First-in-Class Autologous CD7-CAR-T Cells Exhibited Promising Clinical Efficacy for Relapsed and Refractory T-Lymphoblastic Leukemia/Lymphoma

Introduction

CD7 is an attractive therapeutic target for T-lymphoblastic leukemia/lymphoma (T-ALL/LBL). Chimeric antigen receptor T (CAR-T) cell therapy has achieved great success against B cell malignancies, and therefore promoted the exploration of CD7-CAR-T therapy to T-ALL/LBL. However, some big challenges have to be overcome for CD7-CAR-T therapy, including 1) potential contamination by abnormal T cells in CAR-T products; 2) life-threatening T cell hypoplasia; and 3) CAR-T cell fratricide due to CD7 expression on normal T cells.

In current study, a nanobody-derived CD7-CAR-T with a highly optimized structure and a clinically feasible strategy to overcome CAR-T cell fratricide and exclude abnormal T cell contamination were developed. A single-arm, open-label phase I pilot study was initiated to investigate the autologous CD7-CAR-T cell manufacturing feasibility, as well as the safety and efficacy of the CD7-CAR-T cells on patients with Relapsed/Refractory (R/R) T-ALL/LBL.

Methods

A CD7-targeting nanobody (CD7Nb) was recombinantly fused with an ER/Golgi-retention motif peptide to generate an anti-CD7 protein expression blocker (7PEBL) which can induce the intracellular retention of CD7 and prevent CAR-T cell fratricide. The best CAR candidate (PA3-17) was identified by using our CAR function verification platform and in vivo models.

Thereafter, a first-in-human clinical trial was initiated and approved by the institutional review board at the First Affiliated Hospital of Zhengzhou University (NCT04004637). 8 subjects, including 3 Early T-cell precursor (ETP)-ALL/LBL patients were enrolled in this study. All Pts were pretreated with fludarabine and cyclophosphamide prior to CAR-T infusion. PA3-17 was then administered at a single dose of 1.0x10⁶ (N=7) or 1.5x10⁶ (N=1; Pt#1) CAR-T cells/kg. Adverse events were categorized by NCI-CTCAE V5.0. Tumor responses were assessed based on the 2014 Lugano Evaluation Criteria for Lymphoma and 2016 Chinese Guideline for Diagnosis and Treatment of Acute Lymphoblastic Leukemia.

Results

7PEBL successfully abrogated CD7 expression from T cell surface. The resulted CAR-T cells had no impaired proliferation, cytotoxicity, and cytokine release. No CAR-T cell fratricide was observed during manufacturing. PA3-17 showed strong cytotoxicity against CCRF-CEM cells at an extremely low effector-to-target cell ratio of 1:100, suggesting a great potential of PA3-17 as a tumor serial killer which was most-likely resulted from highly optimized CD7Nb affinity. Both CCRF-CEM cell and T-ALL patient derived xenograft models demonstrated the outstanding cytotoxicity of PA3-17.

In current clinical trial, 5 Pts achieved CR. Case 2 and 6 were T-ALL and both of them achieved bone marrow (BM) MRD- CR at day 14 of post-infusion. Case 3, 4, and 5 were T-ALL/LBL who achieved BM MRD- CR at day 14, and CR for lymphoma on 1 or 2 months (mo) after PA3-17 infusion. Pt#2 died due to abdominal infection at 3 mo although he was still in MRD- CR status then. Pt#3 has been achieving PFS more than 6 mo. Other 3 CR Pts are still in remission for 1.5 to 4 mo (Fig 1). Interestingly, despite Pt#1 appeared grade 2 CRS, other 7 Pts only had grade 1 CRS. And there was no neurotoxicity was observed for all Pts. Superior PA3-17 in vivo expansion and persistence were observed in these CR Pts. Moderate in vivo cytokine release levels were found which could partially explain the lower CRS grade. In addition, only grade 2 lymphopenia in CR Pts was observed after 1 mo of PA3-17 treatments which might be due to in vivo expansion of PA3-17 and existence of CD7 negative normal T cells. Impressively, all ETP-ALL/LBL Pts (N=3) achieved CR which is clinically significant because this malignancy represents the high-risk T-ALL/LBL subgroup.

Please note that 2 unqualified PA3-17s were identified due to poor viability (Pt#7) or worse expansion (Pt#8, 0.4-fold). Considering all Pts were of end-stage, defective PA3-17s were still given to them as a compassionate use. Both Pts were excluded from this study but their responses to the PA3-17s were displayed in Figure 1 for reference. Pt#7 achieved short-term partial remission (PR) at 1 mo, Pt#8 did not response to the treatment.

Conclusions

A first-in-class autologous CD7-CAR-T cells were developed and exhibited exciting clinical efficacy and safety in treating R/R T-ALL/LBL. The manufacturing of autologous CD7-CAR-T cells was challenging but feasible in majority cases.