Science University Research Symposium (SURS)
Publication Date
Fall 11-10-2025
College
College of Sciences & Mathematics
Department
Biology, Department of
SURS Faculty Advisor
Erick Spears, Andrea Florian
Presentation Type
Poster Presentation
Abstract
PD-1 Blockade Induced Bone Loss Occurs in a T-Cell Dependent Manner and May Be Mediated by IFNγ-Driven Osteoclast Activation
†Elena Amonette1, †Paige Hill1, Gwenyth J. Joseph2, Rachelle W. Johnson2,3
1Belmont University, Nashville, TN; 2Vanderbilt University, Nashville, TN; 3Vanderbilt University Medical Center, Nashville, TN
†These authors contributed equally to this work
Immune checkpoint inhibitors (ICIs) are becoming increasingly prevalent in the treatment of various cancers due to their ability to reduce tumor mediated T cell death and lengthen the anti-tumor response. One such therapy that is increasingly utilized in clinical settings and across multiple tumor types is the blockade of programmed cell death protein 1 (PD-1). Despite its success in reducing tumor burden, ɑ-PD-1 can cause immune related adverse events, including bone loss and increased fracture risk. However, the mechanism by which ɑ-PD-1 impacts the bone microenvironment is still unknown. To explore this question further, we performed in vivo studies using a C57BI/6 8-week-old female mouse model treated with ɑ-PD-1 to confirm the PD-1-blockade-induced bone loss phenotype seen clinically. Alongside a reduction in bone density, volume, and strength, we also saw an increase in osteoclast resorptive activity, which is likely driving the observed bone loss. In addition, we observed an expansion in interferon-gamma (IFNg)+ T cell populations. Previous work suggests that in settings of chronic inflammation, IFNg may promote osteoclastogenesis which could contribute to increased bone loss. To identify whether T cells were required for ɑ-PD-1 induced bone loss to occur, we repeated this study in a T cell deficient mouse model. Here, we observed no bone loss with ɑ-PD-1 treatment, suggesting a T cell dependent bone loss mechanism. We hypothesize that IFNg stimulates T cells to secrete pro-osteoclastogenic factors that promote the formation of more aggressive osteoclasts in settings of PD-1 blockade, thereby driving the bone loss phenotype observed with ɑ-PD-1 treatment. To further investigate the relationship between T cells, osteoclasts, and IFNg, we performed an in vitro study to examine the effects of IFNg and ɑ-PD-1 on osteoclast differentiation and activity. We isolated and treated bone marrow from WT mice to investigate the impact of IFNg and ɑ-PD-1 on osteoclasts derived from a diverse immune precursor pool which included activated T cells. Separately, bone marrow macrophages (BMMs) were differentiated from flushed bone marrow and treated independently to investigate the effects of IFNg and ɑ-PD-1 on osteoclasts in the absence of T cells. Our results show that in the absence of T cells, no osteoclast differentiation occurs when treated with IFNg, suggesting T cells are required for IFNg to promote osteoclastogenesis. However, we do see differentiation with IFNg at comparable levels to controls when T cells are present, suggesting T cells are required for IFNg to promote osteoclastogenesis. In addition, we saw an increase in osteoclast size, but not number, upon treatment with ɑ-PD-1, both in the absence and presence of T cells. As osteoclast size directly correlated with resorptive activity, these data support our previous work suggesting that PD-1 blockade increases osteoclast activity but not differentiation. Taken together, our data suggests PD-1 blockade stimulates the production of more resorptive osteoclasts through a T cell dependent mechanism which may be driven by IFNg. Elucidating the relationship between PD-1 blockade, IFNg, T cells, and osteoclasts is important in determining the mechanism of bone loss associated with ɑ-PD-1 treatment of cancer and paving the way for future work to develop ways to minimize skeletal related adverse events.
Recommended Citation
Amonette, Elena and Hill, Paige M., "PD-1 Blockade Induced Bone Loss Occurs in a T-Cell Dependent Manner and May Be Mediated by IFNγ-Driven Osteoclast Activation" (2025). Science University Research Symposium (SURS). 308.
https://repository.belmont.edu/surs/308
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