T-cell receptor J beta gene segment usage in immature and mature human thymocytes

Development of Human Peripheral TCRBJ Gene Repertoire

Previous studies of TCRBJ gene repertoires of human peripheral T lymphocytes showed that all TCRBV family transcripts had some common features in BJ gene usage, and nevertheless, transcripts of each BV family gene had a distinct pattern. To discern how the development of the peripheral BJ repertoire is controlled, the effects of preferential BJ gene rearrangement, thymic selection, and peripheral stimulation on the repertoire formation were investigated. A PCR-ELISA technique was used to examine the immature CD3−CD4+CD8−, and mature CD3+CD4+CD8− and CD3+CD4−CD8+ thymocytes, and peripheral CD4+ and CD8+ T lymphocytes for their BJ gene repertoires. Analogous to the peripheral repertoire, the BJ gene repertoires of the immature thymocytes displayed common features, and each BV transcript had a distinct pattern. All features were conserved well by those of mature thymocytes and peripheral T lymphocytes. In addition, the BJ gene repertoires of mature CD4 and CD8 thymocytes and peripheral lymphocytes with the same coreceptors were apparently different in a few BV-BJ combinations. The results showed that the overall BJ gene repertoire pattern was developed before antigenic selection. Thus, the preferential BJ gene expression, primarily based on preferential use of certain BJ gene rearrangements, dictates the peripheral BJ gene repertoire, which is then further modified by thymic selection and peripheral stimulation.

T cell receptor repertoire diversity and clonal expansion in human neonates

Newborn human infants, particularly those born prematurely, are susceptible to infection with a variety of microorganisms. We questioned whether limitations in the T cell repertoire contribute to the neonatal immunocompromised state. To describe developmental changes of the T cell repertoire, cDNA segments corresponding to third complementarity regions (CDR3) of human umbilical cord blood T cell receptors (TCR) from 24-41-wk gestational age were amplified with TCR family-specific probes. The resulting amplified CDRs were visualized by fingerprinting and single strand conformation polymorphism (SSCP) analysis. At 24-wk gestation there were no limitations in TCRBV family usage, and the degree of CDR3 size heterogeneity was not different from the adult. However, earlier in gestation, CDR3s were shorter for all families and gradually increased in size until term. The extent of oligoclonal expansion observed in cord blood was greater than in adult peripheral blood (p = 0.03). T cell oligoclonal expansion was greatest at 29-33-wk gestation and declined toward term. Expansions were detectable in both CD4+ and CD8+ subpopulations. Our findings indicate that the genetic mechanisms of repertoire diversification appear intact as early as 24 wk of gestation, but repertoire diversity is limited as a result of smaller CDR3 sizes. In addition, there was a developmentally regulated progression of oligoclonally expanded T cells. These differences in the TCRBV repertoire add to the body of evidence demonstrating immaturity of the neonatal immune system. However, the role that these subtle differences are likely to play in the relative immunodeficiency of the neonate remains to be determined.