BIOMEDICAL ETHICS SEMINARBIOMEDICAL ETHICS SEMINAR

Embryonic Stem Cell Chimera Research: What is it? What are Embryonic Stem Cell Chimera Research: What is it? What are its benefits?its benefits?

What concerns does it raise?What concerns does it raise?

Mark Mercola, Ph.D. Professor, Stem Cell and Regeneration Program,Mark Mercola, Ph.D. Professor, Stem Cell and Regeneration Program,The Burnham Institute, and Department of Pathology (adjunct), UCSD School The Burnham Institute, and Department of Pathology (adjunct), UCSD School

of Medicineof Medicine

March . 17 , 2004March . 17 , 2004

……the sovereignty of man lieth hid in knowledge…the sovereignty of man lieth hid in knowledge…

Heritage of Experimental Biology Leading to Heritage of Experimental Biology Leading to Research Using Chimeric EmbryosResearch Using Chimeric Embryos

17th-18th centuries: 17th-18th centuries: Initial experiments challenging spontaneous generation and Initial experiments challenging spontaneous generation and

demonstration that sperm activate eggs (Redi, Spallanzani)demonstration that sperm activate eggs (Redi, Spallanzani) Regeneration in amphibians, worms, snails (Spallanzani, Tremblay)Regeneration in amphibians, worms, snails (Spallanzani, Tremblay)

19th and early 20th Centuries:19th and early 20th Centuries: Concept of a germ cell as set aside distinct from somatic cell (August Concept of a germ cell as set aside distinct from somatic cell (August

Weismann)Weismann) Wilhelm Roux: hot needle killing one blastomere of frog embryo -> Wilhelm Roux: hot needle killing one blastomere of frog embryo ->

mosaic embryosmosaic embryos Driesch, isolation of sea urchin blastomeres and McClendon, isolated Driesch, isolation of sea urchin blastomeres and McClendon, isolated

frog blastomeres -> regulative developmentfrog blastomeres -> regulative development Horstadius, Speman: inductive interactions between blastomeresHorstadius, Speman: inductive interactions between blastomeres

Hans Spemann and Hilde MangoldHans Spemann and Hilde Mangold

Organizer experimentOrganizer experiment Transplantation of cells from one (pigmented) to Transplantation of cells from one (pigmented) to

another (unpigmented) embryoanother (unpigmented) embryo Evaluated ability of transplanted tissue to Evaluated ability of transplanted tissue to

induce/organize structures in host tissueinduce/organize structures in host tissue

Potency of Individual Cells in Mammalian Potency of Individual Cells in Mammalian EmbryosEmbryos

Potency tested by dispersion and reaggregation Potency tested by dispersion and reaggregation with different embryo to make chimeric embryos, with different embryo to make chimeric embryos, tracking the donor cells within the host embryotracking the donor cells within the host embryo

Totipotency of individual Totipotency of individual cellscells probably persists probably persists until implantationuntil implantation

Nuclear potency persists longer, perhaps in Nuclear potency persists longer, perhaps in many somatic nuclei remain totipotent or can be many somatic nuclei remain totipotent or can be “re-booted”.“re-booted”.

Embryonic Stem CellsEmbryonic Stem Cells

Derived from pre-Derived from pre-implantation embryos; implantation embryos; cultures of inner cell mass cultures of inner cell mass cells maintained in a cells maintained in a totipotent state in culturetotipotent state in culture

Totipotency demonstrated Totipotency demonstrated by chimerasby chimeras

Regenerative potential is Regenerative potential is only beginning to be only beginning to be explored and requires explored and requires understanding how to understanding how to direct differentiation to direct differentiation to target tissuestarget tissues

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Spontaneous Cardiomyocyte Formation in Spontaneous Cardiomyocyte Formation in Aggregate Cultures of hES CellsAggregate Cultures of hES Cells

How to channel this ability to differentiate to produce target tissues?How to channel this ability to differentiate to produce target tissues?

Examples of Tissues for which Interspecies Examples of Tissues for which Interspecies Chimeras have helped define Potency, Fate, and Chimeras have helped define Potency, Fate, and

FunctionFunction

Neural crestNeural crest SomitesSomites BrainBrain TumorsTumors

These experiments do not elicit much ethical concernThese experiments do not elicit much ethical concern

A Few Possible Reasons for Minimal A Few Possible Reasons for Minimal Concern of Grafting ExperimentsConcern of Grafting Experiments

Adult, so no chance of germline transmissionAdult, so no chance of germline transmission Non-human hostNon-human host No involvement of human CNS functionNo involvement of human CNS function Degree of mosaicism is poor - e.g. large bits of Degree of mosaicism is poor - e.g. large bits of

tissues generally transplantedtissues generally transplanted

Mouse Embryonic Stem Cell-based Mouse Embryonic Stem Cell-based ChimerasChimeras

Introduction of ES cells into pre-Introduction of ES cells into pre-implantation blastocystimplantation blastocyst

Mix with host cellsMix with host cells Generate high degree of Generate high degree of

mosaicismmosaicism Contribute to germline = sperm Contribute to germline = sperm

and eggand egg Basis for gene knockout Basis for gene knockout

technology, which underlies a technology, which underlies a substantial national research substantial national research effort effort

Most people do not voice ethical Most people do not voice ethical concerns about this technologyconcerns about this technology

Human ES cell linesHuman ES cell lines

Derived similarly to mouse ES linesDerived similarly to mouse ES lines Pluripotency is assumed from teratoma assaysPluripotency is assumed from teratoma assays Pluripotency makes them advantageous for Pluripotency makes them advantageous for

tissue regenerationtissue regeneration Many people voice ethical concernsMany people voice ethical concerns Restrictions on use with federal fundingRestrictions on use with federal funding Relatively few restrictions with private fundingRelatively few restrictions with private funding

Human ES Cell Line -Mouse Embryo Chimera Human ES Cell Line -Mouse Embryo Chimera

Pros and Cons:Pros and Cons: Pro: Test potency of Pro: Test potency of

human ES cellhuman ES cell Pro: Create disease Pro: Create disease

models for researchmodels for research Con: Widely available hES Con: Widely available hES

cell lines probably will not cell lines probably will not incorporate effectivelyincorporate effectively

Con: Fear that might Con: Fear that might contribute to germlinecontribute to germline

Con: Moderate ethical Con: Moderate ethical uneaseunease

Consider:Consider: Similar issues with other Similar issues with other

cell types, except germline cell types, except germline potential; therefore a large potential; therefore a large debate is looming on debate is looming on horizonhorizon

How to establish How to establish mechanisms to ensure mechanisms to ensure ethical practice at research ethical practice at research institutions?institutions?

What Makes a Procedure Ethically What Makes a Procedure Ethically Challenging?Challenging?

Example 1: Human ES cells into human embryosExample 1: Human ES cells into human embryos Consider hES cells placed into preimplantation embryos, even if Consider hES cells placed into preimplantation embryos, even if

to cure a genetic disease?to cure a genetic disease? What if cells are differentiated first, so that they rescue a defect What if cells are differentiated first, so that they rescue a defect

but cannot contribute to germline?but cannot contribute to germline? Example 2: Human hematopoietic stem cells into Example 2: Human hematopoietic stem cells into

primates to generate animals that could donate bloodprimates to generate animals that could donate blood What makes people uneasy?What makes people uneasy? How to draw line between ethical and unethical?How to draw line between ethical and unethical? If chimeras are to be permitted, is there a tissue that If chimeras are to be permitted, is there a tissue that

must remain free from donor cells?must remain free from donor cells?

Ethical Advisory BoardEthical Advisory Board

Distinct from animal use and human subject IRB Distinct from animal use and human subject IRB committeescommittees

Consists of lawyers and ethicistsConsists of lawyers and ethicists Reduces risk of performing a procedure that Reduces risk of performing a procedure that

might be illegal, unethical or otherwise engender might be illegal, unethical or otherwise engender adverse publicityadverse publicity