Bone Metastases Promote Immature Immune Cell Development, Impeding Immunotherapy

Recent research has shed light on the mechanisms that render bone metastases resistant to immunotherapy, a treatment that can be highly effective against various cancers. The study, conducted by a team at Ludwig Cancer Research and Weill Cornell Medicine, in collaboration with Nanjing University, reveals that bone tumors actively modify immune cells in a way that suppresses their ability to combat cancer.

Bone metastases are a common complication in advanced cancers, particularly those affecting the lungs, breasts, and prostate. These metastases not only cause significant pain and morbidity for patients but are also notoriously difficult to treat. The research focuses on the role of neutrophils, a type of immune cell that typically acts as a first responder to infections and foreign bodies.

In the context of bone tumors, neutrophils are found to be reprogrammed into an immature state that inhibits anti-tumor immune responses. This transformation is primarily driven by a protein known as DKK1, which is secreted by the tumor cells. The study demonstrates that blocking DKK1 can reverse this immature state of neutrophils, restoring their function and allowing them to effectively participate in anti-tumor immunity.

According to the researchers, the accumulation of these immature neutrophils in bone metastases creates a profoundly immunosuppressive environment, which is a major reason why immunotherapy often fails in patients with these types of metastases. While neutrophils can play a significant role in enhancing anti-tumor immunity in other contexts, their dysfunctional state in bone tumors highlights the complexity of immune responses in cancer.

In addition to the effects of DKK1, the study also identified another molecule, CHI3L3, produced by immature neutrophils, which further impairs the function of cytotoxic T cells--key players in the adaptive immune system that are critical for targeting cancer cells. The presence of elevated DKK1 levels was corroborated by analyses of patient data, particularly in individuals with gastric cancer and bone metastases.

In experimental models, the application of a DKK1-blocking antibody demonstrated promising results. The treatment not only led to the maturation of neutrophils but also resulted in the reduction of tumor size and an enhanced efficacy of immunotherapy, particularly with anti-PD-1 treatments. Some mice even experienced complete tumor regression.

This research opens new avenues for potential combination therapies that incorporate DKK1 blockade alongside existing immunotherapies, particularly for bone tumors where treatment options remain limited. The possibility of using a DKK1-blocking antibody, which is already in clinical trials, could expedite the translation of these findings into clinical practice.

Furthermore, the study suggests that biomarkers associated with CHI3L3 and the gene expression profile triggered by immature neutrophils could aid in identifying patients who are more likely to benefit from tailored treatments. This highlights the necessity of focusing not only on T cells but also on reprogramming innate immune cells like neutrophils in the pursuit of effective cancer therapies.