Temperature elevation synergises with and enhances the type-I IFN-mediated restriction of MPXV

Fever is an evolutionary conserved host pro-inflammatory immune response that governs the regulation of multiple biological processes to control the outcome of infection. In January 2022, the World Health Organization (WHO) reported a global outbreak in mpox cases with a high incidence of human-to-human transmission. A frequent prodromal symptom of monkeypox virus (MPXV) infection is fever, with a febrile temperature range of 38.3 to 40.5 °C. However, the outcome of temperature elevation on MPXV infection remains poorly defined. Here, we isolated a circulating strain of MPXV from a patient who presented with fever (38.5 °C) and rash from the 2022 outbreak. Genomic sequencing identified this isolate to belong to the epidemic Clade IIb.B1. Transcriptomic analysis of infected cells demonstrated this virus to induce a strong IL6 pro-inflammatory immune response, consistent with a role for this pyrogen in the regulation of fever. We identify host-cell temperature at both physiological skin (33 °C) and clinical febrile temperatures (38.5 and 40 °C) to be a key determinant in the outcome of infection through the differential regulation of MPXV transcription and associated amplitude of host cytokine response to infection. Incubation of infected cells at 38.5 or 40 °C led to a restriction or ablation in MPXV replication, respectively. Importantly, this thermal inhibition was reversible upon temperature downshift to 37 °C without detriment to viral replication fitness. Co-stimulation of the type-I interferon (IFN) response led to a dose- and temperature-dependent inhibition in MPXV replication that restricted the re-establishment of infection upon temperature downshift and withdrawal of IFN as an immune stimulus. Our data identify febrile temperatures associated with mpox disease to be a critical component of the host pro-inflammatory immune response to infection which can synergise with the type-I IFN response to enhance the host-cell mediated restriction of MPXV.