Adoptive transfer of tumor-primed, in vitro–activated, CD4+ T effector cells (TEs) combined with CD8+ TEs provides intratumoral TE proliferation and synergistic antitumor response

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Abstract
The importance of CD4+ Th1 cells during the effector phase of the antitumor response has been overshadowed by emphasis on CD8+ cytotoxic T lymphocytes (CTLs). To determine their respective functions, we purified antigen-primed T cells from tumor-draining lymph nodes and separately activated CD4+ and CD8+ subsets in vitro. Adoptive transfer of CD4+ T effector cells (TEs) combined with CD8+ TEs provided synergistic therapy for mice bearing subcutaneous, intracranial, or advanced pulmonary metastases. CD4+ TEs augmented IFN-γ production by CD8+ TEs when cells were stimulated by tumor digest–containing antigen-presenting cells (APCs). CD4+ TEs infiltrated and proliferated extensively in pulmonary tumors, while also stimulating tumor antigen–specific CD8+ T cells. By contrast, CD8+ TEs showed minimal intratumoral proliferation in the absence of CD4+ cells or when systemically transferred CD4+ cells were prevented from infiltrating pulmonary tumors by pretreatment with pertussis toxin. Irradiation of CD4+ T cells immediately prior to adoptive transfer abrogated their intratumoral proliferation and direct antitumor efficacy but did not block their capacity to stimulate intratumoral CD8+ TE proliferation or tumor regression. These results highlight the importance of cross-presentation of tumor antigens during the effector phase of immunotherapy and suggest that approaches to stimulate CD4+ TE function and boost APC cross-presentation within tumors will augment cancer immunotherapy.