To Örebro University

Patients with chronic lymphocytic leukemia (CLL) are at increased risk of Streptococcus pneumoniae infections due to disease- and treatment-related immune dysfunction. Vaccine responses are often impaired. This thesis evaluates the immune response to primary immunization with pneumococcal conjugate vaccine (PCV) versus pneumococcal polysaccharide vaccine (PPSV), long-term antibody persistence and the effect of revaccination in CLL patients.

Study I was a randomized trial in treatment-naïve CLL patients comparing PCV and PPSV, demonstrating that PCV elicits an enhanced immune response.

Study II was a prospective study evaluating B-cell subsets and plasmablast dynamics before and after revaccination. It showed that repeated revaccinations with PCV in CLL patients improves early humoral response.

Study III assessed antibody persistence 5 years after primary immunization and response to revaccination, showing that CLL patients have poor long-term antibody persistence, but that revaccination with PCV enhances immunity.

Study IV examined the impact of two analytical methods, multiplex immunoassay (MIA) and enzyme immunoassay (EIA), on serotypespecific IgG measurements and demonstrated their influence on vac-cine response interpretation in CLL patients. The findings in this thesis emphasize the importance of pneumococcal conjugate vaccines in CLL patients and suggest a need for revaccination to maintain protection against severe pneumococcal disease.

Patients with chronic lymphocytic leukemia (CLL) have impaired response to vaccination, which calls for improved vaccination strategies. This study aimed to evaluate antibody persistence five years after pneumococcal vaccination and response to revaccination. Seventyfour CLL patients and 31 controls, all primary immunized with 13-valent conjugated pneumococcal vaccine (PCV13) or 23-valent polysaccharide vaccine (PPSV23), were included. Antibody persistence was assessed, followed by revaccination with PCV13 and a second revaccination with PCV13 or PPSV23. Serological protection (SP), defined as serum serotype specific IgG concentration ≥0.35 μg/mL for ≥70% of shared serotypes, did not differ significantly in CLL patients primary immunized with PCV13 or PPSV23 (RR 2.7 (95% CI 0.5-13.1)), but was lower in patients compared to controls (10% vs 32%; RR 0.3 (0.1-0.7)). Following revaccination with PCV13, serological response (SR), defined as ≥2-fold increase for ≥70% of shared serotypes, was 24% in patients primary immunized with PCV13 vs 12% with PPSV23 (RR 2.0 (0.6-6.9)). A second revaccination with PCV13 significantly improved SR while PPSV23 did not further improve immunity. Our findings suggest that repeated doses of a T-cell dependent pneumococcal vaccine improve protection in CLL patients. The study is registered at www.clinicaltrials.gov (NCT05316831).

Profound immune dysregulation and impaired response to the SARS-CoV-2 vaccine put patients with chronic lymphocytic leukemia (CLL) at risk of severe COVID-19. We compared humoral memory and T-cell responses after booster dose vaccination or breakthrough infection. (Green) Quantitative determination of anti-Spike specific antibodies. Booster doses increased seroconversion rate and antibody titers in all patient categories, ultimately generating humoral responses similar to those observed in the postinfection cohort. In detail, humoral response with overscale median antibody titers arose in >80% of patients in watch and wait, off-therapy in remission, or under treatment with venetoclax single-agent. Anti-CD20 antibodies and active treatment with BTK inhibitors (BTKi) represent limiting factors of humoral response, still memory mounted in ~40% of cases following booster doses or infection. (Blue) Evaluation of SARS-CoV-2-specific T-cell responses. Number of T-cell functional activation markers documented in each patient. The vast majority of patients, including those seronegative, developed T-cell responses, qualitatively similar between treatment groups or between vaccination alone and infection cases. These data highlight the efficacy of booster doses in eliciting T-cell immunity independently of treatment status and support the use of additional vaccination boosters to stimulate humoral immunity in patients on active CLL-directed treatments.

BACKGROUND: Patients with chronic lymphocytic leukemia (CLL) show an immune dysfunction with increased risk of infections and poor response to vaccination. Streptococcus pneumoniae is a common cause of morbidity and mortality in CLL patients. In a previous randomized clinical trial, we found a superior immune response in CLL patients receiving conjugated pneumococcal vaccine compared to non-conjugated vaccine. The response to revaccination in CLL patients is scarcely studied. In this study, early humoral response to repeated revaccinations with pneumococcal vaccines was evaluated, by determination of B cell subsets and plasmablast dynamics in peripheral blood.

METHOD: CLL patients (n = 14) and immunocompetent controls (n = 31) were revaccinated with a 13-valent pneumococcal conjugate vaccine (PCV13) after previous primary immunization (3-6 years ago) with PCV13 or a 23-valent pneumococcal polysaccharide vaccine (PPSV23). Eight weeks after the first revaccination, all CLL patients received a second revaccination with PCV13 or PPSV23. B cell subsets including plasmablasts were analyzed in peripheral blood by flow cytometry, before and after the first and the second revaccination.

RESULTS: None of the CLL patients, but all controls, had detectable plasmablasts at baseline (p < 0.001). After the first revaccination with PCV13, the plasmablast proportions did not increase in CLL patients (p = 0.13), while increases were seen in controls (p < 0.001). However, after a second revaccination with PCV13 or PPSV23, plasmablasts increased compared to baseline also in CLL patients (p < 0.01). If no response was evident after first revaccination, only a second revaccination with PCV13 increased plasmablasts in contrast to PPSV23 revaccination. Patients with hypogammaglobulinemia and ongoing/previous CLL specific treatment responded poorly, also to a second revaccination.

CONCLUSION: In CLL patients, pneumococcal revaccination induced minor early plasmablast response compared to controls, but the response improved using a strategy of repeated doses with of conjugated T cell dependent pneumococcal vaccine.

Aim: To determine if patients with untreated chronic lymphocytic leukemia (CLL) benefit from vaccination with a 13-valent pneumococcal conjugated vaccine (PCV13), Prevenar13 (R), compared to a 23-valent pneumococcal polysaccharide vaccine (PPSV23), Pneumovax (R), in terms of immune response.

Background: Streptococcus pneumoniae causes substantial morbidity in patients with CLL, a group known to respond poorly to polysaccharide vaccines. Comparative studies with conjugated vaccines are lacking.

Methods: 128 treatment naive CLL patients from eight hematology clinics in Sweden were randomized to vaccination with PCV13 (n = 63) or PPSV23 (n = 65) after stratification by IgG level and CLL clinical stage (Rai). Blood samples for evaluation of immune response were obtained at baseline, and at one and six months after vaccination. Analyses for each of the 12 pneumococcal serotypes common for PCV13 and PPSV23 were performed by opsonophagocytic assay (OPA) and enzyme-linked immunosorbent assay (ELISA).

Results: PCV13 elicited a superior immune response than PPSV23 in 10/12 serotypes one month after vaccination and in 5/12 serotypes six months after vaccination, measured as OPA geometric mean titers (GMTs). Geometric mean concentrations of serotype-specific IgG antibodies elicited by PCV13 as measured by ELISA, were higher than those elicited by PPSV23 in half of the common serotypes, both after one and six months. PPSV23 did not trigger a better immune response than PCV13 for any of the serotypes, regardless of analysis method or time point of analysis. Negative predictive factors for vaccination response were hypogammaglobulinemia and long disease duration. Both vaccines were well tolerated.

Conclusions: In patients with previously untreated CLL, the efficacy of PCV13 in terms of immune response is superior to PPSV23 for most serotypes common for the two vaccines. We therefore propose that PCV13 should be included in vaccination programs against Streptococcus pneumoniae for CLL patients and administered as early as possible during the course of the disease.

Key Clinical Message

Inherited conditions associated with thrombocytopenia should be included in the differential diagnosis of young patients with refractory immune thrombocytopenia (ITP), even in the absence of a positive family history. Early identification of such conditions is of vital importance in order to reach the right diagnosis and avoid unnecessary or even harmful medication.