Tobacco mosaic virus efficiently targets DC uptake, activation and antigen-specific T cell responses in vivo

Over the past 20 years, dendritic cells (DCs) have been utilized to activate immune responses capable of eliminating cancer cells. Currently, ex vivo DC priming has been the mainstay of DC cancer immunotherapies. However, cell-based treatment modalities are inherently flawed due to a lack of standardization, specialized facilities and personnel, and cost. Therefore, direct modes of DC manipulation, circumventing the need for ex vivo culture, must be investigated. To facilitate the development of next-generation, in vivo targeted DC vaccines, we characterized the DC interaction and activation potential of the Tobacco Mosaic virus (TMV), a plant virus that enjoys a relative ease of production and the ability to deliver protein payloads via surface conjugation. In this study we show that TMV is readily taken up by mouse bone marrow-derived DCs, in vitro. Footpad injection of fluorophore-labeled TMV reveals preferential uptake by draining lymph node resident DCs in vivo. Uptake leads to activation, as measured by the upregulation of key DC surface markers. When peptide antigen-conjugated TMV is injected into the footpad of mice, DC-mediated uptake and activation leads to robust antigen-specific CD8(+) T cell responses, as measured by antigen-specific tetramer analysis. Remarkably, TMV priming induced a greater magnitude T cell response than Adenovirus (Ad) priming. Finally, TMV is capable of boosting either Ad-induced or TMV-induced antigen-specific T cell responses, demonstrating that TMV, uniquely, does not induce neutralizing self-immunity. Overall, this study elucidates the in vivo DC delivery and activation properties of TMV and indicates its potential as a vaccine vector in stand alone or prime-boost strategies.

FGFR1-WNT-TGF-β signaling in prostate cancer mouse models recapitulates human reactive stroma

The reactive stroma surrounding tumor lesions performs critical roles ranging from supporting tumor cell proliferation to inducing tumorigenesis and metastasis. Therefore, it is critical to understand the cellular components and signaling control mechanisms that underlie the etiology of reactive stroma. Previous studies have individually implicated fibroblast growth factor receptor 1 (FGFR1) and canonical WNT/β-catenin signaling in prostate cancer progression and the initiation and maintenance of a reactive stroma; however, both pathways are frequently found to be coactivated in cancer tissue. Using autochthonous transgenic mouse models for inducible FGFR1 (JOCK1) and prostate-specific and ubiquitously expressed inducible β-catenin (Pro-Cat and Ubi-Cat, respectively) and bigenic crosses between these lines (Pro-Cat × JOCK1 and Ubi-Cat × JOCK1), we describe WNT-induced synergistic acceleration of FGFR1-driven adenocarcinoma, associated with a pronounced fibroblastic reactive stroma activation surrounding prostatic intraepithelial neoplasia (mPIN) lesions found both in in situ and reconstitution assays. Both mouse and human reactive stroma exhibited increased transforming growth factor-β (TGF-β) signaling adjacent to pathologic lesions likely contributing to invasion. Furthermore, elevated stromal TGF-β signaling was associated with higher Gleason scores in archived human biopsies, mirroring murine patterns. Our findings establish the importance of the FGFR1-WNT-TGF-β signaling axes as driving forces behind reactive stroma in aggressive prostate adenocarcinomas, deepening their relevance as therapeutic targets.

Delivery of a genetic cancer vaccine containing a small molecule inducible immune adjuvant by in vivo electroporation (eVac) (P4332)

The use of dendritic cell vaccines to treat cancer has significant potential, however that potential has yet to be achieved in treating patients. Fortunately, pioneering biotechnologies are paving the way for more effective cancer vaccines. Our lab has developed a drug inducible MyD88/CD40 (iMC) composite adjuvant that promotes robust cytotoxic T cell priming in iMC activated DCs. Despite the iMC innovation, the use of patient-tailored ex vivo DC vaccines is impractical for widespread use, due to issues of scalability and cost. We have therefore begun to address the delivery of DC vaccines as “off-the-shelf” therapies using in vivo electroporation (EP) of plasmid DNA (pDNA) encoding both the iMC adjuvant and tumor antigen (eVac). Intradermal EP of pDNA encoding the model antigen LacZ in mice suggests that LacZ-specific T cell responses were induced, as mice receiving LacZ + EP prophylactically were either protected from establishment of B16/LacZ tumors or demonstrated significantly slower tumor growth compared to controls. In mice bearing pre-established B16/LacZ tumors, LacZ-eVac, but not EP with LacZ antigen alone significantly reduced tumor burden and increased survival. Taken together, these data indicate that eVac with iMC-antigen is an effective “off-the-shelf” cancer vaccine. These findings warrant elucidation of the underlying immunological mechanisms responsible for the anti-tumor responses observed with eVac treatment to guide further refinement of the vaccine.

Abstract 3287: Intra- and intercellular Wnt pathway induction synergistically accelerates FGFR1-mediated prostate tumorigenesis

Cancer growth and metastasis requires proliferation, cell migration, and stromal remodeling, functions also found during organogenesis and wound repair. The fibroblast growth factor (FGF) and canonical Wnt/β-catenin signaling pathways are two pathways central to these functions. FGFs and their receptors (FGFRs) are expressed in most tissues and play pivotal roles in development, wound healing and neovascularization, and are also upregulated in many solid cancers, including prostate, mammary, renal, kidney, bladder, and testicular tumors. We previously demonstrated in the JOCK1 (juxtaposition of CID and kinase) prostate cancer (PCa) mouse model that chemically induced dimerization (CID) of FGFR1 signaling in the prostate is sufficient for tumor initiation and early tumor maintenance and prolonged (42 weeks) FGFR1 activation results in PCa with distant metastasis. The Wnt pathway is also vital for proper embryogenesis and homeostasis of adult tissues by regulating stem cell self-renewal, pluripotency, and differentiation in several tissues, including colon, hair shaft, and chondrocyte stem/progenitor cells. The uncontrolled activation of this important stem pathway is also associated with various cancers, including colon, breast and prostate. Recently, we have discovered that induced crosslinking of the Wnt co-receptor LRP5 is sufficient to induce canonical Wnt signaling and nuclear localization of β-catenin. We subsequently developed two novel mouse models where Wnt can be specifically activated in the prostate epithelium, Pro-Cat (prostate-targeted inducible β-catenin), or in virtually every tissue sub-layer, Ubi-Cat (ubiquitously expressed inducible β-catenin). Consistent with previous literature, induced Pro-Cat mice never progressed beyond prostatic hyperplasia, however, after a year of pathway induction, 2 out of 6 Ubi-Cat mice developed adenocarcinoma, indicating a yet unexplored role for stromal Wnt signaling in tumorigenesis. In order to delineate possible crosstalk and synergism between FGF and Wnt pathways, we bred JOCK1 mice unto Pro-Cat and Ubi-Cat transgenic lines. Both Pro-Cat/JOCK1 and Ubi-Cat/JOCK1 mice developed widespread hyperplasia, high-grade PIN and adenocarcinoma with an extensive reactive stroma by 24 weeks of CID injections. Fascinatingly, Pro-Cat/JOCK1 mice do not continue to progress beyond the timeline established by JOCK1 induction alone whereas Ubi-Cat/JOCK1 mice continue to progress to advanced transitional sarcomatoid lesions. These results suggest that intracellular crosstalk between Wnt and FGFR1 in the epithelia is sufficient to accelerate tumor initiation, however accelerated progression requires intercellular crosstalk between the stroma and the epithelia. Additional experiments necessary to definitively implicate the stroma in accelerated tumorigenesis are underway and will be discussed.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3287. doi:1538-7445.AM2012-3287

Activation of Wnt signaling by chemically induced dimerization of LRP5 disrupts cellular homeostasis

Wnt signaling is crucial for a variety of biological processes, including body axis formation, planar polarity, stem cell maintenance and cellular differentiation. Therefore, targeted manipulation of Wnt signaling in vivo would be extremely useful. By applying chemical inducer of dimerization (CID) technology, we were able to modify the Wnt co-receptor, low-density lipoprotein (LDL)-receptor-related protein 5 (LRP5), to generate the synthetic ligand inducible Wnt switch, iLRP5. We show that iLRP5 oligomerization results in its localization to disheveled-containing punctate structures and sequestration of scaffold protein Axin, leading to robust β-catenin-mediated signaling. Moreover, we identify a novel LRP5 cytoplasmic domain critical for its intracellular localization and casein kinase 1-dependent β-catenin signaling. Finally, by utilizing iLRP5 as a Wnt signaling switch, we generated the Ubiquitous Activator of β-catenin (Ubi-Cat) transgenic mouse line. The Ubi-Cat line allows for nearly ubiquitous expression of iLRP5 under control of the H-2K^b promoter. Activation of iLRP5 in isolated prostate basal epithelial stem cells resulted in expansion of p63⁺ cells and development of hyperplasia in reconstituted murine prostate grafts. Independently, iLRP5 induction in adult prostate stroma enhanced prostate tissue regeneration. Moreover, induction of iLRP5 in male Ubi-Cat mice resulted in prostate tumor progression over several months from prostate hyperplasia to adenocarcinoma. We also investigated iLRP5 activation in Ubi-Cat-derived mammary cells, observing that prolonged activation results in mammary tumor formation. Thus, in two distinct experimental mouse models, activation of iLRP5 results in disruption of tissue homeostasis, demonstrating the utility of iLRP5 as a novel research tool for determining the outcome of Wnt activation in a precise spatially and temporally determined fashion.

Abstract 756: Genetically enhanced DC vaccines for cancer: Bringing the ex vivo, in vivo

Background and Objectives: Dendritic Cells (DCs) are potent antigen presenting cells, capable of activating naïve T-cells to recognize and kill tumor cells. Since DCs are also able to reverse the tumor-induced dormancy of killer and helper T-cells, DC vaccines have been developed to induce anti-tumor immune responses. To improve DC vaccine efficacy, we have focused on augmenting DC function using an inducible MyD88/CD40 signaling switch (iMC) capable of stimulating DC activation in a Th1-polarizing manner. iMC abrogates the need for more traditional, toxic DC activators such as LPS and allows for spatio-temporal control of DC activation, further increasing vaccine efficacy. In ex vivo pre-established tumor studies, DCs pulsed with tumor-specific antigen (TSA) and manipulated to express iMC significantly decreased tumor growth in mice relative to DCs pulsed with TSA alone.

While potentially efficacious, ex vivo modification and re-delivery of DCs requires specialized and expensive methods, which limit their utility as primary cancer-fighting agents. Therefore, we have focused on developing a strategy capable of TSA and iMC delivery to in vivo DCs using adenovectors. Treatment of tumor-bearing mice with adenovectors expressing only TSA was effective in significantly decreasing tumor growth. Combining this therapy with adenovectors expressing iMC resulted in only modest therapeutic enhancement.

We hypothesize that reliance on simultaneous transgene expression by two separate vectors in the same cell may prevent more potent immunogenicity. Our lab has shown that such double expression occurs in only about 20-50% of relevant cells. Therefore, we have developed a bicistronic adenovector (BAV), encoding both TSA and iMC.

Methods: To test dual transgene expression by BAV, DCs were transduced and both β-galactosidase activity (the TSA) and IL-12 secretion (by iMC) were assessed using X-gal staining and IL-12p70 ELISA, respectively. To evaluate anti-tumor response, mice bearing pre-established B16-LacZ tumors were treated via footpad injection of BAV followed by two days of dimerizer drug.

Results: DCs transduced with BAV were shown to express the TSA and secrete high levels of IL-12p70 when compared to empty vector or LPS-treated DCs. Treatment of B16-LacZ tumor-bearing mice with BAV resulted in significantly enhanced tumor reduction versus Ad-LacZ alone.

Conclusions: In order to further enhance BAV's ability to induce anti-tumor immune responses, we are adapting a method of targeting adenovectors to CD40+ DCs using bi-functional molecules (CFm40L), described by Pereboev et al. (Molecular Therapy, 2004). Our preliminary results have shown that adenoviral modification with CFm40L significantly increases DC transduction efficiency. This technology should further increase the therapeutic efficacy of BAV by specifically targeting it to DCs while at the same time reducing total viral dosage.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 756. doi:10.1158/1538-7445.AM2011-756

A composite MyD88/CD40 switch synergistically activates mouse and human dendritic cells for enhanced antitumor efficacy

The in vivo therapeutic efficacy of DC-based cancer vaccines is limited by suboptimal DC maturation protocols. Although delivery of TLR adjuvants systemically boosts DC-based cancer vaccine efficacy, it could also increase toxicity. Here, we have engineered a drug-inducible, composite activation receptor for DCs (referred to herein as DC-CAR) comprising the TLR adaptor MyD88, the CD40 cytoplasmic region, and 2 ligand-binding FKBP12 domains. Administration of a lipid-permeant dimerizing ligand (AP1903) induced oligomerization and activation of this fusion protein, which we termed iMyD88/CD40. AP1903 administration to vaccinated mice enabled prolonged and targeted activation of iMyD88/CD40-modified DCs. Compared with conventionally matured DCs, AP1903-activated iMyD88/CD40-DCs had increased activation of proinflammatory MAPKs. AP1903-activated iMyD88/CD40-transduced human or mouse DCs also produced higher levels of Th1 cytokines, showed improved migration in vivo, and enhanced both antigen-specific CD8+ T cell responses and innate NK cell responses. Furthermore, treatment with AP1903 in vaccinated mice led to robust antitumor immunity against preestablished E.G7-OVA lymphomas and aggressive B16.F10 tumors. Thus, the iMyD88/CD40 unified "switch" effectively and safely replaced exogenous adjuvant cocktails, allowing remote and sustained DC activation in vivo. DC "licensing" through iMyD88/CD40 may represent a mechanism by which to exploit the natural synergy between the TLR and CD40 signaling pathways in DCs using a single small molecule drug and could augment the efficacy of antitumor DC-based vaccines.

Correlation of serum cytokines with clinical responses in patients treated with BPX-101, a drug-activated vaccine for metastatic castration-resistant prostate cancer (mCRPC)

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Background: We report the correlation of clinical and immune monitoring results for subjects enrolled in a phase I/IIa clinical trial of BPX-101, a drug-activated dendritic cell vaccine for mCRPC.

Methods: Men with progressive mCRPC were enrolled in a 3+3 dose escalation trial evaluating BPX-101 and activating agent AP1903. BPX-101 was administered intradermally every 2 weeks for 6 doses, during the induction phase, and for non-progressing patients, every 8 weeks for up to 5 doses during the maintenance phase. AP1903 (0.4 mg/kg) was infused 24 hours after each BPX-101 dose. Blood samples for immune monitoring were collected weekly during the induction phase, and before and one week after each maintenance dose. GM-CSF, TNF-α, IFN-γ, IP-10, MCP-1, MIP-1α, MIP-1β, and RANTES levels were measured by Luminex microspheres, and IL-6 by ELISA.

Results: Planned enrollment of 12 subjects is complete, including 3 each at 4 × 106 and 12.5 × 106 cells/dose, and 6 at 25 x 106 cells/dose. A pattern of spiking levels of serum cytokines one week after each dose, returning to baseline the following week, was observed in subjects with greater disease burden. In one low dose subject who experienced a PR after one year on study, panel cytokines spiked 4-fold on average after each induction phase dose, less than 2-fold after the first two boosters, and between 6-fold and 56-fold after the final three boosters. IL-6, which had declined during the induction phase to below 1 pg/mL through two boosters, spiked between 1,680-fold and 13,000-fold after each of the last three boosters. In a second, high dose subject (#1008), who experienced a near CR of multiple lung metastases with otherwise stable disease, panel cytokines spiked 150-fold on average during the induction phase. In both cases, TNF-α, MIP-1α and MIP-1β spiked the most, including a more than 1,000-fold average spike in TNF-α for subject 1008. Cytokine spikes were not associated with AEs.

Conclusions: BPX-101 induces a spiking pattern of cytokine elevations after each dose. In patients who experienced measurable disease reductions, more dramatic spikes in serum inflammatory cytokine levels were seen.

[Table: see text]

Antigen-specific immunity and tumor inflammation after vaccination with BPX-101, a drug-activated dendritic cell vaccine for metastatic castration-resistant prostate cancer (mCRPC)

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Background: We report evidence of antigen-specific immunity and severe prostate cancer inflammation and necrosis after vaccination in patients enrolled in a phase I-IIa clinical trial of BPX-101, a drug-activated DC vaccine for mCRPC.

Methods: Twelve men with progressive, mCRPC were enrolled in a 3+3 dose escalation trial evaluating BPX-101 and activating agent AP1903. BPX-101, which targets prostate-specific membrane antigen (PSMA), was administered intradermally every 2 weeks for 6 doses, followed 24 hours after each dose by infusion of AP1903 (0.4 mg/kg). Injection site skin biopsies were performed after the fourth vaccination. T cells cultured from the skin biopsy ex vivo were stimulated with PSMA protein or control antigens, and were analyzed using Luminex microspheres for 30 inflammatory cytokines/chemokines. One patient (#1007) with an intact prostate developed lower urinary tract bleeding after the fifth vaccination and underwent a transurethral resection of bleeding prostate cancer tissue. Paraffin-embedded blocks were stained for hematoxylin and eosin (H&E). Immunohistochemical stains for CD3, CD4, CD8 and CD34 were also performed.

Results: Of 5 subjects with evaluable injection site biopsy results, all exhibited PSMA-specific immunity (3 TH1-biased and 2 TH2- biased). Subject 1007's injection site biopsy demonstrated a significant >10-fold increase in IFN-gamma and IL-2 after stimulation by PSMA, compared to stimulation by ovalbumin, consistent with induction of a strong PSMA-specific CTL or TH1-biased immune response. H&E stained resected prostate tissue demonstrated Gleason 8 (4+4) prostate adenocarcinoma exhibiting a severe inflammatory response, consisting of infiltrating plasma cells and CD4+ and CD8+ T cells. Large areas of necrosis were seen adjacent to inflamed prostate cancer tissue.

Conclusions: Vaccination with BPX-101 followed by AP1903 can induce a strong, PSMA-specific immune response. Furthermore, evidence of severe prostate cancer-specific inflammation and necrosis, associated with a strong PSMA-specific immune response has been observed after multiple doses of BPX-101.

[Table: see text]

Results of a phase I/II clinical trial of BPX-101, a novel drug-activated dendritic cell (DC) vaccine for metastatic castration-resistant prostate cancer (mCRPC)

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Background: We report results of a phase I/II clinical trial of BPX-101, a drug- activated autologous DC vaccine targeting PSMA.

Methods: Men with progressive mCRPC following up to one prior chemotherapy regimen were enrolled in a 3+3 dose escalation trial evaluating BPX-101 and CD40 activating agent AP1903. BPX-101 was administered intradermally every 2 weeks for 6 doses, during the induction phase, and for nonprogressing patients, every 8 weeks for up to 5 doses during the maintenance phase. AP1903 (0.4 mg/kg) was infused 24 hours after each BPX-101 dose. Radiologic evaluation was performed every 12 weeks.

Results: Planned enrollment of 12 subjects has been completed, including 3 each at 4 × 106 and 12.5 × 106 cells/dose, and 6 at 25 × 106 cells/dose. All vaccine products were releasable. Median Halabi- predicted survival was 13.8 months. Two subjects went off protocol prior to the end of induction due to progression, 8 reached end of induction, and 2 are nearing completion of induction. Toxicities (e.g. injection site reactions) were generally mild. One high dose subject experienced a single acute cytokine reaction during infusion of AP1903 at the second vaccination, but continued induction without further drug-related adverse events. Notably, one post- docetaxel subject in the low dose cohort achieved a RECIST PR, and one chemo-naive subject in the mid-dose cohort with extensive visceral, nodal, and bone metastases experienced a RECIST CR with docetaxel-based chemotherapy after induction and maintains an undetectable ultrasensitive PSA (0.009 ng/mL) 10 months after enrollment. A third subject, in the high-dose cohort, experienced near complete elimination of multiple lung metastases with otherwise stable disease by the end of induction. Robust immune responses were seen in all three.

Conclusions: BPX-101 can be reliably manufactured and safely administered, followed by AP1903, at doses of at least 25 × 106 cells. Contrary to the observation that cancer vaccine therapy improves survival without short-term response, BPX-101-treated patients have experienced measurable disease responses, including near elimination of poor-risk visceral disease.

[Table: see text]

The phosphatase SRC homology region 2 domain-containing phosphatase-1 is an intrinsic central regulator of dendritic cell function

Dendritic cells (DCs) initiate proinflammatory or regulatory T cell responses, depending on their activation state. Despite extensive knowledge of DC-activating signals, the understanding of DC inhibitory signals is relatively limited. We show that Src homology region 2 domain-containing phosphatase-1 (SHP-1) is an important inhibitor of DC signaling, targeting multiple activation pathways. Downstream of TLR4, SHP-1 showed increased interaction with several proteins including IL-1R-associated kinase-4, and modulated LPS signaling by inhibiting NF-κB, AP-1, ERK, and JNK activity, while enhancing p38 activity. In addition, SHP-1 inhibited prosurvival signaling through AKT activation. Furthermore, SHP-1 inhibited CCR7 protein expression. Inhibiting SHP-1 in DCs enhanced proinflammatory cytokines, IL-6, IL-12, and IL-1β production, promoted survival, and increased DC migration to draining lymph nodes. Administration of SHP-1-inhibited DCs in vivo induced expansion of Ag-specific cytotoxic T cells and inhibited Foxp3(+) regulatory T cell induction, resulting in an enhanced immune response against pre-established mouse melanoma and prostate tumors. Taken together, these data demonstrate that SHP-1 is an intrinsic global regulator of DC function, controlling many facets of T cell-mediated immune responses.

Development of an inducible MyD88.CD40 gene switch for potent anti-tumor dendritic cell (DC) vaccines (131.22)

We previously generated an inducible CD40 (iCD40) costimulatory switch enabling prolonged CD40 signaling in DCs in a ligand-independent manner. However, follow-up studies showed the requirement for an additional danger stimulus, lipopolysaccharide, for complete DC activation and licensing. To overcome drawbacks of systemic toxicity associated with endotoxin in a clinical trial, we proposed the development of a synthetic drug-inducible TLR4. Toward this goal, we have generated an inducible version of downstream adaptor MyD88 and combined it with iCD40 to generate a unified, inducible composite receptor, iMyD88.CD40. In vitro, in addition to upregulating maturation markers, iMyD88.CD40 activation by dimerizing drug led to elevated IL-12 production by both mouse and human DCs, prolonged DC survival and improved T cell responses to endogenous tumor antigens. Increased magnitudes of p38, IKK and JNK activation along with early activation of NF-kB family members, RelA, RelB and c-Rel form the molecular basis for the observed synergistic effects of iMyD88.CD40. In vivo, iMyD88.CD40-activated DCs migrated more efficiently to draining lymph nodes, promoted Th1 responses and abolished pre-established E.G7-OVA tumors and the less immunogenic B16 tumors. In conclusion, we have generated a novel chimeric DC activation switch combining signaling elements from adjuvant receptors enabling prolonged DC activation both ex vivo as well as in vivo following DC and drug delivery.

An essential role for Akt1 in dendritic cell function and tumor immunotherapy

Current dendritic cell (DC) vaccine preparations involving ex vivo differentiation and maturation produce short-lived, transiently active DCs that may curtail T-cell responses in vivo. We demonstrate that Akt1, downregulation of which decreases DC lifespan, is critical for proinflammatory signal-mediated DC survival and maturation. Lipopolysaccharide or CD40 signaling stabilizes Akt1, promoting both activation and Bcl-2-dependent survival of DCs. Expression of a potent allele encoding a lipid raft-targeted Akt1, M(F)-DeltaAkt, is sufficient for maturation and survival of murine bone marrow-derived DCs in vivo. M(F)-DeltaAkt-transduced DCs enhanced T-cell proliferation, activation and long-term memory responses, enabling eradication of large pre-established lymphomas and aggressive B16 melanomas. Human myeloid DCs expressing constitutively active M(F)-DeltahAkt also survived significantly longer and promoted antigen-specific T-cell responses. Thus, Akt1 is a critical regulator of DC lifespan, and its manipulation in DCs can improve the clinical efficacy of DC-based tumor vaccines.