This work was done in a massive collaboration with many talented people and amazing labs, as well as top pathologists- be sure to note them. All conducted under the unparalleled mentorship of Leonard Zon at @bostonchildrens.bsky.social.
As a great fish once said- Just keep swimming!

Want to learn more? Dive into the details right here (open access): www.cell.com/cell/fulltex...
Keep scrolling for the last but not least!

Conclusions: We get a glimpse into the tumor black box. We see what an efficient anti-tumor immune response looks like. Which means we may: 1. Be able to tell if a treatment works or not, if we measure them. 2. Make treatments more efficient, if we find how to expand CRATERs.

Yes. Not only do they exist in great similarity to the zebrafish, CRATERs multiply during successful immunotherapy- when the patient presented clinical benefit post treatment. But there are extremely few CRATERs when treatment failed, even if the T cells entered the tumor.

It is in the CRATERs that we find multiple, lasting interactions of CD8+ T cells and melanoma, cell death, IFN-γ production. A battlefield. Indicating that the CRATERs are a major site for tumor killing following immunotherapy. Now the big question is- in human melanoma too?

Without treatment, CD8+ T cells don't harm tumors too much. But immunotherapy is aimed at activating CD8+ T cells against tumors. When we give immunotherapy these pockets–CRATERs; Cancer Regions of Antigen presentation and T cell engagement and Retention- come alive.

This behavior is characteristic of antigen recognition. Indeed, those pockets are rich with antigen presenting molecules, needed for the observed T cell retention. Simply put, the melanoma in those pockets shines bright to the T cells. And it has consequences during therapy.

And we found that infiltrating CD8+ T cells don’t just randomly distribute across the tumor. They go into pockets. But they are not stuck there (as we would have thought if it wasn’t a movie). They stay there for many hours interacting with melanoma cells and then move on. How come?

The unique angle in our study was that we were able to “film”, by time lapse imaging, a day (~24 hours) in the life of CD8+ T cells in intact melanomas of live, anesthetized fish (Is it the only reality show I’ve ever watched? 🤔).

That’s a bit ambitious- how to see what is going on within the tumor? You could cut it and stain it, but even with the most sophisticated methods, you will lose a lot of information on tumor architecture and cellular dynamics.
Well, the zebrafish gave us a little advantage here.

Immunotherapy may fail to create an efficient anti-tumor immune response. Even when CD8+ T cells do infiltrate the tumor. The approach we took was to look closely at CD8+ T cells behavior within melanoma tumor, to understand how to recognize an efficient anti-immune response.

What’s it about? You can activate CD8+ T cells against tumors and get them to kill it. This notion was developed into immunotherapy and has saved many lives to date (and won a Nobel prize). But it doesn’t always work.