In theory, all somatic cells can be reprogrammed. Usually one would choose a cell source that is easier to obtain and expandable so that you can obtain a large number of starting cells. Fibroblasts fit both criteria and have been widely used. As a result, there are many papers and protocols available for reprogramming fibroblasts. Blood cells are also increasing in popularity, because blood draw is usually a routine procedure, and there are many reagents available for enrichment and expansion of hematopoietic cell types.