Anti-PTHrP blockade limits CD8+ T-cell exhaustion in anti-cancer immunotherapy

Cancer is a major global health concern, with immune suppression hindering treatment. Immunotherapy, specifically immune checkpoint blockage on T cells, has revolutionized cancer treatment. T-cell exhaustion is an abnormal activation state that develops when continuous exposure to antigens, like cancer. In this context, recent evidence suggests that parathyroid hormone-related protein (PTHrP) plays a previously underappreciated role in fostering an immunosuppressive tumor microenvironment. Further, blocking PTHrP activity reduces primary tumor growth, prevents metastasis, and prolongs survival in mice with various cancers. Here, we confirm that administration of anti-PTHrP monoclonal antibodies can reduce the growth of B16-PDL1 melanoma tumors and that although the therapy did not alter the presence of CD4+ and CD8+ TILs, we noted that all stages of T-cell exhaustion were reduced. Further, the expression of cytolytic proteins PERFORIN and GZMB also increased. By contrast, anti-PTHrP therapy increased the relative presence of pre-pro B cells with a decline in mature B cells in the bone marrow. Overall, our data indicates that anti-PTHrP therapy acts by reducing T-cell exhaustion and by affecting B-cell development. These provide further mechanistic evidence to support the application of anti-PTHrP blockade as an alternate therapeutic approach to boost anti-tumor immunity.