Indeed, our previous work38,45 demonstrated that Th1 cells typically comprise a median of 22% (between 10% and 30%) of the CD4+ T-cell response to other immunization regimens, including a human adenovirus 5 (Ad5)-based vaccine vector and a replication-competent mouse cytomegalovirus (mCMV)-based vector (both expressing F-MLV gp70), FV-induced FBL-3 leukemia cells expressing F-MLV gp70, and env122–141 peptide immunization in the Sigma Adjuvant System. Here, CD4 is linked to leukemia.