The goal of this clinical study is to evaluate the safety and efficacy of autologous COVID-19 antigen specific T cell (LB-DTK-COV19) treatment in prolonged SARS-CoV-2 infected patients. The main questions it aims to answer are:

• What adverse events occur after the infusion of LB-DTK-COV19?
• Is there a clinically significant improvement in clinical symptoms within 4 weeks after the infusion?
• Is there a clinically significant reduction in SARS-CoV-2 viral load within 4 weeks after the infusion?

The patients will:

• Receive a single infusion of LB-DTK-COV19 either intravenously or using central venous catheter during the baseline visit at a dose of 1x10^7/m^2.
• Receive a second infusion of LB-DTK-COV19 either intravenously or using central venous catheter at the same dose 14 days after the first infusion.
• Attend follow-up visits at the clinic for 6 months after the first infusion.

Inclusion Criteria:

1. Patients aged 19 years or older.

2. Patients who tested positive for COVID-19 RT-PCR with persistent COVID-19 symptoms and experienced initial symptoms or received a first COVID-19 diagnosis more than 21 days prior to treatment.

   • Given that LB-DTK-COV19 requires 21 days to manufacture, patients who experienced initial symptoms or received a first COVID-19 diagnosis more than 7 days prior to screening may be eligible for enrollment. Following registration, COVID-19 RT-PCR positivity will be reassessed 21 days later. Eligible patients with confirmed positive COVID-19 test results will receive the study product infusion. Patients who test negative for COVID-19 will be withdrawn from the study.

3. Patients who fulfill Inclusion Criteria 2) and are moderately immunocompromised.

4. Patients who fulfill Inclusion Criteria 2) and are refractory to standard of care (including steroids, immunosuppressants, etc depending on the severity of the disease).

5. Patients with a life expectancy longer than 3 months.

6. Patients who have voluntarily decided to participate in this clinical study and have provided written consent to comply with the restrictions.

Exclusion Criteria:

1. Critically ill patients (WHO ordinal scale, category 7 or higher) who meet any of the following criteria:

   • Require invasive mechanical ventilation or extracorporeal membrane oxygenation (ECMO)
   • Diagnosed with acute respiratory distress syndrome (ARDS), shock, or multiple organ failure.

2. Patients with lung diseases other than COVID-19 pneumonia (including chronic obstructive pulmonary disease, asthma, cystic lung disease, tuberculosis, etc)

3. Female subjects who are pregnant, breastfeeding, of childbearing potential, or not using appropriate contraceptive methods.

4. Patients with active infection or fever (≥38°C) of unknown etiology, or ongoing bacterial or fungal infection.

5. Patients aged less than 19 years.

6. Patients who have been diagnosed with HIV, uncontrollable hypertension, unstable angina, congestive heart failure (NY class II or higher), uncontrollable severe diabetes, coronary angioplasty within the past 6 months, acute myocardial infarction or non-malignant disease, including uncontrollable atrial or ventricular fibrillation, within the past 6 months.

   • Uncontrollable hypertension is defined as Systolic BP ≥160 mmHg or Diastolic BP ≥100 mmHg despite taking blood pressure medications.

   • Severe diabetes is defined as follows:

     • Severe hyperglycemia with HbA1c ≥ 10.0%
     • Individuals who have been hospitalized for diabetic ketoacidosis within the past 12 weeks
     • Individuals who have received emergency treatment or been hospitalized within the past 12 weeks for severe hypoglycemia (glucose < 54mg/dL) accompanied by seizures and loss of consciousness

7. Patients with mental illness or drug intoxication that may affect the results of this clinical study.

8. Patients who are participating in another clinical study.

9. Patients deemed ineligible for participation in this clinical study by the investigator.

10. Patients with other severe medical conditions that may compromise compliance with the clinical study.