Look for vitamin E that says d-alpha tocopherol, not dl-alpha.
The spleen and liver enlarge because there is a high turnover of red blood cells, RBC's. The defective RBC's produced because of the defective beta globin genes are filtered out by these organs, causing them to enlarge. RBC's are even manufactured in these organs, causing further enlargement.
The best thing you can do is provide the proper nutrients to help build RBC's, but even with this, defective RBC's will still be produced.