NF-κB and IRF3 activation, driving transcription of type I interferons and pro-inflammatory cytokines. These responses are crucial for establishing an antiviral state and priming adaptive immunity.
What is the specific role of RIG-I and MDA5 in the context of rVSV vaccine-induced immunity?
RIG-I and MDA5 detect viral RNA replication intermediates in the cytosol. Upon recognition, they recruit the adaptor MAVS, which activates downstream kinases (TBK1 and IKKε) leading to IRF3 phosphorylation. This cascade results in the production of type I interferons (IFN‑α/β), which are key in both establishing an antiviral environment and enhancing antigen presentation.
How does the secretion of type I interferons enhance the vaccine-induced immune response?
Type I interferons (IFN‑α/β) upregulate the expression of MHC class I and II molecules on antigen-presenting cells, enhance the maturation of dendritic cells, and establish an antiviral state in surrounding cells. This cytokine burst promotes efficient antigen presentation and recruits additional immune cells, setting the stage for a robust adaptive response.
What is the role of IL-12 in T cell differentiation after rVSV vaccination?
IL‑12, secreted by activated dendritic cells, is critical for the polarization of naïve CD4+ T cells into Th1 cells. Th1 cells produce IFN‑γ and IL‑2, which further enhance cytotoxic T lymphocyte (CTL) activation and proliferation, thereby strengthening the cell-mediated immune response.
Explain the concept of cross-presentation and its significance in the rVSV vaccine response.
Cross-presentation is the process by which certain dendritic cells present extracellular antigens on MHC class I molecules. This allows the exogenous spike antigen from the rVSV vaccine to be presented to CD8+ T cells, effectively priming CTLs to recognize and kill infected cells displaying the antigen.
Which signaling pathways are activated in dendritic cells (DCs) during their maturation post rVSV infection?
DC maturation is triggered by PRR engagement (via TLR7/TLR3 and RIG-I/MDA5 pathways). This leads to activation of NF-κB and IRF3, which drive the upregulation of MHC class II and costimulatory molecules (CD80, CD86, CD40) and secretion of cytokines (e.g., IL‑12), facilitating T cell priming and migration to lymph nodes.
Outline the cellular interactions that drive B cell activation following rVSV vaccination.
B cell activation begins when the B cell receptor (BCR) binds to the native spike protein. The antigen is internalized, processed, and presented on MHC class II molecules. Interaction with T follicular helper (Tfh) cells via CD40-CD40L and cytokines (IL‑21, IL‑4) in germinal centers drives B cell proliferation, somatic hypermutation, and class-switch recombination, culminating in the production of high-affinity antibodies.
