Hmmm, full answer is proving more difficult to research than I'd anticipated. Let me know if this is on track...
Early Yervoy dose finding studies seem to have determined that schedule of 4 doses vs. continuous dosing produced as good efficacy and with less risk for development of toxicities over time. Hence, Yervoy monotherapy dosing is for 4 doses, and basically all CTLA-4 development seemed to follow suit over the years.
Until recently, that is. As you point out, looks like BMS is using continuous dosing for CheckMate 227. However, they also have reduced dose amount for Yervoy substantially. Approved dose in melanoma is 3 mg/kg every 3 weeks, but for 227 they're using 1 mg/kg every 6 weeks. The idea is that combo is better tolerated with lower, less frequent dose, allowing for more drug exposure and better efficacy (already borne out with ORR in Phase 1 study, BMS is really hoping it's borne out with PFS & OS in 227).
AZN hasn't done the same dose-ranging work with durvalumab + tremelimumab combination, so they've stuck with the "traditional" 4 doses for CTLA-4. I think they're doing every 4 weeks, though, so still somewhat less frequent than the normal every 3 weeks. Outside of NSCLC, all the CTLA-4 combo studies I'm aware (for BMY and AZN) are still using 4 doses.
Not aware of any differences in the antibodies themselves that would allow continuous dosing for Yervoy but not for treme...
