What is regenerative medicine? To bystanders, regenerative medicine might be merely a catch-all category or simply a current medical fashion. The reality, however, is that regenerative medicine represents a conceptual, material, and historical transformation of human medical care. Even the key researchers and clinicians who are moving this field ahead are often so busy in […]
Regenerative Medicine: What Is It? Where Is It Going?
What is regenerative medicine?
To bystanders, regenerative medicine might be merely a catch-all category or simply a current medical fashion. The reality, however, is that regenerative medicine represents a conceptual, material, and historical transformation of human medical care. Even the key researchers and clinicians who are moving this field ahead are often so busy in advancing the technology that they are less aware of the extraordinary changes that they represent, changes that are about to change the face of human medicine forever.
Regenerative medicine has marked differences, both conceptual and concrete differences, when compared to previous approaches to clinical intervention. These differences not only define the field, but they point our way to future progress and, frankly, to improvements in our health and in our lives.
The conceptual key is that regenerative medicine results in long-term (rather than transient) clinical improvements. Regenerative medicine is just that: an intervention that re-generates. Effective regenerative interventions change the body itself – and not merely a set of biomarkers or symptoms. Bluntly, regenerative medicine aims to improve biological function, rather than merely attempting to normalize abnormal biomarkers or symptoms of biological dysfunction. Even admitting the often impressive utility and efficacy of our standard medical interventions to date – for certainly we have come a long way in our ability to treat human disease – such approaches act as pharmacological Band-Aids. In contrast, regenerative medicine seeks to optimize the underlying genetic, cellular, and tissues processes that go awry.
Nor is this the only conceptual difference, for the time course is equally different. Standard clinical interventions generally have transient effects, for example in modifying inflammation, cholesterol, glucose levels, etc., while regenerative interventions generally have long-term (even permanent) changes to tissue and organ function. When most standard interventions may last for hours to days, regenerative interventions may last for years to decades. Even “definitive” surgical approaches (CABG, joint replacements, etc) have no effect upon the underlying disease process and are often merely recurrent stopgaps. Why replace an artificial joint (every decade or so), if we can possibly regrow a normal joint that might last a lifetime?
At its conceptual core, regenerative medicine offers us a more accurate and enlightened view of biological function. Regenerative medicine encompasses a view of biology that is active and dynamic, a view in which we aim to alter the processes rather than the products of biology. Consider diabetes, in which a regenerative approach strives to recreate normal islet cell function, where standard approaches strive to manage glucose levels. The difference is critical to understanding the efficacy of regenerative medicine: it views pathology as a dynamic process and aims to alter the process itself, rather than focusing on the products of such processes and aiming to alter the clinical results of those processes. The same pertains to surgical interventions in which regenerative medicine aims to alter the process of joint failure, rather than the product of joint failure. Regenerative medicine would regenerate a normal joint, where standard approaches implant an artificial joint.
Essentially, regenerative medicine aims to reset biological processes to those of a normal, healthy body.
The material features of regeneration medicine are equally distinctive. Instead of employing what are current called “small molecular” approaches, regenerative medicine uses “large molecular” approaches, generally by employing genes, stem cells, and other large biological structures. We might legitimately include immunization in this category: it not only employs a large biological structure (i.e.., an active virus or a complex set of antibodies), but it also results in a long-term change to the organism (i.e., improved immunity). Contrast this approach to the more common “small molecular” approach, typified by the use of non-steroidal anti-inflammatories, statins, blood pressure medications, antibiotics, etc. While many such molecules are fairly complex and certainly not simple, nor are they large-scale biological structures such as viral vectors, plasmids, genes, or stem cells.
Regeneration medicine is typified by two common approaches: genes and cells. In either case, these interventions are large and active biological structures rather than small and passive chemical structures. Genes and cells do not merely interact with biological structures, they ARE biological structures. They not only interact with genes and cells, they ARE genes and cells.
The historical perspective on regenerative medicine is enlightening. What can the past tell us and what does the future hold? An apt historical analogy is that of infectious disease, particularly when we compare antibiotics and immunization. No one would be so naïve as to underestimate the value of antibiotics, but nor should we underestimate the limits of antibiotics. Faced with most viral infections, such as polio, tetanus, or diphtheria, antibiotics are ineffective. Those same viral infections are readily preventable, however, by immunization, using large and active biological structures (whether antigens or live virus).
Immunization is essentially a form of regenerative medicine, in that it results in a long-term change in the human body, a change that results in long-term health. The one difference is that immunizations don’t “re-generate” so much as they “generate” a healthier organism. Nonetheless, the similarity in addressing basic biological functions, in having a long-term effect, and in using large, active biological structures places immunization an historical forerunner for regenerative medicine. Consider a further analogy, that of Ebola. During the height of the Ebola epidemic, small molecular approaches (IV fluid, pressor support, etc) were useful, but far from optimal. Only an effective Ebola vaccine promises to lower the fatality rate into the single digit percent range. In viral infections (as we look backwards) and for the entirety of medicine (as we look forward) standard small molecular approaches are simply not good enough.
Such is the past, but what of the future? Our current standards of medical care cannot reasonably be considered optimal standards of care. We can do better, but only by moving to a regenerative approach. The upcoming standards of medical care will encompass two main approaches: genetic interventions and cellular interventions. In the first case, we will deliver both genes meant to replace pathologic genes and genes that are intended to reset gene expression. In the second case, we will deliver cells that are meant to replace pathologic (or absent) cells.
Genetic interventions encompass both genetic and epigenetic optimization. While the bulk of interest is currently focused on gene changes, remember that genes that regulate expression are far more important than genes that express proteins, both clinically and in terms of percentage of genes in our genome (we have 10-20 times more regulatory genes than we have protein-expressing genes). Although 20th century medicine has made dramatic inroads in our understanding of genes and disease, it remains to the 21st century to move into the far more difficult – and more important – task of understanding patterns of gene expression. In short, it is not genetics, but epigenetics that will prove to be the key to medical interventions. Viral delivery, telomere effects, cell senescence, and a host of other factors will define what we will soon be capable of. We have scarcely begun to enter this complex and confusing field.
Cellular interventions encompass a spectrum of cells, from somatic cells to pluripotent stem cells – and the entire gamut in between those extremes. It has become clear that pluripotent stem cells need not derive from fetal sources, but equally clear that our understanding of the complex path from stem cell to somatic cell is still inadequate – although increasing by the month.
Using an historical perspective to project forward, we begin to see where we can – finally – begin to address diseases that we have long ignored as being “facts of life”, such as the diseases of aging. Although public understanding (indeed, even academic understanding) lags behind the tantalizing and growing data, there is mounting evidence that we will be able to slow, stop, prevent, and even reverse diseases that we have no current treatment for. Consider, for example, osteoporosis. Until now, we have had no therapy that alters the clinical course that begins in the aging osteocyte and the bony matrix. Likewise, our treatment for osteoarthritis, joint replacement, may have value to the patient, but is an admission of failure when we realize that we have no therapy that alters the clinical course of this pathology, that begins in the aging chondrocyte and its matrix either. Arterial disease, Alzheimer’s disease, and a host of other diseases, almost all of which appear to be linked to basic cellular-related aging processes, are fast becoming viable targets for the advances of regenerative medicine.
From a purely practical perspective, how will a regenerative approach change medical care? Currently, medicine is – to a large extent – organized by organ (nephrology, neurology, cardiology, dermatology, etc.), although with an overlay based on the type of intervention (surgical versus medical). At the moment, regenerative medicine is something of a step-child, although gaining traction yearly. Although the approach is innovative, the tools themselves are adaptable within the current framework of medical specialties. There is, for instance, no reason that gene or cell therapy cannot be adopted by and adapted to most current medical specialties, a process that will come to completion within the coming two decades. Regenerative medical techniques equally become the intervention-of-choice for the pulmonologist, the gastroenterologist, or the endocrinologist. For medical specialties, regenerative medicine is an approach which is largely specialty-agnostic.
Surgical specialties, however, will fare a bit differently: where is the need for cardiovascular or orthopedic surgical approaches when we can regenerate both normal coronary arteries and normal joints? Over the next two decades, the face of surgical practice will change rapidly and will lose many of the most common procedures, as regenerative medicine makes effective inroads. Yet there will remain a place for both standard medical care (small molecular drugs) and for surgical procedures, even within a transformed medical landscape. The landscape will continue to change, requiring rapid adaptation for specialties and their practitioners as our knowledge and our capacity to intervene evolve.
Ultimately – if the word is even remotely appropriate to the future of medicine – medical care will still be left with two prongs: a medical approach that fixes the genetic, epigenetic, and cellular problems and a surgical approach that deals with acute, externally imposed disasters, such as trauma. The role of the first specialty will be to deal with non-emergent and known problems at cellular levels. The role of the second specialty will be to deal with emergent and largely unpredictable problems at the organ (rather than cellular) level. The parallel with the modern division between medicine and surgery is apt, but the tools will have evolved, as will the ability to not merely ameliorate, but actually cure disease and to optimize health.
If we are to define regenerative medicine, we might best understand its conceptual underpinnings, its materially different approach, or the historical inflection point that it now represents. In the venue of human disease, regenerative medicine thinks differently, uses different tools, and represents an historic sea-change. Looking at it practically, however, the most striking feature – and perhaps the defining feature – of regenerative medicine is that it offers all of us a more compassionate and a far more effective medical future.