Obsidian Therapeutics is developing tumor infiltrating lymphocyte (TIL) therapies for patients with intractable diseases. Conventional TIL therapies have had some success for cancer patients but are still limited by toxicity concerns caused by concomitant IL2 therapy. Using their proprietary cytoDRIVE platform, Obsidian is engineering cytoTIL therapies to express therapeutic proteins that enhance anti-tumor activity and reduce toxicity. Obsidian’s lead program, cytoTIL15, has been engineered to eliminate the need for concomitant IL2 therapy improving the magnitude and duration of response. cytoTIL15 will enter clinical trials for patients with metastatic melanoma.