T cells (CD8+ / CD4+)

T cells are the white blood cells central to neoantigen vaccines. CD8+ cytotoxic (“killer”) T cells recognize peptides on MHC class I and kill the cell presenting them — the desired anti-tumor effect. CD4+ helper T cells recognize MHC class II and orchestrate and sustain the broader response.

A vaccine succeeds when it expands a population of T cells specific for the tumor's neoantigens. Measuring that T-cell response is a key readout in early clinical trials.