Hendrik W. van Deventer

The inflammasome component NLRP3 impairs antitumor vaccine by enhancing the accumulation of tumor-associated myeloid-derived suppressor cells.

The inflammasome is a proteolysis complex that generates the active forms of the proinflammatory cytokines interleukin (IL)-1β and IL-18. Inflammasome activation is mediated by NLR proteins that respond to microbial and nonmicrobial stimuli. Among NLRs, NLRP3 senses the widest array of stimuli and enhances adaptive immunity. However, its role in antitumor immunity is unknown. Therefore, we evaluated the function of the NLRP3 inflammasome in the immune response using dendritic cell vaccination against the poorly immunogenic melanoma cell line B16-F10. Vaccination of Nlrp3(-/-) mice led to a relative 4-fold improvement in survival relative to control animals. Immunity depended on CD8(+) T cells and exhibited immune specificity and memory. Increased vaccine efficacy in Nlrp3(-/-) hosts did not reflect differences in dendritic cells but rather differences in myeloid-derived suppressor cells (MDSC). Although Nlrp3 was expressed in MDSCs, the absence of Nlrp3 did not alter either their functional capacity to inhibit T cells or their presence in peripheral lymphoid tissues. Instead, the absence of Nlrp3 caused a 5-fold reduction in the number of tumor-associated MDSCs found in host mice. Adoptive transfer experiments also showed that Nlrp3(-/-) MDSCs were less efficient in reaching the tumor site. Depleting MDSCs with an anti-Gr-1 antibody increased the survival of tumor-bearing wild-type mice but not Nlrp3(-/-) mice. We concluded that Nlrp3 was critical for accumulation of MDSCs in tumors and for inhibition of antitumor T-cell immunity after dendritic cell vaccination. Our findings establish an unexpected role for Nlrp3 in impeding antitumor immune responses, suggesting novel approaches to improve the response to antitumor vaccines by limiting Nlrp3 signaling.

C-C chemokine receptor 5 on pulmonary fibrocytes facilitates migration and promotes metastasis via matrix metalloproteinase 9.

Previously, our group has used a B16-F10 melanoma model to show that C-C chemokine receptor 5 (CCR5) knockout (CCR5(-/-)) mice form fewer pulmonary metastases than wild-type mice. This advantage can be eliminated by injecting CCR5(-/-) mice with wild-type pulmonary mesenchymal cells before tumor injection. In this article, we present the mechanisms underlying this finding. First, we demonstrate that wild-type mesenchymal cells migrate to CCL4 more efficiently in vitro than CCR5(-/-) cells. Wild-type mesenchymal cells were also 3.6 (1.85 to 5.85) times more efficient than CCR5(-/-) cells at migrating into the lung after intravenous injection (P < 0.01). The injection of wild-type but not CCR5(-/-) mesenchymal cells led to a 7.0 +/- 1.6 (P < 0.05)-fold induction of matrix metalloproteinase 9 (MMP9) in the host lung. Neither wild-type nor CCR5(-/-) cells caused significant increases in MMP2, MMP3, or MMP8. Inhibition of the gelatinase activity of MMP9 decreased the number of metastases and restored the advantage that CCR5(-/-) mice have over wild-type mice. Further analysis showed that the CCR5(+) mesenchymal cells expressed CD45(+) and CD13(+) but did not express alpha-smooth muscle actin. This phenotype is characteristic of a subset of mesenchymal cells called fibrocytes. Together, these data suggest a novel role for CCR5 in the migration of pulmonary fibrocytes and the promotion of metastasis.

Transfection of Macrophage Inflammatory Protein 1α into B16 F10 Melanoma Cells Inhibits Growth of Pulmonary Metastases But Not Subcutaneous Tumors

Macrophage inflammatory protein 1α (MIP-1α), a CC chemokine, is a chemoattractant for T cells and immature dendritic cells. Plasmacytoma cells expressing MIP-1α generate a cytotoxic T cell response without affecting tumor growth. To understand this discrepancy, we compared a local tumor model with a metastatic one using MIP-1α-transfected B16 F10 melanoma cells. Clonal idiosyncrasies were controlled by selecting three lipotransfected tumor clones and two pcDNA vector transfected control clones with equivalent in vitro proliferative capacities. No significant differences were seen between the MIP-1α-producing and control melanoma cells after s.c. injection in the hind leg. All animals had a leg diameter of 10 cm in 18.5–21.5 days. However, after i.v. injection the number of pulmonary foci was significantly reduced in the MIP-1α-producing clones. Injection of 106 control transfected cells resulted in a median of 98.5 tumor foci in 2 wk, whereas the injection of the MIP-1α-producing clones resulted in 89.5, 26.5, and 0 foci. The number of metastatic foci was inversely proportional to the amount of MIP-1α produced by the clone in vitro. Flow cytometry showed a significant increase in CD8+ cells in lungs of mice with MIP-1α-transfected tumors 3 days after injection. This increase was not maintained 10 days later despite continued production of MIP-1α. The protection offered by transfection with MIP-1α was significantly impaired in β2-microglobulin−/− mice. Our findings suggest that MIP-1α is effective in preventing the initiation of metastasis, but not at sustaining an effective antitumor response.

C-C Chemokine Receptor 5 on Stromal Cells Promotes Pulmonary Metastasis

We have shown that mice that express the C-C chemokine receptor 5 (CCR5) have enhanced local tumor growth and an impaired response to vaccine therapy compared with CCR5 knockout (CCR5(-/-)) mice. Here, we extend these observations to evaluate the function of CCR5 in pulmonary metastasis and the mechanism underlying the diminished tumor growth in CCR5(-/-) mice. Lung metastases were counted in wild-type (WT) and CCR5(-/-) mice following the injection of 1 x 10(6) B16-F10 melanoma cells. These results were compared with those from syngeneic bone marrow chimeric mice formed by the transfer of WT bone marrow into irradiated CCR5(-/-) and CCR5(-/-) marrow into irradiated WT mice. Intact CCR5(-/-) mice developed fewer metastases than WT mice (40.2 versus 70.6; P < 0.05). Bone marrow chimeras formed by the transfer of WT bone marrow into CCR5(-/-) hosts had fewer metastases than WT hosts injected with knockout marrow (46.6 versus 98.6; P < 0.01). Adoptive transfer of CCR5-expressing leukocytes also failed to promote metastasis in CCR5(-/-) mice. However, the i.v. transfer of WT pulmonary stromal cells into CCR5(-/-) mice increased the number of metastases compared with transfer of CCR5(-/-) stromal cells (102.8 versus 26.0; P < 0.05). These results show for the first time that CCR5 expression on stromal and not hematopoietic cells contributes to tumor metastasis. Therefore, recently developed CCR5 inhibitors may have a novel benefit in cancer therapy.

Circulating Fibrocytes Prepare the Lung for Cancer Metastasis by Recruiting Ly-6C+ Monocytes Via CCL2

Fibrocytes are circulating, hematopoietic cells that express CD45 and Col1a1. They contribute to wound healing and several fibrosing disorders by mechanisms that are poorly understood. In this report, we demonstrate that fibrocytes predispose the lung to B16-F10 metastasis by recruiting Ly-6C+ monocytes. To do so, we isolated fibrocytes expressing CD45, CD11b, CD13, and Col1a1 from the lungs of wild type (WT) and Ccr5−/− mice. WT but not Ccr5−/− fibrocytes increased the number of metastatic foci when injected into Ccr5−/− mice (73 ± 2 versus 32 ± 5; p < 0.001). This process was MMP9 dependent. Injection of WT enhanced GFP+ fibrocytes also increased the number of Gr-1Int, CD11b+, and enhanced GFP– monocytes. Like premetastatic-niche monocytes, these recruited cells expressed Ly-6C, CD117, and CD45. The transfer of these cells into Ccr5−/− mice enhanced metastasis (90 ± 8 foci) compared with B cells (27 ± 2), immature dendritic cells (31 ± 6), or alveolar macrophages (28 ± 3; p < 0.05). WT and Ccl2−/− fibrocytes also stimulated Ccl2 expression in the lung by 2.07 ± 0.05- and 2.78 ± 0.36-fold compared with Ccr5−/− fibrocytes (1.0 ± 0.06; p < 0.05). Furthermore, WT fibrocytes did not increase Ly-6C+ monocytes in Ccr2−/− mice and did not promote metastasis in either Ccr2−/− or Ccl2−/− mice. These data support our hypothesis that fibrocytes contribute to premetastatic conditioning by recruiting Ly-6C+ monocytes in a chemokine-dependent process. This work links metastatic risk to conditions that mobilize fibrocytes, such as inflammation and wound repair.

CC chemokine receptor 8 potentiates donor Treg survival and is critical for the prevention of murine graft-versus-host disease.

The infusion of donor regulatory T cells (Tregs) has been used to prevent acute graft-versus-host disease (GVHD) in mice and has shown promise in phase 1 clinical trials. Previous work suggested that early Treg migration into lymphoid tissue was important for GVHD prevention. However, it is unclear how and where Tregs function longitudinally to affect GVHD. To better understand their mechanism of action, we studied 2 Treg-associated chemokine receptors in murine stem cell transplant models. CC chemokine receptor (CCR) 4 was dispensable for donor Treg function in the transplant setting. Donor Tregs lacking CCR8 (CCR8(-/-)), however, were severely impaired in their ability to prevent lethal GVHD because of increased cell death. By itself, CCR8 stimulation was unable to rescue Tregs from apoptosis. Instead, CCR8 potentiated Treg survival by promoting critical interactions with dendritic cells. In vivo, donor bone marrow-derived CD11c(+) antigen-presenting cells (APCs) were important for promoting donor Treg maintenance after transplant. In contrast, host CD11c(+) APCs appeared to be dispensable for early activation and expansion of donor Tregs. Collectively, our data indicate that a sustained donor Treg presence is critical for their beneficial properties, and that their survival depends on CCR8 and donor but not host CD11c(+) APCs.

Mature B-cell acute lymphoblastic leukemia with associated translocations (14;18)(q32;q21) and (8;9)(q24;p13): A Burkitt variant?

The translocation t(14;18)(q32;q21) is most commonly associated with follicular lymphoma but has also been described in acute lymphoblastic leukemia (ALL) of B-cell origin. Although these ALL cases have had a pre-pre-B, pre-B, or mature B-cell immunophenotype and L2 or L3 morphology, all have been associated with an abnormality of 8q24. In fact, 91% (10 of 11) have been associated with t(8;22) or t(8;14), marker chromosomes for Burkitt-type ALL. The other case was associated with del(8)(q24). Thus, Burkitt-type ALL may have various immunophenotypes and morphology when associated with t(14;18). We describe a case of mature B-cell ALL associated with t(14;18) and t(8;9)(q24;p13). The morphology was suggestive but not entirely characteristic of the L3 subtype. However, on the basis of the cytogenetic findings and the review of the literature, perhaps this case represents a variant of Burkitt-type ALL, which would be important to recognize for prognostic and therapeutic purposes. We describe our findings and review the literature to heighten awareness of this group of ALLs associated with t(14;18). Additional cases need to be accrued and documented to determine the significance of an associated abnormality of 8q24 in this setting.

TNF superfamily member TWEAK exacerbates inflammation and demyelination in the cuprizone-induced model.

Inflammatory cytokines have been implicated in the pathology of multiple neurologic diseases, including multiple sclerosis. We examined the role of the TNF family member TWEAK in neuroinflammation. Cuprizone-fed mice undergo neuroinflammation and demyelination in the brain, but upon removal of cuprizone from the diet, inflammation is resolved and remyelination occurs. Using this model, we demonstrate that mice lacking TWEAK exhibit a significant delay in demyelination and microglial infiltration. During remyelination, mice lacking the TWEAK gene demonstrate only a marginal delay in remyelination. Thus, this study identifies a primary role of TWEAK in promoting neuroinflammation and exacerbating demyelination during cuprizone-induced damage.

Downregulation of immune signaling genes in patients with large surface burn injury.

We sought to evaluate the temporal pattern of expression of important immune signaling genes in patients with varied TBSA burn injury during the first week after burn. Peripheral blood mononuclear cell fractions were collected from each patient (N = 10) at two time points, one immediately following burn injury, and the other 1 week later. The change in gene expression was correlated with all clinical data including burn size. It was found that gene expression was indirectly proportional with burn size. Smaller burns (<30%) TBSA resulted in an up-regulation of several genes measured, while larger burns (>30%) TBSA resulted in significant down-regulation. In conclusion, a larger burn establishes conditions for severe immunosuppression by down-regulating key immune signaling genes and could be one explanation for the increased susceptibility of major burns to infection. These data shed light on the etiology of burn-induced immune dysfunction in humans and support a more comprehensive genomic profile study in burn patients.

A phase I dose-escalation study of clofarabine in combination with fractionated gemtuzumab ozogamicin in patients with refractory or relapsed acute myeloid leukemia

Abstract Clofarabine and gemtuzumab ozogamicin (GO) are active agents against acute myeloid leukemia (AML), but have not previously been tested in combination. We conducted a phase I study to determine the maximum tolerated dose (MTD) and dose limiting toxicities (DLTs) of clofarabine when combined with GO in adult patients with relapsed or refractory AML. Twenty patients received clofarabine (10, 20 or 30 mg/m2) on days 1–5, with GO 3 mg/m2/day on days 1, 4 and 7. Common dose-limiting toxicities were prolonged myelosuppression and hepatotoxicity. Clofarabine 20 mg/m2 was the MTD, but with a DLT rate of 0.38 (5/13) – a rate that is prohibitively high to recommend for phase II study. The overall response rate (complete response [CR] + complete response with incomplete hematologic recovery [CRi]) was 42% among all patients. Thus, this combination demonstrated activity in relapsed and refractory patients, but further testing of the combination using lower doses of GO may identify more favorable rates of toxicity while maintaining efficacy.