SARS-CoV-2 variants of concern elicit divergent early immune responses in hACE2 transgenic mice

Knowledge about early immunity to SARS-CoV-2 variants of concern mainly comes from the analysis of human blood. Such data provide limited information about host responses at the site of infection and largely miss the initial events. To gain insights into compartmentalization and the early dynamics of host responses to different SARS-CoV-2 variants, we utilized human angiotensin converting enzyme 2 (hACE2) transgenic mice and tracked immune changes during the first days after infection by RNAseq, multiplex assays, and flow cytometry. Viral challenge infection led to divergent viral loads in the lungs, distinct inflammatory patterns, and innate immune cell accumulation in response to ancestral SARS-CoV-2, Beta (B.1.351) and Delta (B.1.617.2) variant of concern (VOC). Compared to other SARS-CoV-2 variants, infection with Beta (B.1.351) VOC spread promptly to the lungs, leading to increased inflammatory responses. SARS-CoV-2-specific antibodies and T cells developed within the first 7 days postinfection and were required to reduce viral spread and replication. Our studies show that VOCs differentially trigger transcriptional profiles and inflammation. This information contributes to the basic understanding of immune responses immediately postexposure to SARS-CoV-2 and is relevant for developing pan-VOC interventions including prophylactic vaccines. Fricke et al. report on early immune responses to various SARS-CoV-2 variants in the K18-hACE2 mouse. Beta triggers recruitment of neutrophils and monocytes, whereas Delta depletes alveolar macrophages. Spike-specific T and B cells mutually control virus dissemination and growth in this model. These insights inform the development of pan-variant interventions. (Created with BioRender.com)image

Automated summary

Our study on hACE2 transgenic mice reveals the early immune responses to different SARS-CoV-2 variants. Infection with Beta (B.1.351) VOC leads to prompt viral spread to the lungs and increased inflammatory responses. SARS-CoV-2-specific antibodies and T cells developed within the first 7 days postinfection play a crucial role in reducing viral transmission and replication. These findings contribute to the understanding of immediate immune responses to SARS-CoV-2 and are important for developing interventions against various variants.