Among patients with B-cell acute lymphoblastic leukemia (ALL) who received an infusion of 19-28z CAR T cells, patients with low disease burden had better survival outcomes and fewer toxic effects than did patients with a high disease burden, according to long-term follow-up results of a phase 1 study.

Median overall survival for B-cell ALL patients with low disease burden was 20.1 months, compared with 12.4 months for those with a high disease burden (P = .02), and 12.9 months for the entire cohort, according to results published in the New England Journal of Medicine.

The 12.9-month overall survival for the full study cohort “compares favorably” to results from another recently reported clinical trial showing overall survival of 7.7 months for adult B-cell ALL patients treated with blinatumomab, an anti–CD19/CD3 bispecific T-cell engager, wrote Jae H. Park, MD , of the Leukemia Service, Memorial Sloan Kettering Cancer Center, New York, and his coauthors.

The CAR T-cell and blinatumomab results cannot be directly compared owing to the differences in study design, patient characteristics, and posttreatment consolidation, but “the observation of patients with durable remissions in these two studies highlights the potential of CD19-targeted immunotherapies,” Dr. Park and his colleagues wrote in their report.

The phase 1 trial by Dr. Park and his colleagues included 53 adults with relapsed B-cell ALL who received a single infusion of 19-28z CAR T-cell therapy manufactured at Memorial Sloan Kettering Cancer Center.

After the infusion, 41% of patients with high disease burden (at least 5% bone marrow blasts or extramedullary disease) experienced severe cytokine release syndrome, compared with 5% of those with low disease burden, according to the report.

Likewise, neurotoxic effects were seen in 59% of high disease burden B-ALL patients, compared with 14% of those with low disease burden, the investigators reported.

Low disease burden was associated with a higher rate of complete remission, but this finding did not reach statistical significance. However, low disease burden patients not only had improved overall survival, as noted, but also had a significantly longer event-free survival versus high disease burden patients (10.6 and 5.3 months, respectively; P = .01).

Robust expansion of CAR T cells in vivo was a good predictor of short-term response and toxic effects but did not correlate with longer-term efficacy, according to the researchers. Instead, the ratio of peak CAR T-cell expansion to tumor burden correlated significantly with event-free and overall survival.

That finding “raises the hypothesis that an effective ratio of CAR T cells to target CD19+ leukemia cells is more likely to occur in patients with a low disease burden than in those with a high disease burden, despite a smaller number of expanded T cells in patients with a low disease burden,” the investigators wrote.

The study was funded by the Commonwealth Foundation for Cancer Research, Juno Therapeutics, and others. Several study authors reported ties to Juno Therapeutics and other pharmaceutical companies.

SOURCE: Park JH et al. N Engl J Med 2018 Feb 1;378:449-59.