Sorafenib but not sunitinib affects the induction of immune responses

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Background: The tyrosine kinase inhibitors (TKIs) sorafenib and sunitinib are approved for the treatment of patients with metastatic renal cell cancer. To analyze the possible use of these compounds in combination with immunotherapeutic approaches we investigated the effects of both TKIs on function of human dendritic cells (DCs) and induction of primary immune responses in vitro and in vivo. Methods: Human monocytes-derived DCs were treated with DMSO, sorafenib or sunitinib. Functional and phenotypic analyses as well as the possible impact on signal transduction pathways were performed. Furthermore, induction of immune responses in vivo was analyzed in animals treated with both compounds. Results: Sorafenib but not sunitinib inhibits function of DCs. Exposure of DCs to sorafenib reduces expression of CD1a, MHC and costimulatory molecules in response to stimuli via TLR ligands. Sorafenib reduces cytokine production by DCs as well as their ability to migrate and stimulate T cell (TC) responses. We found that these inhibitory effects of sorafenib are mediated via inhibition of PI3K, MAP kinases and NFκB signaling. The TKIs have no influence on phenotype and proliferation of TCs. To analyze the effects of TKIs on the generation of immune responses in vivo, induction of TC responses was assessed by peptide vaccination with the model antigen OVA-001 in C57BL/6 mice. When mice were pretreated with both TKIs which were also given during vaccination, it was observed that sorafenib, but not sunitinib significantly reduces the generation of vaccine-specific CD8+ TCs. Numbers of CD4+ CD25+ regulatory TCs are reduced in sunitinib-treated mice, but not in sorafenib-treated animals. All effects of the TKIs are reversible, and the immune responses go back to normal levels if mice are immunized after discontinuation of treatment. Conclusions: In summary, sunitinib represents an interesting compound to be used in combination with immunotherapeutic approaches to treat cancer patients.

No significant financial relationships to disclose.

The heat shock protein Gp96 links innate and specific immunity

Among other heat shock proteins (HSPs), the ER-resident chaperone Gp96 has been described as a potent tumour vaccine in animal models. A growing list of data underlines that Gp96 triggers both arms of pathogen defence-innate and specific immunity-in a synergistic and most efficient way: It enables specific immune responses by transferring immunogenic peptides that have been acquired in the ER to the MHC class I pathway of antigen presenting cells (APCs). For this, two important features of Gp96 are required. First, its ability to bind immunogenic peptides. Secondly, its acquisition by specialized antigen presenting cells capable of inducing cellular immune responses. Due to specific receptors on the surface of APCs, this uptake from the extracellular space occurs very efficiently and rapidly. Serving the innate branch of immunity, Gp96 unspecifically activates APCs, which then provide a pro-inflammatory cytokine milieu and co-stimulation to cytotoxic T cells. Thus, Gp96 uses all resources of the immune system to trigger cytotoxic T cell responses against associated peptides.

The role of heat shock proteins and their receptors in the activation of the immune system

Heat shock proteins (HSPs) have been described as potent tumor vaccines in animal models and are currently studied in clinical trials. The underlying immune response relies on immunogenic peptides that the HSPs have acquired intracellularly by interfering with the classical antigen processing pathways. There have been numerous reports shedding light on how HSPs are able to gain this function and a number of important requirements for HSP-mediated specific immunity have been described: first, the ability of HSPs to bind immunogenic peptides. Second, the acquisition of HSPs by specialized antigen presenting cells with efficient antigen processing pathways capable of inducing cellular immune responses. Third, the existence of specific receptors on the surfaces of antigen presenting cells, allowing efficient and rapid uptake of HSP-peptide complexes from the extracellular fluid. And fourth, the ability of heat shock proteins to activate antigen presenting cells, enabling the latter to prime cytotoxic T cell responses against the peptides associated to HSPs.

The heat shock protein gp96 induces maturation of dendritic cells and down-regulation of its receptor

Peptides associated with the heat shock protein gp96 induce a specific T cell response against cells from which gp96 is isolated. Recently, we have shown that gp96 binds to a yet unknown receptor present on dendritic cells (DC) and that receptor-mediated uptake is required for cross-presentation of gp96-associated peptides by DC. We now describe that gp96 mediates maturation of DC as determined by up-regulation of MHC class II and CD86 molecules, secretion of the cytokines IL-12 and TNF-alpha and enhanced T cell stimulatory capacity. Heat-denatured gp96 is not able to induce DC maturation and cytokine secretion. Furthermore, we show that mature DC are no longer able to bind gp96 molecules. Hence, the gp96 receptor is down-regulated on mature DC, suggesting that this receptor behaves similar to other receptors involved in antigen uptake like the scavenger receptor CD36, the mannose receptor or the integrins alpha(v)beta(3) and alpha(v)beta(5). Together, our findings provide an additional explanation for the remarkable immunogenicity of gp96 as a cross-priming antigen carrier and direct activator of DC.

The heat shock protein gp96 induces maturation of dendritic cells and down-regulation of its receptor

Peptides associated with the heat shock protein gp96 induce a specific T cell response against cells from which gp96 is isolated. Recently, we have shown that gp96 binds to a yet unknown receptor present on dendritic cells (DC) and that receptor-mediated uptake is required for cross-presentation of gp96-associated peptides by DC. We now describe that gp96 mediates maturation of DC as determined by up-regulation of MHC class II and CD86 molecules, secretion of the cytokines IL-12 and TNF-alpha and enhanced T cell stimulatory capacity. Heat-denatured gp96 is not able to induce DC maturation and cytokine secretion. Furthermore, we show that mature DC are no longer able to bind gp96 molecules. Hence, the gp96 receptor is down-regulated on mature DC, suggesting that this receptor behaves similar to other receptors involved in antigen uptake like the scavenger receptor CD36, the mannose receptor or the integrins alpha(v)beta(3) and alpha(v)beta(5). Together, our findings provide an additional explanation for the remarkable immunogenicity of gp96 as a cross-priming antigen carrier and direct activator of DC.