3D Bioprinted Tumor Spheroid Model for the Assessment of Adoptive Cell Therapy

Adoptive cell therapies (ACT) intend to redirect the patient’s immune system to effectively recognize and target tumor cells. Although these therapies have shown significant success in the treatment of hematological malignancies, the response has not been as favorable in patients with solid tumors¹. This is mainly caused by the immunosuppressive nature of the tumor microenvironment (TME) which prevents immune cells from infiltrating, penetrating, and homing into the tumor site².<br/><br/>Current <i>in vitro</i> models to test ACT for solid tumors measure cytotoxicity, chemotaxis and suppression a 2-dimensional(2D) arrangement. However, therapeutics tested in 2D models fail to exhibit the same effects in vivo, due to their inability to accurately display the characteristics of the TME, such as 3-dimensional (3D) architecture, chemoresistance, hypoxia, cell heterogeneity and the presence of an extracellular matrix (ECM)³. For this reason, spheroids have been proposed as an alternative to model human solid tumors. Spheroid refers to an aggregate of cells that grow and adhere to each other, adopting a 3D sphere-like structure without the need of a substrate or foreign material. This type of model has greater accuracy and similarity to the TME <i>in vivo</i> by exhibiting a 3D architecture comprised of three distinct cell layers (necrotic quiescent and proliferative) with different gradients of nutrients, gas, waste and oxygen⁴. Efficiency in this models is also increased by allowing a higher throughput capacity and reducing the need to use animal models⁵.<br/>While there are several methods to generate spheroids (i.e. suspension, polymeric chambers, microfluidics), bioprinting displays more advantages than other methods due to its tight spatial control over spheroid growth and initial cell location that allows it to fully capture cell-cell and cell-ECM interactions⁶. Here, we aim to develop a 3D bioprinted tumor spheroid model to accurately evaluate the performance of ACT.<br/><br/>For the proposed model, spheroids were bioprinted by embedding breast cancer cells within several bioink formulations resembling the components of the ECM and then extruded. Cell viability, spheroid size and number were monitored throughout a 14-day period post-printing using high-throughput image-based approaches. Human T-cells were bioprinted in the same bioink formulations and tested for initial cell viability, infiltration and motility through image and flow cytometry based approaches. In conclusion, 3D bioprinting of spheroids is a promising tool to generate high-throughput, flexible and reproducible models that can be used to accurately evaluate ACT versus solid tumors without animal sacrifice.<br/><br/>References<br/>(1) Rohaan, M. W.; Wilgenhof, S.; Haanen, J. B. A. G. Adoptive Cellular Therapies: The Current Landscape. <i>Virchows Arch.</i> 2019, <i>474</i> (4), 449–461.<br/>(2) Joyce, J. A.; Fearon, D. T. T Cell Exclusion, Immune Privilege, and the Tumor Microenvironment. <i>Science (80-. ).</i> 2015, <i>348</i> (6230), 74–79. https://doi.org/10.1017/CBO9781107415324.004.<br/>(3) Kapalczynska, M.; Kolenda, T.; Przybyla, W.; Zajaczkowska, M.; Teresiak, A.; Filas, V.; Ibbs, M.; Blizniak, R.; Luczewski, L.; Lamperska, K. 2D and 3D Cell Cultures – a Comparison of Different Types of Cancer Cell Cultures. <i>Arch. Med. Sci.</i> 2018, <i>14</i> (4), 910–919. https://doi.org/10.5114/aoms.2016.63743.<br/>(4) Carvalho, M. P.; Costa, E. C.; Miguel, S. P.; Correia, I. J. Tumor Spheroid Assembly on Hyaluronic Acid-Based Structures: A Review. <i>Carbohydr. Polym.</i> 2016, <i>150</i>, 139–148. https://doi.org/10.1016/j.carbpol.2016.05.005.<br/>(5) Bahcecioglu, G.; Basara, G.; Ellis, B. W.; Ren, X.; Zorlutuna, P. Breast Cancer Models: Engineering the Tumor Microenvironment. <i>Acta Biomater.</i> 2020, <i>106</i>, 1–21. https://doi.org/10.1016/j.actbio.2020.02.006.<br/>(6) Gopinathan, J.; Noh, I. Recent Trends in Bioinks for 3D Printing. <i>Biomater. Res.</i> 2018, <i>22</i> (1), 1–15. https://doi.org/10.1186/s40824-018-0122-1.