Spermatids are the earliest male germ cells with haploid set of chromosomes. Spermatid injection was introduced in human assisted reproduction for the treatment of men with non-obstructive azoospermia. Spermatozoa can be recovered in half of patients with nonobstructive azoospermia. The use of spermatids for intracytoplasmic injection (ICSI) has been proposed for cases in which no spermatozoa can be retrieved. However, there are low pregnancy rates following ICSI using round spermatids from men with no elongated spermatids or spermatozoa in their testes. The in vitro culture of immature germ cells has been proposed as a means to improve this poor outcome. Oocyte activation rarely occurs when injected with a spermatid. Therefore, spermatid injection requires use of calcium ionophores for oocyte activation which is otherwise carried out by PLC zeta from mature sperms. This is the only option available for the nonobstructive azoospermic patients to have their own biological child.
Full Article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4601178/