Complement and myoblast transfer therapy: Donor myoblast survival is enhanced following depletion of host complement C3 using cobra venom factor, butnot in the absence of C5

Myoblast transfer therapy (MTT) is a potential cell therapy for myopathies such as Duchenne Muscular Dystrophy and involves the injection of cultured muscle precursor cells ('myoblasts') isolated from normal donor skeletal mu scles into dystrophic host muscle. The failure of donor myoblast survival f ollowing MTT is widely accepted as being due to the immune response of the host. The role of complement as one possible mechanism for the initial, ver y rapid death of myoblasts following MTT was investigated. Donor male myobl asts were injected into the tibialis anterior (TA) muscles of female host m ice that were: (i) untreated; (ii) depleted of C3 complement (24 h prior to MTT) using cobra venom factor (CVF); and/or (iii) deficient in C5 compleme nt. Quantification of surviving male donor myoblast DNA was performed using the Y-chromosome specific (Y1) probe on slot blots for samples taken at 0 h, 1 h, 24 h, 1 week and 3 weeks after MTT. Peripheral depletion of C3 was confirmed using double immunodiffusion, and local depletion of C3 in host T A muscles was confirmed by immunostaining of muscle samples. Cobra venom fa ctor treatment significantly increased the initial survival of donor myobla sts, but there was a marked decline in myoblast numbers after Ih and little long-term benefit by 3 weeks. Strain specific variation in the immediate s urvival of donor male myoblasts following MTT in untreated C57BL/10Sn, DBA- 1 and DBA-2 (CS-deficient) female hosts was observed. Cobra venom factor de pletion of C3 increased initial donor male myoblast survival (approximately twofold at 0 h) in C57BL/10Sn and DBA-1 host mice and approximately threef old in DBA-2 hosts at 0 h and 1 h after MTT The rapid and extensive number (approximately 90%) of donor male myoblasts in untreated DBA-2 mice (that l ack C5) indicates that activation of the membrane attack complex (MAC) play s no role in this massive initial cell death. The observation that myoblast survival was increased in all mice treated with CVF suggests that CVF may indirectly enhance donor myoblast survival by a mechanism possibly involvin g activated C3 fragments.