Merck was working on STING and cGAS a few years ago - both agonists/antagonists of each. they were advanced projects, meaning they had chemical compounds in hand sufficient to justify the time and cost of testing them in cellular experiments. This Roche deal will certainly get their attention.
I'm pretty sure the primary effector cells in most patients able to induce an immune response in anti-PD1/L1 therapies are innate lymphocytes and other cell types - not T cells. Conversely, those patients enjoying several years in complete remission may be the ones that mounted a T cell response to the tumor/cancer - but these are relatively few. Fact is, most tumors are not sufficiently immunogenic to generate a T cell response but innate immunity may be induced to recognize an abnormal growth...