Dr. Robert Grant developed a treatment — a daily pill known as pre-exposure prophylaxis, or PrEP — that could stop the AIDS crisis. We look at why that hasn’t happened. Guests: Dr. Grant, who has been working on H.I.V. treatment and prevention for over 30 years, and Donald G. McNeil Jr., a science and health reporter for The New York Times. For more information on today’s episode, visit nytimes.com/thedaily. Background reading: Gilead Sciences, the maker of Truvada, the only drug approved to prevent H.I.V. infection, will donate enough of the drug to supply 200,000 patients, but critics questioned the company’s motives.The high cost of drugs remains a major obstacle to ending the AIDS epidemic.Here’s more information about PrEP from the Centers for Disease Control and Prevention website.