Optimizing the exogenous antigen loading of monocyte-derived dendritic cells

Combined p14ARF and Interferon-β Gene Transfer to the Human Melanoma Cell Line SK-MEL-147 Promotes Oncolysis and Immune Activation

Immune evasion is an important cancer hallmark and the understanding of its mechanisms has generated successful therapeutic approaches. Induction of immunogenic cell death (ICD) is expected to attract immune cell populations that promote innate and adaptive immune responses. Here, we present a critical advance for our adenovirus-mediated gene therapy approach, where the combined p14ARF and human interferon-β (IFNβ) gene transfer to human melanoma cells led to oncolysis, ICD and subsequent activation of immune cells. Our results indicate that IFNβ alone or in combination with p14ARF was able to induce massive cell death in the human melanoma cell line SK-MEL-147, though caspase 3/7 activation was not essential. In situ gene therapy of s.c. SK-MEL-147 tumors in Nod-Scid mice revealed inhibition of tumor growth and increased survival in response to IFNβ alone or in combination with p14ARF. Emission of critical markers of ICD (exposition of calreticulin, secretion of ATP and IFNβ) was stronger when cells were treated with combined p14ARF and IFNβ gene transfer. Co-culture of previously transduced SK-MEL-147 cells with monocyte-derived dendritic cells (Mo-DCs) derived from healthy donors resulted in increased levels of activation markers HLA-DR, CD80, and CD86. Activated Mo-DCs were able to prime autologous and allogeneic T cells, resulting in increased secretion of IFNγ, TNF-α, and IL-10. Preliminary data showed that T cells primed by Mo-DCs activated with p14ARF+IFNβ-transduced SK-MEL-147 cells were able to induce the loss of viability of fresh non-transduced SK-MEL-147 cells, suggesting the induction of a specific cytotoxic population that recognized and killed SK-MEL-147 cells. Collectively, our results indicate that p14ARF and IFNβ delivered by our adenoviral system induced oncolysis in human melanoma cells accompanied by adaptive immune response activation and regulation.

Myeloid-derived suppressor cells impair the quality of dendritic cell vaccines

Myeloid-derived suppressor cells (MDSC) are important regulators of the immune system and key players in tumor-induced suppression of T-cell responses. CD14+HLA-DR-/low MDSC have been detected in a great number of malignancies, including melanoma. MDSC are known to be impaired in their ability to differentiate along the myeloid lineage, e.g., into dendritic cells (DC). This is a concern for utilization of monocyte-derived DC for vaccination of patients with melanoma or other cancers exhibiting accumulation of CD14+ MDSC. When producing DC according to standard operating procedures of two currently ongoing clinical trials, we found that MDSC co-purified with monocytes isolated by elutriation. MDSC frequencies did not affect yield or viability of the produced DC, but induced a dose-dependent decrease in DC maturation, ability to take up antigen, migrate and induce T-cell IFNγ production. Changes in DC characteristics were most notable when 'pathological' frequencies of >50% CD14+HLA-DR- cells were present in the starting culture. The impaired DC quality could not be explained by altered cytokine production or increased oxidative stress in the cultures. Tracking of HLA-DR- cells throughout the culture period revealed that the observed changes were partially due to the impaired maturation and functionality of the originally HLA-DR- population, but also to their negative effects on HLA-DR+ cells. In conclusion, MDSC could be induced to differentiate into DC but, due to the impairment of overall DC vaccine quality when >50% HLA-DR- cells were present in the starting culture, their removal could be advisable.

A double-blind randomized phase I clinical trial targeting ALVAC-HIV vaccine to human dendritic cells

Background

We conducted a novel pilot study comparing different delivery routes of ALVAC-HIV (vCP205), a canarypox vaccine containing HIV gene inserts: env, gag and pol. We explored the concept that direct ex vivo targeting of human dendritic cells (DC) would enhance the immune response compared to either conventional intramuscular or intradermal injections of the vaccine alone.

Methodology/Principal Findings

Healthy HIV-1 uninfected volunteers were administered ALVAC-HIV or placebo by intramuscular injection (IM), intradermal injection (ID) or subcutaneous injection (SQ) of autologous ex vivo transfected DC at months 0, 1, 3 and 6. All vaccine delivery routes were well tolerated. Binding antibodies were observed to both the ALVAC vector and HIV-1 gp160 proteins. Modest cellular responses were observed in 2/7 individuals in the DC arm and 1/8 in the IM arm as determined by IFN-γ ELISPOT. Proliferative responses were most frequent in the DC arm where 4/7 individuals had measurable responses to multiple HIV-1 antigens. Loading DC after maturation resulted in lower gene expression, but overall better responses to both HIV-1 and control antigens, and were associated with better IL-2, TNF-α and IFN-γ production.

Conclusions/Significance

ALVAC-HIV delivered IM, ID or SQ with autologous ex vivo transfected DC proved to be safe. The DC arm was most immunogenic. Proliferative immune responses were readily detected with only modest cytotoxic CD8 T cell responses. Loading mature DC with the live viral vaccine induced stronger immune responses than loading immature DC, despite increased transgene expression with the latter approach. Volunteers who received the autologous vaccine loaded mature DC developed a broader and durable immune response compared to those vaccinated by conventional routes.

Trial Registration

ClinicalTrials.gov NCT00013572

Forced expression of HLA-DM at the surface of dendritic cells increases loading of synthetic peptides on MHC class II molecules and modulates T cell responses

Adoptive transfer of autologous dendritic cells (DCs) loaded with tumor-associated CD4 and CD8 T cell epitopes represents a promising avenue for the immunotherapy of cancer. In an effort to increase the loading of therapeutic synthetic peptides on MHC II molecules, we used a mutant of HLA-DM (DMY) devoid of its lysosomal sorting motif and that accumulates at the cell surface. Transfection of DMY into HLA-DR(+) cells resulted in increased loading of the exogenously supplied HA(307-318) peptide, as well as increased stimulation of HA-specific T cells. Also, on transduction in mouse and human DCs, DMY increased loading of HEL(48-61) and of the tumor Ag-derived gp100(174-190) peptides, respectively. Interestingly, expression of DMY at the surface of APCs favored Th1 differentiation over Th2. Finally, we found that DMY(-) and DMY(+) mouse APCs differentially stimulated T cell hybridomas sensitive to the fine conformation of peptide-MHC II complexes. Taken together, our results suggest that the overexpression of HLA-DMY at the plasma membrane of DCs may improve quantitatively, but also qualitatively, the presentation of CD4 T cell epitopes in cellular vaccine therapies for cancer.

Intracellular delivery of major histocompatibility complex class I-binding epitopes: dendritic cells loaded and matured with cationic peptide/poly(I:C) complexes efficiently activate T cells

Based on their role for the induction of T-cell responses, dendritic cells (DCs) are popular candidates in cancer vaccine development. We established a novel single-step intracellular delivery of peptide/poly(I:C) complexes for antigen loading and Toll-like receptor-3 (TLR3)-mediated maturation of human DCs using a cell-penetrating peptide (tat(49-57): RKKRRQRRR) as delivery vector. Towards this end, a cationic tat-sequence was fused with an antigenic, major histocompatibility complex (MHC) class I-binding melanoma epitope (Melan-A/Mart-1 sequence: ELAGIGILTV) and then mixed with negatively charged poly(I:C) dsRNA to form peptide/nucleic acid complexes. Flow cytometry and confocal laser scanning microscopy confirmed intracellular localization of TLR3 in monocyte-derived immature DCs (iDCs). Peptide/poly(I:C) complexes were readily internalized by iDCs without negatively affecting cell viability. They induced DC maturation and secretion of bioactive interleukin (IL)-12p70. When peptide/poly(I:C) complex-loaded DCs were used for autologous T cell stimulation, epitope-specific interferon-gamma secretion was quantitatively superior in comparison to peptide-loaded DCs matured by a cytokine cocktail, as detected by enzyme-linked immunospot assays. Thus, complexes of cationic antigenic peptides and poly(I:C) might be of great utility for a TLR3-mediated DC maturation and intracellular peptide targeting in a single step. Resulting DCs induce a strong expansion/activation of antigen-specific T cells in the context of an IL-12p70 secretion.

Multiple T-cell responses to human immunodeficiency virus type 1 are enhanced by dendritic cells

Human immunodeficiency virus type 1 (HIV-1)-specific T-cell reactivity has been related to protection from disease progression. Optimal T-cell reactivity to HIV-1 presumably requires antigen processing and presentation by professional antigen-presenting cells, particularly dendritic cells (DC). Here we examined whether multiple HIV-1-specific T-cell functions are enhanced by stimulation with HIV-1 peptide-loaded DC derived from HIV-1-infected subjects on antiretroviral therapy. We first found that mature DC increased the number of gamma interferon (IFN-gamma)-producing T cells detected by enzyme-linked immunospot assay to overlapping 15-mer peptides of HIV-1 Gag and Nef, compared to stimulation with peptide-loaded, immature DC or to peptides without DC. IFN-gamma production was lower in response to large pools of the Gag and Nef peptides, regardless of presentation by DC. We further observed that HIV-1 peptide-loaded, mature DC stimulated greater CD8(+) and CD4(+) T-cell proliferation than did the peptides without DC and that T-cell proliferation was lower in response to larger pools of the peptides. The lower T-cell IFN-gamma and proliferation responses to the larger peptide pools were related to lower T-cell viability. Finally, the number of polyfunctional CD8(+) and CD4(+) T cells stimulated by HIV-1 peptide-loaded, mature DC, defined as positive by intracellular staining for more than one immune mediator (IFN-gamma, interleukin 2, tumor necrosis factor alpha, macrophage inhibitory protein 1beta, or CD107a), was greater than that stimulated by the peptides alone. These results indicate that DC can enhance multiple types of HIV-1-specific T-cell functions.

Clinical grade OK432-activated dendritic cells: in vitro characterization and tracking during intralymphatic delivery

Dendritic cells (DC) are under intense preclinical and early clinical evaluation for the immunotherapy of cancer. However, the optimal culture conditions and route of delivery for DC vaccination have not been established. Here we describe the first human application of DC matured with the bacterial agent OK432 (OK-DC), using a short-term serum-free culture protocol, which generates mature DC from CD14+ precursors after 5 days. These cells were prepared within the framework of a National Blood Service facility, demonstrating that DC represent a product which is potentially deliverable alongside current standardized cell therapies within the UK National Health Service. In vitro analysis confirmed that OK-DC were mature, secreted tumor necrosis factor-alpha, interleukin-6, and interleukin-12, and stimulated both T cell and natural killer cell function. To explore effective delivery of OK-DC to lymph nodes, we performed an initial clinical tracking study of radioactively labeled, unpulsed OK-DC after intralymphatic injection into the dorsum of the foot. We showed that injected DC rapidly localized to ipsilateral pelvic lymph nodes, but did not disseminate to more distant nodes over a 48-hour period. There was no significant toxicity associated with OK-DC delivery. These results show that OK-DC are suitable for clinical use, and that intralymphatic delivery is feasible for localizing cells to sites where optimal priming of innate and adaptive antitumor immunity is likely to occur.

Enhanced antigen presentation and CTL activity by transduction of mature rather than immature dendritic cells with octaarginine-modified liposomes

To improve uptake and cross-presentation of exogenous antigens (Ag) by dendritic cells (DCs), octaarginine-modified liposomes (R8-Lip) were used as a novel strategy for protein-Ag transduction. Immature DCs endocytose macromolecules efficiently. While mature DCs lose their ability to capture Ag, but have an increased capacity for T-cell activation. Thus Ag-transduction has been performed mostly in immature DCs. In the present study, R8-Lip were efficiently taken up by both immature and mature DCs. DCs transduced after maturation were highly efficient at cross-presentation of Ag and induced higher cytotoxic T-lymphocytes (CTL) activity than were DCs transduced before maturation. The mechanism of Ag presentation involved the escape of R8-Lip from endosomes to cytosol, which require the acidic environment. The Ag released was then processed by a proteasome-dependent pathway. This novel transduction approach is clinically applicable, easy to perform, and has more practical advantages than current protein transduction methods.

Late dendritic cells are still able to evoke a potent alloreactive CTL response

On exposure to maturation stimuli, immature dendritic cells (DCs) undergo changes that turn them into potent amplifiers of innate immunity and into antigen-presenting cells (APCs) able to prime naïve T cells. However, their progression through the maturation process is very rapid and finally ends in apoptosis. The aim of our study was to investigate the importance of the maturation stage of DCs, defined by morphology, expression of surface markers and IL-12 production, for their immunostimulatory capacity. DCs were matured with LPS, monocyte-conditioned medium (MCM) or TNF-alpha, sampled several times during a 3-day long maturation period and used as stimulators of allogeneic T cells over a wide range of DC/T cell ratios. T-cell response was assessed by cell proliferation, CTL generation and IFN-gamma production. Our results indicate that the in vitro T cell response is determined mainly by the level of expression of co-stimulatory molecules on DCs and the DC/T cell ratio in the culture. Thus, DCs matured for over 20h, with high expression of co-stimulatory molecules, can still induce a potent CTL response at DC/T cell ratios of 1:10 and 1:20, although their IL-12 production, as well as their ability to induce IFN-gamma production by T cells, are both decreased. In contrast, the CTL response at DC/T cell ratios of 1:2 and 1:5 can be profoundly decreased. Notably, the proportion of proliferating CD4+ T cells in these cultures is reduced. This could well be the reason for the absence of CTL response, since we showed that, even in the case of high expression of co-stimulatory molecules on DCs, generation of CTLs still depends on CD4+ T cells. Our study emphasizes the importance of strong expression of co-stimulatory molecules on DCs and of their ability to activate CD8+ and CD4+ T cells concomitantly in order to initiate a potent cell-mediated immune response. We therefore suggest that a combination of early DCs, which are strong producers of cytokines, and late DCs, which have high expression of co-stimulatory molecules, could prove beneficial in the attempt to initiate in vitro and in vivo cell-mediated immune responses for therapeutic purposes.

Dendritic cells for active immunotherapy: optimizing design and manufacture in order to develop commercially and clinically viable products

Dendritic cell (DC) active immunotherapy is potentially efficacious in a broad array of malignant disease settings. However, challenges remain in optimizing DC-based therapy for maximum clinical efficacy within manufacturing processes that permit quality control and scale-up of consistent products. In this review we discuss the critical issues that must be addressed in order to optimize DC-based product design and manufacture, and highlight the DC based platforms currently addressing these issues. Variables in DC-based product design include the type of antigenic payload used, DC maturation steps and activation processes, and functional assays. Issues to consider in development include: (a) minimizing the invasiveness of patient biological material collection; (b) minimizing handling and manipulations of tissue at the clinical site; (c) centralized product manufacturing and standardized processing and capacity for commercial-scale production; (d) rapid product release turnaround time; (e) the ability to manufacture sufficient product from limited starting material; and (f) standardized release criteria for DC phenotype and function. Improvements in the design and manufacture of DC products have resulted in a handful of promising leads currently in clinical development.

Specific targeting of whole lymphoma cells to dendritic cells ex vivo provides a potent antitumor vaccine

Background

Dendritic cells (DC) pulsed with tumor-derived antigenic material have widely been used in antitumor vaccination protocols. However, the optimal strategy of DC loading has not yet been established. Our aim was to define requirements of optimal DC vaccines in terms of in vivo protection in a murine B-cell lymphoma model.

Methods

We compare various loading reagents including whole parental and modified tumor cells and a single tumor-specific antigen, namely the lymphoma idiotype (Id). Bone marrow-derived DC were pulsed in vitro and used for therapy of established A20 lymphomas.

Results

We show that a vaccine with superior antitumor efficacy can be generated when DC are loaded with whole modified tumor cells which provide both (i) antigenic polyvalency and (ii) receptor-mediated antigen internalization. Uptake of cellular material was greatly enhanced when the tumor cells used for DC pulsing were engineered to express an anti-Fc receptor immunoglobulin specificity. Upon transfer of these DC, established tumor burdens were eradicated in 50% of mice. By contrast, pulsing DC with unmodified lymphoma cells or with the lymphoma Id, even when it was endowed with the anti-Fc receptor binding arm, was far less effective. A specific humoral anti-Id response could be detected, particularly following delivery of Id protein-pulsed DC, but it was not predictive of tumor protection. Instead a T-cell response was pivotal for successful tumor protection. Interaction of the transferred DC with CD8⁺ T lymphocytes seemed to play a role for induction of the immune response but was dispensable when DC had received an additional maturation stimulus.

Conclusion

Our analyses show that the advantages of specific antigen redirection and antigenic polyvalency can be combined to generate DC-based vaccines with superior antitumor efficacy. This mouse model may provide information for the standardization of DC-based vaccination protocols.

Immunologic and Clinical Effects of Injecting Mature Peptide-Loaded Dendritic Cells by Intralymphatic and Intranodal Routes in Metastatic Melanoma Patients

PURPOSE

A phase I/II trial was conducted to evaluate clinical and immunologic responses after intralymphatic and intranodal injections of mature dendritic cells.

EXPERIMENTAL DESIGN

Fourteen patients with a metastatic melanoma received matured dendritic cells, loaded with Melan-A/MART-1 and/or NA17-A peptides and keyhole limpet hemocyanin. The cells were matured overnight with Ribomunyl, a toll-like receptor ligand, and IFN-gamma, which ensured the production of high levels of interleukin-12p70. Dendritic cells were injected at monthly intervals, first into an afferent lymphatic and then twice intranodally. Immunologic responses were monitored by tetramer staining of circulating CD8(+) lymphocytes and delayed-type hypersensitivity tests.

RESULTS

Dendritic cell vaccination induced delayed-type hypersensitivity reactivity toward NA17-A-pulsed, keyhole limpet hemocyanin-pulsed, and Melan-A-pulsed dendritic cells in 6 of 10, 4 of 11, and 3 of 9 patients, respectively. Four of the 12 patients analyzed by tetramer staining showed a significantly increased frequency of Melan-A-specific T cells, including one patient vaccinated only with NA17-A-pulsed dendritic cells. Furthermore, 2 of the 12 analyzed patients had a significant increase of NA17-A-specific T cells, including one immunized after an optional additional treatment course. No objective clinical response was observed. Two patients were stabilized at 4 and 10 months and three patients are still alive at 30, 39, and 48 months.

CONCLUSIONS

Injections into the lymphatic system of mature peptide-loaded dendritic cells with potential TH1 polarization capacities did not result in marked clinical results, despite immunologic responses in some patients. This highlights the need to improve our understanding of dendritic cell physiology.

Induction of specific T cell immunity in patients with prostate cancer by vaccination with PSA146-154 peptide

T cell immunotherapy of prostate cancer (CaP) offers the potential for less toxic, more effective outcomes. A clinical trial was conducted in 28 patients with locally advanced or metastatic CaP to determine whether an HLA-A2 binding epitope of prostate-specific antigen, PSA146-154 (PSA-peptide), can induce specific T cell immunity. Patients were vaccinated either by intradermal injection of PSA-peptide and GM-CSF or by intravenous administration of autologous dendritic cells pulsed with PSA-peptide at weeks 1, 4 and 10. Delayed-type hypersensitivity (DTH) skin testing was performed at weeks 4, 14, 26 and 52. Fifty percent of the patients developed positive DTH responses to PSA-peptide. The size of the DTH induration progressively increased over time in the majority of responding patients. Skin biopsies from seven DTH-positive patients were available and T cells that developed in situ were also characterized. The phenotype of recovered T cells demonstrated variable proportions of CD4+CD8-, CD4-CD8+ and CD4+CD8+ T cell populations. Cytokine analysis of PSA-peptide stimulated T cells per bead array assay exhibited specific IFN-gamma and TNF-alpha response in six of seven patients. Specific IL-4 response was observed in five patients, while IL-10 response was detected in one patient. Purified CD4-CD8+ T cells isolated from four patients demonstrated specific cytolytic activity per chromium release assay. In conclusion, immunization with PSA-peptide induced specific T cell immunity in one-half of the patients with locally advanced and hormone-sensitive, metastatic CaP. DTH-derived T cells exhibited PSA-peptide-specific cytolytic activity and predominantly expressed a type-1 cytokine profile.