Scientists Identify Key Cause Behind Fertility Loss in Long-Term Frozen Testicular Tissue
Researchers from the University of Pennsylvania’s School of Veterinary Medicine and the Children’s Hospital of Philadelphia are making important strides toward helping childhood cancer survivors regain fertility. Their work, recently published in Stem Cell Reports, investigates why testicular tissue preserved through cryopreservation sometimes fails to restore sperm production after transplantation.
Childhood cancer treatments, like chemotherapy and radiation, often damage reproductive cells. Boys who receive these treatments before puberty can lose the ability to produce sperm later in life. As a result, doctors have turned to cryopreserving testicular tissue as a way to preserve fertility. However, the success of this method after long periods of freezing has been limited.
Led by Dr. Eoin Whelan and Dr. Ralph Brinster, the research team studied how sperm cells develop. They used advanced single-cell multiomic tools to trace how male germ cells mature into sperm. This process, called spermatogenesis, includes two major stages: meiosis, where reproductive cells are formed, and spermiogenesis, where these cells become mature sperm (spermatozoa).
Their findings revealed that each stage of development is marked by specific changes in chromatin accessibility—the way DNA is packed and accessed inside cells. “This enhanced understanding of sperm development helps set the stage for better fertility restoration in boys treated for cancer,” said Dr. Brinster, senior author and professor of reproductive physiology.
Brinster had long envisioned this fertility preservation approach. Nearly two decades ago, he proposed that freezing and re-implanting testicular tissue could one day help cancer survivors. That vision took a major step forward in November 2023, when a 24-year-old male cancer survivor received a transplant of his own frozen testicular tissue. Dr. Kyle Orwig, who studied under Brinster, led that procedure at the University of Pittsburgh.
Still, success is not guaranteed. In a 2022 study published in PLOS Biology, Whelan and Brinster found that testis cells frozen for more than 20 years could still produce sperm—but at much lower levels. The reduced efficiency pointed to a disruption in sperm cell development after meiosis. Even after transplantation, these problems persisted, suggesting that epigenetic changes—modifications in gene activity that don’t alter DNA sequence—may build up during long-term storage and pass down through the cells.
“This breakdown in the sperm cell formation process shows that we still need to improve how we freeze and store reproductive tissue,” said Whelan. “Our goal is to refine the process so that frozen stem cells can still follow their genetic program after being thawed and re-implanted.”
To advance this effort, the research team created a detailed map—or atlas—of how genes behave and change throughout normal sperm development. This reference can now be used to compare cells from long-frozen tissue, helping scientists spot exactly where and how the process breaks down.
“By identifying the defects that come from long-term freezing, we hope to one day correct or even prevent these issues,” Whelan added. “This research offers real hope for families affected by childhood cancer who still want the chance to have children in the future.”
Related topics:
