Functional characterization of human terminal deoxynucleotidyl transferase polymorphisms

Terminal deoxynucleotidyl transferase (TdT) contributes to antigen receptor diversity of B and T lymphocytes of the adaptive immune system. TdT is a DNA polymerase catalyzing template independent addition of nucleotides during the process of V(D)J recombination. This thesis investigates whether the polymerase activities of naturally occurring single nucleotide polymorphic (SNP) forms of human TdT vary and the possible effects on the antigen receptor repertoire. Two SNPs (A445T/L397S) demonstrated significantly lower in vitro polymerization activities compared to the wild type enzyme, while one (R431C) was completely inactive. In vivo extrachromosomal recombination assay demonstrated over 3 fold difference in the proportion of N-containing joints and significantly lower numbers of N-nucleotides per joint for both L397S and R431C variants compared to WT hTdTS. Variability in enzymatic activities of the SNPs may affect the diversity of antigen receptors, thus potentially impact the downstream adaptive immune response in healthy and autoimmune-prone individuals possessing these SNPs.