WASHINGTON (AP) — A new strategy to fight an extremely aggressive type of brain tumor showed promise in a pair of experiments with a handful of patients.

Scientists took patients’ own immune cells and turned them into “living drugs” able to recognize and attack glioblastoma. In the first-step tests, those cells shrank tumors at least temporarily, researchers reported Wednesday.

So-called CAR-T therapy already is used to fight blood-related cancers like leukemia but researchers have struggled to make it work for solid tumors. Now separate teams at Massachusetts General Hospital and the University of Pennsylvania are developing next-generation CAR-T versions designed to get past some of glioblastoma’s defenses.

“It’s very early days,” cautioned Penn’s Dr. Stephen Bagley, who led one of the studies. But “we’re optimistic that we’ve got something to build on here, a real foundation.”