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Cancer immunotherapy using monoclonal antibodies targeting immune checkpoints has undoubtedly revolutionized the cancer treatment landscape in the last decade. Immune checkpoint inhibitors can elicit long-lasting, previously unheard-of responses in a number of tumor entities. Yet, even in such tumors as metastatic melanoma and non-small cell-lung cancer, in which immune checkpoint inhibition has become the first-line treatment of choice, only a minority of patients will benefit considerably from these treatments. This has been attributed to a number of factors, including an immune-suppressive tumor microenvironment (TME). Using different modalities to break these barriers is of utmost importance to expand the population of patients that benefit from immune checkpoint inhibition. The multifunctional cytokine transforming growth factor-β (TGF-β) has long been recognized as an immune-suppressive factor in the TME. A considerable number of drugs have been developed to target TGF-β, yet most of these have since been discontinued. The combination of anti–TGF-β agents with immune checkpoint inhibitors now has the potential to revive this target as a viable immunomodulatory therapeutic approach. Currently, a limited number of small molecular inhibitor and monoclonal antibody candidates that target TGF-β are in clinical development in combination with the following immune checkpoint inhibitors: SRK 181, an antibody inhibiting the activation of latent TGF-β1; NIS 793, a monoclonal antibody targeting TGF-β; and SHR 1701, a fusion protein consisting of an anti-PD-L1 monoclonal antibody fused with the extracellular domain of human TGF-β receptor II. Several small molecular inhibitors are also in development and are briefly reviewed: LY364947, a pyrazole-based small molecular inhibitor of the serine-threonine kinase activity of TGFβRI; SB-431542, an inhibitor targeting several TGF-β superfamily Type I activin receptor-like kinases as well as TGF-β1-induced nuclear Smad3 localization; and galunisertib, an oral small molecular inhibitor of the TGFβRI kinase. One of the most advanced agents in this area is bintrafusp alfa, a bifunctional fusion protein composed of the extracellular domain of TGF-β receptor II fused to a human IgG1 mAb blocking PD-L1. Bintrafusp alfa is currently in advanced clinical development and as an agent in this space with the most clinical experience, is a focused highlight of this review. [ABSTRACT FROM AUTHOR]

A number of cancer vaccine strategies for the treatment of colorectal cancer have entered clinical trials. Whole tumor cell vaccines have been developed from both patients’ autologous tumor cells as well as established allogeneic tumor cell lines. A vaccine consisting of autologous tumor cells along with bacillus Calmette-Guerin (BCG) has shown a potential clinical benefit in patients with stage II colon cancer. Other approaches using autologous tumor cells have involved transfection of primary tumor cells with cytokine genes. Allogeneic tumor cell vaccines have also been modified to express cytokine genes. Vectors have been studied extensively as a means of vaccine strategy. One tumor-associated antigen (TAA) that has been extensively studied in viral vector vaccines is carcinoembryonic antigen (CEA). A recombinant vaccinia virus containing the CEA transgene (rV-CEA) has been shown to elicit CEA-specific immune responses in advanced carcinoma patients. However, patients receiving multiple vaccinations had limited increases in CEA-specific responses by the third vaccination. This problem may be overcome by the use of non-replicating poxviruses, which have been shown in clinical trials to be safe and to elicit CEA-specific responses. However, recent clinical studies have shown that the optimal use of poxviruses is to prime with vaccinia, followed by boosts with avipox vectors. A recent randomized clinical trial showed that patients primed with rV-CEA and boosted with avipox-CEA had greater immune responses compared with patients receiving three 1-monthly avipox-CEA vaccinations followed by an rV-CEA vaccination. Furthermore, a statistically significant survival advantage was noted in the prime/boost arm. Ongoing studies are now incorporating the genes for costimulatory molecules along with TAA in these vectors. Another vaccine strategy involving TAA that is currently in clinical trials for colorectal cancer is the peptide vaccine. Dendritic cells (DCs) are considered to be the most potent antigen-presenting cell, thus providing an attractive modality for cancer vaccines. In addition to using DCs for peptide-based vaccines, a number of other strategies, including transfection with messenger RNA, have produced specific T-cell responses in clinical trials. In addition, several clinical trials using murine anti-idiotype antibodies as vaccines for patients with advanced colorectal cancer have shown both immunologic responses as well as clinical responses. [ABSTRACT FROM AUTHOR]

A concurrent multicenter, randomized Phase II trial employing a recombinant poxviral vaccine provided evidence of enhanced median overall survival (OS) (p = 0.0061) in patients with metastatic castrate-resistant prostate cancer (mCRPC). The study reported here employed the identical vaccine in mCRPC to investigate the influence of GM-CSF with vaccine, and the influence of immunologic and prognostic factors on median OS. Thirty-two patients were vaccinated once with recombinant vaccinia containing the transgenes for prostate-specific antigen (PSA) and three costimulatory molecules. Patients received boosters with recombinant fowlpox containing the same four transgenes. Twelve of 32 patients showed declines in serum PSA post-vaccination and 2/12 showed decreases in index lesions. Median OS was 26.6 months (predicted median OS by the Halabi nomogram was 17.4 months). Patients with greater PSA-specific T-cell responses showed a trend (p = 0.055) toward enhanced survival. There was no difference in T-cell responses or survival in cohorts of patients receiving GM-CSF versus no GM-CSF. Patients with a Halabi predicted survival of <18 months (median predicted 12.3 months) had an actual median OS of 14.6 months, while those with a Halabi predicted survival of ≥18 months (median predicted survival 20.9 months) will meet or exceed 37.3 months, with 12/15 patients living longer than predicted (p = 0.035). Treg suppressive function was shown to decrease following vaccine in patients surviving longer than predicted, and increase in patients surviving less than predicted. This hypothesis-generating study provides evidence that patients with more indolent mCRPC (Halabi predicted survival ≥18 months) may best benefit from vaccine therapy. [ABSTRACT FROM AUTHOR]

New gene expressed in prostate (NGEP) is a prostate-specific gene encoding either a small cytoplasmic protein (NGEP-S) or a larger polytopic membrane protein (NGEP-L). NGEP-L expression is detectable only in prostate cancer, benign prostatic hyperplasia and normal prostate. We have identified an HLA-A2 binding NGEP epitope (designated P703) which was used to generate T cell lines from several patients with localized and metastatic prostate cancer. These T cell lines were able to specifically lyse HLA-A2 and NGEP-expressing human tumor cells. NGEP-P703 tetramer binding assays demonstrated that metastatic prostate cancer patients had a higher frequency of NGEP-specific T cells when compared with healthy donors. Moreover, an increased frequency of NGEP-specific T cells was detected in the peripheral blood mononuclear cells of prostate cancer patients post-vaccination with a PSA-based vaccine, further indicating the immunogenicity of NGEP. These studies thus identify NGEP as a potential target for T cell-mediated immunotherapy of prostate cancer. [ABSTRACT FROM AUTHOR]