Atara ATA520

ATA520 is a cytotoxic T lymphocyte (CTL) product candidate that is precision targeted against the tumor associated antigen, wilms tumor 1 (WT1), and is being studied as a treatment for hematologic malignancies including multiple myeloma (MM) and plasma cell leukemia (PCL) in Phase 1 clinical trials.

WT1 is an intracellular protein that is overexpressed in a number of cancers, including multiple myeloma (MM) and non-small cell lung, breast, pancreatic, ovarian, and colorectal cancers. Memorial Sloan Kettering (MSK) has two ongoing Phase 1 clinical trials evaluating primary donor derived WT1-CTL.

The first trial is a dose escalation trial of ATA520 for residual or relapsed leukemia after HCT. The second trial is a dose escalation trial of ATA520 following T-cell depleted HCT for patients with relapsed or refractory MM, including plasma cell leukemia (PCL). In 2011, it was reported in the journal Blood that the prognosis of PCL is poor, with a median survival of seven to eleven months and that survival is even shorter, two to seven months, when PCL occurs in the context of refractory or relapsing MM.

At the ASH 2015 Annual Meeting, MSK presented results from this Phase 1 clinical trial of primary donor-derived ATA520. In this trial, response assessments were conducted utilizing criteria consistent with those defined by the International Myeloma Working Group.

  • Patients with relapsed-refractory MM, including PCL were treated with allogeneic HCT followed by WT1-CTLs
  • At one year, a response rate of greater than 50% was observed in these patients. For these data, the response rate was determined by adding the complete responses to the partial responses and then dividing by the number of patients
  • Two patients who developed a complete response remained in remission for more than one year
  • There were no treatment-related SAEs with WT1-CTLs

Based on data from these trials, we expect to initiate a Phase 1/2 clinical trial in patients with hematologic malignancies in 2018.