CD7.Pebl-CART for Patients with Relapsed/Refractory (r/r) T-Cell Acute Lymphoblastic Leukemia (T-ALL)

Background and aim Prognosis of patients with r/r T-ALL is dismal and there is an urgent need for novel, more effective, salvage therapies. The development of chimeric antigen receptor (CAR) T cells against T-ALL has been hampered by the expression of target antigens on both leukemia blasts and healthy T-cells, leading to CAR T cell fratricide. To overcome this obstacle, Png et al. developed a technology consisting of an anti-CD7 41BB-CD3ζ CAR and an anti-CD7 protein expression blocker (PEBL), which prevents CD7 expression on CAR T-cell surface (CD7.PEBL-CART) [Blood Adv 2017]. At the Bambino Gesù Children's Hospital, Rome, we investigated the safety and efficacy of autologous CD7.PEBL-CART in pediatric/young adult patients with r/r T-ALL, with at least 300 CD3+ cells/μL and less than 5% blasts in peripheral blood (PB), treated in a hospital exemption setting. Methods CD7.PEBL-CART were manufactured in our academic GMP facility with a 12-day-long process, starting from a fresh or cryopreserved leukapheresis, using a 2nd-generation lentiviral vector supplied by MediSix Therapeutics. Final drug products (DP) were cryopreserved and patients were treated with a single infusion after lymphodepletion including fludarabine and cyclophosphamide (30 mg/sqm/d for 4 days and 60 mg/kg/d for 2 days, respectively). All patients received letermovir as prophylaxis against CMV reactivation. Results As of July 20, 2024, 9 patients with r/r T-ALL, including early-thymocyte precursor ALL (ETP-ALL, 4 patients) received CD7.PEBL-CART at a median dose of 1x106 CAR+ cells/kg (range: 0.5-3). All patients had previously failed 2-3 lines of therapy, and 3/9 had relapsed after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Before treatment, CD7+ blasts were detectable in the bone marrow (BM) of all patients (median blast percentage: 12.1%; range: 0.1-70%), and 2/9 had combined BM/extramedullary disease. Manufacturing was successful in all patients, with a median total cell at the end of production of 1.75x109 (range: 0.05-3x109); median transduction and viability were 90.7% (range: 66.7-97.1%) and 86.8% (range: 82.2-94.1%), respectively. Median vector copy number was 3.3 (range: 1.8-6.6). CD7.PEBL-CART expanded in all patients, reaching a peak of 365.10+112.41 cells/µl and leading to the complete elimination of CD7+ cells. Seven patients had Grade 1 cytokine release syndrome (CRS) and 1 patient had Grade 2 CRS; none had immune effector cell-associated neurotoxicity syndrome. Hematological toxicity after lymphodepleting chemotherapy consisted of Grade 4 neutropenia (n=9), Grade 3-4 thrombocytopenia (n=9), Grade 1-2 anemia (n=4), Grade 3 anemia (n=5). Adenovirus reactivation was detected in 2 patients in both blood and stools and was successfully treated with twice-a-week infusions of cidofovir. BK virus infection causing hemorrhagic cystitis occurred in 2 patients, and CMV reactivation in 1 patient (successfully treated with foscarnet). No fungal infections were observed. All patients achieved a minimal residual disease (MRD)-negative complete remission (CR) 28 days after the infusion of CD7.PEBL-CART; 6 patients received an allo-HSCT as consolidation treatment. Of the 3 non-transplanted patients, one remains in CR with MRD negativity 4 months post-infusion, one relapsed with a lineage switch to a CD7- acute myeloid leukemia (AML) 7 months post-infusion and one had a relapse in the central nervous system with CD7+ blasts 3 months post-infusion. This patient received a second infusion of CD7.PEBL-CART, with a new expansion of the CAR T cells, and attained a new CR. Noteworthy, there was T- and NK-cell reconstitution in the non-transplanted patients, consisting of CD7- cells that retain an antiviral response. With a median follow-up of 9 months (range: 2-14), 4 patients (44%) are alive and in CR, 2 relapsed after CD7.PEBL-CART, 1 relapsed after allo-HSCT, and 2 died in continuous CR due to allo-HSCT-related toxicities (thrombotic microangiopathy and idiopathic pneumonia). Conclusion Our data indicate that CD7.PEBL-CART are an extremely effective option for inducing MRD-negative CR in patients with advanced r/r T-ALL, being associated with a manageable toxicity profile. The role of allo-HSCT as consolidation remains to be determined. A phase I/II clinical trial to confirm these promising results is active and currently enrolling at our Institution (NCT06064903).