Combined Ultrasound and Photoacoustic Imaging Can Monitor Adoptive T Cell Therapies and Antitumor Immune Response

Introduction:: Adoptive cell therapy (ACT) continues to fail at treating solid tumors, including breast cancer. In ACT, immune cells are isolated and expanded from the patient, followed by re-infusion. To accelerate development of these novel cell therapies, better tools are needed to understand the in vivo requirements to generate a robust immune response. Furthermore, lymphocyte infiltration and immune activation at the primary tumor are predictive of clinical outcomes. However, in vivo feedback is lacking to evaluate cell trafficking, status, and mechanism of action in the context of morphological/functional changes at the primary tumor, making it difficult to guide and plan treatments. Here, we demonstrate an ultrasound and photoacoustic (US/PA) imaging approach that can track nanoparticle-labeled T cells and assess ACT progression in vivo by analyzing imaging biomarkers.

Materials and Methods:: Maleimide-modified (mm) silica-coated (SiO2) gold nanorods (AuNRs) were synthesized in-house and conjugated to thiol groups on the T cell surface via a 30-minute incubation (Fig. A). T cell viability (Fig. B; left) and ability to eliminate cancer cells (Fig. B; right) post-labeling and PA detection were verified in vitro. For in vivo studies, T cells were isolated from OT-1 mice, which have receptors that match and target OVA-positive cancer cells. C57BL/6 mice (n≥3 per group) were inoculated with EG7-OVA cancer cells or their OVA-negative counterpart, EL4 cancer cells, representing “hot” or “cold” tumors, respectively. At tumor volumes of 100 – 200 mm^3, AuNR-T cells in 100 μl saline were systemically injected. Volumetric US/PA imaging datasets were acquired with the Vevo LAZR (20 MHz; 680 – 970 nm) and analyzed offline.

Results, Conclusions, and Discussions:: AuNR-labeled T cells that matched the tumor type (Fig. C; left) showed decreasing tumor volume in 3D US images (grayscale) and increasing T cell accumulation at the primary tumor in PA images (color scale). AuNR-T cells that were unmatched to the tumor type (Fig. C; right) showed opposite trends. Quantification of US/PA data showed striking differences in the longitudinal changes in tumor volume (Fig. D) and cell accumulation (Fig. E). In addition, mice that received matched AuNR-T cells at high (5x10^6) vs. low (1x10^6) doses showed a 2.5-fold increase in the rate of T cell accumulation. Results indicate feasibility of our US/PA imaging approach to safely track nanoparticle-augmented T cell infiltration and evaluate ACT response. In the future, US/PA biomarkers can be expanded to further analyze ACT progression and stratify treatment response with greater granularity for other types of cancer or cellular immunotherapies, i.e. chimeric antigen receptor (CAR) T cells.

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