By Chris Wack

Allogene Therapeutics Inc. shares fell 38% to $15 in premarket trading after the company said the U.S. Food and Drug Administration put a hold on AlloCAR T clinical trials following a report of a chromosomal abnormality in a patient.

The biotechnology company said it expects to provide additional updates following consultation with the FDA, which is continuing to review the end of Phase 1 materials submitted in anticipation of an ALLO-501A phase 2 trial.

The clinical hold follows the company's notification to the FDA of a chromosomal abnormality in an ALPHA2 study patient, which was detected in a bone marrow biopsy undertaken to assess pancytopenia.

The single case involves a patient with Stage IV transformed follicular lymphoma and c-myc rearrangement whose cancer was refractory to two prior lines of immune-chemotherapy and additional radiation therapy. The patient couldn't receive an autologous CD19 CAR T cell therapy due to manufacturing failure associated with inadequate expansion of autologous CAR T cells. The patient subsequently developed progressive pancytopenia and a bone marrow biopsy showed aplastic anemia and the presence of ALLO-501A CAR T cells with the chromosomal abnormality.

Allogene has dosed more than 100 patients with its gene edited AlloCAR T products. The company said it believes the data generated from the trials support a favorable clinical profile for ALLO-501A in patients with large B cell lymphoma.

Write to Chris Wack at chris.wack@wsj.com

(END) Dow Jones Newswires

10-08-21 0705ET