Generation of inner ear sensory cells from bone marrow-derived human mesenchymal stem cells

Serum-Free Cultures: Could They Be a Future Direction to Improve Neuronal Differentiation of Mesenchymal Stromal Cells?

Mesenchymal stem/stromal cells (MSCs) are undifferentiated cells with multilinear potential, known for their immunomodulatory and regenerative properties. Although the scientific community is working to improve their application, concerns limit their use to repair tissues following neurological damage. One of these obstacles is represented by the use of culture media supplemented with fetal bovine serum (FBS), which, due to its xenogenic nature and the risk of contamination, has increased scientific, ethical and safety problems. Therefore, the use of serum-free media could improve MSC culture methods, avoiding infectious and immunogenic transmission problems as well as MSC bioprocesses, without the use of animal components. The purpose of our review is to provide an overview of experimental studies that demonstrate that serum-free cultures, along with the supplementation of growth factors or chemicals, can lead to a more defined and controlled environment, enhancing the proliferation and neuronal differentiation of MSCs.

Recent advancements in cell-based models for auditory disorders

Introduction: Cell-based models play an important role in understanding the pathophysiology and etiology of auditory disorders. For the auditory system, models have primarily focused on restoring inner and outer hair cells. However, they have largely underrepresented the surrounding structures and cells that support the function of the hair cells.

Methods: In this article, we will review recent advancements in the evolution of cell-based models of auditory disorders in their progression towards three dimensional (3D) models and organoids that more closely mimic the pathophysiology in vivo.

Results: With the elucidation of the molecular targets and transcription factors required to generate diverse cell lines of the components of inner ear, research is starting to progress from two dimensional (2D) models to a greater 3D approach. Of note, the 3D models of the inner ear, including organoids, are relatively new and emerging in the field. As 3D models of the inner ear continue to evolve in complexity, their role in modeling disease will grow as they bridge the gap between cell culture and in vivo models.

Conclusion: Using 3D cell models to understand the etiology and molecular mechanisms underlying auditory disorders holds great potential for developing more targeted and effective novel therapeutics.

Achievements and Challenges in Transplantation of Mesenchymal Stem Cells in Otorhinolaryngology

Otorhinolaryngology enrolls head and neck surgery in various tissues such as ear, nose, and throat (ENT) that govern different activities such as hearing, breathing, smelling, production of vocal sounds, the balance, deglutition, facial animation, air filtration and humidification, and articulation during speech, while absence of these functions can lead to high morbidity and even mortality. Conventional therapies for head and neck damaged tissues include grafts, transplants, and artificial materials, but grafts have limited availability and cause morbidity in the donor site. To improve these limitations, regenerative medicine, as a novel and rapidly growing field, has opened a new therapeutic window in otorhinolaryngology by using cell transplantation to target the healing and replacement of injured tissues. There is a high risk of rejection and tumor formation for transplantation of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs); mesenchymal stem cells (MSCs) lack these drawbacks. They have easy expansion and antiapoptotic properties with a wide range of healing and aesthetic functions that make them a novel candidate in otorhinolaryngology for craniofacial defects and diseases and hold immense promise for bone tissue healing; even the tissue sources and types of MSCs, the method of cell introduction and their preparation quality can influence the final outcome in the injured tissue. In this review, we demonstrated the anti-inflammatory and immunomodulatory properties of MSCs, from different sources, to be safely used for cell-based therapies in otorhinolaryngology, while their achievements and challenges have been described too.

Therapeutic Application of Mesenchymal Stem Cells for Cochlear Regeneration

Hearing loss is one of the major worldwide health problems that seriously affects human social and cognitive development. In the auditory system, three components outer ear, middle ear and inner ear are essential for the hearing mechanism. In the inner ear, sensory hair cells and ganglion neuronal cells are the essential supporters for hearing mechanism. Damage to these cells can be caused by long-term exposure of excessive noise, ototoxic drugs (aminoglycosides), ear tumors, infections, heredity and aging. Since mammalian cochlear hair cells do not regenerate naturally, some therapeutic interventions may be required to replace the damaged or lost cells. Cochlear implants and hearing aids are the temporary solutions for people suffering from severe hearing loss. The current discoveries in gene therapy may provide a deeper understanding in essential genes for the inner ear regeneration. Stem cell migration, survival and differentiation to supporting cells, cochlear hair cells and spiral ganglion neurons are the important foundation in understanding stem cell therapy. Moreover, mesenchymal stem cells (MSCs) from different sources (bone marrow, umbilical cord, adipose tissue and placenta) could be used in inner ear therapy. Transplanted MSCs in the inner ear can recruit homing factors at the damaged sites to induce transdifferentiation into inner hair cells and ganglion neurons or regeneration of sensory hair cells, thus enhancing the cochlear function. This review summarizes the potential application of mesenchymal stem cells in hearing restoration and combining stem cell and molecular therapeutic strategies can also be used in the recovery of cochlear function.

Upregulation of Neuroprogenitor and Neural Markers via Enforced miR-124 and Growth Factor Treatment

Previous studies have shown that miR-124 plays an important role in the development of auditory neurons, which are degenerated in the sensorineural hearing loss. However, whether the combined use of miR-124 and growth factors can increase the expression of neural related markers in human dental pulp stem cells has been remained unknown so far. In this study, human dental pulp stem cells were transfected with miR-124 following treatment with brain-derived neurotrophic factor or epidermal growth factor/basic fibroblast growth factor. The expression of some neural related markers (nestin, SOX2, β-tubulin III, MAP2, and peripherin) was analyzed in two groups by qRT-PCR or immunofluorescence. Cellular treatment resulted in morphological changes including neurosphere-like colonies formation. Nestin and SOX2 were up-regulated, and MAP2 and peripherin were down-regulated in dental pulp stem cells transfected by miR-124 following treatment with brain-derived neurotrophic factor. Replacement of brain-derived neurotrophic factor with epidermal growth factor/ basic fibroblast growth factor resulted in the up-regulation of nestin, MAP2, peripherin, and β-tubulin III and down-regulation of SOX2. The expression of SOX2 and nestin was also confirmed by immunofluorescence. The combination of miR-124 and growth factors would provide a promising starting point for upregulating the neural progenitor markers in human dental pulp stem cells.

Stem cell-based approaches: Possible route to hearing restoration?

Disabling hearing loss is the most common sensorineural disability worldwide. It affects around 466 million people and its incidence is expected to rise to around 900 million people by 2050, according to World Health Organization estimates. Most cases of hearing impairment are due to the degeneration of hair cells (HCs) in the cochlea, mechano-receptors that transduce incoming sound information into electrical signals that are sent to the brain. Damage to these cells is mainly caused by exposure to aminoglycoside antibiotics and to some anti-cancer drugs such as cisplatin, loud sounds, age, infections and genetic mutations. Hearing deficits may also result from damage to the spiral ganglion neurons that innervate cochlear HCs. Differently from what is observed in avian and non-mammalian species, there is no regeneration of missing sensory cell types in the adult mammalian cochlea, what makes hearing loss an irreversible process. This review summarizes the research that has been conducted with the aim of developing cell-based strategies that lead to sensory cell replacement in the adult cochlea and, ultimately, to hearing restoration. Two main lines of research are discussed, one directed toward the transplantation of exogenous replacement cells into the damaged tissue, and another that aims at reactivating the regenerative potential of putative progenitor cells in the adult inner ear. Results from some of the studies that have been conducted are presented and the advantages and drawbacks of the various approaches discussed.

Quantitative assessment of cochlear and vestibular ganglion neurons in temporal bones with chronic otitis media

PURPOSE

In this study, we aimed to determine whether or not COM leads to loss of spiral and Scarpa ganglion neurons.

METHODS

From the human temporal bone (HTB) collection at the University of Minnesota we selected human temporal bones with COM, defined as the presence of clinically intractable tissue abnormalities in the middle ear (cholesteatoma, perforation of the eardrum, granulation tissue, fibrosis, tympanosclerosis, and cholesterol granuloma). We also selected HTBs from donors with no ear diseases as controls. We quantitatively analyzed the number of spiral and Scarpa ganglion cells and compared the results obtained in the control and study groups.

RESULTS

In both COM and control groups we observed a significant negative correlation between age and number of both spiral (R = -0.632; P < 0.001; 95% CI - 0.766 to - 0.434) and Scarpa ganglion (R = - 0.404; P = 0.008; 95% CI - 0.636 to - 0.051) cells. We did not find any significant differences in the number of spiral ganglion cells (in total or per segment) or in the density of Scarpa ganglion cells (in each vestibular nerve or both) in the COM group as compared with controls (P > 0.05).

CONCLUSIONS AND RELEVANCE

Our results did not demonstrate significant loss of cochlear or vestibular peripheral ganglion neuron loss in HTBs with COM as compared with controls.

Generation of Otic Lineages from Integration-Free Human-Induced Pluripotent Stem Cells Reprogrammed by mRNAs

Damage to the sensory hair cells and the spiral ganglion neurons of the cochlea leads to deafness. Induced pluripotent stem cells (iPSCs) are a promising tool to regenerate the cells in the inner ear that have been affected by pathology or have been lost. To facilitate the clinical application of iPSCs, the reprogramming process should minimize the risk of introducing undesired genetic alterations while conferring the cells the capacity to differentiate into the desired cell type. Currently, reprogramming induced by synthetic mRNAs is considered to be one of the safest ways of inducing pluripotency, as the transgenes are transiently delivered into the cells without integrating into the genome. In this study, we explore the ability of integration-free human-induced pluripotent cell lines that were reprogrammed by mRNAs, to differentiate into otic progenitors and, subsequently, into hair cell and neuronal lineages. hiPSC lines were induced to differentiate by culturing them in the presence of fibroblast growth factors 3 and 10 (FGF3 and FGF10). Progenitors were identified by quantitative microscopy, based on the coexpression of otic markers PAX8, PAX2, FOXG1, and SOX2. Otic epithelial progenitors (OEPs) and otic neuroprogenitors (ONPs) were purified and allowed to differentiate further into hair cell-like cells and neurons. Lineages were characterised by immunocytochemistry and electrophysiology. Neuronal cells showed inward Na⁺ (I_Na) currents and outward (I_k) and inward K⁺ (I_K1) currents while hair cell-like cells had inward I_K1 and outward delayed rectifier K⁺ currents, characteristic of developing hair cells. We conclude that human-induced pluripotent cell lines that have been reprogrammed using nonintegrating mRNAs are capable to differentiate into otic cell types.

Hearing regeneration and regenerative medicine: present and future approaches

More than 5% of the world population lives with a hearing impairment. The main factors responsible for hearing degeneration are ototoxic drugs, aging, continued exposure to excessive noise and infections. The pool of adult stem cells in the inner ear drops dramatically after birth, and therefore an endogenous cellular source for regeneration is absent. Hearing loss can emerge after the degeneration of different cochlear components, so there are multiple targets to be reached, such as hair cells (HCs), spiral ganglion neurons (SGNs), supporting cells (SCs) and ribbon synapses. Important discoveries in the hearing regeneration field have been reported regarding stem cell transplantation, migration and survival; genetic systems for cell fate monitoring; and stem cell differentiation to HCs, SGNs and SCs using adult stem cells, embryonic stem cells and induced pluripotent stem cells. Moreover, some molecular mediators that affect the establishment of functional synapses have been identified. In this review, we will focus on reporting the state of the art in the regenerative medicine field for hearing recovery. Stem cell research has enabled remarkable advances in regeneration, particularly in neuronal cells and synapses. Despite the progress achieved, there are certain issues that need a deeper development to improve the results already obtained, or to develop new approaches aiming for the clinical application.

Stem-cell therapy for hearing loss: are we there yet?

Introduction

Mammalian hair cells and auditory neurons do not show regenerative capacity. Hence, damage to these cell types is permanent and leads to hearing loss. However, there is no treatment that re-establishes auditory function. Regenerative therapies using stem cells represent a promising alternative.

Objective

This article aims to review the current literature about the main types of stem cells with potential for application in cell therapy for sensorineural hearing loss, the most relevant experiments already performed in animals, as well as the advances that have been recently made in the field.

Methods

Research included the databases PubMed/MEDLINE, Web of Science, Science Direct and SciELO, as well as gray literature. Search strategy included the following main terms: “stem cells”, “hair cells” and “auditory neurons”. Additionally, the main terms were combined with the following secondary terms: “mesenchymal”, “iPS”, “inner ear”, “auditory”. The research was conducted independently by three researchers.

Results

Differentiation of stem cells into hair cells and auditory neurons has a high success rate, reaching up to 82% for the first and 100% for the latter. Remarkably, these differentiated cells are able to interact with hair cells and auditory neurons of cochlear explants through formation of new synapses. When transplanted into the cochlea of animals with hearing loss, auditory restoration has been documented to date only in deafferented animals.

Conclusion

Advances have been more prominent in cases of auditory neuropathy, since partial improvement of auditory nerve conditions through cell-based therapy may increase the number of patients who can successfully receive cochlear implants.

Increased levels of miR-124 in human dental pulp stem cells alter the expression of neural markers

Auditory neuropathy is the particular form of deafness in humans which cannot be treated by replacement therapy. Human dental pulp stem cells (hDPSCs) are derived from an ectomesenchymal neural crest cell population. Therefore, they possess a promising capacity for neuronal differentiation and repair. miR-124, a key regulator of neuronal development in the inner ear, is expressed at high levels in auditory and vestibular neurons. Here, we evaluated the possible effect of miR-124 in alteration of neural protein markers expression. Using quantitative reverse transcription-PCR (qRT-PCR) analyses and immunofluorescence staining, we studied the expression patterns of neural progenitor markers (Nestin, NOTCH1, and SOX2) and neural markers (β-tubulin III, GATA-3, and peripherin) upon transfection of hDPSCs with miR-124. The qRT-PCR results showed that Nestin was upregulated 6 h post-transfection. In contrast, Nestin expression exhibited a decreasing trend 24 h and 48 h post-transfection. Higher levels of β-tubulin III, 6 h and 16 h post transfection in RNA level as compared with control cells, were determined in transfected DPSCs. However, β-tubulin-III expression decreased 48 h post-transfection. The immunoflourescence results indicated that transfection of hDPSCs with miR-124, only affected Nestin among the studied neural progenitor and neural marker expression in protein level.

Stem Cells: A New Hope for Hearing Loss Therapy

Permanent hearing loss was considered which cannot be cured since cochlear hair cells and primary afferent neurons cannot be regenerated. In recent years, due to the in-depth study of stem cell and its therapeutic potential, regenerating auditory sensory cells is made possible. By using two strategies of endogenous stem cell activation and exogenous stem cell transplantation, researchers hope to find methods to restore hearing function. However, there are complex factors that need to be considered in the in vivo application of stem cell therapy, such as stem cell-type choice, signaling pathway regulations, transplantation approaches, internal environment of the cochlea, and external stimulation. After years of investigations, some theoretic progress has been made in the treatment of hearing loss using stem cells, but there are also many problems which limited its application that need to be solved. Understanding the future perspective of stem cell therapy in hearing loss, solving the encountered problems, and promoting its development are the common goals of audiological researchers. In this review, we present critical experimental findings of stem cell therapy on treatment of hearing loss and intend to bring hope to researchers and patients.

Transcription factor induced conversion of human fibroblasts towards the hair cell lineage

Hearing loss is the most common sensorineural disorder, affecting over 5% of the population worldwide. Its most frequent cause is the loss of hair cells (HCs), the mechanosensory receptors of the cochlea. HCs transduce incoming sounds into electrical signals that activate auditory neurons, which in turn send this information to the brain. Although some spontaneous HC regeneration has been observed in neonatal mammals, the very small pool of putative progenitor cells that have been identified in the adult mammalian cochlea is not able to replace the damaged HCs, making any hearing impairment permanent. To date, guided differentiation of human cells to HC-like cells has only been achieved using either embryonic stem cells (ESCs) or induced pluripotent stem cells (iPSCs). However, use of such cell types suffers from a number of important disadvantages, such as the risk of tumourigenicity if transplanted into the host´s tissue. We have obtained cells expressing hair cell markers from cultures of human fibroblasts by overexpression of GFI1, Pou4f3 and ATOH1 (GPA), three genes that are known to play a critical role in the development of HCs. Immunocytochemical, qPCR and RNAseq analyses demonstrate the expression of genes typically expressed by HCs in the transdifferentiated cells. Our protocol represents a much faster approach than the methods applied to ESCs and iPSCs and validates the combination of GPA as a set of genes whose activation leads to the direct conversion of human somatic cells towards the hair cell lineage. Our observations are expected to contribute to the development of future therapies aimed at the regeneration of the auditory organ and the restoration of hearing.

Concomitant differentiation of a population of mouse embryonic stem cells into neuron-like cells and schwann cell-like cells in a slow-flow microfluidic device

BACKGROUND

To send meaningful information to the brain, an inner ear cochlear implant (CI) must become closely coupled to as large and healthy a population of remaining spiral ganglion neurons (SGN) as possible. Inner ear gangliogenesis depends on macrophage migration inhibitory factor (MIF), a directionally attractant neurotrophic cytokine made by both Schwann and supporting cells (Bank et al., 2012). MIF-induced mouse embryonic stem cell (mESC)-derived "neurons" could potentially substitute for lost or damaged SGN. mESC-derived "Schwann cells" produce MIF, as do all Schwann cells (Huang et al., a; Roth et al., 2007; Roth et al., 2008) and could attract SGN to a "cell-coated" implant.

RESULTS

Neuron- and Schwann cell-like cells were produced from a common population of mESCs in an ultra-slow-flow microfluidic device. As the populations interacted, "neurons" grew over the "Schwann cell" lawn, and early events in myelination were documented. Blocking MIF on the Schwann cell side greatly reduced directional neurite outgrowth. MIF-expressing "Schwann cells" were used to coat a CI: Mouse SGN and MIF-induced "neurons" grew directionally to the CI and to a wild-type but not MIF-knockout organ of Corti explant.

CONCLUSIONS

Two novel stem cell-based approaches for treating the problem of sensorineural hearing loss are described. Developmental Dynamics 246:7-27, 2017. © 2016 Wiley Periodicals, Inc.

Alginate microcapsules co-embedded with MSCs and anti-EGF mAb for the induction of hair cell-like cells in guinea pigs by taking advantage of host EGF

The strategy of co-embedding rBMSCs and anti-EGF mAb in alginate microcapsules is a promising modality for the regeneration of hair cell-like cells.

Limited hair cell induction from human induced pluripotent stem cells using a simple stepwise method

Disease-specific induced pluripotent stem cells (iPS) cells are expected to contribute to exploring useful tools for studying the pathophysiology of inner ear diseases and to drug discovery for treating inner ear diseases. For this purpose, stable induction methods for the differentiation of human iPS cells into inner ear hair cells are required. In the present study, we examined the efficacy of a simple induction method for inducing the differentiation of human iPS cells into hair cells. The induction of inner ear hair cell-like cells was performed using a stepwise method mimicking inner ear development. Human iPS cells were sequentially transformed into the preplacodal ectoderm, otic placode, and hair cell-like cells. As a first step, preplacodal ectoderm induction, human iPS cells were seeded on a Matrigel-coated plate and cultured in a serum free N2/B27 medium for 8 days according to a previous study that demonstrated spontaneous differentiation of human ES cells into the preplacodal ectoderm. As the second step, the cells after preplacodal ectoderm induction were treated with basic fibroblast growth factor (bFGF) for induction of differentiation into otic-placode-like cells for 15 days. As the final step, cultured cells were incubated in a serum free medium containing Matrigel for 48 days. After preplacodal ectoderm induction, over 90% of cultured cells expressed the genes that express in preplacodal ectoderm. By culture with bFGF, otic placode marker-positive cells were obtained, although their number was limited. Further 48-day culture in serum free media resulted in the induction of hair cell-like cells, which expressed a hair cell marker and had stereocilia bundle-like constructions on their apical surface. Our results indicate that hair cell-like cells are induced from human iPS cells using a simple stepwise method with only bFGF, without the use of xenogeneic cells.

Directing human induced pluripotent stem cells into a neurosensory lineage for auditory neuron replacement

Emerging therapies for sensorineural hearing loss include replacing damaged auditory neurons (ANs) using stem cells. Ultimately, it is important that these replacement cells can be patient-matched to avoid immunorejection. As human induced pluripotent stem cells (hiPSCs) can be obtained directly from the patient, they offer an opportunity to generate patient-matched neurons for transplantation. Here, we used an established neural induction protocol to differentiate two hiPSC lines (iPS1 and iPS2) and one human embryonic stem cell line (hESC; H9) toward a neurosensory lineage in vitro. Immunocytochemistry and qRT-PCR were used to analyze the expression of key markers involved in AN development at defined time points of differentiation. The hiPSC- and hESC-derived neurosensory progenitors expressed the dorsal hindbrain marker (PAX7), otic placodal marker (PAX2), proneurosensory marker (SOX2), ganglion neuronal markers (NEUROD1, BRN3A, ISLET1, ßIII-tubulin, Neurofilament kDa 160), and sensory AN markers (GATA3 and VGLUT1) over the time course examined. The hiPSC- and hESC-derived neurosensory progenitors had the highest expression levels of the sensory neural markers at 35 days in vitro. Furthermore, the neurons generated from this assay were found to be electrically active. While all cell lines analyzed produced functional neurosensory-like progenitors, variabilities in the levels of marker expression were observed between hiPSC lines and within samples of the same cell line, when compared with the hESC controls. Overall, these findings indicate that this neural assay was capable of differentiating hiPSCs toward a neurosensory lineage but emphasize the need for improving the consistency in the differentiation of hiPSCs into the required lineages.

Sensational placodes: neurogenesis in the otic and olfactory systems

For both the intricate morphogenetic layout of the sensory cells in the ear and the elegantly radial arrangement of the sensory neurons in the nose, numerous signaling molecules and genetic determinants are required in concert to generate these specialized neuronal populations that help connect us to our environment. In this review, we outline many of the proteins and pathways that play essential roles in the differentiation of otic and olfactory neurons and their integration into their non-neuronal support structures. In both cases, well-known signaling pathways together with region-specific factors transform thickened ectodermal placodes into complex sense organs containing numerous, diverse neuronal subtypes. Olfactory and otic placodes, in combination with migratory neural crest stem cells, generate highly specialized subtypes of neuronal cells that sense sound, position and movement in space, odors and pheromones throughout our lives.

Inner ear symptoms and disease: pathophysiological understanding and therapeutic options

In recent years, huge advances have taken place in understanding of inner ear pathophysiology causing sensorineural hearing loss, tinnitus, and vertigo. Advances in understanding comprise biochemical and physiological research of stimulus perception and conduction, inner ear homeostasis, and hereditary diseases with underlying genetics. This review describes and tabulates the various causes of inner ear disease and defines inner ear and non-inner ear causes of hearing loss, tinnitus, and vertigo. The aim of this review was to comprehensively breakdown this field of otorhinolaryngology for specialists and non-specialists and to discuss current therapeutic options in distinct diseases and promising research for future therapies, especially pharmaceutic, genetic, or stem cell therapy.

Inner ear progenitor cells can be generated in vitro from human bone marrow mesenchymal stem cells

AIM

Mouse mesenchymal stem cells (MSCs) can generate sensory neurons and produce inner ear hair cell-like cells. An equivalent source from humans is highly desirable, given their potential application in patient-specific regenerative therapies for deafness. In this study, we explored the ability of human MSCs (hMSCs) to differentiate into otic lineages.

MATERIALS & METHODS

hMSCs were exposed to culture media conditioned by human fetal auditory stem cells.

RESULTS

Conditioned media induced the expression of otic progenitor markers PAX8, PAX2, GATA3 and SOX2. After 4 weeks, cells coexpressed ATOH1, MYO7A and POU4F3 (indicators of hair cell lineage) or neuronal markers NEUROG1, POU4F1 and NEFH. Inhibition of WNT signaling prevented differentiation into otic progenitors, while WNT activation partially phenocopied results seen with the conditioned media.

CONCLUSION

This study demonstrates that hMSCs can be driven to express key genes found in the otic lineages and thereby promotes their status as candidates for regenerative therapies for deafness.

New strategies for the restoration of hearing loss: challenges and opportunities

INTRODUCTION

For most types of hearing impairments, a definitive therapy would rest on the ability to restore hair cells and the spiral ganglion neurons. The only established technique to treat deafness is based on the functional replacement of hair cells with a cochlear implant, but this still has important limitations.

SOURCES OF DATA

A systematic revision of the relevant literature is presented.

AREAS OF AGREEMENT

New curative strategies, ranging from stem cells to gene and molecular therapy, are under development.

AREAS OF CONTROVERSY

Although still experimental, they have delivered some initial promissory results that allow us to look at them with cautious optimism.

GROWING POINTS

The isolation of human auditory cells, the generation of protocols to control their differentiation into sensory lineages, their promising application in vivo and the identification of key genes to target molecularly offer an exciting landscape.

AREAS TIMELY FOR DEVELOPING RESEARCH

In this chapter, I discuss the latest advances in the field and how they are being translated into a clinical application.