Dendritic Cells for Immunotherapy of Metastatic Endometrial Cancer Patients

Dendritic cell vaccination Prevention of infectious diseases through immunization is one of the greatest achievements of modern medicine. Nonetheless, considerable challenges remain for improving the efficacy of existing vaccines for therapeutic immunizations for diseases such as cancer. The investigators were amongst the first groups worldwide that introduced tumor antigen-loaded dendritic cell (DC)-based vaccines in the clinic1-3. Effective immune responses and favorable clinical outcomes have indeed been observed4-7. Thus far, mainly conventional in vitro generated monocyte-derived DCs (moDC) have been used in clinical trials worldwide. In the past 14 years the investigators have treated more than 375 patients and proven that DC therapy is feasible and non-toxic. The investigators observed that long lasting tumor specific T cell-mediated immunological responses are clearly linked to increased progression free survival as well as overall survival8.

However, moDC may not be the optimal source of DCs for DC vaccination studies, due to extensive culture periods and compounds required to obtain mature moDC. Peripheral blood-derived DC (plasmacytoid dendritic cells (pDC) and myeloid dendritic cells (myDC)) are possibly a better alternative since they do not require extensive culture periods. The investigators recently completed a clinical trial in stage IV melanoma patients using plasmacytoid pDC. The results on both immunological outcome as well as clinical outcome are promising. These freshly isolated natural pDC prolonged median overall survival to 22 months in comparison to 7.6 months in matched historical melanoma patients who had received standard chemotherapy9. In patients receiving moDC-vaccinations, the investigators did not observe such a clear increase in overall survival, suggesting that pDC-vaccines may induce even more potent anti-tumor responses than moDC-vaccines. In terms of immunological outcome transcription of both interferon-alpha (IFN-α) and interferon-beta (IFN-β) genes was clearly induced 4 hours after vaccination and decreased 20 hours later. An IFN gene signature is known to be highly important for eradication of viruses. This signature is indicative for a temporal systemic induction of type I IFNs. Type I IFN might also stimulate myDC and enhance their ability to cross-prime CD8+ T cells, thereby inducing more efficient anti-tumor T cell responses when compared with in vitro generated DC. This is supported by studies in mice: type I IFN were critical for the induction of anti-tumor immune responses10,11. In the 14 stage IV melanoma patients included in our myDC trial the investigators observed already in 3 patients highly functional tumour-specific T-cells in peripheral blood and in DTH sites coinciding with tumour regression12. For comparison: in the investigators trials with monocyte-derived DC, less bonafide T cell responses were seen after DC vaccination, suggesting that blood myDC induce more potent immune responses compared to monocyte-derived DC.

In conclusion, based on all these observations the investigators are convinced that pDC and myDC employ different, and probably more optimal mechanisms to combat cancer. In addition, based on in vitro data and preclinical studies that suggest that blood pDC and myDC act synergistically, the investigators hypothesize that the combination of myDC and pDC may induce stronger anti-tumor immune responses as compared to pDC or myDC alone, or moDC.

Immunotherapy in endometrial cancer Endometrial cancer is the only gynaecologic malignancy with a rising incidence and mortality. While cure is routinely achieved with surgery alone or in combination with adjuvant pelvic radiotherapy when disease is confined to the uterus, patients with metastatic or recurrent disease exhibit limited response rates to cytotoxic chemotherapy, targeted agents, or hormonal therapy. Some figures: at the time of diagnosis, 67% of women have disease confined to the uterus and an associated 5-year survival rate of 95%. In contrast, the 8% of patients with distant metastases at the time of diagnosis have a 5-year survival rate of 17% and face the prospect of cytotoxic chemotherapy (primarily with taxanes, platinum and anthracyclines).

Given the unmet clinical need in this patient population, exploration of novel therapeutic approaches is warranted, and attention is turning to immunomodulation. Existing evidence suggests that endometrial cancer is sufficiently immunogenic to be a reasonable candidate for immunotherapy.

Dendritic cell vaccination after chemotherapy Tumors exploit several mechanisms to suppress anti-tumor immune responses, including the recruitment of suppressive cells, such as myeloid-derived suppressor cells (MDSCs), into the tumor microenvironment13. The presence of MDSCs in the suppressive tumor microenvironment is correlated with decreased efficacy of several immunotherapies, including DC vaccination and ipilimumab14,15. Data obtained in the investigators lab indicates that MDSCs can be targeted with platinum-based chemotherapeutics. In head-and-neck squamous cell carcinoma patients treated with six weekly dosages of cisplatin, the frequency as well as suppressive capacity of MDSCs were significantly inhibited two weeks after the last dose. Treating the patients with DC vaccination after six cycles of chemotherapy with carboplatin, might therefore have a positive impact on the clinical outcome of DC vaccination.

Antigen loading of dendritic cells To be effective as an antigen-presenting cell, the MHC molecules of a DC must be loaded with antigenic cargo. The investigators selected well-defined common tumor antigens in the form of long peptides of two tumor associated antigens frequently shared by endometrial cancer, survivin and MUC1. This DC antigen-loading strategy allows accurate monitoring of the ensuing immunity against the defined peptides.