15 Antony PA, Piccirillo CA, Akpinarli A, et al. Cd8+ T cell immunity against a tumor/self- antigen is augmented by CD4+ T helper cells and hindered by naturally occurring T regulatory cells. J Immunol 2005;174:2591–601. 16 Janssen EM, Lemmens EE, Wolfe T, et al. CD4+ T cells are required for secondary expansion and memory in CD8+ T lymphocytes. Nature 2003;421:852–6.