If there is life on that planet, I wonder if it would be similar enough to host infectious diseases. I know the Apollo team was quarantined when they got back from the moon. As someone living on a continent that has undergone one apocalypse, I hope we have a similar procedure to prevent the spread of spacepox.
Seems unlikely that anything would be physically going there and back any time soon. We haven't even been able to get some soil from Mars back to Earth yet.
2) Some types of molecules involved with life have chirality so the chances are small that our biological components as a whole would be compatible. (Think of it as several different kinds of "endianess." There would be a coin-flip for each molecule type with chirality.) So at worst, if we ate each other, we'd give each other molecular "indigestion."
More complicated operations, like that of viruses hijacking our cells to replicate themselves are probably right out. Invading foreign cells couldn't get very far in our bodies if all of their enzymes malfunction and they find our material "indigestible."
