The present disclosure provides methods, pharmaceutical compositions, and kits for treating cancer or autoimmune disease in patients in need thereof. The methods comprise administering to a patient in need a small ubiquitin-like modifier (SUMO) activating enzyme (SAE) inhibitor, such as [(1R,2S,4R)-4-{[5-({4-[(1R)-7-chloro-1,2,3,4-tetrahydroisoquinolin-1-yl]-5-methyl-2-thienyl}carbonyl)pyrimidin-4-yl]amino}-2-hydroxy-cyclopentyl]methyl sulfamate (Compound I-263a) or a pharmaceutically acceptable salt, in combination with one or more anti-CD20 antibodies. Also provided are medicaments for use in treating cancer or autoimmune disease.