How do you know that you have immune cell infiltration?

double check with Sean that we can talk about CD3/CD28 publicly At the end of the assay, we add a third treatment phase using CD3/CD28 as a positive control to drive maximal T-cell activation, which forces immune cells into producing interferon gamma that we measure. We see that production in a large fraction of samples, even when they don't respond to ICI. This control is especially useful for interpreting non-responsive specimens, since it helps distinguish between two very different biological reasons for non-response. In some non-responding specimens, CD3/CD28 does drive a clear increase in interferon gamma � that tells us T cells were present, but the checkpoint inhibitor simply couldn't activate them. In others, there's no increase even with the positive control, which suggests either no T cells were present, or they were terminally exhausted. Two specimens that look identical through the first phase of treatment can turn out to be biologically distinct non-responders. When we have viable tissue and tumor content but don't see infiltrating T cells or other immune cells at all, that absence is itself one of the most predictive factors for non-response.