TACTOPS is a suboptimal trial for assessing the therapeutic potential of Multi-TAA + chemo in pancreatic cancer for several reasons:
1) Multi-TAA was started AFTER multiple cycles of chemotherapy. Especially in the case of Folfirinox, where oxaloplatin induces immunogenic cell death, the most chemosensitive cells likely died in the early rounds of chemo and we may have missed the opportunity for maximum immune response to non Multi-TAA antigens
2) Only 6 monthly doses of cells were given. 2 patients on Folfirinox, the best chemo, progressed only after cells were discontinued. No patient in the trial who responded progressed while on cells
3) Only Survivin of the 5 antigens in the mix is expressed in vivo in high concentration on pancreatic cancer.
4) The dose of cells was quite low.
Even with these short comings, there was 1/4 CRs in patients treated with Folfirinox (the best chemo therapy) and cells. 2/4 Folfirinox patients progressed only after cells were discontinued and 1/4 had a mixed response. The expected CR rate to Folfirinox alone is 0.6%. Group A is a select group that responded to Folfirinox (70% do). Therefore the Multi-TAA/Folfirinox response rate is on the order of ~20% after accounting for the selection of responders into group A. 20% vs 0.6% and that's for a sub optimal study testing the impact of Multi-TAA. So is the market logical when it dismisses Multi-TAA for pancreatic cancer? I don't think so. Sure the CR could have occurred by chance, but then you also have to dismiss the epitope/antigen spreading as further evidence that this treatment is working in pancreatic cancer.
I think to get another CR in the remaining patients for group A, which will essentially prove treatment effect, we should select patients responding to Folfirinox. It's likely the combination of a chemosensitive tumor plus Multi-TAA cells that will yield the highest chance of another CR, which is what's need to close the book on the debate over Multi-TAA efficacy in pancreatic cancer IMO.
