Patient-Derived Tumor Organoids Demonstrate Microbial Influence on Immune Function

By Brittany Wade

August 25, 2022 | Immune checkpoint blockade (ICB) is a form of immunotherapy showing promising results in the fight against cancer, specifically in battling the aggressive and often fatal metastatic triple-negative breast cancer (TNBC). However, with a clinical response rate of only 40%, the treatment is not as universal as oncologists hoped.

Of course, a patient’s reaction to any treatment is contingent upon their disease type, medical history, genetic makeup, and lifestyle. Recently, individual microbiomes have also emerged as a noteworthy influence on treatment outcomes.

To find a link between microbiomes and immune response, researchers from the Wake Forest Institute for Regenerative Medicine (WFIRM) and Wake Forest Organoid Research Center (WFORCE) developed an innovative immune-enhanced tumor organoid to study microbial metabolites and their effect on immunotherapy.

“Immune checkpoint blockade immunotherapy is one of the newest and most promising developments in cancer treatment,” said Konstantinos I. Votanopoulos, MD, Ph.D., Atrium Health Wake Forest Baptist Comprehensive Cancer Center Surgery professor and WFORCE director, in a press release. “It can show profound effects in patients who respond; however, a large portion of patients display either a total lack of response or develop a resistance to the treatment over time, and we need to understand why.”

ICB therapy assists cytotoxic T-lymphocytes or T cells—immune cells that develop and mature in the thymus—in performing checkpoints. T cells roam the body and scan the surfaces of other cells, seeking to demolish tumors and foreign invaders. When a cell expresses a checkpoint protein on its surface, T cells deem it “safe” and move to another target.

Under healthy conditions, checkpoint proteins prevent T cells from destroying vital tissue and contributing to an overactive immune system. However, some tumors express the same checkpoint protein, thereby successfully evading T-cell-mediated doom. In response, ICB therapy blocks these tumors from expressing checkpoint proteins and marks them for destruction.

Immune-Enhanced Organoid Model

The microbiome is the human body's collection of bacteria, fungi, protists, and archaea. Many scientists refer to it as a supporting organ due to its contributions to immune health, neural function, and hormonal equilibrium. These contributions are made primarily through metabolites: molecules produced by microbes as they break down food and other substances.

Gut microbes garner a lot of attention, but the focus is shifting to the microbiome’s influence over other organs, including those in the immune system. Votanopoulos and his colleagues sought to “study the unique and complex interactions between tumor, immune system, and microbiome” to understand how metabolites influence immune responsiveness to ICB.

Published in Scientific Reports (DOI: 10.1038/s41598-022-13930-7), the WFIRM and WFORCE teams developed a miniature organ model, also called an organoid, to depict tumor interactions with metabolites, surrounding cells, and non-cellular components in the extracellular environment. Organoids are particularly useful because they provide a more accurate representation of human tissue and allow for the independent manipulation of several tumor environmental factors.

The organoid, consisting of primed cytotoxic T cells from the spleen, murine TNBC cells, and an extracellular hydrogel matrix, was exposed to various metabolites presumed beneficial to ICB. These metabolites—3-indolepropioninc acid, hippuric acid, pyocyanin, butyrate, and inosine—upregulated critical elements in the immune response pathway when administered in concentrations consistent with systemic circulation. 

When combined with ICB therapy, the metabolites produced a marked increase in anti-tumor cell activity and T-cell viability, confirming that metabolites enhance immunotherapy responsiveness.

Like in vivo tumors, the organoid was reactive to metabolite exposure independent of and in conjunction with ICB. Therefore, the study confirmed that organoids could be used for future tumor studies where mimicking the human body is a critical component. 

“These results suggest that further development of this model will eventually be an important clinical tool in designing and analyzing future trials for anti-cancer treatments,” said Anthony Atala, MD and WFIRM director. “Our goal is to integrate the immune-enhanced tumor organoid platform into the treatment decision process to better treat patients.” 

Microbial Power in Precision Oncology

The teams acknowledge that while the organoids show promising results, additional study is needed, particularly in other immune cells. For example, the researchers would be interested to see how macrophages—phagocytic immune cells that engulf pathogens and cellular debris—would respond to organoid-facilitated metabolite exposure, given their potential to consume metabolites.

Nevertheless, the WFIRM and WFORCE teams believe that a better understanding of microbial-metabolite-immune interactions could lead to diagnostic testing and screening for therapeutic responsiveness.

“Further understanding of the relationship between specific bacterial metabolites and overall response to immune checkpoint blockage could be used to push for positive potential outcomes,” said Shay Soker, Ph.D., WFIRM organoid research team lead and WFORCE co-director. “Procedures such as fecal transfer or diet modification could also effectively induce a more conducive microbiome for therapy.” 

The teams’ findings mark an exciting time in microbial research and precision oncology. Last month, Bio-IT World covered a story regarding microbial mapping and creating target functions from designer microbial communities. Perhaps designer organoids could facilitate the next wave in cancer therapy, where probiotic cocktails, and their resulting metabolites, bolster the immune system with targeted supportive power to rid the body of disease.