Vaccell, a Japanese dendritic cell-based vaccine, is declared with “the vaccine which was optimized to fight against a cancer”. What is “optimized”?

The DCs play central roles in deciding the direction of host immune reactions as well as antigen presentation. The DCs are “headquarters” of antigen-specific host immune responses[10,11]. The antigen presentation have to be done under the helper T-cell 1 (Th1) condition that is interferon (IFN)- and interleukin (IL)-12-rich condition for inducing antigen-specific cytotoxic T lymphocytes (CTLs) and eliciting anti-cancer effects (Figure 1A), however it is difficult to predict what kinds of immune responses, e.g., Th1, Th2, Th17 and regulatory T cells (Treg), will be induced by the dendritic cells in patients’ bodies. This is the serious problem of the conventional cancer vaccines which are the methods only using cancer antigens such as peptides, proteins and whole cells without DCs. The strategy to perform “optimization” of DCs in Th1-inducing type by processing DCs ex vivo should be reasonable.

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Figure 1 The dendritic cells play central roles in deciding the direction of host immune reactions as well as antigen presentation. A: Role of various dendritic cells in CD4⁺ T-cell differentiation; B: Antigen presentation and CTL induction under Th1 condition. CTL: Cytotoxic T lymphocytes; DC: Dendritic cell.

We have reported that DCs stimulated with a streptococcal immune adjuvant OK-432 which has been developed in Japan 1970’[12], produce IL-12, induce Th1-dominant state, and elicit anti-tumor effect, that these effects are more powerful than those of the known DC-maturating factors such as tumor necrosis factor (TNF)- and LPS, and that these reactions are caused via Toll-like receptor signaling (Figure 1B)[13-17].

A Th1-inducing type of DC vaccine, Vaccell is made as follows. Peripheral blood monocytes were cultured in medium containing granulocyte macrophage-colony stimulating factor (GM-CSF) and IL-4 to generate immature DCs. Five days later, the DCs were stimulated with the OK-432 and prostaglandin E2 for 24 h. The DCs were then pulsed with peptide antigens according to the HLA pattern. Based on previous reports, Several antigens such as WT1 and MUC1, were selected to be pulsed into DCs[18] (Figure 2A).

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Figure 2 A Th1-inducing type of dendritic cell vaccine, Vaccell is made as follows. A: Preparation of the DC vaccine “Vaccell”; B and C: Vaccell for pancreatic cancer patients; B: Two hundred fifty five patients who received standard chemotherapy combined with DC vaccines were analyzed. DTH skin reaction after vaccination was an independent prognostic factor for better survival; B: The WT1-specific DTH positive patients showed significantly improved OS and PFS compared with the DTH negative patients[20,21]. DC: Dendritic cell; DTH: Delayed type hypersensitivity; PFS: Progressive-free survival; OS: Overall survival.

The DCs were cryopreserved and kept until the day of administration. The phenotype CD14^−/low/HLA-DR⁺/HLA-ABC⁺/CD80⁺/CD83⁺/CD86⁺/CD40⁺/CCR7⁺ was taken to define mature DCs. The DCs were prepared by well-trained technical staff in each institutional cell processing center under the Standard Operating Procedure (SOP). Regarding release criteria, testing for sterility, mycoplasma (PCR method), and endotoxin was done using the supernatant or cell suspension just before the tube filling.

Vaccell has become to be served for lots of patients with various malignancies, and then not only large-scale retrospective observations but also prospective clinical trials have been done or are ongoing.

At the point of writing, we have published 13 original articles related to the clinical application of Vaccel. Five articles described for pancreatic cancer[19-23], 2 for biliary tract cancer[24,25], 1 for lung cancer[26], 1 for ovarian cancer[27], 1 for pediatric patient with relapsed leukemia[28], 1 for gastric cancer[29], 1 for malignant glioma[30], and 1 for several types of advanced cancers treated with radiation therapy in combination with DC vaccine[31]. Here, we introduce the Vaccell’s effects in pancreatic cancer patients in which the analysis has been progressed to most among these cases.

First, the clinical and immunological evaluation of DC-based immunotherapy in combination with standard chemotherapy mainly gemcitabine and S-1, in 49 patients with inoperable, advanced pancreatic carcinoma has been done retrospectively[19]. Prolongation of survival in this cohort was highly likely (median OS: 360 d from the 1^st vaccination). There were the patients whose numbers of Tregs were decreased in peripheral blood, and the overall survival (OS) from 1^st vaccination tended to be prolonged in these patients.

We have conducted the next retrospective observation by expanding sample size as a multicenter analysis[20]. The 255 patients with inoperable pancreatic cancer who received standard chemotherapy combined with peptide-pulsed DC vaccines, were analyzed. Relapse cases were excluded. The median OS from diagnosis was 16.5 mo and that from the 1^st vaccination was 9.9 mo. Interestingly, The median survival time (MST) of the patients with positive delayed type hypersensitivity (DTH) skin reaction was significantly prolonged compared to that of the patients with negative DTH (P = 0.0157 by log-rank test) (Figure 2B). These findings strongly suggest that there may be “Responders” for the DC vaccine in advanced pancreatic patients. This is the first report of a multicenter clinical study suggesting the feasibility and possible clinical benefit of an add-on DC vaccine in patients with advanced pancreatic combined with standard chemotherapy.

Based on the results of the above retrospective analysis, we conducted 2 small-scale prospective clinical studies for advanced pancreatic cancer patients. One protocol is the combination therapy with gemcitabine and DC vaccine pulsed with only HLA class I-restricted WT1 peptide[23]. In 10 patients, the disease control associated with a low neutrophil⁄ lymphocyte (N/L) ratio was observed in all 3 patients with DTH positivity. In another protocol of gemcitabine in combination with DC vaccine for pancreatic cancer, we loaded the WT1-specific HLA class II-restricted epitope (WT1-II) as well as the HLA class I-restricted epitope (WT1-I) into the DCs[21,22]. Ten stage IV patients with pancreatic ductal adenocarcinoma who showed HLA-positive for A*02:01, A*02:06, A*24:02, DRB1*04:05, DRB1*08:03, DRB1*15:01, DRB1*15:02, DPB1*05:01, or DPB1*09:01 were enrolled. The survival of 7 patients received WT1-I and -II pulsed DC vaccine was significantly extended compared to that of the 3 patients received DC vaccine pulsed with WT1-I or WT1-II alone [P = 0.036 in OS, P = 0.010 in Progressive-free survival (PFS)]. WT1-specific DTH positive patients showed significantly improved OS and PFS as compared to the DTH negative patients (P = 0.021 in OS, P = 0.018 in PFS) (Figure 2C). In particular, all 3 patients with strong DTH reactions (erythema > 5 mm) had a median OS of 717 d. In addition, it was also observed in this protocol that the decreased N/L ratio may be prognostic markers of longer survival (P = 0.018).

The activation of WT1-specific immune responses by DC vaccine pulsed with WT1-I as well as with WT1-II in combination with standard chemotherapy may be associated with disease stability in advanced pancreatic cancer.

DTH skin reaction was associated with good clinical outcome or clinical response in pancreatic cancer patients received DC vaccine in a large-scale retrospective observation as well as in 2 small-scale prospective studies. Moreover, N/L ratio was a marker for clinical benefit both in 2 prospective studies. In retrospective analysis of 255 cases, N/L ratio was not statistically significant, but tended to be a good prognostic marker. It is a notable thing that the much similar result was provided in a large-scale retrospective observation and in the 2 independent prospective trials. Additionally, a number granulocytic myeloid-derived suppressor cells (MDSCs) was a marker for poor clinical response[23]. Rodriguez et al[32] reported that MDSCs are a subpopulation of activated granulocytes. We have also observed that the infiltration of CD66b-positive neutrophils in a tumor site may be a negative prognostic marker (authors’ personal observation, manuscript in preparing). Granulocytic MDSCs may be a core population of neutrophils which may suppress anti-tumor immunity.

Previously, there have been some reports describing the advantage of the use of HLA-class II-restricted antigen epitope(s)[33], while it is also suggested the possibility that HLA-class II-restricted epitope may induce suppressive immune responses such as Th2, Th17 and Tregs. I believe that it is reasonable and useful to make a cancer vaccine using the DCs optimized ex vivo for Th1-inducing type.