Restoration of the American Chestnut has been a project for decades. It started almost immediately after the chestnut blight destroyed one of the most valuable trees on the continent and has continued ever since with some success in the recent past. There have been several different ways attempted to achieve a blight resistant chestnut tree.
1) Chinese- American crosses have some blight resistant but depending on the level of Chinese genetics may not have the characteristics of the American chestnut. We now have crosses that are very close to 100% American chestnut but still have a little bit of Chinese in them.
2) Some native American chestnuts have demonstrated differing levels of blight resistance. Those have been bred with a brute force approach- plant as many trees as you can, wait until they are sapling size and innoculate them with blight spores. Those that survive become the next generation. This is the longest running program but is hampered because even trees with little resistance will often live 5-10 years before succumbing to the blight. That means this is a very slow process.
3) A more recent development has been attempting to identify blight resistance in the DNA and either insert those genes chestnut to chestnut or insert genes from other trees into the chestnut. This has great promise but again, because of the time involved to determine survival hasn't yet yielded proven results.
I recently received 8 seedlings which are from native stock without crossing or genetic modification. I planted yesterday in two rows of four trees- 20' between the rows and 10' between the trees in the row. If all goes well, they will survive long enough to yield honest to goodness American chestnuts. The person working with breeding the trees said they MIGHT survive 15-30 years. If they make it 15, I will be very, very happy. If they make it 30, I might not be around to know it but in any case, it will be an interesting experiment. With ash trees now on the decline, it would be awesome of the true American chestnut could once again be a viable tree.