Statistics of large scale insertions in B-cell receptors

Adaptive immune systems neutralize pathogens using diverse receptors on B-cells (BCR). Their neutralization power is increased during a Darwinian maturation process in each individual, where random sequence modifications are selected. We show that these modification include large scale deletions and insertions (indels) of non-templated genomic material. We describe the statistics of these hyperindels in healthy and HIV-infected people, where they seem to play an important role. We introduce a statistical model for the occurrence of these indels, inferring the parameters of such a model from real data through maximum-likelihood approaches.