P599: acalabrutinib improves innate immune function in patients with chronic lymphocytic leukemia

Background: CLL-cells interact with the surrounding immune microenvironment (IME) for survival. These interactions, however, induce immune changes that result in immune dysfunction, reflected in the increased risk of severe and fatal infections in CLL patients. The innate immune response constitutes a critical component of the host defense against microbes, by eliciting an acute inflammatory response and engaging the adaptive immune system for efficient infection control. BTK inhibition has previously been shown to disrupt CLL-IME interactions (Niemann et al, CCR, 2016), and may thus improve immune function in CLL patients. Aims: To assess whether treatment with the BTK inhibitor acalabrutinib improves innate immune responses and restores immune dysfunction in patients with CLL. Methods: 17 patients treated with acalabrutinib in the ASSURE trial (NCT04008706) were included in this study. Blood samples were assessed at baseline, cycle 3, and cycle 15. Innate immune function was characterized using TruCulture, a whole blood-ligand stimulation assay, applying lipopolysaccharide (LPS, bacterial endotoxin; TLR4) and resiquimod (R848, single-stranded RNA-virus analog; TLR7/8), with subsequent measurement of cytokine release. Concurrently, circulating blood immune cell subsets were assessed by an 8-tube, 10 color flow cytometry panel (DuraClone), including one tube containing beads for calculating absolute concentrations. Clinical baseline characteristics and data on infections prior to and during treatment were collected from electronic health records, eCRFs, and prescription data on antimicrobial drugs. Patients provided informed consent within a translational sub-study approved by the National Ethics Committee and the Data Protections Agency. Results: At baseline (n=17), the levels of LPS-stimulated IFN-γ, IL-10, IL-12, IL-1β, and TNF-α, and R848-stimulated IFN-α, IFN-γ, and IL-10 were below normal reference interval, while unstimulated IL-8 and TNF-α levels were elevated. At cycle 15, partial or complete normalization of most LPS- and R848 stimulated cytokine levels were observed, while improvements were detected already at cycle 3. Significant improvements were seen for LPS-stimulated IL-1β and TNF-α, and R848-stimulated IFN-α (p.adj = 0.004, 0.02, 0.03 respectively, Fig. 1) Also, unstimulated IL-8 and TNF-α decreased to normal levels (p.adj = 0.02 and 0.02 respectively). Preliminary results from immune cell subset characterization revealed elevated levels of monocytes and neutrophils, with expansion of immature neutrophil subsets and myeloid derived suppressor cells. Analysis of immune cell subsets during follow-up along with assessment of clinical parameters are currently ongoing and will be included for presentation. Summary/Conclusion: Patients with CLL displayed an impaired activation of innate cytokine responses upon infectious stimuli prior to acalabrutinib treatment, despite increased levels of myeloid immune cells. This suggests functional impairment, potentially due to expansion of immature and suppressive immune cells. Importantly, acalabrutinib normalized cytokine responses after 14 cycles of treatment, with detectable improvements already at cycle 3. We have previously reported impaired LPS- and R848 stimulated cytokine responses to predict severe disease course in hospitalized COVID-19 patients (Svanberg et al, Commun Med, 2022). Thus, we hypothesize that the improved innate immune function upon acalabrutinib treatment in patients with CLL may also translate into a reduced risk of infection-related complications, which will be subject for further investigation.Keywords: Targeted therapy, Chronic lymphocytic leukemia, Immune response, Microenvironment