Introduction: Immunization of patients with chronic lymphocytic leukemia (CLL) with vaccines against several infectious diseases has proven insufficient. Data on seroconversion of patients with CLL after vaccination against severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2) are still young, but accumulating evidence shows low seroconversion rates. Methods: We conducted a prospective, noninterventional study evaluating the safety and immunogenicity of two doses of the BNT162b2 mRNA Covid-19 vaccine, administered 21 days apart in consecutive adult patients with CLL. Patients vaccinated with other vaccines against SARS-CoV-2, with a history of confirmed Coronavirus Disease 19 (COVID-19), with known human immunodeficiency virus infection, or with an inability to provide written informed consent were excluded. Sera were tested before the first and after the second dose of the vaccine for anti-SARS-CoV-2 receptor binding domain (RBD) spike protein IgG (anti-RBD), using the Abbott SARS-CoV-2 IgG II Quant assay (Abbott Laboratories, Abbott Park, IL, USA), with a cutoff value for seroconversion at 50 AU/ml. Results: Sixty-one patients (28 males/33 females) with CLL, with a median age of 61 years, were included in the study. The majority of the patients (82.0%) were lower (0–2) stage per the RAI staging system. The seroconversion rate at 14 days after the second dose was 45% and was correlated with RAI stage (0–2 versus 3–4; 51.0% versus 18.3%, p = 0.047), the treatment status (treatment naïve, previously treated, or actively treated patients; 63.0% versus 40.0% versus 26.1%, respectively, p = 0.031), the number of previous treatment lines (0–2 versus >2; 55.3% versus 8.3%, p = 0.004), and the platelet count of the patients (over or under 100 × 109/L; 52.9% versus 10.0%, p = 0.015). Moreover, there was a positive linear relationship between the antibody titers and the gamma-globulin levels ( r = 0.182, p = 0.046) and platelet count ( r = 0.277, p = 0.002). Finally, patients actively treated with venetoclax had higher antibody titers than those treated with ibrutinib (15.8 AU/ml versus 0.0 AU/ml, p = 0.047). No safety issues were identified while the emergence of adverse events was not correlated with immunogenicity. Discussion: This study confirms results from previous studies on the low seroconversion rates in patients with CLL vaccinated with the BNT162b2 mRNA Covid-19 vaccine and on the detrimental effect of advanced disease and multiple treatment lines on seroconversion, while it is suggested that treatment with venetoclax may offer a chance for higher antibody titers, suggesting a treatment strategy change during the pandemic provided that this result is confirmed by larger studies specifically designed to address this issue.

Patients with chronic lymphocytic leukemia (CLL) show suboptimal responses to the vaccines against SARS-CoV-2; it has been shown though that a booster dose of the BNT162b2 vaccine may lead to a significant increase in the seroconversion rates of immunocompromised patients. We conducted a prospective, non-interventional study to evaluate the immunogenicity of a third dose of the BNT162b2 vaccine in adult patients with CLL. Sera were tested before the first, after the second, and before and after the third dose for anti-SARS-CoV-2 receptor binding domain (RBD) spike protein IgG (anti-RBD). Thirty-nine patients with CLL were included in the study. The seroconversion rate increased from 28.2% before the third dose to 64.1% after the third dose and was higher in treatment-naïve patients (72.7% versus 47.1% in actively treated patients, p = 0.042). All but one patient achieving a seroconversion after the second dose retained after the third, while eight patients not achieving a seroconversion after the second dose (38.1%), did so after the third. Moreover, patients actively treated with venetoclax had a higher seroconversion rate than those treated with ibrutinib (87.5% versus 14.3%, p = 0.001). This study confirms the beneficial effect of a third dose of the BNT162b2 vaccine on the seroconversion rate in patients with CLL. Our results also strongly suggest that the use of venetoclax is correlated with higher immunogenicity/seroconversion rates than that of ibrutinib, a finding that has been reported by another study. A treatment strategy change during the pandemic favoring the use of venetoclax may be suggested based on our results, although these results should be validated in larger studies.

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