Differential Expression of a Human Sperm‐specific Isozyme in Seminoma Cells Transplanted in Scid‐nu(str) Mice

An isozyme of human sperm‐specific lactate dehydrogenase, LDH‐X (C(4)) (EC 1.1.1.27), which is expressed only in differentiated germ cells (spermatozoa, spermatids and primary spermatocytes after midpachytene), appeared in the xenografted tumor cells of human seminoma and its metastatic lesions (lymph node and kidney) in scid (severe combined immunodeficiency)‐nude(streaker) double mutant mice, though it was not expressed in the original tumor of the patient. The morphological pattern of seminoma cells also changed in the xenografts and metastatic lesions as in normal spermatogenesis. Thus, the human seminoma cells showed differential expression of the sperm‐specific isozyme in parallel with their morphological changes. However, the sperm‐specific isozyme disappeared in the mitotically dividing seminoma cells which were newly established from the LDH‐X positive xenograft.