Evaluation of Safety, Tolerance, and Efficacy of Allogeneic LB-DTK-COV19 in Severe Coronavirus Disease 2019 Patients

The goal of this clinical trial is to evaluate the safety, tolerability, and efficacy of allogeneic SARS-CoV-2-Specific T cells (LB-DTK-COV19) in patients with persistent clinical symptoms following a positive SARS-CoV-2 PCR test for 14 days or longer. The main questions it aims to answer are: * What is the maximum tolerated dose of LB-DTK-COV19 based on dose-limiting toxicity? * What treatment emergent adverse events occur following LB-DTK-COV19 infusion? * Does LB-DTK-COV19 result in clinically significant improvement or worsening of clinical symptoms following infusion? Participants will: * Receive a single intravenous infusion of LB-DTK-COV19 (low dose: 5x10\^6/m\^2; mid dose:1x10\^7/m\^2; high dose: 2x10\^7/m\^2). * Attend follow-up visits at the clinic for 6 months after the infusion.