First AML patient successfully transplanted with investigational drug 

Cancer cells

Vor Bio, a clinical-stage cell and genome engineering company, has announced initial clinical data from VBP101, its Phase I/IIa multicentre, open-label, first-in-human study of tremtelectogene empogeditemcel or “trem-cel” (formerly VOR33) in patients with acute myeloid leukaemia (AML).  

The data observed from the first treated patient support the potential of a trem-cel transplant to be successfully manufactured, to engraft normally, and to maintain blood counts following treatment with the CD33-targeted therapy Mylotarg. The clinical trial continues to enroll patients and additional data are expected in 2023. 

Trem-cel displayed normal engraftment 

A product dose of 7.6 x106 CD34+ viable cells/kg, with a CD33 editing efficiency of 88% was manufactured. Following myeloablative conditioning, trem-cel was infused with no infusion reactions. The patient achieved neutrophil engraftment 10 days post-transplant which was within expectations for CD34-enriched transplants. Platelet recovery was observed on Day 22. Hematopoietic cell sub-population reconstitution was robust with over 90% of peripheral blood cells negative for CD33 expression, and 100% donor chimerism was achieved. These data provide proof-of-concept that trem-cel can engraft as expected and that CD33 does not appear to be biologically necessary for engraftment and hematopoietic reconstitution. 

Mylotarg tolerated at initial dose level 

The patient received Mylotarg at a dose of 0.5 mg/m2. At this dose, Mylotarg saturates CD33 antigen in patients with relapsed/refractory AML1, and in the original Phase I trial of Mylotarg2, neutropenia was observed across dose levels starting at 0.25mg/m2 within 14 days of infusion. No treatment related adverse events and no liver enzyme changes were observed through day 20 following Mylotarg dosing. No negative impacts to neutrophil and platelet counts were observed through day 20, suggesting tolerability at this initial dose level. 

Official comments 

“The unmet medical need for AML is significant and hematopoietic cell transplant is the best hope for these patients,” said Brenda Cooper, MD, Professor of Medicine in the Cellar Therapy Program at University Hospitals, Seidman Cancer Center, and an investigator in the VBP101 study. “Early treatment data in the first patient show that trem-cel can engraft normally and maintain normal hematopoiesis following Mylotarg dosing, which typically causes severe cytopenias. These data support the promise of this approach.” 

 “These early engraftment data represent the first time genome engineering has been used to genetically alter donor cells by removing an antigen present on blood cells, thereby allowing treatment using a CD33 targeted therapy while protecting normal blood cells,” said Dr. Robert Ang, Vor Bio’s President and Chief Executive Officer. “These encouraging data represent the first clinical validation of our platform to potentially enable next-generation transplants for patients with blood cancers. We look forward to sharing additional data updates in 2023.” 


  1. Mylotarg ODAC 2017 
  2. Sievers 1999 Blood 93:3678 

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