Even as the first vaccines for SARS-CoV-2, the virus that causes COVID-19, are being distributed, scientists and clinicians around the world have remained steadfast in their efforts to better understand how the human immune system responds to the virus and protects people against it. Now, a research team—led by Johns Hopkins Medicine and in collaboration with ImmunoScape, a U.S.-Singapore biotechnology company—has published one of the most comprehensive characterizations to date of a critical contributor to that protection: the response of immune system cells called T lymphocytes (more commonly known as T cells) in people who have recovered from SARS-CoV-2 infection.