- Shares of cell therapy developer Nkarta fell nearly 40% on Tuesday after the company reported its latest results from an early-stage study of an experimental leukemia treatment harnessing natural killer cells.
- Nkarta said that three of six acute myeloid leukemia patients who received its cell therapy and a newer chemotherapy regimen meant to prepare them for treatment were driven into remission. But the remission rate associated with its therapy and a previously tested conditioning regimen is now lower than it was last year, with only four of 18 patients on the highest tested dose still meeting that criteria.
- Nkarta believes the results with the newer regimen are “very meaningful” for AML patients with no other options, and “demonstrate the power” of natural killer, or NK cells, CEO Paul Hastings told BioPharma Dive. But it’s unclear how long the effects will hold up, a key hurdle for cell therapies to clear. All of the responders were treated less than six months ago.
The last couple years have been difficult for developers of so-called allogeneic or “off-the-shelf” cell therapies, which are meant to be convenient alternatives to the personalized CAR-T treatments marketed for a handful of blood cancers.
Those findings have “clouded the entire allogeneic cell therapy space,” Hastings said, including developers of NK cell therapies. Shares of some, including Nkarta and Fate Therapeutics, are trading at or near record lows.
For allogeneic cell therapy developers to change the narrative, they’ll need to prove their treatments can hold up for longer than they have. Nkarta believes it’s shown signs of being able to. Hastings, for his part, pointed to the early results disclosed Tuesday as well as more mature findings the company disclosed in December from a study of an experimental lymphoma treatment. In its latest update, Nkarta also didn’t observe the type of severe immune or neurological side effects associated with CAR-T treatments.
Still, the responses in patients treated with Nkarta’s older conditioning regimen, a combination of the chemotherapies fludarabine and cyclophosphamide, “did not pan out as hoped,” wrote Salim Syed, an analyst at Mizuho Securities.
Nkarta has learned “just how heterogeneous a disease AML is and how there aren’t any clear predictors or response,” as the company first thought, Hastings added.
Nkarta is now trying to convince investors that its newer approach will be different. The updated conditioning regimen, which swaps in cytarabine for cyclophosphamide, has “known anti-leukemic activity” in combination with other therapies, Hastings said. It also increases the expression of the protein its treatment is designed to target.
Nkarta is enrolling another 12 to 20 patients in its study. The next update, slated for the first half of 2024, should include more patients and a better gauge of the treatment’s durability.
Shares once worth more than $18 in 2022 fell to less than $3 apiece on Tuesday.