Primary lung cancer accounts for approximately 20% of all cancer-related deaths, with 71,518 deaths reported worldwide in 2012. Lung cancer is the primary cause of cancer-related mortality in Japan. As non-small-cell lung cancer (NSCLC) accounts for ≥80% of all lung cancers, it is imperative to manage this disease. Although surgical resection is the conventional method for the early treatment of lung cancer, patients with stage II–III disease have poor prognoses even after complete resection.

As recurrence is common after conventional surgery, powerful suppression of distant metastases and of potentially existing micrometastatic lesions throughout the body is important for the improvement of survival. Therefore, to control the micrometastatic lesions, postoperative adjuvant chemotherapy is often administered to advanced-stage patients. In order to improve the surgical performance, a treatment strategy combining chemotherapy with surgery has been attempted in three clinical trials since 2003 (The International Adjuvant Lung Trial [1], JBR.10 [2], and Adjuvant Navelbine International Trialist Association [3]). Although the efficacy of postoperative adjuvant chemotherapy was confirmed in a long-term follow-up observational study [4], the incorporation of the Adjuvant Lung Cancer Project Italy [5] and the Big Lung Trial [6] into five comparative trials resulted in a meta-analysis of the data from 4584 cases of lung cancer (Lung Adjuvant Cisplatin Evaluation (LACE) [7]). The results of the meta-analysis showed that, compared to the group that did not receive any postoperative treatment (standard treatment group), the group that received postoperative adjuvant chemotherapy had significantly longer disease-free survival (DFS; hazard ratio (HR), 0.84; 95% confidence interval (CI), 0.78–0.91; p < 0.001) and overall survival (OS) rates (HR, 0.89; 95% CI, 0.82–0.96; p = 0.005). In the present study, we showed that, compared to those in the standard treatment group, the 5-year DFS and OS rates improved by 5.8% and 5.4%, respectively, in the postoperative adjuvant chemotherapy group.

In the LACE subgroup analysis [8], patients who received cisplatin plus vinorelbine were confirmed to have superior survival rates compared to patients who received other cisplatin-based postoperative adjuvant chemotherapies. The cisplatin plus vinorelbine treatment did not improve the 5-year survival rate in stage IB NSCLC patients compared to the standard treatment group; however, for stage II and stage III NSCLC cases, the 5-year survival rates of the treatment groups improved by 11.6% (HR, 0.74; 95% CI, 0.60–.91) and 14.7% (HR, 0.66; 95% CI, 0.53–0.83), respectively. Meanwhile, toxicity grade ≥3 was observed in 90% and 49% of the patients who received combination treatments with vinorelbine and other combination treatments, respectively. The frequency of toxicity was higher in the patients treated with the vinorelbine-based combination treatments than in those treated with other combination treatments. The treatment-related death rate was 1.4%. Although cisplatin plus vinorelbine treatment showed a high frequency of toxicity, it was also efficacious in reducing the recurrence-associated mortality rate by approximately 20% compared to the standard treatment group. Therefore, cisplatin plus vinorelbine is the current standard regimen for postoperative adjuvant chemotherapy.

Natural killer T (NKT)-cells are unique cells expressing both T-cell receptors and natural killer (NK)-cell receptors on their surfaces [9]. The T-cell receptor on the NKT-cell surfaces is composed of an extremely limited α-chain (Vα24Jα18 in humans) and a β-chain (Vβ11 in humans). The ligand for this receptor is the CD1d molecule which is an antigen-presenting molecule similar to the major histocompatibility complex class-I ligand. NKT-cells recognize α-galactosylceramide (α-GalCer), a type of glycolipid displayed by CD1d, and are specifically activated to rapidly produce interferon-γ (IFN-γ) and interleukin-4 in large volumes. At the same time, they demonstrate powerful cytotoxic activity through perforin/granzyme B [10, 11]. In addition to its direct antitumor effect, the NKT-cells also regulate the damaging activity of NK-cells, CD8+ T-cells, and other effectors or dendritic cells (DCs). Thus, they can be considered to be unique cells [12, 13].

In a mouse model, an increase in intrapulmonary NKT-cell numbers and IFN-γ production was observed after the intravenous administration of α-GalCer-pulsed DCs [14, 15]. In a mouse lung metastasis model, it was possible to eliminate the already small, established lung metastatic tumors [16, 17].

In order to assess the powerful antitumor effects of the NKT-cells, from 2001 onward, we administered α-GalCer-pulsed DC therapy to 11 patients with unresectable advanced-stage and postoperative recurrent NSCLC at Chiba University [18]. The initial number of cells treated was 5 × 107 units/m2. This number was increased to between 2.5 × 108 and 1 × 109 units/m2 to assess the safety of intravenously administered treatment modalities. The procedure was repeated four times. The NKT-cell-specific immune response and its antitumor effects were assessed. No toxic events of more than grade 2 were observed, showing complete fulfillment of the safety protocols. Among the patients who showed grade 2 or higher toxic events, none of the patients required treatment despite the presence of test value abnormalities such as in the form of fever, and minor increases such as in the aspartate aminotransferase (AST) level. In order to assess the NKT-cell-specific immune response, we analyzed the peripheral blood NKT-cell counts and the IFN-γ production capacity of the NKT-cells. With the administration of the maximum cell count, a clear increase was observed in the peripheral blood NKT-cell count of three patients. In addition, a further increase and reinforcement of IFN-γ production from NKT-cells was observed in one patient. Although none of the patients showed clear tumor shrinkage, one of the three patients who received the maximum cell administration volume showed disease progression; however, they achieved a survival period of 59 months with good quality of life.

Subsequently, we have performed α-GalCer-pulsed DC therapy in a phase I–II trial that commenced in March 2004 [19]. Subsequent to the administration of standard treatment, patients with inoperable advanced-stage lung cancers, or postoperative patients showing recurrence, received 1 × 109 units/m2 of α-GalCer-pulsed DCs. As a result, in 17 of the 23 enrolled patients, the protocol could be completed. In one patient, recurrence of deep-vein thrombosis and grade 3 toxic events were observed, and hospitalization and treatment were required. Among patients with grade 2 or higher toxic events, none of the patients required treatment despite the presence of test value abnormalities in the form of fever, etc.; minor increases in AST level, etc.; and a decrease in hemoglobin levels. On analysis of the NKT-cell-specific immune response, a clear increase in the cell counts of α-GalCer-reactive IFN-γ-producing peripheral blood mononuclear cells was observed in 10 patients. Although significant changes were not identified in terms of tumor size, the median survival rate for all 23 patients was 17.4 months. Ten patients with increased IFN-producing cells (more than two-fold) showed prolonged median survival time (MST) (31.9 months; range, 14.5 to 36.3 months) as compared with poor-responder patients (n =7) MST (9.7 months; range, 3.8 to 25.0 months) (log-rank test, p = 0.0015) [19].

Upon the meta-analysis of large-scale clinical trials (LACE) for the standard cisplatin-based adjuvant chemotherapies, the postoperative adjuvant chemotherapy group showed a 5.8% improvement in the 5-year recurrence-free survival (RFS) rate compared to the standard treatment group. During subgroup analysis, the 5-year survival rates of the cisplatin plus vinorelbine treatment group were observed to have improved by 11.6% for stage II NSCLC, and by 14.7% for stage III NSCLC, compared to those of the standard treatment group. However, the treatment group also showed strong toxicity, leading to the conclusion that the therapeutic effects of cisplatin plus vinorelbine were inadequate.

As the toxicity associated with the α-GalCer-pulsed DC therapy could be considered insignificant, its addition to postoperative adjuvant chemotherapy would be expected to greatly improve the therapeutic effect, and could result in prolonged survival.