(PA-180) Revealing Clonal Evolution and Assessing Immune Reconstitution in Multiple Myeloma Using Next-Generation Sequencing-Based Minimal Residual Disease (NGS-MRD) Analysis

It is generally believed that clonal CDR3 sequences identified at baseline for MRD detection are stable and unique throughout the disease course. However, Munshi et al. reported the emergence of evolved clones post-treatment, though the prognostic significance of these findings remains undefined. Recently, Martinez-Lopez et al. proposed "clonal diversity" from NGS-MRD as a surrogate for immune competence to evaluate immune system reconstitution in MM patients.

Methods:

A total of 183 NDMM patients who underwent at least 1 NGS-MRD assessment were enrolled, including 109 patients with ≥2 time points. Clonotypes fulfilling clonal rearrangement criteria were defined as malignant, which called index clone at baseline. Clonal evolution was defined as either the emergence of new malignant Ig clonotypes or a discordant change in the relative frequency of the index clone between baseline and post-treatment samples. To assess immune reconstitution, BCR diversity was quantified by the number and Shannon index of unique IGH, IGK, and IGL clonotypes.

Results:

Among 109 patients, 8 patients exhibited new Ig clones post-treatment, while 5 showed discordant change in the relative frequency of the index clone. All 13 cases were persistent/recurrent MRD-positive. For example, in patient P07, new clones emerged after achieving CR with a residual MRD level of 10^-3, while the original index clone diminished. Among persistent/recurrent MRD-positive patients, those with clonal evolution had significantly shorter PFS (1-year PFS: 40.0% vs. 86.5%, P = 0.022).

Higher BCR diversity was found to be associated with better immune reconstitution. High IGH-Shannon index correlated with increased serum IgM levels (P = 0.001) and a higher proportion of normal plasma cells in the bone marrow (P < 0.001). High BCR diversity at the start of maintenance therapy showed a trend toward association with better PFS (IGH-counts: P = 0.18; IGK-counts: P = 0.034; IGL-counts: P = 0.15; IGH-Shannon: P = 0.077; IGK-Shannon: P = 0.0012; IGL-Shannon: P = 0.019).

Among patients who experienced disease progression, those with clonal evolution exhibited higher BCR diversity (P < 0.05), which may be explained by the presence of a broader spectrum of low-frequency tumor subclones. This observation suggests that BCR diversity may not accurately represent the immune status in patients with clonal evolution. Among persistent/recurrent MRD-positive patients, low BCR diversity at the start of maintenance—indicative of incomplete immune reconstitution—effectively identified a subgroup with poor prognosis independent of clonal evolution (all P < 0.05 for Shannon index and clonotype count of IGH, IGK, and IGL).

Conclusions:

NGS-MRD provides insights into clonal evolution and immune status, both of which contribute to risk stratification in MRD-positive multiple myeloma patients. The complementary information provided by NGS-MRD may facilitate earlier identification and intervention for patients at higher risk of relapse.