**4. Organoids in the study and treatment of disease**

Recent advances in the development of human patient-derived organoids have allowed a more accurate study of diseases. This technology has opened a new horizon in biomedical research, and provides unprecedented opportunities in translational medicine, and personalized therapy [32].

#### **4.1 Disease modeling and drug screening approaches**

Recent discoveries involving organoids as a disease model reflect that researchers have started to unravel the potential of this tool. To date, organoids have been mostly applied in cancer, cystic fibrosis and studies on host–microbe interactions. However, a growing interest in this field has promoted an exponential increase of publications using organoids technology to study many other diseases (**Table 1**). The fact that organoids are 3D structures originated from stem cells with similar architecture, multi-lineage differentiation and many of the original tissue functions, make them the perfect candidate for disease pathogenesis studies [33, 34].

Organoids can be designed to reproduce patient conditions of disease-relevant genetic and epigenetics. Thanks to the development of new techniques like the CRISPR/CRISPR -Cas9 genome engineering tool, is currently feasible to efficiently manipulate genomic sequences in hESCs and hiPSCs [35, 36]. In the case of host– microbe interactions, organoids can also reproduce the infection process allowing its study in more life-like manner.

Organoids can also be applied to study cellular dysfunction in diseased tissues, as well as to identify strategies for its restoration. For example, Dekkers *et al*. used organoids to study cystic fibrosis (CF), a disease caused by mutations in the CF transmembrane conductance regulator (CFTR) gene, severely reducing the CFTR protein function [37]. Thus, rectal organoids from CF patients were used to evaluate CFTR function as well as the response to CFTR-modulating drugs. Their results demonstrated the pharmacological restoration of CFTR function in the rectal organoids of individual donors, suggesting that *in vitro* functional measurements of CFTR may be used to preclinically identify CF patients who would benefit from CFTR-modulating treatments, independent of their CFTR mutation [38].

A major challenge in clinical practice is the absence of appropriate models for drug screening and pre-evaluation of the pharmacological effects prior administration to patients. For cancer research, the development of tumor organoids, also known as tumoroids, represents an overwhelming step to be able to reproduce *in vitro* such a heterogeneous microenvironment. Tumor organoids can be generated *in vitro* for the analysis of cancer phenotypes [39], anticancer drug discovery, and to evaluate the response of patient cancer cells to a specific treatment [39, 40]. Lazzari *et al*. reported a triple co-culture of pancreatic cancer cells fibroblasts and endothelial cells. As a result, cells assembled in a hetero-type multicellular tumor-spheroid (MCTS) that reliably reproduced the impact of the surrounding environment, on the sensitivity of cancer cells to chemotherapy. This approach can be successfully applied as a predictive tool of various therapeutic strategies [41]. In this sense, the establishment of patient-derived tumor organoids (PDTO) biobanks provides exciting new insights into developmental biology. Different researchers have started to develop methods for generating and bio-banking PDTO. Among them, a nonprofit organization called HUB (Hubrecht Organoid Technology) has initiated and established "Living Biobank", a collection of organoids representing different organs and disease models (huborganoids.nl). Overall, these biobanks maintain the key features to resemble the parental tumors and can be therefore used to evaluate patient-specific treatment approaches [42].


#### *Cell Interaction - Molecular and Immunological Basis for Disease Management*

