Clinical trials of the combination of the DPP4 nonselective inhibitor Val-boro-Pro and rituximab in the treatment of primary drug-resistant and indolent non-Hodgkin’s lymphoma and chronic lymphocytic leukemia (CLL) have been conducted in the early years (Al-Katib et al., 2004; Khan et al., 2005). This evidence concerns the gene DPP4 and B-cell chronic lymphocytic leukemia.