Recurrence of COVID-19 associated with reduced T-cell responses in a monozygotic twin pair

Abstract

Recurrence of COVID-19 in recovered patients has been increasingly reported. However, the immune mechanisms behind the recurrence have not been thoroughly investigated. The presence of neutralizing antibodies (nAbs) in recurrence/reinfection cases suggests that other types of immune response are involved in protection against recurrence. Here, we investigated the innate type I/III interferon (IFN) response, binding and nAb assays and T-cell responses to severe acute respiratory distress syndrome coronavirus 2 (SARS-CoV-2) with IFN gamma (IFNγ) enzyme-linked spot assay (ELISPOT) in three pairs of young adult monozygotic (MZ) twins with previous confirmed COVID-19, one of them presenting a severe recurrence four months after the initial infection. Twin studies have been of paramount importance to comprehend the immunogenetics of infectious diseases. Each MZ twin pair was previously exposed to SARS-CoV-2, as seen by clinical reports. The six individuals presented similar overall recovered immune responses except for the recurrence case, who presented a drastically reduced number of recognized SARS-CoV-2 T-cell epitopes on ELISPOT as compared to her twin sister and the other twin pairs. Our results suggest that the lack of a broad T-cell response to initial infection may have led to recurrence, emphasizing that an effective SARS-CoV-2-specific T-cell immune response is key for complete viral control and avoidance of clinical recurrence of COVID-19.

Keywords: COVID-19; T cell; immunity; recurrence; severe acute respiratory distress syndrome coronavirus 2; twins.

Figure 1.

Early transcriptional type I/type III IFN innate immune response. PBMCs were stimulated with 1 µg ml^–1 of double-stranded RNA Poly I:C for 1, 4 and 8 h. Total RNA was extracted for qPCR. Gene expression is relative to unstimulated cells. Expression kinetics of type I/type III genes after TLR3 stimulus for twin pair 1 (female): (a) ID 01 = severe clinical recurrence of COVID-19, (b) ID 02 = mild COVID-19 (non-recurrence); twin pair 2 (male): (c) ID 03 and (d) ID 04, asymptomatic infections; twin pair 3 (male): (e) ID 05 = mild COVID-19 and (f) ID 06 = asymptomatic infection. All subjects presented an early and strong (FC = 20 or higher) mRNA expression of at least one of the four type I/III IFN (IFNA2, IFNB1, IFNL2 and IFNL3) at the earliest time point after Poly I:C stimulus.

Figure 2.

Humoral immune response profiles. (a–c) SARS-CoV-2-binding specific antibodies (IgG, IgA and IgM) against trimeric spike (S), the receptor-binding domain (RBD) and the nucleocapsid protein (NP). (d) IgG against RBDs of human endemic alpha- and beta-coronaviruses NL63, 229E, HKU1 and OC43. (e) SARS-CoV-2 neutralizing antibody activity using pseudotyped and chimeric viruses. Antibody responses for SARS-CoV-2 and endemic human coronaviruses were evaluated by ELISA. All subjects displayed IgG against the spike protein, confirming that all of them had been infected by SARS-CoV-2. Besides, the antibody response to endemic human coronaviruses was virtually identical in each twin pair, indicating no difference in exposure to these potentially cross-reactive viruses. Neutralizing antibodies (nAb) were detected in all of them except for ID 06 (asymptomatic infection).

Figure 3.

CD4+ and CD8+ T-cell responses to SARS-CoV-2 T-cell epitopes in isolated PBMCs, three to four months after COVID-19 episodes and the recurrence. T-cell responses were assessed using human ex vivo IFNγ ELISPOT against a set of 20 CD4+ (a) and 26 CD8+ (b) SARS-CoV-2 T-cell epitopes with high HLA allelic population coverage identified with bioinformatics tools. PBMC were stimulated with synthetic peptides for 18 h. All subjects recognized greater than 70% of CD4+ and CD8+ epitopes except the patient with severe recurring infection (ID 01) who recognized only 7 of 46 CD4+ and CD8+ T-cell epitopes (15%). Overall, the SARS-CoV-2 T-cell response is the only immune parameter that was substantially lower in the COVID-19 recurrence case (ID 01).