Peak lymphocyte count flagged delayed neurotoxicity risk after cilta-cel

Design

Flow cytometry kinetics study plus multicentre retrospective cohort

Population

532 patients with relapsed or refractory myeloma treated with cilta-cel or ide-cel

Primary outcome

Delayed neurotoxicity by peak absolute lymphocyte count

Effect

Peak ALC ≥3 × 10³/μL (or ≥2.5 after twofold rise): sensitivity 81%, specificity 59%

A study of CAR T-cell therapy in relapsed or refractory myeloma combined two parts. In 90 patients with a uniform flow cytometry assay, cilta-cel expanded more than ide-cel (median peak 106 vs 49 cells/μL), and in the cilta-cel group very high expansion was associated with delayed neurotoxicity (median peak 1,009 vs 96 cells/μL). In a multicentre cohort of 532 patients (256 cilta-cel, 276 ide-cel), the routine absolute lymphocyte count was tested as a stand-in for expansion.

A higher peak lymphocyte count was associated with delayed neurotoxicity, especially parkinsonism after cilta-cel. A peak of at least 3 × 10³/μL, or at least 2.5 × 10³/μL after a twofold or greater rise, identified higher risk with 81% sensitivity and 59% specificity.

The value here is that a full blood count is available everywhere, whereas CAR T-cell assays are not. The threshold misses about one in five cases and flags many who will not develop neurotoxicity, so it is a prompt for closer neurological watch rather than a decision rule. Whether acting on it prevents harm has not been tested.

• Report and trend absolute lymphocyte counts closely in the weeks after cilta-cel infusion.
• Consider flagging a peak of at least 3 × 10³/μL, or 2.5 × 10³/μL after a twofold rise, to the treating team.
• Remember the threshold misses about one in five cases; a normal count is not reassurance.
• Agree locally with haematology how such a flag should prompt neurological monitoring.

Why it matters

It turns a test every laboratory already runs into an early warning for a disabling CAR T-cell complication.

Don't overread it

Observational and threshold-derived — acting on the count has not been shown to prevent neurotoxicity.

The statistics, in plain English

Sensitivity of 81% means the threshold caught about four in five patients who developed delayed neurotoxicity; specificity of 59% means about four in ten unaffected patients were also flagged. That suits a prompt for closer watching, not a firm prediction.

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