The Scientist: Bhushan Dharmadhikari
1. What led you to your current role in Herbert Schwarz’s lab?
After completing my engineering degree in Biotechnology and spending 3 years in a company developing recombinant therapeutic proteins, I realized that research and development was something that I was really interested in. However, I also realized that I needed advanced training and skill sets to take up a career in biomedical research. So I started searching for a PhD position that focused on translational research and new approaches to cancer therapy. During this time I was awarded a scholarship by the National University of Singapore’s YLL School of Medicine to pursue a PhD. I accepted the scholarship and joined Herbert Schwarz’s Lab due to the novel cell based therapy project I was offered.
2. What do you enjoy most about research?
The fact that it keeps challenging you with a new question every time you find an answer for the previous one.
The Science: Dendritic Cell Therapy
1. Tell us about your research.
My research is focused on a novel in vitro generated dendritic cell (DC) cancer immunotherapy. The induction of CD137 ligand (CD137L) initiates reverse signaling in human monocytes, resulting in the generation of DCs. This is a novel method that does not require any cytokines for monocyte to DC differentiation. My research has identified that these DCs have a novel phenotype and are closely related to pro-inflammatory DCs found in vivo1. In addition, these DCs are significantly more potent in activating T cells in an antigen specific manner than the conventionally used in vitro generated DCs.
2. What is the significance of your research?
To date, DCs used for therapy are generated from GM-CSF- and IL-4-stimulated monocytes. However, monocytes in human body are unlikely to encounter the high levels of these cytokines that are required for DC differentiation. CD137L reverse signaling is physiologically relevant, as monocytes receive CD137L reverse signal at all inflammatory sites in vivo, where they can differentiate into DCs1. The novel DC generation protocol we developed results in more potent DCs that have the potential to be used for the next DC based immunotherapy.
3. Where do you think DC-based immunotherapy field is heading?
DC based therapy has always been considered a therapy with high potential; however, its efficacy has been low in various clinical trials, primarily due to lack of induction of a strong enough immune response. Now that we understand the immune system better, we know that a combination of immune activation and prevention of immune suppression would be required to improve the efficacy of immunotherapy. Thus, combinations of DC-based therapies with immune checkpoint inhibitors to overcome immune suppression is the way ahead.
4. What do you think is the most important advancement in the field in the past 5 years?
I believe the most important advancement in the past 5 years is our advancements in understanding how the immune system can control and inhibit immune responses via immune checkpoint mechanisms such as PD1-PDL1 and CTLA-4.
5. What is the most controversial aspect of this research area?
The most controversial aspect of DC research has been the identification of biomarkers that can unambiguously differentiate different functional DC subsets in humans.
6. What is the most challenging aspect of DC research?
The lack of knowledge on exact mechanism by which various human DC subsets function to dictate the nature of immune responses, and how DCs are generated in vivo. In addition, there is limited characterizing tools available for human DC research.
EasySep™: Immune Cell Isolation
1. What do you use EasySep™ for?
I use EasySep™ to isolate human monocytes and T cells.
2. How has EasySep™ helped your research?
EasySep™ saves significant amount of hands-on time for cell isolation, thus allowing me to invest more time on experimentation, functional assays and improve productivity.
3. Have you used a column-based cell isolation?
Column-based methods are time intensive and are not so user-friendly compared to EasySep™. Also, the overall cost of column-based method is high.
STEMCELL's Scientific Summaries
On dendritic cell therapy for cancer
Dendritic cells (DCs) are potent antigen-presenting cells that can sample tumor antigens and migrate to lymph nodes to present them, resulting in the activation of adaptive immunity towards tumor cells. Researchers have been testing the use of DCs for cancer therapy since the 1990’s2. Although clinical trials show that DC-based monotherapy is safe for cancer patients, the clinical efficacy is considered suboptimal. Tumor-induced immunosuppression and insufficient DC function are hypothesized to be the primary reasons for limited efficacy3,4. Scientists aim to improve DC therapy by inhibiting immunosuppression and optimizing methods to generate more potent DCs. Blockade of inhibitory factors such as CTLA-4 have indeed been shown to improve the outcome of DC therapy2, perhaps by creating a more favorable environment for tumor-infiltrating lymphocytes induced by DCs. Interestingly, the preparation of tumor lysates as antigen source for DC therapy can have direct effects on DC function. Tumor lysates prepared using methods that induce immunogenic cell death, including ultraviolet radiation, oxidative stress induction and heat shock can yield more activated and functional DCs compared to the commonly used freeze-thaw cycles that induce necrosis2. Scientists are also exploring variations of DC-based therapy, such as the use of DC-derived exosomes carrying defined molecular compositions tailored to each patient5. Researchers predict that DC-based therapy alone may not be sufficient, and combinatorial therapies with agents that counteract the immunosuppressive tumor microenvironment is needed to enhance clinical efficacy.
More on cancer immunology
On CD137 (4-1BB) immunotherapy
CD137 (also known as 4-1BB) is a member of the TNF receptor superfamily, and is expressed on various immune cells, including T cells, B cells, DCs and NK cells6. Upon ligation of its ligand (CD137L), an intracellular signaling cascade is initiated, leading to the activation of several pathways, including JNK, ERK and AKT6. CD137 is known for its co-stimulatory effects on T cells, which result in the inhibition of activation-induced cell death, and enhanced proliferation, survival, memory formation and effector function of T cells. Researchers have also shown that CD137L stimulation can increase cytokine secretion (ex. IL-12) and expression of co-stimulatory molecules (CD80 and CD86) by DCs, resulting in increased ability to induce T cell proliferation7. These properties make CD137 a desirable target to induce immune responses against tumor cells. Monotherapy using CD137 agonists only resulted in modest efficacy in cancer patients, but combining CD137 agonists with other forms of therapy, including checkpoint blockades, oncolytic viruses or DC vaccines can improve clinical outcomes6,8. The potency of CD137 co-stimulation for inducing antitumor responses is also being utilized to design chimeric antigen receptor (CAR) T cells. CD137 signaling domains are often incorporated in the intracellular portions of CARs9. Overall, the role of CD137 signaling in T cell and DC function suggest that modulation of this pathway can contribute to the development of effective therapeutic strategies against cancer.