Long-term Outcomes of Diffuse or Recurrent Tenosynovial Giant Cell Tumor Treated with Postoperative External Beam Radiation Therapy

PURPOSE

Tenosynovial giant cell tumor (TGCT) is a rare proliferative disorder of synovial membrane that previously was known as pigmented villonodular synovitis. Primary treatment involves surgical resection; however, complete removal of all disease involvement is difficult to achieve. Radiation may be useful to reduce the risk of recurrence. We report and update our institutional experience treating diffuse and recurrent TGCT with postsurgical external beam radiation therapy.

METHODS AND MATERIALS

We performed a retrospective chart review of 30 patients with TGCT from 2003 to 2019 treated with radiation therapy. Each patient was evaluated for demographics, radiation treatment parameters, surgical management, complications, and outcome.

RESULTS

With mean follow-up of 82 months (range, 3-211), 24 patients (80%) who underwent surgery followed by radiation therapy did not experience any further relapse, and all 30 patients achieved local control (100%) with additional salvage therapy after radiation therapy. The most common site of disease was the knee (n = 22, 73%), followed by the ankle (n = 5, 16%) and the hand (n = 3, 10%). Seven patients (24%) presented at time of initial diagnosis and 23 (76%) presented with recurrent disease after surgical resection, with an average of 2.6 surgical procedures before radiation therapy. After resection, 18 of 30 patients (67%) demonstrated residual TGCT by imaging. The median radiation therapy dose delivered was 36 Gy (range, 34-36 Gy) in 1.8 to 2.5 Gy/fractions for 4 weeks. In the assessment of posttreatment joint function, 26 sites (86%) exhibited excellent or good function, 2 (7%) fair, and 2 poor (7%) as determined by our scoring system. There were no cases of radiation-associated malignancy.

CONCLUSIONS

Among patients with diffuse or recurrent TGCT, postsurgical external beam radiation therapy provided excellent local control and good functional status, with minimal treatment-related complications. Postsurgical radiation therapy is a well-tolerated noninvasive treatment that should be considered after maximal cytoreductive resection to prevent disease progression and recurrence.

Abstract 4055: Immune checkpoint DNA vaccines enhance anti-tumor immunity in murine melanoma model

Background: Immune checkpoint blockade has emerged as an important cancer treatment strategy. However, the cost of repeat injections of these antibodies limits its availability to many patients globally. We have been developing DNA vaccines targeting immune checkpoints as a potentially more affordable approach to cancer immunotherapy. We have reported this platform could induce endogenous anti-CTLA-4 antibody and anti-tumor immunity. Here, we tested a DNA vaccine targeting PD-1 for anti-tumor responses.

Methods: Murine CTLA-4 or PD-1 DNA sequences were inserted into an expression plasmid, pVAC-1, forming DNA vaccines targeting CTLA-4 or PD-1 respectively. Mouse melanoma models were established by inoculating B16F10 cells in the flank of C57BL/6 mice. The mice were randomized into treatment groups, including vector (control), radiation therapy (RT), or RT plus DNA vaccinations targeting CTLA-4 and/or PD-1. Vaccinations were given weekly via intra-muscular injection of the DNA plasmids in conjunction with electroporation. RT was given in 3 daily fractions of 8 Gy during the second week of vaccination. Serum samples were collected and subjected to ELISA for antibody titers. Tumors were measured twice weekly. Tumor samples were collected and subjected to IHC staining for immune markers.

Results: Vaccination with plasmids encoding CTLA-4 (pVAC-1-CTLA-4) and PD-1 (pVAC-1-PD-1) induced endogenous antibodies against CTLA-4 and PD-1, respectively. The antibodies were detected beginning 2 weeks after the first vaccination, reached peak concentrations of 3-15 μg/mL in the following 1-2 weeks, and declined within a week once vaccination stopped. Compared with vector alone, preliminary studies using vaccination with both pVAC-1-CTLA-4 and pVAC-1-PD-1 suggested enhanced B16F10 tumor response without evidence of toxicities such as body weight loss or organ damage. In further preliminary studies, adding of both pVAC-1-CTLA-4 and pVAC-1-PD-1 DNA vaccines to RT resulted in increased CD8+ tumor infiltrating lymphocytes compared to either RT or vaccine alone and suggested enhanced tumor response.

Conclusions: Immune checkpoint DNA vaccines induced endogenous specific antibodies, demonstrated a favorable safety profile, and may confer anti-tumor immunity. This DNA vaccine platform holds potential as a cost-effective approach to immunotherapy. Further studies are warranted to compare the effects of these immune checkpoint DNA vaccines with those of exogenous immune checkpoint targeting antibodies.

Citation Format: Keng-Hsueh Lan, Raghava Sriramaneni, Justin C. Jagodinsky, Claire Baniel, Amy Erbe-Gurel, Jacquelyn A. Hank, Sung-Hsin Kuo, Keng-Li Lan, Zachary S. Morris. Immune checkpoint DNA vaccines enhance anti-tumor immunity in murine melanoma model [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 4055.

Thousands of new antigens are recognized in mice via endogenous antibodies after being cured of a B78 melanoma via immunotherapy

Antibodies can play an important role in innate and adaptive immune responses against cancer. Using a high-density peptide array, we assessed potential protein-targets for antibodies activated in mice cured of their melanoma through a combined immunotherapy regimen. Our goal was to determine the linear peptide sequences recognized by anti-tumor antibodies produced in mice cured of their melanoma with immunotherapy.

Mice with GD2-expressing syngeneic B78 melanoma were treated with a combination immunotherapy capable of inducing an “in situ vaccine” effect (ISV), enabling mice to be cured of their tumors with long-term immune memory. Naïve and immune sera were collected from these mice. Using flow cytometry, immune sera showed strong antibody-binding against B16 (parental cell line of B78 without GD2 expression). These sera were then used on a Nimble Therapeutics’ peptide-array (either whole proteome or a curated list of ~650 proteins) to determine specific antibody-binding sites, and data were analyzed using a probabilistic model. Using the “curated list” peptide array, proteins were selected if the protein was bound in immune sera but not bound in the sera from naïve or non-responding tumor-bearing mice. When focusing on the whole mouse proteome data, thousands of peptides were targeted by 2 or more mice and exhibited strong antibody binding only by immune sera.

We are continuing to refine our analytical methods and are further investigating all identified proteins. These peptides may be new targets for antibody-based or cellular therapies and some of the tumor-specific endogenous antibodies that we have identified may be used as biomarkers to predict response to our ISV regimen and potentially other immunotherapy treatments.

Protective Epitope Discovery and Design of MUC1-based Vaccine for Effective Tumor Protections in Immunotolerant Mice

Human mucin-1 (MUC1) is a highly attractive antigen for the development of anticancer vaccines. However, in human clinical trials of multiple MUC1 based vaccines, despite the generation of anti-MUC1 antibodies, the antibodies often failed to exhibit much binding to tumor presumably due to the challenges in inducing protective immune responses in the immunotolerant environment. To design effective MUC1 based vaccines functioning in immunotolerant hosts, vaccine constructs were first synthesized by covalently linking the powerful bacteriophage Qβ carrier with MUC1 glycopeptides containing 20-22 amino acid residues covering one full length of the tandem repeat region of MUC1. However, IgG antibodies elicited by these first generation constructs in tolerant human MUC1 transgenic (Tg) mice did not bind tumor cells strongly. To overcome this, a peptide array has been synthesized. By profiling binding selectivities of antibodies, the long MUC1 glycopeptide was found to contain immunodominant but nonprotective epitopes. Critical insights were obtained into the identity of the key protective epitope. Redesign of the vaccine focusing on the protective epitope led to a new Qβ-MUC1 construct, which was capable of inducing higher levels of anti-MUC1 IgG antibodies in MUC1.Tg mice to react strongly with and kill a wide range of tumor cells compared to the construct containing the gold standard protein carrier, i.e., keyhole limpet hemocyanin. Vaccination with this new Qβ-MUC1 conjugate led to significant protection of MUC1.Tg mice in both metastatic and solid tumor models. The antibodies exhibited remarkable selectivities toward human breast cancer tissues, suggesting its high translational potential.

Antitumor Humoral and T Cell Responses by Mucin-1 Conjugates of Bacteriophage Qβ in Wild-type Mice

Mucin-1 (MUC1) is one of the top ranked tumor associated antigens. In order to generate effective anti-MUC1 immune responses as potential anticancer vaccines, MUC1 peptides and glycopeptides have been covalently conjugated to bacteriophage Qβ. Immunization of mice with these constructs led to highly potent antibody responses with IgG titers over one million, which are among the highest anti-MUC1 IgG titers reported to date. Furthermore, the high IgG antibody levels persisted for more than six months. The constructs also elicited MUC1 specific cytotoxic T cells, which can selectively kill MUC1 positive tumor cells. The unique abilities of Qβ-MUC1 conjugates to powerfully induce both antibody and cytotoxic T cell immunity targeting tumor cells bode well for future translation of the constructs as anticancer vaccines.

In situ vaccination with local radiation and intratumoral immunocytokine to elicit a tumor-specific memory B-cell response

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Background: In a murine melanoma (MEL) model, we reported an in situ vaccination response to combined radiation (RT) and intra-tumor (IT) injection of anti-GD2 hu14.18-IL2 immunocytokine (IC). This treatment resulted in 71% complete regression of 5-week (~ 200mm3) tumors, a memory T cell response, and augmented response to systemic anti-CTLA-4 antibody (mAb) checkpoint blockade. We hypothesized that mice rendered disease-free (DF) by RT, IT-IC, and anti-CTLA-4 mAb might also exhibit a memory B cell response. Methods: C57BL/6 mice were implanted with 2x106 syngeneic, GD2+ B78 MEL cells and tumors developed for 5 weeks. Mice were treated with 12 Gy RT to this tumor followed by 5 daily IT injections of hu14.18-IL2 d6-10 after RT and IP injection of anti-CTLA-4 d3, 6, and 9 after RT. DF mice and naïve controls were challenged by subcutaneous implantation with 2x106 B78 MEL cells. Peripheral blood was collected from mice before and after B78 challenge and serum was evaluated for presence of tumor-specific mAbs using flow cytometry and ELISA. Results: Seventy-three percent of mice were rendered DF by treatment with RT, IT-hu14.18-IL2, and anti-CTLA-4. All of these (13/13) rejected a rechallange B78 implantation > 1 year later (range d378 – 511), whereas no naïve mice rejected B78 implantation (0/66). IgG from serum of DF mice bound selectively to B78 and parental GD2- B16 MEL cells and the level of this mAb response appeared to increase modestly d14 after B78 challenge. In naïve mice, a modest increase in tumor-specific mAb was identified between non-tumor implanted mice and d35 post-implantation mice (bearing tumors > 200mm3), however this level remained ~ 5 fold below that observed in DF mice prior to B78 rechallenge. In contrast, no appreciable mAb response was observed for unrelated syngeneic GD2+ Panc02 pancreatic tumor cells in serum of DF or naïve mice. Conclusions: We report an endogenous anti-tumor IgG humoral response in DF mice > 1 year after treatment with RT, IT-IC, and anti-CTLA-4 mAb, concurrent with demonstration of long lasting immune protection from re-challenge. Studies are underway to determine whether this response is involved in the therapeutic efficacy of this in situ vaccination regimen.

Chemical Synthesis of GM2 Glycans, Bioconjugation with Bacteriophage Qβ, and the Induction of Anticancer Antibodies

The development of carbohydrate-based antitumor vaccines is an attractive approach towards tumor prevention and treatment. Herein, we focused on the ganglioside GM2 tumor-associated carbohydrate antigen (TACA), which is overexpressed in a wide range of tumor cells. GM2 was synthesized chemically and conjugated with a virus-like particle derived from bacteriophage Qβ. Although the copper-catalyzed azide-alkyne cycloaddition reaction efficiently introduced 237 copies of GM2 per Qβ, this construct failed to induce significant amounts of anti-GM2 antibodies compared to the Qβ control. In contrast, GM2 immobilized on Qβ through a thiourea linker elicited high titers of IgG antibodies that recognized GM2-positive tumor cells and effectively induced cell lysis through complement-mediated cytotoxicity. Thus, bacteriophage Qβ is a suitable platform to boost antibody responses towards GM2, a representative member of an important class of TACA: the ganglioside.

Significant Impact of Immunogen Design on the Diversity of Antibodies Generated by Carbohydrate-Based Anticancer Vaccine

Development of an effective vaccine targeting tumor associated carbohydrate antigens (TACAs) is an appealing approach toward tumor immunotherapy. While much emphasis has been typically placed on generating high antibody titers against the immunizing antigen, the impact of immunogen design on the diversity of TACA-specific antibodies elicited has been overlooked. Herein, we report that the immunogen structure can significantly impact the breadth and the magnitude of humoral responses. Vaccine constructs that induced diverse TACA-binding antibodies provided much stronger recognition of a variety of Tn positive tumor cells. Optimization of the breadth of the antibody response led to a vaccine construct that demonstrated long lasting efficacy in a mouse tumor model. After challenged with the highly aggressive TA3Ha cells, mice immunized with the new construct exhibited a statistically significant improvement in survival relative to controls (0% vs 50% survival; p < 0.0001). Furthermore, the surviving mice developed long-term immunity against TA3Ha. Thus, both the magnitude and the breadth of antibody reactivity should be considered when designing TACA-based antitumor vaccines.