<scp>CD72</scp> as a complementary B‐lineage marker for longitudinal measurable residual disease surveillance after <scp>CD19 CAR</scp> ‐T therapy in R/R B‐ <scp>ALL</scp>

This study aimed to evaluate the feasibility of CD72 as a complementary CD19-independent B-lineage gating marker for longitudinal measurable residual disease (MRD) surveillance in relapsed/refractory B-cell acute lymphoblastic leukemia (R/R B-ALL) following CD19 CAR-T therapy. Correlation analyses were performed in 66 B-ALL samples to compare MRD detection using CD72, CD19, and cytoplasmic CD79a. CD72 expression specificity was further evaluated in 129 leukemia patients. In addition, 129 patients with R/R B-ALL treated with autologous CD19 CAR-T therapy in registered clinical trials (ChiCTR-IIh-16008711; NCT03173417) between January 2021 and December 2022 were retrospectively analyzed, with follow-up continued until January 2025. CD72 gating showed excellent concordance with both CD19- and cCD79a-based strategies for MRD assessment. CD72 expression demonstrated high specificity in B-ALL, with a positivity rate of 95.77%, compared with 29.27% in AML and 23.53% in T-ALL. All 129 heavily pretreated patients achieved MRD-negative CR at day 28 after CAR-T infusion and subsequently underwent allo-HSCT, with a median interval of 54 days (range, 40-338). A total of 16 patients experienced MRD relapse during follow-up, including four clinically confirmed CD19-negative relapses that retained CD72 expression. Patients with pre-CAR-T MRD ≤1% showed earlier B-cell recovery than those with MRD >1% (median 30 [18-45] vs. 32 [26-79] days, p = 0.028). The MRD ≤1% cohort demonstrated significantly improved 3-year overall survival compared with the MRD >1% cohort (88.1% vs. 69.2%, p = 0.014). The 3-year cumulative incidence of MRD relapse was significantly lower in the MRD ≤1% cohort than in the MRD >1% cohort (3.96% vs. 17.95%, p = 0.019), while non-relapse mortality was also numerically lower in the MRD ≤1% cohort (5.92% vs. 17.95%, p = 0.053). Multivariate analysis identified KMT2A rearrangement, IKZF1 mutation, TP53 mutation, and elevated pre-CAR-T MRD as independent predictors of inferior outcomes. CD72 represents a feasible complementary B-lineage marker for longitudinal MRD surveillance following CD19 CAR-T therapy. Retention of CD72 expression in clinically confirmed CD19-negative relapses supports its potential utility when CD19 expression is lost after targeted therapy.