Ethical aspects of gene therapy

9th Postgraduate Course for Training in Reproductive Medicine and Reproductive Biology

Alex Mauron
Associate professor of bioethics

Gene therapy consists of a wilful modification of the genetic material in cells of a patient in order to bring about a therapeutic effect. This modification usually occurs by introducing exogenous DNA using viral vectors or other means. Although gene therapy is still in its infancy as a clinically useful therapeutic modality, a discussion of the ethical issues is useful in several respects because it involves ethical principles of broad applicability in clinical medicine. Furthermore, many current applications of genetic engineering in medicine (DNA vaccines, therapeutic use of encapsulated genetically modified cells) are conceptually close to gene therapy, so that the border between gene therapy in the narrow sense and other gene-based therapies is getting fuzzier as time goes by.

Two conceptual distinctions are central to an understanding of the ethical issues of gene therapy:

1 - Therapy vs. enhancement. There is a consensus that gene therapy should be therapy, i.e. the correction of bona fide disease conditions, rather than enhancement, which would mean "improving the human species" (whatever that means...) and therefore would entail the introduction in human subjects of novel characteristics going beyond the usual, medical, understanding of health (i.e. health as absence of serious disease).

2 - Somatic vs. germ line gene therapy. All current research on humans deals with somatic gene therapy. In these projects somatic cells such as bone-marrow, liver, lung or vascular epithelium etc. are genetically modified. Since the germ line is not affected, all effects of therapy end with the life of the patient, at the very latest. In fact, most somatic therapies will probably require repeated applications, much like ordinary pharmacological treatments.

Initially, gene therapy was conceptualised mainly as a procedure to correct recessive monogenic defects by bringing a healthy copy of the deficient gene in the relevant cells. In fact, somatic gene therapy has a much broader potential if one thinks of it as a sophisticated means of bringing a therapeutic gene product to the right place in the body. The field has moved increasingly from a "gene correction" model to a "DNA as drug" model (ADN médicament, A. Kahn). This evolution towards an understanding of gene therapy as "DNA-based chemotherapy" underscores why the ethical considerations for somatic gene therapy are not basically different from the well-known ethical principles that apply in trials of any new experimental therapy

Favourable risk-benefit balance (principle of beneficence/non-maleficence);
Informed consent (principle of respect for persons);
Fairness in selecting research subjects (principle of justice).

Clearly, the mere fact that gene therapy has to do with genes and the genome does not, in itself, make it "special" or "suspicious".

A further distinction ought to be made between in vivo and ex vivo somatic gene therapy. Ex vivo procedures entail the extraction of cells from the patient's body (for instance bone-marrow cells), genetic modification of the cells using appropriate vectors or other DNA-transfer methods and reimplantation of the cells in the patient. In vivo therapy uses a vector or DNA-transfer technique that can be applied directly to the patient. This is the case of current experiments aimed at correcting the gene defect of cystic fibrosis by exposing lung epithelium to adenovirus-derived vectors containing the CFTR gene. In the in vivo case, the potential for unintended dissemination of the vector is more of an issue. Therefore, biological safety considerations must also be subjected to ethical scrutiny in addition to the patient-regarding concerns already mentioned.

In germ line therapy, the DNA of germ cells would be affected, the objective being to correct a genetic defect once and for all, in all descendants of the therapy recipient who will inherit the modified allele. Although germ line therapy is far more speculative than somatic gene therapy at this time, it is widely discussed because it raises important and difficult ethical questions that have relevance for other medical practices as well. The consensus against germ line therapy is broad, but not unanimous. The ethical debate on germ line therapy has usually revolved around two kinds of issues:

1 - Germ line therapy is "open-ended" therapy. Its effects extend indefinitely into the future. This basically fits the objective of germ line therapy (assuming that it becomes possible one day), namely to correct a genetic defect once and for all. But precisely there lies also an ethical problem: an experiment in germ line therapy would be tantamount to a clinical experiment on unconsenting subjects, which are the affected members of future generations. This raises a number of very complex questions and is, in my view, an important but not necessarily overriding argument. A recent symposium on germ line engineering has concluded with a cautious "yes-maybe" for germ line gene therapy (see references).

2 - Germ line therapy may involve invasive experimentation on human embryos. Although there are other potential targets for germ-line interventions, much of the discussion revolves around the genetic modification of early embryos, where the germ line has not yet segregated from the precursors of the various somatic cell types. As a result, the ethical assessment of germ line gene therapy will hinge in part on the ethical standing accorded to the early human embryo and the moral (dis)approval of early embryo experimentation. Those who believe the early embryo to be the bearer of considerable intrinsic moral worth or even that it is "like" a human person in a morally-relevant sense will conclude that embryo experimentation is to be rejected and germ-line therapy as well. Others think that it is only later in development that humans acquire those features that make them ethically and legally protected human subjects to the fullest degree. For them, the use of early embryos is not objectionable and germ line therapy cannot be ruled out on these grounds alone. As might be expected in view of the moral pluralism of modern societies, the policies of European countries differ in this respect: some permit some invasive research on human embryos (UK, Spain, Denmark), others ban it (Germany, Norway), others are still undecided. More generally, embryo-centred controversies are expected to increase as the field of embryonic stem-cell research becomes ever more promising. It is expected that this field will catch much of the public attention that was devoted to gene therapy in the nineties.

Clearly, the question of the ethical standing of the human embryo is also of major importance for other medical procedures in reproductive medicine such as in-vitro fertilisation, pre-implantation diagnosis, experimentation on human embryos in general and abortion.

To go back to gene therapy, or rather to the therapeutic innovations due to genetic engineering such as DNA vaccines: some of these could potentially benefit a great number of people world-wide, contrary to early developments of genetic engineering in medicine, which where largely geared towards the health problems of rich countries. Although the course of biomedical progress is often unpredictable, the setting of research priorities does raise troubling issues of social ethics.

REFERENCES

Engineering the Human Germ line Symposium, Los Angeles, June 1998: http://www.ess.ucla.edu:80/huge/report.html
University of Pennsylvania Health System, The Institute for Human Gene Therapy: http://www.med.upenn.edu/ihgt/info/links.html
Mauron A. La thérapie génique sous l’angle de l’éthique et du droit. Médecine et Hygiène, 55, 1552-1554, 1997.