Oncolytic immunotherapy: where are we clinically?

Oncolytic adenoviruses as a therapeutic approach for osteosarcoma: A new hope

Osteosarcoma is the most common bone cancer among those with non-hematological origin and affects mainly pediatric patients. In the last 50 years, refinements in surgical procedures, as well as the introduction of aggressive neoadjuvant and adjuvant chemotherapeutic cocktails, have increased to nearly 70% the survival rate of these patients. Despite the initial therapeutic progress the fight against osteosarcoma has not substantially improved during the last three decades, and almost 30% of the patients do not respond or recur after the standard treatment. For this group there is an urgent need to implement new therapeutic approaches. Oncolytic adenoviruses are conditionally replicative viruses engineered to selectively replicate in and kill tumor cells, while remaining quiescent in healthy cells. In the last years there have been multiple preclinical and clinical studies using these viruses as therapeutic agents in the treatment of a broad range of cancers, including osteosarcoma. In this review, we summarize some of the most relevant published literature about the use of oncolytic adenoviruses to treat human osteosarcoma tumors in subcutaneous, orthotopic and metastatic mouse models. In conclusion, up to date the preclinical studies with oncolytic adenoviruses have demonstrated that are safe and efficacious against local and metastatic osteosarcoma. Knowledge arising from phase I/II clinical trials with oncolytic adenoviruses in other tumors have shown the potential of viruses to awake the patient´s own immune system generating a response against the tumor. Generating osteosarcoma immune-competent adenoviruses friendly models will allow to better understand this potential. Future clinical trials with oncolytic adenoviruses for osteosarcoma tumors are warranted.

Tumor-directed immunotherapy can generate tumor-specific T cell responses through localized co-stimulation

The most important goals for the field of immuno-oncology are to improve the response rate and increase the number of tumor indications that respond to immunotherapy, without increasing adverse side effects. One approach to achieve these goals is to use tumor-directed immunotherapy, i.e., to focus the immune activation to the most relevant part of the immune system. This may improve anti-tumor efficacy as well as reduce immune-related adverse events. Tumor-directed immune activation can be achieved by local injections of immune modulators in the tumor area or by directing the immune modulator to the tumor using bispecific antibodies. In this review, we focus on therapies targeting checkpoint inhibitors and co-stimulatory receptors that can generate tumor-specific T cell responses through localized immune activation.

Going viral: a review of replication-selective oncolytic adenoviruses

Oncolytic viruses have had a tumultuous course, from the initial anecdotal reports of patients having antineoplastic effects after natural viral infections a century ago to the development of current cutting-edge therapies in clinical trials. Adenoviruses have long been the workhorse of virotherapy, and we review both the scientific and the not-so-scientific forces that have shaped the development of these therapeutics from wild-type viral pathogens, turning an old foe into a new friend. After a brief review of the mechanics of viral replication and how it has been modified to engineer tumor selectivity, we give particular attention to ONYX-015, the forerunner of virotherapy with extensive clinical testing that pioneered the field. The findings from those as well as other oncolytic trials have shaped how we now view these viruses, which our immune system has evolved to vigorously attack, as promising immunotherapy agents.

Experimental Adaptation of Rotaviruses to Tumor Cell Lines

A number of viruses show a naturally extended tropism for tumor cells whereas other viruses have been genetically modified or adapted to infect tumor cells. Oncolytic viruses have become a promising tool for treating some cancers by inducing cell lysis or immune response to tumor cells. In the present work, rotavirus strains TRF-41 (G5) (porcine), RRV (G3) (simian), UK (G6-P5) (bovine), Ym (G11-P9) (porcine), ECwt (murine), Wa (G1-P8), Wi61 (G9) and M69 (G8) (human), and five wild-type human rotavirus isolates were passaged multiple times in different human tumor cell lines and then combined in five different ways before additional multiple passages in tumor cell lines. Cell death caused by the tumor cell-adapted isolates was characterized using Hoechst, propidium iodide, 7-AAD, Annexin V, TUNEL, and anti-poly-(ADP ribose) polymerase (PARP) and -phospho-histone H2A.X antibodies. Multiple passages of the combined rotaviruses in tumor cell lines led to a successful infection of these cells, suggesting a gain-of-function by the acquisition of greater infectious capacity as compared with that of the parental rotaviruses. The electropherotype profiles suggest that unique tumor cell-adapted isolates were derived from reassortment of parental rotaviruses. Infection produced by such rotavirus isolates induced chromatin modifications compatible with apoptotic cell death.

Targeting adeno-associated virus and adenoviral gene therapy for hepatocellular carcinoma

Human hepatocellular carcinoma (HCC) heavily endangers human heath worldwide. HCC is one of most frequent cancers in China because patients with liver disease, such as chronic hepatitis, have the highest cancer susceptibility. Traditional therapeutic approaches have limited efficacy in advanced liver cancer, and novel strategies are urgently needed to improve the limited treatment options for HCC. This review summarizes the basic knowledge, current advances, and future challenges and prospects of adeno-associated virus (AAV) and adenoviruses as vectors for gene therapy of HCC. This paper also reviews the clinical trials of gene therapy using adenovirus vectors, immunotherapy, toxicity and immunological barriers for AAV and adenoviruses, and proposes several alternative strategies to overcome the therapeutic barriers to using AAV and adenoviruses as vectors.

HAdV-2-suppressed growth of SV40 T antigen-transformed mouse mammary epithelial cell-induced tumours in SCID mice

Human adenovirus (HAdV) vectors are promising tools for cancer therapy, but the shortage of efficient animal models for productive HAdV infections has restricted the evaluation of systemic effects to mainly immunodeficient mice. Previously, we reported a highly efficient replication of HAdV-2 in a non-tumorigenic mouse mammary epithelial cell line, NMuMG. Here we show that HAdV-2 gene expression and progeny formation in NMuMG cells transformed with the SV40 T antigen (NMuMG-T cells) were as efficient as in the parental NMuMG cells. Injection of HAdV-2 into tumours established by NMuMG-T in SCID mice caused reduced tumour growth and signs of intratumoural lesions. HAdV-2 replicated within the NMuMG-T-established tumours, but not in interspersed host-derived tissues within the tumours. The specific infection of NMuMG-T-derived tumours was verified by the lack of viral DNA in kidney, lung or spleen although low levels of viral DNA was occasionally found in liver.

Immunological data from cancer patients treated with Ad5/3-E2F-Δ24-GMCSF suggests utility for tumor immunotherapy

Oncolytic viruses that selectively replicate in tumor cells can be used for treatment of cancer. Accumulating data suggests that virus induced oncolysis can enhance anti-tumor immunity and break immune tolerance. To capitalize on the immunogenic nature of oncolysis, we generated a quadruple modified oncolytic adenovirus expressing granulocyte-macrophage colony-stimulating factor (GMCSF). Ad5/3-E2F-Δ24-GMCSF (CGTG-602) was engineered to contain a tumor specific E2F1 promoter driving an E1 gene deleted at the retinoblastoma protein binding site (“Δ24”). The fiber features a knob from serotype 3 for enhanced gene delivery to tumor cells. The virus was tested preclinically in vitro and in vivo and then 13 patients with solid tumors refractory to standard therapies were treated. Treatments were well tolerated and frequent tumor- and adenovirus-specific T-cell immune responses were seen. Overall, with regard to tumor marker or radiological responses, signs of antitumor efficacy were seen in 9/12 evaluable patients (75%). The radiological disease control rate with positron emission tomography was 83% while the response rate (including minor responses) was 50%. Tumor biopsies indicated accumulation of immunological cells, especially T-cells, to tumors after treatment. RNA expression analyses of tumors indicated immunological activation and metabolic changes secondary to virus replication.

Oncolytic virotherapy for treatment of breast cancer, including triple-negative breast cancer

Breast cancer is a heterogeneous disease, characterized by several distinct biological subtypes, among which triple-negative breast cancer (TNBC) is one associated with a poor prognosis. Oncolytic virus replication is an immunogenic phenomenon, and viruses can be armed with immunostimulatory molecules to boost virus triggered antitumoral immune responses. Cyclophosphamide (CP) is a chemotherapy drug that is associated with cytotoxicity and immunosuppression at higher doses, whereas immunostimulatory and anti-angiogenic properties are observed at low continuous dosage. Therefore, the combination of oncolytic immuno-virotherapy with low-dose CP is an appealing approach. We investigated the potency of oncolytic adenovirus Ad5/3-D24-GMCSF on a TNBC cell line and in vivo in an orthotopic xenograft mouse model, in combination with low-dose CP or its main active metabolite 4-hydroperoxycyclophosphamide (4-HP-CP). Furthermore, we summarized the breast cancer-specific human data on this virus from the Advanced Therapy Access Program (ATAP). Low-dose CP increased the efficacy of Ad5/3-D24-GMCSF in vitro and in a TNBC mouse model. In ATAP, treatments appeared safe and well-tolerated. Thirteen out of 16 breast cancer patients treated were evaluable for possible benefits with modified RECIST 1.1 criteria: 1 patient had a minor response, 2 had stable disease (SD), and 10 had progressive disease (PD). One patient is alive at 1,771 d after treatment. Ad5/3-D24-GMCSF in combination with low-dose CP showed promising efficacy in preclinical studies and possible antitumor activity in breast cancer patients refractory to other forms of therapy. This preliminary data supports continuing the clinical development of oncolytic adenoviruses for treatment of breast cancer, including TNBC.

Biodistribution Analysis of Oncolytic Adenoviruses in Patient Autopsy Samples Reveals Vascular Transduction of Noninjected Tumors and Tissues

In clinical trials with oncolytic adenoviruses, there has been no mortality associated with treatment vectors. Likewise, in the Advanced Therapy Access Program (ATAP), where 290 patients were treated with 10 different viruses, no vector-related mortality was observed. However, as the patient population who received adenovirus treatments in ATAP represented heavily pretreated patients, often with very advanced disease, some patients died relatively soon after receiving their virus treatment mandating autopsy to investigate cause of death. Eleven such autopsies were performed and confirmed disease progression as the cause of death in each case. The regulatory requirement for investigating the safety of advanced therapy medical products presented a unique opportunity to study tissue samples collected as a routine part of the autopsies. Oncolytic adenoviral DNA was recovered in a wide range of tissues, including injected and noninjected tumors and various normal tissues, demonstrating the ability of the vector to disseminate through the vascular route. Furthermore, we recovered and cultured viable virus from samples of noninjected brain metastases of an intravenously treated patient, confirming that oncolytic adenovirus can reach tumors through the intravascular route. Data presented here give mechanistic insight into mode of action and biodistribution of oncolytic adenoviruses in cancer patients.

T-cell subsets in peripheral blood and tumors of patients treated with oncolytic adenoviruses

The quality of the antitumor immune response is decisive when developing new immunotherapies for cancer. Oncolytic adenoviruses cause a potent immunogenic stimulus and arming them with costimulatory molecules reshapes the immune response further. We evaluated peripheral blood T-cell subsets of 50 patients with refractory solid tumors undergoing treatment with oncolytic adenovirus. These data were compared to changes in antiviral and antitumor T cells, treatment efficacy, overall survival, and T-cell subsets in pre- and post-treatment tumor biopsies. Treatment caused a significant (P < 0.0001) shift in T-cell subsets in blood, characterized by a proportional increase of CD8(+) cells, and decrease of CD4(+) cells. Concomitant treatment with cyclophosphamide and temozolomide resulted in less CD4(+) decrease (P = 0.041) than cyclophosphamide only. Interestingly, we saw a correlation between T-cell changes in peripheral blood and the tumor site. This correlation was positive for CD8(+) and inverse for CD4(+) cells. These findings give insight to the interconnections between peripheral blood and tumor-infiltrating lymphocyte (TIL) populations regarding oncolytic virotherapy. In particular, our data suggest that induction of T-cell response is not sufficient for clinical response in the context of immunosuppressive tumors, and that peripheral blood T cells have a complicated and potentially misleading relationship with TILs.