Complex sentence: An alternative system is the use of CD90 (Thy1) alleles, which CD90.1/CD90.2 system is used in the same manner as the CD45.1/CD45.2 system.
Split into simpler sentences: An alternative system is the use of CD90 (Thy1) alleles. The CD90.1/CD90.2 system is used in the same manner as the CD45.1/CD45.2 system.