PureTech Presents Phase 1b Results for LYT-200 in Relapsed/Refractory (R/R) High-Risk Myelodysplastic Syndromes (HR-MDS) and Acute Myeloid Leukemia (AML) at ESMO 2026

Oral presentation highlights depth of responses in heavily pretreated patients with R/R HR-MDS, including two MRD-negative complete responses enabling stem cell transplantation

LYT-200 demonstrated a favorable safety profile across 101 patients with R/R HR-MDS and AML, with no dose-limiting toxicities or LYT-200-related serious adverse events

PureTech Founded Entity, Gallop Oncology, plans to advance LYT-200 into Phase 2 STRIDE-MDS trial in patients with R/R HR-MDS following successful FDA End-of-Phase 1 meeting and receipt of Fast Track designation

BOSTON, October 26, 2026--PureTech Health plc (LSE: PRTC) ("PureTech" or the "Company"), a hub-and-spoke biotherapeutics company dedicated to giving life to science and transforming innovation into value, today announced that results from the Phase 1b clinical trial of LYT-200 were presented in an oral session at the European Society for Medical Oncology (ESMO) Congress 2026 in Madrid, Spain. LYT-200 is a first-in-class monoclonal antibody targeting galectin-9, an important oncogenic driver and potent immunosuppressor. It is being advanced by PureTech's Founded Entity, Gallop Oncology (Gallop).

The completed Phase 1b trial (NCT05829226) was conducted across nine U.S. sites and evaluated LYT-200 both as a monotherapy and in combination regimens across 101 heavily pretreated patients with relapsed/refractory (R/R) high-risk myelodysplastic syndromes (HR-MDS) or acute myeloid leukemia (AML). The trial included dose escalation of LYT-200 monotherapy, followed by dose escalation of LYT-200 in combination with a hypomethylating agent (HMA; azacitidine or decitabine) in patients with R/R HR-MDS and with venetoclax (VEN) and an HMA in R/R AML.

As previously disclosed, topline results showed encouraging clinical activity and favorable safety in a heavily pretreated patient population. The oral presentation at ESMO provided further detail on the depth of responses observed. In R/R HR-MDS, LYT-200 at 12 mg/kg in combination with an HMA demonstrated a 36.4% complete response + partial response rate and a 45.5% overall response rate in 11 efficacy-evaluable1 patients, all of whom had previously received HMA therapy. Notably, two patients in this treatment cohort achieved MRD-negative complete responses and subsequently proceeded to stem cell transplantation.

Efficacy-evaluable R/R HR-MDS patients had a median of 3 prior lines of therapy (range: 1-5), and all (100%) had previously been treated with an HMA. Importantly, clinical responses were observed across patients with a range of mutations (i.e., BCOR, DNMT3A, SF3B1, TET2, PTPN11, KRAS, and RUNX1-RUNX1T1), and all patients had high-risk cytogenetics, which – coupled with prior exposure to treatment – suggests biologically aggressive, treatment-refractory disease with elevated risk of progression and poor clinical outcomes. Taken together, these attributes underscore the potential mutation-agnostic mechanism of LYT-200 and its potential for broad clinical use.