229. Engineered Macrophage-Based Cell Therapy for Cancer Treatment

Abstract

Physiological barriers such as poorly developed vasculature, interstitial pressure, dense extracellular matrix in solid tumors limit distribution of liposomal and polymer drug carriers deep into the disease tissue leading to poor efficacy of treatment. Unlike synthetic drug carriers however, a number of immune cell types, most prominently macrophages, are actively recruited to tumor sites. Macrophages permeate tumor tissue to perform various anti-and pro-tumor functions. Thus, macrophages represent an attractive candidate as a cellular vehicle for intra-tumoral drug delivery and immune modulation.We have devised a strategy to produce therapeutic macrophages ex vivo. The strategy is based on recent advances in controlling macrophage differentiation by over expressing the Hoxb family of transcription factors1. The resulting macrophages can be loaded with liposomal drugs and genetically engineered to express proteins to influence the immune response against tumors when the macrophages are re-introduced in vivo.We have generated isogenic mouse macrophage progenitor cell lines from BALB/c and c57Bl6 genetic backgrounds utilizing CreERT recombinase controlled conditional expression of floxed Hoxb8 and a fluorescent reporter protein. Conditionally immortalized non-adherent macrophage progenitor cell lines expand very rapidly in vitro doubling every 12h in standard cell culture conditions. Upon CreERT activation with 10nM 4-hydroxytmoxifen (three doses every two days the first week), 100% of the progenitors in culture can be differentiated into macrophage-like cells over a 2-week period. Upon differentiation these macrophage-like cells become adherent, develop cytoplasmic granules and become highly phagocytic.We utilize the high phagocytic capacity of ex vivo differentiated macrophages to load them in culture with cytotoxic drugs encapsulated in stable fluorescently–labelled liposomes. Liposome uptake depends upon liposome composition, concentration and is saturable. Results on the in vivo distribution of the macrophages and cargo upon their re-introduction in BALB/c mice containing the 4T1 orthotopic syngeneic mouse breast tumor will be presented. Supported by NIH R21 CA182703. Simon Lee is supported by Fellowship from the Natural Sciences and Engineering Research Council of Canada.