IL7R and leukemia: Moreover, as IL-7 is only available at limited amounts in the thymus and in other lymphoid tissues, leukemia cells that become increasingly sensitive to IL-7 have a survival and proliferative advantage compared with wild type lymphoid cells as a result of increased IL-7 signaling pathway activation, most likely explaining why in many T-ALL cases that carry a mutation in IL7R, additional alterations in JAK1, JAK3, PTPN2, PTPRC and/or DNM2 are found, as described in the following sections.