NorthWest Biotherapeutics Inc (NWBO)

[TheFollower]

If your account is a Roth IRA, generally it's tax free.
http://www.investopedia.com/articles/retirement/03/030403.asp

If it's a normal brokerage it's taxed at Capital Gains rates:
http://en.wikipedia.org/wiki/Capital_gains_tax_in_the_United_States

As for a 401K or similar, it's taxed as income. When you eventually make withdrawals from a traditional defined contribution plan, you'll have to pay regular income taxes on the money you withdraw - whether the money came from your contributions, dividends or capital gains.

So you see, there's a difference in where you are holding your shares, should there be a significant profit.