Neutrophils Of Multiple Myeloma Are Dysfunctional and Immunosuppressive

Multiple Myeloma (MM) is a plasma cell malignancy with a well documented immune dysfunction. However the role and function of neutrophils in MM and monoclonal gammopathy of undetermined significance (MGUS) has been poorly investigated.

on neutrophils (N) of 65 MM at diagnosis, 74 MGUS and 30 healthy subjects we evaluated, by flow cytometer, phagocytic activity and surface expression of CD64, CD16, CD62L and CD11b, markers of neutrophil activation. We tested also the immunosuppressive properties of N isolated from MGUS or MM patients, through functional assays, based on in vitro co-culture of N isolated from patients and T-lymphocytes from healthy subjects and we evaluated the expression of the immunosuppressive molecule arginase-1 (Arg-1) by RT-PCR.

Despite no differences in the absolute number of N between MM, MGUS and healthy subjects, we found a functional impairment in MM not evident in MGUS patients.

The phagocytic activity of MM-N was significantly reduced compared to healthy subjects-N (p<0.001) and MGUS-N (p<0.0001) and restored after induction chemotherapy (p=0.02).

Expression of CD64 was significantly elevated in MM-N compared to MGUS-N or healthy subjects-N (p=0.01 and p= 0.007 respectively) and was inversely correlated with phagocytic activity (p=0,01). No differences were observed among MM, MGUS and healthy subjects for the other surface markers evaluated.

MM-N exhibit an increased expression of ARG-1 compared to MGUS and healthy subjects (25.5 vs 6.2 vs 1 fold changes in gene expression, p=0.003), confirmed by functional assay of enzymatic activity of ARG-1, positively correlated with advanced disease. After PHA-P stimulation,T-lymphocytes isolated from healthy subjects missed the expression of activation markers such CD71, CD69, CD25, CD3ζ in the presence of MM-N for 72 hours, and in a less extensive way in the presence of MGUS-N.

Compared to controls, neutrophils obtained from MM patients have a reduced phagocytic activity, a greater expression of Arg-1 and exhibit an immunosuppressive function on T lymphocytes. Taken together, these findings indicated that neutrophils may contribute to impairment of immune function that characterizes MM patients.

No relevant conflicts of interest to declare.