CD4+CD25+CD127low regulatory T cells associated with the effect of CD19 CAR-T therapy for relapsed/refractory B-cell acute lymphoblastic leukemia

Abstract

Background: CD19-specific chimeric antigen receptor T-cell (CAR-T) therapy has shown promising clinical outcomes in relapsed/refractory acute B-cell lymphoblastic leukemia (R/R B-ALL) patients. However, some patients did not respond to this therapy or relapsed after remission. Regulatory T cells (Tregs) have shown great importance in promoting tumor escape, but little is known about their role in R/R B-ALL patients with CAR-T therapy. Our previous study has proved that higher Tregs before infusion was an independent high-risk factor for relapse-free survival (RFS). To further clarify the relationship between Tregs and the efficacy of CAR-T therapy, the present study tested the levels of CD4⁺CD25⁺CD127^low Tregs in peripheral blood (PB) of R/R B-ALL patients at different stages of CD19 CAR-T therapy, and evaluate their impact on the efficacy and prognosis of CAR-T therapy.

Methods: From November 2015 to May 2019, 47 R/R B-ALL patients successfully received CD19 CAR-T therapy at our institution and followed up for at least 1 month. Among them, one patient did not tested for Tregs, so 46 patients enrolled in this study. We collected clinical information of them and dynamically detected the frequency of CD4⁺CD25⁺CD127^low Tregs within CD4 + T cells at different time points (before infusion and at 1 week after infusion) by flow cytometry, and validated the relationship of circulating Tregs with clinical efficacy, OS, and recurrence of CAR-T therapy.

Results: Circulating Tregs of R/R B-ALL patients in pre-infusion group (median 6.67%) and in 1 week after infusion group (median 6.80%) were all higher than that of the healthy control group (median 5.04%), with statistical significance (P < 0.05). The frequencies of Tregs in not remission (NR) group at baseline (pre-infusion) and at 1 week after infusion were all significantly higher than those in remission group. With cut-off values of 11.54% (before infusion) and 13.56% (1 week after infusion), the specificity for Tregs were 94.6% and 100% , respectively. In remission group, 11 patients underwent allogeneic hematopoietic stem cell transplantation (allo-HSCT) after achieving remission by Sino 19 cell therapy. No significant differences of Tregs expression were found between transplantation and non-transplantation groups. Time-dependent Cox model showed that transplantation group had lower risk of relapse and death when compared with non-transplantation group (HR = 0.664 for RFS and HR = 0.364 for OS), however, no statistical significances were found (P = 0.403 and 0.106, respectively). Higher Tregs before infusion and at 1 week after infusion were significant associated with shorter RFS and OS by Kaplan-Meier analysis. Multivariate analysis showed that higher Tregs at 1 week after infusion was the independently factor for poor RFS (P = 0.032) and shorter OS (P = 0.025) in R/R B-ALL patients with CD19 CAR-T therapy. Besides, Tregs levels before and at 1 week after infusion were negatively correlated with the persistence time of Sino 19 cell.

Conclusion: Higher circulating Tregs, especially 1 week after CD19 CAR-T cell infusion, was a poor predict indicator for CD19 CAR-T therapy in R/R B-ALL patients.

Keywords: Acute lymphoblastic leukemia; CAR T; CD 19; Outcome; Regulatory T cells; Survival.