RTS,S, a WHO-recommended malaria vaccine, targets the circumsporozoite protein (CSP) on the Plasmodium falciparum sporozoite surface. Emerging data suggest off-target (non-CSP) antibody responses are associated with RTS,S-induced protection, but vaccine-derived responses are challenging to differentiate from boosting of naturally acquired immunity in endemic areas. We probed pre-challenge sera from RTS,S-vaccinated malaria-naïve adults who were either protected (n = 18) or unprotected (n = 17) against controlled human malaria infection on a custom peptide array with 1747 total variants from 130 non-CSP proteins from across the parasite lifecycle to assess off-target antibody responses with amino acid-level precision. Compared with the unprotected group, the protected group had increased IgG and/or IgA responses to 124 proteins (95%) studied. Using ssearch36, we found that 22 protein regions associated with protection had sequence similarities to CSP epitopes, including regions not found in RTS,S. The finding that off-target antibody responses are induced by RTS,S and are associated with protection in this and other studies suggests that they could be a marker of improved avidity, improved effector functions, or could be mediating improved protection by binding CSP or other proteins. Differentially reactive epitopes without linear sequence homology with CSP could represent conformational epitopes. Further study of these off-target antibody responses could help identify improved strategies for next-generation malaria vaccines.
SARS-CoV-2-specific immunity has been shaped in recent years by a combination of natural infection, complicated by ongoing viral evolution, and vaccination. However, it has remained unclear to what extent combined antigen challenge, which elicits so-called hybrid immunity, impacts clinical outcomes and subsequent protection against COVID-19. In this study, we evaluated spike-specific humoral and cellular immune responses elicited by hybrid antigen exposure versus vaccination alone, considering the order of challenge and disease severity after infection with SARS-CoV-2. Hybrid antigen exposure was characterized by enhanced humoral and cellular immune responses compared with vaccination alone. CD8+ T cell responses were also more cross-reactive and displayed skewed epitope targeting hierarchies in the context of hybrid immunity. These features were maintained in older adults, who typically exhibit age-related deficits in de novo immunity, especially after breakthrough infections (BTIs). BTIs were further associated with more coordinated adaptive immune responses compared with those elicited by vaccination after infection with SARS-CoV-2. We also found that humoral immune responses, specifically IgG antibody titers targeting the spike protein receptor-binding domain, were better maintained after mRNA vaccination and that cellular immune responses were better maintained after vectored vaccination in the wake of BTIs. Moreover, vaccination was associated with mild disease after subsequent infection, especially among individuals who had received a booster dose. These results suggest that vaccine-induced memory responses, which generally wane over time, can be reactivated and reshaped by BTIs, amplifying features associated with enhanced immunity against SARS-CoV-2.
Linear cap-independent mRNA (LciRNA) is an emerging vaccine platform enabling cap-independent translation while retaining a linear RNA architecture. This review summarizes LciRNA design principles, including IRES-mediated initiation, stability engineering, and immune regulation, and compares LciRNA with major mRNA vaccine platforms. We discuss current preclinical progress, particularly in cancer vaccines, and analyze challenges in potency, manufacturability, application scope, and clinical translation.
Immunization with radiation-attenuated sporozoites (PfRAS) is highly protective against Plasmodium falciparum malaria, but our understanding of protective correlates is incomplete. The IMRAS study used a PfRAS dose aimed at 50% efficacy to enable discovery of protective correlates. We performed serum proteomics, assaying 2925 serum proteins at five IMRAS study timepoints for 6 protected and 5 non-protected donors, to identify secreted proteins that correlate with immunization and/or protection. We next integrated this serum proteomics dataset with whole blood transcriptomic responses and proportions of circulating immune cells to identify involved signaling pathways and cell subsets. We identified 21 vaccine-induced proteins, including IFNG and IL15. IFNG-stimulated PBMCs from protected IMRAS participants showed increased CXCL9 and CXCL10 responses vs. non-protected participants. IFNG levels in protected individuals correlated with IL15, as well as interferon response gene expression levels in whole blood, and circulating activated CD14+ monocytes. Altogether, this analysis showed that PfRAS can prevent blood-stage malaria infection via coordinated IFNG and IL15 production, activation of CD14+ monocytes, and subsequent production of CXCL9, CXCL10, and CXCL11.
Circular RNA (circRNA) is an emerging vaccine modality that is proposed to improve stability, reduce reactogenicity and extend antigen expression compared with linear mRNA. However, the relative contributions to vaccine performance of its covalently closed structure, its preparation quality and nucleotide modifications remain poorly described. Here, we systematically dissected these parameters in vivo across two antigen systems. We identified RNA preparation quality as a major contributor to markers of circRNA reactogenicity, with innate immune activation tracking with the abundance of residual low molecular weight RNA species in less refined preparations. High-quality circRNA exhibited markedly reduced innate immune activation compared with linear mRNA, independent of nucleotide modification. Despite these differences, circRNA and mRNA vaccines elicited comparable antibody titres and T cell responses, indicating that reduced innate activation did not translate into enhanced adaptive immune magnitude. Incorporating N6-methyladenosine (m6A) did not affect markers of reactogenicity or antigen expression but was associated with increased antibody avidity across both antigen systems, with neutralisation trending in the same direction. CircRNA vaccination also altered the anatomical distribution of germinal centre responses, reducing splenic antigen-specific germinal centre B cells at the measured timepoint while preserving lymph node responses. Together, these findings indicate that circRNA vaccine performance is shaped by RNA preparation quality and epitranscriptomic modification, rather than differences in innate immune activation.
