However, depletion of CD4+ T lymphocytes prior to tumor growth had an impact around the therapeutic outcome (Fig. Sequence analysis of T cell receptors of CD8+ T cells revealed the presence of H-2Ld/AH1-specific T cells and an expansion of sequence diversity in treated mice. Overall, our findings provide evidence that retroviral genes contribute to TLR-4 tumoral immune surveillance in a process that can be generally boosted by F8-TNF and doxorubicin treatment. in 1992, revealed that more than 50 percent of sarcoma patients, who had been treated with Coleys toxin, enjoyed durable complete remissions (CRs) from the disease (5), while CRs are virtually never observed with modern chemotherapy (2,3). The author concluded that: in the light of the pre-dominantly disappointing results with chemotherapy in the treatment of such advanced stages of cancer, an approach based on Coleys toxin or on related immunostimulatory strategies is certainly a reasonable place to concentrate our efforts. The endotoxins in Coleys vaccine stimulated the release of high concentrations of TNF, among other pro-inflammatory cytokines. The sensitivity of tumors of mesodermal origin to TNF has prompted numerous investigations. Carswell (6) used a sarcoma in the initial discovery of TNF, while Berendt (7) used STS to describe the essential importance of tumor immunogenicity and a corresponding T cell immune response to the curative effects of endotoxin therapy. The systemic use of recombinant TNF was not successful in the clinic. However, the use of TNF in isolated limb perfusion procedures in combination with melphalan for the treatment of inoperable soft-tissue sarcomas was found to be potently active even for the eradication of large tumor masses and has received marketing authorization in Europe (8). We have previously reported that this therapeutic index of murine TNF can be dramatically enhanced by fusion to suitable antibody fragments capable of selective localization to the tumor environment. In particular, a strong activity in mouse models of sarcoma has been observed for TNF fusions to the F8 or the L19 antibody, specific to the alternatively-spliced EDA and EDB domains of fibronectin, respectively (9,10). These splice isoforms of fibronectin are virtually undetectable in normal adult tissues (exception made for placenta, endometrium and some vessels in the ovaries) (11), but are abundantly found around the tumor blood vessels in most malignancies (11,12). In two immunocompetent mouse models of soft-tissue sarcoma, doxorubicin did not exhibit any detectable inhibition of tumor growth, while its combination with F8-TNF was curative (9). Similarly, potent therapeutic activity in sarcoma has been reported for L19-TNF in combination with melphalan (10). The fully-human version of L19-TNF has been shown to be clinically active in isolated limb perfusion procedures (13) and for the intralesional administration to patients with stage III melanoma (14). The systemic administration of L19-TNF has been found to be safe for up to 1 mg/patient. A clinical trial featuring a combination with doxorubicin in soft-tissue sarcoma patients is currently on going in Italy and in Germany LY2835219 (abemaciclib) (Eudra-CT no. 2012-000950-75). Here, we present a detailed analysis of how the antibody-based delivery of TNF to sarcoma potently synergizes with doxorubicin and confers a protective immunity against homologous and heterologous tumors. The combination of T cell receptor and exome sequencing, as well as the analysis of MHC class I bound peptides, led to the identification of the retroviral AH1 peptide (SPSYVYHQF) as a contributor to the tumor rejection process. Materials and Methods Cell lines, animals and tumor models All tumor cell lines were obtained from the American Type Culture Collection (ATTC) with exception of C51 colon carcinoma and F1F fibrosarcoma (both kindly provided by M.P. Colombo, Istituto Nazionale Tumori, Milan, Italy). Cell lines were received between 2010 and 2017, expanded and stored as cryopreserved aliquots in liquid nitrogen. Cells were grown according the suppliers LY2835219 (abemaciclib) protocol and kept in culture for no longer than 2 months. Authentication of the cell lines also including check of post-freeze viability, growth properties and morphology, test for mycoplasma contamination, isoenzyme assay and sterility test were performed by the cell bank before shipment. Eight-week-old female BALB/c mice were purchased LY2835219 (abemaciclib) from Charles River (Germany). All animal experiments were performed under a project license granted by the Veterin?ramt des Kantons Zrich, Switzerland (42/2012, 27/2015) in agreement with Swiss regulations. Antibodies and drugs for therapy experiments The F8-TNF immunocytokine was produced as previously described (9). Doxorubicin was purchased in the commercially available form of 10 mg/5 mL solution for injection (Sandoz Pharmaceuticals AG, Switzerland). Rat anti-CD4 (GK1.5, BioXCell), rat anti-CD8 (YTS169.4, BioX-Cell) and rabbit anti-Asialo GM1 (Wako Chemicals) antibodies were used for depletion. Therapy study and depletion of NK,.