Session: 614. Acute Lymphoblastic Leukemia: Therapy, excluding Transplantation: Poster I
Hematology Disease Topics & Pathways:
Biological, ALL, Leukemia, Animal models, bone marrow, Diseases, Therapies, Biological Processes, immune cells, Technology and Procedures, Cell Lineage, immunotherapy, Study Population, Lymphoid Malignancies, imaging, microenvironment, molecular interactions
The murine lymphoblastic cell line, 70Z/3, was transfected with either a constitutively active GFP marker (70Z/3-GFP) or a lentivirus expressing mCherry and IL12 (70Z/3-IL12-mCherry). The FWC was installed by shaving the femoral corticalis to reveal the BM cavity and securing a cover glass on top. Mice were then intravenously (IV) injected with 3x106 70Z/3-GFP cells 2 weeks post-surgery. Fluorescent cellular activity within the BM was monitored two times a week for four weeks via confocal microscopy (Zeiss LSM710). 3x106 70Z/3-IL12-mCherry cells were then injected into mice IV, intraperitoneally (IP), or intrafemorally (IF) at each experimental time point following initial inoculation. Leukemic burden was quantified as the percent total GFP signal within the BM space while immune cell activity was monitored using injected fluorescently-conjugated antibodies and ex vivo flow cytometry. Nonfluorescent leukemic and healthy mice were also imaged as controls.
Intravital imaging revealed that IV injected 70Z/3-GFP cells first enter the BM, on average, 10 days post-inoculation and achieve 90% infiltration within 3 weeks. Based on this timeline, we evaluated the effect of IL12 treatment administered 1, 2, or 3 weeks post-inoculation, as well as at the time of inoculation itself (co-injection). Mice treated with a single administration of 70Z/3-IL12-mCherry cells at 1 week showed a 26% reduction (p<0.05) in overall leukemia burden at the experimental endpoint, while mice treated at 3 weeks did not have a statistically significantly reduction in burden compared to untreated controls. We also observed a significant decline in BM immune cell populations, particularly macrophages, associated with increasing ALL percentage. We hypothesize that IL12 therapy is only effective below a specific threshold of disease, which corresponds to a minimum effective immune population still remaining in the BM. Current efforts are now underway to characterize this threshold and test the ability of repeated infusions to maintain immune cells within this effective range for the entirety of the treatment course. Interestingly, 70Z/3-IL12-mCherry cells co-injected with 70Z/3-GFP cells prevented ALL establishment in the BM altogether. Additionally, while IP injection has been the sole treatment administration technique used in previous IL12 studies, our results indicate that IV administration is the more effective option; not only do IV injected cells reach the BM faster and with greater quantity as compared to all other techniques tested, but it is also the more clinically relevant modality.
Our study not only demonstrates the ability of cell-based IL12 therapy to elicit a therapeutic response in ALL-bearing mice, it also reveals important insights into the biology of the immunotherapy, which can be applied to further augment the treatment’s effect.
Disclosures: DaCosta: SBI ALApharma Canada: Current Employment, Current equity holder in private company; MolecuLight Inc.: Current Employment, Current equity holder in private company, Patents & Royalties: Device and Method for Fluorescence-Based Imaging and Monitoring.
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