SignificanceActivated T cells play an important role in the complications following COVID-19 infection. Anti-CD3 monoclonal antibody (mAb) binds to the T cell receptor and dampens inflammation by modulating T cell function. We show here that nasal administration of a fully human anti-CD3 Mab (Foralumab) modulates T cell inflammatory responses in COVID-19 by suppressing effector features in multiple T cell subsets, an effect also seen in subjects with multiple sclerosis. Immunomodulation by nasal anti-CD3 mAb represents a novel avenue for treatment of inflammatory human diseases.