CD31 and JAM-a Expressing Circulating Tumor Plasma Cells As Prognostic Biomarkers for Multiple Myeloma Disease

Circulating tumor plasma cells (CTCs) provide valuable prognostic information and are proposed as a strong factor for risk stratification of multiple myeloma (MM) patients. CD31-expressing plasma cells (PCs) have been described in bone marrow (BM), extramedullary sites, and in peripheral blood (PB), but the prognostic significance of CD31-expressing malignant PCs has remained unclear. Recent reports indicate that Junctional Adhesion Molecule A (JAM-A), expressed on BM malignant PCs is a potential therapeutic target and prognostic factor in MM. Therefore, we investigated CD31 expression on circulating PCs and its correlation with JAM-A expressing CTCs throughout disease stages.

Peripheral blood samples from 5 monoclonal gammopathy of undetermined significance (MGUS), 15 smoldering multiple myeloma (SMM), 144 newly diagnosed multiple myeloma (NDMM) patients and 20 healthy controls, BM aspirates from 40 matched MM patients and 7 healthy controls were collected. Using adapted Euroflow protocols and flow cytometry analysis, we analyzed normal and malignant PCs. Data were processed with Infinicyt and Metaflow software and statistically analyzed with Metaflow and GraphPad software.

In the group of matched samples, CD31 expression on CTCs was significantly higher in NDMM compared to MGUS (p=0.0061), and significantly higher in SMM compared to MGUS (p=0.0073). The expression of CD31 on normal PCs in healthy controls was significantly lower compared to any myeloma disease stage (p<0.0001 for MGUS, p=0.0001 for SMM and p=0.0001 for NDMM). JAM-A values on CTCs from healthy controls were significantly lower compared to JAM-A levels on CTCs from SMM (p=0.0001) and NDMM (p=0.0009). However, no statistically significant differences in CD31 and JAM-A levels were observed in BM across different groups.

We also evaluated JAM-A levels on CTCs at diagnosis in high-risk patients, based on cytogenetic abnormalities defined as t(4;14), del(17p13), t(14;16) or 1qamp/gain (24 with 1q gain/amp, 22 with other HR factors and 98 with standard risk). High JAM-A-expressing CTCs correlated with high-risk (HR) cytogenetic abnormalities. Significant differences were observed between the 1q gain/amp group and patients with other HR factors (p<0.0114), or no cytogenetic abnormalities (p<0.0001). However, JAM-A levels in BM counterparts did not correlate with HR cytogenetic abnormalities. Patients with low JAM-A on CTCs at diagnosis had better prognosis compared to those with high JAM-A-expressing CTCs (n = 67). The median progression-free survival in NDMM with higher JAM-A expression was 19 months, significantly shorter than the 23 months in patients with the lower JAM-A (p=0,0013, Log-rank test).

Pearson's correlation analysis revealed that the frequency of JAM-A on CTCs correlated with BM JAM-A levels on malignant PCs in the ND group (Pearson´s r=0.71, p=0.002). In the RRMM setting, CD31⁺ CTCs strongly correlated with JAM-A⁺ CTCs (Pearson´s r=0,85, p=0.044) and BM malignant PCs (Pearson´s r=0.52, p=0.084). Additionally, CD31 levels on CTCs correlated with BM CD31 levels on malignant PCs (Pearson´s r=0.62, p=0.03247). CD31 and JAM-A expressing CTCs correlated with clinical parameters such as β2 microglobulin and lactate dehydrogenase in the NDMM group.

Collectively, these results underscore the potential of CD31 and JAM-A on CTCs as promising biomarkers for risk stratification in myeloma, in a non-invasive fashion. JAM-A-expressing CTCs are notably associated with cytogenetic risk factors and disease outcomes. The expression of CD31 and JAM-A on CTCs provide insights into CTC biology and conceivable mechanisms of malignant PC dissemination. Beyond prognosis, JAM-A levels on CTCs are linked to cytogenetic risk factors and, thus, they may play a key role in MM patient risk stratification and guiding personalized approaches.