Engdahl, C. | bioRxiv Science

bioRxiv2025

Disrupted bone microenvironment and immune recovery following total body irradiation in a murine model

Irradiation is an effective therapy for killing cancer cells and a critical preparative regimen for hematopoietic stem cell transplantation (HSCT). However, irradiation causes side effects on healthy tissue, disrupting bone tissue and bone marrow homeostasis and leading to skeletal and immune dysfunction. To investigate these effects, we utilized a female murine model to examine the mechanisms underlying skeletal damage caused by total body irradiation. Experiments were conducted over a 12-week period of total body irradiation and HSCT, complemented by an acute study involving only total body irradiation. Irradiation led to a transient depletion of bone marrow immune cells, followed by a late increased bone marrow cellularity 12 weeks after irradiation and HSCT compared to naive, indicative of late-stage local immune induction. Cortical and trabecular bone damage emerged two weeks post-irradiation and HSCT and persisted throughout the study. This bone damage was accompanied by a sustained increase in bone marrow adiposity. Accumulation of apoptotic cells was observed in the bone marrow within six hours post-irradiation and persisted up to 12 weeks post-irradiation and HSCT. Accompanied by elevated local expression of the pro-apoptotic BAX gene and a gene elevated with the clearance of apoptotic cells, TGF-{beta}1. In vitro studies revealed that macrophages and pre-osteoclasts, but not fully differentiated osteoclasts, efficiently cleared apoptotic cells with an elevation of TGF-{beta}1 in culture supernatant. While the clearance of apoptotic cells and associated TGF-{beta}1 signaling were evident, their direct role in skeletal outcomes remains unclear. These findings suggest that persistent apoptotic cells contribute to impaired bone remodeling, possibly influencing osteoclast function and the bone microenvironment. Further research is warranted to explore whether targeting apoptotic cell clearance could reduce bone damage and support skeletal recovery following irradiation.

molecular biology↗

bioRxiv2023

Epitope Engineered Human Haematopoietic Stem Cells are Shielded from CD123-targeted Immunotherapy

Targeted eradication of transformed or otherwise dysregulated cells using monoclonal antibodies (mAb), antibody-drug conjugates (ADC), T cell engagers (TCE) or chimeric antigen receptor (CAR) cells is very effective for haematologic diseases. Unlike the breakthrough progress achieved for B cell malignancies, there is a pressing need to find suitable antigens for immunotherapy of myeloid malignancies. CD123, the interleukin-3 (IL-3) receptor alpha-chain, is highly expressed in various haematological malignancies, including acute myeloid leukaemia (AML) and blastic plasmacytoid dendritic cell neoplasm (BPDCN). However, shared expression of CD123 on healthy haematopoietic stem and progenitor cells (HSPCs) bears the risk for extensive myelotoxicity upon targeted depletion. Here, we demonstrate that rationally designed, epitope-engineered HSPCs were completely shielded from CD123-targeted immunotherapy but remained fully functional while CD123-deficient HSPCs displayed a competitive disadvantage. Thus, molecularly shielded HSPCs could allow tumor-selective targeted immunotherapy and in parallel enable rebuilding a fully functional haematopoietic system. We envision that this approach is broadly applicable to many targets and cells, could render hitherto undruggable targets accessible to immunotherapy and will allow continued posttransplant immunotherapy, for instance to treat minimal residual disease (MRD) or be used as a salvage therapy. Since the function of the engineered targets is preserved, multiplexed molecular shielding could also enable targeted combination immunotherapies to address tumor heterogeneity. More generally, epitope shielding will be applicable for replacement of other cell types including the many immune cells which are currently being considered for engineered cellular therapies.

bioengineering↗