|
MGH researchers confirm that bone marrow
restores fertility in female mice
Donor-derived egg cells present in
ovaries, but all offspring are from marrow recipients' own eggs
BOSTON - July 31, 2007 - A new study from Massachusetts General
Hospital (MGH) researchers confirms that female mice that receive
bone marrow transplantation after fertility-destroying chemotherapy
can go on to have successful pregnancies throughout their normal
reproductive life. The report in the August 1 Journal of Clinical
Oncology verifies that donor marrow can restore fertility in
female mice through an as-yet unidentified mechanism. While donor-derived
egg cells or oocytes were observed in the ovaries of marrow recipients,
all pups born were from the recipients' own eggs.
"Consistent with our past work, cells derived from the donor
bone marrow are getting into the ovaries and developing into immature
oocytes," says Jonathan Tilly, PhD, director of the Vincent
Center for Reproductive Biology at MGH, the study's senior author.
"Although these oocytes derived from marrow cells don't appear
competent, at least thus far, to make fertilizable eggs, marrow
does contribute something that allows a resumption of fertility
in female mice sterilized by chemotherapy."
In a 2005
paper published in the journal Cell, Tilly's group found
that the ovaries of female mice that had received bone marrow or
blood cell transplants after fertility-destroying doses of chemotherapy
appeared normal and contained immature oocytes expressing a marker
protein indicating they came from the donor cells. This report followed
a 2004
Nature paper, also from Tilly's team, reporting
that female mice continued producing eggs well into adulthood, in
contrast to the long-held belief that female mammals are born with
a finite supply of eggs that is depleted throughout life. Both those
papers have been extremely controversial, and the current study
was designed to follow up the 2005 paper and to address criticisms
raised by other researchers.
In the current study, adult female mice treated with infertility-inducing
chemotherapy received bone marrow transplants from non-treated,
healthy adult females either one week or two months after chemotherapy.
The mice were then housed with healthy adult males and followed
for 7 months, a time period in which a group of control females
achieved at least five successful pregnancies each. Both the males
and the donor females were black in coat color while the recipient
females were white-coated. As a result, the coat color of any pups
would indicate the source of egg cells used to make the offspring,
with tan coats signifying eggs from the recipients and black coats
indicating that the eggs had come from marrow donors.
Of the 10 females that received bone marrow transplants one week
after chemotherapy, all but one achieved several successful pregnancies
during the study period. One gave birth to four litters, one gave
birth to five litters, and seven gave birth to six litters of pups.
All pups were offspring of the recipients. In a comparison group
of 13 females that did not receive marrow after chemotherapy, 10
did become pregnant, but none delivered more than three litters.
Additional experiments indicated that mice receiving transplants
one week after chemotherapy had better fertility outcomes than did
those transplanted at eight weeks. Similarly, resuming mating sooner
after transplantation also improved fertility rates. When chemotherapy
doses were increased to levels expected to cause death in half the
mice, those that also received bone marrow transplants had improved
rates of both survival and long-term fertility.
The coat-color results of the mating trial indicated that the transplanted
marrow's contribution to restoring fertility did not involve cells
destined to becoming fertilizable eggs. To further investigate this
observation, the MGH-Vincent researchers gave chemotherapy-treated
females marrow from transgenic females that express a green fluorescent
protein (GFP) marker only on germline cells, which are precursor
cells involved in producing oocytes. Two months after the transplant,
the researchers observed GFP-marked oocytes in immature follicles
within recipient ovaries. However, donor-derived oocytes made up
less than 2 percent of the total number of oocytes contained within
follicles, and no mature follicles contained GFP-marked cells.
Among the published reports raising objections to the previous
work of Tilly's group - none of which actually attempted to duplicate
those experiments - one theorized that GFP-marked cells observed
in recipient ovaries in the 2005 Cell paper might be donor
immune cells rather than oocytes. To address that conjecture, the
MGH-Vincent team isolated immune cells from normal mice, from the
germline-only GFP strain used in their experiments, and from a strain
of mice expressing GFP in all cells. Careful analysis confirmed
that no immune cells from the germline-only GFP strain contained
the marker protein, making it highly unlikely that GFP-labeled cells
in the ovaries of females receiving germline-only-labeled marrow
were anything other than oocytes. This was further confirmed by
experiments showing that isolated immune cells did not express the
oocyte-specific marker genes previously used by Tilly's group to
identify the marrow-derived oocytes.
Tilly and his colleague note that, since agents that protect fertility
most likely would need to be given before chemotherapy to be effective,
whatever the donor marrow contributes probably acts by restoring
rather than preserving fertility. "Right now, we really don't
know exactly what it is in marrow that restores recipient oocyte
production and rescues long-term fertility. However, we do know
without question that immature oocytes can be generated from cells
in adult bone marrow, but they are probably not critical to the
fertility rescue observed after the transplants."
Since the 2005 Cell paper, Tilly points out, three studies
have been published by other groups showing that, similar to his
team's work in females, bone marrow cells from adult male mice or
from men can be coaxed to make immature sperm cells, both in lab
dishes and after transplantation into the testes. "Clearly,
something is going on here regarding the ability of stem cells in
bone marrow to produce immature egg and sperm cells, and we need
to figure out what it is," he says. Tilly is an associate professor
of Obstetrics, Gynecology and Reproductive Biology at Harvard Medical
School.
The first author of the study is Ho-Joon Lee, PhD, of the MGH-Vincent
Center for Reproductive Biology. Co-authors are Kaisa Selesniemi,
PhD, Yuichi Niikura, PhD, and Teruko Niikura, also of MGH-Vincent;
and Rachael Klein and David Dombkowski of the MGH Center for Regenerative
Medicine. The work was supported by grants from the National Institutes
of Health, Sea Breeze Foundation, JM Foundation and Vincent Memorial
Research Funds.
Massachusetts General Hospital, established in 1811, is the original
and largest teaching hospital of Harvard Medical School. The MGH
conducts the largest hospital-based research program in the United
States, with an annual research budget of more than $500 million
and major research centers in AIDS, cardiovascular research, cancer,
computational and integrative biology, cutaneous biology, human
genetics, medical imaging, neurodegenerative disorders, regenerative
medicine, systems biology, transplantation biology and photomedicine.
MGH and Brigham and Women's Hospital are founding members of of
Partners HealthCare HealthCare System, a Boston-based integrated
health care delivery system.
Media Contact: Sue
McGreevey, MGH Public Affairs
Physician Referral Service: 1-800-388-4644
Information about Clinical Trials
|
|
|
