Transient activation of tumor-associated T-effector/memory cells promotes tumor eradication via NK-cell recruitment: minimal role for long-term T-cell immunity in cure of metastatic disease

Localized Interleukin-12 for Cancer Immunotherapy

Interleukin-12 (IL-12) is a potent, pro-inflammatory type 1 cytokine that has long been studied as a potential immunotherapy for cancer. Unfortunately, IL-12's remarkable antitumor efficacy in preclinical models has yet to be replicated in humans. Early clinical trials in the mid-1990's showed that systemic delivery of IL-12 incurred dose-limiting toxicities. Nevertheless, IL-12's pleiotropic activity, i.e., its ability to engage multiple effector mechanisms and reverse tumor-induced immunosuppression, continues to entice cancer researchers. The development of strategies which maximize IL-12 delivery to the tumor microenvironment while minimizing systemic exposure are of increasing interest. Diverse IL-12 delivery systems, from immunocytokine fusions to polymeric nanoparticles, have demonstrated robust antitumor immunity with reduced adverse events in preclinical studies. Several localized IL-12 delivery approaches have recently reached the clinical stage with several more at the precipice of translation. Taken together, localized delivery systems are supporting an IL-12 renaissance which may finally allow this potent cytokine to fulfill its considerable clinical potential. This review begins with a brief historical account of cytokine monotherapies and describes how IL-12 went from promising new cure to ostracized black sheep following multiple on-study deaths. The bulk of this comprehensive review focuses on developments in diverse localized delivery strategies for IL-12-based cancer immunotherapies. Advantages and limitations of different delivery technologies are highlighted. Finally, perspectives on how IL-12-based immunotherapies may be utilized for widespread clinical application in the very near future are offered.

Neoadjuvant immunotherapy with chitosan and interleukin-12 to control breast cancer metastasis

Metastasis accounts for approximately 90% of breast cancer-related deaths. Therefore, novel approaches which prevent or control breast cancer metastases are of significant clinical interest. Interleukin-12 (IL-12)-based immunotherapies have shown promise in controlling metastatic disease, yet modest responses and severe toxicities due to systemic administration of IL-12 in early trials have hindered clinical application. We hypothesized that localized delivery of IL-12 co-formulated with chitosan (chitosan/IL-12) could elicit tumor-specific immunity and provide systemic protection against metastatic breast cancer while minimizing systemic toxicity. Chitosan is a biocompatible polysaccharide derived primarily from the exoskeletons of crustaceans. In a clinically relevant resection model, mice bearing spontaneously metastatic 4T1 mammary adenocarcinomas received intratumoral injections of chitosan/IL-12, or appropriate controls, prior to tumor resection. Neoadjuvant chitosan/IL-12 immunotherapy resulted in long-term tumor-free survival in 67% of mice compared to only 24% or 0% of mice treated with IL-12 alone or chitosan alone, respectively. Antitumor responses following chitosan/IL-12 treatment were durable and provided complete protection against rechallenge with 4T1, but not RENCA renal adenocarcinoma, cells. Lymphocytes from chitosan/IL-12-treated mice demonstrated robust tumor-specific lytic activity and interferon-γ production. Cell-mediated immune memory was confirmed in vivo via clinically relevant delayed-type hypersensitivity (DTH) assays. Comprehensive hematology and toxicology analyses revealed that chitosan/IL-12 induced transient, reversible leukopenia with no changes in critical organ function. Results of this study suggest that neoadjuvant chitosan/IL-12 immunotherapy prior to breast tumor resection is a promising translatable strategy capable of safely inducing to tumor-specific immunity and, in the long term, reducing breast cancer mortality due to progressive recurrences.

Chronic chemoimmunotherapy achieves cure of spontaneous murine mammary tumors via persistent blockade of posttherapy counter-regulation

Intratumoral delivery of IL-12 and GM-CSF induces local and systemic antitumor CD8(+) T cell activation and tumor kill. However, the effector response is transient and is rapidly countered by CD4(+) Foxp3(+) T suppressor cell expansion. To determine whether depletion of the pre-existing T suppressor cell pool prior to treatment could diminish posttherapy regulatory cell resurgence, FVBneuN mice bearing advanced spontaneous mammary tumors were treated with cyclophosphamide (CY) 1 d before IL-12/GM-CSF therapy. Administration of CY mediated a significant delay in the post-IL-12/GM-CSF T suppressor cell rebound, resulting in a 7-fold increase in the CD8(+) CTL/T suppressor cell ratio, a 3-fold enhancement of CTL cytotoxicity, and an extension of the effector window from 3 to 7 d. In long-term therapy studies, chronic chemoimmunotherapy promoted a dramatic enhancement of tumor regression, resulting in complete cure in 44% of the mice receiving CY plus IL-12/GM-CSF. Tumor eradication in the chronic therapy setting was associated with the ability to repeatedly rescue and maintain cytotoxic CD8(+) T cell activity. These findings demonstrated that chronic administration of CY in conjunction with immune therapy enhances the initial induction of antitumor T effector cells and, more importantly, sustains their cytotoxic activity over the long-term via persistent blockade of homeostatic counter-regulation.

Nitric oxide short-circuits interleukin-12-mediated tumor regression

Interleukin-12 (IL-12) can promote tumor regression via activation of multiple lymphocytic and myelocytic effectors. Whereas the cytotoxic mechanisms employed by T/NK/NKT cells in IL-12-mediated tumor kill are well defined, the antitumor role of macrophage-produced cytotoxic metabolites has been more controversial. To this end, we investigated the specific role of nitric oxide (NO), a major macrophage effector molecule, in post-IL-12 tumor regression. Analysis of tumors following a single intratumoral injection of slow-release IL-12 microspheres showed an IFNγ-dependent sevenfold increase in inducible nitric oxide synthase (iNOS) expression within 48 h. Flow cytometric analysis of tumor-resident leukocytes and in vivo depletion studies identified CD11b(+) F4/80(+) Gr1(lo) macrophages as the primary source of iNOS. Blocking of post-therapy iNOS activity with N-nitro-L: -arginine methyl ester (L-NAME) dramatically enhanced tumor suppression revealing the inhibitory effect of NO on IL-12-driven antitumor immunity. Superior tumor regression in mice receiving combination treatment was associated with enhanced survival and proliferation of activated tumor-resident CD8+ T-effector/memory cells (Tem). These findings demonstrate that macrophage-produced NO negatively regulates the antitumor activity of IL-12 via its detrimental effects on CD8+ T cells and identify L-NAME as a potent adjuvant in IL-12 therapy of cancer.

Tumor-resident CD8+ T-cell: the critical catalyst in IL-12-mediated reversal of tumor immune suppression

Tumor-resident T cells display a functionally impaired effector/memory (Tem) phenotype. Sustained intratumoral administration of IL-12, on the other hand, can restore cytolytic function to pre-existing CD8+ Tem, resulting in effective tumor kill. Whereas cytotoxic T lymphocytes (CTL) are generally assumed to mediate tumor regression via direct tumor cytotoxicity, recent work revealed that activated CD8+ Tem mobilize a systemic, multi-component effector cascade that includes both innate and adaptive immune mechanisms. Here we summarize these mechanisms, review how tumor-resident CD8+ Tem orchestrate this cascade and discuss the potential clinical implications of these findings.

Activated CD8+ T-effector/memory cells eliminate CD4+ CD25+ Foxp3+ T-suppressor cells from tumors via FasL mediated apoptosis

Tumor-resident CD8(+) T cells display a quiescent effector/memory phenotype that is maintained in part by infiltrating CD4(+) CD25(+) Foxp3(+) T-suppressor cells. Intratumoral delivery of IL-12, in contrast, can restore cytotoxic function to tumor-associated CD8(+) T cells and induce the apoptotic death of T-suppressor cells. Depletion of CD8(+) T cells from tumors before IL-12 treatment resulted in the abrogation of treatment-mediated T-suppressor cell apoptosis revealing a link between CD8(+) T cell activation and T-suppressor elimination. Furthermore, IL-12 failed to induce T-suppressor cell loss in IFN-gamma- or FasL-deficient mice demonstrating a requirement for IFN-gamma and FasL in this process. Adoptive transfer of wild-type CD8(+) T cells to FasL-knockout mice restored posttherapy T-suppressor cell elimination from tumors establishing that expression of FasL on CD8(+) T cells was sufficient to promote T-suppressor cell death. IL-12 failed to induce FasL on T-effectors in IFN-gamma-knockout mice demonstrating a requirement for IFN-gamma in FasL up-regulation. Adoptive transfer of wild-type CD8(+) T cells induced T-suppressor cell death in IFN-gamma-knockout mice confirming that autocrine IFN-gamma was sufficient for CD8(+) T cell FasL expression. These findings reveal a mechanism by which cytotoxic T cells can abrogate regulatory cell activity.

Central role of IFNgamma-indoleamine 2,3-dioxygenase axis in regulation of interleukin-12-mediated antitumor immunity

Sustained intratumoral delivery of interleukin-12 (IL-12) and granulocyte macrophage colony-stimulating factor induces tumor regression via restoration of tumor-resident CD8+ T-effector/memory cell cytotoxicity and subsequent repriming of a secondary CD8+ T-effector cell response in tumor-draining lymph nodes (TDLN). However, treatment-induced T-effector activity is transient and is accompanied with a CD4+ CD25+ Foxp3+ T-suppressor cell rebound. Molecular and cellular changes in posttherapy tumor microenvironment and TDLN were monitored to elucidate the mechanism of counterregulation. Real-time PCR analysis revealed a 5-fold enhancement of indoleamine 2,3-dioxygenase (IDO) expression in the tumor and the TDLN after treatment. IDO induction required IFNgamma and persisted for up to 7 days. Administration of the IDO inhibitor D-1-methyl tryptophan concurrent with treatment resulted in a dramatic enhancement of tumor regression. Enhanced efficacy was associated with a diminished T-suppressor cell rebound, revealing a link between IDO activity and posttherapy regulation. Further analysis established that abrogation of the regulatory counterresponse resulted in a 10-fold increase in the intratumoral CD8+ T-cell to CD4+ Foxp3+ T-cell ratio. The ratio of proliferating CD8+ T-effector to CD4+ Foxp3+ T-suppressor cells was prognostic for efficacy of tumor suppression in individual mice. IFNgamma-dependent IDO induction and T-suppressor cell expansion were primarily driven by IL-12. These findings show a critical role for IDO in the regulation of IL-12-mediated antitumor immune responses.

Rapid release of cytoplasmic IL-15 from tumor-associated macrophages is an initial and critical event in IL-12-initiated tumor regression

This study reveals that the IL-15 rapidly released into serum upon IL-12 injection into tumor-bearing mice is critical for the subsequent leukocytic infiltration of the tumor and tumor-bearing tissue. The increase in serum IL-15 occurs within 2 h after IL-12 injection concomitantly with a decrease in cytoplasmic IL-15 in tumor-associated Mphi (TAM). Injection of anti-IL-15 one hour prior to IL-12 abrogates subsequent leukocytic infiltration into the tumor and prevents the IL-12-induced reduction of primary tumor mass and the clearance of metastases. Administration of anti-IL-15 18 h after IL-12 did not have a detectable impact on IL-12-induced leukocytic infiltration of the tumor. Deletion of NK cells had no impact on the IL-12-induced change in the functional phenotype of TAM or on the subsequent initiation of leukocytic infiltration of the tumor. In concert with our previous studies demonstrating that IL-12 reduces tumor-supportive activities of TAM, the current study supports the hypothesis that functional re-programming of TAM not only undermines Mphi support for tumor growth but also contributes to a critical step in the initiation of anti-tumor immune responses. In this context, the functional plasticity and pro-immunogenic potential of TAM may constitute a significant and unappreciated target in existing cytokine therapies.

Central role of tumor-associated CD8+ T effector/memory cells in restoring systemic antitumor immunity

Sustained delivery of IL-12 and GM-CSF to tumors induces the activation of tumor-resident CD8(+) T effector/memory cells (Tem) followed by cytotoxic CD8(+) T effector cell expansion. To determine whether the secondary effectors expanded from tumor-associated Tem or were primed de novo, activation kinetics of tumor-draining lymph node (TDLN) CD8(+) T cells were analyzed. Treatment promoted a 4-fold increase in the numbers of TDLN CD8(+) T cells displaying a CD69(+)CCR5(+)CD62L(-) periphery-homing effector phenotype by day 4 posttherapy. Pulse labeling of tumor and TDLN T cells with BrdU confirmed that proliferation occurred exclusively within the draining lymph nodes between days 1 and 4 with subsequent migration of primed CD8(+) T effectors to tumors on day 7. Day 4 CD8(+) T effector cells preferentially homed to and lysed experimental, but not control, tumors, establishing tumor specificity. To determine whether the secondary CD8(+) T effector cell response was dependent on activation of tumor-resident CD8(+) Tem, mice that were selectively depleted of tumor-infiltrating CD8(+) T cells were treated and monitored for T effector priming. In the absence of tumor-resident CD8(+) Tem, T effector cell expansion was completely abrogated in the TDLN, revealing that restoration of CD8(+) Tem function was critical to the induction of secondary T effectors. T cell priming failed to occur in IFN-gamma or perforin knockout mice, demonstrating that the requirement for Tem activation was associated with induction of Tem cytotoxicity. These data confirm that intratumoral IL-12 plus GM-CSF induces de novo priming of tumor-specific CD8(+) T effector cells in the TDLN and establish the critical role of preexisting intratumoral CD8(+) Tem in driving this process.

Genomic-wide analysis of lymphatic metastasis-associated genes in human hepatocellular carcinoma

AIM: To identify the genes related to lymph node metastasis in human hepatocellular carcinoma (HCC), 32 HCC patients with or without lymph node metastasis were investigated by high-throughput microarray comprising 886 genes.

METHODS: The samples of cancerous and non-cancerous paired tissue were taken from 32 patients with HCC who underwent hepatectomy with lymph node dissection. Total RNA was extracted from the cells obtained by means of laser microdissection (LCM) and was amplified by the T7-based amplification system. Then, the amplified samples were applied in the cDNA microarray comprising of 886 genes.

RESULTS: The results demonstrated that 25 up-regulated genes such as cell membrane receptor, intracellular signaling and cell adhesion related genes, and 48 down-regulated genes such as intracellular signaling and cell cycle regulator-related genes, were correlated with lymph node metastasis in HCC. Amongst them were included some interesting genes, such as MET, EPHA2, CCND1, MMP2, MMP13, CASP3, CDH1, and PTPN2. Expression of 16 genes (MET, CCND1, CCND2, VEGF, KRT18, RFC4, BIRC5, CDC6, MMP2, BCL2A1, CDH1, VIM, PDGFRA, PTPN2, SLC25A5 and DSP) were further confirmed by real-time quantitative reverse transcriptional polymerase chain reaction (RT-PCR).

CONCLUSION: Tumor metastasis is an important biological characteristic, which involves multiple genetic changes and cumulation. This genome-wide information contributes to an improved understanding of molecular alterations during lymph node metastasis in HCC. It may help clinicians to predict metastasis of lymph nodes and assist researchers in identifying novel therapeutic targets for metastatic HCC patients.

Cure of established GL261 mouse gliomas after combined immunotherapy with GM-CSF and IFNgamma is mediated by both CD8+ and CD4+ T-cells

We were the first to demonstrate that combined immunotherapy with GM-CSF producing GL261 cells and recombinant IFNgamma of preestablished GL261 gliomas could cure 90% of immunized mice. To extend these findings and to uncover the underlying mechanisms, the ensuing experiments were undertaken. We hypothesized that immunizations combining both GM-CSF and IFNgamma systemically would increase the number of immature myeloid cells, which then would mature and differentiate into dendritic cells (DCs) and macrophages, thereby augmenting tumor antigen presentation and T-cell activation. Indeed, the combined therapy induced a systemic increase of both immature and mature myeloid cells but also an increase in T regulatory cells (T-regs). Cytotoxic anti-tumor responses, mirrored by an increase in Granzyme B-positive cells as well as IFNgamma-producing T-cells, were augmented after immunizations with GM-CSF and IFNgamma. We also show that the combined therapy induced a long-term memory with rejection of intracerebral (i.c.) rechallenges. Depletion of T-cells showed that both CD4+ and CD8+ T-cells were essential for the combined GM-CSF and IFNgamma effect. Finally, when immunizations were delayed until day 5 after tumor inoculation, only mice receiving immunotherapy with both GM-CSF and IFNgamma survived. We conclude that the addition of recombinant IFNgamma to immunizations with GM-CSF producing tumor cells increased the number of activated tumoricidal T-cells, which could eradicate established intracerebral tumors. These results clearly demonstrate that the combination of cytokines in immunotherapy of brain tumors have synergistic effects that have implications for clinical immunotherapy of human malignant brain tumors.