I second jorats. Neuter helped my aggressive ones.
How old is your boy? Do you have other rats? Is he alone, or in a group? Can you remove him from the cage, and see if he still bites, or lunges? What does he look like before he bites you? Make sure you wash your hands with unscented soap before trying to handle him. Also if you have handled other rats, or animals, maybe try changing your shirt, and washing any parts of your arms or hands that have come in contact with them before approaching him. There are lots of other good tips on
www.joinrats.com to help with socialization. Most importantly, DON'T give up on him! There are ways to turn around the biters. I've had my fair share of them, and it's not fun, but very rewarding when you see progress with them.
As for the bites, make sure to always wash them with antibacterial soap, and warm water, put neosporin on them, and take some ibuprofen to help with swelling.