Detection of CSRP2 Transcript Levels By Real-Time Quantitative PCR May be a Useful Tool for Monitoring Minimal Residual Disease in B-Cell ALL
Authors: Cao Lei-Ming , Wu Li-Xin , Zhao Ming-Yue , Zhou Ya-Lan , Li Jin-Lan , Sun Qiu-Yu , Jiang Hao , Qian Jiang , Xu Lan-Ping , Zhang Xiao-Hui , Liu Kai-Yan , Huang Xiao-Jun , Ruan Guo-Rui 
Published: November 2021

Abstract
Introduction Cysteine and glycine-rich protein 2 (CSRP2) is gaining increasing attention as a therapeutic target due to its high expression in acute leukemias and its involvement in the development of cancer. However, whether it can be used as a reliable marker for minimal residual disease (MRD) remains unknown.
Methods A total of 155 adult B-cell acute lymphoblastic leukemia (ALL) patients who received at least two cycles of consolidation chemotherapy were enrolled. Their leukemia-associated aberrant immune phenotypes (LAIPs) and CSRP2 transcript levels at the second consolidation chemotherapy (CON2) were detected by flow cytometry (FCM) and real-time quantitative reverse transcriptase-polymerase chain reaction (RQ-PCR). According to our published work, 1.80% and 0.01% were set as the positive threshold of CSRP2 transcript level and the FCM test for diagnosis, respectively. Pearson correlation coefficient was calculated to describe the relationship between the CSRP2 transcript level and the FCM test. Competing risk model and Cox proportional hazard regression model were conducted to estimated associations between the CSRP2 transcript level at CON2 and the prognosis.
Results The median CSRP2 transcript level of all 155 patients was 0.2% (0.02%-108.17%). Among them, 108 patients were negative for both FCM and CSRP2, and 8 patients were positive for both FCM and CSRP2. The coincidence rate was 74.84%. There was a significant positive correlation between FCM and CSRP2 (r=0.73, 95% CI 0.64-0.79; P &lt;0.001)(Figure 1a).
Patients were divided into a high CSRP2 group (N=17) and a low CSRP2 group (N=138) based on the transcript level of 1.00% settled by the ROC curve. Nine of 17 patients with high transcript level of CSRP2 suffered from leukemia relapse during the follow-up. Moreover, among the nine relapse patients, three patients had positive CSRP2 and negative FCM at CON2. In univariate analysis, patients with high CSRP2 transcript level showed a significantly lower 5-year leukemia-free survival (LFS) (33.0% vs. 48.6%, P =0.014) and 5-year survival (OS) (28.6% vs. 72.5%, P &lt;0.001), higher 5-year cumulative incidence of relapse (CIR) (60.6% vs. 47.3%; P =0.042) (Figure 1b-d). Variates with P-value lower than 0.1 including BCR-ABL1(Y/N), treatment (chemotherapy only vs. allo-HSCT), CSRP2 transcript level (high vs. low), WBC (≥ vs. &lt; 53.6×10E+9/L [settled by ROC curve]), were put into multivariate analysis. In multivariate analysis, no BCR-ABL1 (LFS, HR 0.43, 95% CI 0.26-0.71, P =0.001; OS, HR 0.41, 95% CI 0.21-0.81, P =0.010; CIR, HR 0.39, 95% CI 0.22-0.68, P =0.001), allo-HSCT (LFS, HR 0.29, 95% CI 0.17-0.51, P &lt; 0.001; OS, HR 0.21, 95% CI 0.11-0.42, P &lt;0.001; CIR, HR 0.29, 95% CI 0.17-0.50, P &lt;0.001), and low CSRP2 (LFS, HR 0.37, 95% CI 0.19-0.74, P =0.005; OS, HR 0.21, 95% CI 0.10-0.44, P &lt;0.001; CIR, HR 0.44, 95% CI 0.21-0.93, P =0.031) were independently associated with higher LFS, OS and lower CIR.
Conclusions Our study suggested that patients with a high CSRP2 transcript level at CON2 had poor survival and was an independent risk factor for relapse. The transcript level of CSPR2 at CON2 may be a valuable marker to complement the MRD assessment system and improve the number of evaluable patients.
Figure 1 Figure 1.

Disclosures
No relevant conflicts of interest to declare.