Immunotherapy is rapidly transforming cancer treatment, where majority of approved immune modulators are used in combination with chemotherapy or radiotherapy agents that modulate the tumour microenvironment (TME). In solid tumours, the heterogeneous TME poses difficult challenges, demanding combined therapeutic interventions. Photothermal therapy (PTT) precisely ablates solid tumours through localised hyperthermia. This study investigates the temporal dynamics of PTT-induced immune responses, locally within the TME and systemically, to identify a critical window for combined therapeutic intervention. Further, we show enhanced therapeutic precision achieved by combining PTT with dual innate and adaptive immune modulators in advanced-stage malignancies.
PTT was performed in a syngenic orthotopic Balb/c TNBC mouse model via intratumoral Au-SLN administration followed by a 5-minute NIR laser (750nm, 3.3W/cm²). Tumour progression was longitudinally monitored using bioluminescence imaging. Flow cytometry and histology-based immunophenotyping of TME-infiltrating immune cells and systemic inflammatory mediators were assessed at 24 hours, 4 days, and 11 days post-PTT. A bilateral tumour model was employed to evaluate PTT-induced abscopal effects, with the untreated contralateral tumour serving as a readout. Subsequently, single-dose PTT was combined with two doses (once a week) of intraperitoneal anti-PDL1 and anti-CD47 antibodies administration in tumour-bearing mice and assessed for tumour growth, metastatic delay, and survival benefit.
Single-dose PTT achieved rapid tumour ablation, with a significant reduction in bioluminescence signal (p<0.05) within 24 hours. Early post-PTT TME exhibited enhanced infiltration of pro-inflammatory M1 macrophages (p=0.0068), activated dendritic cells (p=0.03), CD4+ helper T cells (p=0.0084), and CD8+ cytotoxic T cells (p<0.05), accompanied by elevated serum Th1 cytokines, such as IL-12, and chemokines like CCL3, through Day 4. However, by day 11, immune activation significantly decreased, along with a decline in systemic Th1/Th2 cytokine ratios, reflecting late-stage immune reprogramming. Nevertheless, PTT elicited systemic abscopal effects in a bilateral tumour model by delaying secondary tumour growth, suppressing metastasis by 14 days and extending survival beyond 20 days. The biphasic immune response, i.e., from initial activation to late immunosuppression, highlighted a critical window for therapeutic intervention between Days 4 and 11 post-PTT. Combining single-dose PTT with anti-PDL1 and anti-CD47 blockades significantly suppressed primary tumour growth (p<0.05) and extended overall survival by 17 days, compared to the untreated control group.
These overall findings demonstrate that integrating mild PTT with dual anti-PDL1 and anti-CD47 synergistically restrains tumour progression by engaging both innate and adaptive immunity to sustain T cell function and macrophage polarisation for durable anti-tumour responses.