May 27, 2002
La Jolla, CA – A team led by Salk Institute scientists has used gene therapy to reverse infertility in male mice. Treated mice produced healthy offspring that did not contain the introduced gene or vector, alleviating concerns that treating infertility via gene therapy would genetically alter any progeny produced from the treatment, as well as their descendants in perpetuity.
About one out of every five couples worldwide experience fertility problems, and one third to one half of these cases result from male infertility.
“The overwhelming majority of male infertility cases arise from inability to make sperm cells,” said Inder Verma, a professor of genetics at Salk and senior author of the study appearing in today’s Proc. Natl. Acad. Sci. “Most of those cases are not due to defects in sperm cells themselves, but in other cells that support sperm production.”
The mice in the study had mutations in a gene called KL2 (for c-kit ligand 2) in their Sertoli cells, cells in the testis that aid in sperm cell development by providing structural support and growth factors. The mutant mice failed to make sperm.
Functional KL2 genes were delivered to the mice using lentiviral vectors, based on a crippled version of HIV that was first developed by Verma and Salk Institute colleagues in 1996. Treatment with the vectors restored sperm production to substantial levels in all nine animals treated, without inducing any discernable side effects.
Sperm cells from the treated mice were tested for their ability to generate offspring. While not enough sperm could be collected to carry out normal in vitro fertilization, in which sperm and eggs are simply mixed together, a procedure known as assisted fertilization was successful. Fertilized embryos appeared to develop normally in vitro, and healthy pups were born from some implanted females.
“Assisted fertilization involves microinjecting spermatozoa directly into eggs,” said Masahito Ikawa, a postdoctoral fellow in Verma’s lab and first author on the study. “It’s an accepted technique for helping men with low sperm counts.
“But most men with fertility problems don’t make viable sperm at all or make too little for even assisted fertilization to work,” he added. “For them, the gene therapy approach may eventually offer another option.”
None of the offspring tested positive for the presence of the normal KL2 gene carried by the gene therapy vector.
“This result indicates that the vectors transduced the Sertoli cells only, and not the actual spermatozoa,” said Verma. “It’s an important point, because a high level of concern exists about making permanent alterations to a patient’s germ line that would be perpetuated to his descendants.
“The current result suggests we may, in fact, be able to treat male infertility using gene therapy without worrying about those types of consequences.”
Salk co-authors include Vinay Tergaonkar, a postdoctoral fellow in Verma’s laboratory. Additional authors include Atsuo Ogura, Narumi Ogonuki and Kimiko Inoue at The Institute of Physical and Chemical Research (RIKEN) in Tsukuba, Japan. The study, titled “Restoration of spermatogenesis by lentiviral gene transfer: Offspring from infertile mice,” was funded by the National Institutes of Health, the March of Dimes Birth Defects Foundation, the Wayne and Gladys Valley Foundation, and the H. N. and Frances C. Berger Foundation. Verma is an American Cancer Society Professor of Molecular Biology. Ikawa is supported by the Valley Foundation and Terganokar is supported by a fellowship from the Leukemia and Lymphoma Society.
The Salk Institute for Biological Studies, located in La Jolla, Calif., is an independent nonprofit institution dedicated to fundamental discoveries in the life sciences, the improvement of human health and conditions, and the training of future generations of researchers. The Institute was founded in 1960 by Jonas Salk, M.D., with a gift of land from the City of San Diego and the financial support of the March of Dimes Birth Defects Foundation.