T cell function and immune checkpoint inhibition in chronic lymphocytic leukaemia.

Abstract

Background: The global burden of lymphoid malignancies gradually increased over the past decade, with chronic lymphocytic leukaemia (CLL) accounting for a quarter of the burden of all haematological malignancies. Chemotherapy in combination with rituximab has been used as standard care for patients with CLL. This regimen has been characterized by variable responses, relapses, and remissions. The exploration of the predictive value of prognostic factors in patients on chemoimmunotherapy (CIT) is crucial, however, such studies on the multi-ethnic group remain scant. Methods: This study consist of two phases, firstly we performed a systematic review and meta-analysis on the predictive value of protein biomarkers in patients with CLL on rituximab-based therapy. A total of 10 prognostic factors were identified and evaluated. In a subsequent prospective cross-sectional study comprising of treatment-naïve patients with CLL, we evaluated immune checkpoint profiles on T helper and cytotoxic T cells. The expression of selected inhibitory proteins (Programmed death 1; PD-1, programmed death ligand 1; PD-L1, cytotoxic T lymphocyte-associated antigen 4; CTLA-4 and CD56) were measured at baseline, and post-stimulation with phorbol 12-myristate 13-acetate (PMA), and following ex vivo blockade with monoclonal antibody therapy (anti-PD1 and anti-PDL1). Furthermore, correlations between beta-2-microglobulin (B2M), a marker of disease progression, and immune checkpoints was evaluated. Results: In our meta-analysis, chemoimmunotherapy with rituximab improved progression-free survival (PFS) (HR= 0.58; 95% Cl 0.49 – 0.68; p <0.001) and overall survival (OS) (HR= 0.77; 95% Cl 0.63 – 0.91; p <0.001) in patients with CLL. The following prognostic factors were confirmed and associated with poor patient outcomes; deletion 17p (HR = 4.88), Immunoglobulin heavy chain variable region gene mutation status (HR = 0.96), WCC (HR = 1.27), β2-microglobulin (HR = 0.96), and lactate dehydrogenase levels (HR = 1.20). Our results from the cross-sectional study demonstrated an increase in expression levels of PD-1, PD-L1 and CTLA-4 (p > 0.05) and no significant differences in expression levels of CD56 (p = 0.4126) on CD4+ T cells following stimulation. There were no statistically significant differences in the expression levels of PD-1 (p = 0.1826), while there were significant reductions in the expression levels of CTLA-4 and CD56 (p > 0.05), conversely, there was an increase in the expression levels of PD-L1 following CD8+ T cells stimulation. PD-1 and PD-L1 immune checkpoint blockade failed to reduce the expression levels of PD-1, PD-L1 and CTLA-4 on CD4+ and CD8+ T cells. Furthermore, the results showed novel positive correlation between B2M and soluble PD-1 (r = 0.65, p = 0.022), PD-L1 (r = 0.60, p = 0.036) and CD56 expression (r = 0.63, p = 0.033) on CD8+ T cells. Conclusions: Prognostic factors such as deletion 17p and 11q, white cell count, LDH, and most importantly B2M retained predictive value in patients with CLL on rituximab-containing CIT. These factors should be included in future prognostic factors in CIT and chemotherapy-free era of patient management. Our novel findings of the correlation between B2M and PD-1/PD-L1 suggests that monitoring B2M levels in patients with CLL may also be valuable in predicting patient responses to immunotherapy targeting the PD-1/PD-L1 axis