Sequential CD19-Directed CAR T-Cell Therapy and Allogeneic Transplant Provide Long-Term Responses in Pediatric B-ALL

Sequential therapy with CD19.28ζ-directed CAR T cells followed by allogeneic hematopoietic stem cell transplant (allo-HSCT) induced durable disease control in a significant population of children and young adult (CAYA) patients with relapsed/refractory B-cell acute lymphoblastic leukemia (B-ALL), according to findings from a long-term follow-up analysis of a phase 1 study (NCT01593696) that was published in the Journal of Clinical Oncology.¹

At a median follow-up of 4.8 years, the median overall survival (OS) was 10.5 months (95% CI, 6.3-29.2) with CD19.28ζ-directed CAR T cells. In those patients who proceeded to allo-HSCT (n = 21), the median OS was 70.2 months (95% CI, 10.4–not estimable).

Complete responses (CRs) were observed in 62% (n = 31) of patients infused with the CD19.28ζ-directed CAR T cells (n = 50). Moreover, 90.3% (n = 28) of patients who achieved a CR were minimal residual disease (MRD) negative by flow cytometry, which translated to a 56% MRD-negative CR rate. Concurrent next-generation sequencing (NGS), which was conducted in 12 patients who were MRD negative by flow cytometry, revealed that 5 patients were NGS-positive at day 28, with MRD levels ranging from 1 x 10¹ to 1 x 10³ cells/million.

“We demonstrate durable relapse-free survival in those who underwent post-CAR HSCT, providing evidence that HSCT is important for maintaining remissions in CAYAs receiving CD19[-directed] CAR T cells for B-ALL. Our data additionally support treatment of active CNS [central nervous system] disease, expanding the therapeutic index for CAR T cells,” Nirali N. Shah, MD, MHSc, head of the Hematologic Malignancies Section, the Lasker Clinical Research Scholar, and the National Institutes of Health (NIH) Distinguished Scholar at the Pediatric Oncology Branch of the NIH, and co-authors wrote in the study publication.

CD19-directed CAR T-cell therapies have demonstrated high rates of early responses in patients with B-ALL; however, long-term data with these therapies are limited. Additionally, although allo-HSCT has been shown to improve long-term disease-free survival in patients with relapsed/refractory B-ALL after chemotherapy, data have not definitively demonstrated whether consolidative transplant after CAR T-cell therapy is clinically relevant.

Initial findings from the phase 1 study established a 90% feasibility rate in manufacturing the CD19-directed CAR T-cell therapy among 21 patients.² The maximum-tolerated dose was defined as 1 x 10⁶ CAR T cells/kg. Notably, all cases of toxicity, including grade 4 cytokine release syndrome (CRS; n = 3; 14%), were fully reversible.

Two dose levels of CAR T-cell therapy were utilized in the study.1 One regimen consisted of one infusion of 1 x 10⁶ CAR T cells/kg given on day 0, and the other regimen consisted of one infusion of 3 x 10⁶ CAR T cells/kg given on day 0.

In the initial patient cohort (n = 21), pre-treatment for CAR T-cell therapy included lymphodepletion chemotherapy with standard low-dose fludarabine at 25 mg/m² for 3 days plus cyclophosphamide at 900 mg/m² for 1 day on days -4 to -2. In all subsequent patients enrolled, pre-treatment was tailored to further reduce disease burden prior to infusion. As such, patients with a high disease burden, defined as 25% or more bone marrow blasts, circulating peripheral blasts, or lymphomatous disease, received high-dose fludarabine plus cyclophosphamide (n = 7), fludarabine and cytarabine with prior filgrastim (FLAG; n = 6), or ifosfamide plus etoposide (n = 2). The remaining 14 patients received the same regimen as the initial cohort.

Overall, 53 patients were enrolled to the study; 51 patients had B-ALL, and the 2 had diffuse large B-cell lymphoma. The infused patient population included 50 CAYA patients with B-ALL.

Patients were a median age of 13.5 years (range, 4.3-30.4), and the majority of patients were male (n = 40; 80%). Patients had a median of 4 prior lines of therapy (range, 1-16); 22% of patients (n = 11) had primary refractory disease and 44% (n = 22) had undergone prior HSCT. Additionally, 14% of patients (n = 7) received prior CD19-directed therapy, including CAR T-cell therapy (n = 2) and blinatumomab (Blincyto; n = 5).

More than half (n = 32; 64%) of patients had 5% or greater marrow blasts and 8% (n = 4) had non-CNS extramedullary disease. Of the 26% (n = 13) of patients who had CNS disease, 6% (n = 3) had CNS3 disease, defined as more than 5 white blood cells (WBC)/µL in cerebrospinal fluid (CSF) and cytospin-positive blasts, 4% (n = 2) had CNS2 disease, defined as less than 5 WBC/µL in CSF and cytospin-positive blasts, and 16% (n = 8) had CNS1 disease, defined as absence of blasts in CSF on cytospin, regardless of WBC number.

Further efficacy results demonstrated that patients with primary refractory disease (P = .0035), those who had fewer prior lines of therapy (P = .033), those who had an M1 marrow (P = .0007; defined as MRD positivity with less than 5% blasts), and those who received fludarabine plus cyclophosphamide lymphodepletion (P = .041) had higher CR rates.

Specifically, the CR rate was 94.1% in patients with low disease burden (n = 17) vs 45.5% in patients with high disease burden (n = 33; P = .0007).

Moreover, patients who achieved CRs had higher CAR T-cell expansion and grade 3/4 CRS.

Additional long-term data demonstrated that the median event-free survival (EFS) was 3.1 months (95% CI, 0.9-7.7) with the CD19-directed CAR T-cell therapy. The 3-month EFS rate was 52% (95% CI, 37.4%-64.7%), and the 6-month EFS rate was 38% (95% CI, 24.8%-51.1%).

Patients who received any fludarabine/cyclophosphamide had improved EFS and OS; the median EFS was not reached among patients with an M1 marrow vs 0.9 months (95% CI, 0.9-2.0) in patients with M2 or greater marrow (P ≤ .0001).

The median time to allo-HSCT was 54 days from CAR T-cell therapy infusion (range, 42-97). The median EFS was not reached in the population who underwent transplant. The 5-year EFS rate after allo-HSCT was 61.9% (95% CI, 38.1%-78.8%).

Eight patients died between 0.8 and 71 months after transplant because of transplant-related complications, graft-vs-host disease, or infection (n = 6), complications from a second primary malignancy 3 years post-transplant (n = 1), and relapsed disease (n = 1).

Additionally, 2 patients relapsed after allo-HSCT. Of the 7 patients with MRD-negative CRs who did not proceed to allo-HSCT, the median time to relapse was 152 days after CAR T-cell therapy infusion (range, 94-394).

Regarding safety, all patients (n = 50) developed some grade of CRS, based on Lee Scale evaluation. Of these cases, 30% (n = 15) were grade 0, 26% (n = 13) were grade 1, 26% (n = 13) were grade 2, 12% (n = 6) were grade 3, and 6% (n = 3) were grade 4. Similar results were found based on the American Society for Transplantation and Cellular Therapy Scale, which stated that 30% (n = 15) had grade 0 CRS, 30% (n = 15) had grade 1 CRS, 18% (n = 9) had grade 2 CRS, 16% (n = 8) had grade 3 CRS, and 6% (n = 3) had grade 4 CRS.

Additionally, 14% (n = 7) of patients received tocilizumab (Actemra) and 8% (n = 4) received steroids for CRS.

The median time to CRS onset was 5 days (range, 1-12 days). Notably, disease burden was associated with CRS severity.

Overall, 20% (n = 10) of patients developed neurotoxicity; 12% (n = 6) had mild neurotoxicity and 8% (n = 4) had severe neurotoxicity, including seizures (n = 2) and grade 3 dysphasia (n = 2).

Neurotoxicity was also associated with high-grade CRS and high disease burden.

All patients, including those with CNS3 disease, experienced symptom resolution to baseline. One patient experienced cardiac arrest during CRS but made a full recovery.

References

1. Shah NN, Lee DW, Yates B, et al. Long-term follow-up of CD19-CAR T-cell therapy in children and young adults with B-ALL. J Clin Oncol. Published online March 25, 2021. doi:10.1200/JCO.20.02262
2. Lee DW, Kochenderfer JN, Stetler-Stevenson M, et al. T cells expressing CD19 chimeric antigen receptors for acute lymphoblastic leukaemia in children and young adults: a phase 1 dose-escalation trial. Lancet. 2015;385(9967):517-528. doi:10.1016/S0140-6736(14)61403-3