Poster R10 - Noninvasive Assessment of Adoptive Cell Therapy Response Using Ultrasound and Photoacoustic Imaging Biomarkers

Introduction: Adoptive cell therapy (ACT) is a revolutionary cancer treatment approach that enhances the endogenous antitumor immune responses. Despite great potential, a positive response to therapy is difficult to assess and is limited to a small subset of patients. Typically, response to therapy is evaluated by imaging changes in the tumor volume. However, changes in tumor volume occur slowly in response to therapy and do not accurately capture the immune response early. Biomolecular approaches to evaluate response to therapy, such as tissue biopsy or analysis of blood samples, are invasive and require complex screening. Therefore, a noninvasive, functional imaging method is needed to guide immunotherapies by providing feedback on therapy progression. Here, we are developing an ultrasound and photoacoustic imaging (US/PA) tool to evaluate responders and non-responders to therapy. Non-invasive, cost-effective US/PA imaging can be used to visualize both anatomical and functional changes at the primary tumor. By developing and accessing a set of imaging biomarkers, including changes in tissue morphology, blood flow, blood oxygen saturation, and concentrations of deoxy/oxygenated hemoglobin, we aim to identify responders and non-responders before volumetric changes at the primary tumor become apparent (Fig 1A). Identifying patterns in these imaging biomarkers will inform more timely adjustments to ACT to improve treatment outcomes.

Materials and

Methods: C57BL/6 mice (female, 6 – 8 weeks old; Jackson Laboratory) were inoculated with either B16-F10 or B16-OVA melanoma cells on the left flank. Antigen-specific CD8+ T cells were isolated from the spleens of OT-1 transgenic mice, which specifically recognize and target OVA-positive cancer cells. OT-1 CD8+ T cells were subsequently transferred via intravenous injection to the tumor bearing mice. Tumor development and treatment response were monitored using US/PA imaging at various timepoints. In vivo US/PA images were acquired using a Vevo LAZR 2100 imaging system (FUJIFILM VisualSonics) equipped with a pulsed laser (5 frames/sec, 7 ns pulse duration). Two-dimensional spectroscopic US/PA images were acquired by scanning tumors within a wavelength range of 680-970 nm in 5 nm increments. Three-dimensional US/PA images were obtained using a translational motorized stage, scanning with a step size of 0.152 mm. Tumor volume was assessed using ultrasound imaging. The changes in oxygen saturation, and deoxy/oxygenated hemoglobin were quantified using photoacoustic imaging. Blood flow velocity was measured using ultrasound color Doppler. Data analysis was performed using the Vevo LAB 5.7.0 software and MATLAB, enabling comprehensive evaluation of treatment responses and tumor dynamics.

Results, Conclusions, and Discussions: Results and

Discussion:
Following ACT and longitudinal monitoring in US/PA, notable trends emerged in the imaging biomarkers over the 14-day period. Responders to the treatment exhibited a decrease in tumor volume measured using ultrasound, indicative of a positive treatment response (Fig 1B). In contrast, the non-responders displayed an increase in tumor volume, suggesting continued disease progression despite intervention. For the imaging biomarkers, responders demonstrated a progressive increase in oxygen saturation levels (Fig 1C, 1D, and 1E). By day 10, discernible differences in oxygen saturation levels between responders and non-responders became apparent, indicating a potential imaging biomarker. Conversely, non-responders displayed little change in oxygen saturation levels until day 10, followed by a decrease between day 10 and day 14. Further analysis of oxygenated and deoxygenated hemoglobin levels revealed distinct patterns between responders and non-responders. (Fig 1C, D, and F). Responders displayed a gradual decrease in deoxygenated hemoglobin levels and an increase in oxygenated hemoglobin, consistent with enhanced tissue oxygenation and metabolic activity associated with treatment response. On the other hand, non-responders exhibited minimal alterations in oxygenated hemoglobin and deoxygenated hemoglobin, indicative of persistent hypoxia and limited treatment. By day 7, there was noticeable differences in deoxygenated hemoglobin and oxygenated hemoglobin between responders and non-responders.

Conclusion:
In summary, our findings demonstrate the potential of US/PA imaging biomarkers to monitor adoptive cell therapy. The insights gained in this study offer valuable perspectives into treatment response before conventional metrics such as tumor size become evident. Particularly noteworthy were the changes in deoxygenated hemoglobin and oxygenated hemoglobin among responders by day 7, indicating the potential of these imaging biomarkers. Overall, these findings emphasize the importance of personalized medicine approach, where the use of imaging biomarkers can inform tailored treatment strategies, thereby optimizing patient outcomes. Looking ahead, further exploration and validation of these imaging biomarkers in larger cohorts and diverse tumor types hold immense promise for advancing immunotherapies and transforming cancer care.

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