To verify the effect of l-serine on the efficacy of anti-PD1 immunotherapy, we also downloaded RNA-seq data (GSE 91061) for clinical anti-PD1-treated melanoma patients from the Gene Expression Omnibus (GEO) database, which showed that the expression of PHGDH and PSPH was significantly lower in patients who achieved a PR or CR in response to anti-PD1 treatment than in drug-resistant patients with PD (Fig. 7A and B). The gene discussed is PSPH; the disease is melanoma.