As I’ve noted several times before, regulatory T cells are important reasons for the poor immune response to tumors. TRegs are normal components of an immune response, “designed” to keep inflammation from running riot in general and to prevent responses to self-antigens in particular. Whether it’s because tumors are mostly (though not solely) self antigens, because tumors are chronic sources of stimulation that could lead to inflammation running riot, or because tumors “learn” how to specifically trigger TReg-like responses, TRegs are common features of tumors.
Eliminating TRegs, in mouse models of cancer, often allows a strong immune response to the tumor. An interesting spin on this was shown in a recent J Immunol paper.1 It seems that the TRegs don’t generally suppress all the response, they shut down the responses to some targets harder than others:
Our results indicate, therefore, that depletion of Tregs uncovers cryptic responses to Ags that are shared among different tumor cell lines. CT26-specific T cell responses can be elicited by different forms of vaccination in the presence of regulatory cells, but in these cases T cell responses are highly focused on a single tumor-specific epitope …Taken together, these data suggest that immune responses to some Ags are more tightly regulated than others. 1
In other words, even though you might be able to force a protective immune response to a tumor by vaccinating in the presence of TRegs, when you get rid of TRegs the response is broader, and targets T cell epitopes that otherwise wouldn’t look like they’re epitopes at all.
I wonder if this goes on with “normal” (say, viral or other non-tumor) epitopes – whether this sort of thing might help explain some forms of immunodominance. I kind of doubt it, but the phenomenon does sounds a little like revealing a subdominant response.
I wonder also how this ties in with a recent paper that suggested TRegs in tumors are highly focused on a small subset of tumor epitopes. Could they be more broadly-based, but on epitopes that are otherwise invisible? Again, I kind of doubt it, but it’s an intriguing idea. Maybe the universe of tumor epitopes available for attack is much larger than we realize.