Reply - Infect and Regenerate
The infect keyword reads “this card deals damage as -1/-1 counters”… So could you regenerate infect damage to stop the counters being put on a creature?
119.3. Damage may have one or more of the following results, depending on whether the recipient of the damage is a player or permanent, the characteristics of the damage’s source, and the characteristics of the damage’s recipient (if it’s a permanent).
119.3d Damage dealt to a creature by a source with wither and/or infect causes that many -1/-1 counters to be put on that creature.
119.3e Damage dealt to a creature by a source with neither wither nor infect causes that much damage to be marked on that creature.
702.88c Damage dealt to a creature by a source with infect isn’t marked on that creature. Rather, it causes that many -1/-1 counters to be put on that creature. See rule 119.3.
In summary, damage is not marked by creatures with Infect or Wither. So this kind of damage can’t be removed (and thus, regenerated).