A method for diagnosing or treating a mammalian subject having, or at risk of developing cancer, comprising: generating a circulating anti-cancer CD4+ Th1 response from antigen presenting cells or their precursors and CD4+ T-cells from a sample of said subject's blood which causes secretion of interferon-gamma (“IFN-γ”)； and detecting said anti-cancer CD4+ Th1 response to determine if said response is depressed. A method for restoring HER2-specific CD4+ Th1 immune response in a HER2-positive breast cancer patient in need thereof, comprising: administering to said patient a therapeutically effective amount of a dendritic cell (“DC”) vaccine comprising autologous DCs pulsed with HER2-derived MHC class II binding peptides (“DC vaccination”) to elevate said patient's anti-HER2 CD4+ Th1 response, and measuring said anti-HER2 Th1 response of said patient pre- and post-DC vaccination to determine the amount of increase in said response.
