NONRANDOM EMPLOYMENT OF V(BETA)6 AND J(BETA) GENE ELEMENTS AND CONSERVED AMINO-ACID USAGE PROFILES IN CDR3 REGIONS OF HUMAN FETAL AND ADULT TCR BETA-CHAIN REARRANGEMENTS

We have studied the usage of V(beta)6, D-beta, and J(beta) elements, and the composition of the CDR3 regions of human fetal TCR beta chain rearrangements in a 17 week old fetal thymus and in fetal liver, bone marrow, spleen, and cord blood at 11 and 13 weeks of gestation. These fetal sequences were compared with TCR beta chain rearrangements obtained from post-partum thymus, adult spleen, and adult peripheral blood mononuclear cells. Both fetal and adult TCR V(beta)6 rearrangements exhibited a non-random usage of V-beta and J(beta) elements. Up to 90% of the sequences obtained at 11 weeks of gestation used J(beta)2 elements, most notably J(beta)2.1. In the 13 and 17 week old fetal and in the adult tissues, J(beta)1 elements were used in similar to 30% of the rearrangements while, within the J(beta)2 rearrangements, J(beta)2.1 and J(beta)2.7 were used most frequently. Both fetal and adult TCR beta chain CDR3 regions showed non-random usage of amino acids. However, the early fetal repertoire was further limited due to the relative absence of N-regions in up to 60% of the 11 and 13 week old TCR beta chain rearrangements, resulting in smaller antigen binding sites. In fetal and adult TCR beta chain rearrangements the distribution patterns of the length of N-regions and the usage profiles of J(beta) elements were similar in hematopoietic and peripheral organs, suggesting no apparent preference for particular TCR beta chain rearrangements. On the whole, the data showed that both the available fetal and adult TCR V(beta)6 repertoires are seemingly smaller than expected on the basis of random usage of V-beta and J(beta) elements and amino acid composition of the CDR3 regions.