Innate and adaptive immunity to tumors: IL-12 is required for optimal responses

Tumor growth accelerated by chemotherapy-induced senescent cells is suppressed by treatment with IL-12 producing cellular vaccines

Standard-of-care chemo- or radio-therapy can induce, besides tumor cell death, also tumor cell senescence. While senescence is considered to be a principal barrier against tumorigenesis, senescent cells can survive in the organism for protracted periods of time and they can promote tumor development. Based on this emerging concept, we hypothesized that elimination of such potentially cancer-promoting senescent cells could offer a therapeutic benefit. To assess this possibility, here we first show that tumor growth of proliferating mouse TC-1 HPV-16-associated cancer cells in syngeneic mice becomes accelerated by co-administration of TC-1 or TRAMP-C2 prostate cancer cells made senescent by pre-treatment with the anti-cancer drug docetaxel, or lethally irradiated. Phenotypic analyses of tumor-explanted cells indicated that the observed acceleration of tumor growth was attributable to a protumorigenic environment created by the co-injected senescent and proliferating cancer cells rather than to escape of the docetaxel-treated cells from senescence. Notably, accelerated tumor growth was effectively inhibited by cell immunotherapy using irradiated TC-1 cells engineered to produce interleukin IL-12. Collectively, our data document that immunotherapy, such as the IL-12 treatment, can provide an effective strategy for elimination of the detrimental effects caused by bystander senescent tumor cells in vivo.

Cytokines reinstate NK cell-mediated cancer immunosurveillance

In healthy individuals, cells that lose expression of MHC class I molecules are quickly targeted for elimination by NK lymphocytes. A paradox in cancer immunology is the observation that many tumor cells often have a drastic reduction of MHC class I molecules, yet these cells are not eliminated by NK cells, as they should be. In this issue of the JCI, Ardolino et al. demonstrate that NK cells that infiltrate MHC class I-deficient tumors acquire an anergic state that can be reversed by particular combinations of exogenous cytokines. These results indicate that IL-12 plus IL-18 or a recombinant interleukin engineered to stimulate the IL-2 receptor β/γ heterodimer (but not the IL-2 receptor α/β/γ complex) have the potential to be used clinically to reinstate immunosurveillance against MHC class I-deficient tumors.

Cytokine therapy reverses NK cell anergy in MHC-deficient tumors

Various cytokines have been evaluated as potential anticancer drugs; however, most cytokine trials have shown relatively low efficacy. Here, we found that treatments with IL-12 and IL-18 or with a mutant form of IL-2 (the "superkine" called H9) provided substantial therapeutic benefit for mice specifically bearing MHC class I-deficient tumors, but these treatments were ineffective for mice with matched MHC class I+ tumors. Cytokine efficacy was linked to the reversal of the anergic state of NK cells that specifically occurred in MHC class I-deficient tumors, but not MHC class I+ tumors. NK cell anergy was accompanied by impaired early signal transduction and was locally imparted by the presence of MHC class I-deficient tumor cells, even when such cells were a minor population in a tumor mixture. These results demonstrate that MHC class I-deficient tumor cells can escape from the immune response by functionally inactivating NK cells, and suggest cytokine-based immunotherapy as a potential strategy for MHC class I-deficient tumors. These results suggest that such cytokine therapies would be optimized by stratification of patients. Moreover, our results suggest that such treatments may be highly beneficial in the context of therapies to enhance NK cell functions in cancer patients.

Day 3 Poly (I:C)-activated dendritic cells generated in CellGro for use in cancer immunotherapy trials are fully comparable to standard Day 5 DCs

BACKGROUND

Dendritic cells (DCs) are professional antigen-presenting cells that are capable of inducing immune responses. DC-based vaccines are normally generated using a standard 5- to 7-day protocol. To shorten the DC-based vaccine production for use in cancer immunotherapy, we have developed a fast DC protocol by comparing standard DCs (Day 5 DCs) and fast DCs (Day 3 DCs).

METHODS

We tested the generation of Day 5 versus Day 3 DCs using CellGro media and subsequent activation by two activation stimuli: Poly (I:C) and LPS. We evaluated DC morphology, viability, phagocyte activity, cytokine production and ability to stimulate antigen-specific T cells.

RESULTS

Day 5 and Day 3 DCs exhibited similar phagocytic capacity. Poly (I:C)-activated Day 5 DCs expressed higher levels of the costimulatory and surface molecules CD80, CD86 and HLA-DR compared to Poly (I:C)-activated Day 3 DCs. Nevertheless, LPS-activated Day 5 and Day 3 DCs were phenotypically similar. Cytokine production was generally stronger when LPS was used as the maturation stimulus, and there were no significant differences between Day 5 and Day 3 DCs. Importantly, Day 5 and Day 3 DCs were able to generate comparable numbers of antigen-specific CD8(+) T cells. The number of Tregs induced by Day 5 and Day 3 DCs was also comparable.

CONCLUSION

We identified monocyte-derived DCs generated in CellGro for 3 days and activated using Poly (I:C) similarly potent in most functional aspects as DCs produced by the standard 5 day protocol. These results provide the rationale for the evaluation of faster protocols for DC generation in clinical trials.

Co-delivery of antigen and IL-12 by Venezuelan equine encephalitis virus replicon particles enhances antigen-specific immune responses and antitumor effects

We recently demonstrated that Venezuelan equine encephalitis virus-based replicon particle (VRPs) encoding tumor antigens could break tolerance in the immunomodulatory environment of advanced cancer. We hypothesized that local injection of VRP-expressing interleukin-12 (IL-12) at the site of injections of VRP-based cancer vaccines would enhance the tumor-antigen-specific T cell and antibody responses and antitumor efficacy. Mice were immunized with VRP encoding the human tumor-associated antigen, carcinoembryonic antigen (CEA) (VRP-CEA(6D)), and VRP-IL-12 was also administered at the same site or at a distant location. CEA-specific T cell and antibody responses were measured. To determine antitumor activity, mice were implanted with MC38-CEA-2 cells and immunized with VRP-CEA with and without VRP-IL-12, and tumor growth and mouse survival were measured. VRP-IL-12 greatly enhanced CEA-specific T cell and antibody responses when combined with VRP-CEA(6D) vaccination. VRP-IL-12 was superior to IL-12 protein at enhancing immune responses. Vaccination with VRP-CEA(6D) plus VRP-IL-12 was superior to VRP-CEA(6D) or VRP-IL-12 alone in inducing antitumor activity and prolonging survival in tumor-bearing mice. Importantly, local injection of VRP-IL-12 at the VRP-CEA(6D) injection site provided more potent activation of CEA-specific immune responses than that of VRP-IL-12 injected at a distant site from the VRP-CEA injections. Together, this study shows that VRP-IL-12 enhances vaccination with VRP-CEA(6D) and was more effective at activating CEA-specific T cell responses when locally expressed at the vaccine site. Clinical trials evaluating the adjuvant effect of VRP-IL-12 at enhancing the immunogenicity of cancer vaccines are warranted.

The role of CD4 T cell help for CD8 CTL activation

CD4 T cells play an important role in the initiation and persistence of CD8 T cells responses. In this review, we report on and evaluate the mechanisms by which CD4 T cells contribute to activation of CD8 T cells and the signal pathways of the down-streaming events after CD4 T cell help.

Dendritic cell maturation with poly(I:C)-based versus PGE2-based cytokine combinations results in differential functional characteristics relevant to clinical application

In vitro maturation of dendritic cells (DCs) for cancer immunotherapy may be accomplished by cytokine cocktails containing prostaglandin E2 (PGE2). More recently, a poly(I:C)-based protocol has been proposed as a potentially superior alternative because of a strong induction of interleukin (IL)-12 secretion by resulting DCs. As optimal DC maturation represents a crucial issue for cancer vaccination trials, we performed a systematic and comprehensive comparison of both protocols with respect to important indicators of DC function. Although both methods yielded phenotypically mature DCs, transcriptional profiling revealed a substantially higher number of differentially regulated genes after poly(I:C)-based than PGE2-based maturation. Several of these are involved in immunologic processes, indicating that both DC types exhibit subtle, but distinct, molecular properties. Up-regulation of genes encoding the T-cell-attracting chemokines CXCL9, 10, and 11 in poly(I:C)-DC but not PGE2-DC was confirmed on a protein level. Although poly(I:C)-based maturation induced substantial IL-12p70 secretion, poly(I:C)-DC also secreted low levels of IL-10 and showed a significantly higher expression of functionally active indoleamine-2,3-dioxygenase than PGE2-DC, which might mediate immune inhibitory functions. Nonetheless, the number of peptide-specific T cells tended to be higher after in vitro priming with poly(I:C)-DC compared with PGE2-DC. Finally, PGE2-DC displayed superior migratory abilities, which are essential for in vivo applications. In summary, we have identified previously unrecognized shared and distinct molecular features of DCs matured by 2 commonly used protocols that lead to subtle, but significant, immunologic features of the resulting cells relevant to clinical applications.

A role for interleukin-12/23 in the maturation of human natural killer and CD56+ T cells in vivo

Natural killer (NK) cells have been originally defined by their "naturally occurring" effector function. However, only a fraction of human NK cells is reactive toward a panel of prototypical tumor cell targets in vitro, both for the production of interferon-gamma (IFN-gamma) and for their cytotoxic response. In patients with IL12RB1 mutations that lead to a complete IL-12Rbeta1 deficiency, the size of this naturally reactive NK cell subset is diminished, in particular for the IFN-gamma production. Similar data were obtained from a patient with a complete deficit in IL-12p40. In addition, the size of the subset of effector memory T cells expressing CD56 was severely decreased in IL-12Rbeta1- and IL-12p40-deficient patients. Human NK cells thus require in vivo priming with IL-12/23 to acquire their full spectrum of functional reactivity, while T cells are dependent upon IL-12/23 signals for the differentiation and/or the maintenance of CD56(+) effector memory T cells. The susceptibility of IL-12/23 axis-deficient patients to Mycobacterium and Salmonella infections in combination with the absence of mycobacteriosis or salmonellosis in the rare cases of human NK cell deficiencies point to a role for CD56(+) T cells in the control of these infections in humans.

CCL21-induced immune cell infiltration

Cellular immune responses can be initiated via peptide presentation by specialized antigen presenting cells, dendritic cells (DCs), which stimulate naïve T cells. The trafficking of DCs and T cells is regulated by chemokines such as CCL21. CCL21 is normally expressed in the lymphoid organs and coordinates the interactions between DCs and T cells, thereby contributing to the initiation of T cell responses. In order to comprehend the mechanisms of CCL21 activity and to utilize CCL21 optimally in therapy, understanding the kinetics of the responses of various cell types to CCL21 would be beneficial. Therefore, in this study, we injected mice subcutaneously (s.c.) with CCL21 and examined the DC and T cell infiltration of the local draining lymph node. CCL21 injection resulted in significantly increased numbers of lymphoid and myeloid DCs and effector T lymphocytes in the local node at 4 days. Furthermore, at 4 days small lymphoid-like structures were visible in the injection areas. These results provide guidance for the optimal timing of CCL21 use in combination with vaccines.

Inhibition of tumor rejection by gammadelta T cells and IL-10

Although many tumors express tumor-specific antigens, most fail to stimulate effective immune responses. Tumors generally lack co-stimulatory molecules, which can lead to tolerance of tumor-specific T cells and progressive tumor growth. Here, we demonstrate that the ovalbumin (OVA) transfected EL4 tumor, E.G7-OVA, grows progressively in syngeneic mice even though the tumor can be rejected if the mice are immunized with OVA in adjuvant. E.G7-OVA grew more rapidly in RAG-1 deficient than sufficient mice suggesting that normal mice make an abortive immune response to this tumor. Depletion of gammadelta T cells or IL-10 augmented the ability of B6 mice to reject E.G7-OVA. Spleen cells from normal, but not IL-10 knockout, mice reconstituted rapid tumor growth in gammadelta T cell-deficient mice. Thus, gammadelta T cells play an important role in preventing immune elimination of this tumor by a mechanism that directly or indirectly involves IL-10.

Natural killer and dendritic cell contact in lesional atopic dermatitis skin--Malassezia-influenced cell interaction

The regulation of dendritic cells is far from fully understood. Interestingly, several recent reports have suggested a role for natural killer cells in affecting dendritic cell maturation and function upon direct contact between the cells. It is not known if this interaction takes place also in vivo, or if a potential interaction of natural killer cells and dendritic cells would be affected by allergen exposure of the dendritic cells. The yeast Malassezia can act as an allergen in atopic eczema/dermatitis syndrome, and induce maturation of dendritic cells. Our aims were to study the distribution of natural killer cells in the skin from atopic eczema/dermatitis syndrome patients with the emphasis on possible natural killer cell-dendritic cell interaction, and to assess whether the interaction of Malassezia with dendritic cells would affect subsequent interaction between dendritic cells and natural killer cells. A few scattered natural killer (CD56+/CD3-) cells were found in the dermis of healthy individuals and in nonlesional skin from atopic eczema/dermatitis syndrome patients. In lesional skin and in biopsies from Malassezia atopy-patch-test-positive skin, however, natural killer cells were differentially distributed and for the first time we could show close contact between natural killer cells and CD1a+ dendritic cells. Dendritic cells preincubated with Malassezia became less susceptible to natural-killer-cell-induced cell death, suggesting a direct effect imposed by Malassezia upon interaction of dendritic cells with natural killer cells. These findings indicate that natural killer cells and dendritic cells can interact in the skin and that Malassezia affects the interaction between natural killer cells and dendritic cells. Our data suggest that natural killer cells may play a role in regulating dendritic cells in atopic eczema/dermatitis syndrome.

Prostaglandin E2 is a key factor for CCR7 surface expression and migration of monocyte-derived dendritic cells

Dendritic cells (DCs) are potent antigen-presenting cells that are able to initiate and modulate immune responses and are hence exploited as cellular vaccines for immunotherapy. Their capacity to migrate from peripheral tissues to the T-cell areas of draining lymph nodes is crucial for the priming of T lymphocytes. In this study, we investigated how the maturation of human monocyte-derived DCs (MoDCs) by several different stimuli under serum-free conditions affected their T-cell stimulatory function, cytokine secretion, and migratory behavior. Surprisingly, we found that for all maturation stimuli tested, the addition of prostaglandin E2 (PGE2) was required for effective migration of MoDCs toward the lymph node-derived chemokines CCL19 (EBI1 ligand chemokine/macrophage inflammatory protein--3beta) and CCL21 (secondary lymphoid tissue chemokine [SLC]/6Ckine). Costimulation with PGE2 enhanced the expression of the CCL19/CCL21 receptor CCR7 on the cell surface of MoDCs when they were matured with soluble CD40 ligand or proinflammatory cytokines, but did not affect CCR7 expression of polyI:C-stimulated MoDCs. The effects of PGE2 on MoDCs were mediated through increased cyclic adenosine monophosphate by 2 of the known PGE2 receptors, EP2 and EP4, which are expressed and down-regulated after PGE2 binding in these cells. In conclusion, our results suggest that signals provided by the proinflammatory mediator PGE2 are crucial for MoDCs to acquire potent T-helper cell stimulatory capacity and substantial chemotactic responsiveness to lymph node-derived chemokines. This is a new and important parameter for the preparation of MoDCs as cellular vaccines in tumor immunotherapy. (Blood. 2002;100:1354-1361)

Tumour escape from immune surveillance through dendritic cell inactivation

Dendritic cells (DC) are central to the initiation of immunity. To induce immune reactivity, DC are recruited at the site of antigen expression, uptake antigens and migrate to secondary lymphoid organs while receiving activation signals delivered by pathogens, dying cells, and/or T cells. Tumours can escape the immune system by interfering with the migration of DC or by not providing the necessary activation signals. Moreover, tumours promote the secretion of factors that inhibit DC differentiation and functions. We will review the current knowledge of the physiopathology of DC in cancer, which paves the way for novel strategies of therapeutic intervention.

Dendritic cell-derived IL-12 is not required for the generation of cytotoxic, IFN-gamma-secreting, CD8(+) CTL in vivo

By using adoptive transfer of Ag-loaded bone marrow-derived dendritic cells (BMDC), we have established an in vivo model of CTL priming. Activation of CTL in these experiments required both CD4(+) T cells and CD154, demonstrating that this model reflects CD4(+) T cell-dependent dendritic cell (DC) licensing. Because IL-12 has been suggested to play an important role in CTL activation by DC, we examined the ability of BMDC to prime CTL in the complete absence of IL-12 using p40-deficient mice. We observed that the absence of IL-12 does not affect the phenotype or allostimulatory function of BMDC after in vitro maturation. Moreover, there was no difference in the ability of Ag-loaded DC to elicit CTL cytotoxicity, whether the Ag was delivered by virus infection or peptide pulsing. Equal frequencies of Ag-specific, IFN-gamma-secreting CD8(+) T cells developed in both wild-type and IL-12-deficient backgrounds. Finally, CTL generated in the IL-12-deficient environment were capable of protecting immunized mice against tumor challenge, demonstrating that these CTL were fully functional, despite the absence of IL-12 during the maturation process in vivo. These results indicate that IL-12 is not critical for the development of IFN-gamma secreting, CD8(+) T cells and that another mechanism must be used by licensed DC to prime and activate CTL.

Type I interferon is required to mount an adaptive response to immunostimulatory DNA

Immunostimulatory DNA sequences (ISS, CpG motifs) potently stimulate Th1 and cytotoxic T lymphocyte (CTL) responses to antigens and have thus generated considerable interest due to their potential use in immunotherapeutics. An array of cytokines are produced in response to ISS exposure, but the relative importance of each of these mediators in the stimulation of innate and adaptive ISS-induced immunity has yet to be fully investigated. To address this issue, we measured immune responses in mice with targeted deletions of the ISS-induced genes encoding IL-12 (IL-12(-/-)), IFN-gamma (IFN-gamma(-/-)), the IFN-gamma receptor (IFN-gammaR(-/-)), and the IFN-alpha/beta receptor (IFN-alpha/betaR(-/-)) after immunization with ISS-containing oligodeoxynucleotides and model antigens. IL-12(-/-) and IFN-alpha/betaR(-/-) mice were compromised in their ability to develop a cross-primed CTL response, whereas IFN-gamma(-/-) and IFN-gammaR(-/-) mice were not. In addition, lymphocytes from immunized IFN-alpha/betaR(-/-) mice had defective IFN-gamma responses to antigen restimulation. Antigen nonspecific ISS-induced B cell proliferation was normal in the four deficient strains; however, innate IL-6 production was reduced in IFN-gamma(-/-) and IFN-gammaR(-/-) splenocytes and eliminated in IFN-alpha/betaR(-/-) cells. While IL-12 production was defective in only the IFN-gamma(-/-) splenocytes, innate natural killer cell IFN-gamma synthesis was virtually absent in the IL-12(-/-) and IFN-alpha/betaR(-/-) mice. Thus, while IFN-alpha/beta, IFN-gamma, and IL-12 each play important and distinct roles in the development of the innate and adaptive immune responses to ISS, IFN-alpha/beta is a particularly crucial and currently under-appreciated factor in this system.

Rae1 and H60 ligands of the NKG2D receptor stimulate tumour immunity

Natural killer (NK) cells attack many tumour cell lines, and are thought to have a critical role in anti-tumour immunity; however, the interaction between NK cells and tumour targets is poorly understood. The stimulatory lectin-like NKG2D receptor is expressed by NK cells, activated CD8+ T cells and by activated macrophages in mice. Several distinct cell-surface ligands that are related to class I major histocompatibility complex molecules have been identified, some of which are expressed at high levels by tumour cells but not by normal cells in adults. However, no direct evidence links the expression of these 'induced self' ligands with tumour cell rejection. Here we demonstrate that ectopic expression of the murine NKG2D ligands Rae1beta or H60 in several tumour cell lines results in potent rejection of the tumour cells by syngeneic mice. Rejection is mediated by NK cells and/or CD8+ T cells. The ligand-expressing tumour cells induce potent priming of cytotoxic T cells and sensitization of NK cells in vivo. Mice that are exposed to live or irradiated tumour cells expressing Rae1 or H60 are specifically immune to subsequent challenge with tumour cells that lack NKG2D ligands, suggesting application of the ligands in the design of tumour vaccines.