Interfer'n with antibody responses

Self-amplifying mRNA-Based Vaccine Technology and Its Mode of Action

Self-amplifying mRNAs derived from the genomes of positive-strand RNA viruses have recently come into focus as a promising technology platform for vaccine development. Non-virally delivered self-amplifying mRNA vaccines have the potential to be highly versatile, potent, streamlined, scalable, and inexpensive. By amplifying their genome and the antigen encoding mRNA in the host cell, the self-amplifying mRNA mimics a viral infection, resulting in sustained levels of the target protein combined with self-adjuvanting innate immune responses, ultimately leading to potent and long-lasting antigen-specific humoral and cellular immune responses. Moreover, in principle, any eukaryotic sequence could be encoded by self-amplifying mRNA without the need to change the manufacturing process, thereby enabling a much faster and flexible research and development timeline than the current vaccines and hence a quicker response to emerging infectious diseases. This chapter highlights the rapid progress made in using non-virally delivered self-amplifying mRNA-based vaccines against infectious diseases in animal models. We provide an overview of the unique attributes of this vaccine approach, summarize the growing body of work defining its mechanism of action, discuss the current challenges and latest advances, and highlight perspectives about the future of this promising technology.

Immunogenicity and Protection Efficacy of a Naked Self-Replicating mRNA-Based Zika Virus Vaccine

To combat emerging infectious diseases like Zika virus (ZIKV), synthetic messenger RNAs (mRNAs) encoding viral antigens are very attractive as they allow a rapid, generic, and flexible production of vaccines. In this work, we engineered a self-replicating mRNA (sr-mRNA) vaccine encoding the pre-membrane and envelope (prM-E) glycoproteins of ZIKV. Intradermal electroporation of as few as 1 µg of this mRNA-based ZIKV vaccine induced potent humoral and cellular immune responses in BALB/c and especially IFNAR1^-/- C57BL/6 mice, resulting in a complete protection of the latter mice against ZIKV infection. In wild-type C57BL/6 mice, the vaccine resulted in very low seroconversion rates and antibody titers. The potency of the vaccine was inversely related to the dose of mRNA used in wild-type BALB/c or C57BL/6 mice, as robust type I interferon (IFN) response was determined in a reporter mice model (IFN-β^+/Δβ-luc). We further investigated the inability of the sr-prM-E-mRNA ZIKV vaccine to raise antibodies in wild-type C57BL/6 mice and found indications that type I IFNs elicited by this naked sr-mRNA vaccine might directly impede the induction of a robust humoral response. Therefore, we assume that the efficacy of sr-mRNA vaccines after intradermal electroporation might be increased by strategies that temper their inherent innate immunogenicity.

Fc gamma receptor IIa suppresses type I and III interferon production by human myeloid immune cells

Type I and type III interferons (IFNs) are fundamental for antiviral immunity, but prolonged expression is also detrimental to the host. Therefore, upon viral infection high levels of type I and III IFNs are followed by a strong and rapid decline. However, the mechanisms responsible for this suppression are still largely unknown. Here, we show that IgG opsonization of model viruses influenza and respiratory syncytial virus (RSV) strongly and selectively suppressed type I and III IFN production by various human antigen-presenting cells. This suppression was induced by selective inhibition of TLR, RIG-I-like receptor, and STING-dependent type I and III IFN gene transcription. Surprisingly, type I and III IFN suppression was mediated by Syk and PI3K independent inhibitory signaling via FcγRIIa, thereby identifying a novel non-canonical FcγRIIa pathway in myeloid cells. Together, these results indicate that IgG opsonization of viruses functions as a novel negative feedback mechanism in humans, which may play a role in the selective suppression of type I and III IFN responses during the late-phase of viral infections. In addition, activation of this pathway may be used as a tool to limit type I IFN-associated pathology.

Late arising T follicular helper cells cultivate the B cell crop during chronic infections

Follicular helper CD4⁺ T cells are essential for the development of neutralizing antibodies that contain chronic viral infection.

Viral subversion of B cell responses within secondary lymphoid organs

Antibodies play a crucial role in virus control. The production of antibodies requires virus-specific B cells to encounter viral antigens in lymph nodes, become activated, interact with different immune cells, proliferate and enter specific differentiation programmes. Each step occurs in distinct lymph node niches, requiring a coordinated migration of B cells between different subcompartments. The development of multiphoton intravital microscopy has enabled researchers to begin to elucidate the precise cellular and molecular events by which lymph nodes coordinate humoral responses. This Review discusses recent studies that clarify how viruses interfere with antibody responses, highlighting how these mechanisms relate to our topological and temporal understanding of B cell activation within secondary lymphoid organs.