SCIENCE: CELL BIOLOGY

By ABIGAIL MILLER

MICE CD45 IS THE LEUKOCYTE COMMON ANTIGEN EXPRESSED ON ALL LEUKOCYTES AND THEIR PROGENITOR CELLS, INCLUDING ADULT HSCS, BUT NOT ON RED BLOOD CELLS, PLATELETS, AND THEIR COMMITTED PROGENITORS A MINIMUM CRITERION IS THAT MYELOID, B-LYMPHOID, AND T-LYMPHOID POPULATIONS NEED TO BE DEMONSTRABLY RECONSTITUTED WITH TEST DONOR– DERIVED CELLS FOR 3–4 MONTHS TO SHOW THAT TEST DONOR CELLS CONTAINED HSCS WHEN THESE THREE LINEAGES ARE DEMONSTRABLY RECONSTITUTED, ERYTHROID AND MEGAKARYOCYTIC LINEAGES WILL ALMOST CERTAINLY HAVE BEEN RECONSTITUTED WITH PROGENY OF THE SAME TEST DONOR CELLS HOWEVER, A BETTER SYSTEM, ONE THAT PERMITS SIMULTANEOUS ANALYSIS OF LEU- KOCYTES OF ALL LINEAGES, RED BLOOD CELLS, AND PLATELETS, SHOULD BE USED WHEN IT IS AVAIL- ABLE AMONG THESE THREE LINEAGES, THE MYELOID LINEAGE IS MORE IMPORTANT THAN THE LYMPHOID LINEAGES IN RARE INSTANCES, THE MYELOID LINEAGE IS DEMONSTRABLY RECONSTI- TUTED 4 MONTHS AFTER TRANSPLANTATION, BUT THE LYMPHOID LINEAGES ARE NOT LYMPHOID LINEAGE RECONSTITUTION MIGHT BECOME DETECTABLE LATER ON IN SUCH CASES WHEN MULTILINEAGE RECONSTITUTION TAKES PLACE 4 MONTHS AFTER TRANSPLANTATION, THIS IS CONCEIVABLY DUE TO SELF-RENEWAL AND DIFFERENTIATION POTENTIALS IN HSCS TO CON- FIRM SELF-RENEWAL POTENTIAL, HOWEVER, SECONDARY TRANSPLANTATION NEEDS TO BE PER- FORMED WHEN LONG-TERM MULTILINEAGE RECONSTITUTION TAKES PLACE AGAIN IN SECONDARY RECIPIENT MICE, THIS IS CERTAINLY DUE TO SELF-RENEWAL AND DIFFERENTIATION POTENTIALS IN HSCS WE HAVE RECENTLY REALIZED THAT SOME HSCS SHOW LITTLE RECONSTITUTION ACTIVITY 4 MONTHS AFTER PRIMARY TRANSPLANTATION, BUT SHOW SIGNIFICANT RECONSTITUTION ACTIVITY SCIENCE: CELL BIOLOGY