High-throughput TCRB enrichment sequencing of human cord blood exhibited a distinct fetal T cell repertoire in the third trimester of pregnancy

Abstract

Study questionWhat are the molecular characteristics during the maturation process of the human fetal immune system in the third trimester of pregnancy? Summary answerBoth the diversity and length of complementarity determining region 3 (CDR3s) in the fetal TCRB repertoire were less than those of adult CDR3s, and the fetal CDR3 length increased with gestation weeks in late pregnancy. What is known alreadyThe adaptive immune system recognizes various pathogens based on a large repertoire of T-cell receptors (TCR repertoire), but the maturation dynamics of the fetal TCR repertoire in the third trimester are largely unknown. The CDR3is the most diversified segment in the T-cell receptor {beta} chain (TCRB) that binds and recognizes the antigen. Study design, size, and durationThis was a basic research to assess the composing characteristics of TCRBs in core blood and the dynamic pattern with fetal development in the third trimester of pregnancy. Participants/materials, setting methodsHigh-throughput TCRB-enrichment sequencing was utilized to characterize the TCRB repertoire of cord blood at 24~38 weeks of gestational age (WGA) with nonpreterm fetuses and to investigate their difference compared with that of adult peripheral blood. Main results and the role of chanceCompared to the adult control, the fetal TCRB repertoire had a 4.8-fold lower number of unique CDR3s, a comparable Shannon diversity index (p=0.7387), a lower mean top clone rate (p < 0.001) and a constrictive top 1000 unique clone rates. Although all kinds of TCRBV and TCRBJ genes present in adult CDR3s were identified in fetuses, nearly half of these fragments showed a significant difference in usage. Moreover, the fetal TCRB repertoire held a shorter CDR3 length, and the CDR3 length showed a progressive increase with fetal development. Jensen-Shannon (JS) divergences of TCRBV and TCRBJ gene usage in dizygotic twins were much lower than those in unrelated pairs. In the parental-fetal pair, JS divergence of TCRBV gene usage was not obviously different, while that of TCRBJ gene usage was only slightly lower. Limitations, reasons for cautionThe sample size is limited due to the limited accessibility to cord blood in late pregnancy with healthy nonpreterm fetuses. Wider implications of the findingsOur findings reveal the unique properties of fetal TCRB repertoires in the third trimester, fill the gap in our understanding of the maturation process of prenatal fatal immunity, and deepen our understanding of the immunologically relevant problems in neonates. Study funding/competing interest(s)This work was supported by the National Natural Science Foundation of China (82171661) and Tianjin Municipal Science and Technology Special Funds for Enterprise Development (NO. 14ZXLJSY00320). The authors declare that they have no competing interests.