Scientific leaders discuss emerging trends and technologies in experimental hematology
With each passing year, the number and magnitude of scientific breakthroughs in hematological research seem to increase. 2015 was no exception as numerous outstanding studies were published, so many that to only name a few would be unjust. These advances have not only paved the way for developing future therapies and technologies but they will also shape the scientific trends and avenues of investigation for the coming years. As members of the ISEH New Investigator Committee, we wondered what scientific themes and technologies will become vogue in the fields of normal and malignant hematopoiesis in the near future. We therefore asked leaders from our field what topics they foresee will emerge in 2016 and beyond.
Many of the experts that we spoke with emphasized that exciting developments are expected on several fronts. Past ISEH president Paul Frenette (The Ruth L. and David S. Gottesman Institute for Stem Cell and Regenerative Medicine Research, Albert Einstein College of Medicine, USA) replied: "I don’t think there is a single area but many areas that are being transformed. Our understanding is in constant evolution and the pace is very exciting with the rapid technological innovations (genetic engineering, sequencing, imaging, etc.).”
Dr. Iannis Aifantis (Langone Medical Center, New York University, USA) also displayed excitement saying: “This is the best time in blood research and obviously the most exciting time to be a hematologist. We have witnessed astonishing development in the treatment and understanding of blood malignancy.” Dr. Aifantis went on to emphasize that multiple areas are emerging in malignant hematopoiesis: “Obviously, immunotherapy is becoming one of the most exciting fields. We should not forget that CAR T cells were introduced first in blood tumors with amazing outcomes. Targeted therapies are also here to stay with a huge amount of studies testing compounds that can target the epigenome in blood malignancies, including BET, DOT1L, DNMT inhibitors to mention just a few. As we enter the “metagenomic” era we will see novel areas to open, including the study of 3D genome topology and the role of long non coding RNAs in blood cancer initiation, progression and treatment.” Dr. Jonas Larsson (Division of Molecular Medicine and Gene Therapy, Lund University, SWE) also hinted to the emergence of ncRNAs: "A fundamentally new mechanism of gene regulation mediated by non-coding RNAs."
A major contributor to the acceleration of any scientific field is technology and one technology that is revolutionizing biology is gene editing. Dr. Margaret Goodell (Stem Cell and Regenerative Medicine Center, Baylor College of Medicine, USA) remarks: "CRISPR will transform hematology research. I think even for primary cells, it is just around the corner and it will change the way we do a lot of things.” Dr. Louise Purton (St. Vincent’s Institute for Medical Research, University of Melbourne, AUS) also agrees that the application of gene editing technology will continue to move hematological research forward: “A focus on CRISPR/Cas9 technology and getting it to work properly in human cells and thus leading to gene therapy in future”. Dr. Keith Humphries (Terry Fox Laboratory, University of British Columbia, CAN) also predicts that gene editing will play a large role in the development of new models for normal and malignant hematological research: “I think even a fairly cloudy crystal ball will accurately predict that "next generation" gene editing will revolutionize much of experimental hematology. "Simple" gene insertion using lentiviral vectors and traditional gene knockout/knockin methods will seem so old school compared to accurately placing a gene of interest into a safe harbour or engineering a specific mutation or knockout/knockin using CRISPR/Cas9 gene editing. And all of this will be possible in primary cells, such as hematopoietic stem cells, and open up unprecedented ways to create disease models, study gene function and carry out complex screens.”
While it is clear that gene editing will have huge impacts on both hematological research and therapy, Dr. David Scadden (Center for Regenerative Medicine, Massachusetts General Hospital, USA) anticipates that: “new solutions to old problems of efficient mobilization, engraftment and conditioning will emerge and help deliver on the promise of gene editing technologies." This sentiment was also echoed by Dr. Derrick Rossi (Stem Cell and Regenerative Biology Department, Harvard University, USA) who offered that: “In order to fully realize the therapeutic potential offered by gene therapy and gene editing, methodologies for preparing patients for transplantation that don’t rely on chemotherapy or irradiation — that are associated with significant collateral damage — need to be developed."
Single cell analysis
Several experts emphasized the need for techniques for improving our ability to carry out single cell analysis. Dr. Hartmut Geiger (Institute for Molecular Medicine, University of Ulm, DEU) comments: “Will there be a post-omics time? A lot of mid- and high throughput data collecting approaches that we currently apply are weak with respect to taking dynamics and spatial distribution into consideration. We urgently need novel post-omics approaches that will allow us to address regulatory mechanisms in space and time, which will comprise exciting novel developments in single cell stem cell biology.” Dr. Marella de Bruijn (Radcliffe Department of Medicine, University of Oxford, GBR) adds: “The increasing sophistication with which molecular processes can be analyzed at the single cell level will greatly facilitate our understanding of cell fate decisions during the birth of the hematopoietic system.”
Dr. Ravi Majeti (Division of Hematology & Stem Cell Biology and Regenerative Medicine, Stanford School of Medicine, USA) also commented on the importance of single cell analytic tools: “I think one of the next hot/big topics or technologies that will emerge in malignant and normal hematopoiesis is the investigation of subclonal epigenetic heterogeneity. The concept of subclonal genetic heterogeneity has been extensively investigated over the last few years using next generation sequencing and genomic technologies. The use of single cell RNA-seq has advanced studies of single cells and revealed a great amount of heterogeneity within functionally-defined cell populations. The development of low cell/single cell methodologies to characterize epigenetic features will enable the investigation of subclonal epigenetic heterogeneity over the next few years. This will allow the field to examine the role such heterogeneity plays in hematopoiesis and hematologic malignancies.” Dr. Atsushi Iwama (Department of Cellular and Molecular Medicine, Chiba University, JPN) adds: “Although already noticed, application of single cell RNA sequencing to the hematological malignancies without specific selection markers is a really powerful approach to unravel the whole picture of the diseases.”
Dr. Cristina Lo Celso (Department of Life Sciences, Imperial College London, GBR) predicts: “In the next few years I expect that we will start making sense of the heterogeneity we observe and especially of the 'noise' that single cell analyses invariably bring up to light. This will no doubt exponentially increase our understanding of the haematopoietic system and inform the development of novel and more successful curative and preventative therapies.”
The contribution of HSCs to long-term and clonal hematopoiesis
In 2015, several publications shed new insights into clonal hematopoiesis and the contribution of HSCs and MPPs to long-term hematopoiesis in mice, which have provoked interest from some of our experts. Dr. Len Zon (Stem Cell and Regenerative Biology Department, Harvard University, USA) remarks: "I think that understanding clonal hematopoiesis (including establishment of long term progenitors) is a new area that is really developing." Dr. Purton predicts: “We will revisit the concept of HSC and MPPs and what really are the cells that are most useful in steady-state and therapeutically- both in mouse and human. I think the Sun and Busch Nature papers from 2015 are starting to challenge our concepts of these cells.” Dr. Toshio Suda (The Cancer Science Institute Singapore, National University of Singapore, SPG) points out that: “Steady state hematopoiesis is different from hematopoiesis in emergency under the stress such as BMT [bone marrow transplant] and inflammation. Thus, BMT might be not a real functional HSC assay. We should clarify the difference of [these two states] from the various aspects of cell cycle, niche and cytokines.”
Dr. Scadden also highlights that, “Defining how heterogeneous populations of stem and progenitor cells respond to physiologic challenges and change with age will give us new insight into how the system produces what we see as the hematopoietic response.” Dr. Scadden continues: “Clonal diversity in hematopoiesis will emerge as a basis for declining immune function and increased inflammation related disease with age. This will become a topic of therapeutic interest.”
The HSC Niche
The hematopoietic stem cell (HSC) niche has been a hot topic since Richard Schofield first put forth his hypothesis in 1978 that HSCs are influenced by their surrounding cellular microenviroment. However, there has been a recent explosion of papers redefining the HSC niche and based on the responses from several experts this trend will continue. Dr. Frenette believes that: “a greater understanding of the microenvironment will be transformative.” In agreement, Dr. Hartmut Geiger (Institute for Molecular Medicine, University of Ulm, DEU) points out that: “HSCs and stem cell niches are like Siamese Twins. We will, over the next decade, better understand the regulatory networks of interactions [between HSCs and the niche] and how they influence each other reciprocally in health and disease, in addition to novel information on localization of niches and stem cells. This will start a new paradigm for stem cell biology in general, and hematopoietic stem cells will be again at the forefront.” Hartmut Geiger also hints: “Maybe there will be also a focus on HSCs niches outside bone marrow.”
Dr. Scadden indicates that a clearer definition of the HSC niche will also contribute to the development of novel therapeutics: “Heterogeneity in hematopoietic cells is likely to be paralleled by heterogeneity in cells comprising the niche and matching those populations will help us understand how blood production is governed and may be manipulated for therapy or corrupted by disease. Dr. Purton also discusses the relationship between the HSC niche and therapy: “A better understanding of how haematopoiesis is regulated by microenvironment cells will lead to new therapies to manipulate haematopoiesis in vivo - we are getting there but still have a lot to learn.”
HSC Aging and Disease
The observation that HSC-derived hematological malignancies commonly arise in older individuals has fueled the study of aging HSCs. This trend will continue in the near future according to Dr. Gerald de Haan (Department of Stem Cell Biology, University Medical Center Groningen, NLD): “We will see the emergence of multiple papers delineating the epigenetic changes that occur in hematopoietic stem cells as they develop and age, and will witness how these changes are brought about and how they may contribute to clonal dominance. In addition, the relevance, or irrelevance, of assessing clonal hematopoiesis in aged mice or humans will become apparent.” Dr. Iwama also mentioned that: “Epigenomic alterations in aged HSCs could be a hot topic in association with the pathogenesis of age-related hematological malignancies.”
In addition to epigenetics in aging HSCs, Dr. Geiger suggests that models for studying aging hematopoiesis in disease will emerge in the next few years: “Diseases in Hematology are usually diseases of older adults. Myelodysplastic Syndrome (MDS) for example is a classical HSC-driven disease and most patients are 70 years and older. An emerging innovative trend we will see in the next couple of years is the development of disease models in aged model organisms.”
The Progression of Pre-leukemia to Overt Leukemia
The advent of next-generation sequencing has resulted in a surge of newly identified mutations in hematological malignancies such as myelodyplastic syndrome (MDS), acute myeloid leukemia (AML) and many others. Dr. Benjamin Ebert (Brigham and Women’s Hospital, Harvard Medical School, USA) comments that we are on the verge of understanding how these mutations contribute to the leukemogenic process: “Large-scale genetic studies have identified many mutations that are associated with hematologic diseases, but the molecular consequences of most of these lesions are poorly understood. In the coming years, mechanistic insights into the activity of human disease genes will inform the basic biology of hematopoiesis and lead to the development of novel therapeutics.”
The emergence of pre-leukemic clones have provided new insights into leukemogenesis and Dr. Ross Levine (Human Oncology and Pathogenesis Program, Memorial Sloan Kettering Cancer Center, USA) says that now it is time to take it to the next level: “New studies into the factors, which govern progression from pre-leukemic states to overt hematologic malignancies, and the development of therapies, which might be used to target pre-leukemic states which can be tested pre-clinically and then subsequently in the clinic, as a first example of true preventative medicine in hematology.” Dr. Suda provides his insight into factors that could contribute to the development of frank leukemia: “Age-related diseases such as MDS and CLL should be analyzed by the accumulation of DNA damage in HSCs. It will be interesting to see how pre-leukemic clones will develop to overt leukemia.
Human HSC biology
For years the mouse has provided a stellar model for studying HSC biology, whereas comparable assays in human HSCs has lagged. However, Dr. Stefan Karlsson (Division of Molecular Medicine and Gene Therapy, Lund University, SWE) suggests that advances in human HSC biology are coming on strong: “One area that could be important in the coming years is human hematopoiesis. John Dick’s recent work, improves substantially the possibility to purify/enrich human HSC and progenitors and this may make it possible to perform better molecular studies and even functional studies of human HSC.”
Paul Frenette also commented: “I hope to see in my lifetime the development of protocols to make expandable and functional HSC from ES cells. Dr. Hal Broxmeyer (Department of Microbiology and Immunology, Indiana University School of Medicine, USA) suggests that: “Generation of human engrafting HSCs from pluripotent cells (such as ESC and iPSC) in numbers and functional capacity so that they can be used clinically for transplantation” is on the horizon as well as a “means to expand HSCs without expansion of other cell types and more in depth understanding of HSC self-renewal, proliferation, and migration at a molecular level”.
Between the novel insights that have resulted from recent publications to the emerging trends/technologies that have been discussed here, echoing Dr. Aifantis it is indeed an exciting time to be a hematologist. In fact, Dr. Humphries exclaimed: “I wish I were starting my career today!” While we consulted expert hematologists to identify emerging scientific trends Dr. Suda emphasizes that: “Trends should be cultivated and made by the strong interest of young investigators!! When you just ride on the apparent trend, it may be too late.”
We would like to thank all of the experts who participated in this article – we are deeply appreciative.
Written by: Stephen Sykes & Peter Van Galen
Edited by: Mick Milsom & Sofie Singbrant Söderberg
Quotes obtained by: All NIC members