Studies of other coronaviruses, together with the ones that trigger SARS and MERS, show that T cells play integral roles in stamping out illness, says Stephanie Langel, a virologist and immunologist at Duke University. Compared to antibodies, however, T cells—which usually hole up in hard-to-reach tissues like the lungs—are more difficult to extract and analyze. That makes T-cell detection unlikely to play much of a role in clinical checks for immune responses in opposition to SARS-CoV-2.…