Longitudinal Immunogenomic Profiling of Tumor and Immune Cells for Minimally-Invasive Monitoring of Smoldering Multiple Myeloma (SMM): The Immunocell Study

Background: Although great strides were made in the management of MM, our best chances to eradicate this malignancy may lie in preventing its progression.Most current models to predict risk of transformation in SMM are commonly established at diagnosis and not reevaluated over time, because some parameters such as tumor burden or genetic abnormalities require invasive bone marrow (BM) aspirates. It could be hypothesized that periodic monitoring of tumor biomarkers is needed to improve risk-stratification of SMM patients, and so would be new minimally-invasive methods that can replace those performed in BM samples. Such methods should also monitor immune profiles, to identify patients with stable tumor burden/genetics but at risk of progression due to lost immune surveillance.

Aim: Determine the level of concordance between the tumor/immune landscape in BM vs peripheral blood (PB) of SMM patients, as well as to evaluate immune profiles together with circulating tumor cell (CTC) numbers and genetic alterations every 6 months in PB, as minimally-invasive methods for identification of SMM patients at risk of developing active MM.

Methods: 300 patients are planned to be enrolled in the iMMunocell study that includes 24 sites across 8 European countries. PB samples are collected every 6 months during three years for next-generation flow (NGF) cytometry monitoring of CTCs and immune profiles. Additionally, CTCs and various immune cells are FACSorted to evaluate, every 6 months, their molecular profile in SMM patients with stable vs progressive disease. BM samples are taken at baseline and every 12 months according to patients’ choice, in which the same methods described previously for PB are performed. An interim analysis was preplanned to the moment when 150 patients were enrolled.

Results: A total of 170 SMM patients were enrolled and we report here data on the first 150. Thus far, 18/150 (12%) patients progressed to MM and according to 20/20/20 criteria, 1 had low, 7 intermediate and 10 had high risk SMM. Only 7/18 cases who progressed had >20% BM plasma cells (PC) by morphology. CTCs were detectable in 107/150 (71%) patients at baseline (median of 0.001% [0% - 0.42%] and 0.03 [0 - 21] CTCs/µL of PB). There was no correlation (or only modestly-significant) between the percentage of CTCs and BMPC by morphology (r=0.156, p=0.065) or flow cytometry (r=0.293, p=0.02). Median CTC counts were 0.02, 0.03 and 0.11 in SMM patients with low, intermediate and high risk disease according to 20/20/20 criteria, respectively (p=0.002).

Median CTC numbers were significantly different between cases with stable vs progressive disease (0.02 vs 0.11, p=0.005). As compared to those with ≤1 CTC/µL of PB, patients with >1 CTC/uL showed significantly higher risk of transformation (8% vs 47%, p<0.001) with a median time to progression of 6 months. In addition to the 150 PB samples analyzed at baseline, another 139 specimens were processed at 6, 12 and 18 months. The fluctuation in CTC numbers every 6 months was generally low (median, 0.03 CTCs/uL; IQR, 0.003 - 0.12), though in 10% of patient-samples the absolute variation was >0.5 CTCs/uL. Data on the genetic landscape of CTCs analyzed every 6 months from baseline to disease progression will be shown at the meeting.

Immune monitoring in patient-paired PB and BM samples at baseline (n=50) uncovered that 48 of 74 innate and adaptive immune cell types measured by multidimensional flow cytometry had similar distribution. Furthermore, we found significant differences in the distribution of three CD8 T cell subsets defined by differential expression of CD28, CD127, PD1, TIGIT, in PB of SMM patients with stable vs progressive disease. In patients with longitudinal PB samples from baseline until progression to active MM (n=7), there was a significant decrease in helper effector memory CXCR3+CCR4+ and cytotoxic CD127+TIGIT+PD1+ T cells, together with a significant increase in adaptive NK cells and Tγδ CD69+ T cells.

Conclusions: This is the first study performing CTC and immune monitoring every 6 months in PB samples from patients with SMM. Our results show a significant correlation between CTC counts and stable vs progressive disease, and suggest that CTC kinetics could be complementary to the 20/20/20 criteria for real-time identification of individual SMM patients at risk of developing active MM. Beyond CTC numbers, this study is uncovering key immune cell types associated with disease progression.