P-166: Characteristics of immune-genes rearrangements in Chinese Multiple Myeloma patients

Introduction: Immune genes may play effective roles in malignant hematological diseases. In multiple myeloma (MM), the study of immune genes landscape was rare. MRD monitoring is the most important application of immune genes in MM, providing a strong prognostic measurement for treatment efficiency. Though microenvironment could be crucial in MM, related research was limited.

Methods:
BM and PB samples from patients and health donor (HD) were collected. Using CD138 beads to sort malignant plasma cells in BM, and extracting gDNA from CD138+ plasma cells and T cells from BM and PB to construct libraries for NGS.

Results:
NGS of Ig repertoire (IR) was used to identify tumor clonotypes and build the Ig genes landscape. Based on 269 dominant clonotypes, IGH V3-74 is the most biased gene to use in patients with 1q21 duplication while IGH V1-69 presented higher usage frequency in patients with 13q14 deletion.

NGS of IR had higher sensitivity than MFC in MRD detection. There were 22 MFC-negative patients tested positive in NGS of IR in our study, breaking the susceptive MRD-negative situation and also the temporary CR in early therapy. Results of NGS-MRD were highly relative to therapy response, we classified patients into PD, VGPR and CR group that PD group had the highest MRD value, followed the VGPR group, CR group had the lowest value.

Then, we performed bulk TCR-seq in BM and PB. Interestingly, the consistency between PB and BM in Shannon diversity and Clonality were great well. However, the clonotypes’ uniformity in PB and BM was poor.

After that, we build the receiver operating characteristics (ROC) curve of TCR diversity. Compared to HD, TCR Shannon diversity and clonotypes were lower in MM patients while the clonality was higher. The AUC values of TCR diversity were over 0.7 which were reliable. TCR diversity results correlated great well with clinical diagnosis that the ISS-1 group presented the highest TCR diversity index included Shannon index and clonotypes, and the lowest clonality, followed ISS-2 group and then ISS-3 group. According to the clinical responses which were classified into PR-PD group and CR group, TCR diversity index presented great indications, especially Shannon diversity and clonotypes. Most of patients could reach the CR status temporarily during the early therapy, and the CR group showed higher diversity and more clonotypes than the VGPR group. Overall, the above results suggested the huge potency of TCR diversity index to be biomarkers of indicating the clinical responses and prognosis of NDMM.

Conclusions: In this study, we established the immune-genes rearrangements landscape in Chinese MM patients under different genetic backgrounds, presented a sensitive method in MRD monitoring and uncovered the potency of TCR diversity index to be regarded as biomarkers for MM prognosis.