Efficacy of a Third BNT162b2 mRNA COVID-19 Vaccine Dose in Patients with CLL who Failed Standard Two-dose Vaccination.

Patients with chronic lymphocytic leukemia (CLL) have an impaired antibody response to COVID-19 vaccination. Here, we evaluated the antibody response to a third BNT162b2 mRNA vaccine in patients with CLL/small lymphocytic lymphoma (SLL) who failed to achieve a humoral response after standard two-dose vaccination regimen. Anti-SARS-CoV-2S and neutralizing antibodies were measured 3 weeks after administration of the third dose. In 172 patients with CLL the antibody response rate was 23.8%. Response rate among actively treated patients (12.0%, n=12/100) was lower compared to treatment-naïve patients (40.0%, n=16/40; OR=4.9, 95% CI 1.9-12.9; p<0.001) and patients off-therapy (40.6%, n=13/32; OR=5.0, 95% CI 1.8-14.1; p<0.001), (p<0.001). In those actively treated with BTK inhibitors or venetoclax ± anti-CD20 antibody, response rates were extremely low (15.3%, n=9/59 and 7.7%, n=3/39, respectively). Only one of the 28 patients (3.6%) treated with anti-CD20 antibodies <12 months prior to vaccination responded. The anti-SARS-CoV-2S antibody levels correlated linearly with neutralizing antibody titers (r=0.732, p<0.001). In a multivariate analysis, the independent variables that were associated with response included lack of active therapy (OR=5.6, 95% CI 2.3-13.8; p<0.001) and serum IgA levels ≥80 mg/dL (OR=5.8, 95% CI 2.1-15.9; p<0.001) In conclusion, in patients with CLL/SLL who failed to achieve a humoral response after standard two-dose BNT162b2 mRNA vaccination regimen, close to a quarter responded to the third dose of vaccine. The antibody response rates were lower during active treatment and in patients with a recent exposure (<12 months prior to vaccination) to anti-CD20 therapy.