Abstract: The present invention relates to a process for determining the quantity of a DNA fragment of interest in a sample wherein:1) a standard DNA fragment can be amplified with the same oligonucleotide primers is added to the sample to be analyzed containing the DNA fragment of interest, the standard DNA fragment and the fragment of interest differing in sequence and/or in size by not more than 10%,2) the DNA fragment of interest and the standard fragment are coamplified with the same primers, preferably to saturation of the amplification of the DNA fragment of interest,3) one or more labeled oligonucleotide primer(s), specific for the DNA fragment of interest and the standard fragment and different from the primers of step 2), is/are added to the reaction medium obtained in step 2), so that, after denaturation of the DNA, said primer(s) hybridize(s) with said fragments at a suitable site in order that an elongation with the DNA polymerase generates labeled DNA fragments of different sizes and/or sequences or with

Abstract: In a method for describing repertoires of antibodies (Ab) and T cell recers (TcR) of the immune system of an individual, reverse transcription is carried out on the mRNA contained in a biological sample, separate amplifications are then carried out on the transcription product (or directly on the DNA extracted from the sample) by a PCR type method for each primer pair V, C, where V corresponds to a variable segment of the repertoire of interest and C hybridizes on the constant segment of the repertoire of interest. For each J segment of the labelled repertoire, an elongation step is carried out on each of the amplification products using a specific oligonucleotide of this segment J as primer and the amplification product as matrix. For each elongation product corresponding to a triplet (V, C)J thus obtained, the size of the different elongation products is revealed. The description of the repertoires corresponds to a VCJ triplet and to the element size for each element of the repertoire.