The most tumors express mutant epitopes that could be detected by T cells. According to current paradigm, CD4+ T cells provides help to CD8+ T cells that in turn attack tumors. As tumor cells ordinarily express class I recognized by CD8+ T cells but not class II molecules recognized by CD4+ T cells, primary focus on CD8+ T cell epitopes made a lot of sense. But what about CD4+ T cell 'help' to CD8 T cells?
Indeed, a new 'classically-done' immunology study from Robert Schreiber's lab clearly showed that irrespective class II expression, tumor cells must express both CD8+ and CD4+ T cell neo-epitopes to achieve efficient local tumor control following immunotherapy.
As a starting point, they used nonimmunogenic oncogene-driven KP9025 sarcoma cells (KP), which lack mutational neoantigens. Next they re-expressed in KP cells 2 mutant epitopes, one for class I, mLAMA4, and another for class II, mITGB1 (identified using a hidden Markov model (HMM)-based MHC binding predictor the authors claim is better than other available algorithms).
A mutant but not wild-type version of ITGB1 was detected by CD4+ TILs.
Next, the authors showed that only KP tumors expressing both neo-epitopes but not single expressors, could be eliminated by T cells following immunotherapy.
As expected, presence of CD4+ T cell epitope enhanced CD8+ T cell response.
Interestingly, both class I and II neo-epitopes must be expressed by the same tumor to mediate protection when used as immunized agents (mixing of single expressor tumors was not enough).
And notably, expression of both class I and II neo-epitopes were necessary to mediate efficient local tumor control (single expressor tumors were resistant against CD8+ or CD4+ T cells)
In summary, this is a simple, easy to follow experments that indicate the authors' thought process. It shows that CD4+ T cells 'help' to CD8+ T cells are required both at priming and as well as at effector stage. It is not clear if it is simply a quantitative or rather qualitative issue. It is not known either whether CD4+ T cells do something directly against tumor beyond simply helping CD8+ T cells here.
posted by David Usharauli
