Tumor-specific CD4+ T lymphocytes from cancer patients are required for optimal induction of cytotoxic T cells against the autologous tumor

This study focuses on the specific CD4(+) T cell requirement for optimal induction of cytotoxicity against MHC class II negative autologous tumors (AuTu) collected from patients with various types of cancer at advanced stages. CD4(+) T cells were induced in cultures of cancer patients' malignant effusion-associated mononuclear cells with irradiated AuTu (mixed lymphocyte tumor cultures (MLTC)) in the presence of recombinant IL-2 and recombinant IL-7, Tumor-specific CD4(+) T cells did not directly recognize the AuTu cells, but there was an MHC class II-restricted cross-priming by autologous dendritic cells (DCs), used as APC, CD8(+) CTL, also induced during the MLTC, lysed specifically AuTu cells or DCs pulsed with AuTu peptide extracts (acid wash extracts (AWE)) in an MHC class I-restricted manner. Removal of CD4(+) T cells or DCs from the MLTC drastically reduced the CD8(+) CTL-mediated cytotoxic response against the AuTu. AWE-pulsed DCs preincubated with autologous CD4(+) T cells were able, in the absence of CD4(+) T cells, to stimulate CD8(+) T cells to lyse autologous tumor targets. Such activated CD8(+) T cells produced IL-2, IFN-gamma, TNF-alpha, and GM-CSF, The process of the activation of AWE-pulsed DCs by CD4(+) T cells could be inhibited with anti-CD40 ligand mAb, Moreover, the role of CD4(+) T cells in activating AWE-pulsed DCs was undertaken by anti-CD40 mAb, Our data demonstrate for the first time in patients with metastatic cancer the essential role of CD4+ Th cell-activated DCs for optimal CD8(+) T cell-mediated killing of autologous tumors and provide the basis for the design of novel protocols in cellular adoptive immunotherapy of cancer, utilizing synthetic peptides capable of inducing T cell help in vivo.