Supplementary Figure S1. Gal-1 antibodies were identified in the posttreatment plasma samples from melanoma patients on Ipi-Bev and pembrolizumab treatment. Supplementary Figure S2. Gal-1 antibody titers in pretreatment and posttreatment plasma samples from melanoma patients receiving ipilimumab and PD-1 blockade. Supplementary Figure S3. Longitudinal analyses of Gal-1 antibody responses to Ipi-Bev in metastatic melanoma patients. Supplementary Figure S4. Purification of recombinant human Gal-1 with His, biotinylated Avi, and SUMO tags at the N terminus (HAS-Gal-1). Supplementary Figure S5. Enrichment of Gal-1 antibodies from patient plasma. Supplementary Figure S6. Binding of Gal-1 to CD45. Supplementary Figure S7. Immunohistochemistry of Gal-1 expression in pretreatment and posttreatment tumor biopsies of patients on Ipi-Bev therapy. Supplementary Figure S8. Kaplan-Meier survival curves of patients based on pretreatment circulating Gal-1 levels. Supplementary Figure S9. Kaplan-Meier survival curves of patients based on circulating Gal-1 fold changes as a result of ipilimumab treatment.