The major difference between gene and cell therapy is the way they used to delivered the content to the patients. In cell therapy the whole/intact cells used to transfer which contains the medicine or other related material to relieve the patients from the disease burden. This can achieve either translating the damaged area by replacing with the new cells either through the draft, injection or by implantation. However, presently in most of the cell therapies the cells which has been using they are from the patients body's own (autologous).
On the other hand, the gene therapy concept of use is slightly different but the motivation is the same which is to heal the damaged area or cells. But here the complete cells doesn't transplant or transfer, instead the genetic content like DNA which also know as the gene replace or transfer inside the body to treat the diseases like autoimmune diseases or genetic disorders.
The basic difference is in cell therapy whole cells are used for the replacement and diseases treatment but in gene therapy the genetic material of the cells.