Antibody landscape of C57BL/6 mice cured of B78 melanoma via a combined radiation and immunocytokine immunotherapy regimen

Sera of immune mice that were previously cured of their melanoma through a combined radiation and immunocytokine immunotherapy regimen consisting of 12 Gy of external beam radiation and the intratumoral administration of an immunocytokine (anti-GD2 mAb coupled to IL-2) with long-term immunological memory showed strong antibody-binding against melanoma tumor cell lines via flow cytometric analysis. Using a high-density whole-proteome peptide array (of 6.090.593 unique peptides), we assessed potential protein-targets for antibodies found in immune sera. Sera from 6 of these cured mice were analyzed with this high-density, whole-proteome peptide array to determine specific antibody-binding sites and their linear peptide sequence. We identified thousands of peptides that were targeted by these 6 mice and exhibited strong antibody binding only by immune (after successful cure and rechallenge), not naïve (before tumor implantation) sera and developed a robust method to detect these differentially targeted peptides. Confirmatory studies were done to validate these results using 2 separate systems, a peptide ELISA and a smaller scale peptide array utilizing a slightly different technology. To the best of our knowledge, this is the first study of the full set of germline encoded linear peptide-based proteome epitopes that are recognized by immune sera from mice cured of cancer via radio-immunotherapy. We furthermore found that although the generation of B-cell repertoire in immune development is vastly variable, and numerous epitopes are identified uniquely by immune serum from each of these 6 immune mice evaluated, there are still several epitopes and proteins that are commonly recognized by at least half of the mice studied. This suggests that every mouse has a unique set of antibodies produced in response to the curative therapy, creating an individual "fingerprint." Additionally, certain epitopes and proteins stand out as more immunogenic, as they are recognized by multiple mice in the immune group.

Cyclophosphamide augments the efficacy of in situ vaccination in a mouse melanoma model

Introduction

We have previously shown that an intratumoral (IT) injection of the hu14.18-IL2 immunocytokine (IC), an anti-GD2 antibody linked to interleukin 2, can serve as an in situ vaccine and synergize with local radiotherapy (RT) to induce T cell-mediated antitumor effects. We hypothesized that cyclophosphamide (CY), a chemotherapeutic agent capable of depleting T regulatory cells (Tregs), would augment in situ vaccination. GD2+ B78 mouse melanoma cells were injected intradermally in syngeneic C57BL/6 mice.

Methods

Treatments with RT (12Gy) and/or CY (100 mg/kg i.p.) started when tumors reached 100-300 mm3 (day 0 of treatment), followed by five daily injections of IT-IC (25 mcg) on days 5-9. Tumor growth and survival were followed. In addition, tumors were analyzed by flow cytometry.

Results

Similar to RT, CY enhanced the antitumor effect of IC. The strongest antitumor effect was achieved when CY, RT and IC were combined, as compared to combinations of IC+RT or IC+CY. Flow cytometric analyses showed that the combined treatment with CY, RT and IC decreased Tregs and increased the ratio of CD8+ cells/Tregs within the tumors. Moreover, in mice bearing two separate tumors, the combination of RT and IT-IC delivered to one tumor, together with systemic CY, led to a systemic antitumor effect detected as shrinkage of the tumor not treated directly with RT and IT-IC. Cured mice developed immunological memory as they were able to reject B78 tumor rechallenge.

Conclusion

Taken together, these preclinical results show that CY can augment the antitumor efficacy of IT- IC, given alone or in combination with local RT, suggesting potential benefit in clinical testing of these combinations.

Antibody landscape of C57BL/6 mice cured of B78 melanoma via immunotherapy

Hoefges et al. utilized a whole-proteome peptide array approach to show that C57BL/6 mice develop a large repertoire of antibodies against linear peptide sequences of their melanoma after receiving a curative immunotherapy regimen consisting of radiation and an immunocytokine. Antibodies can play an important role in innate and adaptive immune responses against cancer, and in preventing infectious disease. Flow cytometry analysis of sera of immune mice that were previously cured of their melanoma through a combined immunotherapy regimen with long-term memory showed strong antibody-binding against melanoma tumor cell lines. Using a high-density whole-proteome peptide array, we assessed potential protein-targets for antibodies found in immune sera. Sera from 6 of these cured mice were analyzed with this high-density, whole-proteome peptide array to determine specific antibody-binding sites and their linear peptide sequence. We identified thousands of peptides that were targeted by 2 or more of these 6 mice and exhibited strong antibody binding only by immune, not naive sera. Confirmatory studies were done to validate these results using 2 separate ELISA-based systems. To the best of our knowledge, this is the first study of the "immunome" of protein-based epitopes that are recognized by immune sera from mice cured of cancer via immunotherapy.

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.

Abstract 1385: The influence of MHC class I and II on T cell responses in mouse melanoma

Introduction: Using an in situ vaccine (ISV) regimen consisting of radiation combined with immunocytokine (tumor-targeting mAb linked to IL2), we can cure mice of well established B78 melanoma tumors (B78s). Mice cured of their B78s with ISV demonstrate long-term immune memory, evidenced by rejection of engraftment of a tumor rechallenge >180 days post initial cure of tumor. Traditionally, immaune 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. While not commonly expressed on solid tumors, MHCII is expressed on 50-60% of melanomas in humans. Here we explored implications of MHCI and MHCII expression in both the primary and long-term memory anti-tumor responses generated with ISV.

Methods: CD4+ or CD8+ T cells were depleted in mice during the primary anti-tumor response (i.e. B78 tumor bearing mice receiving the ISV regimen) or during tumor rechallenge experiments (i.e. B78-cured mice rechallenged with B78s). Tumor growth was monitored. In separate studies, tumors and tumor draining lymphnodes (TDLNs) were harvested during the primary antitumor response and analyzed via flow cytometry to assess T cell activation and immune infiltrate. Finally, TDLNs were harvested from B78-cured mice, 7 days after tumor rechallenge, to define memory T cell subsets.

Results: Depletion studies revealed CD4+ T cells are required for both the antitumor response to ISV and the long-term memory response in B78-cured mice, but CD8+ T cells are not required for either of these responses. Increased CD8+ and CD4+ T cell infiltrates are observed in the tumor microenvironment during the primary anti-tumor response. In B78-cured mice, though not required for memory responses, CD8+ central memory T cells are significantly increased in the TDLNs compared to naïve or primary tumor bearing mice. The amount of CD4+ effector memory T cells are significantly increased in the TDLN of B78-cured mice compared to CD8+ effector memory T cells.

Conclusion: Often not expressed on solid tumors, MHCII is expressed on some melanoma tumors, and its expression has been correlated with a positive response to immunotherapies. CD4+ cytotoxic T cells can directly engage MHCII on tumors, suggesting this interaction has an important role in the response to immunotherapy for MHCII expressing tumors. Our data suggest that CD4+ T cells drive both the primary anti-tumor and long-term immune memory responses in the B78 model when treating with this effective ISV. We are continuing our efforts to understand the characteristics of the B78 cell line that may be relevant to its response to immunotherapy and its resistance to single agent checkpoint blockade. Understanding the cellular and molecular mechanisms involved in ISV-induced immune recognition and destruction of B78s may guide future improvements of this clinically-relevant immunotherapy regimen.

Citation Format: Amy K. Erbe, Arika Feils, Mackenzie Heck, Sabrina VandenHeuvel, Julianna Castillo, Alina Hampton, Lizzie Frankel, Anna Hoefges, Peter Carlson, Alex A. Pieper, Taylor Aiken, Lauren Zebertavage, David Komjathy, Dan Spiegelman, Noah Tsarovsky, Zachary S. Morris, Ravi Patel, Alexander Rakhmilevich, Paul M. Sondel. The influence of MHC class I and II on T cell responses in mouse melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1385.

Abstract 2019: Tumor-targeting and efficacy of B7H3/GD2 bispecific SNIPER antibodies

Introduction: GD2 is expressed on neuroblastoma, melanomas, small cell lung cancers and sarcomas. While it is expressed minimally on normal tissues, it is expressed on nerve cells and, anti-GD2 (dinutuximab) treatment can cause neuropathic pain. To increase tumor specificity, we developed a bispecific SNIPER antibody to simultaneously target two tumor antigens (GD2 and B7H3). B7H3 is overexpressed on multiple tumor types, with minimal expression on most normal cells and is absent on nerve cells. The goal of this SNIPER is to enhance tumor-specificity, while reducing toxicity, ultimately improving efficacy for cancers expressing both targets.

Experimental Procedures: SNIPER specificity was tested by flow cytometry for binding to GD2 +/- B7H3 expressing cells. Using an Incucyte S3, we tested antibody internalization properties [compared to anti-B7H3 and dinutuximab monoclonal antibodies (mAbs)] and antibody dependent cellular-cytotoxicity (ADCC) capabilities. Mice bearing variants of GD2/B7H3-expressing tumors were intravenously injected with 89Zr- radiolabeled SNIPER and its longitudinal in vivo biodistribution was monitored via positron emission tomography imaging. In vivo efficacy studies of SNIPER were tested against mice bearing either melanoma or neuroblastoma tumors that express both GD2 and B7H3.

Summary of Data: In vitro and in vivo tumor specificity testing confirmed that SNIPER specifically targets B7H3+/GD2+ cells, but it does not bind to GD2+/B7H3- cells (which simulate nerve cells). We observed high internalization of anti-GD2 mAbs; we did not observe antibody internalization of either the SNIPER or anti-B7H3 mAbs. SNIPER was as effective at ADCC as the dinutuximab, but we saw minimal ADCC with the anti-B7H3 mAbs. An afucosylated version of SNIPER showed significantly enhanced ADCC compared to dinutuximab. Our in vivo efficacy studies found that SNIPER was as as dinutuximab when given at the same dose.

Conclusions: The Fab arms of SNIPER targeting GD2 and B7H3 each have low-to-moderate affinity. SNIPER binds with strong avidity when both arms bind to their antigens on the same cell. Stronger avidity through both arms binding results in high-tumor specificity. Because SNIPER should not bind to nerves, it may be possible to administer increased doses of SNIPER beyond the tolerable dose of dinutuximab, which could further improve efficacy. Ongoing studies include antitumor efficacy testing, nerve binding assays and assessing reduction of pain in vivo with SNIPER.

Citation Format: Amy K. Erbe, Arika Feils, Zack Rosenkrans, Jessica Wiwczar, Daniel Gerhardt, Bonnie Hammer, Mildred Felder, Mark Bercher, Alina Hampton, Lizzie Frankel, Dan Spiegelman, Noah Tsarovsky, Alexander Rakhmilevich, Jacquelyn Hank, Bryan Glaser, Reinier Hernandez, Roland Green, Paul M. Sondel. Tumor-targeting and efficacy of B7H3/GD2 bispecific SNIPER antibodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2019.

599 Cyclophosphamide augments the efficacy of an in situ vaccine in a mouse melanoma model

Background

We have previously shown that a direct intratumoral (IT) injection of the hu14.18-IL2 immunocytokine (IC), an anti-GD2 antibody linked to interleukin 2, can serve as an in situ vaccine and synergize with local radiotherapy (RT) to induce T cell-mediated antitumor effects. We hypothesized that cyclophosphamide (CY), a chemotherapeutic agent capable of depleting T regulatory cells (Tregs), would augment in situ vaccination.

Methods

GD2+ B78 mouse melanoma cells were injected intradermally in syngeneic C57BL/6 mice. Treatments with RT (12Gy) and/or CY (100 mg/kg i.p.) started when tumors reached the size of 100–200 mm3 (day 0) followed by five daily injections of IT-IC (25 mcg) on days 5–9. In some experiments, CY was given prior or after RT. Tumor growth and survival were followed. In addition, tumors were analyzed by flow cytometry.

Results

A single injection of CY led to an enhanced antitumor effect of IC comparable to that of RT. The strongest antitumor effect was achieved when CY, RT and IC were combined, as compared to combinations of CY+RT, CY+IC or RT+IC. This augmented effect of the triple combination was seen when CY was given on the same day as RT. Flow cytometric analyses showed that CY treatment decreased Tregs and increased the ratio of CD8+ cytotoxic cells to Tregs within the tumors. Moreover, the combination of RT, CY and IT-IC led to a systemic antitumor effect against the untreated tumor in a two-tumor model. Cured mice developed immunological memory as they were able to reject B78 tumor rechallenge.

Conclusions

CY can augment the antitumor efficacy of IT- IC given alone or in combination with local RT in tumor-bearing mice. These preclinical results suggest the value of initiating clinical testing of the combination of CY, RT and IT-IC as an in situ vaccine.