Intratumoural administration of an NKT cell agonist with CpG promotes NKT cell infiltration associated with an enhanced antitumour response and abscopal effect

Intratumoural administration of unmethylated cytosine-phosphate-guanine motifs (CpG) to stimulate toll-like receptor (TLR)-9 has been shown to induce tumour regression in preclinical studies and some efficacy in the clinic. Because activated natural killer T (NKT) cells can cooperate with pattern-recognition via TLRs to improve adaptive immune responses, we assessed the impact of combining a repeated dosing regimen of intratumoural CpG with a single intratumoural dose of the NKT cell agonist α-galactosylceramide (α-GalCer). The combination was superior to CpG alone at inducing regression of established tumours in several murine tumour models, primarily mediated by CD8⁺ T cells. An antitumour effect on distant untreated tumours (abscopal effect) was reliant on sustained activity of NKT cells and was associated with infiltration of KLRG1⁺ NKT cells in tumours and draining lymph nodes at both injected and untreated distant sites. Cytometric analysis pointed to increased exposure to type I interferon (IFN) affecting many immune cell types in the tumour and lymphoid organs. Accordingly, antitumour activity was lost in animals in which dendritic cells (DCs) were incapable of signaling through the type I IFN receptor. Studies in conditional ablation models showed that conventional type 1 DCs and plasmacytoid DCs were required for the response. In tumour models where the combined treatment was less effective, the addition of tumour-antigen derived peptide, preferably conjugated to α-GalCer, significantly enhanced the antitumour response. The combination of TLR ligation, NKT cell agonism, and peptide delivery could therefore be adapted to induce responses to both known and unknown antigens.

NKT Cell-Driven Enhancement of Antitumor Immunity Induced by Clec9a-Targeted Tailorable Nanoemulsion

Invariant natural killer T (iNKT) cells are a subset of lymphocytes with immune regulatory activity. Their ability to bridge the innate and adaptive immune systems has been studied using the glycolipid ligand α-galactosylceramide (αGC). To better harness the immune adjuvant properties of iNKT cells to enhance priming of antigen-specific CD8⁺ T cells, we encapsulated both αGC and antigen in a Clec9a-targeted nanoemulsion (TNE) to deliver these molecules to cross-presenting CD8⁺ dendritic cells (DC). We demonstrate that, even in the absence of exogenous glycolipid, iNKT cells supported the maturation of CD8α⁺ DCs to drive efficient cross-priming of antigen-specific CD8⁺ T cells upon delivery of Clec9a/OVA-TNE. The addition of αGC to the TNE (Clec9a/OVA/αGC) further enhanced activation of iNKT cells, NK cells, CD8α⁺ DCs, and polyfunctional CD8⁺ T cells. When tested therapeutically against HPVE7-expressing TC-1 tumors, long-term tumor suppression was achieved with a single administration of Clec9a/E7 peptide/αGC TNE. Antitumor activity was correlated with the recruitment of mature DCs, NK cells, and tumor-specific effector CD8⁺ T cells to the tumor-draining lymph node and tumor tissue. Thus, Clec9a-TNE codelivery of CD8⁺ T-cell epitopes with αGC induces alternative helper signals from activated iNKT cells, elicits innate (iNKT, NK) immunity, and enhances antitumor CD8⁺ T-cell responses for control of solid tumors.

Interaction of neurotransmitters and neurochemicals with lymphocytes

Neurotransmitters and neurochemicals can act on lymphocytes by binding to receptors expressed by lymphocytes. This review describes lymphocyte expression of receptors for a selection of neurotransmitters and neurochemicals, the anatomical locations where lymphocytes can interact with neurotransmitters, and the effects of the neurotransmitters on lymphocyte function. Implications for health and disease are also discussed.

Recruitment of Antigen Presenting Cells to Skin Draining Lymph Node From HPV16E7-Expressing Skin Requires E7-Rb Interaction

“High-risk” human papillomaviruses (HPV) infect keratinocytes of squamous epithelia. The HPV16E7 protein induces epithelial hyperplasia by binding Rb family proteins and disrupting cell cycle termination. Murine skin expressing HPV16E7 as a transgene from a keratin 14 promoter (K14.E7) demonstrates epithelial hyperplasia, dysfunctional antigen presenting cells, ineffective antigen presentation by keratinocytes, and production of immunoregulatory cytokines. Furthermore, grafted K14.E7 skin is not rejected from immunocompetent non-transgenic recipient animals. To establish the contributions of E7, of E7-Rb interaction and of epithelial hyperplasia to altered local skin immunity, K14.E7 skin was compared with skin from K14.E7 mice heterozygous for a mutant Rb unable to bind E7 (K14.E7xRb^ΔL/ΔL mice), that have normoplastic epithelium. Previously, we demonstrated that E7-speicfic T cells do not accumulate in K14.E7xRb^ΔL/ΔL skin grafts. Here, we further show that K14.E7xRb^ΔL/ΔL skin, like K14.E7 skin, is not rejected by immunocompetent non-transgenic animals. There were fewer CD11b⁺ antigen presenting cells in skin draining lymph nodes from animals recipient of K14.E7xRb^ΔL/ΔL grafts, when compared with animals receiving K14.E7 grafts or K5mOVA grafts. Maturation of migratory DCs derived from K14.E7xRb^ΔL/ΔL grafts found in the draining lymph nodes is significantly lower than that of K14.E7 grafts. Surprisingly, K14.E7xRb^ΔL/ΔL keratinocytes, unlike K14.E7 keratinocytes, are susceptible to E7 directed CTL-mediated lysis in vitro. We conclude that E7-Rb interaction and its associated epithelial hyperplasia partially contribute to the suppressive local immune responses in area affected by HPV16E7 expression.

The prognostic significance of circulating tumor cells in head and neck and non-small-cell lung cancer

Tumor biopsy is the gold standard for the assessment of clinical biomarkers for treatment. However, tumors change dynamically in response to therapy, and there remains a need for a more representative biomarker that can be assayed over the course of treatment. Circulating tumor cells (CTCs) may provide clinically important and comprehensive tumoral information that is predictive of treatment response and outcome. Blood samples were processed for CTCs from 56 patients using the ClearCell FX system. Captured cells were phenotyped for CTC clusters and markers for immunotherapy (PD‐L1) CTC chromosomal architecture (ALK, EGFR). CTCs were isolated in 11/23 (47.8%) of head and neck cancer (HNC) patients and 17/33 (51.5%) of non‐small‐cell lung cancer (NSCLC) patients. CTCs were determined to be PD‐L1‐positive in 6/11 (54.4%) HNC and 11/17 (64.7%) NSCLC cases, respectively. 3D chromosomal DNA FISH for ALK and EGFR molecular targets showed better resolution than in 2D when imaging CTCs. HNC CTC‐positive patients had shorter progression‐free survival (PFS) (hazard ratio[HR]: 4.946; 95% confidence internal[CI]:1.571‐15.57; P = 0.0063), and PD‐L1‐positive CTCs were found to be significantly associated with worse outcome ([HR]:5.159; 95% [CI]:1.011‐26.33; P = 0.0485). In the advanced stage NSCLC patient cohort, PFS was not found to be associated with CTCs prior to therapy ([HR]:2.246; 95% [CI]:0.9565‐5.273; P = 0.0632), nor the presence of PD‐L1 expression ([HR]:1.646; 95% [CI]:0.5128‐5.283; P = 0.4023). This study demonstrated that CTCs are predictive of poorer outcomes in HNC and provides distinct and separate utility for CTCs in HNC and NSCLC, which may be more representative of the disease burden and overall survival than the parameters used to measure them.

Therapeutic vaccination with 4-1BB co-stimulation eradicates mouse acute myeloid leukemia

Immunomodulatory therapies can effectively control haematological malignancies. Previously we reported the effectiveness of combination immunotherapies that centre on 4-1BB-targeted co-stimulation of CD8 + T cells, particularly when simultaneously harnessing the immune adjuvant properties of Natural Killer T (NKT) cells. The objective of this study was to assess the effectiveness of agonistic anti-4-1BB antibody-based combination therapy against two aggressive forms of acute myeloid leukemia (AML). Anti-4-1BB treatment alone resulted in transient suppression of established AML-ETO9a tumor growth in 50% of mice, however the majority of these mice subsequently succumbed to disease. Combining alpha-galactosylceramide (α-GalCer)-loaded tumor cell vaccination with anti-4-1BB antibody treatment increased the proportion of responding mice to 100%, and protection led to long-term, tumor-free survival, demonstrating complete eradication of AML. This finding was extended to established mixed lymphocytic leukemia (MLL)-AF9 tumors, whereby vaccine plus anti-4-1BB combination similarly resulted in 100% protection. The addition of anti-PD-1 to anti-4-1BB treatment, although improving survival outcomes compared to anti-4-1BB alone, was not as effective as NKT cell vaccination. The effectiveness of 4-1BB combination therapies was dependent on IFN-γ signaling within host cells, but not tumors. Vaccine plus anti-4-1BB therapy elicited potent generation of functional effector and memory CD8 + T cells in all tumor-associated organs. Therapy induced KLRG1+ effector CD8 T cells were the most effective at controlling disease. We show that combining NKT cell-targeting vaccination with anti-4-1BB provides excellent therapeutic responses against AML and MLL in mice, and these results will guide ongoing efforts in finding immunotherapeutic solutions against acute myeloid leukemias.

HPV16E7-Induced Hyperplasia Promotes CXCL9/10 Expression and Induces CXCR3+ T-Cell Migration to Skin

Chemokines regulate tissue immunity by recruiting specific subsets of immune cells. Mice expressing the E7 protein of human papilloma virus 16 as a transgene from a keratin 14 promoter (K14.E7) show increased epidermal and dermal lymphocytic infiltrates, epidermal hyperplasia, and suppressed local immunity. Here, we show that CXCL9 and CXCL10 are overexpressed in non-hematopoietic cells in skin of K14.E7 mice when compared with non-transgenic animals, and recruit CXCR3⁺ lymphocytes to the hyperplastic skin. Overexpression of CXCL9 and CXCL10 is not observed in E7 transgenic mice with mutated Rb gene whose protein product cannot interact with E7 (K14.E7xRb^ΔL/ΔL) and in consequence lack hyperplastic epithelium. CXCR3⁺ T cells are preferentially recruited by CXCL9 and CXCL10 in supernatants of K14.E7 but not K14.E7xRb^ΔL/ΔL skin cultures in vitro. CXCR3 signalling promotes infiltration of a subset of effector T lymphocytes that enables donor lymphocyte deficient, E7-expressing skin graft rejection. Taken together, this suggests that recruitment of CXCR3⁺ T cells can be an important factor in the rejection of precancerous skin epithelium providing they can overcome local immunosuppressive mechanisms driven by skin-resident lymphocytes.

B cell lymphoma progression promotes the accumulation of circulating Ly6Clo monocytes with immunosuppressive activity

Monocytosis is considered a poor prognostic factor for many cancers, including B cell lymphomas. The mechanisms by which different monocyte subsets support the growth of lymphoma is poorly understood. Using a pre-clinical mouse model of B cell non-Hodgkin's lymphoma (B-NHL), we investigated the impact of tumor progression on circulating monocyte levels, subset distribution and their activity, with a focus on immune suppression. B-NHL development corresponded with significant expansion initially of classical (Ly6Chi) and non-classical (Ly6Clo) monocytes, with accumulation and eventual predominance of Ly6Clo cells. The lymphoma environment promoted the conversion, preferential survival and immune suppressive activity of Ly6Clo monocytes. Ly6Clo monocytes expressed higher levels of immunosuppressive genes including PD-L1/2, Arg1, IDO1 and CD163, compared to Ly6Chi monocytes. Both monocyte subsets suppressed CD8 T cell proliferation and IFN-γ production in vitro, but via different mechanisms. Ly6Chi monocyte suppression was contact dependent, while Ly6Clo monocytes suppressed via soluble mediators, including IDO and arginase. Ly6Clo monocytes could be selectively depleted in tumor-bearing hosts by liposomal doxorubicin treatment, further enhanced by co-administration of anti-4-1BB monoclonal antibody. This treatment led to a reduction in tumor growth, but failed to improve overall survival. Analogous immunosuppressive monocytes were observed in peripheral blood of diffuse large B cell lymphoma patients and actively suppressed human CD8 T cell proliferation. This study highlights a potential immune evasion strategy deployed by B cell lymphoma involving accumulation of circulating non-classical monocytes with immunosuppressive activity.

Natural killer cell metabolism

Natural killer (NK) cells are a critical component in the innate immune response against disease. NK cell function is tightly regulated by specific cytokine and activation/inhibitory receptor signalling, leading to diverse effector responses. Like all living cells, energy metabolism is a fundamental requirement for NK cell activation and survival. There is growing evidence that distinct functional profiles of NK cells are determined by alterations to cellular metabolic pathways. In this review, we summarise current literature that has explored NK cell metabolism to provide insight into how metabolic regulation controls NK cell function. We focus on metabolism pathways induced by different NK cell stimuli, metabolic regulatory proteins, and nutrient and hormonal levels in health and disease which impact on NK cell metabolic and functional activity.

Invariant Natural Killer T Cells in Immune Regulation of Blood Cancers: Harnessing Their Potential in Immunotherapies

Invariant natural killer T (iNKT) cells are a unique innate T lymphocyte population that possess cytolytic properties and profound immunoregulatory activities. iNKT cells play an important role in the immune surveillance of blood cancers. They predominantly recognize glycolipid antigens presented on CD1d, but their activation and cytolytic activities are not confined to CD1d expressing cells. iNKT cell stimulation and subsequent production of immunomodulatory cytokines serve to enhance the overall antitumor immune response. Crucially, the activation of iNKT cells in cancer often precedes the activation and priming of other immune effector cells, such as NK cells and T cells, thereby influencing the generation and outcome of the antitumor immune response. Blood cancers can evade or dampen iNKT cell responses by downregulating expression of recognition receptors or by actively suppressing or diverting iNKT cell functions. This review will discuss literature on iNKT cell activity and associated dysregulation in blood cancers as well as highlight some of the strategies designed to harness and enhance iNKT cell functions against blood cancers.

The duality of macrophage function in chronic lymphocytic leukaemia

Chronic lymphocytic leukaemia (CLL) is the most common adult leukaemia and, in some patients, is accompanied by resistance to both chemotherapeutics and immunotherapeutics. In this review we will discuss the role of tumour associated macrophages (TAMs) in promoting CLL cell survival and resistance to immunotherapeutics. In addition, we will discuss mechanisms by which TAMs suppress T-cell mediated antitumour responses. Thus, targeting macrophages could be used to i) reduce the leukaemic burden via the induction of T-cell-mediated antitumour responses, ii) to reduce pro-survival signalling and enhance response to conventional chemotherapeutics or iii) enhance the response to therapeutic antibodies in current clinical use.

Control of B-cell lymphoma by therapeutic vaccination and acquisition of immune resistance is independent of direct tumour IFN-gamma signalling

Immunomodulatory therapies can effectively control haematological malignancies by promoting antitumour immunity. Previously, we reported transient growth of poorly immunogenic murine non-Hodgkin B-cell lymphomas (B-NHL) by targeting natural killer T (NKT) cells with a therapeutic vaccine approach. Therapeutic efficacy was highly dependent on the ability of the vaccine to provoke rapid interferon-gamma (IFNγ) production from NKT and NK cells. By manipulating the capacity of either host or lymphoma cells to signal through the IFNγ receptor (IFNγR), we investigated whether the therapeutic effect conferred by vaccine-induced IFNγ is a result of immune cell activation, lymphoma IFNγ sensitivity or a combination of both. We demonstrated that antitumour immunity elicited by vaccination requires IFNγ signalling within host cells but not tumour cells. IFNγR-deficient mice failed to mount an effective antitumour immune response following vaccination despite elevated IFNγ levels. With successive exposure to vaccination, lymphomas acquired an increasingly therapy-resistant phenotype and displayed a reduction in major histocompatibility complex I and CD1d surface expression, which is independent of tumour intrinsic IFNγ signalling. Our results suggest that immunotherapy-induced IFNγ production mainly exerts its therapeutic effect via signalling through host cells, rather than directly to tumour cells in B-NHL. This signifies that intact IFNγ signalling within patients' immune compartment rather than tumour cell sensitivity to IFNγ is more critical for successful treatment. Finally, tumour IFNγ signalling alone does not drive acquired tumour resistance to vaccination, implying that additional immunoediting pathways are responsible for tumour immune escape.

Molecular and Translational Classifications of DAMPs in Immunogenic Cell Death

The immunogenicity of malignant cells has recently been acknowledged as a critical determinant of efficacy in cancer therapy. Thus, besides developing direct immunostimulatory regimens, including dendritic cell-based vaccines, checkpoint-blocking therapies, and adoptive T-cell transfer, researchers have started to focus on the overall immunobiology of neoplastic cells. It is now clear that cancer cells can succumb to some anticancer therapies by undergoing a peculiar form of cell death that is characterized by an increased immunogenic potential, owing to the emission of the so-called “damage-associated molecular patterns” (DAMPs). The emission of DAMPs and other immunostimulatory factors by cells succumbing to immunogenic cell death (ICD) favors the establishment of a productive interface with the immune system. This results in the elicitation of tumor-targeting immune responses associated with the elimination of residual, treatment-resistant cancer cells, as well as with the establishment of immunological memory. Although ICD has been characterized with increased precision since its discovery, several questions remain to be addressed. Here, we summarize and tabulate the main molecular, immunological, preclinical, and clinical aspects of ICD, in an attempt to capture the essence of this phenomenon, and identify future challenges for this rapidly expanding field of investigation.

Langerhans cell homeostasis and activation is altered in hyperplastic human papillomavirus type 16 E7 expressing epidermis

It has previously been shown that expression of human papillomavirus type 16 (HPV) E7 in epidermis causes hyperplasia and chronic inflammation, characteristics of pre-malignant lesions. Importantly, E7-expressing epidermis is strongly immune suppressed and is not rejected when transplanted onto immune competent mice. Professional antigen presenting cells are considered essential for initiation of the adaptive immune response that results in graft rejection. Langerhans cells (LC) are the only antigen presenting cells located in normal epidermis and altered phenotype and function of these cells may contribute to the immune suppressive microenvironment. Here, we show that LC are atypically activated as a direct result of E7 expression in the epidermis, and independent of the presence of lymphocytes. The number of LC was significantly increased and the LC are functionally impaired, both in migration and in antigen uptake. However when the LC were extracted from K14E7 skin and matured in vitro they were functionally competent to present and cross-present antigen, and to activate T cells. The ability of the LC to present and cross-present antigen following maturation supports retention of full functional capacity when removed from the hyperplastic skin microenvironment. As such, opportunities are afforded for the development of therapies to restore normal LC function in hyperplastic skin.

Interleukin-17A Promotes Arginase-1 Production and 2,4-Dinitrochlorobenzene-Induced Acute Hyperinflammation in Human Papillomavirus E7 Oncoprotein-Expressing Skin

Human papillomaviruses (HPVs) have evoked numerous mechanisms to subvert host innate immunity and establish a local immunosuppressive environment to facilitate persistent virus infection. Topical application of 2,4-dinitrochlorobenzene (DNCB) was speculated to overcome this immunosuppressive environment and was employed in the immunotherapy of HPV-associated lesions. We have previously shown that DNCB treatment of skin expressing HPV16.E7 protein, the major oncogenic protein expressed in HPV-associated premalignant cervical epithelium, results in a hyperinflammatory response, with an associated induction of Th2 cytokines and infiltration of myeloid cells producing arginase-1, which also contributes to the hyperinflammation. However, the molecular mechanisms underlying arginase-1 induction and arginase-mediated hyperinflammation in K14.E7 skin have not been elucidated. Here, we show that HPV16.E7 protein expression as a transgene in skin is associated with enhanced IL-17A production by macrophages exposed to DNCB. Interestingly, induction of arginase-1 by DNCB is not seen in K14.E7 animals unable to express IL-17A. Further, blockade of either IL-17A or arginase activity alleviates DNCB-induced hyperinflammation through reduced recruitment of neutrophils, as a consequence of decreased CXCL1 and CXCL5 chemokine production. Thus, our findings suggest that increased IL-17A expression by macrophages in E7-expressing skin exposed to DNCB promotes arginase-1 induction and contributes directly to the observed hyperinflammation.

NKT cell-targeted vaccination plus anti-4-1BB antibody generates persistent CD8 T cell immunity against B cell lymphoma

Harnessing the immune adjuvant properties of natural killer T (NKT) cells is an effective strategy to generate anticancer immunity. The objective of this study was to increase the potency and durability of vaccine-induced immunity against B cell lymphoma by combining α-galactosylceramide (α-GalCer)-loaded tumor cell vaccination with an agonistic antibody targeting the immune checkpoint molecule 4–1BB (CD137). We observed potent synergy when combining vaccination and anti-4–1BB antibody treatment resulting in significantly enhanced survival of mice harboring Eμ-myc tumors, including complete eradication of lymphoma in over 50% of mice. Tumor-free survival required interferon γ (IFNγ)-dependent expansion of CD8⁺ T cells and was associated with 4–1BB-mediated differentiation of KLRG1⁺ effector CD8⁺ T cells. 'Cured' mice were also resistant to lymphoma re-challenge 80 days later indicating successful generation of immunological memory. Overall, our results demonstrate that therapeutic anticancer vaccination against B cell lymphoma using an NKT cell ligand can be boosted by subsequent co-stimulation through 4–1BB leading to a sustainable immune response that may enhance outcomes to conventional treatment.

NKT cell adjuvants in therapeutic vaccines against hematological cancers

Immune adjuvants aimed at initiating or re-activating host immunity against poorly immunogenic cancers represent a potential tool for immunotherapy. By employing the natural killer T (NKT) cell agonist α-galactosylceramide in a whole tumor cell therapeutic vaccine approach, we have achieved potent suppression of established hematological cancers upon the elicitation of innate and adaptive antitumor immunity.

IL-17 suppresses immune effector functions in human papillomavirus-associated epithelial hyperplasia

Persistent infection with high-risk human papillomaviruses (HPV) causes epithelial hyperplasia that can progress to cancer and is thought to depend on immunosuppressive mechanisms that prevent viral clearance by the host. IL-17 is a cytokine with diverse functions in host defense and in the pathology of autoimmune disorders, chronic inflammatory diseases, and cancer. We analyzed biopsies from patients with HPV-associated cervical intraepithelial neoplasia grade 2/3 and murine skin displaying HPV16 E7 protein-induced epithelial hyperplasia, which closely models hyperplasia in chronic HPV lesions. Expression of IL-17 and IL-23, a major inducer of IL-17, was elevated in both human HPV-infected and murine E7-expressing lesions. Using a skin-grafting model, we demonstrated that IL-17 in HPV16 E7 transgenic skin grafts inhibited effective host immune responses against the graft. IL-17 was produced by CD3(+) T cells, predominantly CD4(+) T cells in human, and CD4(+) and γδ T cells in mouse hyperplastic lesions. IL-23 and IL-1β, but not IL-18, induced IL-17 production in E7 transgenic skin. Together, these findings demonstrate an immunosuppressive role for IL-17 in HPV-associated epithelial hyperplasia and suggest that blocking IL-17 in persistent viral infection may promote antiviral immunity and prevent progression to cancer.

Human papillomavirus e7 oncoprotein transgenic skin develops an enhanced inflammatory response to 2,4-dinitrochlorobenzene by an arginase-1-dependent mechanism

We have shown that the expression of human papillomavirus type 16 E7 (HPV16.E7) protein within epithelial cells results in local immune suppression and a weak and ineffective immune response to E7 similar to that occuring in HPV-associated premalignancy and cancers. However, a robust acute inflammatory stimulus can overcome this to enable immune elimination of HPV16.E7-transformed epithelial cells. 2,4-Dinitrochlorobenzene (DNCB) can elicit acute inflammation and it has been shown to initiate the regression of HPV-associated genital warts. Although the clinical use of DNCB is discouraged owing to its mutagenic potential, understanding how DNCB-induced acute inflammation alters local HPV16.E7-mediated immune suppression might lead to better treatments. Here, we show that topical DNCB application to skin expressing HPV16.E7 as a transgene induces a hyperinflammatory response, which is not seen in nontransgenic control animals. The E7-associated inflammatory response is characterized by enhanced expression of Th2 cytokines and increased infiltration of CD11b(+)Gr1(int)F4/80(+)Ly6C(hi)Ly6G(low) myeloid cells, producing arginase-1. Inhibition of arginase with an arginase-specific inhibitor, N(omega)-hydroxy-nor-L-arginine, ameliorates the DNCB-induced inflammatory response. Our results demonstrate that HPV16.E7 protein enhances DNCB-associated production of arginase-1 by myeloid cells and consequent inflammatory cellular infiltration of skin.

An intact immune system is required for the anticancer activities of histone deacetylase inhibitors

Cell-intrinsic effects such as induction of apoptosis and/or inhibition of cell proliferation have been proposed as the major antitumor responses to histone deacetylase inhibitors (HDACi). These compounds can also mediate immune-modulatory effects that may contribute to their anticancer effects. However, HDACi can also induce anti-inflammatory, and potentially immunosuppressive, outcomes. We therefore sought to clarify the role of the immune system in mediating the efficacy of HDACi in a physiologic setting, using preclinical, syngeneic murine models of hematologic malignancies and solid tumors. We showed an intact immune system was required for the robust anticancer effects of the HDACi vorinostat and panobinostat against a colon adenocarcinoma and two aggressive models of leukemia/lymphoma. Importantly, although HDACi-treated immunocompromised mice bearing established lymphoma succumbed to disease significantly earlier than tumor bearing, HDACi-treated wild-type (WT) mice, treatment with the conventional chemotherapeutic etoposide equivalently enhanced the survival of both strains. IFN-γ and tumor cell signaling through IFN-γR were particularly important for the anticancer effects of HDACi, and vorinostat and IFN-γ acted in concert to enhance the immunogenicity of tumor cells. Furthermore, we show that a combination of vorinostat with α-galactosylceramide (α-GalCer), an IFN-γ-inducing agent, was significantly more potent against established lymphoma than vorinostat treatment alone. Intriguingly, B cells, but not natural killer cells or CD8(+) T cells, were implicated as effectors of the vorinostat antitumor immune response. Together, our data suggest HDACi are immunostimulatory during cancer treatment and that combinatorial therapeutic regimes with immunotherapies should be considered in the clinic.

CCL2/CCR2-dependent recruitment of functional antigen-presenting cells into tumors upon chemotherapy

The therapeutic efficacy of anthracyclines relies, at least partially, on the induction of a dendritic cell- and T-lymphocyte-dependent anticancer immune response. Here, we show that anthracycline-based chemotherapy promotes the recruitment of functional CD11b(+)CD11c(+)Ly6C(high)Ly6G(-)MHCII(+) dendritic cell-like antigen-presenting cells (APC) into the tumor bed, but not into lymphoid organs. Accordingly, draining lymph nodes turned out to be dispensable for the proliferation of tumor antigen-specific T cells within neoplastic lesions as induced by anthracyclines. In addition, we found that tumors treated with anthracyclines manifest increased expression levels of the chemokine Ccl2. Such a response is important as neoplasms growing in Ccl2(-/-) mice failed to accumulate dendritic cell-like APCs in response to chemotherapy. Moreover, cancers developing in mice lacking Ccl2 or its receptor (Ccr2) exhibited suboptimal therapeutic responses to anthracycline-based chemotherapy. Altogether, our results underscore the importance of the CCL2/CCR2 signaling axis for therapeutic anticancer immune responses as elicited by immunogenic chemotherapy.

Combining low-dose or metronomic chemotherapy with anticancer vaccines: A therapeutic opportunity for lymphomas

Therapeutic vaccination is regarded as a promising strategy against multiple hematological malignancies including lymphoma. However, this approach alone possesses limited potential for the treatment of established tumors. As several anticancer regimens relies on the combination of multiple drugs, it is reasonable to predict that also cancer vaccination will be most effective in the context of multimodal approaches. In particular, low-dose or metronomic chemotherapy could be coupled to anticancer vaccines to improve the efficacy of this immunotherapeutic interventions. This review summarizes recent findings in support of the use of anticancer vaccines combined with low-dose or metronomic chemotherapy for the treatment and management of lymphoid malignancies.

Expression of a single, viral oncoprotein in skin epithelium is sufficient to recruit lymphocytes

Established cancers are frequently associated with a lymphocytic infiltrate that fails to clear the tumour mass. In contrast, the importance of recruited lymphocytes during premalignancy is less well understood. In a mouse model of premalignant skin epithelium, transgenic mice that express the human papillomavirus type 16 (HPV16) E7 oncoprotein under a keratin 14 promoter (K14E7 mice) display epidermal hyperplasia and have a predominant infiltrate of lymphocytes consisting of both CD4 and CD8 T cells. Activated, but not naïve T cells, were shown to preferentially traffic to hyperplastic skin with an increased frequency of proliferative CD8+ T cells and CD4+ T cells expressing CCR6 within the tissue. Disruption of the interaction between E7 protein and retinoblastoma tumour suppressor protein (pRb) led to reduced epithelial hyperplasia and T cell infiltrate. Finally, while K14E7 donor skin grafts are readily accepted onto syngeneic, non-transgenic recipients, these same skin grafts lacking skin-resident lymphocytes were rejected. Our data suggests that expression of a single oncoprotein in the epidermis is sufficient for lymphocyte trafficking (including immunosuppressive lymphocytes) to premalignant skin.

Role of γδ T cells in α-galactosylceramide-mediated immunity

Attempts to harness mouse type I NKT cells in different therapeutic settings including cancer, infection, and autoimmunity have proven fruitful using the CD1d-binding glycolipid α-galactosylceramide (α-GalCer). In these different models, the effects of α-GalCer mainly relied on the establishment of a type I NKT cell-dependent immune cascade involving dendritic cell, NK cell, B cell, or conventional CD4(+) and CD8(+) T cell activation/regulation as well as immunomodulatory cytokine production. In this study, we showed that γδ T cells, another population of innate-like T lymphocytes, displayed a phenotype of activated cells (cytokine production and cytotoxic properties) and were required to achieve an optimal α-GalCer-induced immune response. Using gene-targeted mice and recombinant cytokines, a critical need for IL-12 and IL-18 has been shown in the α-GalCer-induced IFN-γ production by γδ T cells. Moreover, this cytokine production occurred downstream of type I NKT cell response, suggesting their bystander effect on γδ T cells. In line with this, γδ T cells failed to directly recognize the CD1d/α-GalCer complex. We also provided evidence that γδ T cells increase their cytotoxic properties after α-GalCer injection, resulting in an increase in killing of tumor cell targets. Moreover, using cancer models, we demonstrated that γδ T cells were required for an optimal α-GalCer-mediated anti-tumor activity. Finally, we reported that immunization of wild-type mice with α-GalCer enhanced the adaptive immune response elicited by OVA, and this effect was strongly mediated by γδ T cells. We conclude that γδ T cells amplify the innate and acquired response to α-GalCer, with possibly important outcomes for the therapeutic effects of this compound.

γδ T cells augment rejection of skin grafts by enhancing cross-priming of CD8 T cells to skin-derived antigen

Gamma delta T cells (γδ T cells) possess innate-like properties and are proposed to bridge the gap between innate and adaptive immunity. In this study, we explored the role of γδ T cells in cutaneous immunity using a skin transplantation model. Following engraftment of skin expressing cell-associated model antigen (Ag) (ovalbumin) in epithelial keratinocytes, skin-resident γδ T cells enhanced graft rejection. Although the effector function of CD8 T cells was intact in the absence of γδ T cells, cross-priming of CD8 T cell to graft-derived Ag was impaired in the absence of γδ T cells. The reduced graft rejection and graft priming of γδ T-cell-deficient mice was evident in both acutely inflamed and well-healed grafting models. Furthermore, expression of the CD40 activation marker on migrating dendritic cells was lower in TCRδ(-/-) mice compared with wild-type mice, regardless of the presence or absence of inflammation associated with grafting. These results indicate that γδ T cells enhance graft priming and consequently the likelihood of a successful immune outcome in the context of skin graft rejection, suggesting that γδ T cells may be an important component of immunity to epithelial cancers or infection.

Regulation of immune responses to HPV infection and during HPV-directed immunotherapy

The recent development of vaccines prophylactic against human papillomavirus (HPV) infection has the potential to reduce the incidence of cervical cancer globally by up to 70% over the next 40 years, if universal immunization is adopted. As these prophylactic vaccines do not alter the natural history of established HPV infection, immunotherapies to treat persistent HPV infection and associated precancers would be of benefit to assist with cervical cancer control. Efforts to develop immuno-therapeutic vaccines have been hampered by the relative non-immunogenicity of HPV infection, by immunoregulatory processes in skin, and by subversion of immune response induction and immune effector functions by papillomavirus proteins. This review describes HPV-specific immune responses induced by viral proteins, their regulation by host and viral factors, and highlights some conclusions from our own recent research.

NKT cells inhibit antigen-specific effector CD8 T cell induction to skin viral proteins

We recently demonstrated that CD1d-restricted NKT cells resident in skin can inhibit CD8 T cell-mediated graft rejection of human papillomavirus E7-expressing skin through an IFN-γ-dependent mechanism. In this study, we examined the role of systemically derived NKT cells in regulating the rejection of skin grafts expressing viral proteins. In lymph nodes draining transplanted skin, Ag-specific CD8 T cell proliferation, cytokine production, and cytotoxic activity were impaired by NKT cells. NKT cell suppression was mediated via CD11c(+) dendritic cells. Inhibition of CD8 T cell function did not require Foxp3(+) regulatory T cells or NKT cell-secreted IFN-γ, IL-10, or IL-17. Thus, following skin grafting or immunization with human papillomavirus-E7 oncoprotein, NKT cells reduce the capacity of draining lymph node-resident APCs to cross-present Ag to CD8 T cell precursors, as evidenced by impaired expansion and differentiation to Ag-specific CD8 T effector cells. Therefore, in the context of viral Ag challenge in the skin, systemic NKT cells limit the capacity for effective priming of adaptive immunity.

Prevention and treatment of papillomavirus-related cancers through immunization

Cervical and other anogenital cancers are initiated by infection with one of a small group of human papillomaviruses (HPV). Virus-like particle-based vaccines have recently been developed to prevent infection with two cancer-associated HPV genotypes (HPV16, HPV18) and have been ∼95% effective at preventing HPV-associated disease caused by these genotypes in virus-naive subjects. Although immunization induces virus-neutralizing antibody sufficient to prevent infection, persistence of antibody as measured by current assays does not appear necessary to maintain protection over time. Investigators have not identified a reliable surrogate immunological marker of protection against disease following immunization. The prophylactic vaccines are not therapeutic for existing infection. Trials of HPV-specific immunotherapy have shown some efficacy for existing disease, although animal modeling suggests that a combination of immunization and local enhancement of innate immunity may be necessary for optimal therapeutic outcome. HPV prophylactic vaccines are the first vaccines designed to prevent a human cancer and are the practical outcome of a global collaborative effort between basic and applied scientists, clinicians, and industry.

Contribution of IL-17-producing gamma delta T cells to the efficacy of anticancer chemotherapy

IL-17 production by γδ T cells is required for tumor cell infiltration by IFN-γ–producing CD8⁺ T cells and inhibition of tumor growth in response to anthracyclines.

By triggering immunogenic cell death, some anticancer compounds, including anthracyclines and oxaliplatin, elicit tumor-specific, interferon-γ–producing CD8⁺ αβ T lymphocytes (Tc1 CTLs) that are pivotal for an optimal therapeutic outcome. Here, we demonstrate that chemotherapy induces a rapid and prominent invasion of interleukin (IL)-17–producing γδ (Vγ4⁺ and Vγ6⁺) T lymphocytes (γδ T17 cells) that precedes the accumulation of Tc1 CTLs within the tumor bed. In T cell receptor δ^−/− or Vγ4/6^−/− mice, the therapeutic efficacy of chemotherapy was compromised, no IL-17 was produced by tumor-infiltrating T cells, and Tc1 CTLs failed to invade the tumor after treatment. Although γδ T17 cells could produce both IL-17A and IL-22, the absence of a functional IL-17A–IL-17R pathway significantly reduced tumor-specific T cell responses elicited by tumor cell death, and the efficacy of chemotherapy in four independent transplantable tumor models. Adoptive transfer of γδ T cells restored the efficacy of chemotherapy in IL-17A^−/− hosts. The anticancer effect of infused γδ T cells was lost when they lacked either IL-1R1 or IL-17A. Conventional helper CD4⁺ αβ T cells failed to produce IL-17 after chemotherapy. We conclude that γδ T17 cells play a decisive role in chemotherapy-induced anticancer immune responses.

Secretion of IFN-gamma but not IL-17 by CD1d-restricted NKT cells enhances rejection of skin grafts expressing epithelial cell-derived antigen

NKT cells are key regulators of autoimmunity, tumor immune surveillance, and the immune response to pathogens. The role of NKT cells in regulating adaptive immunity to cutaneous Ags is largely unknown. This study explores the role of CD1d-restricted NKT cells in cross-priming of CD8 effector T cells to OVA expressed in epithelial keratinocytes (K5mOVA transgenic mouse). In a skin grafting model, we show that NKT cells enhance the rejection of K5mOVA skin grafts by promoting generation of OVA-specific CD8 effector T cells in the skin-draining lymph nodes. This is associated with a decrease in the proportion of both Th17 cells and IL-17-producing NKT cells within the lymph node, thereby inducing a Th1-biased response by increasing the ratio of IFN-gamma to IL-17 production. Administration of a strong agonist ligand (alpha-galactosylceramide) for NKT cells induced higher levels of local IFN-gamma production, enhancing the rate of K5mOVA graft rejection. Thus, NKT cells can promote adaptive immunity to cell-associated Ag expressed in skin by local regulation of IFN-gamma production in secondary lymphoid tissue during cross-priming of effector CD8 T cells.

Invariant NKT cells in hyperplastic skin induce a local immune suppressive environment by IFN-gamma production

NKT cells can promote or inhibit adaptive immune responses. Cutaneous immunity is tightly regulated by cooperation between innate and adaptive immune processes, but the role of NKT cells in regulating cutaneous immunity is largely unknown. In this study, we show, in a mouse model, that skin-infiltrating CD1d-restricted NKT cells in HPV16-E7 transgenic hyperplastic skin produce IFN-gamma, which can prevent rejection of HPV16-E7-expressing skin grafts. Suppression of graft rejection is associated with the accumulation of CD1d(hi)-expressing CD11c(+)F4/80(hi) myeloid cells in hyperplastic skin. Blockade of CD1d, removal of NKT cells, or local inhibition of IFN-gamma signaling is sufficient to restore immune-mediated graft rejection. Thus, inhibition of NKT cell recruitment or function may enable effective immunity against tumor and viral Ags expressed in epithelial cells.

V gamma 9 V delta 2 T cell cytotoxicity against tumor cells is enhanced by monoclonal antibody drugs--rituximab and trastuzumab

V gamma 9 V delta 2 T cells exert potent cytotoxicity toward various tumor cells and adoptive transfer of V gamma 9 V delta 2 T cells is an attractive proposition for cell based immunotherapy. V gamma 9 V delta 2 T cells expanded in the presence of Zoledronate and IL-2 express CD16 (Fc gamma RIII), which raises the possibility that V gamma 9 V delta 2 T cells could be used in conjunction with tumor targeting monoclonal antibody drugs to increase antitumor cytotoxicity by antibody dependent cellular cytotoxicity (ADCC). Cytotoxic activity against CD20-positive B lineage lymphoma or chronic lymphocytic leukemia (CLL) and HER2-positive breast cancer cells was assessed in the presence of rituximab and trastuzumab, respectively. Cytotoxicity of V gamma 9 V delta 2 T cells against CD20-positive targets was higher when used in combination with rituximab. Similarly, V gamma 9 V delta 2 T cells used in combination with trastuzumab resulted in greater cytotoxicity against HER2-positive cells in comparison with either agent alone and this effect was restricted to the CD16(+)V gamma 9 V delta 2 T cell population. Our results show that CD16(+)V gamma 9 V delta 2 T cells recognize monoclonal antibody coated tumor cells via CD16 and exert ADCC similar to that observed with NK cells, even when target cells are relatively resistant to monoclonal antibodies or V gamma 9 V delta 2 T cells alone. Combination therapy involving ex vivo expanded CD16(+)V gamma 9 V delta 2 T cells and monoclonal antibodies may enhance the clinical outcomes for patients treated with monoclonal antibody therapy.

Chemotherapy and zoledronate sensitize solid tumour cells to Vgamma9Vdelta2 T cell cytotoxicity

Combinations of cellular immune-based therapies with chemotherapy and other antitumour agents may be of significant clinical benefit in the treatment of many forms of cancer. Gamma delta (gammadelta) T cells are of particular interest for use in such combined therapies due to their potent antitumour cytotoxicity and relative ease of generation in vitro. Here, we demonstrate high levels of cytotoxicity against solid tumour-derived cell lines with combination treatment utilizing Vgamma9Vdelta2 T cells, chemotherapeutic agents and the bisphosphonate, zoledronate. Pre-treatment with low concentrations of chemotherapeutic agents or zoledronate sensitized tumour cells to rapid killing by Vgamma9Vdelta2 T cells with levels of cytotoxicity approaching 90%. In addition, zoledronate enhanced the chemotherapy-induced sensitization of tumour cells to Vgamma9Vdelta2 T cell cytotoxicity resulting in almost 100% lysis of tumour targets in some cases. Vgamma9Vdelta2 T cell cytotoxicity was mediated by perforin following TCR-dependent and isoprenoid-mediated recognition of tumour cells. Production of IFN-gamma by Vgamma9Vdelta2 T cells was also induced after exposure to sensitized targets. We conclude that administration of Vgamma9Vdelta2 T cells at suitable intervals after chemotherapy and zoledronate may substantially increase antitumour activities in a range of malignancies.

Chemotherapy pretreatment sensitizes solid tumor-derived cell lines to Vα24+ NKT cell-mediated cytotoxicity

There is an increasing awareness of the therapeutic potential for combining immune-based therapies with chemotherapy in the treatment of malignant diseases, but few published studies evaluate possible cytotoxic synergies between chemotherapy and cytotoxic immune cells. Human V alpha 24+/V beta 11+ NKT cells are being evaluated for use in cell-based immunotherapy of malignancy because of their immune regulatory functions and potent cytotoxic potential. In this study, we evaluated the cytotoxicity of combinations of chemotherapy and NKT cells to determine whether there is a potential to combine these treatment modalities for human cancer therapy. The cytotoxicity of NKT cells was tested against solid-tumor derived cell lines NCI-H358, DLD-1, HT-29, DU-145, TSU-Pr1 and MDA-MB231, with or without prior treatment of these target cells, with a range of chemotherapy agents. Low concentrations of chemotherapeutic agents led to sensitization of cell lines to NKT-mediated cytotoxicity, with the greatest effect being observed for prostate cancer cells. Synergistic cytotoxicity occurred in an NKT cell in a dose-dependent manner. Chemotherapy agents induced upregulation of cell surface TRAIL-R2 (DR5) and Fas (CD95) expression, increasing the capacity for NKT cells to recognize and kill via TRAIL- and FasL-mediated pathways. We conclude that administration of cytotoxic immune cells after chemotherapy may increase antitumor activities in comparison with the use of either treatment alone.