Chimeras, Hybrids, and Interspecies Research: Politics and Policymaking

Introduction

Introduction AT ISSUE IN THIS BOOK are studies that combine genes, gametes, embryos, or embryonic stem (ES) cells from human and nonhuman species at the earliest stages of development. What is here called early interspecies research (ISR) involves the shared presence of human and/ or animal embryos and ES cells in a potentially inheritable way. The prospect of such studies has been flagged, whether justifiably or not, by a number of observers and policy makers as problematic. One example of early ISR is the injection of human ES cells into a mouse blastocyst (four- to six-day embryo of approximately three hundred cells) in order to understand how human ES cells function over time in a living system. As the fetal mouse develops, the human cells differentiate and integrate. The ultimate goal is to understand the properties of ES cells better in order to develop cell-based therapies for humans. The recipient mice, studied before or after birth, would be chimeras, with some human cells existing side by side with mouse cells. A second example is the substitution of animal eggs for human eggs in investigations geared to developing cell therapies for humans. In theory, if the nucleus from a patient’s somatic cell is introduced to an enucleated egg, the egg can be stimulated to cleave and will yield an inner cell mass from which ES cells can be derived after about five days. These ES cells, which are capable of differentiating to virtually any type of body cell, can be coaxed to differentiate and used for cell replacement therapies. The goal is to derive ES cells that have the same genome as the patient who provided the nucleus. Many eggs would be needed in these preliminary studies, so investigators have proposed using animal eggs, which 1 2 Introduction are abundant, in the early stages of research. The embryonic entity with a human nucleus and animal cytoplasm would be a cybrid or cytoplasmic hybrid. Combining human and nonhuman cells is common in research, as when human cells are injected into adult mice to test a vaccine. Early ISR is used as a concept here to look beyond these traditional interspecies investigations in order to focus on studies that combine human and nonhuman embryos and/or ES cells in a way that could have a systemic effect on the organism if it were allowed to develop. Any studies using human embryos or ES cells have been contentious in the United States and other countries. The question here is whether pairing human and nonhuman biological material to produce such entities as chimeras or cybrids elevates the stakes by raising new and distinct ethical and policy issues. Exploring the dimensions of this research, regardless of the conclusions , helps to clarify recurring opposition to early ISR, as evidenced in preemptive restrictions in various countries and deliberations in the scholarly literature and in policy advisory groups. From one point of view, the concept of early ISR is curious at best and unnecessarily provocative at worst. Whether the cell mix is all human, all animal, or a combination is, according to this view, insignificant. Of more importance is the purpose of studies and their feasibility, reliability, justification , and promise, all of which supersede distinctions about heritable human-nonhuman combinations. Here early ISR is not morally distinct, aside from underlying questions about whether human ES-cell research is appropriate in any form. If the human-nonhuman aspect is perceived as troublesome, efforts can be made to appease concerns. Lee Silver, a Princeton geneticist, typifies this perspective by positing that many scientists view early ISR as a red herring—much ado about very little. He predicts that members of society will take such interventions “in stride” and “continue to move along an orderly moral path” (Silver 2006, 187). From a second point of view, the combined presence of nonhuman and human cells at the embryonic level is a clarion call for further attention. Here more than a difference of degree separates early ISR from ongoing research techniques. The mere combination is qualitatively different, and it poses implications for future and more problematic interchanges. Leon Kass, the first chair of George W. Bush’s appointed President’s Council Introduction 3 on Bioethics, for example, points to a “growing number of experiments that are now putting human stem cells and their derivatives into animals to test them for . . . their therapeutic potential.” He cautions that “it is not...