Purpose: To augment intratumoral immune cell trafficking following thermal tumor ablation using adjuvant systemic liposomal GM-CSF.
Materials and Methods: Subcutaneous R3230 rat breast adenocarcinoma tumors implanted in Fisher rats (total n=72 tumors, treated at 11-13 mm diameter) were randomly assigned to 6 groups: a) sham; b, c) liposomal or free GM-CSF(1.4µg/ml) alone; and d, e, f) RF alone (21g 1 cm active tip electrode, 5 min @ 70⁰C), and in combination with liposomal GM-CSF or blank liposomes. Animals were sacrificed at 3 and 7 days post-RFA. Outcome measures included gross tissue coagulation, tumor growth and immunohistochemical characterization (cell positivity/high power field) of markers of dendritic cells (DCs) (CD11c), M1 macrophages (CD68), and cytotoxic T-cells (CD8+) in the periablational rim and in untreated tumor two high power fields away from the ablation zone.
Results: Adjuvant lip-GM-CSF with RFA markedly increased periablational CD8+ cell infiltration at 3d and 7d (113.3±39.3 vs. RFA: 59.3±11.1 cells/hpf; and 218.4± 20.5 vs. RFA: 38.5±15.5, respectively), and M1 cells at 7d (123.3±44.5 vs. RFA: 59.9±16.5) (p< 0.05, all comparisons). Additionally, RFA/lip-GM-CSF markedly increased intratumoral M1 cells early at 3d (297.4±35.5 vs. RFA: 195.5±20.1) and DCs (51.6± 40.2 vs. RFA: 8.9±11.1) and CD8+cell trafficking later at 7d (123.9±55.6 vs. RFA: 63.5±27.6)(p< 0.05, all group comparisons)in untreated tumor. No statistical significant differences were observed in overall coagulation or tumor growth at 3d and 7d (p >0.05, all comparisons).
Conclusion: Adjuvant systemic liposomal GM-CSF administered at the time of RF ablation combined with nanoparticle-based GM-CSF results in significantly increased periablational and overall tumor immune cellular trafficking, specifically cell populations associated with initiating anti-tumor immunity.
Clinical relevance: Liposomal immunomodulating preparations can potentially improve RFA-induced anti-tumor immunity over conventional thermal modalities, further refining the combined ablation / nanodrug paradigm.