Inhibition of TGFbeta1 makes nonimmunogenic tumor cells effective for therapeutic vaccination

From the Hellstrom paradox toward cancer cure

Several decades ago we published some of the first papers showing that both murine and human cancers are recognized in vitro as immunologically foreign and that this is the case also in the presence of a growing tumor. The latter situation, sometimes referred to as the Hellstrom paradox, implies that the tumor is protected in vivo by a highly immunosuppressive environment. After many disappointments, the discovery that tumor-related immunosuppression can be counteracted by administrating monoclonal antibodies (mAbs) to checkpoint inhibitors such as CTLA-4, PD-1, and PD-L1 is now revolutionizing cancer therapy. Over the past several years we have applied mouse models in attempts to further improve the ability of such mAbs to cause long-term complete tumor rejection. This review is focused on that work and emphasizes that successful immunotherapy is associated with a shift from a tumor-promoting Th2 inflammation to a tumor-inhibiting Th1 response.

Curing tumor-bearing mice by shifting a Th2 to a Th1 anti-tumor response

Over the past several years remarkable therapeutic responses have been obtained with immunomodulatory monoclonal antibodies (mAbs), both in mice \cite{10,18,20,48,54,61} and human cancer patients \cite{1,3,14,28,30,39,80}. However, complete regressions and cures are infrequent and not predictable and some tumor types respond much worse than others. As an attempt to increase curability, we have investigated in mouse models the therapeutic efficacy of several mAb combinations, focusing on anti-PD-1/CTLA-4/CD137 and anti-PD-1/CTLA-4/CD137/CD19, and we have also combined mAbs with the chemotherapeutic drug cisplatin. Our data demonstrate an important contribution of anti-CD19 mAb to therapeutic efficacy, they show that intratumoral delivery of the mAbs is therapeutically more effective than systemic delivery, and that there is synergy when the mAbs are combined with cisplatin. In an attempt to improve predictability, we developed an in vitro model that may also be employed to search for novel immunomodulatory agents and combinations. This article reviews our data and discusses what is known about the underlying mechanisms.

Overexpression of apolipoprotein A-I fused to an anti-transforming growth factor beta peptide modulates the tumorigenicity and immunogenicity of mouse colon cancer cells

Transforming growth factor beta (TGF-β) promotes tumor growth, invasion and metastasis in established tumors. In this study, we analyzed the effect of overexpressing an anti-TGF-β peptide fused to apolipoprotein A-I (ApoA-I) as a scaffold molecule. We generated and characterized stable MC38 colon carcinoma clones expressing ApoA-I fused to the anti-TGF-β peptide P144 and ApoA-I as control cells. We evaluated in vitro the gene expression profile, cell cycle and anchorage-independent growth. The in vivo tumorigenic potential and immunogenicity were analyzed inoculating the MC38 clones into C57BL/6 mice, recombination-activating gene 1 knockout mice or mice deficient in NK cells either subcutaneously or intrasplenically to generate hepatic metastases. While overexpression of ApoA-I had no effect on the parameters analyzed, ApoA-I fused to P144 markedly diminished the tumorigenic capacity and metastatic potential of MC38 in vitro and in vivo, thus generating a highly immunogenic cell line. MC38 cells transfected with ApoA-I fused to P144 triggered memory T cell responses able to eliminate the parental cell line upon re-challenge. In summary, expression of ApoA-I fused to P144 is a novel strategy to modulate TGF-β in tumor cells. These results highlight the potential of TGF-β as a target in the development of new antitumor treatments.

Curing mice with large tumors by locally delivering combinations of immunomodulatory antibodies

PURPOSE

Immunomodulatory mAbs can treat cancer, but cures are rare except for small tumors. Our objective was to explore whether the therapeutic window increases by combining mAbs with different modes of action and injecting them into tumors.

EXPERIMENTAL DESIGN

Combinations of mAbs to CD137/PD-1/CTLA-4 or CD137/PD-1/CTLA-4/CD19 were administrated intratumorally to mice with syngeneic tumors (B16 and SW1 melanoma, TC1 lung carcinoma), including tumors with a mean surface of approximately 80 mm(2). Survival and tumor growth were assessed. Immunologic responses were evaluated using flow cytometry and qRT-PCR.

RESULTS

More than 50% of tumor-bearing mice had complete regression and long-term survival after tumor injection with mAbs recognizing CD137/PD-1/CTLA-4/CD19 with similar responses in three models. Intratumoral injection was more efficacious than intraperitoneal injection in causing rejection also of untreated tumors in the same mice. The three-mAb combination could also induce regression, but was less efficacious. There were few side effects, and therapy-resistant tumors were not observed. Transplanted tumor cells rapidly caused a Th2 response with increased CD19 cells. Successful therapy shifted this response to the Th1 phenotype with decreased CD19 cells and increased numbers of long-term memory CD8 effector cells and T cells making IFNγ and TNFα.

CONCLUSIONS

Intratumoral injection of mAbs recognizing CD137/PD-1/CTLA-4/CD19 can eradicate established tumors and reverse a Th2 response with tumor-associated CD19 cells to Th1 immunity, whereas a combination lacking anti-CD19 is less effective. There are several human cancers for which a similar approach may provide clinical benefit.

Long-lasting complete regression of established mouse tumors by counteracting Th2 inflammation

Mice with intraperitoneal ID8 ovarian carcinoma or subcutaneous SW1 melanoma were injected with monoclonal antibodies (mAbs) to CD137PD-1CTLA4 7-15 days after tumor initiation. Survival of mice with ID8 tumors tripled and >40% of mice with SW1 tumors remained healthy >150 days after last treatment and are probably cured. Therapeutic efficacy was associated with a systemic immune response with memory and antigen specificity, required CD4 cells and involved CD8 cells and NK cells to a less extent. The 3 mAb combination significantly decreased CD19 cells at tumor sites, increased IFN-γ and TNF-α producing CD4 and CD8 T cells and mature CD86 dendritic cells (DC), and it increased the ratios of effector CD4 and CD8 T cells to CD4Foxp3 regulatory T (Treg) cells and to CD11bGr-1 myeloid suppressor cells (MDSC). This is consistent with shifting the tumor microenvironment from an immunosuppressive Th2 to an immunostimulatory Th1 type and is further supported by PCR data. Adding an anti-CD19 mAb to the 3 mAb combination in the SW1 model further increased therapeutic efficacy. Data from ongoing experiments show that intratumoral injection of a combination of mAbs to CD137PD-1CTLA4CD19 can induce complete regression and dramatically prolong survival also in the TC1 carcinoma and B16 melanoma models, suggesting that the approach has general validity.

The impact of the myeloid response to radiation therapy

Radiation therapy is showing potential as a partner for immunotherapies in preclinical cancer models and early clinical studies. As has been discussed elsewhere, radiation provides debulking, antigen and adjuvant release, and inflammatory targeting of effector cells to the treatment site, thereby assisting multiple critical checkpoints in antitumor adaptive immunity. Adaptive immunity is terminated by inflammatory resolution, an active process which ensures that inflammatory damage is repaired and tissue function is restored. We discuss how radiation therapy similarly triggers inflammation followed by repair, the consequences to adaptive immune responses in the treatment site, and how the myeloid response to radiation may impact immunotherapies designed to improve control of residual cancer cells.

Silencing of the TGF-β1 gene increases the immunogenicity of cells from human ovarian carcinoma

Cells from many tumors produce transforming growth factor (TGF)-β which facilitates their escape from control by the immune system. We previously reported that nonimmunogenic cells from either of 2 transplantable mouse tumors became effective as therapeutic tumor vaccines after lentivirus-mediated shRNA interference to "silence" the TGF-β1 gene. We now show that cells from in vitro cultured human ovarian carcinomas (OvC) make large amounts of TGF-β1 and that this can be prevented by "silencing" the TGF-β1 gene. We further show that in vitro sensitization of peripheral blood mononuclear cells in the presence of either mitomycin-treated OvC cells whose TGF-β1 gene was silenced or in vitro matured dendritic cells that had been pulsed with homogenates from OvC cells with silenced TGF-β1 generated a stronger Th1/Tc1 immune response to the respective wild-type OvC and also to the OvC antigens mesothelin and HE4 as measured by ELIspot assays. The percentage of interferon-γ and tumor necrosis factor-α-producing CD4+ and CD8+ T cells increased while there were fewer cells expressing markers characteristic for regulatory T cells or myeloid-derived suppressor cells. Similar results were obtained when peripheral blood mononuclear cells from a patient with OvC were sensitized to dendritic cells pulsed with homogenate from autologous TGF-β1-silenced tumor cells, and a cytolytic lymphocyte response was generated to autologous OvC cells. Our results support clinical evaluation of TGF-β1-silenced tumor vaccines for immunotherapy of OvC.

Administration of cyclophosphamide changes the immune profile of tumor-bearing mice

Cyclophosphamide (CTX) is often used to create a "window" for more effective therapeutic tumor vaccination. According to a commonly applied protocol, we injected 2 mg CTX intraperitoneally to mice with small (2 to 3 mm diameter) or large (5 to 7 mm, and in one experiment 8 to 10 mm diameter) subcutaneously growing tumors from the SW1 clone of the K1735 melanoma, euthanized the mice 4 days later and studied the composition of lymphoid cells by flow cytometry in both spleens and tumors. Administration of CTX increased the percentage of CD3, CD4, and CD8 cells with the increase in tumors being significantly greater than in spleens, and it also increased the percentage of B cells in spleens and tumors. Furthermore, CTX dramatically increased the frequency of tumor-infiltrating CD4 and CD8 cells containing interferon gamma, of cells expressing NK1.1, and of cells expressing the dendritic cell markers CD11c, CD80, and CD86, with the greatest increases seen among tumor-infiltrating lymphoid cells (TIL) from mice with small tumors. Although CTX decreased the percentage of TIL that expressed CD4 or CD8 together with CD25 and FoxP3 and were therefore considered to be regulatory T cells, it increased the frequency of TIL that stained for Gr1/CD11b, a marker for myeloid-derived suppressor cells. We conclude that the administration of CTX can favorably impact several cell populations that are involved in tumor rejection. However, since CTX has a limited effect on TIL from tumors larger than a few millimeter in diameter and in view of an increased percentage of myeloid-derived suppressor cells among TIL from mice given CTX there is a need for more effective ways to improve tumor vaccination.