Pro-Inflammatory State of MGUS and Myeloma Patients Presenting with a Monoclonal Immunoglobulin Specific for an Infectious Pathogen

Background: Multiple myeloma (MM) and its pre-cancerous stage monoclonal gammopathy of undetermined significance (MGUS) allow to study immune responses and the chronology of inflammation in the context of chronic blood malignancies. MM is characterized by the accumulation of malignant plasma cells, which secrete >30g/L of monoclonal immunoglobulin (mc Ig), and by chronic inflammation. Inflammation may influence the structure of both polyclonal (pc) Ig and mc Ig produced by malignant plasma cells via the sialylation of Ig Fc fragment. Recently independent groups reported that chronic antigenic stimulation by lysoplipids or infectious pathogens, identified as the targets of mc Ig, likely initiated subsets of MGUS and MM.

Objective: Our aim was to investigate the links between infection, inflammation, and mc Ig specificity in MGUS and in MM.

Methods: The level of sialylation of the purified mc and pc IgGs from 148 patients (68 MGUS, 80 MM) was assessed via ELLA (Enzyme Linked Lectin Assay) and ELISAs, and compared to pc IgGs from 46 healthy volunteers (HV). The inflammatory state of patients was assessed by the quantification in serum of 40 inflammation-linked cytokines, using Luminex technology. Cytokine and Ig sialylation data were analyzed according to the infectious antigen specificity of the purified mc IgG, as determined by the "Multiplex Infectious Antigen Array" (MIAA). The MIAA assay used in this study allows testing for panels of antigens from 9 pathogens: EBV (HHV-4), HCV, cytomegalovirus (CMV, or HHV-5), HSV-1 (HHV-1), HSV-2 (HHV-2), varicella zoster virus (VZV, or HHV-3), H. pylori, Toxoplasma gondii (T. gondii), and Borrelia burgdorferi (B. burgdorferi).

Results: Inflammation was found to be remarkably similar in MGUS and in MM. Fourteen cytokines were similarly elevated with a p value <0.0001 in both MGUS and MM, compared to HV. MM differed from MGUS by higher levels of 4 cytokines: HGF, IL-11, RANTES, SDF-1α (p<0.05). In both MGUS and MM, purified mc IgGs exhibited a very low level of sialylation compared to pc IgGs from HV. Furthermore, mc IgGs from MM patients were less sialylated than mc IgGs from MGUS patients (p<0.01). Interestingly, MGUS and MM patients presenting hyposialylated pc IgGs had significantly higher levels of several inflammation cytokines: HGF, IL-6, TNFα, TGF-β1, IL-17 and IL-33, compared to patients with hyper-sialylated pc IgGs (p<0.05).

The MIAA assay performed on 128/148 patients showed that for 35 patients (19 MGUS and 16 MM), the purified mc IgG specifically targeted an infectious pathogen in the MIAA assay. The purified mc IgG of 22 patients targeted EBV, and EBNA-1 was the main target (20/22 patients). The purified mc IgG from the 13 other patients specifically targeted HSV-1 (n=6), CMV (n=2), VZV (n=2), and H. pylori (n=3). The sialylation results of mc and pc IgGs from these 35 "MIAA+" patients were analyzed separately: mc IgGs found to target an infectious pathogen showed a lower level of sialylation than mc IgGs of undetermined specificity (p=0.048). In addition, the degree of sialylation of mc and pc IgGs and the levels of 4 cytokines important for anti-microbial response (IFN-α₂, IL-13, IL-17, IL-33) were correlated.

Conclusion: Except for 4 cytokines, inflammation was found to be similar in MGUS and in MM. In both MGUS and MM, mc IgG were hyposialylated, and mc IgG specific for an infectious pathogen had the lowest level of sialylation. Hypo-sialylation of mc IgGs was concomitant with increased levels of cytokines that play a major role in inflammation and anti-microbial response. Altogether, these findings are consistent with infection, inflammation and abnormal immune response playing an important role in the pathogenesis of subsets of MGUS and MM.