Immune imprinting: The persisting influence of the first antigenic encounter with rapidly evolving viruses

Editorial on: Protection against influenza hospitalizations from enhanced influenza vaccines among older adults: A systematic review and network meta-analysis

See related article by Ferdinands et al.

Virus-Induced Pathogenic Antibodies: Lessons from Long COVID and Dengue Hemorrhage Fever

Virus-induced antibodies represent a dual-edged sword in the immune response to viral infections. While antibodies are critical for neutralizing pathogens, some can paradoxically exacerbate disease severity through mechanisms such as antibody-dependent enhancement (ADE), autoantibody, and prolonged inflammation. Long coronavirus disease (COVID) and dengue hemorrhagic fever (DHF) exemplify conditions where pathogenic antibodies play a pivotal role in disease progression. Long COVID is associated with persistent immune dysregulation and autoantibody production, leading to chronic symptoms and tissue damage. In DHF, pre-existing antibodies against dengue virus contribute to ADE, amplifying viral replication, immune activation, and vascular permeability. This review explores the mechanisms underlying these pathogenic antibody responses, highlighting the shared pathways of immune dysregulation and comparing the distinct features of both conditions. By examining these studies, we identify key lessons for therapeutic strategies, vaccine design, and future research aimed at mitigating the severe outcomes of viral infections.

K. pneumoniae ghosts serve as a novel vaccine formulation to enhance immune responses of A. baumannii subunit vaccine in mice

Acinetobacter baumannii (A. baumannii) is a prominent nosocomial pathogen, posing a significant threat to public health. Urgent efforts are required to develop a safe and effective vaccine. Bacterial ghosts (BGs), comprising empty bacterial cell envelopes, offer a promising platform for vaccine adjuvant development. In the present study, Klebsiella pneumoniae (K. pneumoniae, KP) ghosts were generated via PhiX-174 lysis gene E-mediated inactivation. The present study results demonstrated that KP ghosts greatly promoted maturation and activation of BMDCs by upregulating the expression of surface molecules (CD40, CD80, CD86 and MHCII) and improving the secretion of cytokines (IL-1β, TNF-α and IL-12p70). In addition, to assess the immunogenicity and protective efficacy of the vaccine candidate, C57BL/6 mice were immunized with either A. baumannii OmpA or A. baumannii OmpA plus KP ghosts. The results showed that OmpA plus KP ghosts elicited higher levels of specific IgG antibody responses compared to OmpA alone. Furthermore, OmpA plus KP ghosts also increased lymphocyte proliferation and expression of the early activation marker CD69 on T cells, augmented frequency of central memory T cells (TCM) and IFN-γ+CD4+ T cells with production of increased IFN-γ in response to OmpA stimulation, as compared to OmpA alone. Furthermore, post-challenge with A. baumannii, mice immunized with OmpA plus KP ghosts exhibit a higher survival rate and lower bacterial loads in the spleen and lungs compared to those immunized with OmpA alone. In conclusion, these findings underscore the potential of KP ghosts as a candidate vaccine formulation or immunomodulators for designing a novel vaccine against A. baumannii infection.

Antigenic Imprinting Dominates Humoral Responses to New Variants of SARS-CoV-2 in a Hamster Model of COVID-19

The emergence of SARS-CoV-2 variants escaping immunity challenges the efficacy of current vaccines. Here, we investigated humoral recall responses and vaccine-mediated protection in Syrian hamsters immunized with the third-generation Comirnaty® Omicron XBB.1.5-adapted COVID-19 mRNA vaccine, followed by infection with either antigenically closely (EG.5.1) or distantly related (JN.1) Omicron subvariants. Vaccination with the YF17D vector encoding a modified Gamma spike (YF-S0*) served as a control for SARS-CoV-2 immunity restricted to pre-Omicron variants. Our results show that both Comirnaty® XBB.1.5 and YF-S0* induce robust, however, poorly cross-reactive, neutralizing antibody (nAb) responses. In either case, total antibody and nAb levels increased following infection. Intriguingly, the specificity of these boosted nAbs did not match the respective challenge virus, but was skewed towards the primary antigen used for immunization, suggesting a marked impact of antigenic imprinting, confirmed by antigenic cartography. Furthermore, limited cross-reactivity and rapid decline in nAbs induced by Comirnaty® XBB.1.5 with EG.5.1 and, more concerning, JN.1, raises doubts about sustained vaccine efficacy against recent circulating Omicron subvariants. In conclusion, we demonstrate that antigenic imprinting plays a dominant role in shaping humoral immunity against emerging SARS-CoV-2 variants. Future vaccine design may have to address two major issues: (i) overcoming original antigenic sin that limits the breadth of a protective response towards emerging variants, and (ii) achieving sustained immunity that lasts for at least one season.

A polygeneric immunogen composed of 22 venoms from sub-Saharan African snakes to expand the neutralization scope of the EchiTAb-plus-ICP antivenom

Recent research suggests that a polygeneric immunogen made from the venoms of the most medically important viperid and elapid snakes in sub-Saharan Africa could elicit a broader antibody response in horses compared to the current EchiTAb-plus-ICP antivenom, especially against neurotoxic elapid venoms. To test this, 25 horses that have been regularly immunized to produce this antivenom were reimmunized with an immunogen containing 22 venoms from various snake species from the genera Bitis, Echis, Dendroaspis, and both spitting and non-spitting Naja. The plasma collected from these horses was processed using the caprylic acid method to produce an industrial-scale freeze-dried antivenom. The anti-lethal neutralization scope of this new formulation was then compared to that of EchiTAb-plus-ICP which is designed to target the venoms of Bitis arietans, Echis ocellatus, Naja nigricollis, and Dendroaspis polylepis. The results indicated that adding more venoms to the immunogen did not significantly enhance the neutralization of the lethal effect of viperid venoms (except for Bitis nasicornis) or of venoms of spitting cobras (except for Naja katiensis). However, incorporating additional venoms from non-spitting neurotoxic Naja spp. and Dendroaspis spp. improved the neutralization scope of EchiTAb-plus-ICP against these neurotoxic venoms. The antivenom generated showed a wider anti-lethal neutralizing scope, as compared to the standard EchiTAb-plus-ICP antivenom and constitutes a good candidate to be tested in clinical trials in sub-Saharan Africa.

Contribution of immunoglobulin products in influencing seasonal influenza infection and severity in antibody immune deficiency patients receiving immunoglobulin replacement therapy

Seasonal and pandemic influenza infection present a potential threat to patients with antibody deficiency. The acceptance and effect of the current recommendation for annual vaccination against influenza for patients with antibody deficiency is not well investigated and due to antigenic drift or shift the protective capacity of regular IgG replacement therapy (IgRT) is considered low. This narrative review considers the effect of influenza vaccination in immunodeficient patients and discusses available information on the effect of immunoglobulin products on seasonal influenza infectivity and severity in antibody deficiency patients receiving IgRT. The humoral immune response to seasonal influenza vaccination is reduced in patients with antibody immune deficiency. However, there is no evidence that the proportion of patients with primary antibody deficiency who develop influenza illness, and the severity of such illness, is increased when compared with the general population. The IgRT that patients receive has been shown to contain neutralizing antibodies as a consequence of past flu infections against both the hemagglutinin and neuraminidase surface proteins and other viral internal proteins of different influenza A virus strains. Studies have demonstrated not only significant levels of specific but also cross-reactive antibodies against seasonal influenza virus strains. Thus, despite the yearly changes in influenza viral antigenicity that occur, IgRT could potentially contribute to the protection of patients against seasonal influenza. Currently, only limited clinical data are available confirming a preventative effect of IgRT with respect to seasonal influenza infection. In conclusion, there is some evidence that IgRT could contribute to protection against seasonal influenza in patients with antibody-related immunodeficiency. However, additional clinical data are needed to confirm the extent and relevance of this protection and identify the main responsible virus targets of that protection.