Some think the swelling and inflamation of lesions with IPI is caused by the killer T-cells invading the lesion(s), which is what you want, however, I’m not familiar with any study which says that’s indeed the case.
There are also other things you can look for as signs your immune system is responding to the IPI. When I say responding, I mean the IPI “down regulates”(techno-babble for putting the brakes on) a portion of your immune system which helps keep the number of killer T-cells in check. This allows those T-cell to expand in number and proliferate in your system. However, too many killer T-cells and you run the risk of them turning on healthy cells, which is why they are watching you like a hawk for certain symptoms.
One sign is the Absolute Lymphocyte Count (ALC). It is usually quoted in your blood testing. Look for an increasing trend from say ~900-1000 to north of 1700 or so over the course of the four IPI infusions. This would indicate a proliferation of killer T-cells in your body.
Also look for subjective changes in your hair color (head and eyebrow in particular), specifically a lighter shade or bleaching and you may notice white patches developing on your skin.
And as you’ve found out, digestive problems and itching, rashes, fatigue to name some others.
So if you see or have some of these effects, it’s a good bet the IPI is at least doing its job in putting the brakes on a portion of your immune system.
Hope this helps.