I may be a little off on some of the details there, but that's the main idea lol

The super soldier syrum... The 2 compounds clash to the degree that they combine and create a super virus. One that has the horrible appearance of a second plague, but is actually life preserving in nature due to the syrum. It spreads to certain heroes before an antibody is found to destroy it. Those who already have it though can not be rid of its effects; and their lives are prolonged many times over. Many years later it is discovered that the aliens were never truly repelled, and the began their second wave of attacks. Now again nearly 60 years down the road, nearly all non-infected beings have died off, and the world is over-run by the aliens. At this point Tony Stark is more machine than man, and after an attack during a cloning attempt left him on the brink of death, Tony was forced to wire himself permanently into his Heavy Duty suite. With his resources for advanced technologies gone he has been forced to improvise, thus the gathered item armor...

Haha, yeah it probably would be, sorry about that. Well it's not my setting but I think I remember enough to get the idea across. So some point in the near future an alien race comes into the marvel universe, they are repelled by a great many heroes but leave behind them a virus not known to our world. The virus appears first in Captain Steve Rogers, spreading through his arm from a cut with dangerous speed and having the appearance of another plague. The Captain cuts off his own arm in an attempt to stop the spread of the alien vieus to his beloved world, but alas it has already spread into his bloodstream. The virus tries to shut down his organs but is unable to get around...

Maybe some sort of back story would be helpful?