A previously healthy 40-year-old male, whose mother had been diagnosed with SARS-CoV-2 infection a week ago, started to have fever without dry cough, dyspnea and diarrhea on Jan.18, 2020 (day 1). He received antivirus therapy (Arbidol) for a week because of his contact history and symptoms. On Jan. 20, 2020 (day 3), the chest CT scan revealed bilateral pneumonia. He was transferred from fever clinic to isolation ward of Tongji hospital in Wuhan. On Jan. 23 (day 6), he was diagnosed with SARS-CoV-2 infection confirmed by the positive oropharyngeal swab test (detail shown in ). His inspiratory dyspnea was obvious with < 80% arterial oxygen saturation. The follow-up CT scan on Jan. 24 (day 7) and 27 (day 10) revealed a typical CT feature of COVID-19, manifested as bilateral multiple irregular areas of ground-glass opacities (GGO) and consolidation. He had severe COVID-19 and was put on BiPAP ventilator. Methylprednisolone (1 mg/kg/d) and immunoglobulin (10 g/d) were intravenously administrated for 10 days. His symptoms gradually improved, body temperature returned to normal, and BiPAP ventilator was replaced by nasal cannula to maintain oxygen saturation. On Feb. 8 (day 21), he was discharged from hospital after a CT examination on Feb. 3 (day 17) showing significantly decreased lesions and two negative oropharyngeal swab tests for SARS-CoV-2 on Feb. 4 (day 18) and Feb. 6 (day 20). He was placed on home quarantine. Five days later, he had fever again. On Feb.14, 2020 (day 27), he was admitted to the isolation ward, as he was retested positive for SARS-CoV-2 and the CT showed higher density of consolidation. The patient received oxygen support and methylprednisolone (10 mg/d) for 5 days. Within 2 days of treatment, his temperature dropped back to normal. Although the sixth CT scan showed higher density of consolidation, his symptoms disappeared completely. On March 1 (day 44), he was discharged from hospital after negative test for SARS-CoV-2 and improved absorption of inflammation on CT scan. His test for SARS-CoV-2 remained negative after 14 days of further isolation at home,. Of note, the number of lymphocytes significantly decreased alone with aggravation and recurrence of the disease, but was recovered accompanied with improvement of respiratory symptom. LDH was elevated during the course of disease and peaked on day 13 after initial symptom onset with the lowest number of lymphocytes, and maintained at higher levels during the recurrence. In addition, serum levels of ferritin and IL2R also significantly increased after recurrence, although the concentrations of these two molecules increased only a little after the initial infection (data not shown). Serological tests on Feb. 12 (day 31), 14 (day 33) and March 1 (day 44), 2020 showed lower levels of antibodies against SARS-CoV-2, respectively. The anti-SARS-CoV-2 IgM ranged from 19.27 to 36.44 AU/ml and IgG ranged from 24.68 to 28.81 AU/ml (detail shown in ). Total exon sequencing revealed a point mutation and an insertion of 6 nucleotides of TRNT1 (tRNA nucleotidyl transferase 1) gene, encoding a CCA-adding enzyme. Mutations in this gene may be associated with B cell immunodeficiency (detail shown in ).