Many tumor-associated antigens are derived from nonmutated “self” proteins. T cells infiltrating tumor deposits recognize self-antigens presented by tumor cells and can be expanded in vivo with vaccination. These T cells exist in a functionally tolerant state, as they rarely result in tumor eradication. We found that tumor growth and lethality were unchanged in mice even after adoptive transfer of large numbers of T cells specific for an MHC class I–restricted epitope of the self/tumor antigen gp100. We sought to develop new strategies that would reverse the functionally tolerant state of self/tumor antigen-reactive T cells and enable the destruction of large (with products of perpendicular diameters of >50 mm2), subcutaneous, unmanipulated, poorly immunogenic B16 tumors that were established for up to 14 d before the start of treatment. We have defined three elements that are all strictly necessary to induce tumor regression in this model: (a) adoptive transfer of tumor-specific T cells; (b) T cell stimulation through antigen-specific vaccination with an altered peptide ligand, rather than the native self-peptide; and (c) coadministration of a T cell growth and activation factor. Cells, vaccination, or cyto-kine given alone or any two in combination were insufficient to induce tumor destruction. Autoimmune vitiligo was observed in mice cured of their disease. These findings illustrate that adoptive transfer of T cells and IL-2 can augment the function of a cancer vaccine. Furthermore, these data represent the first demonstration of complete cures of large, established, poorly immunogenic, unmanipulated solid tumors using T cells specific for a true self/tumor antigen and form the basis for a new approach to the treatment of patients with cancer.

Depletion of immune elements before adoptive cell transfer (ACT) can dramatically improve the antitumor efficacy of transferred CD8+ T cells, but the specific mechanisms that contribute to this enhanced immunity remain poorly defined. Elimination of CD4+CD25+ regulatory T (T reg) cells has been proposed as a key mechanism by which lymphodepletion augments ACT-based immunotherapy. We found that even in the genetic absence of T reg cells, a nonmyeloablative regimen substantially augmented CD8+ T cell reactivity to self-tissue and tumor. Surprisingly, enhanced antitumor efficacy and autoimmunity was caused by increased function rather than increased numbers of tumor-reactive T cells, as would be expected by homeostatic mechanisms. The γ C cytokines IL-7 and IL-15 were required for augmenting T cell functionality and antitumor activity. Removal of γ C cytokine–responsive endogenous cells using antibody or genetic means resulted in the enhanced antitumor responses similar to those seen after nonmyeloablative conditioning. These data indicate that lymphodepletion removes endogenous cellular elements that act as sinks for cytokines that are capable of augmenting the activity of self/tumor-reactive CD8+ T cells. Thus, the restricted availability of homeostatic cytokines can be a contributing factor to peripheral tolerance, as well as a limiting resource for the effectiveness of tumor-specific T cells.

Central memory CD8 ؉ T cells (TCM) and effector memory CD8

IntroductionThe role of CD4 ϩ cells in antitumor immunity remains controversial and poorly understood. 1,2 They are known to mediate potent therapeutic effect in the setting of hematopoietic stem cell allotransplantation and donor lymphocyte infusion in hematologic malignancy, 3,4 but antigen-specific T helper (Th) cells have been studied to much lesser extent. A lack of clarity regarding CD4 ϩ cells is due, in no small part, to the complexity of their biology. CD4 ϩ T cells can differentiate into diverse subsets with specific phenotypes that can have self-reinforcing and opposing functions, but these T-cell subsets have not been comprehensively studied in tumor-bearing mice.Historically, CD4 ϩ T lymphocytes have been thought of as mere providers of stimuli to help the putatively more important CD8 ϩ effectors, which eliminate cancer by direct cytotoxicity. [5][6][7] There are several studies showing that CD4 ϩ T helper (Th) cells are capable of protecting the host against tumor challenge and even of mediating tumor regression on their own in the setting of either solid or hematopoietic disease. [8][9][10][11][12][13] Furthermore, protection was maintained against MHC class II-negative multiple myeloma model and involved cross-presentation by professional antigenpresenting cells (APCs) and activation of tumoricidal activity mediated by macrophages secreting IFN-␥. 14 A similar IFN-␥-dependent mechanism was involved in the rejection of MHC class II-negative tumor in severe combined immunodeficient (SCID) mice. 15 In some cases, the ability to reject antigen-expressing tumor by specific naive Th cells was thought to be substantially better than the ability of CD8 ϩ cells. 16 Classically, effector CD4 ϩ T cells have been categorized into T helper 1 (Th1) and T helper 2 (Th2) subsets. 17,18 Limited studies indicate that both subtypes elicit antitumor effects, 19-21 but the Th1-polarized cells, secreting IFN-␥ and capable of enhancing activity of cytotoxic CD8 ϩ lymphocytes, have traditionally been regarded as more efficient. [22][23][24][25] However, it is also clear that CD4 ϩ T regulatory cells (T regs ) can efficiently suppress the function of antitumor CD8 ϩ T cells. 5,[26][27][28] Recently, the novel Th17 lineage, generated in the presence of TGF-␤ and IL-6 and expanded under the influence of IL-23, [29][30][31] has been associated with responses against certain infections and implicated in the development of autoimmunity in animal models that had been previously linked to Th1-type responses (experimental autoimmune encephalitis, collagen-induced arthritis). 32,33 They also seem to play an important role in the pathogenesis of graft-versus-host disease (GVHD). 34,35 Th17 cells have been found in various tumors, including mycosis fungoides, Sézary syndrome, and prostate cancer. 36,37 Kryczek et al reported the presence of naturally occurring Th17 cells and T regs in the tumor microenvironment and tumor-draining lymph nodes in both human and mice tumors. 38 Proinflammatory cytokines including IL-17A, IL-6, and I...

Adoptive transfer of large numbers of tumor-reactive CD8+ cytotoxic T lymphocytes (CTLs) expanded and differentiated in vitro has shown promising clinical activity against cancer. However, such protocols are complicated by extensive ex vivo manipulations of tumor-reactive cells and have largely focused on CD8+ CTLs, with much less emphasis on the role and contribution of CD4+ T cells. Using a mouse model of advanced melanoma, we found that transfer of small numbers of naive tumor-reactive CD4+ T cells into lymphopenic recipients induces substantial T cell expansion, differentiation, and regression of large established tumors without the need for in vitro manipulation. Surprisingly, CD4+ T cells developed cytotoxic activity, and tumor rejection was dependent on class II–restricted recognition of tumors by tumor-reactive CD4+ T cells. Furthermore, blockade of the coinhibitory receptor CTL-associated antigen 4 (CTLA-4) on the transferred CD4+ T cells resulted in greater expansion of effector T cells, diminished accumulation of tumor-reactive regulatory T cells, and superior antitumor activity capable of inducing regression of spontaneous mouse melanoma. These findings suggest a novel potential therapeutic role for cytotoxic CD4+ T cells and CTLA-4 blockade in cancer immunotherapy, and demonstrate the potential advantages of differentiating tumor-reactive CD4+ cells in vivo over current protocols favoring in vitro expansion and differentiation.

CD4+ T cells control the effector function, memory, and maintenance of CD8+ T cells. Paradoxically, we found that absence of CD4+ T cells enhanced adoptive immunotherapy of cancer when using CD8+ T cells directed against a persisting tumor/self-Ag. However, adoptive transfer of CD4+CD25− Th cells (Th cells) with tumor/self-reactive CD8+ T cells and vaccination into CD4+ T cell-deficient hosts induced autoimmunity and regression of established melanoma. Transfer of CD4+ T cells that contained a mixture of Th and CD4+CD25+ T regulatory cells (Treg cells) or Treg cells alone prevented effective adoptive immunotherapy. Maintenance of CD8+ T cell numbers and function was dependent on Th cells that were capable of IL-2 production because therapy failed when Th cells were derived from IL-2−/− mice. These findings reveal that Th cells can help break tolerance to a persisting self-Ag and treat established tumors through an IL-2-dependent mechanism, but requires simultaneous absence of naturally occurring Treg cells to be effective.

Th17 cells have been described as short-lived but this view is at odds with their capacity to trigger protracted damage to normal and transformed tissues. We report that Th17 cells, despite displaying low expression of CD27 and other phenotypic markers of terminal differentiation, efficiently eradicated tumors and caused autoimmunity, were long-lived and maintained a core molecular signature resembling early memory CD8+ cells with stem cell-like properties. In addition, we found that Th17 cells had high expression of Tcf7, a direct target of the Wnt and β-catenin signaling axis, and accumulated β-catenin, a feature observed in stem cells. In vivo, Th17 cells gave rise to Th1-like effector cell progeny and also self-renewed and persisted as IL-17A-secreting cells. Multipotency was required for Th17 cell-mediated tumor eradication because effector cells deficient in IFN-γ or IL-17A had impaired activity. Thus, Th17 cells are not always short-lived and are a less-differentiated subset capable of superior persistence and functionality.

In vitro differentiated CD8+ T cells have been the primary focus of immunotherapy of cancer with little focus on CD4+ T cells. Immunotherapy involving in vitro differentiated T cells given after lymphodepleting regimens significantly augments antitumor immunity in animals and human patients with cancer. However, the mechanisms by which lymphopenia augments adoptive cell therapy and the means of properly differentiating T cells in vitro are still emerging. We demonstrate that naive tumor/self-specific CD4+ T cells naturally differentiated into T helper type 1 cytotoxic T cells in vivo and caused the regression of established tumors and depigmentation in lymphopenic hosts. Therapy was independent of vaccination, exogenous cytokine support, CD8+, B, natural killer (NK), and NKT cells. Proper activation of CD4+ T cells in vivo was important for tumor clearance, as naive tumor-specific CD4+ T cells could not completely treat tumor in lymphopenic common gamma chain (γc)–deficient hosts. γc signaling in the tumor-bearing host was important for survival and proper differentiation of adoptively transferred tumor-specific CD4+ T cells. Thus, these data provide a platform for designing immunotherapies that incorporate tumor/self-reactive CD4+ T cells.