Sperm Safes: Maximizing the preservation and recovery of limited numbers of male germ cells

Cancer treatments such as radiation, chemotherapy, and surgery, while life preserving, can threaten fertility in men, women, and children. Thus, numerous strategies to preserve fertility have been and continue to be developed. In general, fertility preservation strategies for males are considered simpler than for females because large numbers of sperm are present in the ejaculate of healthy males, and it is relatively straightforward to obtain and freeze sperm in comparison to harvesting and freezing eggs. However, fertility preservation in males with conditions of extremely low numbers of germ cells is more complex. These conditions include males with cryptozoospermia (rare sperm found only in centrifuged, pelleted samples) or males who have undergone testicular or epididymal biopsy where only limited numbers of immature germ cells may be recovered. Fortunately, the advent of intracytoplasmic sperm injection (ICSI) now means that fertility can be restored with technically only a single sperm. With ICSI, pregnancies and live births can be achieved with ejaculated, seminal, and testicular spermatozoa, even in cases of low sperm number or quality. In addition, injection of immature round spermatids can be performed clinically. Despite the success of ICSI, a significant challenge in male fertility preservation is the reliable recovery of small number of germ cells post-cryopreservation. This challenge is going to become even more pronounced as advances are made to derive germ cells in vitro because these techniques will likely only generate limited numbers of sperm for fertility preservation. Thus, there is an urgent need to develop robust and reliable methods to store and recover small numbers of germ cells for male fertility preservation- which is the goal of the current proposal.. These methods will ultimately benefit prepubertal males whose only fertility preservation option is to cryopreserve testicular tissue for future use for transplantation or in vitro growth or derivation of germ cells.