CD4 and influenza: Cryopreserved PBMC from HIV+ donors have been widely used for enumeration of antigen-specific T cells (50) or measurement of the proviral reservoir within activated CD4 + T cells (51).We observed lower response rates to influenza after long-term cryopreservation, compared with a recent study where we detected influenza-specific CD4 T-cell responses in fresh blood from five out of six control donors, and in recently cryopreserved PBMC from 42 out of 45 convalescent COVID-19 patients (20).