A heterobifunctional compound for use in a method of treating an adverse immune response in a human caused by an activated immune effector cell that expresses a chimeric antigen receptor polypeptide; wherein the subject has previously been administered the immune effector cell expressing the chimeric antigen receptor polypeptide; wherein the chimeric antigen receptor polypeptide comprises: i. an extracellular ligand binding protein; ii. a transmembrane protein; iii. a cytoplasmic protein comprising at least one intracellular signaling protein; and, iv. a heterobifunctional compound targeting protein capable of being bound by the heterobifunctional compound, wherein the heterobifunctional compound targeting protein is selected from the group consisting of SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, and SEQ ID NO: 9; the method comprising administering to the human the heterobifunctional compound; wherein the heterobifunctional compound binds to i) the chimeric antigen receptor polypeptide through the heterobifunctional compound targeting protein and ii) a ubiquitin ligase in a manner that brings the chimeric antigen receptor polypeptide into proximity of the ubiquitin ligase; and wherein the chimeric antigen receptor polypeptide, when bound by the heterobifunctional compound, is ubiquitinated and then degraded by a proteasome, provided that when the heterobifunctional targeting protein is SEQ ID NO: 1,-the heterobifunctional compound is selected from: and and when the heterobifunctional targeting protein is SEQ ID NO: 2, the heterobifunctional compound is selected from: and and when the heterobifunctional targeting protein is SEQ ID NO: 3, the heterobifunctional compound is selected from: and; and when the heterobifunctional targeting protein is SEQ ID NO: 9, the heterobifunctional compound is selected from: wherein the subject has previously been administered the immune effector cell expressing the chimeric antigen receptor polypeptide; wherein the chimeric antigen receptor polypeptide comprises: i. an extracellular ligand binding protein; ii. a transmembrane protein; iii. a cytoplasmic protein comprising at least one intracellular signaling protein; and, iv. a heterobifunctional compound targeting protein capable of being bound by the heterobifunctional compound, wherein the heterobifunctional compound targeting protein is selected from the group consisting of SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, and SEQ ID NO: 9; i. an extracellular ligand binding protein; ii. a transmembrane protein; iii. a cytoplasmic protein comprising at least one intracellular signaling protein; and, iv. a heterobifunctional compound targeting protein capable of being bound by the heterobifunctional compound, wherein the heterobifunctional compound targeting protein is selected from the group consisting of SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, and SEQ ID NO: 9; the method comprising administering to the human the heterobifunctional compound; wherein the heterobifunctional compound binds to i) the chimeric antigen receptor polypeptide through the heterobifunctional compound targeting protein and ii) a ubiquitin ligase in a manner that brings the chimeric antigen receptor polypeptide into proximity of the ubiquitin ligase; and wherein the chimeric antigen receptor polypeptide, when bound by the heterobifunctional compound, is ubiquitinated and then degraded by a proteasome, provided that when the heterobifunctional targeting protein is SEQ ID NO: 1,-the heterobifunctional compound is selected from: and and when the heterobifunctional targeting protein is SEQ ID NO: 2, the heterobifunctional compound is selected from: and and when the heterobifunctional targeting protein is SEQ ID NO: 3, the heterobifunctional compound is selected from: and; and when the heterobifunctional targeting protein is SEQ ID NO: 9, the heterobifunctional compound is selected from: