*Organoids Models for the Study of Cell-Cell Interactions DOI: http://dx.doi.org/10.5772/intechopen.94562*

**Table 1.** *Use of organoids as disease models.*

Jacob *et al.* reported the generation of patient-derived glioblastoma organoids (GBOs) biobanks [42]. The authors successfully transplanted the GBOs into adult rodent brains and performed personalized tests. Calandrini *et al.* have recently established the first pediatric cancer organoid biobank [59]. This biobank contains a collection of over 50 tumors matching normal kidney organoids and also covers a diversity of tumor subtypes. Similarly, a primary gastric cancer organoid (GCO) biobank was established by Leung and coworkers [63], including a total of 34 patients with different gastric cancer subtypes. In this study, whole-exome sequencing and transcriptome analysis were performed, as well as large-scale drug screening studies. Overall, the establishment of organoids biobanks provides a rich resource for cancer cell biology and drug-screening studies to test personalized therapies. Patient-specific drug sensitivities could be achieved as the organoids closely resemble the *in vivo* tumors. Furthermore, these biobanks could play a prominent role in biomarker discovery and represent a powerful tool to predict disease development, recurrence and progression [42, 51, 64].

## **4.2 Applications in regenerative medicine**

Several of the most life-threatening diseases require organ transplantation in order to save patients life. Nevertheless, transplantations are not always an option due to the high cost, organ availability or potential organ rejection. Therefore, other alternatives needed to be explored in order to overcome this challenge. The development of organoids brought hope to the scientific community and patients themselves. This technology could potentially serve as an unlimited source for replacing damaged tissues. Furthermore, the transplantation of organoids derived from healthy tissue of the same patient would prevent immune responses related to non-autologous transplants. In this sense, diseases involving dysfunctional organs such as kidneys or the liver, can significantly benefit from the opportunity that liver-derived organoids bring. Researchers have already developed strategies to allow long-term *in-vitro* expansion of liver progenitors into "liver organoids" [56]. The huge expansion and differentiation potential of liver organoids cultures has facilitated the engraftment [56] and survival of livers in murine models, as it happened in a study with liver organoids transplanted to a tyrosinemia type I liver disease model, partially restoring the hepatic function [57]. Similarly, transplantation of human adult stem cell-derived liver organoids into chemically damaged-liver immune-deficient mice produced functional hepatocytes containing grafts [58]. Cultured organoids have also shown the potential to expand, engraft, reconstitute and recover the colon and intestinal epithelia as well as their function in several murine models [52–54].

Despite all the advances in the field, there is still a long way before organoids transplantation becomes a reality. Current resources and techniques do not provide a suitable organ niche, limiting the formation of optimal organ sizes and tissue structures *in vivo*, as well as the appropriate intercellular communication required for functional restoration. Thus, alternative approaches are required, such as the combination of organoids with gene therapy, to implement organ transplantation [65]. Experts on the field will still have to poise excitement with reality before organoid research can be successfully translated to clinical practice and become a real therapy option [66].

#### **4.3 Personalized medicine**

Over the past decades, medicine has discovered novel ways of changing the course of many human diseases [67–70]. Nowadays, researches all over the globe

#### *Organoids Models for the Study of Cell-Cell Interactions DOI: http://dx.doi.org/10.5772/intechopen.94562*

are discovering new therapies which bring new options for previously untreatable diseases [71, 72]. However, the key challenge is that the efficacy of most of these new treatments will depend on the complex and unique nature of each individual human being. Lastly, the efficacy of a treatment is significantly determined by behavioral factor, environmental influences as well as genetic particularities.

Moreover, currently available therapies might cause a high impact on patient's quality of life due to the unpleasant side effects directly related to the treatment. Thus, research groups and pharmaceutical companies are developing strategies to personalize their treatments in order to predict the outcome of the proposed therapy and avoid unnecessary aggressive treatments. These aspects are key to achieve the ultimate goal of any therapy: to ensure patients´ health and integrity.

The concept of Personalized Medicine arose with the aim of tailoring the best response and highest safety standards to preserve patient's well-being. This optimized health care strategy would also lead to reduced treatment costs and shorter diagnosis times required for each patient [73–75].

Organoids have revolutionized personalized medicine due to their unique ability of simulate, even mimic, specific cellular microenvironments with remarkable similarity to *in vivo* organs/tissues under normal or pathological conditions [76]. Such models have started to be used in the clinic, mainly in cancer research, to evaluate the response to experimental therapies prior administration of certain drugs or other treatments to patients [77]. The possibility of using accessible models of organ diseases allows to understand the effect of experimental therapy in a deeper manner than in a traditional culture assay or "sphere" culture assays, applied over the last decades [78].

Personalized medicine could also be linked to regenerative medicine which is based on the capacity of the stem cells to derive into many different cell subtypes. Currently, this basic characteristic is key for the understanding of normal and abnormal cell behavior and organization, and is leading to improved tissue engineering approaches [60].

In this scenario, organoids constitute a solid foundation on which personalized and regenerative medicine is taking long steps forward.

One of the best examples of this input on current society is the novel application of organoids cultures to optimize treatment to cancer patients [55, 79]. Oncologic centers are developing translational procedures to understand as much as possible the specific characteristics of each tumor in order to optimize the therapy approach.

Once the tumor is detected, a biopsy of the mass is obtained to culture organoids derived from patient's tumor cells. A complete biological profile of the tumor could be developed combining this information together with histopathological analysis of primary tumor sample, histopathological analysis of the organoids, gene sequencing and cytotoxicity analysis from *in vitro* drug assays or studies using avatar mice.

This complete analysis only takes 2–4 weeks and it could provide physicians relevant information regarding the best treatment for the patient according to the characteristics of the tumor.

Furthermore, in cases of progressive disease or metastasis, new tumor biopsies could be collected, new organoids lines could be established, and new therapeutic strategies could be carried out giving a new opportunity and new hopes to the patient [80–82].

According to the website ClinicalTrials-gov, by 2019 there were 30 projects related to cancer organoids. Most of them (73%) focused on studying anti-cancer therapies, including among others T-cell immunotherapy, or evaluation of radiotherapy sensitivity. The rest aimed to generate patient-derived cancer organoid models (13%) or to evaluate the mechanisms related to cancer progression [83].

A large number of cancer patients are insensitive to immunotherapy due to the heterogeneity of the T cell repertoire [83]. Thus, the use of cancer organoids allows studying the effectiveness of combining immune therapy with specific anti-cancer drugs. To date, two clinical trials involving cancer organoids for immunotherapy have been registered (NCT03778814, NCT02718235). Overall, the inclusion of PDTO into clinic represents an enormous potential to understand the onset of diseases such as cancer and, moreover, to evaluate the individual response to specific therapies for personalized approaches.

### **5. Limitations and future perspectives**

Regardless of the advances made in this emerging technology, a series of limitations still need to be addressed in order to fully exploit its potential. For instance, despite the development of specific culture conditions and growing techniques, there are still tissues that withstand to organoid derivation [84, 85]. Organoid technology requires further advances to achieve less laborious protocols as well as the establishment of standardized conditions for proper differentiation and maturation. A reduction of the heterogeneity seen in organoids size and shape should also be achieved [85]. In addition, it requires the co-induction of the essential cell types, the associated extracellular matrices and native microenvironment that will allow the recapitulation of the *in vivo* tissue sizes, structures, organization, inter-cellular communication and functionality. Also, shorter processes and more affordable culture conditions are required to ensure that the organoids system becomes accessible to a large number of academic and clinical researchers, thereby helping to maximize its potential [5]. Moreover, the protocols used for generating one specific type of organoid are usually not transferable to another organ system. Due to this drawback, scalable and cross-system parameters are challenging to generate via bioengineering tools. Computational prediction models are also difficult to design limiting the capacity to predict phenotypic, toxicological and drug screening results. Lastly, organoids technology requests the development of a complex vasculature network to provide not only oxygen, nutrient and waste exchange, but also an inductive biochemical exchange and a structural template for growth. The advances in microvascular patterning and organ-on-a-chip microfluidic technology would bridge this limitation supporting the use of perfusable organoids generation [86, 87].

In this context, different strategies are currently under research and new ideas have arisen to implement the potential use of organoids. As stated before, the development of organoid biobanks constitutes an important step in this direction. Currently, there are organoid biobanks with healthy organoids as well as patientderived intestine, liver, pancreatic, lung and mammary gland organoids related to cancer, cystic fibrosis or inflammatory bowel disease [88]. Thus, organoid biobanks are becoming a demanding business and several companies worldwide have already started to commercialize organoids after the establishment of optimized organoid biobanks [88]. Advantages of organoid biobanks include immediate accessibility or cost-effectiveness, as well as the possibility to access a large repository of data related to patient's diseases [83, 88]. This, however, involves some ethical and regulatory challenges that need to be addressed such as donor confidential information or the organoid source itself [89].

The development of microfluidic organoid-on-a-chip platforms [90] and 3D bioprinting [91, 92] constitute two major advances in the last years that are contributing to speed up organoid manufacturing and commercialization [88]. Organ-on-a-chips are devices containing living cells, extra-cellular matrix (ECM)

#### *Organoids Models for the Study of Cell-Cell Interactions DOI: http://dx.doi.org/10.5772/intechopen.94562*

and microstructures emulating key features of organs or issues, and their functions [83, 93]. These devices aim to provide continuous flow perfusion culture to simulate organ microenvironments. Nevertheless, most of these systems are made of primary cell lines or stem-cell-derived cells to mimic organs, but they are unable yet to imitate the cellular interactions taking place in the native sources [94].

Similarly, advances in 3D printing technology and biomaterials research have led to the creation of 3D bioprinting, with the aim to resemble *in vitro* the interactions between tumor cells, ECM and the 3D tumor microenvironment [83, 95]. With this technology, different cell types can be printed in hydrogels and mixed with other cells and/or specific factors to simulate a healthy or pathological microenvironment. Increasing evidence has pointed to the tumor microenvironment as a major modulator of the tumorgenic process [96]. Thus, in order to understand the mechanisms by which tumor cells become metastatic, different studies are benefiting with the use of 3D bioprinting strategy. For example, Grolman JM *et al.* designed a 3D environment with breast adenocarcinoma and macrophage cell lines printed in hydrogel to evaluate the effect of paracrine signals in the regulation of breast cancer metastasis [97]. In the same way, Pang Y *et al*. developed an *in vitro* cervical tumor model to demonstrate the epithelial-to mesenchymal transition (EMT), by mixing *HeLa* cells with hydrogel. These authors were able to evaluate the effect of different activators and inhibitors over the EMT in the 3D system designed [98].

Despite the benefits of using these techniques, there are still several factors that need to be optimized. For instance, biomaterials represent a limiting feature for 3D bioprinting, and the development of improved materials is required. A consensus in the best printing strategy (i.e. polymerization steps, light-based 3D bioprinting *vs* inkjet printing) should be also reached.
