  The adaptive immune response relies on T cells that combine phenotypic
specialization with diversity of T cell receptors (TCRs) to recognize a wide
range of pathogens. TCRs are acquired and selected during T cell maturation in
the thymus. Characterizing TCR repertoires across individuals and T cell
maturation stages is important for better understanding adaptive immune
responses and for developing new diagnostics and therapies. Analyzing a dataset
of human TCR repertoires from thymocyte subsets, we find that the variability
between individuals generated during the TCR V(D)J recombination is maintained
through all stages of T cell maturation and differentiation. The
inter-individual variability of repertoires of the same cell type is of
comparable magnitude to the variability across cell types within the same
individual. To zoom in on smaller scales than whole repertoires, we defined a
distance measuring the relative overlap of locally similar sequences in
repertoires. We find that the whole repertoire models correctly predict local
similarity networks, suggesting a lack of forbidden T cell receptor sequences.
The local measure correlates well with distances calculated using whole
repertoire traits and carries information about cell types.
