Summary Chronic lymphocytic leukaemia (CLL) is associated with immunocompromise and high risk of severe COVID‐19 disease and mortality. Monoclonal B‐cell lymphocytosis (MBL) patients also have immune impairment. We evaluated humoural and cellular immune responses in 181 patients with CLL (160) and MBL (21) to correlate failed seroconversion [<50 AU/ml SARS‐CoV‐2 II IgG assay, antibody to spike protein; Abbott Diagnostics)] following each of two vaccine doses with clinical and laboratory parameters. Following first and second doses, 79.2% then 45% of CLL, and 50% then 9.5% of MBL patients respectively remained seronegative. There was significant association between post dose two antibody level with pre‐vaccination reduced IgM (p < 0.0001), IgG2 (p < 0.035), and IgG3 (p < 0.046), and CLL therapy within 12 months (p < 0.001) in univariate analysis. By multivariate analysis, reduced IgM (p < 0.0002) and active therapy (p < 0.0002) retained significance. Anti‐spike protein levels varied widely and were lower in CLL than MBL patients, and both lower than in normal donors. Neutralisation activity showed anti‐spike levels <1000 AU/ml were usually negative for both an early viral clade and the contemporary Delta variant and 72.9% of CLL and 53.3% of MBL failed to reach levels ≥1000 AU/ml. In a representative sample, ~80% had normal T‐cell responses. Failed seroconversion occurred in 36.6% of treatment‐naïve patients, in 78.1% on therapy, and in 85.7% on ibrutinib.

Chronic lymphocytic Leukemia (CLL) and Monoclonal B-Lymphocytosis (MBL) patients have impaired response to COVID-19 vaccination. A total 258 patients (215 CLL and 43 MBL) had anti-spike levels evaluable for statistical analysis. The overall seroconversion rate for CLL was 94.2% (anti-spike ³50AU/mL Abbott Diagnostics) and for MBL 100%. After 3 doses (post-D3) in 167 CLL patients, 73.7% were seropositive, 17.4% had anti-spike levels 50-999AU/mL, and 56.3% ≥1000AU/mL with a median rise from 144.6AU/mL to 1800.7AU/mL. Of patients seronegative post-D2, 39.7% seroconverted post-D3. For those who then remained seronegative after their prior dose, seroconversion occurred in 40.6% post-D4, 46.2% post-D5, 16.7% post-D6, and 0% after D7 or D8. Following seroconversion, most had a progressive increment in anti-spike antibody level: in CLL after the latest dose, 70.2% achieved anti-spike level ≥1,000AU/mL, 48.1% ≥5,000AU/mL, and 30.3% ≥10,000AU/mL. Neutralization was associated with higher anti-spike levels, more vaccines and earlier COVID variants; 65.3% detected neutralizing antibody against early clade D614G, 52.0% against Delta, and 36.5% against Omicron. COVID-specific T-cell production of IFN-γ occurred in 73.9% and IL-2 in 60.9% of 23 tested, and more consistently with higher anti-spike levels. After multiple vaccine doses, by multivariate analysis, IgM ≥0.53g/L (OR=2.90, p=0.0314), IgG3 ≥0.22g/L (OR=3.26, p=0.0057), and lack of current CLL therapy (OR=2.48, p=0.0574) were independent predictors of positive serological responses. Strong neutralization and T-cell responses had high concordance with high anti-spike levels. Multiple sequential COVID-19 vaccination significantly increased seroconversion and anti-spike antibody levels in CLL and MBL.

Chronic lymphocytic leukemia (CLL) is associated with immunocompromise and high risk of severe COVID-19 disease and mortality. Monoclonal B-Lymphocytosis (MBL) patients also have immune impairment. We evaluated humoral and cellular immune responses in 181 patients with CLL (160) and MBL (21) to correlate failed seroconversion (<50AU/mL SARS-CoV-2 II IgG assay, antibody to spike protein, Abbott Diagnostics) following each of 2 vaccine doses with clinical and laboratory parameters. Following first and second doses, 79.2% then 45% of CLL, and 50% then 9.5% of MBL respectively remained seronegative, indicating 2 vaccine doses are crucial. There was significant association between post-dose 2 antibody level with pre-vaccination reduced IgM (p<0.0001), IgG2 (p<0.035), IgG3 (p<0.046), and CLL therapy within 12 months (p<0.001) in univariate analysis. By multivariate analysis, reduced IgM (p<0.0002) and active therapy (p<0.0002) retained significance. There was no significant correlation with age, gender, CLL duration, IgG, IgA or lymphocyte subsets. Anti-spike protein levels varied widely and were lower in CLL, than MBL, and both lower than normal donors. Neutralization activity showed anti-spike levels <1000AU/mL were usually negative for both an early viral clade and the contemporary Delta variant. There were 72.9% of CLL and 53.3% of MBL who failed to reach anti-spike levels >1000AU/mL. In a representative subset of 32 CLL patients, 80% had normal T-cell responses by IFNγ and IL-2 FluoroSpot assay. Failed seroconversion occurred in 36.6%% of treatment-naive patients, 52.9% treatment-naive with reduced IgM, 78.1% on therapy, and 85.7% on ibrutinib. Vaccination failure is very common in CLL, including early-stage disease.6 Key Novel FindingsComparison CLL vs MBL vs normal-45% of CLL and 9.5% of MBL fail to seroconvert with 2 doses of COVID-19 vaccineNeutralization assay-SARS CoV-2 IgG levels <1000 AU/mL rarely associated with neutralization activity.COVID-19-specific T-cell function by FluoroSpot IFN-g and IL-2 productionIgG, A, M class and IgG subclass: correlations by univariate and multivariate analysis-IgM (OR 7.29 p<0.0001), IgG2 and IgG3 subclass univariate significanceCorrelation with therapy – ICT, targeted therapies, and those on Ig replacementHigh risk of vaccination failure for all CLL, including early-stage disease, and MBLKey PointsCLL and MBL show significantly impaired anti-spike antibody, viral neutralization, with cellular immune response to COVID-19 vaccinationFailure to seroconvert is associated with low IgM, IgG2, IgG3, and recent therapy; many CLL and MBL patients remain COVID-19 vulnerable

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