Bamlanivimab Treatment Leads to Rapid Selection of Immune Escape VariantCarrying the E484K Mutation in a B. To the Editor-Kumar et al [1] reported on the role of single bamlanivimab in preventing hospitalization associated with coronavirus disease 2019 .There is scarce evidence of prevalence of emergent variants in patients treated with bamlanivimab [2].But very little is known about treatment-emergent variants in the B.1.1.7 lineage, which is by now the dominant strain throughout Europe and North America.We hereby report the selection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immune escape mutations in a B.1.1.7 variant 7 days after administration of single bamlanivimab in a patient with deeply impaired cellular immunity (Figure 1).The patient newly diagnosed with acute myeloid leukemia first tested positive for SARS-CoV-2 at day 11 after the start of chemotherapy.Initially, the cycle threshold (Ct) was above 30 and melting point analysis at day 15 suggested B.1.1.7 as the causative agent of this nosocomial infection.Despite starting bamlanivimab therapy, the Ct of SARS-CoV-2 polymerase chain reaction (PCR) tests continued to decline.Molecular surveillance at day 21 gave inconsistent results for position 0 10 20 30 40 Ct value Clinical course Cycle threshold (Ct) value transfusion of 6 platelets concentrates transfusion of 6 PRBCs 700 mg bamlanivimab B. 1.1.7remission bone marrow SARS-CoV-2 PCR negative SARS-CoV-2 PCR negative daunorubicin/cytarabine midostaurin remdesivir hydroxyurea B A B.1.1.7E484K by Tm B.1.1.7VAF 51.4% E484K VAF 42.5% Q493R VAF 8.9% S494P SARS-CoV-2 PCR negative Figure 1.A, Clinical course and antiviral medication.A 55-year-old female patient was admitted to the hospital on 9 January and diagnosed with AML (FLT3-ITD mut allelic ratio ≥ 0,5; NPM1 mut type A, RAD21 mut ; 46 XX; ELN risk stratification intermediate) and experienced an episode of neutropenic fever with absolute leucocyte count of 200/μL, hemoglobin level of 8.4 g/dL, platelet count of 20 000/μL, ECOG 2, and a bacteremia with Enterococcus faecium 11 days after the start of chemotherapy.She reconstituted hematologically on day 21 with a platelet count of 172 000/μL and on day 24 with an absolute leukocyte count of 1200/μL and neutrophil count of 810/μL.Bone marrow aspiration on day 41 showed a complete hematological remission.By the time of diagnosis of SARS-CoV-2 infection she showed no respiratory symptoms, with an oxygen saturation of 99% breathing ambient air.Same-day chest CT displayed no signs of pneumonia.Treatment with bamlanivimab 700 mg was administered on day 14 as a single IV infusion.As on day 23 she developed cough and chest CT showed a small infiltration in lung segment B4, she received remdesivir 200 mg IV day 23 and 100 mg IV from day 24 to 27.Subsequent clinical course was favorable.Fortunately, no other related cases of SARS-CoV-2 infection were detected.B, Results and Ct values of SARS-CoV-2 PCR testing on nasopharyngeal swabs.The day 15 sample showed characteristic B.1.1.7-definingmutations by melting point (Tm) analyses using VirSNiP TIB Molbiol assays, MassARRAY SARS-CoV-2 Variant panel Agena Bioscience, and NGS.The day 21 sample showed inconsistent results for position 484 by Tm analysis and the joint presence of E484 wild-type and E484K by MassARRAY and NGS (VAF 51.4%) E484K as well as mutations Q493R (VAF 42.5%) and S494P (VAF 8.9%).The day 27 sample showed the presence of E484K substitution by Tm analysis.Analyses of stored samples by MassARRAY and NGS at that time could not detect specific SARS-CoV-2 RNA.