Programmed Death-1 and Its Ligand Are Novel Immunotolerant Molecules Expressed on Leukemic B Cells in Chronic Lymphocytic Leukemia

Abstract

Programmed death-1 (PD-1) is an immunoreceptor predominantly expressed on exhausted T cells, which through an interaction with its ligand (PD-L1), controls peripheral tolerance by limiting effector functions of T lymphocytes. qRT-PCR for PD-1, PD-L1 and their splicing forms as well as flow cytometric assessment of surface expression was performed in a cohort of 58 chronic lymphocytic leukemia (CLL) patients. In functional studies, we assessed the influence of the proliferative response of leukemic B-cells induced by IL-4 and CD40L on PD-1 transcripts and expression on the protein level. The median level of PD-1, but not PD-L1, transcripts in CLL patients was higher in comparison to healthy volunteers (HVs, n = 43, p = 0.0057). We confirmed the presence of PD-1 and PD-L1 on the CLL cell surface, and found the expression of PD-1, but not PD-L1, to be higher among CLL patients in comparison to HVs (47.2% vs. 14.8%, p<0.0001). The Kaplan-Meier curves for the time to progression and overall survival in groups with high and low surface expression of PD-1 and PD-L1 revealed no prognostic value in CLL patients. After stimulation with IL-4 and CD40L, protein expression of PD-1 was significantly increased in samples that responded and up-regulated CD38. PD-1, which is aberrantly expressed both at mRNA and cell surface levels in CLL cells might represent a novel immunotolerant molecule involved in the pathomechanism of the disease, and could provide a novel target for future therapies.

The PD-1/PD-L1 axis contributes to T-cell dysfunction in chronic lymphocytic leukemia

“…39 Expression of PD-1 on the neoplastic counterpart was reported in a limited number of diffuse large B-cell lymphomas and in a more significant number of small lymphocytic lymphomas. A fraction of circulating CLL cells is also reported as PD-1 + (see Grzywnowicz et al 17 and Li et al 18 and confirmed in this work) even if the prognostic and functional implications remain unknown.…”

“…Moreover, a fraction of CLL lymphocytes, identified on the basis of CD19/CD5 surface expression, was PD-1 + ( Figure 1C), confirming previous observations. 17 On the contrary, circulating B lymphocytes from controls were mostly PD-1 -( Figure 1C). The PD-L1 ligand was found to be restricted to B lymphocytes in CLL and control samples; however, CLL B lymphocytes expressed significantly more PD-L1 when compared to B lymphocytes cells from controls ( Figure 1D).…”

Catching up with solid tumor oncology: what is the evidence for a prognostic role of programmed cell death-ligand 1/programmed cell death-1 expression in B-cell lymphomas?

“…34 Similar expression patterns were described in flow-cytometry-based studies. 60,61 In contrast, the majority of examined SLL/CLL full tissue sections collected from three different institutions (n=58) were PD-1-in another study, 40 similar to earlier findings of a lack of PD-1 expression on CLL cells. 33 …”

“…34,60,61 Using an extremes of survival approach and a limited number of patient samples, we found significant-…”

“…60 Higher PD-L1 expression on CLL cells was also detected in blood in some 27,60 but not all studies. 61 PD-1 was strongly expressed on ≥50% of tumor cells in the majority of SLL LN specimens and on peripheral blood (PB) neoplastic cells from almost all CLL patients. 34 Similar expression patterns were described in flow-cytometry-based studies.…”