Utilizes re-alignment to identify V(D)J genes and alleles after common local alignment. A methodology is developed to correct the PCR and sequencing errors, and to minimize the PCR bias among various rearranged sequences with different V and J gene families. IMonitor provides general adaptation for sequences from all receptor chains of different species and outputs useful statistics and visualizations. Usefulness of IMonitor was demonstrated on minimal residual disease detection of patients with B-cell Acute Lymphoblastic leukemia.