The T-cell (TCR) repertoire relies on the diversity of receptors composed of
two chains, called α and β, to recognize pathogens. Using results
of high throughput sequencing and computational chain-pairing experiments of
human TCR repertoires, we quantitively characterize the αβ
generation process. We estimate the probabilities of a rescue recombination of
the β chain on the second chromosome upon failure or success on the first
chromosome. Unlike β chains, α chains recombine simultaneously on
both chromosomes, resulting in correlated statistics of the two genes which we
predict using a mechanistic model. We find that ∼28% of cells express
both α chains. We report that clones sharing the same β chain but
different α chains are overrepresented, suggesting that they respond to
common immune challenges. Altogether, our statistical analysis gives a complete
quantitative mechanistic picture that results in the observed correlations in
the generative process. We learn that the probability to generate any
TCRαβ is lower than 10−12 and estimate the generation diversity
and sharing properties of the αβ TCR repertoire
