Cross-priming of T cells to intracranial tumor antigens elicits an immune response that fails in the effector phase but can be augmented with local immunotherapy

Aptamer-functionalized Quercetin Thermosensitive Liposomes for Targeting Drug Delivery and Antitumor Therapy

Chemo-thermotherapy, as a promising cancer combination therapy strategy, has attracted widespread attention. In this study, a novel aptamer functionalized thermosensitive liposome encapsulating hydrophobic drug quercetin was fabricated as an efficient drug delivery system. This aptamer-functionalized quercetin thermosensitive liposomes (AQTSL) combined the merits of high-loading yield, sustained drug release, long-term circulation in the body of PEGylated liposomes, passive targeting provided by 100-200 nm nanoparticles, active targeting and improved internalization effects offered by AS1411 aptamer, and temperature-responsive of quercetin release. In addition, AQTSL tail vein injection combined with 42℃ water bath heating on tumor site (AQTSL+42℃)treatment inhibited the tumor growth significantly compared with the normal saline administration (p<0.01), and the inhibition rate reached 75%. Furthermore, AQTSL+42℃ treatment also slowed down the tumor growth significantly compared with QTSL combined with 42℃ administration (p<0.05), confirming that AS1411 decoration on QTSL increased the active targeting and internalization effects of the drug delivery system, and AS1411 aptamer itself might also contribute to the tumor inhibition. These data indicate that AQTSL is a potential carrier candidate for different hydrophobic drugs and tumor targeting delivery, and this kind of targeted drug delivery system combined with temperature responsive drug release mode is expected to achieve an ideal tumor therapy effect.

Layered and orthogonal assembly of hydrophilic drugs and hydrophobic photosensitizers for enhanced cancer therapy

Combinatorial tumor therapy including chemotherapy and photodynamic therapy (PDT) can compensate for the limitations of each other and significantly increase the therapeutic effect. However, considering the differences of water-soluble characteristics between chemotherapeutic drugs and photosensitizers for photodynamic therapy, simply loading these substances into the same cavities of nanocarriers is rather difficult, leading to the reduced drug loading efficiency. Here, we reported a layered and orthogonal assembly of hydrophilic drugs doxorubicin (Dox) and hydrophobic photosensitizers Chlorin e6 (Ce6) for enhancing the effect of synergistic therapeutics. The assembly was based on polydopamine (PDA) modified with β-cyclodextrin (β-CD) through the addition reaction of -HS in HS-β-CD and-C=C in PDA, then DOX and Ce6 were loaded on the PDA and in the hydrophobic cavities of β-CDs respectively with superior drug loading efficiencies (38.8 ± 0.8% and 5.4 ± 0.3% for DOX and Ce6). PDA was hydrolyzed completely under the lysosomal acidic condition, leading to the controlled release of DOX. Under NIR irradiations, DOX-based chemotherapy was successfully integrated with PDA-based photothermal and Ce6-based photodynamic therapy. Tumor specific aptamer AS1411-modified assembly provides ideal antitumor effects in vitro and in vivo with excellent biocompatibility. Collectively, this layered and orthogonal assembly offers a generalizable solution for delivering matters with distinct aqueous solubility would find broad applications not only in drug delivery but also in bio-nanotechnology.

Brain Tumor Microenvironment and Host State: Implications for Immunotherapy

Glioblastoma (GBM) is a highly lethal brain tumor with poor responses to immunotherapies that have been successful in more immunogenic cancers with less immunosuppressive tumor microenvironments (TME). The GBM TME is uniquely challenging to treat due to tumor cell-extrinsic components that are native to the brain, as well as tumor-intrinsic mechanisms that aid in immune evasion. Lowering the barrier of immunosuppression by targeting the genetically stable tumor stroma presents opportunities to treat the tumor in a way that circumvents the complications of targeting a constantly mutating tumor with tumor antigen-directed therapies. Tumor-associated monocytes, macrophages, and microglia are a stromal element of particular interest. Macrophages and monocytes compose the bulk of infiltrating immune cells and are considered to have protumor and immunosuppressive effects. Targeting these cells or other stromal elements is expected to convert what is considered the "cold" TME of GBM to a more "hot" TME phenotype. This conversion could increase the effectiveness of what have become conventional frontline immunotherapies in GBM-creating opportunities for better treatment through combination therapy.

Myeloablative temozolomide enhances CD8⁺ T-cell responses to vaccine and is required for efficacy against brain tumors in mice

Temozolomide (TMZ) is an alkylating agent shown to prolong survival in patients with high grade glioma and is routinely used to treat melanoma brain metastases. A prominent side effect of TMZ is induction of profound lymphopenia, which some suggest may be incompatible with immunotherapy. Conversely, it has been proposed that recovery from chemotherapy-induced lymphopenia may actually be exploited to potentiate T-cell responses. Here, we report the first demonstration of TMZ as an immune host-conditioning regimen in an experimental model of brain tumor and examine its impact on antitumor efficacy of a well-characterized peptide vaccine. Our results show that high-dose, myeloablative (MA) TMZ resulted in markedly reduced CD4(+), CD8(+) T-cell and CD4(+)Foxp3(+) TReg counts. Adoptive transfer of naïve CD8(+) T cells and vaccination in this setting led to an approximately 70-fold expansion of antigen-specific CD8(+) T cells over controls. Ex vivo analysis of effector functions revealed significantly enhanced levels of pro-inflammatory cytokine secretion from mice receiving MA TMZ when compared to those treated with a lower lymphodepletive, non-myeloablative (NMA) dose. Importantly, MA TMZ, but not NMA TMZ was uniquely associated with an elevation of endogenous IL-2 serum levels, which we also show was required for optimal T-cell expansion. Accordingly, in a murine model of established intracerebral tumor, vaccination-induced immunity in the setting of MA TMZ-but not lymphodepletive, NMA TMZ-led to significantly prolonged survival. Overall, these results may be used to leverage the side-effects of a clinically-approved chemotherapy and should be considered in future study design of immune-based treatments for brain tumors.

Recurrence of Intracranial Tumors following Adoptive T Cell Therapy Can Be Prevented by Direct and Indirect Killing Aided by High Levels of Tumor Antigen Cross-Presented on Stromal Cells

Elimination of peripheral tumors by adoptively transferred tumor-specific T cells may require killing of cancer cells and tumor stromal cells. Tumor Ags are cross-presented on stromal cells, resulting in direct cytotoxic T cell (CTL) killing of both Ag-expressing cancer cells and stromal cells. Indirect killing of Ag loss variant cells also occurs. We show here that similar processes occur in a brain tumor stromal environment. We used murine cancer cell lines that express high or low levels of a peptide Ag, SIYRYYGL (SIY), recognized by transgenic 2C CD8(+) T cells. The two cell lines are killed with equivalent efficiency by 2C T cells in vitro. Following adoptive transfer of 2C T cells into mice with established SIY-Hi or SIY-Lo brain tumors, tumors of both types regressed, but low-Ag-expressing tumors recurred. High-Ag-expressing tumors contained CD11b(+) cells cross-presenting SIY peptide and were completely eliminated by 2C T cells. To further test the role of cross-presentation, RAG1(-/-) H-2(b) mice were infused with H-2(k) tumor cells expressing high levels of SIY peptide. Adoptively transferred 2C T cells are able to kill cross-presenting H-2(b) stromal cells but not H-2(k) tumor cells. In peripheral models, this paradigm led to a small static tumor. In the brain, activated 2C T cells were able to kill cross-presenting CD11b(+) cells and completely eliminate the H-2(k) tumors in most mice. Targeting brain tumor stroma or increasing Ag shedding from tumor cells to enhance cross-presentation may improve the clinical success of T cell adoptive therapies.

Immunotherapy of malignant brain tumors

Despite aggressive multi-modality therapy including surgery, radiation, and chemotherapy, the prognosis for patients with malignant primary brain tumors remains very poor. Moreover, the non-specific nature of conventional therapy for brain tumors often results in incapacitating damage to surrounding normal brain and systemic tissues. Thus, there is an urgent need for the development of therapeutic strategies that precisely target tumor cells while minimizing collateral damage to neighboring eloquent cerebral cortex. The rationale for using the immune system to target brain tumors is based on the premise that the inherent specificity of immunologic reactivity could meet the clear need for more specific and precise therapy. The success of this modality is dependent on our ability to understand the mechanisms of immune regulation within the central nervous system (CNS), as well as counter the broad defects in host cell-mediated immunity that malignant gliomas are known to elicit. Recent advances in our understanding of tumor-induced and host-mediated immunosuppressive mechanisms, the development of effective strategies to combat these suppressive effects, and a better understanding of how to deliver immunologic effector molecules more efficiently to CNS tumors have all facilitated significant progress toward the realization of true clinical benefit from immunotherapeutic treatment of malignant gliomas.

Brain microenvironment promotes the final functional maturation of tumor-specific effector CD8+ T cells

During the priming phase of an antitumor immune response, CD8(+) T cells undergo a program of differentiation driven by professional APCs in secondary lymphoid organs. This leads to clonal expansion and acquisition both of effector functions and a specific adhesion molecule pattern. Whether this program can be reshaped during the effector phase to adapt to the effector site microenvironment is unknown. We investigated this in murine brain tumor models using adoptive transfer of tumor-specific CD8(+) T cells, and in spontaneous immune responses of patients with malignant glioma. Our data show proliferation of Ag-experienced tumor-specific T cells within the brain parenchyma. Moreover, CD8(+) T cells further differentiated in the brain, exhibiting enhanced IFN-gamma and granzyme B expression and induction of alpha(E)(CD103)beta(7) integrin. This unexpected integrin expression identified a subpopulation of CD8(+) T cells conditioned by the brain microenvironment and also had functional consequences: alpha(E)(CD103)beta(7)-expressing CD8(+) T cells had enhanced retention in the brain. These findings were further investigated for CD8(+) T cells infiltrating human malignant glioma; CD8(+) T cells expressed alpha(E)(CD103)beta(7) integrin and granzyme B as in the murine models. Overall, our data indicate that the effector site plays an active role in shaping the effector phase of tumor immunity. The potential for local expansion and functional reprogramming should be considered when optimizing future immunotherapies for regional tumor control.

Immune resistance orchestrated by the tumor microenvironment

It is now little disputed that most if not all cancer cells express antigens that can be recognized by specific CD8(+) T lymphocytes. However, a central question in the field of anti-tumor immunity is why such antigen-expressing tumors are not spontaneously eliminated by the immune system. While in some cases, this lack of rejection may be due to immunologic ignorance, induction of anti-tumor T-cell responses in many patients has been detected in the peripheral blood, either spontaneously or in response to vaccination, without accompanying tumor rejection. These observations argue for the importance of barriers downstream from initial T-cell priming that need to be addressed to translate immune responses into clinical tumor regression. Recent data suggest that the proper trafficking of effector T cells into the tumor microenvironment may not always occur. T cells that do effectively home to tumor metastases are often found to be dysfunctional, pointing toward immunosuppressive mechanisms in the tumor microenvironment. T-cell anergy due to insufficient B7 costimulation, extrinsic suppression by regulatory cell populations, inhibition by ligands such as programmed death ligand-1, metabolic dysregulation by enzymes such as indoleamine-2,3-dioxygenase, and the action of soluble inhibitory factors such as transforming growth factor-beta have all been clearly implicated in generating this suppressive microenvironment. Identification of these downstream processes points to new therapeutic targets that should be manipulated to facilitate the effector phase of anti-tumor immune responses in concert with vaccination or T-cell adoptive transfer.