Iomab-B (apamistamab) to overcome high-risk TP53 mutation resulting in significant improvement in overall survival in patients with active relapsed refractory AML at the European Bone Marrow Transplant Annual Meeting

The results showed that an Iomab-B led bone marrow transplant (BMT) results in higher rates of remissions and durable Complete Remission (dCR), which is the primary endpoint of the SIERRA trial, as well as significant improvement in overall survival in TP53 positive patients.

Iomab-B is a targeted radiotherapeutic comprised of an anti-CD45 monoclonal antibody with the Iodine-131 radioisotope payload. The Phase III SIERRA trial enrolled 153 patients age 55 and above with active relapsed or refractory acute myeloid leukemia (AML) and compared outcomes of patients receiving Iomab-B BMT to those of patients receiving physician's choice of care in the control arm. In total, 24% (37/153) of the patients enrolled on SIERRA had a TP53 mutation, which is associated with limited treatment options and poor outcomes.

Median OS was 6.37 months in TP53 negative patients receiving Iomab-B and 5.72 months for TP53 positive patients demonstrating Iomab-B's ability to overcome TP53 gene mutations.

Dr. Hannah Choe, Assistant Professor of Medicine at Ohio State University and SIERRA trial investigator, commented, "TP53 mutations are associated with very poor outcomes due to resistance to anti-leukemic therapies with patients rarely offered access to potentially curative transplantation. The SIERRA trial showed that Iomab-B was well tolerated and can enable unprecedented access to transplant in this patient population and induce high complete remission rates despite active, relapsed/refractory disease and a TP53 mutation. These results were very well received at EBMT and demonstrate the novelty and safety of a CD45-directed antibody radiation conjugate. More importantly, we see that these response rates translated into improved overall survival, overcoming the increased risk associated with TP53 mutation while no other viable treatment options exist. We are excited for Iomab-B's potential use and safety for disease control in patients with a TP53 mutation."