Abstract 4142: CD4 T cell-driven response to immunotherapy against mouse melanoma tumors

Using an in situ vaccine (ISV) regimen that includes a combination therapy of radiation (given at D0) with hu14.18-IL2 immunocytokine [anti-GD2 linked to IL2, (Anyxis Immuno-Oncology GmbH (Austria)); given at D5-D9], we can cure mice of large B78 melanoma tumors (B78s). GD2 is expressed on many solid tumors, including most melanomas, and is not often expressed on immune cells. Mice cured with ISV of B78 tumors demonstrate long-term immune memory, with mice rejecting tumor rechallenge >180 days post initial cure of tumor. Traditionally, immune effector memory is thought to be mediated via CD8 T cells, which require antigen presentation via MHC Class I (MHCI). However, B78s express little to no MHCI, but do express MHCII when stimulated with IFNγ. Expressed on 50-70% of melanomas in humans, the role of MHCII on response is unclear. We explored implications of MHCII and MHCI expression on response (initial response to ISV and memory response).

Mice bearing B78s depleted of NK cells or CD8 T cells during ISV respond to therapy, but mice depleted of CD4 T cells fail to respond to ISV. Likewise, B78-cured mice depleted of NK and CD8 T cells during rechallenge are able to reject the B78 tumor rechallenge, whereas those depleted of CD4 T cells failed to reject their B78 rechallenge. Together these data suggest that CD4 T cells are required for the initial antitumor response to ISV as well as for immune memory formation and function.

Tumors and tumor draining lymph nodes were harvested during ISV treatment in B78-bearing mice at D8 and assessed by scRNAseq, flow cytometry, IncuCyte and ImageStream (live-cell imaging assays), and IsoPlexis (cytokine profile). Though not required for initial or memory response, both CD8 and NK cells are activated and exhibit cytotoxic phenotypes in the tumor microenvironment (TME). Furthermore, a population of cells co-expressing both GD2 and CD45 was observed in the TME following ISV that was not observed in untreated mice. These GD2+/CD45+ cells were predominantly CD4+ T cells incorporate patchy GD2 expression on their surface via trogocytosis. We hypothesize that the interaction between MHCII on tumor cells and CD4 T cell receptors mediates the trogocytosis, activating CD4 T cells to function as helper T cells, initiating a cascade of antitumor immunity, as well as causing direct CD4 T cell-mediated cytotoxicity.

MHCII is expressed on some melanoma tumors, and its expression has been correlated with a positive response to immunotherapies. MHCII expression on tumors can directly engage CD4 cytotoxic T cells, suggesting an important role in the response to immunotherapy for CD4 T cells in melanoma tumors that express MHCII. Understanding the cellular and molecular mechanisms involved in the ISV-induced immune recognition and destruction of B78 may guide future improvements of this clinically-relevant immunotherapy regimen.

Citation Format: Amy K. Erbe, Arika S. Feils, Alina Hampton, Dan Spiegelman, Noah Tsarovsky, Anna Hoefges, Peter M. Carlson, Alex Pieper, Callie Haertle, Mackenzie Heck, Sabrina VandenHeuvel, Lizzie Frankel, Lauren Zebertavage, Alexa Heaton, Zachary S. Morris, Ravi Patel, Alexander Rakhmilevich, Paul M. Sondel. CD4 T cell-driven response to immunotherapy against mouse melanoma tumors. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4142.

Radiation to all macroscopic sites of tumor permits greater systemic antitumor response to in situ vaccination

BACKGROUND

The antitumor effects of external beam radiation therapy (EBRT) are mediated, in part, by an immune response. We have reported that a single fraction of 12 Gy EBRT combined with intratumoral anti-GD2 hu14.18-IL2 immunocytokine (IC) generates an effective in situ vaccine (ISV) against GD2-positive murine tumors. This ISV is effective in eradicating single tumors with sustained immune memory; however, it does not generate an adequate abscopal response against macroscopic distant tumors. Given the immune-stimulatory capacity of radiation therapy (RT), we hypothesized that delivering RT to all sites of disease would augment systemic antitumor responses to ISV.

METHODS

We used a syngeneic B78 murine melanoma model consisting of a 'primary' flank tumor and a contralateral smaller 'secondary' flank tumor, treated with 12 Gy EBRT and intratumoral IC immunotherapy to the primary and additional EBRT to the secondary tumor. As a means of delivering RT to all sites of disease, both known and occult, we also used a novel alkylphosphocholine analog, NM600, conjugated to 90Y as a targeted radionuclide therapy (TRT). Tumor growth, overall survival, and cause of death were measured. Flow cytometry was used to evaluate immune population changes in both tumors.

RESULTS

Abscopal effects of local ISV were amplified by delivering as little as 2-6 Gy of EBRT to the secondary tumor. When the primary tumor ISV regimen was delivered in mice receiving 12 Gy EBRT to the secondary tumor, we observed improved overall survival and more disease-free mice with immune memory compared with either ISV or 12 Gy EBRT alone. Similarly, TRT combined with ISV resulted in improved overall survival and a trend towards reduced tumor growth rates when compared with either treatment alone. Using flow cytometry, we identified an influx of CD8+ T cells with a less exhausted phenotype in both the ISV-targeted primary and the distant secondary tumor following the combination of secondary tumor EBRT or TRT with primary tumor ISV.

CONCLUSIONS

We report a novel use for low-dose RT, not as a direct antitumor modality but as an immunomodulator capable of driving and expanding antitumor immunity against metastatic tumor sites following ISV.

Radiation Augments the Local Anti-Tumor Effect of In Situ Vaccine With CpG-Oligodeoxynucleotides and Anti-OX40 in Immunologically Cold Tumor Models

Introduction

Combining CpG oligodeoxynucleotides with anti-OX40 agonist antibody (CpG+OX40) is able to generate an effective in situ vaccine in some tumor models, including the A20 lymphoma model. Immunologically "cold" tumors, which are typically less responsive to immunotherapy, are characterized by few tumor infiltrating lymphocytes (TILs), low mutation burden, and limited neoantigen expression. Radiation therapy (RT) can change the tumor microenvironment (TME) of an immunologically "cold" tumor. This study investigated the effect of combining RT with the in situ vaccine CpG+OX40 in immunologically "cold" tumor models.

Methods

Mice bearing flank tumors (A20 lymphoma, B78 melanoma or 4T1 breast cancer) were treated with combinations of local RT, CpG, and/or OX40, and response to treatment was monitored. Flow cytometry and quantitative polymerase chain reaction (qPCR) experiments were conducted to study differences in the TME, secondary lymphoid organs, and immune activation after treatment.

Results

An in situ vaccine regimen of CpG+OX40, which was effective in the A20 model, did not significantly improve tumor response or survival in the "cold" B78 and 4T1 models, as tested here. In both models, treatment with RT prior to CpG+OX40 enabled a local response to this in situ vaccine, significantly improving the anti-tumor response and survival compared to RT alone or CpG+OX40 alone. RT increased OX40 expression on tumor infiltrating CD4+ non-regulatory T cells. RT+CpG+OX40 increased the ratio of tumor-infiltrating effector T cells to T regulatory cells and significantly increased CD4+ and CD8+ T cell activation in the tumor draining lymph node (TDLN) and spleen.

Conclusion

RT significantly improves the local anti-tumor effect of the in situ vaccine CpG+OX40 in immunologically "cold", solid, murine tumor models where RT or CpG+OX40 alone fail to stimulate tumor regression.

Optimizing Flow Cytometric Analysis of Immune Cells in Samples Requiring Cryopreservation from Tumor-Bearing Mice

Most shared resource flow cytometry facilities do not permit analysis of radioactive samples. We are investigating low-dose molecular targeted radionuclide therapy (MTRT) as an immunomodulator in combination with in situ tumor vaccines and need to analyze radioactive samples from MTRT-treated mice using flow cytometry. Further, the sudden shutdown of core facilities in response to the COVID-19 pandemic has created an unprecedented work stoppage. In these and other research settings, a robust and reliable means of cryopreservation of immune samples is required. We evaluated different fixation and cryopreservation protocols of disaggregated tumor cells with the aim of identifying a protocol for subsequent flow cytometry of the thawed sample, which most accurately reflects the flow cytometric analysis of the tumor immune microenvironment of a freshly disaggregated and analyzed sample. Cohorts of C57BL/6 mice bearing B78 melanoma tumors were evaluated using dual lymphoid and myeloid immunophenotyping panels involving fixation and cryopreservation at three distinct points during the workflow. Results demonstrate that freezing samples after all staining and fixation are completed most accurately matches the results from noncryopreserved equivalent samples. We observed that cryopreservation of living, unfixed cells introduces a nonuniform alteration to PD1 expression. We confirm the utility of our cryopreservation protocol by comparing tumors treated with in situ tumor vaccines, analyzing both fresh and cryopreserved tumor samples with similar results. Last, we use this cryopreservation protocol with radioactive specimens to demonstrate potentially beneficial effector cell changes to the tumor immune microenvironment following administration of a novel MTRT in a dose- and time-dependent manner.

Abstract 3060: Temporal analysis of type 1 interferon activation in tumor cells following external beam radiotherapy or targeted radionuclide therapy

Background: Radiation (RT) activates a type 1 interferon (IFN1) response and this is critical to the effect of RT in priming a response to immune checkpoint blockade (ie anti-CTLA4). However, little is known about the time course of this effect. Clinical interest in utilizing systemically administered targeted radionuclide therapy agents (TRT) is growing as these agents can be used to target multiple sites of disease including micro-metastases. It is unclear how IFN1 activation induced by continuous delivery of RT during exponential decay of a TRT source will compare to that induced following instantaneous external beam RT (EBRT). Here we report the time course of IFN1 response following RT in vitro and in vivo.

Methods: For in vitro studies, we utilized murine models of melanoma (B16, B16 STING knockout, B78), and head and neck squamous cell carcinoma (MOC2). EBRT was prescribed to 2.5 Gy, 12 Gy, or 3 fractions of 8 Gy. For in vivo studies, syngeneic C57BL/6 mice were engrafted with either B78 or MOC2 cells on the flank and RT was delivered when mean tumor size was 100-150 mm3. EBRT was prescribed to 2.5 Gy or 12 Gy. For TRT, we used 90Y conjugated to NM600, an alkylphosphocholine analog that exhibits selective uptake and retention in tumor cells of nearly any type, including B78 and MOC2. Tumor-specific dosimetry for 90Y-NM600 was determined using sequential 86Y-NM600 PET/CT imaging (3h, 24h, 48h, 72h) and a Monte Carlo based dose calculation platform. TRT was prescribed to a cumulative absorbed dose of 2.5 Gy or 12 Gy. Following delivery of RT, cells or tumors were harvested at 1d, 7d, and 14d post RT and RNA was isolated. Gene expression of Ifn-β and IFN response elements was quantified by qPCR and normalized to untreated controls.

Results: We observed significant IFN1 activation in all cell lines, with peak activation in B78, B16, and MOC2 cell lines occurring 7, 7, and 1 days, respectively, following RT for all doses. This effect was STING-dependent. Select IFN response genes remained upregulated at 14 days following RT. IFN1 activation following STING agonist treatment in vitro was identical to RT suggesting time course differences between cell lines were mediated by STING pathway kinetics and not DNA damage susceptibility. In vivo delivery of EBRT and TRT to B78 and MOC2 tumors resulted in a comparable time course and magnitude of IFN1 activation. In the MOC2 model, the combination of 90Y-NM600 and anti-CTLA-4 therapy reduced tumor growth and prolonged survival compared to single agent therapy.

Conclusions: We report the time course of the STING-dependent IFN1 response following RT in multiple murine tumor models. We show the potential of TRT to stimulate IFN1 activation that is comparable to that observed with EBRT of equivalent cumulative dose. Further evaluation of the timing and magnitude of IFN1 response following EBRT and TRT may be critical to the optimal integration with immunotherapies.

Citation Format: Justin C. Jagodinsky, Amber M. Bates, Reinier Hernandez, Joseph J. Grudzinski, Ian R. Marsh, Ishan Chakravarty, Ian S. Arthur, Luke M. Zangl, Ryan J. Brown, Erin J. Nystuen, Sarah E. Emma, Caroline Kerr, Won Jong Jin, Peter M. Carlson, Jonathan W. Engle, Eduardo Aluicio-Sarduy, Todd E. Barnhart, Trang Le, KyungMann Kim, Bryan P. Bednarz, Jamey P. Weichert, Ravi B. Patel, Zachary S. Morris. Temporal analysis of type 1 interferon activation in tumor cells following external beam radiotherapy or targeted radionuclide therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3060.

Combination of radiation therapy, bempegaldesleukin, and checkpoint blockade eradicates advanced solid tumors and metastases in mice

Background

Current clinical trials are using radiation therapy (RT) to enhance an antitumor response elicited by high-dose interleukin (IL)-2 therapy or immune checkpoint blockade (ICB). Bempegaldesleukin (BEMPEG) is an investigational CD122-preferential IL-2 pathway agonist with prolonged in vivo half-life and preferential intratumoral expansion of T effector cells over T regulatory cells. BEMPEG has shown encouraging safety and efficacy in clinical trials when used in combination with PD-1 checkpoint blockade. In this study, we investigated the antitumor effect of local RT combined with BEMPEG in multiple immunologically ‘cold’ tumor models. Additionally, we asked if ICB could further enhance the local and distant antitumor effect of RT+BEMPEG in the setting of advanced solid tumors or metastatic disease.

Methods

Mice bearing flank tumors (B78 melanoma, 4T1 breast cancer, or MOC2 head and neck squamous cell carcinoma) were treated with combinations of RT and immunotherapy (including BEMPEG, high-dose IL-2, anti(α)-CTLA-4, and α-PD-L1). Mice bearing B78 flank tumors were injected intravenously with B16 melanoma cells to mimic metastatic disease and were subsequently treated with RT and/or immunotherapy. Tumor growth and survival were monitored. Peripheral T cells and tumor-infiltrating lymphocytes were assessed via flow cytometry.

Results

A cooperative antitumor effect was observed in all models when RT was combined with BEMPEG, and RT increased IL-2 receptor expression on peripheral T cells. This cooperative interaction was associated with increased IL-2 receptor expression on peripheral T cells following RT. In the B78 melanoma model, RT+BEMPEG resulted in complete tumor regression in the majority of mice with a single ~400 mm³ tumor. This antitumor response was T-cell dependent and supported by long-lasting immune memory. Adding ICB to RT+BEMPEG strengthened the antitumor response and cured the majority of mice with a single ~1000 mm³ B78 tumor. In models with disseminated metastasis (B78 primary with B16 metastasis, 4T1, and MOC2), the triple combination of RT, BEMPEG, and ICB significantly improved primary tumor response and survival.

Conclusion

The combination of local RT, BEMPEG, and ICB cured mice with advanced, immunologically cold tumors and distant metastasis in a T cell-dependent manner, suggesting this triple combination warrants clinical testing.

Combination of Bempegaldesleukin and Anti-CTLA-4 Prevents Metastatic Dissemination After Primary Resection or Radiotherapy in a Preclinical Model of Non-Small Cell Lung Cancer

Surgical resection or hypo-fractionated radiation therapy (RT) in early-stage non-small cell lung cancer (NSCLC) achieves local tumor control, but metastatic relapse remains a challenge. We hypothesized that immunotherapy with anti-CTLA-4 and bempegaldesleukin (BEMPEG; NKTR-214), a CD122-preferential IL2 pathway agonist, after primary tumor RT or resection would reduce metastases in a syngeneic murine NSCLC model. Mice bearing Lewis Lung Carcinoma (LLC) tumors were treated with combinations of BEMPEG, anti-CTLA-4, and primary tumor treatment (surgical resection or RT). Primary tumor size, mouse survival, and metastatic disease at the time of death were assessed. Flow cytometry, qRT-PCR, and cytokine analyses were performed on tumor specimens. All mice treated with RT or surgical resection of primary tumor alone succumbed to metastatic disease, and all mice treated with BEMPEG and/or anti-CTLA-4 succumbed to primary tumor local progression. The combination of primary tumor RT or resection and BEMPEG and anti-CTLA-4 reduced spontaneous metastasis and improved survival without any noted toxicity. Flow cytometric immunoprofiling of primary tumors revealed increased CD8 T and NK cells and decreased T-regulatory cells with the combination of BEMPEG, anti-CTLA-4, and RT compared to RT alone. Increased expression of genes associated with tumor cell immune susceptibility, immune cell recruitment, and cytotoxic T lymphocyte activation were observed in tumors of mice treated with BEMPEG, anti-CTLA-4, and RT. The combination of BEMPEG and anti-CTLA-4 with primary tumor RT or resection enabled effective control of local and metastatic disease in a preclinical murine NSCLC model. This therapeutic combination has important translational potential for patients with early-stage NSCLC and other cancers.

Temporal analysis of type 1 interferon activation in tumor cells following external beam radiotherapy or targeted radionuclide therapy

Rationale: Clinical interest in combining targeted radionuclide therapies (TRT) with immunotherapies is growing. External beam radiation therapy (EBRT) activates a type 1 interferon (IFN1) response mediated via stimulator of interferon genes (STING), and this is critical to its therapeutic interaction with immune checkpoint blockade. However, little is known about the time course of IFN1 activation after EBRT or whether this may be induced by decay of a TRT source. Methods: We examined the IFN1 response and expression of immune susceptibility markers in B78 and B16 melanomas and MOC2 head and neck cancer murine models using qPCR and western blot. For TRT, we used 90Y chelated to NM600, an alkylphosphocholine analog that exhibits selective uptake and retention in tumor cells including B78 and MOC2. Results: We observed significant IFN1 activation in all cell lines, with peak activation in B78, B16, and MOC2 cell lines occurring 7, 7, and 1 days, respectively, following RT for all doses. This effect was STING-dependent. Select IFN response genes remained upregulated at 14 days following RT. IFN1 activation following STING agonist treatment in vitro was identical to RT suggesting time course differences between cell lines were mediated by STING pathway kinetics and not DNA damage susceptibility. In vivo delivery of EBRT and TRT to B78 and MOC2 tumors resulted in a comparable time course and magnitude of IFN1 activation. In the MOC2 model, the combination of 90Y-NM600 and dual checkpoint blockade therapy reduced tumor growth and prolonged survival compared to single agent therapy and cumulative dose equivalent combination EBRT and dual checkpoint blockade therapy. Conclusions: We report the time course of the STING-dependent IFN1 response following radiation in multiple murine tumor models. We show the potential of TRT to stimulate IFN1 activation that is comparable to that observed with EBRT and this may be critical to the therapeutic integration of TRT with immunotherapies.

Depth of tumor implantation affects response to in situ vaccination in a syngeneic murine melanoma model

An important component of research using animal models is ensuring rigor and reproducibility. This study was prompted after two experimenters performing virtually identical studies obtained different results when syngeneic B78 murine melanoma cells were implanted into the skin overlying the flank and treated with an in situ vaccine (ISV) immunotherapy. Although both experimenters thought they were using identical technique, we determined that one was implanting the tumors intradermally (ID) and the other was implanting them subcutaneously (SC). Though the baseline in vivo immunogenicity of tumors can depend on depth of their implantation, the response to immunotherapy as a function of tumor depth, particularly in immunologically 'cold' tumors, has not been well studied. The goal of this study was to evaluate the difference in growth kinetics and response to immunotherapy between identically sized melanoma tumors following ID versus SC implantation. We injected C57BL/6 mice with syngeneic B78 melanoma cells either ID or SC in the flank. When tumors reached 190-230 mm3, they were grouped into a 'wave' and treated with our previously published ISV regimen (12 Gy local external beam radiation and intratumoral hu14.18-IL2 immunocytokine). Physical examination demonstrated that ID-implanted tumors were mobile on palpation, while SC-implanted tumors became fixed to the underlying fascia. Histologic examination identified a critical fascial layer, the panniculus carnosus, which separated ID and SC tumors. SC tumors reached the target tumor volume significantly faster compared with ID tumors. Most ID tumors exhibited either partial or complete response to this immunotherapy, whereas most SC tumors did not. Further, the 'mobile' or 'fixed' phenotype of tumors predicted response to therapy, regardless of intended implantation depth. These findings were then extended to additional immunotherapy regimens in four separate tumor models. These data indicate that the physical 'fixed' versus 'mobile' characterization of the tumors may be one simple method of ensuring homogeneity among implanted tumors prior to initiation of treatment. Overall, this short report demonstrates that small differences in depth of tumor implantation can translate to differences in response to immunotherapy, and proposes a simple physical examination technique to ensure consistent tumor depth when conducting implantable tumor immunotherapy experiments.

Abstract 477: Comparing type 1 interferon activation in tumor cells following external beam radiotherapy versus targeted radionuclide therapy

Background: Radiation (RT) activates a type 1 interferon (IFN-1) response and, in preclinical studies, this is critical to the effect of RT in priming a response to immune checkpoint blockade. Recent studies report the impact of external beam radiotherapy (EBRT) dose and fractionation on IFN-1 response, however little is known about the time course of this effect. Clinical interest in utilizing systemically administered targeted radionuclide therapy agents (TRT) is growing. It is unclear how IFN-1 activation induced by continuous delivery of RT during exponential decay of a TRT source will compare to that induced following instantaneous EBRT. Here we report the time course of IFN-1 response following RT in vitro and in vivo.

Methods: For in vitro studies, we utilized murine models of melanoma (B16, B16 STING knockout, B78), and head and neck cancer (MOC2). EBRT was prescribed to 12 Gy, 20 Gy, or 3 fractions of 8 Gy. For in vivo studies, syngeneic C57BL/6 mice were engrafted with either B78 or MOC2 cells on the flank and RT was delivered when mean tumor size was ~ 150 mm3. EBRT was prescribed to 2 Gy or 12 Gy. For TRT, we used 90Y conjugated to NM600, an alkylphosphocholine analog that exhibits selective uptake and retention in tumor cells of nearly any type, including B78 and MOC2. Tumor-specific dosimetry for 90Y-NM600 was determined using sequential 86Y-NM600PET/CT imaging (3h, 24h, 72h) and a Monte Carlo based dose calculation platform. TRT was prescribed to a dose of 2 Gy or 12 Gy. Following delivery of RT in vitro or in vivo, cells or tumors were harvested at 24h, 7d, and 14 d post RT and RNA was isolated. Gene expression of Ifn-β and IFN response elements (Oas2, Oas3, and Mx1) was quantified by qPCR and normalized to untreated controls.

Results: In agreement with prior studies, we observed significant IFN-1 activation 24 hours following 8 Gy x 3 in our B16, B78, and MOC2 tumor cell lines. At 12 Gy and 20 Gy, we continued to detect significant IFN-1 activation. Peak activation was 7d following EBRT for all doses, raising the potential for a lead-time bias when comparing fractionated to single dose treatments. For all doses, select IFN response genes remained upregulated at 14d. In vivo delivery of EBRT and TRT to B78 and MOC2 tumors resulted in a comparable time course of IFN-1 activation peaking 7d after RT and persisting to 14d. Using a STING knockout variant of B16 melanoma, we confirmed that activation of IFN-1 response by RT was STING dependent at all time points evaluated.

Conclusions: We report the time course for activation of a STING-dependent IFN-1 response following RT in multiple murine tumor models. We observe maximal activation 7d following both EBRT and TRT. We show the potential of TRT to generate EBRT comparable IFN-1 activation. Further studies evaluating the time course and magnitude of IFN-1 response following TRT may be critical in metastatic settings to integrating this modality with immunotherapy.

Citation Format: Justin C. Jagodinsky, Ian S. Arthur, Juliana S. Castillo, Ishan Chakravarty, Luke M. Zangl, Ryan J. Brown, Ravi B. Patel, Wonjon J. Jin, Peter M. Carlson, Reinier Hernandez, Joseph J. Grudzinski, Ian R. Marsh, Jamey P. Weichert, Bryan P. Bednarz, Zachary S. Morris. Comparing type 1 interferon activation in tumor cells following external beam radiotherapy versus targeted radionuclide therapy [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 477.

Abstract 4455: Combination of bempegaldesleukin and anti-CTLA-4 prevents metastatic dissemination after primary surgery or radiation therapy in a preclinical model of non-small cell lung cancer

Purpose: Surgical resection or stereotactic ablative radiation therapy (SBRT) in early stage non-small cell lung cancer (NSCLC) have local control rates of 90% or higher. Current treatment paradigms effectively control primary tumor sites, but distant relapse remains a challenge with metastatic failure in more than 30% of patients with primary tumors larger than 5 cm. We hypothesized that adjuvant immune checkpoint blockade with anti-CTLA4 (C4) and /or bempegaldesleukin (NKTR-214), a CD122-preferential pegylated-interleukin-2 (IL2) pathway agonist,in combination with primary tumor ablative radiation or surgical resection would reduce metastases in a spontaneously metastatic syngeneic Lewis Lung Carcinoma (LLC) model.

Methods: LLC flank tumors were established in C57BL/6 mice (n=6 per replicate, 12 total). When tumors were ~100 mm3 they were randomized to receive: vehicle only (VO); NKTR-214 (16 μg on Days 6, 15, 24) + C4 (200 μg IP on Days 4, 7, 10); RT (8Gy x 3 on Days 1, 2, 3); RT + C4, RT + NKTR-214; RT + C4 + NKTR-214; Primary surgery (Day 16), or Surgery + NKTR-214 + C4. Primary tumor size, survival, and a binary assessment of metastatic disease was made for each mouse. Flow cytometry studies examined tumor immune cell infiltrates on Day 21 in mice treated with VO, RT, RT + C4, C4 + NKTR-214, or RT + C4 + NKTR-214.

Results: NKTR + C4 prevented development of spontaneous metastasis (p < 0.01) but did not control primary disease compared to VO treatment. RT alone significantly reduced primary tumor size compared to VO control (p < 0.01), but these mice all developed metastases. Adjuvant NKTR-214 + C4 after RT reduced development of spontaneous metastasis in mice treated by this regimen by 91% and 73% compared to RT alone and RT + C4 respectively. RT + C4 + NKTR-214 also significantly improved survival compared to both RT + C4 and RT + NKTR-214 (p = 0.02, p = 0.003). 58% of mice treated with RT + C4 + NKTR-214 cleared their primary tumors compared to 16% with RT + C4 and 0% in RT + NKTR-214 at day 30 (p = 0.03, p < 0.01). All mice clearing primary tumors rejected LCC rechallenge. Flow cytometric immuneprofiling of the primary tumors demonstrated increased CD8+T cells, NK cells (NK1.1+CD3−), and NKT cells (NK1.1+CD3+) with NKTR-214 + C4 w/wo RT treatment compared to VO controls. NKTR-214 + C4 prior to surgical resection also reduced the development of spontaneous lung metastases compared to surgery alone (p < 0.01).

Conclusions: Addition of systemic NKTR-214 + C4 treatment to RT or primary surgical resection reduces development of distant metastatic disease in a preclinical NSCLC model. Moreover, treatment with NKTR-214 + C4 increases infiltration of innate and adaptive immune effector cells in the primary tumor. This treatment strategy has important translational potential to prevent distant relapse in patients undergoing definitive local therapies for early stage NSCLC.

Citation Format: Ryan J. Brown, Luke Zangl, Ian Arthur, Alex Pieper, Peter M. Carlson, Juliana Castillo, Paul M. Sondel, Alexander Rakhmilevich, Zach S. Morris, Ravi B. Patel. Combination of bempegaldesleukin and anti-CTLA-4 prevents metastatic dissemination after primary surgery or radiation therapy in a preclinical model of non-small cell lung cancer [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 4455.

In situ Vaccine Plus Checkpoint Blockade Induces Memory Humoral Response

In a syngeneic murine melanoma (MEL) model, we recently reported an in situ vaccination response to combined radiation (RT) and intra-tumoral (IT) injection of anti-GD2 hu14. 18-IL2 immunocytokine (IC). This combined treatment resulted in 71% complete and durable regression of 5-week tumors, a tumor-specific memory T cell response, and augmented response to systemic anti-CTLA-4 antibody checkpoint blockade. While the ability of radiation to diversify anti-tumor T cell response has been reported, we hypothesize that mice rendered disease-free (DF) by a RT-based ISV might also exhibit a heightened B cell response. C57BL/6 mice were engrafted with 2 × 10⁶ GD2+ B78 MEL and treated at a target tumor size of ~200 mm³ with 12 Gy RT, IT-IC on day (D)6-D10, and anti-CTLA-4 on D3, 6, and 9. Serum was collected via facial vein before tumor injection, before treatment, during treatment, after becoming DF, and following rejection of subcutaneous 2 × 10⁶ B78 MEL re-challenge on D90. Flow cytometry demonstrated the presence of tumor-specific IgG in sera from mice rendered DF and rejecting re-challenge with B78 MEL at D90 after starting treatment. Consistent with an adaptive endogenous anti-tumor humoral memory response, these anti-tumor antibodies bound to B78 cells and parental B16 cells (GD2-), but not to the unrelated syngeneic Panc02 or Panc02 GD2+ cell lines. We evaluated the kinetics of this response and observed that tumor-specific IgG was consistently detected by D22 after initiation of treatment, corresponding to a time of rapid tumor regression. The amount of tumor-specific antibody binding to tumor cells (as measured by flow MFI) did not correlate with host animal prognosis. Incubation of B16 MEL cells in DF serum, vs. naïve serum, prior to IV injection, did not delay engraftment of B16 metastases and showed similar overall survival rates. B cell depletion using anti-CD20 or anti-CD19 and anti-B220 did not impact the efficacy of ISV treatment. Thus, treatment with RT + IC + anti-CTLA-4 results in adaptive anti-tumor humoral memory response. This endogenous tumor-specific antibody response does not appear to have therapeutic efficacy but may serve as a biomarker for an anti-tumor T cell response.

In situ vaccination at a peripheral tumor site augments response against melanoma brain metastases

BACKGROUND

Immune checkpoint inhibition (ICI) alone is not efficacious for a large number of patients with melanoma brain metastases. We previously established an in situ vaccination (ISV) regimen combining radiation and immunocytokine to enhance response to ICIs. Here, we tested whether ISV inhibits the development of brain metastases in a murine melanoma model.

METHODS

B78 (GD2+) melanoma 'primary' tumors were engrafted on the right flank of C57BL/6 mice. After 3-4 weeks, primary tumors were treated with ISV (radiation (12 Gy, day 1), α-GD2 immunocytokine (hu14.18-IL2, days 6-10)) and ICI (α-CTLA-4, days 3, 6, 9). Complete response (CR) was defined as no residual tumor observed at treatment day 90. Mice with CR were tested for immune memory by re-engraftment with B78 in the left flank and then the brain. To test ISV efficacy against metastases, tumors were also engrafted in the left flank and brain of previously untreated mice. Tumors were analyzed by quantitative reverse transcription-PCR, immunohistochemistry, flow cytometry and multiplex cytokine assay.

RESULTS

ISV+α-CTLA-4 resulted in immune memory and rejection of B78 engraftment in the brain in 11 of 12 mice. When B78 was engrafted in brain prior to treatment, ISV+α-CTLA-4 increased survival compared with ICI alone. ISV+α-CTLA-4 eradicated left flank tumors but did not elicit CR at brain sites when tumor cells were engrafted in brain prior to ISV. ISV+α-CTLA-4 increased CD8+ and CD4+ T cells in flank and brain tumors compared with untreated mice. Among ISV + α-CTLA-4 treated mice, left flank tumors showed increased CD8+ infiltration and CD8+:FOXP3+ ratio compared with brain tumors. Flank and brain tumors showed minimal differences in expression of immune checkpoint receptors/ligands or Mhc-1. Cytokine productions were similar in left flank and brain tumors in untreated mice. Following ISV+α-CTLA-4, production of immune-stimulatory cytokines was greater in left flank compared with brain tumor grafts.

CONCLUSION

ISV augmented response to ICIs in murine melanoma at brain and extracranial tumor sites. Although baseline tumor-immune microenvironments were similar at brain and extracranial tumor sites, response to ISV+α-CTLA-4 was divergent with reduced infiltration and activation of immune cells in brain tumors. Additional therapies may be needed for effective antitumor immune response against melanoma brain metastases.

Trophic redundancy and predator size class structure drive differences in kelp forest ecosystem dynamics

Ecosystems are changing at alarming rates because of climate change and a wide variety of other anthropogenic stressors. These stressors have the potential to cause phase shifts to less productive ecosystems. A major challenge for ecologists is to identify ecosystem attributes that enhance resilience and can buffer systems from shifts to less desirable alternative states. In this study, we used the Northern Channel Islands, California, as a model kelp forest ecosystem that had been perturbed from the loss of an important sea star predator due to a sea star wasting disease. To determine the mechanisms that prevent phase shifts from productive kelp forests to less productive urchin barrens, we compared pre- and postdisease predator assemblages as predictors of purple urchin densities. We found that prior to the onset of the disease outbreak, the sunflower sea star exerted strong predation pressures and was able to suppress purple urchin populations effectively. After the disease outbreak, which functionally extirpated the sunflower star, we found that the ecosystem response-urchin and algal abundances-depended on the abundance and/or size of remaining predator species. Inside Marine Protected Areas (MPAs), the large numbers and sizes of other urchin predators suppressed purple urchin populations resulting in kelp and understory algal growth. Outside of the MPAs, where these alternative urchin predators are fished, less abundant, and smaller, urchin populations grew dramatically in the absence of sunflower stars resulting in less kelp at these locations. Our results demonstrate that protected trophic redundancy inside MPAs creates a net of stability that could limit kelp forest ecosystem phase shifts to less desirable, alternative states when perturbed. This highlights the importance of harboring diversity and managing predator guilds.

Combined innate and adaptive immunotherapy overcomes resistance of immunologically cold syngeneic murine neuroblastoma to checkpoint inhibition

BACKGROUND

Unlike some adult cancers, most pediatric cancers are considered immunologically cold and generally less responsive to immunotherapy. While immunotherapy has already been incorporated into standard of care treatment for pediatric patients with high-risk neuroblastoma, overall survival remains poor. In a mouse melanoma model, we found that radiation and tumor-specific immunocytokine generate an in situ vaccination response in syngeneic mice bearing large tumors. Here, we tested whether a novel immunotherapeutic approach utilizing radiation and immunocytokine together with innate immune stimulation could generate a potent antitumor response with immunologic memory against syngeneic murine neuroblastoma.

METHODS

Mice bearing disialoganglioside (GD2)-expressing neuroblastoma tumors (either NXS2 or 9464D-GD2) were treated with radiation and immunotherapy (including anti-GD2 immunocytokine with or without anti-CTLA-4, CpG and anti-CD40 monoclonal antibody). Tumor growth, animal survival and immune cell infiltrate were analyzed in the tumor microenvironment in response to various treatment regimens.

RESULTS

NXS2 had a moderate tumor mutation burden (TMB) while N-MYC driven 9464D-GD2 had a low TMB, therefore the latter served as a better model for high-risk neuroblastoma (an immunologically cold tumor). Radiation and immunocytokine induced a potent in situ vaccination response against NXS2 tumors, but not in the 9464D-GD2 tumor model. Addition of checkpoint blockade with anti-CTLA-4 was not effective alone against 9464D-GD2 tumors; inclusion of CpG and anti-CD40 achieved a potent antitumor response with decreased T regulatory cells within the tumors and induction of immunologic memory.

CONCLUSIONS

These data suggest that a combined innate and adaptive immunotherapeutic approach can be effective against immunologically cold syngeneic murine neuroblastoma. Further testing is needed to determine how these concepts might translate into development of more effective immunotherapeutic approaches for the treatment of clinically high-risk neuroblastoma.

Development of an In Situ Cancer Vaccine via Combinational Radiation and Bacterial-Membrane-Coated Nanoparticles

Neoantigens induced by random mutations and specific to an individual's cancer are the most important tumor antigens recognized by T cells. Among immunologically "cold" tumors, limited recognition of tumor neoantigens results in the absence of a de novo antitumor immune response. These "cold" tumors present a clinical challenge as they are poorly responsive to most immunotherapies, including immune checkpoint inhibitors (ICIs). Radiation therapy (RT) can enhance immune recognition of "cold" tumors, resulting in a more diversified antitumor T-cell response, yet RT alone rarely results in a systemic antitumor immune response. Therefore, a multifunctional bacterial membrane-coated nanoparticle (BNP) composed of an immune activating PC7A/CpG polyplex core coated with bacterial membrane and imide groups to enhance antigen retrieval is developed. This BNP can capture cancer neoantigens following RT, enhance their uptake in dendritic cells (DCs), and facilitate their cross presentation to stimulate an antitumor T-cell response. In mice bearing syngeneic melanoma or neuroblastoma, treatment with BNP+RT results in activation of DCs and effector T cells, marked tumor regression, and tumor-specific antitumor immune memory. This BNP facilitates in situ immune recognition of a radiated tumor, enabling a novel personalized approach to cancer immunotherapy using off-the-shelf therapeutics.

Tumor-Specific Inhibition of In Situ Vaccination by Distant Untreated Tumor Sites

In situ vaccination is an emerging cancer treatment strategy that uses local therapies to stimulate a systemic antitumor immune response. We previously reported an in situ vaccination effect when combining radiation (RT) with intratumor (IT) injection of tumor-specific immunocytokine (IC), a fusion of tumor-specific antibody and IL2 cytokine. In mice bearing two tumors, we initially hypothesized that delivering RT plus IT-IC to the "primary" tumor would induce a systemic antitumor response causing regression of the "secondary" tumor. To test this, mice bearing one or two syngeneic murine tumors of B78 melanoma and/or Panc02 pancreatic cancer were treated with combined external beam RT and IT-IC to the designated "primary" tumor only. Primary and secondary tumor response as well as animal survival were monitored. Immunohistochemistry and quantitative real-time PCR were used to quantify tumor infiltration with regulatory T cells (Treg). Transgenic "DEREG" mice or IgG2a anti-CTLA-4 were used to transiently deplete tumor Tregs. Contrary to our initial hypothesis, we observed that the presence of an untreated secondary tumor antagonized the therapeutic effect of RT + IT-IC delivered to the primary tumor. We observed reciprocal tumor specificity for this effect, which was circumvented if all tumors received RT or by transient depletion of Tregs. Primary tumor treatment with RT + IT-IC together with systemic administration of Treg-depleting anti-CTLA-4 resulted in a renewed in situ vaccination effect. Our findings show that untreated tumors can exert a tumor-specific, Treg-dependent, suppressive effect on the efficacy of in situ vaccination and demonstrate clinically viable approaches to overcome this effect. Untreated tumor sites antagonize the systemic and local antitumor immune response to an in situ vaccination regimen. This effect is radiation sensitive and may be mediated by tumor-specific regulatory T cells harbored in the untreated tumor sites. Cancer Immunol Res; 6(7); 825-34. ©2018 AACR.

Comparative study of guanidine-based and lysine-based brush copolymers for plasmid delivery

Polyethylenimine (PEI), one of the most frequently used polycations for non-viral nucleic acid delivery, exhibits good transfection efficiency to cultured cells but generally has to be used in restricted concentration ranges due to high cytotoxicity. We recently reported a family of HPMA-co-oligolysine brush copolymers that show nucleic acid delivery efficiencies approaching that of PEI. Guanidine-containing polymers have been reported in some systems to be more effective at cellular delivery of cargo than their primary-amine analogs. The goal of this work is to investigate the effect of guanidinylation on gene transfer ability of HPMA-co-oligolysine copolymers. Several parameters were evaluated: arginine versus homoarginine monomers, oligopeptide length, and charge density within the peptide. Using reversible addition-fragmentation chain transfer (RAFT) polymerization, a series of six copolymers were synthesized containing the cationic peptides K₁₀, R₁₀, K₅, and (GK)₅. Lysine-containing copolymers were functionalized with guanidine by reaction with O-methylisourea to generate an additional five homoarginine-based copolymers. All eleven copolymers readily condensed DNA into small, < 150 nm polyplexes and remained stable in physiological salt conditions. The best performing copolymers provided more efficient gene transfection with less associated cytotoxicity than PEI. Reducing the number of charge centers (from 10 to 5) further reduced toxicity while retaining comparable transfection efficiency to PEI.

Reducible HPMA-co-oligolysine copolymers for nucleic acid delivery

Biodegradability can be incorporated into cationic polymers via use of disulfide linkages that are degraded in the reducing environment of the cell cytosol. In this work, N-(2-hydroxypropyl)methacrylamide (HPMA) and methacrylamido-functionalized oligo-l-lysine peptide monomers with either a non-reducible 6-aminohexanoic acid (AHX) linker or a reducible 3-[(2-aminoethyl)dithiol] propionic acid (AEDP) linker were copolymerized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Both of the copolymers and a 1:1 (w/w) mixture of copolymers with reducible and non-reducible peptides were complexed with DNA to form polyplexes. The polyplexes were tested for salt stability, transfection efficiency, and cytotoxicity. The HPMA-oligolysine copolymer containing the reducible AEDP linkers was less efficient at transfection than the non-reducible polymer and was prone to flocculation in saline and serum-containing conditions, but was also not cytotoxic at charge ratios tested. Optimal transfection efficiency and toxicity were attained with mixed formulation of copolymers. Flow cytometry uptake studies indicated that blocking extracellular thiols did not restore transfection efficiency and that the decreased transfection of the reducible polyplex is therefore not primarily caused by extracellular polymer reduction by free thiols. The decrease in transfection efficiency of the reducible polymers could be partially mitigated by the addition of low concentrations of EDTA to prevent metal-catalyzed oxidation of reduced polymers.

HPMA-oligolysine copolymers for gene delivery: optimization of peptide length and polymer molecular weight

Polycations are one of the most frequently used classes of materials for non-viral gene transfer in vivo. Several studies have demonstrated a sensitive relationship between polymer structure and delivery activity. In this work, we used reverse addition-fragmentation chain transfer (RAFT) polymerization to build a panel of N-(2-hydroxypropyl)methacrylamide (HPMA)-oligolysine copolymers with varying peptide length and polymer molecular weight. The panel was screened for optimal DNA-binding, colloidal stability in salt, high transfection efficiency, and low cytotoxicity. Increasing polyplex stability in PBS correlated with increasing polymer molecular weight and decreasing peptide length. Copolymers containing K(5) and K(10) oligocations transfected cultured cells with significantly higher efficiencies than copolymers of K(15). Four HPMA-oligolysine copolymers were identified that met the desired criteria. Polyplexes formed with these copolymers demonstrated both salt stability and transfection efficiencies on-par with poly(ethylenimine) PEI in cultured cells.

‘Participate to learn’: A promising practice for community ABI rehabilitation

OBJECTIVE

To identify best practices and promising practices to enhance participation in meaningful and productive activities.

METHOD

An electronic search of the ABI rehabilitation research literature since 1990 yielded 974 articles of which 30 focused on interventions that targeted participation and evaluated effectiveness using direct measures of participation. Three reviewers rated these articles according to the standards set out by the Centre for Reviews and Dissemination. Following the systematic review, an interpretive review of the same articles was completed.

RESULTS

Only three studies were rated as strong. No best practices were identified. Three promising practices found some support. The interpretive review suggested 'Participate to learn' as a useful rehabilitation model. The model rests on roles as goals, learning by experience in real-life contexts and the use of personal and environmental support to enable participation.

CONCLUSIONS

'Participate to learn' is both a credible rehabilitation model and deserving of more study.