Tumour‐mediated disruption of dendritic cell function: Inhibiting the MEK1/2‐p44/42 axis restores IL‐12 production and Th1‐generation

Abstract

Disfunctional dendritic cells (DC) are common in cancer patients; however, the underlying molecular targets are poorly understood. Nevertheless, adoptive-transfer and in situ vaccination protocols continue, largely without addressing immune-suppression. Understanding tumour-mediated DC suppression would assist rational design of next generation immunotherapy. This study used a tumour-lysate loaded DC model of adoptive immunotherapy and also necrotic cells common in many tumours. Patient-derived and healthy-donor monocyte-derived DC were examined for disruptions in mitogen-activated protein kinase (MAPK) signalling pathways associated with their capacity to generate Type-1 helper-T cell populations (Th1). Melanoma-lysate markedly suppressed TLR4-dependent IL-12p40 and p70 production. Suppression of IL-12p70 occurred independently of maturation markers (e.g., CD40, CD80, CD83) and correlated with depressed p35 and p40 transcription. Decreased IL-12 secretion was not associated with IL-10, TGFb, VEGF, PGE 2 or ganglioside in tumour lysates or attributable to endogenous PGE 2 release from DC. In contrast to HUVEC lysate, melanoma-lysate-treated DC were less able to generate Th1-responses from na€ ıve T-cells. The p44/42 MAPK was hyper-activated by melanoma lysate, but not that of HUVEC. Blockade of MEK1/2, the upstream kinase for p44/42, with U0126 prevented p44/42 activation, restored IL-12p70, and permitted effective generation of Th1-responses. Therefore the p44/42 MAPK is a target for tumour-mediated immune suppression of DC resulting in transcriptional down-regulation of IL-12 p35 and p40 genes, reduced IL-12 secretion and suppressed Th1-responses. Pharmacological intervention in the MEK-p44/42 axis may be applicable to render DC resistant to the suppressive effects of tumour lysates and may form part of a combination immunotherapy. ' 2008 Wiley-Liss, Inc.Key words: dendritic cell; melanoma; IL-12; MAPK; Th1 Dendritic cells (DC) play a central role for priming na€ ıve T-cell responses and act as a bridge between adaptive and innate immune systems by communicating with NK cells and neutrophils. 1 In their immature state (iDC), they serve as peripheral sentinels surveying for pathogens and would likely also encounter tumours. In the absence of endogenous danger, DC may take-up tumour antigen, either in soluble form or released from dying cells, and present this to T-cells in such a way as to maintain peripheral tolerance or promote regulation. However, even in the presence of significant endogenous or exogenous danger, DC often fail to function efficiently in tumour-bearing hosts due to pronounced immune suppression. 2 The body of evidence suggests that there are decreased numbers of DC in cancer patients and functional defects that impair priming of appropriate T-cell responses [reviewed in, 2,3 ]. Thus inhibition of DC is a key barrier to effective immunotherapy and strategies that restore DC-function will result in effective T-cell priming.To date the results from clinical trials with DC based therapies hav...

CTLA-4 positive breast cancer cells suppress dendritic cells maturation and function

“…As shown in Figure 7A, there was obviously high ERK and STAT3 activation in the DCs treated with soluble CTLA-4-Fc and CTLA-4 + BCCs compared with that in control mDCs. This was in paralleled with the result that maturation of DCs with LPS in the presence of CTLA-4-Fc resulted in robust phosphorylation of STAT3 and incubation of DCs with tumor lysates increased ERK phosphorylation [21, 22]. In contrast, the ERK and STAT3 activation were remarkably weakened in the CTLA-4 mAb-treated DCs.…”

The MAPK-Activated Kinase MK2 Attenuates Dendritic Cell–Mediated Th1 Differentiation and Autoimmune Encephalomyelitis

“…7). Additionally, multiple studies have shown that increased activity of the ERK1/2 signaling pathway in DCs attenuates IL-12 and Th1 immunity while strongly inducing IL-10 secretion and therefore serving as a molecular switch in immune regulatory processes (7,52,55,56). Interestingly, we observed both reduced ERK1/2 and enhanced p38 activation in DCs upon MK2 inhibition.…”

“…IL-10 has also been reported to be involved in various other aspects of DC-T cell interaction, such as inhibiting costimulatory molecule expression (46), down-modulating MHC class II expression (47,48), or overall hindering DC maturation (49,50). Blockade of MK2 activity does not affect expression of CD80/86 (data not shown) but triggers IL-12 and IL-1a production, and hence, as shown by others and us, Th1-mediated responses (6,16,51,52). Nevertheless, in our study enhanced IL-12 secretion became evident only in the presence of T cells and was corroborated by increased levels of IL-12Rb2 and IFN-g in T cells, pointing to the involvement of additional T cell-associated signals.…”

IFNγ Markedly Cooperates with Intratumoral Dendritic Cell Vaccine in Dog Tumor Models

“…Inefficiency in immune stimulation may be due to the degradation of DCs after their inoculation into the body of patients in which the specified cytokines abundantly supplied in vitro were deficient (8,9). In addition, some tumors, such as melanoma (10) and transmissible venereal tumor (11), inhibit DC function. It is therefore vital to obtain a clinical response that prevents DC degradation, and is important to promote the maturation and activation of DCs at the site of DC inoculation.…”