Therapy of 4s Chimeric Antigen Receptor T Cells Achieves Long-Term Disease-Free Survival with No Severe CRS or Cres in Patients with Relapsed and Refractory Acute Lymphoblastic Leukemia

Background: CD19 targeting chimeric antigen receptor T cells(CART19) therapy have shown great therapeutic potential in relapsed and refractory B cell acute lymphoblastic leukemia (ALL), but associated with risk of life-threatening adverse effects as severe cytokine release syndrome (sCRS) and CAR-T-cell-related encephalopathy syndrome (CRES).It's been reported that high leukemia burden before CART therapy, and high does infused CART cells are associated with severity of CRS and CRES. To decrease the risk of severe adverse effect, we applied integrated therapeutic strategy of using fourth generation CART cells , reducing leukemia blasts burden in bone marrow, and decreasing the dose of infused CART cells (www.clinicaltrials.gov; #NCT03407859 and #NCT03125577 ).

Methods: Between May 23, 2016 and July 2, 2018,the trial enrolled 20 patients (pts) who were exhausted with all available treatment options, life expectancy >2 months,CD19-positive and diagnosis of B lineage ALL.T cells were apheresis collected and transduced with an apoptosis-inducible, safety-engineered lentivector CAR with the following intracellular signaling domains: CD28/CD27/CD3ζ-iCasp9 (4SCAR). In vitro amplication of CART was not performed. In pts with bone marrow blasts exceeding 50.0%, VDCP or similar chemotherapy was given to reduce the tumor burden, and then received FC conditioning regimen (FLU 30mg/m², d1-3; CTX 300mg/m², d1-3), while FC regimen was directly carried out in pts with bone marrow blasts less than 50.0%.In this trial, Pts received single CD19-targeted CARTs or multi-CARTs targeting CD19 and an additional antigen of CD22 or CD123.The level of CAR-T cells and cytokines in peripheral blood, as well as tumor burden was measured after infusion.

Results: 20 pts were enrolled and infused with CAR-T cells. The median age is 37.5 (16-67) years old. Of these pts, 5 had prior HSCT and 14 had adverse genetic abnormalities, including 4 pts (20%) who were Philadelphia chromosome-positive(Ph+). All pts were previously treated with 2-22 courses of cytotoxic chemotherapy regimens. The overall objective response rate was 85%(17/20), and the complete response(CR) rate was 80%(16/20). The complete remission rate of 12 pts receiving single CD19-targeted CART therapy was 83 %(10/12), while 33%(4/12) of them had disease relapse at 6 months after infusion. Of the 7 people who received multi-CARTs infusion, 71%(5/7) achieved complete remission, with relapse rate of 29%(2/7) at 6 months after infusion. 3 pts who relapsed post transplantation received combination therapy of anti-CD19 CART and anti-CD123 CART, and all achieved minimal residual disease-negative CR within 1 month after CART infusion, 2 of whom maintained disease-free survival for 7 months and 11 months to date, respectively. Among the 7 people who underwent HSCT after achieving CR, 6 of them maintained disease-free survival for 3 months to 9 months. At a median follow-up of 115.5 days (ranging from14 to 384), the median overall survival was 269 days and the median event-free survival was 232 days. During treatment and follow-up, the most common adverse events were grade 1-2 cytokine release syndrome (CRS), with an incidence of 55%.No grade 3 or higher CRS was observed.12 pts were infused with a dose equal to or exceeding 5*10^5/kg, 10 of whom had CRS response. While only 2 of the 8 pts who received the infusion dose of less than 5*10^5/kg had CRS reaction and both of them were grade 1 CRS, suggesting low CAR-T cell doses decrease the risk of CRS (P=0.009). Interestingly, the objective response rate did not differ significantly between the low dose and high dose group.

Conclusions: Based on fourth generation CART system, a therapeutic strategy of low tumor burden and low CART infusion dose shows a safer profiling while remaining potent efficacy against leukemia.