Project Summary The COVID-19 pandemic continues to grow at an exponential pace around the globe threatening health systems and the world economy. In the 9 months since the novel SARS-CoV-2 virus was identified as the cause of the life-threatening disease COVID-19, there have been over 20.6 million confirmed cases and over 750,000 deaths globally. With few options for treatment and no vaccine, the immediate outlook remains grim. Even in less severe cases, illness can be prolonged, recovery slow with long term consequences, such as immunity to re-infection and chronic complications remain largely unknown. Convalescent plasma from recovered individuals is being increasingly used as a stopgap treatment to mitigate disease morbidity and mortality and slow the spread of SARS-CoV-2 infection. Although COVID-19 convalescent plasma appears to be well-tolerated and there is general enthusiasm for the treatment, randomized clinical trials will be required to determine efficacy not to mention optimum delivery. Surprisingly, convalescent plasma therapy (CPT) has been used historically for the treatment and prevention of numerous infectious diseases, but the mechanisms of action are not fully understood. Likewise, the effects of CPT on the host immune response to the specific pathogen are not well defined. The primary goal of this application is to identify cellular and molecular immune signatures that predict COVID-19 outcomes and clinical response to therapy. We propose to leverage samples from ongoing convalescent plasma clinical trials at Johns Hopkins to link CPT-induced immune signatures with clinical outcomes. We will utilize a unique pipeline of advanced flow cytometry, single cell next generation sequencing and antibody profiling to provide a focused map charting the effects of CPT on SARS-CoV-2- specific T cells and antibody. We will determine the COVID-19 antibody profile and neutralization capacity in convalescent donors and define how CPT subsequently shapes the COVID-19 antibody profile at epitope resolution in recipients. These exploratory studies will provide a basis for identifying disease-associated immune signatures with prognostic and/or predictive value which is a critical step in identifying targets for intervention and correlates of protection.