Development of a Mouse Model to Study Targeted Therapy to Prevent CNS Invasion by Pediatric T-ALL

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TITLE: Development of a Mouse model to test targeted therapy to prevent CNS Invasion by Pediatric T- ALL Abstract Leukemia is the most frequent pediatric cancer with acute lymphoblastic leukemia (ALL) being the most common leukemia type in children. In 15-20% of pediatric T-cell ALL (T-ALL) patients, the cancer invades the Central Nervous System (CNS), a site which is protected from systemic chemotherapies by the blood brain barrier. The invading leukemic cells are reservoirs, which can emerge and re-enter the circulation following treatment and cause T-ALL relapse. To prevent relapse, pediatric patients are treated with cranial irradiation and toxic chemotherapies, which are injected directly into the CNS. It is not surprising that these treatments can lead to morbid life-long side effects such as reduced intelligence, stunted growth, and secondary cancers in the CNS. Generally, the T-ALL has entered the CNS prior to diagnosis, and it is unclear if blocking the entry of T-ALL into the CNS at that point, after they have already entered, provides any therapeutic benefit. The overarching three goals of this proposal are: 1) to develop a mouse model of T- ALL that recapitulates human T-ALL, in which we can see the cells in living animals 2) to determine if blocking T-ALL cells from entering the CNS, prevents further T-ALL CNS invasion and 3) to determine if the T-ALL that has invaded the CNS will eventually clear the CNS and return to the circulation. Our long-term goal is to reduce or eliminate the need for damaging intrathecal or cranial treatments in patients with T-ALL. Our studies are based on a human xenograft mouse model of T-ALL, which revealed that during leukemogenesis, expression of NOTCH1, a transcription factor which is expressed in more than 80% of pediatric T-ALLs, induces expression of CC chemokine receptor 7 (CCR7). The study revealed that activation of CCR7 in T-ALL by one of its ligands, CCL19 promotes chemotactic migration of T-ALL into the CNS. Our proposal is based on a mouse model obtained from Dr. Monica Justice which uses an inducible CCR7(+)ROSA26 floxed-stop-PRDM14 (R26PR) locus. When crossed to an MX1-Cre these R26PR mice develop leukemia in response to overexpression of NOTCH1, which invades the CNS. Subsequent breeding of these mice with ROSA26 floxed-stop luciferase mice will result in Cre-recombinase induced expression of bioluminescent luciferase in T-ALL cells. To confirm a role for CCR7 in the invasion of the CNS, these R26PR mice will be crossed with our own CCR7 conditional knockout mice (CCR7floxed/floxed (CCR7f/f)) to produce R26PRDM14/CCR7f/f/MX1-CRE mice. Generation of this mouse is aim 1. Determining which immune cells co-localize with T-ALL cells upon entry into the CNS is aim2 and determining if blocking CCR7 using the CCL19 antagonist, CCL198-83 prevents or significantly reduces T-ALL CNS invasion, clears the CNS of T-ALL and increases mouse survival is aim 3. Ultimately, if successful, this mouse model will provide a tool for developing novel peptide therapies that can block T-ALL CNS invasion, without causing long-term CNS damage in patients and to study mechanisms of CNS invasion.