Dendritic Cells Loaded with Ultrasound-Ablated Tumour Induce in vivo Specific Antitumour Immune Responses

Abstract

Previous studies have shown that high-intensity focused ultrasound (HIFU) ablation can induce a local inflammation with marked infiltration of dendritic cells (DCs). The purpose of this study was to investigate whether DCs could capture and present activating signals delivered by necrotic tumour cells that remain in situ after HIFU, thus initiating specific antitumour immunity. Tumour debris was derived from a mouse H22 tumour model after HIFU ablation. Bone marrow-derived DCs were loaded with HIFU-treated tumour, tumour lysate and mouse serum. Syngeneic naïve C57BL/6J mice were immunised with three loaded DCs followed by a subsequent H22 tumour challenge. Tumour size and survival were then recorded in each vaccinated mouse. The results showed that both HIFU-ablated tumour and tumour lysate could significantly increase the number of mature DCs and the secretion of IL-12 and IFN-γ (p < 0.001). The proliferation of splenic lymphocytes co-incubated with the loaded-DCs was significantly higher in both HIFU-ablated tumour and tumour lysate groups (p < 0.01). Cytotoxocity and TNF-α and IFN-γ secretion of cytotoxic T lymphocytes against H22 cells were significantly higher in HIFU-ablated tumour group than that in tumour lysate group (p < 0.01). After the H22 tumour challenge, a significant decrease of tumour volume was observed in HIFU-ablated tumour group (p < 0.01). However, there was no statistical difference of long-term survival rates among three groups (p > 0.05). It is concluded that DCs can be activated by HIFU-ablated tumour debris and, thus, initiate host specific antitumour immune response after HIFU therapy. (E-mail: [email protected])

Introduction

With development of medical techniques, minimally invasive therapies, such as radio-frequency, microwave, laser, high-intensity focused ultrasound (HIFU) and cryosurgery, have recently become an alternative approach to surgical intervention in the clinical management of solid malignancies. The main advantage of these alternatives is less invasive than surgical procedure, resulting in an associated reduction in mortality, morbidity, hospital stay and cost for cancer patients (Hong et al., 2006, Liapi and Geschwind, 2007, Timmerman et al., 2009).

Of all of these minimally invasive therapies, HIFU is the only noninvasive approach proposed to date. This technique employs extracorporeal ultrasound energy to ablate a targeted tumour at depth, with no damage to the skin and overlying tissues. It has been used for the treatment of patients with solid tumours, including those of prostate, liver, pancreas, breast, kidney, uterus, bone and soft tissue (Chaussy et al., 2005, Kennedy, 2005, Wu, 2006). Much of the clinical application is recent, where clinical results are very promising for local destruction of targeted tumours. In addition, previous studies have shown that HIFU therapy can enhance host antitumour immune response (Hu et al. 2007; Hundt et al. 2007; Lu et al., 2009, Rosberger et al., 1994, Wang and Sun, 2002, Wu et al., 2004). This may be of benefit in local recurrence and metastasis control in cancer patients who have previous dysfunction of antitumour immunity.

Dendritic cells (DCs) are the potent antigen presenting cells, which play a major role in induction of adaptive immunity against cancer (Melief 2008). They capture and present tumour antigens to naïve T lymphocytes in a major histocompatibility complex (MHC) restricted fashion, thus initiating specific antitumour immune responses. Activating signals, delivered directly or indirectly by tumour cells, can induce the progression of DCs from an immature to a mature stage (Lutz and Schuler 2002). Recent studies have shown that bone marrow-derived DCs are able to promote prophylactic antitumour immunity when loaded with relevant apoptotic or necrotic tumour cells (Goldszmid et al., 2003, Neidhardt-Berard et al., 2004; Schnurr et al. 2005).

It has been noted that large amounts of tumour debris remain in situ after HIFU therapy, which may contain tumour antigens and heat shock proteins (HSP), such as HSP60 (Hu et al. 2005), HSP27 (Madersbacher et al. 1998), HSP72 and HSP73 (Kramer et al. 2004), and HSP70 (Wu et al. 2007). Our previous findings have revealed that HIFU therapy can significantly induce local infiltration of activated DCs in the debris of HIFU-treated breast cancer (Xu et al. 2009). However, it is still unknown whether DCs could capture and present activating signals delivered by necrotic tumour cells and, thus, initiate host specific antitumour immunity. In this study, we used tumour debris created by in situ HIFU therapy to load with bone marrow-derived DCs and then inoculated naïve animals against a subsequent tumour challenge. The purpose of this study was to investigate whether DCs could be activated by HIFU-ablated tumour debris and, thus, initiate host specific antitumour immune response in a murine tumour model.