Posted on July 1, 2025

Key lessons from the remote suppressive axis of osteopontin-producing osteoclasts

Article Details

Paper: Bone metastases diminish extraosseous response to checkpoint blockade immunotherapy through osteopontin-producing osteoclast

Journal / IF: Cancer Cell (2025, impact factor ? 44)

Publication date: June 2025

Corresponding authors: Qi-Jing Li (A*STAR, Singapore); Qingzhu Jia & Bo Zhu (Army Medical University)

DOI: 10.1016/j.ccell.2025.03.036

Why This Study - When the Skeleton Becomes an Immunotherapy “Reef”

Immune-checkpoint blockade (ICB) has redrawn survival curves for many solid tumours. Yet in everyday oncology clinics physicians notice an awkward rule-of-thumb: once a patient develops bone metastasis, the once-reliable PD-1/PD-L1 antibodies often “go silent”. Are the drugs simply failing to reach bone, or is bone disease actively suppressing systemic immunity? This Cancer Cell study provides a coherent, data-rich answer. A real-world dataset covering five tumour types (> 1,800 cases) shows that patients with bone metastases have a two- to three-fold shorter median PFS under ICB, while no such disadvantage appears in chemotherapy or targeted-therapy cohorts, hinting at a bone-specific immune mechanism.

Research Roadmap - From Clinical Observation to Molecular Culprit

To test the “bone-derived remote immunosuppression” hypothesis, the authors established a dual-tumour mouse model carrying both an intratibial lesion and a subcutaneous lesion. Repeated intraperitoneal dosing with Bio X Cell’s InVivoPlus anti-PD-L1 (clone 10F.9G2) ensured low-endotoxin, azide-free conditions. Strikingly, as long as an osseous tumour was present, the distant subcutaneous tumour became refractory to PD-L1 blockade. Proteomics pointed to osteopontin (OPN) as the top up-regulated serum factor; conditioned osteoclast cultures confirmed massive OPN secretion. Neutralising OPN with Bio X Cell’s anti-OPN (clone MPIIIB10) or deleting Spp1 in osteoclasts restored ICB sensitivity. Blocking upstream RANKL with Bio X Cell anti-RANKL (clone IK22/5) or with clinical Denosumab produced the same rescue, cementing the RANKL → osteoclast → OPN axis as the driver of resistance. Single-cell RNA/TCR profiling showed that high OPN depletes TCF1+ Tpex precursors and

pushes them into terminal exhaustion, whereas OPN blockade replenishes the Tpex pool and revives anti-PD-L1 efficacy.

Experimental Approach - A Relay from Clinic to Multi-layered Models

  1. Real-world validation: five ICB cohorts (> 1,800 cases) compared PFS/ORR between patients with or without bone metastasis.
  2. Mouse modelling: C57BL/6 mice with intratibial + subcutaneous tumours; PD-L1 blocked weekly with Bio X Cell 10F.9G2.
  3. Serum proteomics: label-free LC-MS; osteopontin had the highest fold-change.
  4. Causality tests: neutralisation with Bio X Cell MPIIIB10; Ctsk-Cre::Spp1fl/fl knockout; upstream block with Bio X Cell IK22/5 or Denosumab.
  5. Single-cell omics: scRNA-seq + scTCR-seq on CD8+ T cells; flow & IHC validated cytokine restoration.
  6. Retrospective analysis: 150 patients on Denosumab + ICB versus bisphosphonate + ICB; serum OPN tracked.

Key Findings - A Remote Immune “Brake” That Can Be Cut

  • Bone metastasis systemically blunts ICB via immune circuitry rather than drug distribution.
  • Osteoclast-derived OPN is the pivotal messenger; blocking OPN or RANKL revokes resistance body-wide.
  • Circulating OPN predicts response: high/rising levels forecast poor benefit, while Denosumab lowers OPN and prolongs PFS.

Why It Matters - From Bone-marrow Ecology to Actionable Combinations

The study elevates bone from a passive depot to an active systemic immunomodulator. Combining Denosumab or other OPN/RANKL antibodies with PD-1/PD-L1 blockers is ready for clinical testing and may offer bone-metastatic patients durable remission. OPN emerges as both target and biomarker.

Bio X Cell In Vivo-grade Antibodies - The Experimental Linchpins

Experimental Step

Product (In Vivo Grade)

Clone

Catalog No.

Contribution

Check-point blockade baseline

anti-mouse PD-L1

10F.9G2

BP0101

Provides the single-agent control and the backbone for the TFF2-MSA + PD-1 combination

RANKL-osteoclast axis blockade

anti-mouse RANKL

IK22/5

BE0191

Tests whether abnormal granulopoiesis upstream of CXCR4 also drives resistance

OPN causality test

anti-mouse Osteopontin

103D6

BE0373

Neutralises OPN to rule out CXCR4-independent long-range immunosuppression

IgG2a isotype control

rat IgG2a isotype

2A3

BE0089

Matched control for PD-L1 / RANKL antibodies to exclude Fc-mediated artefacts

IgG2b isotype control

rat IgG2b isotype

LTF-2

BP0090

Baseline control for certain cytokine-neutralisation experiments

IgG2c isotype control

mouse IgG2c isotype

DV5-1

BE0366

Matched control for the OPN antibody, ensuring result specificity

All reagents are supplied in InVivoPlus grade (< 2 EU mg⁻¹ endotoxin) with full COA, ready for multi‑dose regimens.