Genetically Engineered Hematopoietic Stem Cells As Delivery System For Immunotherapy Of Bone Metastases

Bone metastasis is a common destination for breast cancer,prostate cancer,and lung cancer,with over 60%of bone metastases progressing to systemic dissemination.resulting in patient mortality.Bone metastatic lesions often cause bone pain and destruction,severely compromising patients’ quality of life.Immune checkpoint blockade(ICB)therapy,which involves blocking immune checkpoint molecules to activate the body’s immune system,has shown promising results in some tumor clinical trials.However.ICB treatment has minimal or no effect on the majority of bone metastasis patients,largely due to the immunosuppressive microenvironment of the bone.Transforming growth factor-β(TGF-(3),a key factor in bone metastasis,is not only secreted by tumor cells but also by the disrupted bone matrix in the bone metastatic site.The high levels of TGF-β in the bone marrow contribute to the low responsiveness of bone metastases to ICB therapy.In this study,based on the unique immunosuppressive microenvironment of bone metastasis,we engineered hematopoietic stem cells(HSCs)overexpressing programmed cell death protein 1(PD-1)and used them as a drug delivery platform to target the bone and deliver the TGF-β small molecule inhibitor SB-505124(SB).By reversing the immunosuppressive microenvironment within bone metastasis,we aimed to enhance the responsiveness of bone metastasis to ICB therapy.The main research objectives of this study include:Chapter 1:Provides a concise introduction to the detrimental effects of bone metastasis,elucidates the cellular mechanisms underlying its development,reviews current treatment modalities,and highlights recent advances in novel drug delivery systems.Additionally,it establishes the research background and outlines the scope of the study.Chapter 2:Constructs a bone metastasis model and conducts a comparative analysis of the immune microenvironment between subcutaneous tumors and bone metastasis.Notably,the investigation reveals that the elevated TGF-β levels within bone metastasis foster the differentiation of CD4+T cells into T helper 17 cells(TH17)and regulatory T cells(Treg),while failing to induce CD8+T cell activation,thereby giving rise to the unique immunosuppressive microenvironment observed in bone metastasis.Chapter 3:Capitalizes on the targeting capacity of hematopoietic stem cells(HSCs)to develop a drug delivery system,denoted as SB@HSCs,by incorporating the lipophilic TGF-β small molecule inhibitor SB into the lipid membrane of HSCs.This chapter focuses on characterizing the engineered drug delivery system and evaluates its efficacy following intravenous administration via tail vein injection.The main objective is to reshape the immunosuppressive microenvironment within bone metastasis and enhance the responsiveness of bone metastases to ICB therapy.Chapter 4:Genetically modifies hematopoietic stem cells to overexpress PD-1 and assesses the binding affinity of these engineered cells to PD-L1,along with evaluating their bone-targeting efficacy,proliferation within the bone niche,and safety profile.Administering SB@HSCs-PD-1 via tail vein injection in mice effectively inhibits bone metastasis,reduces bone damage,and prolongs the survival of tumor-bearing mice.Chapter 5:Engages in a comprehensive discussion,summarizing the limitations of the study,analyzing its potential value,and providing insights into future research directions.In conclusion,this study developed a HSC-based drug delivery platform,HSCs-PD1@SB,with bone-targeting capability.This technology can also inspire the expression of other therapeutic proteins in hematopoietic stem cells for the treatment of bone diseases.Due to the ease of preparation,high versatility,and excellent biosafety of hematopoietic stem cell drug delivery platforms,it has excellent clinical application potential.