What does the 'in vitro' gene therapy technique involve?

The 'in vitro' gene therapy technique involves removing tissues from a patient, altering the genes in those tissues using vectors, and then returning the modified tissues to the patient. This method leverages the ability to make precise genetic modifications outside of the body (in a controlled laboratory environment) before reintroducing the corrected cells or tissues back into the patient.

This approach allows for targeted and specific alterations to genetic material, which can be crucial in addressing genetic disorders at the cellular level. By handling the tissues outside the body, healthcare professionals can ensure that the changes made to the genes are accurate and effective before re-implantation, minimizing potential complications.

In contrast, other methods listed in the options may involve different processes altogether, such as directly injecting genes into the bloodstream, which typically falls under 'in vivo' therapy, or using viruses for delivery, which can occur in both in vivo and in vitro contexts but does not focus on the tissue alteration element as described in the correct answer.