VBP101 Clinical Trial

Phase 1/2a trial of trem-cel (VOR33) in combination with Mylotarg™

The VBP101 clinical trial is actively enrolling patients. This trial will provide important validating evidence of the potential of trem-cel and our broader engineered Hematopoietic Stem Cell (eHSC) approach.


Study goals

The key goals of the VBP101 trial are to evaluate tolerability and feasibility of allogeneic HCT with trem-cel, with a focus on timely neutrophil engraftment after trem-cel infusion. Once successfully engrafted with trem-cel, patients are eligible for subsequent treatment with Mylotarg as maintenance therapy or as treatment for relapse post-HCT. In patients receiving Mylotarg, we are examining the incidence of hematologic toxicities and determining the appropriate maintenance dose. Any observed protection from such on-target toxicity in this Phase 1/2a trial serves as an important proof of principle for our research and development platform. While this trial is not powered to confirm significance of efficacy, relapse-free survival and overall survival is being assessed.

Enrollment & follow-up

The VBP101 trial (NCT04849910) is open to AML patients who are at high risk of relapse and undergoing myeloablative hematopoietic stem cell transplant (HCT). Participants (18-70 years old) must have a diagnosis of CD33+ AML, an HLA-matched related or unrelated (10/10) donor and be a candidate for myeloablative HCT. Additional key inclusion criteria include morphologic remission with adverse risk factors for relapse. Patients with 5-10% bone marrow-only blasts with any cytogenetic risk are also eligible. Key exclusion criteria include prior auto/allo-HCT or treatment with Mylotarg.

To administer trem-cel, HSCs from matched healthy donors are mobilized and isolated from peripheral blood, engineered into trem-cel and then introduced into patients following myeloablative conditioning. As a safety measure, a portion of the original unmanipulated donor cells are frozen and stored as a backup graft.

At day 60, patients are re-evaluated for disease status and are examined for CD33-negative peripheral blood counts. Those patients remaining in remission and meeting dosing criteria are treated with maintenance doses (escalated in separate dosing cohorts) of Mylotarg once a month for four months to potentially reduce the risk of relapse by killing any residual AML cells. Patients in early relapse may be treated with fractionated dose Mylotarg or other salvage therapies including VBP301 (NCT05984199), Vor Bio’s donor-derived CD33-directed CAR-T trial. Patients are followed for two years after HCT and for up to 15 years post-HCT in a separate long-term follow-up study.

Recent results from VBP101

VBP101 Clinical Data Presented at ASH 2023:


All eight patients transplanted with trem-cel in the VBP101 study achieved primary neutrophil engraftment and high levels of myeloid donor chimerism.

Mylotarg Toxicities

All three patients treated with Mylotarg have demonstrated hematologic protection from deep cytopenias through repeat doses, suggesting that trem-cel transplants shielded patients’ healthy cells from the on-target toxicity (myelosuppression) typically seen with Mylotarg treatment.

Transplant Outcomes

The time for neutrophil engraftment in all eight patients treated with trem-cel (8-11 days) was similar to unedited transplants, further providing evidence that CD33 is biologically dispensable.

To learn more about our clinical trial, VBP101, please see our clinicaltrials.gov listing:

VBP101 – Allogeneic Engineered Hematopoietic Stem Cell Transplant (HCT) Lacking the CD33 Protein, and Post-HCT Treatment With Mylotarg, for Patients With CD33+ AML

If you have questions, please contact us.

The science behind the Vor Bio platform

We are applying proven technologies in new ways by genetically modifying healthy donor HSCs for protection and enabling use of modalities such as ADCs and CAR-Ts post-transplant.