Abstract: The present application provides methods of treating a disease, such as Pompe disease, in a subject, comprising detecting an erythropoiesis biomarker in a sample of the subject after administration of methotrexate and a therapeutic agent to the subject, and administering further treatment with or without concurrently administering additional immune tolerance induction or immunosuppression therapy based on the level of the erythropoiesis biomarker. Further provided by the present application are methods and kits for assessing the level of immune tolerance to a therapeutic agent in a subject based on detection of an erythropoiesis biomarker after administration of methotrexate and the therapeutic agent to the subject.