Pb1944: individuals with chronic lymphocytic leukaemia show impaired humoral but normal cellular immune responses after receiving a complete vaccination schedule against sars-cov-2

Topic: 6. Chronic lymphocytic leukemia and related disorders - Clinical Background: Oncohematological patients may have a lower immune response against SARS-CoV-2, both to natural acquisition and vaccines. Chronic lymphocytic leukaemia (CLL) is the main cause of leukaemia in the western world, characterized by the accumulation of round B lymphocytes. Aims: This study aimed to describe the cellular and humoral immune response induced by SARS-CoV-2 vaccination in CLL patients. Methods: Prospective, observational, longitudinal study with 14 individuals with CLL under the standard-of-care treatment and 11 in the “watch and wait” strategy who had mild COVID-19. Twelve healthy donors who recovered from mild COVID-19 were controls. Peripheral blood samples and clinical data were collected at baseline, one month after the second dose (Sample 1), and one and six months after the booster, respectively (Samples 2 and 3). Direct cellular cytotoxicity (DCC) of PBMCs on Vero E6 cells infected with pseudotyped SARS-CoV-2 was determined and cell populations were analyzed by flow cytometry. Antibody-dependent cellular cytotoxicity (ADCC) was performed by using Annexin V and rituximab-coated Raji cells as targets. Results: 1) Median age of participants was 74 years (IQR 66.0-80.5) and 76 years (IQR: 66.0-80.5) under the standard-of-care treatment and “watch and wait”, respectively. In both groups, most individuals (71.4% and 63.6%, respectively) were men. 2) DCC was similar to healthy donors in individuals from both groups of study. 3) Similarly, no differences were found in ADCC when compared to healthy donors’ response. 3) During the follow-up, 57.1% of patients under treatment did not develop detectable levels of IgGs after vaccination versus 9.1% of the patients in the “watch and wait” strategy (p<0.0001). 4) Levels of IgGs were significantly reduced (11.2-, 3.6- and 11.3-fold; p<0.0001) in samples 2, 3 and 4 in individuals on treatment in comparison with healthy donors. Summary/Conclusion: Individuals with CLL showed low levels of IgGs against SARS-CoV-2 after a complete vaccination schedule against SARS-CoV-2, although the cellular immune response was comparable to healthy donors, which may prevent that these individuals may have severe breakthough infections with SARS-CoV-2. Keywords: Vaccination, Immune response, Chronic lymphocytic leukemia