Programmed cell death protein 1 (PD-1) / programmed cell death ligand 1 (PD-L1) in multiple myeloma

The bone marrow microenvironment in multiple myeloma (MM) is characterized by complex immune dysregulation involving multiple inhibitory pathways. Among these, the programmed cell death protein 1 (PD-1)/programmed cell death ligand 1 (PD-L1) axis contributes to T-cell dysfunction; However, its isolated role within this multifactorial network remains incompletely defined.

This prospective observational study performed a cross-sectional immunophenotypic analysis of 39 newly diagnosed MM (NDMM) patients. PD-1 expression on T cells and PD-L1 expression on bone marrow (BM) plasma cells (PCs) were assessed using flow cytometry. Associations with clinical and laboratory parameters were analyzed using correlation analysis.

PD-L1 mean fluorescence intensity (MFI) on PCs showed a positive correlation with BM T-cell percentage (r = 0.350, p = 0.029). PD-1 MFI on T cells correlated with total leukocytic count (TLC) (r = 0.326, p = 0.043). In International Staging System (ISS) stage III patients, PD-L1 expression on PC correlated with T cells% (r = 0.501, p = 0.018) and TLC (r = 0.427, p = 0.047), while PD-1 expression showed a strong positive correlation with TLC (r = 0.676, p = 0.001) and a negative correlation with age (r = - 0.492, p = 0.020). No significant association was observed with treatment response.

These findings provide an exploratory description of PD-1/PD-L1 expression patterns within the BM microenvironment in MM. Only in advanced cases according to ISS, PD-L1 expression on PC was linked to BM T cells frequency. PD-1/PD-L1 expression patterns were not linked to treatment response.