In chronic lymphocytic leukemia, activation of the thrombopoietin receptor promotes T-cell inhibitory properties, contributing to immunosuppression.

In chronic lymphocytic leukemia (CLL), the immune system is skewed towards a suppressive milieu. Levels of thrombopoietin (TPO), promoting cellular immune regulatory activity in immune thrombocytopenic purpura, were shown to be elevated in CLL patients. This study explored TPO as a potential immunomodulator, supporting CLL progression. We evaluated CLL cell-induced expression of TPO receptor (TPO-R) on T-cells and effects of its activation on T-cell responses. CLL cell involvement in TPO generation was also assessed. Baseline TPO-R expression on CD4 + T-cells was found to be higher in CLL patients than in healthy controls (HC). Exposure of HC-T-cells to B-cells, especially to CLL-B-cells stimulated with B-cell activating molecules, resulted in enhanced TPO-R expression on T-cells. CLL-T-cell stimulation with TPO reduced their proliferation and expanded the regulatory T-cell (Treg) population. At baseline, phosphorylation of STAT5, known to impact the Treg phenotype, was elevated in CLL-T-cells relative to those of HC. Exposure to TPO further enhanced STAT5 phosphorylation in CLL-T-cells, possibly driving the observed Treg expansion. The CLL immune milieu is involved in promotion of inhibitory features in T-cells through increased TPO-R levels and TPO-induced intracellular signaling. TPO and its signaling pathway could potentially support immunosuppression in CLL, and may emerge as novel therapeutic targets.

Impaired migration capacity in monocytes derived from patients with Gaucher disease.

Gaucher disease (GD) is characterized by glucocerebroside (GC) accumulation due to defective activity of the glucocerebrosidase (GlcCerase) enzyme. Monocytes and macrophages exhibit the highest GlcCerase activity and are most prominently affected by GC engorgement. As GD patients tend to exert various immune system-related changes, this study was designed to investigate potential effects of monocyte dysfunction on these alterations. Monocytes were isolated from peripheral blood mononuclear cells (PBMCs) of untreated GD patients and healthy volunteers. Monocyte migration capacity towards SDF1α was assessed. The GD patients exhibited reduced numbers of monocytes and decreased capability of SDF1α-dependent monocyte migration. Evaluation of CXCR4, the SDF1α receptor, revealed reduced expression of surface CXCR4 on GD-derived monocytes, despite similar CXCR4 mRNA transcript levels in the monocytes of healthy volunteers and GD patients. Reduction of surface CXCR4 was accompanied by increased intracellular CXCR4 levels in patient monocytes. This elevated intracellular CXCR4 might reflect significantly increased SDF1α concentrations characterizing patients' serum and the lysosomal impairment of GD, resulting in decreased degradation of CXCR4. Different distributions of CXCR4 expression observed in the two groups explain impaired SDF1α-dependent monocyte migration. Reduced numbers and impaired migration capacity of GD-derived monocytes could contribute to abnormal inflammation and GD-associated immune alterations seen in these patients.