Reports of two patient deaths prompted Celyad Oncology SA to voluntarily pause a phase Ib trial testing its allogeneic CAR T-cell therapy, CYAD-101, in combination with Keytruda (pembrolizumab, Merck & Co. Inc.) in patients with refractory metastatic colorectal cancer (mCRC), the latest safety hitch among efforts to advance the promise of CAR T beyond the first approvals in hematological malignancies.