Why Do Cultured Transplanted Myoblasts Die in Vivo? DNA Quantification Shows Enhanced Survival of Donor Male Myoblasts in Host Mice Depleted of CD4 + and CD8 + Cells or NK1.1 + Cells

Abstract

Overcoming the massive and rapid death of injected donor myoblasts is the primary hurdle for successful myoblast transfer therapy (MTT), designed as a treatment for the lethal childhood myopathy Duchenne muscular dystrophy. The injection of male myoblasts into female host mice and quantification of surviving male DNA using the Y-chromosome-specific (Y1) probe allows the speed and extent of death of donor myoblasts to be determined. Cultured normal C57BL/10Sn male donor myoblasts were injected into untreated normal C57BL/10Sn and dystrophic mdx female host mice and analyzed by slot blots using a ³²P-labeled Y1 probe. The amount of male DNA from donor myoblasts showed a remarkable decrease within minutes and by 1 h represented only about 10–18% of the 2.5 × 10⁵ cells originally injected (designated 100%). This declined further over 1 week to approximately 1–4%. The host environment (normal or dystrophic) as well as the extent of passaging in tissue culture (early “P3” or late “P15–20” passage) made no difference to this result. Modulation of the host response by CD4⁺/CD8⁺-depleting antibodies administered prior to injection of the cultured myoblasts dramatically enhanced donor myoblast survival in dystrophic mdx hosts (15-fold relative to untreated hosts after 1 week). NK1.1 depletion also dramatically enhanced donor myoblast survival in dystrophic mdx hosts (21-fold after 1 week) compared to untreated hosts. These results provide a strategic approach to enhance donor myoblast survival in clinical trials of MTT.