Towards immunotherapy of pancreatic cancer

A new era of immune therapeutics for pancreatic cancer: Monoclonal antibodies paving the way

Pancreatic cancer, particularly pancreatic ductal adenocarcinoma, remains a devastating disease with a dismal prognosis and limited survival rates. Despite various drug treatments and regimens showing promise in managing the disease, the clinical outcomes have not significantly improved. Immunotherapy however, has become a forefront area in pancreatic cancer treatment. This approach comprises a range of agents, including small molecule drugs, antibodies, combination therapies, and vaccines. In the last 5-8 years, there has been an upsurge of research into the use of monoclonal antibodies to block receptors on cancer or immune cells, revolutionising cancer treatment and management. Several targets have been identified and studied, with the most encouraging noted in relation to checkpoint markers, namely, antibodies targeting anti-programmed cell death 1 (PD-1) and its receptor PD-L1. Herein, we present the clinical developments in immunotherapy in the last 5 years especially those which have been tested in humans against pancreatic cancer.

Mannan derivatives induce phenotypic and functional maturation of mouse dendritic cells

Mannan, a polysaccharide isolated from yeast binds to C-type lectins of the mannose receptor family, expressed by antigen-presenting cells (APCs) including dendritic cells (DCs) and macrophages. As these receptors mediate endocytosis, they have been targeted with ligands to deliver antigens into APCs to initiate immune responses. Immunization with tumour antigen MUC1 conjugated to oxidized mannan (OM) or reduced mannan (RM) induced differential immune responses in mice, and only mice immunized with OM-MUC1 elicited strong MUC1-specific cytotoxic T lymphocyte responses and protected mice from a MUC1 tumour challenge. In this study, the adjuvant effect of mannan and its derivatives including OM and RM, in comparison to lipopolysaccharide, on DCs were investigated. Mannan, OM and RM were capable of stimulating mouse bone marrow-derived DC in vitro, eliciting enhanced allogeneic T-cell proliferation and enhancing OTI/OTII peptide-specific T-cell responses. Injection of mice with mannan, OM and RM induced a mature phenotype of lymph node and splenic DCs. Analysis by reverse transcription-polymerase chain reaction indicated that Manna, OM and RM also stimulated up-regulation of inflammatory cytokines including interleukin-1beta and tumour necrosis factor-alpha, and differential T helper 1 (Th1)/Th2 cytokines. Subsequent experiments demonstrated that activation of DCs was Toll-like receptor-4-dependent. The data presented here, together with evidence reported previously on OM and RM in induction of immune responses in vivo, suggest that OM and RM exert a dual capacity to target antigen to APCs as well as mature DCs.

T cell adhesion and cytolysis of pancreatic cancer cells: a role for E-cadherin in immunotherapy?

Pancreatic cancer is an aggressive and potent disease, which is largely resistant to conventional forms of treatment. However, the discovery of antigens associated with pancreatic cancer cells has recently suggested the possibility that immunotherapy might become a specific and effective therapeutic option. T cells within many epithelia, including those of the pancreas, are known to express the alphaEbeta7-integrin adhesion molecule, CD103. The only characterised ligand for CD103 is E-cadherin, an epithelial adhesion molecule which exhibits reduced expression in pancreatic cancer. In our study, CD103 was found to be expressed only by activated T cells following exposure to tumour necrosis factor beta 1, a factor produced by many cancer cells. Significantly, the expression of this integrin was restricted mainly to class I major histocompatibility complex-restricted CD8+ T cells. The human pancreatic cancer cell line Panc-1 was transfected with human E-cadherin in order to generate E-cadherin negative (wild type) and positive (transfected) sub-lines. Using a sensitive flow cytometric adhesion assay it was found that the expression of both CD103 (on T cells) and E-cadherin (on cancer cells) was essential for efficient adhesion of activated T cells to pancreatic cancer cells. This adhesion process was inhibited by the addition of antibodies specific for CD103, thereby demonstrating the importance of the CD103-->E-cadherin interaction for T-cell adhesion. Using a 51Cr-release cytotoxicity assay it was found that CD103 expressing T cells lysed E-cadherin expressing Panc-1 target cells following T cell receptor stimulation; addition of antibodies specific for CD103 significantly reduced this lysis. Furthermore, absence of either CD103 from the T cells or E-cadherin expression from the cancer cells resulted in a significant reduction in cancer cell lysis. Therefore, potentially antigenic pancreatic cancer cells could evade a local anti-cancer immune response in vivo as a consequence of their loss of E-cadherin expression; this phenotypic change may also favour metastasis by reducing homotypic adhesion between adjacent cancer cells. We conclude that effective immunotherapy is likely to require upregulation of E-cadherin expression by pancreatic cancer cells or the development of cytotoxic immune cells that are less dependent on this adhesion molecule for efficient effecter function.

Phase II study of anti-gastrin-17 antibodies, raised to G17DT, in advanced pancreatic cancer

PURPOSE

The prognosis for advanced pancreatic cancer remains poor. Gastrin acts as a growth factor for pancreatic cancer. We describe the first study of the antigastrin immunogen G17DT in pancreatic cancer. Our aims were to determine the antibody response, safety, tolerability, and preliminary evidence of efficacy of G17DT in advanced pancreatic cancer.

PATIENTS AND METHODS

Thirty patients with advanced pancreatic cancer were immunized with three doses of either 100 micro g or 250 micro g of G17DT.

RESULTS

In the whole group, 20 (67%) of 30 patients produced an antibody response. The 250- micro g dose resulted in a significantly greater response rate of 82% compared with 46% for the 100- micro g group (P =.018). The most significant side effects, seen in three patients, were local abscess and/or fever. The median survival for the whole group from the date of the first immunization was 187 days; median survival was 217 days for the antibody responders and 121 days for the antibody nonresponders. The difference in survival between the antibody responders and nonresponders was significant (P =.0023).

CONCLUSION

Patients with advanced pancreatic cancer are able to mount an adequate antibody response to G17DT. The 250- micro g dose is superior to the 100- micro g dose, and it appears to be generally well tolerated. Antibody responders demonstrate significantly greater survival than antibody nonresponders. Phase III studies are currently underway in order to determine efficacy.