One wears a prim white bonnet. Another sticks out its tongue, hands resting over abdomen. A third clutches at its chest, mouth seemingly frozen in a scream. They are faces from the past, trapped in the appearance they bore when laid to rest nearly 300 years ago.

And disturbed from their eternal sleep, these mummies may help unlock the secrets of the immune system.

Resting in cardboard boxes in long rows of cabinets on the top floor of the Hungarian Natural History Museum in Budapest, the 265 mummies are helping scientists find new ways to treat tuberculosis....