Biotech developers working on autoimmune CAR T therapies are testing assumptions about the safety thesis after concerns surfaced around IEC-HS risk (immune effector cell–associated hemophagocytic syndrome). A development brief highlights how teams are linking risk to a mix of factors including rapid manufacturing timelines, CAR construct design, and patient-specific biology. The reporting underscores that IEC-HS remains a key scrutiny point as companies broaden autoimmune targeting strategies. It also signals a continuing emphasis on engineering choices and manufacturing process controls as levers to manage safety signals in next-generation immune cell therapies. For the field, the near-term read is that regulators and investigators will likely continue to press for clearer mechanistic and operational predictors of high-grade toxicities in autoimmune CAR T programs.