Inhibition of TGF-β signaling in genetically engineered tumor antigen-reactive T cells significantly enhances tumor treatment efficacy

Transforming growth factor β (TGF-β) is a cytokine with complex biological functions that may involve tumor promotion or tumor suppression. It has been reported that multiple types of tumors secrete TGF-β, which can inhibit tumor-specific cellular immunity and may represent a major obstacle to the success of tumor immunotherapy. In this study, we sought to enhance tumor immunotherapy using genetically modified antigen-specific T cells by interfering with TGF-β signaling. We constructed three γ-retroviral vectors, one that expressed TGF-β-dominant-negative receptor II (DNRII) or two that secreted soluble TGF-β receptors: soluble TGF-β receptor II (sRII) and the sRII fused with mouse IgG Fc domain (sRIIFc). We demonstrated that T cells genetically modified with these viral vectors were resistant to exogenous TGF-β-induced smad-2 phosphorylation in vitro. The functionality of antigen-specific T cells engineered to resist TGF-β signaling was further evaluated in vivo using the B16 melanoma tumor model. Antigen-specific CD8+ T cells (pmel-1) or CD4+ T cells (tyrosinase-related protein-1) expressing DNRII dramatically improved tumor treatment efficacy. There was no enhancement in the B16 tumor treatment using cells secreting soluble receptors. Our data support the potential application of the blockade of TGF-β signaling in tumor-specific T cells for cancer immunotherapy.

IL-12 triggers a programmatic change in dysfunctional myeloid-derived cells within mouse tumors

Solid tumors are complex masses with a local microenvironment, or stroma, that supports tumor growth and progression. Among the diverse tumor-supporting stromal cells is a heterogeneous population of myeloid-derived cells. These cells are alternatively activated and contribute to the immunosuppressive environment of the tumor; overcoming their immunosuppressive effects may improve the efficacy of cancer immunotherapies. We recently found that engineering tumor-specific CD8(+) T cells to secrete the inflammatory cytokine IL-12 improved their therapeutic efficacy in the B16 mouse model of established melanoma. Here, we report the mechanism underlying this finding. Surprisingly, direct binding of IL-12 to receptors on lymphocytes or NK cells was not required. Instead, IL-12 sensitized bone marrow-derived tumor stromal cells, including CD11b(+)F4/80(hi) macrophages, CD11b(+)MHCII(hi)CD11c(hi) dendritic cells, and CD11b(+)Gr-1(hi) myeloid-derived suppressor cells, causing them to enhance the effects of adoptively transferred CD8(+) T cells. This reprogramming of myeloid-derived cells occurred partly through IFN-γ. Surprisingly, direct presentation of antigen to the transferred CD8(+) T cells by tumor was not necessary; however, MHCI expression on host cells was essential for IL-12-mediated antitumor enhancements. These results are consistent with a model in which IL-12 enhances the ability of CD8(+) T cells to collapse large vascularized tumors by triggering programmatic changes in otherwise suppressive antigen-presenting cells within tumors and support the use of IL-12 as part of immunotherapy for the treatment of solid tumors.

Repression of the DNA-binding inhibitor Id3 by Blimp-1 limits the formation of memory CD8+ T cells

Blimp-1 is a transcriptional repressor that promotes the differentiation of CD8⁺ T cells into short-lived KLRG-1⁺ effector cells (SLEC), but how it operates remains poorly defined. Here we show that Blimp-1 binds and represses the Id3 promoter in SLEC. Repression of Id3 by Blimp-1 was dispensable for SLEC development but limited their capacity to persist as memory cells. Enforced expression of Id3 was sufficient to rescue SLEC survival and enhanced recall responses. Id3 function was mediated in part through inhibition of E2a transcriptional activity and induction of genes regulating genome stability. These findings identify a Blimp-1-Id3-E2a axis as a key molecular switch that determines whether effector CD8⁺ T cells are programmed to die or enter the memory pool.

Determinants of successful CD8+ T-cell adoptive immunotherapy for large established tumors in mice

PURPOSE

Adoptive cell transfer (ACT) of tumor infiltrating or genetically engineered T cells can cause durable responses in patients with metastatic cancer. Multiple clinically modifiable parameters can comprise this therapy, including cell dose and phenotype, in vivo antigen restimulation, and common gamma-chain (γ(c)) cytokine support. However, the relative contributions of each these individual components to the magnitude of the antitumor response have yet to be quantified.

EXPERIMENTAL DESIGN

To systematically and quantitatively appraise each of these variables, we employed the Pmel-1 mouse model treating large, established B16 melanoma tumors. In addition to cell dose and magnitude of in vivo antigen restimulation, we also evaluated the relative efficacy of central memory (T(CM)), effector memory (T(EM)), and stem cell memory (T(SCM)) subsets on the strength of tumor regression as well as the dose and type of clinically available γ(c) cytokines, including IL-2, IL-7, IL-15, and IL-21.

RESULTS

We found that cell dose, T-cell differentiation status, and viral vaccine titer each were correlated strongly and significantly with the magnitude of tumor regression. Surprisingly, although the total number of IL-2 doses was correlated with tumor regression, no significant benefit to prolonged (≥6 doses) administration was observed. Moreover, the specific type and dose of γ(c) cytokine only moderately correlated with response.

CONCLUSION

Collectively, these findings elucidate some of the key determinants of successful ACT immunotherapy for the treatment of cancer in mice and further show that γ(c) cytokines offer a similar ability to effectively drive antitumor T-cell function in vivo.

Tumor-specific CD8+ T cells expressing interleukin-12 eradicate established cancers in lymphodepleted hosts

T-cell-based immunotherapies can be effective in the treatment of large vascularized tumors, but they rely on adoptive transfer of substantial numbers ( approximately 20 million) of tumor-specific T cells administered together with vaccination and high-dose interleukin (IL)-2. In this study, we report that approximately 10,000 T cells gene-engineered to express a single-chain IL-12 molecule can be therapeutically effective against established tumors in the absence of exogenous IL-2 and vaccine. Although IL-12-engineered cells did not perist long-term in hosts, they exhibited enhanced functionality and were detected in higher numbers intratumorally along with increased numbers of endogenous natural killer and CD8(+) T cells just before regression. Importantly, transferred T cells isolated from tumors stably overproduced supraphysiologic amounts of IL-12, and the therapeutic effect of IL-12 produced within the tumor microenvironment could not be mimicked with high doses of exogenously provided IL-12. Furthermore, antitumor effects could be recapitulated by engineering wild-type open-repertoire splenocytes to express both the single-chain IL-12 and a recombinant tumor-specific T-cell receptor (TCR), but only when individual cells expressed both the TCR and IL-12, indicating that arrested migration of T cells at the tumor site was required for their activities. Successful tumor eradication was dependent on a lymphodepleting preconditioning regimen that reduced the number of intratumoral CD4(+) Foxp3(+) T regulatory cells. Our findings reveal an approach to genetically modify T cells to reduce the cell number needed, eliminate the need for vaccines or systemic IL-2, and improve immunotherapy efficacy based on adoptive transfer of gene-engineered T cells.

Naïve tumor-specific CD4+ T cells differentiated in vivo eradicate established melanoma (131.12)

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 naïve tumor/self-specific CD4+ T cells naturally differentiated into T helper type 1 (Th1) 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-, NK and NK-T cells. Proper activation of CD4+ T cells in vivo was important for tumor clearance as naïve tumor-specific CD4+ T cells could not completely treat tumor in lymphopenic common gamma chain deficient (γc-/-) 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.

Tumor-reactive CD4(+) T cells develop cytotoxic activity and eradicate large established melanoma after transfer into lymphopenic hosts

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.

Naive tumor-specific CD4(+) T cells differentiated in vivo eradicate established melanoma

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 (γ_c)–deficient hosts. γ_c 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.

T helper 17 cells promote cytotoxic T cell activation in tumor immunity

Although T helper 17 (Th17) cells have been found in tumor tissues, their function in cancer immunity is unclear. We found that interleukin-17A (IL-17A)-deficient mice were more susceptible to developing lung melanoma. Conversely, adoptive T cell therapy with tumor-specific Th17 cells prevented tumor development. Importantly, the Th17 cells retained their cytokine signature and exhibited stronger therapeutic efficacy than Th1 cells. Unexpectedly, therapy using Th17 cells elicited a remarkable activation of tumor-specific CD8(+) T cells, which were necessary for the antitumor effect. Th17 cells promoted dendritic cell recruitment into the tumor tissues and in draining lymph nodes increased CD8 alpha(+) dendritic cells containing tumor material. Moreover, Th17 cells promoted CCL20 chemokine production by tumor tissues, and tumor-bearing CCR6-deficient mice did not respond to Th17 cell therapy. Thus, Th17 cells elicited a protective inflammation that promotes the activation of tumor-specific CD8(+) T cells. These findings have important implications in antitumor immunotherapies.

Wnt signaling arrests effector T cell differentiation and generates CD8+ memory stem cells

Self-renewing cell populations such as hematopoietic stem cells and memory B and T lymphocytes might be regulated by shared signaling pathways. The Wnt-beta-catenin pathway is an evolutionarily conserved pathway that promotes hematopoietic stem cell self-renewal and multipotency by limiting stem cell proliferation and differentiation, but its role in the generation and maintenance of memory T cells is unknown. We found that induction of Wnt-beta-catenin signaling by inhibitors of glycogen sythase kinase-3beta or the Wnt protein family member Wnt3a arrested CD8(+) T cell development into effector cells. By blocking T cell differentiation, Wnt signaling promoted the generation of CD44(low)CD62L(high)Sca-1(high)CD122(high)Bcl-2(high) self-renewing multipotent CD8(+) memory stem cells with proliferative and antitumor capacities exceeding those of central and effector memory T cell subsets. These findings reveal a key role for Wnt signaling in the maintenance of 'stemness' in mature memory CD8(+) T cells and have major implications for the design of new vaccination strategies and adoptive immunotherapies.

Adoptive immunotherapy of cancer using CD4(+) T cells

CD4(+) T cells are central to the function of the immune system but their role in tumor immunity remains underappreciated. It is becoming clear that there is an enormous diversity of CD4(+) T cell polarization patterns including Th1, Th2, Th17, and regulatory T cells (Tregs). These functionally divergent T cell subsets can have opposing effects -- they can trigger tumor rejection or inhibit treatment after adoptive cell transfer. Some polarized CD4(+) cells have plasticity, and their phenotypes and functions can evolve in vivo. Recent advances in understanding of polarization and differentiation of lymphocytes, as well as some intriguing developments in the clinic, indicate that the use of CD4(+) T cell subsets in the immunotherapy of cancer has unrealized potential.

Toll-like receptors in tumor immunotherapy

Lymphodepletion with chemotherapeutic agents or total body irradiation (TBI) before adoptive transfer of tumor-specific T cells is a critical advancement in the treatment of patients with melanoma. More than 50% of patients that are refractory to other treatments experience an objective or curative response with this approach. Emerging data indicate that the key mechanisms underlying how TBI augments the functions of adoptively transferred T cells include (a) the depletion of regulatory T cells (T(reg)) and myeloid-derived suppressor cells that limit the function and proliferation of adoptively transferred cells; (b) the removal of immune cells that act as "sinks" for homeostatic cytokines, whose levels increase after lymphodepletion; and (c) the activation of the innate immune system via Toll-like receptor 4 signaling, which is engaged by microbial lipopolysaccharide that translocated across the radiation-injured gut. Here, we review these mechanisms and focus on the effect of Toll-like receptor agonists in adoptive immunotherapy. We also discuss alternate regimens to chemotherapy or TBI, which might be used to safely treat patients with advanced disease and promote tumor regression.

Microbial translocation augments the function of adoptively transferred self/tumor-specific CD8+ T cells via TLR4 signaling

Lymphodepletion with total body irradiation (TBI) increases the efficacy of adoptively transferred tumor-specific CD8(+) T cells by depleting inhibitory lymphocytes and increasing homeostatic cytokine levels. We found that TBI augmented the function of adoptively transferred CD8(+) T cells in mice genetically deficient in all lymphocytes, indicating the existence of another TBI mechanism of action. Additional investigation revealed commensal gut microflora in the mesenteric lymph nodes and elevated LPS levels in the sera of irradiated mice. These findings correlated with increased dendritic cell activation and heightened levels of systemic inflammatory cytokines. Reduction of host microflora using antibiotics, neutralization of serum LPS using polymyxin B, or removal of LPS signaling components using mice genetically deficient in CD14 and TLR4 reduced the beneficial effects of TBI on tumor regression. Conversely, administration of microbial ligand-containing serum or ultrapure LPS from irradiated animals to nonirradiated antibody-lymphodepleted mice enhanced CD8(+) T cell activation and improved tumor regression. Administration of ultrapure LPS to irradiated animals further enhanced the number and function of the adoptively transferred cells, leading to long-term cure of mice with large B16F10 tumors and enhanced autoimmune vitiligo. Thus, disruption of the homeostatic balance between the host and microbes can enhance cell-based tumor immunotherapy.

Increased intensity lymphodepletion and adoptive immunotherapy--how far can we go?

In a recent clinical trial involving patients with metastatic melanoma, immunosuppressive conditioning with fludarabine and cyclophosphamide resulted in a 50% response rate in robust long-term persistence of adoptively transferred T cells. Experimental findings indicate that lymphodepletion prior to adoptive transfer of tumor-specific T lymphocytes plays a key role in enhancing treatment efficacy by eliminating regulatory T cells and competing elements of the immune system ('cytokine sinks'). Newly emerging animal data suggest that more profound lymphoablative conditioning with autologous hematopoetic stem-cell rescue might further enhance treatment results. Here we review recent advances in adoptive immunotherapy of solid tumors and discuss the rationale for lymphodepleting conditioning. We also address safety issues associated with translating experimental animal results of total lymphoid ablation into clinical practice.

Large granular lymphocyte (LGL)-like clonal expansions in paroxysmal nocturnal hemoglobinuria (PNH) patients

In paroxysmal nocturnal hemoglobinuria (PNH), clonal expansion of glycosylphosphatidylinositol-anchored proteins (GPI-AP)-deficient cells leads to a syndrome characterized by hemolytic anemia, marrow failure, and venous thrombosis. PNH is closely related to aplastic anemia and may share its immune pathophysiology. In vivo expansion of dominant T-cell clones can reflect an antigen-driven immune response but may also represent autonomous proliferation, such as in large granular lymphocytic (LGL)-leukemia. T-cell clonality can be assessed by a combination of T-cell receptor (TCR) flow cytometry and complementarity-determining-region-3 (CDR3) molecular analysis. We studied 24 PNH patients for evidence of in vivo dominant T-cell responses by flow cytometry; TCR-Vbeta-specific expansions were identified in all patients. In four cases, extreme expansions of one Vbeta-subset of CD8+/CD28-/CD56+ (effector) phenotype mimicked subclinical LGL-disease. The monoclonality of these expansions was inferred from unique CDR3-size peak distributions and sequencing of dominant clonotypes. We conclude that the molecular analysis of TCR-beta chain may demonstrate clonal LGL-like expansions at unexpected frequency in PNH patients. Our observations blur the classical boundaries between different bone marrow failure syndromes such as AA, PNH, and LGL, and support the hypothesis that in PNH, the mutant clone may expand as a result of an immune-escape from antigen-driven lymphocyte attack on hematopoietic progenitors.

Altered selection of CD4+ T cells by class II MHC bound with dominant and low abundance self-peptides

We have investigated the development of CD4(+) T cells in mice expressing low levels of transgenic class II MHC molecules (A(b)) preoccupied with covalent peptide (Ep), which in the presence of invariant chain (Ii) is extensively cleaved and replaced with self-derived peptides. In these mice, the transgenic A(b) molecules, bound with predominant peptide (Ep) and with multiple self-peptides, selected more CD4(+) T cells than A(b)/self-peptide complexes expressed in wild-type mice. The enhanced outcome of thymic selection was a result of impaired negative selection, rather than more efficient positive selection by an overall lowered abundance of self-derived A(b)/peptide complexes. Peripheral CD4(+) T cells in the A(b)EpIi(+) mice had memory phenotype, often followed by polyclonal activation of B cells. The A(b)EpIi(+) mice preserved their good health and had a normal life span despite the profound number of activated CD4(+) T cells and B cells in peripheral lymphoid organs, moderate hypergammaglobulinemia, and deposited complexes in the kidneys. We propose that CD4(+) T cells positively selected due to low avidity for high abundant A(b)Ep complex avoid negative selection on A(b) molecules loaded with low abundant peptides and become self-reactive in the peripheral lymphoid organs.

Mature CD4+ T cells perceive a positively selecting class II MHC/peptide complex in the periphery

A repertoire of TCRs is selected in the thymus by interactions with MHC bound to self-derived peptides. Whether self peptides bound to MHC influence the survival of mature T cells in the periphery remains enigmatic. In this study, we show that the number of naive CD4+ T cells that developed in mice with class II MHC bound with endogenous peptides (Abwt) diminished when transferred into mice with Ab covalently bound with a single peptide (AbEp). Moreover, transfer of a mixture of naive CD4+ T cells derived from Abwt and from AbEp mice into AbEp mice resulted in the expansion of the latter and decline of the former. In contrast, when wild-type activated CD4+ T cells were transferred into AbEp or Abwt mice, these cells survived in both recipients for more than 4 wk, but further expanded in the Abwt host. We conclude that to survive, naive CD4+ T cells favor peripheral expression of the class II MHC/peptide complex(es) involved in their thymic selection, whereas some of activated CD4+ T cells may require them only for expansion.

On the role of high- and low-abundance class II MHC-peptide complexes in the thymic positive selection of CD4(+) T cells

The role of self-peptides bound to MHC molecules in the selection of T cells in the thymus remains controversial. Here, we have tested whether a high-abundance single class II MHC-peptide complex has a dominant effect on the repertoire of CD4(+) T cells selected by low-abundance class II MHC-peptide complexes. For these studies, we have used H-2(b) mice that lack an invariant chain (Ii) (A(b)Ii(-)) and their transgenic variant (A(b)A(b)EpIi(-)) that co-expresses A(b) molecules covalently bound with a single peptide Ep(52-68). In these latter mice, close to 50% of all A(b) molecules are occupied by Ep(52-68) peptide. Although the A(b)Ep complex was abundantly expressed in the thymus under conditions excluding negative selection on bone marrow-derived cells, no striking quantitative difference between repertoires of TCR expressed on CD4(+) T cells in A(b)Ii(-) and A(b)A(b)EpIi(-) mice was noticed. Our results are consistent with the view that diverse, low-abundance self-peptides play an important role in thymic positive selection and do not support the notion that dominant, high-abundance peptides may be critical for shaping the TCR repertoire.

In the Normal Repertoire of CD4+ T Cells, a Single Class II MHC/Peptide Complex Positively Selects TCRs with Various Antigen Specificities

In the thymus, immature T cells are positively and negatively selected by multiple interactions between their Ag receptors (TCRs) and self MHC/peptide complexes expressed on thymic stromal cells. Here we show that in the milieu of negative selection on physiological self class II MHC/peptide complexes (Abwt), a single class II/peptide complex AbEp52–68 positively selects a number of TCRs with various Ag specificities. This TCR repertoire is semidiverse and not biased toward Ep-like Ags. Our finding implies that the degeneracy of positive selection for peptide ligands exceeds peptide-specific negative selection and is essential to increase the efficiency and diversity of the repertoire so that T cells with the same Ag specificity can be selected by different self MHC/peptide complexes.

In the normal repertoire of CD4+ T cells, a single class II MHC/peptide complex positively selects TCRs with various antigen specificities

In the thymus, immature T cells are positively and negatively selected by multiple interactions between their Ag receptors (TCRs) and self MHC/peptide complexes expressed on thymic stromal cells. Here we show that in the milieu of negative selection on physiological self class II MHC/peptide complexes (Abwt), a single class II/peptide complex AbEp52-68 positively selects a number of TCRs with various Ag specificities. This TCR repertoire is semidiverse and not biased toward Ep-like Ags. Our finding implies that the degeneracy of positive selection for peptide ligands exceeds peptide-specific negative selection and is essential to increase the efficiency and diversity of the repertoire so that T cells with the same Ag specificity can be selected by different self MHC/ peptide complexes.