Breast cancer is a tumor entity that is one of the leading causes of mortality among women worldwide. Although numerous treatment options are available, current explorations of personalized vaccines have shown potential as promising new treatment options to prevent the recurrence of cancer. Here we present a small proof of concept study using a prophylactic peptide vaccination approach in four female breast cancer patients who achieved remission after standard treatment. The patients were initially analyzed for somatic tumor mutations and then treated with personalized neoantigen-derived peptide vaccines. These vaccines consisted of HLA class I and class II peptides and were administered intracutaneously followed by subcutaneous application of sargramostim and/or topical imiquimod as an immunological adjuvant. After an initial priming phase of four vaccinations within two weeks, patients received monthly boosting/maintenance vaccinations. Chemotherapy or checkpoint inhibition was not performed during vaccination. One patient received hormone therapy. The vaccines were well tolerated with no serious adverse events. All patients displayed vaccine-induced CD4+ and/or CD8+ T-cell responses against various neoantigens. Furthermore, all patients remained tumor-free and had persistent T-cell responses, even several months after the last vaccination, suggesting the potential of peptide vaccines as an immunosurveillance and long term prophylaxis option.

Localized prostate cancer is curable, but metastatic castration sensitive prostate cancer has a low 5-year survival rate, while broad treatment options are lacking. Here we present an mCSPC patient under remission receiving individualized neoantigen-derived peptide vaccination as recurrence prophylaxis in the setting of an individual treatment attempt. The patient was initially analyzed for somatic tumor mutations and then consecutively treated with two different peptide vaccines over a period of 33 months. The first vaccine contained predicted HLA class I binding peptides only whereas the second vaccine contained both predicted HLA class I and II binding peptides. Intracellular cytokine staining after 12 day in-vitro expansion measuring four T-cell activation markers (IFNg, TNF-α, IL-2, CD154) was used to determine vaccine-induced T-cell responses. While the first vaccine induced only one robust CD4+ T-cell response after 21 vaccinations, co-vaccination of HLA class I and II peptides induced multiple strong and durable CD4+ and CD8+ T-cell responses already after sixth vaccinations. The vaccine-induced immune responses were robust and polyfunctional. PSA remained undetectable for 51 months. The results presented here implicate that neoantigen-targeting vaccines might be considered for those cancer subtypes where therapeutic options are limited. Furthermore, our findings suggest that both HLA class I and II restricted peptides should be considered for future peptide vaccination trials.

Ovarian cancer is one of the most common cancers among women and the most lethal malignancy of all gynecological cancers. Surgery is promising in the early stages; however, most patients are first diagnosed in the advanced stages, where treatment options are limited. Here, we present a 49-year-old patient who was first diagnosed with stage III ovarian cancer. After the tumor progressed several times under guideline therapies with no more treatment options available at that time, the patient received a fully individualized neoantigen-derived peptide vaccine in the setting of an individual healing attempt. The tumor was analyzed for somatic mutations via whole exome sequencing and potential neoepitopes were vaccinated over a period of 50 months. During vaccination, the patient additionally received anti-PD-1 therapy to prevent further disease progression. Vaccine-induced T-cell responses were detected using intracellular cytokine staining. After eleven days of in vitro expansion, four T-cell activation markers (namely IFN-ɣ, TNF-α, IL-2, and CD154) were measured. The proliferation capacity of neoantigen-specific T-cells was determined using a CFSE proliferation assay. Immune monitoring revealed a very strong CD4+ T-cell response against one of the vaccinated peptides. The vaccine-induced T-cells simultaneously expressed CD154, TNF, IL-2, and IFN-ɣ and showed a strong proliferation capacity upon neoantigen stimulation. Next-generation sequencing, as well as immunohistochemical analysis, revealed a loss of Beta-2 microglobulin (B2M), which is essential for MHC class I presentation. The results presented here implicate that the application of neoantigen-derived peptide vaccines might be considered for those cancer stages, where promising therapeutic options are lacking. Furthermore, we provide more data that endorse the intensive investigation of B2M loss as a tumor escape mechanism in clinical trials using anti-cancer vaccines together with immune-checkpoint inhibitors.

Background/Objectives: Fully personalized peptide vaccines targeting tumor-specific mutations are a promising treatment option for patients in an adjuvant but also advanced/metastatic disease situation in addition to non-personalized standard therapies. Here, we report a patient’s case with advanced metastatic colorectal cancer (mCRC) who was treated with a neoantigen-derived multi-peptide vaccine in addition to standard of care. Methods: Tumor-specific mutations were identified by whole exome and transcriptome sequencing. An individualized peptide vaccine was designed using an in-house developed epitope prediction and vaccine design platform. In this case, the vaccine consisted of 20 peptides targeting 18 distinct mutations. The vaccine was administered according to a prime-boost scheme for a total of 12 vaccinations. Vaccine immunogenicity was determined by stimulation of patient T cells with vaccinated peptides and subsequent intracellular cytokine staining (ICS). Tumor-infiltrating lymphocytes (TIL) were analyzed by ICS and T cell receptor beta chain (TCRβ) sequencing. Results: The patient survived for 41 months since initial diagnosis despite continuous disease progression under all therapeutic interventions. The vaccination induced multiple neoantigen-specific T cell responses in the patient without notable side effects. Two liver metastases were resected five months after the start of vaccination, and TIL were extracted and cultured. Analysis of TIL cultures revealed tumor infiltration by vaccine-induced neoantigen-specific T cells in only one of the metastases. TCRβ sequencing of neoantigen-specific T cells and tumor tissues supported this finding. Vaccine-targeted variants were reduced or absent in the metastasis with vaccine-specific T cell infiltration. Conclusions: This case demonstrates immunogenicity of a neoantigen-derived peptide vaccine and highlights tumor-infiltrating capabilities and potential cytotoxicity of vaccine-induced T cells in mCRC.