Autologous CD19-directed CAR-T exhibit promising safety and efficacy in refractory primary immune thrombocytopenia Free

Background:

Refractory primary immune thrombocytopenia (ITP) patients are characterized by great treatment difficulties, markedly reduced quality of life, and high hemorrhagic or infectious morbidity and mortality. New promising strategies are needed. Anti-CD19 Chimeric antigen receptor (CAR) T cell therapy, which can deeply eliminate CD19 positive B cells in circulation and tissues, has demonstrated revolutionary efficacy in autoimmune diseases, especially in SLE-associated ITP and multi-refractory primary ITP. We reported the preliminary safety and efficacy of autologous CD19-targeted CAR-T in the treatment of three refractory primary ITP patients. Here, we present updated data.

Methods: From February 2024 to June 2025, four eligible refractory primary ITP patients were enrolled. The eligibility details are listed in the clinicaltrials.gov as register number NCT06352281. The patients received conventional three-day FC lymphodepletion preconditioning chemotherapy with fludarabine 30mg/m2 and cyclophosphamide 300mg/m2 on days -5, -4, and -3 except one patient. Then, a single dose of 1.5×10⁵/kg or 3×10⁵/kg CAR-T cells were infused intravenously. As to safety profile, cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS) were graded by ASTCT criteria, and other adverse events were evaluated according to Common Terminology Criteria for Adverse Events (CTCAE) 5.0. Clinical efficacy was evaluated based on the platelet counts and platelet glycoprotein (GP) auto-antibodies detected by Enzyme linked immunosorbent assay(ELISA). CAR copy numbers were analyzed by quantitative polymerase chain reaction (qPCR). B cell counts in peripheral blood were detected by Flow cytometry (FCM).

Results: As of the data cut-off on June 15th, 2025, four patients finished side effect analysis and response evaluation. The follow-up time ranges from 2-16 months.

The median age was 12.5 years (range, 8 to 25) and 75.0% of patients were women. The median baseline platelet count was 9×10⁹/L (range, 2×10⁹ to 24×10⁹). The median disease duration of ITP was 7.5 years (range, 5 to 20), and patients had received a median of four different therapies (range, 3 to 5) for ITP previous. The most common previous therapies were glucorticoids, intravenous immune globulin (IVIG), TPO receptor agonists (TPO-RAs) in all patients. Platelet glycoprotein (GP) autoantibodies were detected in three patients.

Grade 1 CRS occurred in three patients. No grade 2 or higher CRS was observed. Grade 3 ICNAS occurred in two patients, which was resolved by high dose of methylprednisolone and the symptomatic treatment.

After infusion, CAR-T expansion was observed in all patients. The expansion peak time of CAR-T was around 10 days. Circulating CD19 positive B cells were fully eliminated in all patients. Consistent B cell aplasia was observed in three patients. B cell recovery happened one month after infusion in one patient.

Three patients achieved an objective response, and one showed no response. One patient achieved a complete response three months after infusion.

For all patients treated, all platelet GP autoantibodies turned below the basline of detection after infusion.

For one patient, her platelet counts got increased from below 10×10⁹/L as basline to a stable value around 30×10⁹/L and became IVIG-independent 3 months after CAR-T. Up to 9 months of follow-up, no signs of platelet increase was observed thus two doses of daratumumab(800mg per dose) were given to eradicate the plasma cells. Her platelet counts quickly increased above 200 ×10⁹/L within one week after daratumumab and maintained to the last follow-up.

Conclusion: Our study suggested that anti-CD19 CAR-T cell therapy had manageable safety and promising efficacy in treating refractory primary ITP. However, the patients had quite different responses to therapy, showing that a single B cell-eradicating intervention may not be enough for some patients. The success of daratumumab use for pt1 indicated the importance of plasma cell-eradication for the treatment of refractory primary immune thrombocytopenia.