The two dead twins however, were found to express the green fluorescent protein. The first question to be raised is why the experiment was done at all. The researchers try to justify it as a model for human gene therapy and as a test for vaccines. At the beginning of the paper, they also give the impression that they were trying to create transgenic primates because primates were closer to humans and therefore better than transgenic mice models. All of these reasons are ethically unacceptable in terms of animal suffering.
Many people also regard the experiment as a slippery slope to germline human gene therapy.
The second question is why the success rate is still so low. The retroviral method would seem to circumvent all the problems of damaging the embryo by injecting directly into the egg. So the problems must be associated with the transgenic process itself. Another reason for the low survival rate may be the vector itself, which raises safety concerns. Chan AWS, Chong KY, Martinovich C, Simerly C and Schatten G. Transgenic monkeys produced by retroviral gene transfer into mature oocytes.