TScan Therapeutics presents Phase 1 clinical results on TSC-100, TSC-101

TScan Therapeutics announced an oral presentation at the 2024 Tandem Meetings: Transplantation & Cellular Therapy Meetings of the American Society for Transplantation and Cellular Therapy and the Center for International Blood and Marrow Transplant Research. The oral presentation, selected for the plenary session as a Best Abstract, highlights updated data from the Phase 1 multi-arm clinical trial evaluating TSC-100 and TSC-101, designed to treat residual disease and prevent relapse following hematopoietic cell transplantation in patients with acute myeloid leukemia, myelodysplastic syndromes, or acute lymphocytic leukemia. The Phase 1 trial is a multi-arm dose escalation study evaluating TSC-100 and TSC-101, which are designed to treat residual disease and prevent relapse following HCT in patients with AML, ALL or MDS undergoing haploidentical donor allogeneic HCT with reduced intensity conditioning. Primary endpoints include safety and dose-finding, and secondary and exploratory endpoints include relapse rates versus standard-of-care as well as supportive surrogates of efficacy, including donor chimerism and minimal residual disease. MRD identifies any residual disease-related DNA present in a patient, and chimerism measures any remaining recipient-derived hematopoietic cells in a patient following HCT. Key Presentation Highlights Include: TSC-100 treatment arm: 4/4 patients treated with TSC-100 achieved complete donor chimerism with no relapse. TSC-101 treatment arm: 4/4 patients treated with TSC-101 achieved complete donor chimerism with no relapse, including a patient with high-risk, TP53-mutated MDS who has reached one year of follow-up. One patient with AML was MRD-positive following HCT and converted to and maintained MRD-negative status following treatment with TSC-101. TSC-100 and TSC-101 persistence noted for prolonged periods: Persistence of TSC-100 and TSC-101 was observed at all time points after dosing, with the longest follow-up of over 9 months. Repeat dosing led to a 3-fold increase in circulating TSC-100 and TSC-101 levels compared to single dosing at the same time points. Six control arm patients have been enrolled and received standard of care HCT alone: One control-arm patient with high-risk, TP53-mutated MDS evolved with MRD positivity and worsening mixed chimerism, experienced clinical relapse approximately six months post-transplant, and succumbed to relapse approximately nine months post-transplant. One control-arm patient with MDS experienced clinical relapse approximately five months post-transplant. One control-arm patient with MDS developed worsening mixed chimerism requiring early termination of immunosuppression, resulting in complete donor chimerism but with grade 1 skin graft-versus-host disease. One control-arm patient never achieved complete donor chimerism, with more than four months follow-up post-transplant. 2/6 control-arm patients achieved complete donor chimerism following HCT.