Dendritic cells (DCs) orchestrate a repertoire of immune responses that bring about resistance to infection and silencing or tolerance to self. In the settings of infection and cancer, microbes and tumours can exploit DCs to evade immunity, but DCs also can generate resistance, a capacity that is readily enhanced with DC-targeted vaccines. During allergy, autoimmunity and transplant rejection, DCs instigate unwanted responses that cause disease, but, again, DCs can be harnessed to silence these conditions with novel therapies. Here we present some medical implications of DC biology that account for illness and provide opportunities for prevention and therapy.

Taking dendritic cells into medicine

Despite the frequent detection of circulating tumor antigen-specific T cells, either spontaneously or following active immunization or adoptive transfer, immune-mediated cancer regression occurs only in the minority of patients. One theoretical rate-limiting step is whether effector T cells successfully migrate into metastatic tumor sites. Affymetrix gene expression profiling done on a series of metastatic melanoma biopsies revealed a major segregation of samples based on the presence or absence of T-cell-associated transcripts. The presence of lymphocytes correlated with the expression of defined chemokine genes. A subset of six chemokines (CCL2, CCL3, CCL4, CCL5, CXCL9, and CXCL10) was confirmed by protein array and/or quantitative reverse transcription-PCR to be preferentially expressed in tumors that contained T cells. Corresponding chemokine receptors were found to be up-regulated on human CD8(+) effector T cells, and transwell migration assays confirmed the ability of each of these chemokines to promote migration of CD8(+) effector cells in vitro. Screening by chemokine protein array identified a subset of melanoma cell lines that produced a similar broad array of chemokines. These melanoma cells more effectively recruited human CD8(+) effector T cells when implanted as xenografts in nonobese diabetic/severe combined immunodeficient mice in vivo. Chemokine blockade with specific antibodies inhibited migration of CD8(+) T cells. Our results suggest that lack of critical chemokines in a subset of melanoma metastases may limit the migration of activated T cells, which in turn could limit the effectiveness of antitumor immunity.

Chemokine Expression in Melanoma Metastases Associated with CD8+ T-Cell Recruitment

Resistance Mechanisms to Immune-Checkpoint Blockade in Cancer: Tumor-Intrinsic and -Extrinsic Factors

Over the past decade, immune therapy has become a standard treatment for a variety of cancers. Monoclonal antibodies, immune adjuvants, and vaccines against oncogenic viruses are now well-established cancer therapies. Immune modulation is a principal element of supportive care for many high-dose chemotherapy regimens. In addition, immune activation is now appreciated as central to the therapeutic mechanism of bone marrow transplantation for hematologic malignancies. Advances in our understanding of the molecular interactions between tumors and the immune system have led to many novel investigational therapies and continue to inform efforts for devising more potent therapeutics. Novel approaches to immune-based cancer treatment strive to augment antitumor immune responses by expanding tumor-reactive T cells, providing exogenous immune-activating stimuli, and antagonizing regulatory pathways that induce immune tolerance. The future of immune therapy for cancer is likely to combine many of these approaches to generate more effective treatments.

Immune therapy for cancer.

Because of the large preexisting antigenic load and immunosuppressive environment within a tumor, inducing therapeutically useful antitumor immunity in cancer patients requires the development of powerful vaccination protocols. An approach gaining increasing popularity in the tumor vaccine field is to immunize cancer patients with their own DCs loaded ex vivo with tumor antigens. The underlying premise of this approach is that the efficiency and control over the vaccination process provided by ex vivo manipulation of the DCs generates an optimally potent APC and a superior method for stimulating antitumor immunity in vivo compared with the more conventional direct vaccination methods, offsetting the added cost and complexity associated with this form of customized cell therapy.

/pdf/dc-based-cancer-vaccines-4iuf3emz61.pdf

DC-based cancer vaccines

Dacarbazine (DTIC) versus vaccination with autologous peptide-pulsed dendritic cells (DC) in first-line treatment of patients with metastatic melanoma: a randomized phase III trial of the DC study group of the DeCOG

Background: Stage IV melanoma has a poor prognosis with a median survival of 3-11 months from diagnosis of distant metastases. Response rates in first-line regimens range around 15-20%. Non-responders have a median survival around 6 months. Currently, no second-line treatment in advanced melanoma has been established. Patients and Methods: In a clinical phase II study we evaluated the efficacy of liposomal doxorubicin (Caelyx?) in 30 patients (17 m, 13 f) with progressing metastatic melanoma who had failed a previous chemotherapy. Liposomal doxorubicin was given in an outpatient setting at a dose of 50 mg/m2 i.v. on d1, d22, d43 and d64, subsequently at 40 mg/m2 at d85 before first staging and in 4-week intervals thereafter. Treatment was very well tolerated with 100 cycles given in total. Response rate, survival time, time-to-progression and toxicity were assessed. Results: Erythrodysesthesia was the most severe toxicity in 6% at CTC grade 3. Liposomal doxorubicin was of limited clinical efficacy with 21 patients progressing within the first 12 weeks. However, 7 patients were treated 3-9 months and were stable for >90 days, achieving 5 SD, 1 PR and 1 CR. Median survival after initiation of second-line treatment was 214 days (95% CI: 151-304 days) with 7 patients surviving >300 and 5 patients >400 days. Conclusions: Liposomal doxorubin as monotherapy is well tolerated but of limited clinical efficacy. Whether the survival benefit of a significant proportion of patients (20%) holds true in larger cohorts and whether the efficacy of liposomal doxorubicin can be improved by combinations without compromising the low toxicity profile needs further studies.

C. Zimpfer-Rechner

Papers

Dacarbazine (DTIC) versus vaccination with autologous peptide-pulsed dendritic cells (DC) in first-line treatment of patients with metastatic melanoma: a randomized phase III trial of the DC study group of the DeCOG

Clinical phase II study of pegylated liposomal doxorubicin as second-line treatment in disseminated melanoma.