Investigating B Cell Function and Immune Checkpoint Expression in Patients with Chronic Lymphocytic Leukemia.

Abstract

Introduction Abnormal accumulation of functionally incompetent B cell and dysregulated immune checkpoint expression are hallmark of chronic lymphocytic leukemia (CLL). In fact, the increased levels of immune checkpoint expression and CD38 positive B cells are consistent with the progression of CLL. Malignant B cell produce immune checkpoints and cytokines that inhibit B cell function and exacerbate the disease progression. In this study, we aimed to investigate the B cell function and immune checkpoint expression in patients with CLL. Methods A systematic review evaluating the effectiveness of chemoimmunotherapy and the associated major severe adverse events in adult patients with CLL was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines. Peripheral blood from a total of 21 patients with CLL and 12 controls were collected. Complete blood count was measured and B cells were isolated using BD IMag isolation system. The baseline levels of B cell subsets, immune checkpoints (cytotoxic T-lymphocyte-associated protein-4, programmed death-ligand-2 and programmed death-1) expression on various B cell subsets and soluble immune checkpoints (soluble interleukin-2 receptor alpha, T cell immunoglobulin and mucin domain-containing protein 3, galectin-9, programmed cell death-1, programmed death-ligand-1 and cytotoxic T-lymphocyte associated protein-4) expression were measured and correlated with prognostic markers and Rai staging. Furthermore, the levels of B cell subsets and immune checkpoint expression on various B cells were measured post protein kinase C activation and immune checkpoint blockage. Results Cumulative evidence from the systematic review that included 14 studies showed that targeted therapy combined with immunotherapy is more effective than chemoimmunotherapy in treatment-naïve and high-risk CLL patients. However, these treatments are associated with some major severe adverse events. In the experimental studies, there was increased levels of activated B cells (P < 0.0001) in patients with CLL. The immune checkpoints PD-1 and CTLA-4 were elevated on total B cells, activated B cells and memory B cells (P < 0.05). However, the increased immune checkpoint expression was not correlated with a prognostic marker, beta-2 microglobulin (B2M) levels. It was demonstrated that the levels of memory B cells and activated memory B cells increased following anti-CTLA-4, anti-PD1 and anti-PD-L1 treatment while levels of activated B cells were significantly decreased (P < 0.01). Moreover, the immune checkpoints CTLA-4, PD-1, PD-L1 and PD-L2 expression levels were increased in B cell subsets following B cell stimulation. However, the levels of CTLA-4, PD-1 and PD-L1 were downregulated on total B cells following anti-PD1, PD-L1 and CTL-4 treatment (P < 0.05). The baseline levels of soluble immune checkpoint CD25, TIM-3, galectin-9, PD-1 and PD-L1 were elevated in patients with CLL (P < 0.001). However, there were no associations between the soluble immune checkpoints and B2M levels, Rai stage, fluorescence in situ hybridization (FISH) status such as del17p and international prognostic index for chronic lymphocytic leukemia (CLL-IPI) score. Conclusion In this study we showed that in patients with CLL there is an increased expression of immune checkpoints on various B cell subsets. However, there is no correlation between these immune checkpoint expressions and prognostic markers or Rai staging. Our study further showed that soluble immune checkpoints associated with more aggressive disease characteristics were also elevated on these patients with CLL. The use of immune checkpoint blockage could benefit patients with CLL. However, the predictive value of the immune checkpoints and the use of immune checkpoint blockage require further study in larger cohorts of patients.