Cross-binding antibodies capable of neutralising diverse hantaviruses are produced in response to Puumala virus infection

BACKGROUND: Orthohantaviruses (hantaviruses) are emerging rodent-borne pathogens that can cause severe human disease. They are present on multiple continents and are responsible for thousands of human cases per year. Despite this, no licenced therapeutics are available, vaccines for most strains are lacking, and the immunological response to infection is poorly characterised. This study aimed to analyse the humoral immune response to Puumala virus (PUUV) infection to inform future studies focussing on the production of therapeutic monoclonal antibodies and vaccination strategies. METHODS: Serum was obtained from a cohort of 24 patients hospitalised with PUUV infection at four time points, covering the early acute, late acute, early convalescent, and late convalescent stages of the disease. The humoral immune responses at each time point were quantified, and cross-binding, cross-neutralising antibody responses were investigated. Serum cytokine levels were also interrogated, and expression was correlated with humoral outputs. FINDINGS: PUUV infection elicited a robust anti-PUUV neutralising antibody response. However, cross-reactive antibodies that were capable of binding diverse hantaviruses were also induced in late convalescence. Modulations in the abundance of IgG subclasses were evident following infection, with significant differences present months after infection. INTERPRETATION: This study demonstrates that broadly reactive anti-hantavirus antibodies are produced in response to Old-World hantavirus infection, but predominantly months after recovery. As this is concomitant with changes in IgG subtypes, our results suggest that PUUV infection promotes prolonged class-switching and somatic hypermutation, favouring conserved epitopes long after exposure. FUNDING: Work at Mount Sinai was supported by Institutional Funds, work at the Medical University of Vienna was supported by Institutional Funds. The study was supported in part by the Styrian government, Austria (project no. ABT12-106729/2022-13) and the Austrian Science Fund (FWF) (number J 4737-B).