Variant-specific humoral immune response to SARS-CoV-2 escape mutants arising in clinically severe, prolonged infection

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Abstract Neutralising antibodies against the SARS-CoV-2 spike (S) protein are major determinants of protective immunity, though insufficient antibody responses may cause the emergence of escape mutants. We studied the intra-host evolution and the humoral immune response in a B-cell depleted, haemato-oncologic patient experiencing clinically severe, prolonged SARS-CoV-2 infection with a virus of lineage B.1.177.81. Bamlanivimab treatment early in infection was associated with the emergence of the bamlanivimab escape mutation S:S494P. Ten days before virus elimination, additional mutations within the N-terminal domain (NTD) and the receptor binding domain (RBD) of S were observed, of which the triple mutant S:Delta141-4 E484K S494P became dominant. Routine serology revealed no evidence of an antibody response in the patient. A detailed analysis of the variant-specific immune response by pseudotyped virus neutralisation test (pVNT), surrogate VNT (sVNT), and immunoglobulin-capture EIA showed that the onset of an IgM-dominated antibody response coincided with the appearance of escape mutations. The formation of neutralising antibodies against S:Delta141-4 E484K S494P correlated with virus elimination. One year later, the patient experienced clinically mild re-infection with Omicron BA.1.18, which was treated with sotrovimab and resulted in a massive increase of Omicron-reactive antibodies. In conclusion, the onset of an IgM-dominated endogenous immune response in an immunocompromised patient coincided with the appearance of additional mutations in the NTD and RBD of S in a bamlanivimab-resistant virus. Although virus elimination was ultimately achieved, this humoral immune response escaped detection by routine diagnosis and created a situation temporarily favouring the emergence of escape variants with known epidemiological relevance.

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