Materials and MethodsAnimals.l--Female BDF1 (C57BL/6 X DBA/2) mice, age 10-12 wk, were used as recipients. Donor mice of similar sex and age were chosen from the C57BL/6, DBA/2, C3H, and BALB/c strains. Rat bone marrow cells were obtained from Sprague-Dawley females, age 10--12 wk. All animals were housed in covered plastic cages, 10 or fewer per cage, and provided with tap water and a standard laboratory diet 2 ad lib.Dmg.a--Cyclophosphamide (CY) mad mechlorethamine (HN2) were dissolved in saline and used within 10 rain.