The only attempts of in vitro maturation of testicular tissues recovered from prepubertal boys after the initiation of chemotherapy (treatment with a Berlin-Frankfurt-Munster-based chemotherapy regimen for acute lymphoblastic leukemia (ALL) prior to the testicular biopsy) were performed in a 3D methylcellulose culture system and led to the production of postmeiotic (acrosin +) cells after 15 weeks for one patient out of four22. Here, ACR is linked to acute lymphoblastic leukemia.