Humoral and Cellular Immunogenicity of COVID-19 Vaccinations in Patients with CLL
Authors: Sun Clare , Gaglione Erika M , Vaughn Lauren T , Mu Rui , Underbayev Chingiz , Chen Jonathan , Pleyer Christopher , Wiestner Adrian 
Published: November 2021

Abstract
Humoral and cellular adaptive immunity likely contribute to protection against coronavirus disease 2019 (COVID-19). Neutralizing antibodies and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific T cells have been detected in convalescent and immunized immunocompetent individuals. Chronic lymphocytic leukemia (CLL) and its treatment, particularly anti-CD20 monoclonal antibodies and Bruton tyrosine kinase inhibitors (BTKis), blunt the antibody response to vaccines. To understand the immunogenicity of COVID-19 vaccination in patients with CLL, assessment of the T-cell response is urgently needed.
Between December 22, 2020 and May 7, 2021, 57 patients with CLL were immunized with either 2 doses of BNT162b2 (n = 30) or mRNA-1273 (n = 25) or 1 dose of Ad26.COV2.S (n = 2). Qualitative and semi-quantitative anti-spike antibodies were measured with serology tests authorized by the FDA under Emergency Use Authorization. A positive humoral response to vaccination was defined as the detection of anti-spike antibodies. Ultra-deep TCRß sequencing (Adaptive Biotechnologies) was performed on total peripheral blood mononuclear cells collected before and after vaccination. These data were analyzed in the immunoSEQ Analyzer. Differential abundance was calculated using the beta-binomial model and two-sided α=.05. SARS-CoV-2 spike-specific T cells were identified in the T-MAP COVID ImmuneCODE database. A positive cellular response to vaccination was defined as significant expansion of ≥1 spike-specific clonotype.
Anti-spike antibodies were detected in 61% (35/57) of patients at a median (interquartile range, IQR) of 45 (30-56) days after the last dose of vaccine. The median (IQR) antibody titer was 19.1 U/mL (3.6-150.9) among 27 patients with humoral response. There were 4 patients with titers above the upper limit of quantification (&gt;250 U/mL) and 4 patients who had qualitative testing only. The rate of humoral response was 71% (15/21) in treatment naïve (TN) patients, 57% (16/28) in patients treated with BTKi, and 0% (0/4) in patients treated with venetoclax and anti-CD20 monoclonal antibody (mAb). Among 16 BTKi-treated patients with anti-spike antibodies, 2 interrupted BTKi during the vaccination period. One patient treated with venetoclax monotherapy and 3 previously treated patients had detectable anti-spike antibodies. The immediate prior therapies were acalabrutinib &gt;1 year before vaccination for 2 patients and chemoimmunotherapy &gt;8 years before vaccination for 1 patient. Vaccination with mRNA-1273 induced numerically higher titers compared to BNT162b2 (median 85.5 U/mL versus 11.0 U/mL; P=.1), but the rate of seroconversion was not significantly different (P=.4). No patients reported a history of SARS-CoV-2 infection and anti-nucleocapsid antibodies were negative in 100% (50/50) of patients tested.
Circulating CD8 + T cells increased from a median (IQR) of 13.2% (7.8-18.8) at baseline to 14.3% (8.8-20.6) after vaccination (P=.015). CD3 + and CD4 + T cells did not significantly change. TCRß sequencing results are available in 7 patients (Table). The median (IQR) number of productive templates, which corresponds to the number of T cells sequenced in each sample, was 447,805 (377,738-503,097). Cellular response was observed in 57% (4/7) of patients. A total of 10 expanded spike-specific clonotypes were identified and ranged between 1 and 6 clonotypes per patient. The cumulative frequency of spike-specific clonotypes after vaccination ranged between 0.0036% and 1.55% per patient. None of these clonotypes were found at baseline despite the large number of productive templates generated in each sample. Spike-specific T cells were detected in 50% (2/4) of patients with anti-spike antibodies and 67% (2/3) of patients without seroconversion.
In conclusion, patients with CLL have impaired humoral and cellular responses to COVID-19 vaccination. Seroconversion occurred less often in patients treated with BTKi than TN patients and was absent in patients treated with venetoclax and anti-CD20 mAb. Cellular responses were seen in the absence of humoral responses. TCRß sequencing is ongoing in additional patients. Updated data will be presented at the meeting.
Figure 1 Figure 1.

Disclosures
Sun: Genmab: Research Funding. Wiestner: Merck: Research Funding; Nurix: Research Funding; Genmab: Research Funding; Verastem: Research Funding; Acerta Pharma: Research Funding; Pharmacyclics: Research Funding.