TGF-β Signaling Prevents MHC Class II-Expressing Lymphatic Endothelial Cells from Reactivating Human Allogenic Memory CD4+ T Cells

Lymphatic endothelial cells (LECs) express MHC class II (MHC-II) upon IFN-γ stimulation, yet recent evidence suggests that LECs cannot activate naive or memory CD4+ T cells. In this article, we show that IFN-γ-activated human dermal LECs can robustly reactivate allogeneic human memory CD4+ T cells (hCD4+ TMs), but only when TGF-β signaling is inhibited. We found that in addition to upregulating MHC-II, IFN-γ also induces LECs to upregulate glycoprotein A repetitions predominant, which anchors latent TGF-β to the membrane and potentially inhibits T cell activation. Indeed, hCD4+ TM proliferation was substantially increased when LEC-CD4+ TM cultures were treated with a TGF-β receptor type 1 inhibitor or when glycoprotein A repetitions predominant expression was silenced in LECs. Reactivated hCD4+ TMs were characterized by their proliferation, CD25 expression, and cytokine secretion. CD4+ TM reactivation was dependent on LEC expression of MHC-II, confirming direct TCR engagement. Although CD80 and CD86 were not detected on LECs, the costimulatory molecules OX40L and ICOSL were upregulated upon cytokine stimulation; however, blocking these did not affect CD4+ TM reactivation by LECs. Finally, we found that human dermal LECs also supported the maintenance of Foxp3-expressing hCD4+ TMs independently of IFN-γ-induced MHC-II. Together, these results demonstrate a role for LECs in directly modulating CD4+ TM reactivation under inflammatory conditions and point to LEC-expressed TGF-β as a negative regulator of this activation.

Abstract 5695: Induction of lymphangiogenesis in breast cancer enhances responsiveness to immunotherapies

Growth and remodeling of tumor-associated lymphatics, termed lymphangiogenesis, has been known to increase metastasis rate in cancer patients. However, a recent study from our group has shown that tumor-associated lymphatics can improve anti-tumor immunity in melanoma upon treatment with immunotherapies. The role of lymphangiogenesis in shaping anti-tumor immune responses in breast cancer, however, remains unexplored. Furthermore, recently approved checkpoint inhibitor immunotherapies have had limited success in breast cancer patients. A better understanding of the role of tumor-associated lymphatics in shaping anti-tumor immune responses could lead to more informed decisions when treating breast cancer patients with immunotherapies. In this study, we investigated the role of induced tumor lymphangiogenesis in modulating responsiveness to different immunotherapies in a murine triple-negative mammary carcinoma model. Spontaneously metastatic 4T1 tumor cells were transduced to over-express the pro-lymphangiogenic growth factor VEGF-C (VC) to induce tumor lymphangiogensis in vivo. Flow cytometry and immunohistochemistry analyses confirmed that VEGF-C over-expressing tumors have an increase in tumor-associated lymphatics than control ones. Higher infiltrations of conv CD4 T cells and macrophages were observed in lymphangiogenic 4T1 tumors. Lymphangiogenic tumors treated with aPD-1 and aCTLA-4 checkpoint inhibitors, or an agonist of the Stimulator of Interferon Genes (STING) pathway, showed improved responsiveness to the therapy compared to the control tumors, as indicated by a reduced tumor growth rate. Moreover, positive correlations between VEGF-C expression and CD4 T cell and macrophage gene expressions were observed in primary human triple-negative breast tumor samples from The Cancer Genome Atlas (TCGA). In conclusion, our study shows that increase in tumor-associated lymphatics in triple-negative breast cancer enhances responsiveness to immunotherapies.

Citation Format: Peyman Hosseinchi, Aslan Mansurov, Léa Maillat, Lambert Potin, Gavin Fujimori, Jeffrey A. Hubbell, Melody A. Swartz. Induction of lymphangiogenesis in breast cancer enhances responsiveness to immunotherapies [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5695.

Targeted antibody and cytokine cancer immunotherapies through collagen affinity

Cancer immunotherapy with immune checkpoint inhibitors (CPIs) and interleukin-2 (IL-2) has demonstrated clinical efficacy but is frequently accompanied with severe adverse events caused by excessive and systemic immune system activation. Here, we addressed this need by targeting both the CPI antibodies anti-cytotoxic T lymphocyte antigen 4 antibody (αCTLA4) + anti-programmed death ligand 1 antibody (αPD-L1) and the cytokine IL-2 to tumors via conjugation (for the antibodies) or recombinant fusion (for the cytokine) to a collagen-binding domain (CBD) derived from the blood protein von Willebrand factor (VWF) A3 domain, harnessing the exposure of tumor stroma collagen to blood components due to the leakiness of the tumor vasculature. We show that intravenously administered CBD protein accumulated mainly in tumors. CBD conjugation or fusion decreases the systemic toxicity of both αCTLA4 + αPD-L1 combination therapy and IL-2, for example, eliminating hepatotoxicity with the CPI molecules and ameliorating pulmonary edema with IL-2. Both CBD-CPI and CBD-IL-2 suppressed tumor growth compared to their unmodified forms in multiple murine cancer models, and both CBD-CPI and CBD-IL-2 increased tumor-infiltrating CD8⁺ T cells. In an orthotopic breast cancer model, combination treatment with CPI and IL-2 eradicated tumors in 9 of 13 animals with the CBD-modified drugs, whereas it did so in only 1 of 13 animals with the unmodified drugs. Thus, the A3 domain of VWF can be used to improve safety and efficacy of systemically administered tumor drugs with high translational promise.

Collagen-binding IL-12 enhances tumour inflammation and drives the complete remission of established immunologically cold mouse tumours

Checkpoint-inhibitor (CPI) immunotherapy has achieved remarkable clinical success, yet its efficacy in 'immunologically cold' tumours has been modest. Interleukin-12 (IL-12) is a powerful cytokine that activates the innate and adaptive arms of the immune system; however, the administration of IL-12 has been associated with immune-related adverse events. Here we show that, after intravenous administration of a collagen-binding domain fused to IL-12 (CBD-IL-12) in mice bearing aggressive mouse tumours, CBD-IL-12 accumulates in the tumour stroma due to exposed collagen in the disordered tumour vasculature. In comparison with the administration of unmodified IL-12, CBD-IL-12 induced sustained intratumoural levels of interferon-γ, substantially reduced its systemic levels as well as organ damage and provided superior anticancer efficacy, eliciting complete regression of CPI-unresponsive breast tumours. Furthermore, CBD-IL-12 potently synergized with CPI to eradicate large established melanomas, induced antigen-specific immunological memory and controlled tumour growth in a genetically engineered mouse model of melanoma. CBD-IL-12 may potentiate CPI immunotherapy for immunologically cold tumours.

Recruitment of CD103+ dendritic cells via tumor-targeted chemokine delivery enhances efficacy of checkpoint inhibitor immunotherapy

Although a clinical breakthrough for cancer treatment, it remains that a minority of patients respond to checkpoint inhibitor (CPI) immunotherapy. The composition of tumor-infiltrating immune cells has been identified as a key factor influencing CPI therapy success. Thus, enhancing tumor immune cell infiltration is a critical challenge. A lack of the chemokine CCL4 within the tumor microenvironment leads to the absence of CD103+ dendritic cells (DCs), a crucial cell population influencing CPI responsiveness. Here, we use a tumor stroma-targeting approach to deliver CCL4; by generating a fusion protein of CCL4 and the collagen-binding domain (CBD) of von Willebrand factor, we show that CBD fusion enhances CCL4 tumor localization. Intravenous CBD-CCL4 administration recruits CD103+ DCs and CD8+ T cells and improves the antitumor effect of CPI immunotherapy in multiple tumor models, including poor responders to CPI. Thus, CBD-CCL4 holds clinical translational potential by enhancing efficacy of CPI immunotherapy.

Abstract 4520: Lymphatic vessels regulate exosome trafficking from tumors

Prior to metastasis, tumor-draining lymph nodes and distant organs are altered by a number of tumor-derived factors that help to both suppress host immunity as well as form an environment that supports metastatic tumor cells, i.e., a pre-metastatic niche. Recent studies suggest that pre-metastatic niches are induced by vesicles, including exosomes, secreted by tumor cells and cells of the tumor microenvironment. Here, we investigated the contribution of lymphatic vessels, particularly the lymphatic endothelial cells (LECs), in the active regulation of tumor exosome production and trafficking. To track exosomes, we purified and fluorescently labeled exosomes from in vitro cultures of the mouse melanoma cell line B16 F10 and of the human melanoma cell line Me260LN. Upon injection into the mouse ear dermis, fluorescent exosomes were observed within minutes in draining lymphatics, but not in surrounding blood vessels. Using the B16 F10 melanoma model overexpressing the lymphangiogenic growth factor VEGF-C, we found that upon intratumoral injection of exosomes, LECs within the tumor microenvironment abundantly take up exosomes, and at higher levels than blood endothelial cells, delivering exosomes to draining lymph nodes and eventually to the blood. In transgenic mice lacking dermal lymphatics, exosomes injected intratumorally were absent in the lymph nodes and present in far lower amounts in the blood compared to those injected into wild type mice. Additionally, while the density of endogenous blood exosomes increased upon tumor growth in wild type mice, no significant change in blood exosome density was observed in transgenic mice. Using an in vitro model where LECs are seeded onto porous inserts, we found that LEC transport of tumor exosomes occurs preferentially from their basal to apical side, and that some of these exosomes were taken up and stored intracellularly. Together, these findings suggest that lymphatic vessels constitute a major route of tumor exosome distribution to the systemic circulation and that LECs actively regulate exosome transport by active uptake.

Citation Format: Lea Maillat, Lambert Potin, Witold W. Kilarski, Melody A. Swartz. Lymphatic vessels regulate exosome trafficking from tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4520.

Abstract 1553: Collagen affinity improves safety and efficacy of antibody and cytokine cancer immunotherapies

Cancer immunotherapy with immune checkpoint inhibitors (CPI), interleukin (IL)-2, and IL-12 have demonstrated clinical antitumor efficacy but is frequently accompanied with severe side-effects caused by excessive and systemic immune system activation. Here, we addressed this need by targeting both the CPI antibodies anti-CTLA4 (αCTLA4) + anti-PD-L1 (αPD-L1) and the cytokines IL-2 and IL-12 to tumors via conjugation (for the antibodies) or recombinant fusion (for the cytokines) to a collagen-binding domain (CBD) derived from the blood protein von Willebrand factor (VWF) A3 domain. This approach harnesses the exposure of tumor stroma collagen to blood components due to the leakiness of the tumor vasculature. We show that intravenously (i.v.) administered CBD protein accumulated mainly in tumors, with 57% of total injected dose depositing in an orthotopic MMTV-PyMT breast tumor model. CBD conjugation or fusion decreased the systemic toxicity of both αCTLA4+αPD-L1 combination therapy and IL-2/IL-12. CBD-conjugation to CPI abolished T cell infiltration into the liver and eliminated hepatotoxicity as well as decreased systemic cytokine release in the blood serum. CBD-fusion to IL-2 ameliorated capillary leak syndrome and pulmonary edema. CBD-fusion to IL-12 significantly decreased hepatotoxicity and systemic IFNg concentration. These side-effects have been reported in the clinic. CBD-CPI and CBD-IL-2 significantly suppressed tumor growth compared to their unmodified forms in B16F10 melanoma, CT26 colon carcinoma and MMTV-PyMT slow growing breast cancer models, and both CBD-CPI and CBD-IL-2 increased tumor-infiltrating CD8+ T cells; increases in the ratio of effector CD8+ T cells to T regulatory cells were observed. In an orthotopic breast tumor model, combination treatment with CPI and IL-2 eradicated tumors in 9/13 animals with the CBD-modified drugs, whereas it did so in only 1/13 animals with the unmodified drugs. CBD-IL-12 therapy induced remission of B16F10 melanoma and EMT6 breast cancer, along with increased intratumoral IFNg concentration compared to normal IL-12 therapy. Our data suggest that the A3 domain of VWF can be used to engineer immunotherapies (e.g. CPI and cytokines) with high translational promise as systemically-administered tumor targeting drugs with improved safety and efficacy compared to their native forms. Unlike other active tumor-targeting approaches, CBD-based targeting is novel in a sense that it exploits abnormal tumor vessel structure; this characteristic affords binding to the ubiquitous extracellular matrix protein in the tumor, while limiting exposure to other tissues. CBD-immunotherapeutics may efficiently activate tumor-antigen-specific T cells and increase intratumoral downstream cytokines while maintaining systemic immune homeostasis by avoiding influencing non-tumor antigen specific T cells and systemic cytokine release.

Citation Format: Jun Ishihara, Ako Ishihara, Aslan Mansurov, Koichi Sasaki, Steve S. Lee, John-Michael Williford, Lambert Potin, Peyman Hosseinchi, Laura T. Gray, Kiyomitsu Katsumata, Stephen J. Kron, Melody A. Swartz, Jeffrey A. Hubbell. Collagen affinity improves safety and efficacy of antibody and cytokine cancer immunotherapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1553.

Tumor-associated factors are enriched in lymphatic exudate compared to plasma in metastatic melanoma patients

Liquid biopsies allow monitoring of cancer progression and detection of relapse, but reliable biomarkers in melanoma are lacking. Because secreted factors preferentially drain to lymphatic vessels before dilution in the blood, we hypothesized that lymph should be vastly enriched in cancer biomarkers. We characterized postoperative lymphatic exudate and plasma of metastatic melanoma patients after lymphadenectomy and found a dramatic enrichment in lymphatic exudate of tumor-derived factors and especially extracellular vesicles containing melanoma-associated proteins and miRNAs, with unique protein signatures reflecting early versus advanced metastatic spread. Furthermore, lymphatic exudate was enriched in memory T cells, including tumor-reactive CD137+ and stem cell-like types. In mice, lymph vessels were the major route of extracellular vesicle transport from tumors to the systemic circulation. We suggest that lymphatic exudate provides a rich source of tumor-derived factors for enabling the discovery of novel biomarkers that may reflect disease stage and therapeutic response.

Abstract IA07: Using matrix protein affinity to modulate the tumor microenvironment

Cancer immunotherapy with immune checkpoint inhibitors (CPI) and interleukin (IL)-2 has demonstrated clinical efficacy but is frequently accompanied with severe adverse events caused by excessive and systemic immune system activation. Here, we addressed this need by targeting both the CPI antibodies anti-cytotoxic T-lymphocyte antigen 4 antibody (CTLA4) + anti-programmed death-ligand 1 antibody (PD-L1) and the cytokine IL-2 to tumors via conjugation (for the antibodies) or recombinant fusion (for the cytokine) to a collagen-binding domain (CBD) derived from the blood protein von Willebrand factor (VWF) A3 domain, harnessing the exposure of tumor stroma collagen to blood components due to the leakiness of the tumor vasculature. We show that intravenously (i.v.) administered CBD protein accumulated mainly in tumors, for example 57% of total injected dose depositing in an orthotopic breast tumor model. The CBD was observed to localize throughout the tumor stroma, not merely in the subendothelial space. CBD conjugation or fusion decreased the systemic toxicity of both CTLA4+PD-L1 combination therapy and IL-2, for example eliminating hepatotoxicity with the CPI molecules and ameliorating capillary leak syndrome and pulmonary edema with IL-2. Both CBD-CPI and CBD-IL-2 significantly suppressed tumor growth compared to their unmodified forms in multiple murine cancer models, and both CBD-CPI and CBD-IL-2 increased tumor-infiltrating CD8+ T cells; increases in the ratio of effector CD8+ T cells to T regulatory cells were observed. In an orthotopic breast tumor model, combination treatment with CPI and IL-2 eradicated tumors in 9/13 animals with the CBD-modified drugs, whereas it did so in only 1/13 animals with the unmodified drugs. Thus, the A3 domain of von Willebrand factor can be used to engineer immunotherapies with high translational promise as systemically-administered tumor targeting drugs with improved safety and efficacy compared to their native forms. The targeting approach exploits vascular permeability in the tumor to render the ubiquitous extracellular matrix protein accessible in the tumor, while sparing most other tissues.

Citation Format: Jun Ishihara, Ako Ishihara, Koichi Saskai, Steve Seung-Young Lee, Mariko Yasui, Hiroyuki Abe, Lambert Potin, Peyman Hosseinchi, Kazuto Fukunaga, Michal M. Raczy, Laura T. Gray, John-Michael Williford, Masashi Fukayama, Tiffany M. Marchell, Aslan Mansurov, Aaron T. Alpar, Stephen J. Kron, Melody Swartz, Jeffrey A. Hubbell. Using matrix protein affinity to modulate the tumor microenvironment [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr IA07.

Improving Efficacy and Safety of Agonistic Anti-CD40 Antibody Through Extracellular Matrix Affinity

CD40 is an immune costimulatory receptor expressed by antigen-presenting cells. Agonistic anti-CD40 antibodies have demonstrated considerable antitumor effects yet can also elicit serious treatment-related adverse events, such as liver toxicity, including in man. We engineered a variant that binds extracellular matrix through a super-affinity peptide derived from placenta growth factor-2 (PlGF-2_123-144) to enhance anti-CD40's effects when administered locally. Peritumoral injection of PlGF-2_123-144-anti-CD40 antibody showed prolonged tissue retention at the injection site and substantially decreased systemic exposure, resulting in decreased liver toxicity. In four mouse tumor models, PlGF-2_123-144-anti-CD40 antibody demonstrated enhanced antitumor efficacy compared with its unmodified form and correlated with activated dendritic cells, B cells, and T cells in the tumor and in the tumor-draining lymph node. Moreover, in a genetically engineered Braf^V600E βCat^STA melanoma model that does not respond to checkpoint inhibitors, PlGF-2_123-144-anti-CD40 antibody treatment enhanced T-cell infiltration into the tumors and slowed tumor growth. Together, these results demonstrate the marked therapeutic advantages of engineering matrix-binding domains onto agonistic anti-CD40 antibody as a therapeutic given by tumori-regional injection for cancer immunotherapy.Implications: Extracellular matrix-binding peptide conjugation to agonistic anti-CD40 antibody enhances antitumor efficacy and reduces treatment-related adverse events. Mol Cancer Ther; 17(11); 2399-411. ©2018 AACR.

Abstract 1750: Inducing therapeutic lymphangiogenesis for potentiating cancer immunotherapy in melanoma

Tumor-associated lymphangiogenesis is well known to promote metastasis and to correlate with poor prognosis in melanoma and other cancers, yet its functional roles in antitumor immunity had remained largely unexplored. In a recent study, we investigated the role of the vascular endothelial growth factor C (VEGF-C)—the main driver of lymphangiogenesis—in regulating antitumor immune response. We showed that in the B16 F10 injectable melanoma model, VEGF-C inhibition prevented T cells from infiltrating the tumor and reduced the efficacy of immunotherapies. Here, we sought to extend this concept to exploit the immunologic benefits of VEGF-C for therapeutic applications. We engineered a VEGF-C variant with an extracellular matrix-binding domain (MB-VEGF-C) allowing retention into the microenvironment after intratumoral injection. MB-VEGF-C induced increased lymphatic vasculature in tumors without reducing tumor growth rate. In an autochthonous melanoma model with reduced immune infiltrates, MB-VEGF-C intratumoral injections promoted the infiltration of cross-presenting DCs, as well as CD8+ and CD4+ T cells. Crucially, in these tumors that are normally unresponsive to immune checkpoint blockade (ICB), we could restore the responsiveness to ICB by delivering MB-VEGF-C together with immune adjuvants. Taken together, our findings suggest that VEGF-C and tumor-associated lymphangiogenesis, albeit promoting metastasis, can also be exploited to promote a T cell-inflamed microenvironment and to subsequently potentiate immunotherapies.

Citation Format: Lambert Potin, Lea Maillat, Priscilla S. Briquez, Jeffrey A. Hubbell, Melody A. Swartz. Inducing therapeutic lymphangiogenesis for potentiating cancer immunotherapy in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1750.

Abstract 959: Extracellular matrix-binding immunotherapies show enhanced antitumor efficacy and reduced adverse events

Immune checkpoint inhibitors (CPI) and co-stimulatory agonist antibody therapies have exhibited considerable antitumor effects, but instances of severe side effects have been previously reported. We hypothesized that conjugation of an extracellular matrix (ECM)-binding peptide derived from placenta growth factor-2 (PlGF-2123-144) to CPI (combination of anti-CTLA4 antibody (αCTLA4) and αPD-L1) or agonistic αCD40 would accomplish local cancer immunotherapy, minimizing the antibodies' systemic exposure. Here, we show that enhanced tissue retention and lower antibody concentrations in blood plasma resulted from PlGF-2123-144 conjugation when the antibodies were administered peri-tumorally compared to unmodified antibodies administered by the same route at the same dose. This resulted in decreases in systemic cytokine release in the blood serum, and in liver tissue damage, as was assessed both biochemically and histologically, indicating lower systemic side effects after CPI and αCD40 therapies. Particularly, we show that PlGF-2123-144 conjugation reduces the risks of αPD-L1-induced autoimmune diabetes in the male nonobese diabetic mouse. Because PD-1/PD-L1-inhibition induced diabetes has been reported in the clinic, this supports the idea that PlGF-2123-144 conjugation to antibodies may reduce adverse events. This observation with localized PlGF-2123-144-antibodies could be an important breakthrough in treating patients who have discontinued immunotherapy due to the associated side effects. Regarding efficacy, we show that either PlGF-2123-144-CPI treatment or PlGF-2123-144-αCD40 treatment showed significantly higher antitumor activity compared to unmodified forms in multiple cancer models: B16F10 and Tyr:Cre-ER+/LSL-BrafV600E/Ptenfl/fl melanoma, CT26 colon carcinoma, and MMTV-PyMT breast cancer. Local injections of PlGF-2123-144-CPI increased the number of activated CD8+ and CD4+ T cells within the tumor, compared to normal CPI. PlGF-2123-144-αCD40 treatment increased the frequency of activated dendritic cells in the tumor-draining lymph node, activated CD8+ T cells within the tumor, and secretion of endogenous antibodies against tumor cells. This immune cell activation resulted in growth suppression of a distant tumor. These data suggest the feasibility of treating patients with oligometastatic tumors by administration of PlGF-2123-144- PlGF-2123-144-CPI or PlGF-2123-144-αCD40 into one accessible metastasis. Our data suggest that local injection of either PlGF-2123-144-CPI or PlGF-2123-144-αCD40 efficiently activates tumor antigen-specific T cells while maintaining systemic immune homeostasis by avoiding influencing nontumor antigen-specific T cells. This simple approach of engineered ECM-binding immunotherapy antibodies may be clinically useful.

Citation Format: Jun Ishihara, Ako Ishihara, Kazuto Fukunaga, Lambert Potin, Peyman Hosseinchi, Melody A. Swartz, Jeffrey A. Hubbell. Extracellular matrix-binding immunotherapies show enhanced antitumor efficacy and reduced adverse events [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 959.

Matrix-binding checkpoint immunotherapies enhance antitumor efficacy and reduce adverse events

Immune checkpoint blockade exhibits considerable antitumor activity, but previous studies have reported instances of severe treatment-related adverse events. We sought to explore local immune checkpoint blockade, with an antibody (Ab) form that would be retained intra- or peritumorally, limiting systemic exposure. To accomplish this, we conjugated the checkpoint blockade Abs to an extracellular matrix (ECM)-super-affinity peptide derived from placenta growth factor-2 (PlGF-2_123-144). We show enhanced tissue retention and lower Ab concentrations in blood plasma after PlGF-2_123-144 conjugation, reducing systemic side effects such as the risk of autoimmune diabetes. Peritumoral injections of PlGF-2_123-144-anti-CTLA4 (cytotoxic T lymphocyte antigen 4) and PlGF-2_123-144-anti-PD-L1 (programmed death ligand 1) Abs delayed tumor growth and prolonged survival compared to the unmodified Abs in genetically engineered murine tumor models of melanoma and breast cancer. The PlGF-2_123-144-Abs increased tumor-infiltrating activated CD8⁺ and CD4⁺ T cells, resulting in a delay of distant tumor growth as well. This simple and translatable approach of engineered ECM-binding Abs may present a viable and safer approach in checkpoint blockade.

Tumor lymphangiogenesis promotes T cell infiltration and potentiates immunotherapy in melanoma

In melanoma, vascular endothelial growth factor-C (VEGF-C) expression and consequent lymphangiogenesis correlate with metastasis and poor prognosis. VEGF-C also promotes tumor immunosuppression, suggesting that lymphangiogenesis inhibitors may be clinically useful in combination with immunotherapy. We addressed this concept in mouse melanoma models with VEGF receptor-3 (VEGFR-3)-blocking antibodies and unexpectedly found that VEGF-C signaling enhanced rather than suppressed the response to immunotherapy. We further found that this effect was mediated by VEGF-C-induced CCL21 and tumor infiltration of naïve T cells before immunotherapy because CCR7 blockade reversed the potentiating effects of VEGF-C. In human metastatic melanoma, gene expression of VEGF-C strongly correlated with CCL21 and T cell inflammation, and serum VEGF-C concentrations associated with both T cell activation and expansion after peptide vaccination and clinical response to checkpoint blockade. We propose that VEGF-C potentiates immunotherapy by attracting naïve T cells, which are locally activated upon immunotherapy-induced tumor cell killing, and that serum VEGF-C may serve as a predictive biomarker for immunotherapy response.

Exploiting lymphatic vessels for immunomodulation: Rationale, opportunities, and challenges

Lymphatic vessels are the primary route of communication from peripheral tissues to the immune system; as such, they represent an important component of local immunity. In addition to their transport functions, new immunomodulatory roles for lymphatic vessels and lymphatic endothelial cells have come to light in recent years, demonstrating that lymphatic vessels help shape immune responses in a variety of ways: promoting tolerance to self-antigens, archiving antigen for later presentation, dampening effector immune responses, and resolving inflammation, among others. In addition to these new biological insights, the growing field of immunoengineering has begun to explore therapeutic approaches to utilize or exploit the lymphatic system for immunotherapy.

Antigen presentation via MHC class II by lymphatic endothelial cells dampens CD4+ T cell response (IRC7P.436)

Lymphatic endothelial cells (LECs) can directly interact with CD8+ T cells via presentation of peptide-MHCI complexes, resulting in tolerance due to lack of costimulatory molecules and high levels of PD-L1 expression by LECs. Moreover, we and others have recently demonstrated that LECs can present peptide-MHCII complexes (pMHCII) to CD4+ T cells. However, the functional implications of antigen presentation by LECs to CD4+ T cells remain unclear. Here, we explore the tolerogenic potential of pMHCII presentation by LECs to CD4+ T cells using ovalbumin (OVA) as a model antigen. In vitro, LECs isolated from mice lacking MHCII could acquire pMHCII from wildtype dendritic cells (DCs). Subsequent LEC interactions with TCR-transgenic CD4+ T cells resulted in increased levels of CD4+ cell apoptosis, indicating deletion. Moreover, the ability of DCs to induce CD4+ T cell proliferation was decreased when LECs were present in the culture system. To examine the role of endogenous MHCII expression by LECs, we created an inducible mouse model lacking MHCII expression in LECs using a Cre-recombinase approach. In these mice, T cell responses to vaccination effects were enhanced with respect to circulating OVA-specific CD8+ T cells, indicating increased T cell help (CD4). Together, these data suggest that LEC expression of MHCII may serve to dampen or regulate immune responses. Further studies are needed to elucidate the functional role of LEC expression of MHCII in pathological conditions.

Lymph node stromal cells acquire peptide-MHCII complexes from dendritic cells and induce antigen-specific CD4⁺ T cell tolerance

LNSCs present peptide–MHCII complexes acquired from DCs to CD4⁺ T cells and induce T cell dysfunction by preventing their proliferation and survival.

Dendritic cells (DCs), and more recently lymph node stromal cells (LNSCs), have been described to tolerize self-reactive CD8⁺ T cells in LNs. Although LNSCs express MHCII, it is unknown whether they can also impact CD4⁺ T cell functions. We show that the promoter IV (pIV) of class II transactivator (CIITA), the master regulator of MHCII expression, controls endogenous MHCII expression by LNSCs. Unexpectedly, LNSCs also acquire peptide–MHCII complexes from DCs and induce CD4⁺ T cell dysfunction by presenting transferred complexes to naive CD4⁺ T cells and preventing their proliferation and survival. Our data reveals a novel, alternative mechanism where LN-resident stromal cells tolerize CD4⁺ T cells through the presentation of self-antigens via transferred peptide–MHCII complexes of DC origin.