The present invention provides methods and compositions for treating a cancer, methods for increasing an immune response against a tumor, methods for treating an autoimmune disease, and methods for decreasing an inflammation response in a subject in need thereof by modulating the expression and/or activity of Siglec 15 and/or its binding ligands.本發明係針對有其需要之個體,經由調節Siglec 15及/或其結合配體之表現及/或活性,而提供用於治療癌症之方法與組成物、用於增強對抗腫瘤之免疫反應之方法、用於治療自體免疫疾病之方法、及用於降低發炎反應之方法。