T cell egress via lymphatic vessels is tuned by antigen encounter and limits tumor control.

Antigen-specific CD8+ T cell accumulation in tumors is a prerequisite for effective immunotherapy, and yet the mechanisms of lymphocyte transit are not well defined. Here we show that tumor-associated lymphatic vessels control T cell exit from tumors via the chemokine CXCL12, and intratumoral antigen encounter tunes CXCR4 expression by effector CD8+ T cells. Only high-affinity antigen downregulates CXCR4 and upregulates the CXCL12 decoy receptor, ACKR3, thereby reducing CXCL12 sensitivity and promoting T cell retention. A diverse repertoire of functional tumor-specific CD8+ T cells, therefore, exit the tumor, which limits the pool of CD8+ T cells available to exert tumor control. CXCR4 inhibition or loss of lymphatic-specific CXCL12 boosts T cell retention and enhances tumor control. These data indicate that strategies to limit T cell egress might be an approach to boost the quantity and quality of intratumoral T cells and thereby response to immunotherapy.

Toward Minimal Residual Disease-Directed Therapy in Melanoma.

Many patients with advanced cancers achieve dramatic responses to a panoply of therapeutics yet retain minimal residual disease (MRD), which ultimately results in relapse. To gain insights into the biology of MRD, we applied single-cell RNA sequencing to malignant cells isolated from BRAF mutant patient-derived xenograft melanoma cohorts exposed to concurrent RAF/MEK-inhibition. We identified distinct drug-tolerant transcriptional states, varying combinations of which co-occurred within MRDs from PDXs and biopsies of patients on treatment. One of these exhibited a neural crest stem cell (NCSC) transcriptional program largely driven by the nuclear receptor RXRG. An RXR antagonist mitigated accumulation of NCSCs in MRD and delayed the development of resistance. These data identify NCSCs as key drivers of resistance and illustrate the therapeutic potential of MRD-directed therapy. They also highlight how gene regulatory network architecture reprogramming may be therapeutically exploited to limit cellular heterogeneity, a key driver of disease progression and therapy resistance.

Endogenous Signaling Molecule Activating (ESMA) CARs: A Novel CAR Design Showing a Favorable Risk to Potency Ratio for the Treatment of Triple Negative Breast Cancer.

As chimeric antigen receptor (CAR) T cell therapy continues to gain attention as a valuable treatment option against different cancers, strategies to improve its potency and decrease the side effects associated with this therapy have become increasingly relevant. Herein, we report an alternative CAR design that incorporates transmembrane domains with the ability to recruit endogenous signaling molecules, eliminating the need for stimulatory signals within the CAR structure. These endogenous signaling molecule activating (ESMA) CARs triggered robust cytotoxic activity and proliferation of the T cells when directed against the triple-negative breast cancer (TNBC) cell line MDA-MB-231 while exhibiting reduced cytokine secretion and exhaustion marker expression compared to their cognate standard second generation CARs. In a NOD SCID Gamma (NSG) MDA-MB-231 xenograft mouse model, the lead candidate maintained longitudinal therapeutic efficacy and an enhanced T cell memory phenotype. Profound tumor infiltration by activated T cells repressed tumor growth, further manifesting the proliferative capacity of the ESMA CAR T cell therapy. Consequently, ESMA CAR T cells entail promising features for improved clinical outcome as a solid tumor treatment option.

Vaccination against galectin-1 promotes cytotoxic T-cell infiltration in melanoma and reduces tumor burden.

Galectin-1 (Gal1) is a glycan-binding protein that promotes tumor progression by several distinct mechanisms. Through direct binding to vascular endothelial growth factor (VEGF)-receptor 2, Gal1 is able to induce VEGF-like signaling, which contributes to tumor angiogenesis. Furthermore, several studies have demonstrated an immunosuppressive function of Gal1 through effects on both effector and regulatory T cells. Elevated Gal1 expression and secretion have been shown in many tumor types, and high Gal1 serum levels have been connected to poor prognosis in cancer patients. These findings suggest that therapeutic strategies directed against Gal1 would enable simultaneous targeting of angiogenesis, immune evasion and metastasis. In the current study, we have analyzed the potential of Gal1 as a cancer vaccine target. We show that it is possible to generate high anti-Gal1 antibody levels in mice immunized with a recombinant vaccine protein consisting of bacterial sequences fused to Gal1. Growth of Gal1 expressing melanomas was significantly impaired in the immunized mice compared to the control group. This was associated with improved perfusion of the tumor vasculature, as well as increased infiltration of macrophages and cytotoxic T cells (CTLs). The level of granzyme B, mainly originating from CTLs in our model, was significantly elevated in Gal1 vaccinated mice and correlated with a decrease in tumor burden. We conclude that vaccination against Gal1 is a promising pro-immunogenic approach for cancer therapy that could potentially enhance the effect of other immunotherapeutic strategies due to its ability to promote CTL influx in tumors.

Development of a novel therapeutic vaccine carrier that sustains high antibody titers against several targets simultaneously.

With the aim to improve the efficacy of therapeutic vaccines that target self-antigens, we have developed a novel fusion protein vaccine on the basis of the C-terminal multimerizing end of the variable lymphocyte receptor B (VLRB), the Ig equivalent in jawless fishes. Recombinant vaccines were produced in Escherichia coli by fusing the VLRB sequence to 4 different cancer-associated target molecules. The anti-self-immune response generated in mice that were vaccinated with VLRB vaccines was compared with the response in mice that received vaccines that contained bacterial thioredoxin (TRX), previously identified as an efficient carrier. The anti-self-Abs were analyzed with respect to titers, binding properties, and duration of response. VLRB-vaccinated mice displayed a 2- to 10-fold increase in anti-self-Ab titers and a substantial decrease in Abs against the foreign part of the fusion protein compared with the response in TRX-vaccinated mice (P < 0.01). VLRB-generated Ab response had duration similar to the corresponding TRX-generated Abs, but displayed a higher diversity in binding characteristics. Of importance, VLRB vaccines could sustain an immune response against several targets simultaneously. VLRB vaccines fulfill several key criteria for an efficient therapeutic vaccine that targets self-antigens as a result of its small size, its multimerizing capacity, and nonexposed foreign sequences in the fusion protein.-Saupe, F., Reichel, M., Huijbers, E. J. M., Femel, J., Markgren, P.-O., Andersson, C. E., Deindl, S., Danielson, U. H., Hellman, L. T., Olsson, A.-K. Development of a novel therapeutic vaccine carrier that sustains high antibody titers against several targets simultaneously.

Vaccines targeting self-antigens: mechanisms and efficacy-determining parameters.

We recently showed that it is possible to compromise tumor vessel function and, as a consequence, suppress growth of aggressive preclinical tumors by immunizing against the tumor vascular markers extra domain-A (ED-A) or -B (ED-B) of fibronectin, using a fusion protein consisting of the ED-A or ED-B peptide fused to bacterial thioredoxin. To address the mechanism behind fusion protein-induced immunization and the specific contribution of the different vaccine constituents to elicit an anti-self-antibody response, we immunized mice with modified or unmodified self-antigens, combined with different adjuvant components, and analyzed antibody responses by ELISA in sera. Several essential requirements to circumvent tolerance were identified: (1) a potent pattern recognition receptor agonist like an oligonucleotide containing unmethylated cytosine and guanine dinucleotides (CpG); (2) a depot adjuvant to keep the CpG at the site of injection; and (3) the presence of foreign sequences in the vaccine protein. Lack of either of these factors abolished the anti-self-response (P = 0.008). In mice genetically deficient for type I IFN signaling, there was a 60% reduction in the anti-self-response compared with wild-type (P = 0.011), demonstrating a key role of this pathway in CpG-induced circumvention of self-tolerance. Identification of these mechanistic requirements to generate a potent anti-self-immune response should significantly aid the design of efficient, specific, and safe therapeutic cancer vaccines.

Quantitative multiplex immunohistochemistry reveals inter-patient lymphovascular and immune heterogeneity in primary cutaneous melanoma.

Introduction: Quantitative, multiplexed imaging is revealing complex spatial relationships between phenotypically diverse tumor infiltrating leukocyte populations and their prognostic implications. The underlying mechanisms and tissue structures that determine leukocyte distribution within and around tumor nests, however, remain poorly understood. While presumed players in metastatic dissemination, new preclinical data demonstrates that blood and lymphatic vessels (lymphovasculature) also dictate leukocyte trafficking within tumor microenvironments and thereby impact anti-tumor immunity. Here we interrogate these relationships in primary human cutaneous melanoma. Methods: We established a quantitative, multiplexed imaging platform to simultaneously detect immune infiltrates and tumor-associated vessels in formalin-fixed paraffin embedded patient samples. We performed a discovery, retrospective analysis of 28 treatment-naïve, primary cutaneous melanomas. Results: Here we find that the lymphvasculature and immune infiltrate is heterogenous across patients in treatment naïve, primary melanoma. We categorized five lymphovascular subtypes that differ by functionality and morphology and mapped their localization in and around primary tumors. Interestingly, the localization of specific vessel subtypes, but not overall vessel density, significantly associated with the presence of lymphoid aggregates, regional progression, and intratumoral T cell infiltrates. Discussion: We describe a quantitative platform to enable simultaneous lymphovascular and immune infiltrate analysis and map their spatial relationships in primary melanoma. Our data indicate that tumor-associated vessels exist in different states and that their localization may determine potential for metastasis or immune infiltration. This platform will support future efforts to map tumor-associated lymphovascular evolution across stage, assess its prognostic value, and stratify patients for adjuvant therapy.

Vaccination against the extra domain-B of fibronectin as a novel tumor therapy.

Monoclonal antibody-based therapies have made an important contribution to current treatment strategies for cancer and autoimmune disease. However, the cost for these new drugs puts a significant strain on the health-care economy, resulting in limited availability for patients. Therapeutic vaccination, defined as induction of immunity against a disease-related self-molecule, is therefore an attractive alternative. To analyze the potential of such an approach, we have developed a vaccine against the extra domain-B (ED-B) of fibronectin. This 91-aa domain, inserted by alternative splicing, is expressed during vasculogenesis in the embryo, but essentially undetectable under normal conditions in the adult. However, ED-B is highly expressed around angiogenic vasculature, such as in tumorigenesis. Here, we demonstrate that it is possible to break self-tolerance and induce a strong antibody response against ED-B by vaccination. Nineteen of 20 vaccinated mice responded with production of anti-ED-B antibodies and displayed a 70% reduction in tumor size compared to those lacking anti-ED-B antibodies. Analysis of the tumor tissue revealed that immunization against ED-B induced several changes, consistent with an attack by the immune system. These data show that tumor vascular antigens are highly interesting candidates for development of therapeutic vaccines targeting solid tumors.

Evolutionary predictability of genetic versus nongenetic resistance to anticancer drugs in melanoma.

Therapy resistance arises from heterogeneous drug-tolerant persister cells or minimal residual disease (MRD) through genetic and nongenetic mechanisms. A key question is whether specific molecular features of the MRD ecosystem determine which of these two distinct trajectories will eventually prevail. We show that, in melanoma exposed to mitogen-activated protein kinase therapeutics, emergence of a transient neural crest stem cell (NCSC) population in MRD concurs with the development of nongenetic resistance. This increase relies on a glial cell line-derived neurotrophic factor-dependent signaling cascade, which activates the AKT survival pathway in a focal adhesion kinase (FAK)-dependent manner. Ablation of the NCSC population through FAK inhibition delays relapse in patient-derived tumor xenografts. Strikingly, all tumors that ultimately escape this treatment exhibit resistance-conferring genetic alterations and increased sensitivity to extracellular signal-regulated kinase inhibition. These findings identify an approach that abrogates the nongenetic resistance trajectory in melanoma and demonstrate that the cellular composition of MRD deterministically imposes distinct drug resistance evolutionary paths.

IFNγ-activated dermal lymphatic vessels inhibit cytotoxic T cells in melanoma and inflamed skin.

Mechanisms of immune suppression in peripheral tissues counteract protective immunity to prevent immunopathology and are coopted by tumors for immune evasion. While lymphatic vessels facilitate T cell priming, they also exert immune suppressive effects in lymph nodes at steady-state. Therefore, we hypothesized that peripheral lymphatic vessels acquire suppressive mechanisms to limit local effector CD8+ T cell accumulation in murine skin. We demonstrate that nonhematopoietic PD-L1 is largely expressed by lymphatic and blood endothelial cells and limits CD8+ T cell accumulation in tumor microenvironments. IFNγ produced by tissue-infiltrating, antigen-specific CD8+ T cells, which are in close proximity to tumor-associated lymphatic vessels, is sufficient to induce lymphatic vessel PD-L1 expression. Disruption of IFNγ-dependent crosstalk through lymphatic-specific loss of IFNγR boosts T cell accumulation in infected and malignant skin leading to increased viral pathology and tumor control, respectively. Consequently, we identify IFNγR as an immunological switch in lymphatic vessels that balances protective immunity and immunopathology leading to adaptive immune resistance in melanoma.

Targeting Serglycin Prevents Metastasis in Murine Mammary Carcinoma.

In hematopoietic cells, serglycin proteoglycans mainly contribute to proper storage and secretion of inflammatory mediators via their negatively charged glycosaminoglycans. Serglycin proteoglycans are also expressed in cancer cells where increased expression has been linked to poor prognosis. However, the serglycin-dependent mediators promoting cancer progression remain to be determined. In the present study we report that genetic ablation of serglycin proteoglycan completely blocks lung metastasis in the MMTV-PyMT-driven mouse breast cancer model, while serglycin-deficiency did not affect primary tumour growth or number of mammary tumours. Although E-cadherin expression was higher in the serglycin-deficient primary tumour tissue, indicating reduced invasiveness, serglycin-deficient tumour cells were still detected in the circulation. These data suggest that serglycin proteoglycans play a role in extravasation as well as colonization and growth of metastatic cells. A microarray expression analysis and functional annotation of differentially expressed genes identified several biological pathways where serglycin may be important. Our results suggest that serglycin and serglycin-dependent mediators are potential drug targets to prevent metastatic disease/dissemination of cancer.

Neutrophil Extracellular Traps Accumulate in Peripheral Blood Vessels and Compromise Organ Function in Tumor-Bearing Animals.

Cancer produces a variety of collateral effects in patients beyond the malignancy itself, including threats to distal organ functions. However, the basis for such effects, associated with either primary or metastatic tumors, are generally poorly understood. In this study, we show how heart and kidney vascular function is impaired by neutrophils that accumulate in those tissues as a result of tumor formation in two different transgenic mouse models of cancer (RIP1-Tag2 model of insulinoma and MMTV-PyMT model of breast cancer). Neutrophil depletion by systemic administration of an anti-Gr1 antibody improved vascular perfusion and prevented vascular leakage in kidney vessels. We also observed the accumulation of platelet-neutrophil complexes, a signature of neutrophil extracellular traps (NET), in the kidneys of tumor-bearing mice that were completely absent from healthy nontumor-bearing littermates. NET accumulation in the vasculature was associated with upregulation of the proinflammatory adhesion molecules ICAM-1, VCAM-1, and E-selectin, as well as the proinflammatory cytokines IL1ß, IL6, and the chemokine CXCL1. Administering DNase I to dissolve NETs, which have a high DNA content, restored perfusion in the kidney and heart to levels seen in nontumor-bearing mice, and also prevented vessel leakage in the blood vasculature of these organs. Taken together, our findings strongly suggest that NETs mediate the negative collateral effects of tumors on distal organs, acting to impair vascular function, and to heighten inflammation at these sites.

Therapeutic vaccination against fibronectin ED-A attenuates progression of metastatic breast cancer.

Therapeutic vaccination targeting self-molecules is an attractive alternative to monoclonal antibody-based therapies for cancer and various inflammatory diseases. However, development of cancer vaccines targeting self-molecules has proven difficult. One complicating factor is that tumor cells have developed strategies to escape recognition by the immune system. Antigens specifically expressed by the tumor vasculature can therefore provide alternative targets. The alternatively spliced extra domain-A and B (ED-A and ED-B) of fibronectin are expressed during vasculogenesis in the embryo, but essentially undetectable under normal conditions in the adult. However, these domains are re-expressed during tumor angiogenesis and matrix remodeling, which renders them highly interesting for targeted cancer therapies. Using the MMTV-PyMT transgenic model of metastatic mammary carcinoma, we show that tumor burden can be significantly decreased by immunization against ED-A in a therapeutic setting. Furthermore, we found that in mice carrying anti-ED-A antibodies the number of metastases was reduced. ED-A immunization increased infiltration of macrophages and compromised tumor blood vessel function. These findings implicate an attack of the tumor vasculature by the immune system, through a polyclonal antibody response. We conclude that tumor vascular antigens are promising candidates for development of therapeutic vaccines targeting growth of primary tumors as well as disseminated disease.

The non-toxic and biodegradable adjuvant Montanide ISA 720/CpG can replace Freund's in a cancer vaccine targeting ED-B--a prerequisite for clinical development.

We have recently shown that immunization against the extra domain-B (ED-B) of fibronectin, using Freund's adjuvant, reduces tumor growth in mice by 70%. In the present study we compare the immune response generated against ED-B using the non-toxic and biodegradable adjuvant Montanide ISA 720/CpG with the response elicited by Freund's adjuvant. Montanide ISA 720/CpG induced anti-ED-B antibodies with higher avidity and less variable levels between individuals than Freund's. Moreover, the duration of the immune response was longer and the generation of anti-ED-B antibodies in naïve mice was faster, when Montanide ISA 720/CpG was used. We conclude that it is possible to replace the mineral oil based adjuvant Freund's with an adjuvant acceptable for human use, which is a prerequisite for transfer of the ED-B vaccine to the clinic.