Azza M. El-Derby ^1,2 Cecilia R. Schaaf ^1,3 Ethan Shelkey ^1,4 Katherine L. Cook ^5,6 Konstantinos I. Votanopoulos ^1,7 Shay Soker ^1,5,7*

• ¹ Wake Forest Institute for Regenerative Medicine, School of Medicine, Wake Forest University, Winston-Salem, North Carolina, United States
• ² Zewail City of Science and Technology, Giza, Beni Suef, Egypt
• ³ Comparative Medicine, School of Medicine, Wake Forest University, Winston-Salem, United States
• ⁴ Lonza, Morrisville, NC, United States
• ⁵ School of Medicine, Wake Forest University, Winston-Salem, North Carolina, United States
• ⁶ Hypertension and Vascular Research Center, School of Medicine, Wake Forest University, Winston-Salem, North Carolina, United States
• ⁷ Department of Cancer Biology, School of Medicine, Wake Forest University, Winston-Salem, North Carolina, United States

Immunotherapies are a revolutionary approach to treating cancer by utilizing the body's immune system to target and combat cancer cells. This approach offers promising alternatives to traditional chemotherapies. Its potential to induce long-lasting remissions and specificity for cancer cells, which minimizes side effects, makes it a cutting-edge treatment with tremendous potential. With the increase of the clinical usage of immunotherapy, evidence emerges of the microbiome's impact on both tumor growth and response to immunotherapy. The proposed involvement of the microbiome can change treatment efficacy by altering drug metabolism and reshaping the immune system response. Understanding the specific interactions between tumor cells, immune cells, and the microbiome is a critical step in the advancement of immunotherapy.To study the complex interaction between cancer immunity and the microbiome, various preclinical in vivo and in vitro models have been developed. We have recently described the use of an ex vivo preclinical model for anti-cancer treatment outcome prediction -tumor tissue equivalents (organoids). Specifically, immune-reactive tumor organoids are proposed as a novel tool for understanding how the microbiome influences cancer immunity and immunotherapy. More importantly, this platform can utilize patient samples to dissect patient-specific elements regulating cancer immune response and microbiome influence. This review presents the rationale for using the immune-reactive tumor organoids model to study the interactions between the microbiome and cancer immunotherapy (Figure 1). It will discuss available components of the model and analyze their interplay, summarize relevant experimental data, and assess their validity. Additionally, it explores the potential of immune-reactive organoids for personalized treatment approaches.Understanding the microbiome's role in immunotherapy outcomes will lead to transformative cancer treatment via a simple change of diet or other microbiome manipulations. Ongoing research on microbiome-cancer interactions utilizing the described model systems will lead to innovative treatment strategies and improved patient outcomes.