Organ-on-a-chip technologies are redefining the way in which in vitro models help understand and recapitulate the in vivo environment. The immune system is particularly difficult to model in an in vitro environment because of the complexity of biological, mechanical, and chemical cues that modulate the immune cells. Prof. Ankur Singh, an assistant professor in the Sibley School of Mechanical and Aerospace Engineering at Cornell University, has led the development of organ-on-a-chip models to mimic the complex immune environment.
B cell lymphomas grow in organoids as clusters, similar to those in patients. The green fluorescent areas represent lymphoma cells, while the red represents support stromal cells.
The organoid captures the early stages of a germinal center, which is the center for initiating an immunological response to infection. These organoids can be tailored to study specific diseases, like asthma, cancer, arthritis and transplant rejection. They represent a quick and easy approach to studying and understanding the mechanisms behind disease initiation and propagation.
Another model being developed in Prof. Singh’s lab is the Lymphoma-on-a-chip technology, that accurately recapitulates the microenvironment for a tumor and can be used to study tumor progression. Moreover, these models can be used to study how the tumors respond to chemotherapy drugs, providing new ways of studying tumor resistance.
Prof. Singh was recently awarded the Society for Biomaterials Young Investigator Award, and has several grants from the National Institute of Health to further develop his technologies. We recently had the opportunity to interview Prof. Singh to learn more about his team’s models.
Rukmani Sridharan, Medgadget: How representative are the immune organoids for studying immune disorders compared to current in vitro and in vivo models?
Prof. Singh: The current version of the immune organoid recapitulates selective aspects of the sub-anatomical parts of a lymph node or spleen where immune cells, which have the potential to respond to infections by producing antibodies, are formed. These immune cells, called B cells, are present in our body as naïve, uneducated cells which receive signaling that transforms them into antibody secreting cells. The organoid mimics the early stages of a germinal center, where B cell differentiation and initiation of immunological responses take place during infection. Maturing cells in current 2D systems are very short lived and lack the supporting tissue niche, on the other hand previous attempts to engineer 3D scaffolds have only shown formation of these highly specialized cells (called Germinal Center B cells) when implanted in vivo, exploiting the host microenvironment. Importantly, these studies did not provide evidence of control over the rate of immune reaction ex vivo or in vivo, and no studies have been reported that demonstrate differentiating B cells can survive ex vivo for successful conversion into the desired phenotype.
We submit that several aspects are still to be incorporated to make it completely similar to the in vivo environment; however, the system is suitable in its current form to determine how extracellular and intracellular factors can affect B cell activation. Understanding the factors that control the production, maturation and long-term survival of B cells is critical for more rapid development of disease-specific B cells, improved immunotherapeutic design (such as vaccines and immunomodulatory drugs) and to provide mechanisms to target disorders resulting from defective B cell process (e.g. immunodeficiency with hyper-IgM, aging, as well as various B cell lymphomas or multiple myeloma).
Medgadget: How long can you keep these organoids in culture? Can they be constantly replenished /maintained to study the changes in immune response over time and changing environmental conditions?
Prof. Singh: The organoids are tunable and can be kept in culture for up to 14 days, however we already see 100-fold superior response over 4 days and have plentiful cells within 8-10 days. Although longer times are possible, we have not tested this as the peak time for in vivo maturation is around 10 days. These are cultured in standard tissue culture plates and can be constantly replenished /maintained to study the changes in immune response over time and changing environmental conditions.
Medgadget: You have used gelatin and polyethylene glycol as base materials for building the organoids. How closely do these mimic the conditions normally found in the germinal centers in vivo? Do you anticipate using other materials in the future?
Prof. Singh: The rationale for using gelatin was the abundance of adhesive motifs that are found in the germinal center phase of the immune reaction. We have however developed a second generation designer immune organoid which allows us to change the signalling ligand/protein as needed. This organoid is composed of maleimide-functionalized PEG where a simple click chemistry is applied to “click” short peptide of interest, and the peptide represents adhesive motifs found in larger bioadhesive proteins such as vitronectin, laminin, and fibronectin. PEG itself is an inert material, so this allows us to precisely control the binding of cells to the material.
Medgadget: Your lymphoma-on-a-chip technology sounds very interesting. Could you explain what your plans are with this model?
Prof. Singh: The Lymphoma-on-a-chip technology recapitulates the microenvironment for a tumor and can be used to study tumor progression. Moreover, these models can be used to study how the tumors respond to chemotherapy drugs, providing new ways of studying tumor resistance.
Medgadget: Organ-on-a-chip technologies are becoming more mainstream and more people are coming on board with the idea of using them. How far are we from replacing existing models with these technologies?
Prof. Singh: Organ-on-a-chip platforms are extremely useful for creating developmental and disease models as well as for conducting drug testing studies. They often recapitulate selective aspect of a target organ system and are very effective. Multiple labs are now moving into whole body-on-chip models. Interestingly, almost all of these approaches lack immune system on chip, primarily because of the layers of complexity of this organ system. It would be less useful to simply put a single type of immune cells in conjunction with body or organ on chip, and I believe we, as engineers, need to think more deeply about multiple components of the immune system and how one immune cell orchestrates the performance of other immune cells. Our immune organoids are a good example of a system that entails much deeper immunology and focuses on a specialized area of the lymph node. Our next steps would be to integrate other sub-anatomical parts of immune organs and make a more holistic organ on a chip.
Medgadget: What are your plans for commercialization of the technology?
Prof. Singh: Our patents are pending and companies have expressed interest, but we are still in the early stages of assessing our best step forward.
