CD274 and skin basal cell carcinoma: discovered that the majority of post‐treatment exhausted (84%) and expanded (68%) T cells have novel TCR clonotypes absent from pre‐treatment samples.[35] Similarly, post‐treatment T cell clones are predominantly composed of novel T cell clonotypes in two cohorts of BCC patients.[39] In some patients, the ratio of novel clonotypes to re‐emerged clonotypes reaches ≈90% and novel TEX clones account for ≈99% of total TEX clones.[39] The emergence of novel TCR clonotypes during PD‐1/PD‐L1 blockade is termed “clonal replacement” (Figure 3B, left panel).