Introduction. Coronavirus disease 2019 continues to spread rapidly throughout the world, causing serious concerns because of its affecting on many systems, long-term effects, and mortality rate. Older patients or patients with diabetes, cardiovascular and respiratory diseases, obesity, chronic kidney disease, and malignancies have a higher risk of severe disease and mortality when infected with SARS-CoV-2. Chronic lymphocytic leukemia (CLL) is the most common form of leukemia found in adults and is characterized by disease- and treatment-related immunodeficiency. A broad range of defects of the innate and adaptive immune response is found in CLL patients since early disease stage. Alterations of the innate immune system include defective function of neutrophils, natural killer cells and decreased complement activity. On the side of the adaptive immune response, deficits in cell-mediated immunity with hypogammaglobulinemia, down-regulation of T-cell function and defects in antibody dependent cellular cytotoxicity were reported. Considering the complex immune dysfunction, it is easy to assume an increased risk of severe SARS-CoV-2 infection in patients with CLL, both untreated and treated.

Aim. To assess the risk factors of severe COVID-19 and elucidate the impact of vaccination on the course of COVID-19 in patients with CLL.

Materials and methods. The study included 54 patients with CLL and confirmed COVID-19 by detecting SARS-CoV-2 RNA by a reverse transcriptase-polymerase chain reaction. The diagnosis of CLL was established based on clinical data, hemogram results, and immunophenotyping of leukocytes. The research was conducted following the Declaration of Helsinki. Written informed consent was obtained from all patients. Determination of complete blood count was performed on an automatic hematology analyzer “Sysmex KX-21” (Japan).

Results. The median age of patients was 68 years, 33.3% were older than 75. The majority (68.5%) were men. Overall, 35.2% (19 of 54) of patients had a mild course of COVID-19, while 64.8% (35 of 54) of patients were hospitalized (26 had a moderate and 9 – severe COVID-19). 73.7% of patients with a mild course of the coronavirus disease, 46.2% of patients with a moderate and 33.3% of patients with a severe COVID-19 have received the COVID-19 vaccine. 35 patients (64.8%) had never received CLL treatment, whereas 19 (35.2%) had received at least one line of treatment. 9 patients developed moderate or severe thrombocytopenia, and 3 patients developed arterial or venous thrombosis. 7 of the 35 patients who were only observed for CLL had progression during 3-6 months after infection with the SARS-CoV-2 virus and required specific treatment. Age greater than 75 years and comorbidity were associated with the risk of severe coronavirus disease in patients with CLL (p < 0.05). The presence of COVID-19 vaccination was associated with a mild course (p < 0.05).

Conclusions. Patients with CLL have a significant and complex impairment of both humoral and cellular immunity reflected by hypogammaglobulinemia, qualitative and quantitative B- and T-cell defects, CD4+ lymphopenia, and innate immune dysfunction. Comorbidities and age over 75 were associated with an increased risk of severe COVID-19 when there was no association with CLL-directed treatment. The absence of COVID-19 vaccination is a risk factor for severe disease. It is important to control the complete blood count in patients with CLL during coronavirus disease, whereas the risk of developing immune thrombocytopenia increases.

Keywords: chronic lymphocytic leukemia, immunity, COVID-19, immune thrombocytopenia.