Citations

Abstract Antitumor T-cell responses raised by first-line therapies such as chemotherapy, radiation, tumor cell vaccines, and viroimmunotherapy tend to be weak, both quantitatively (low frequency) and qualitatively (low affinity). We show here that T cells that recognize tumor-associated antigens can directly kill tumor cells if used at high effector-to-target ratios. However, when these tumor-reactive T cells were present at suboptimal ratios, direct T-cell–mediated tumor cell killing was reduced and the ability of tumor cells to evolve away from a coapplied therapy (oncolytic or suicide gene therapy) was promoted. This T-cell–mediated increase in therapeutic resistance was associated with C to T transition mutations that are characteristic of APOBEC3 cytosine deaminase activity and was induced through a TNFα and protein kinase C–dependent pathway. Short hairpin RNA inhibition of endogenous APOBEC3 reduced rates of tumor escape from oncolytic virus or suicide gene therapy to those seen in the absence of antitumor T-cell coculture. Conversely, overexpression of human APOBEC3B in tumor cells enhanced escape from suicide gene therapy and oncolytic virus therapy both in vitro and in vivo. Our data suggest that weak affinity or low frequency T-cell responses against tumor antigens may contribute to the ability of tumor cells to evolve away from first-line therapies. We conclude that immunotherapies need to be optimized as early as possible so that, if they do not kill the tumor completely, they do not promote treatment resistance.

Abstract Human fibrin hydrogels are a popular choice for use as a biomaterial within tissue engineered constructs because they are biocompatible, nonxenogenic, autologous use compatible, and biodegradable. We have recently demonstrated the ability to culture induced pluripotent stem cell (iPSC)-derived retinal pigment epithelium on fibrin hydrogels. However, iPSCs themselves have relatively few substrate options (e.g., laminin) for expansion in adherent cell culture for use in cell therapy. To address this, we investigated the potential of culturing iPSCs on fibrin hydrogels for three-dimensional applications and further examined the use of fibrinogen, the soluble precursor protein, as a coating substrate for traditional adherent cell culture. iPSCs successfully adhered to and proliferated on fibrin hydrogels. The two-dimensional culture with fibrinogen allows for immediate adaption of culture models to a nonxenogeneic model. Similarly, multiple commercially available iPSC lines adhered to and proliferated on fibrinogen coated surfaces. iPSCs cultured on fibrinogen expressed similar levels of the pluripotent stem cell markers SSea4 (98.7% ± 1.8%), Oct3/4 (97.3% ± 3.8%), TRA1-60 (92.2% ± 5.3%), and NANOG (96.0% ± 3.9%) compared with iPSCs on Geltrex. Using a trilineage differentiation assay, we found no difference in the ability of iPSCs grown on fibrinogen or Geltrex to differentiate to endoderm, mesoderm, or ectoderm. Finally, we demonstrated the ability to differentiate iPSCs to endothelial cells using only fibrinogen coated plates. On the basis of these data, we conclude that human fibrinogen provides a readily available and inexpensive alternative to laminin-based products for the growth, expansion, and differentiation of iPSCs for use in research and clinical cell therapy applications. Stem Cells Translational Medicine 2019;8:512–521

Abstract We have previously shown that a vesicular stomatitis virus-based cDNA library expressing xenogeneic altered self-epitopes led to T-cell mediated rejection of prostate cancer, glioma and melanoma. The use of a library of altered self-peptides which reflects the transcriptome of the tumor circumvents the necessity for a priori knowledge of which antigens may be immunogenic in a patient, and primes a polyclonal T-cell response that provides strong cumulative antitumor selective pressure. We have expanded this concept of altered-self library vaccination using tumor vaccines modified by the overexpression of APOBEC3B, a cytosine deaminase that generates C to T transition mutations. A freeze-thawed whole tumor cell vaccine prepared from B16 melanoma cells stably overexpressing human APOBEC3B treated established subcutaneous parental B16 tumors and, when combined with PD-1 checkpoint blockade, cured between 75%-100% of mice. T-cells from mice treated with the vaccine and anti-PD1 produced high levels of IFN-γ when restimulated with parental unmodified B16 melanoma cells in vitro. Whole-genome sequencing of B16APOBEC3B overexpressing cells identified 301 C to T or G to A missense mutations unique to the APOBEC3B line. Using an in silico MHC binding affinity algorithm, we identified and experimentally validated a short list of 10 APOBEC3B- induced heteroclitic peptides. We have also shown that this approach can be extended to an orthotopic brainstem model of high grade glioma. GL261 tumors stereotactically implanted into the brainstem were significantly responsive to treatment with an APOBEC3B- modified GL261 vaccine in combination with anti-PD-1 checkpoint blockade. In summary, when overexpressed in tumor cells, APOBEC3B generates a library of heteroclitic sequences that primes both CD4 and CD8 T-cells that have escaped central tolerance and that recognize both newly mutated antigens from the vaccine, and the corresponding unaltered self epitopes expressed on the tumor cells. Citation Format: Richard Vile, Laura Evgin, Timothy Kottke, Matthew Schuelke, Christopher B. Driscoll, Amanda L. Huff, Jill Thompson, Amy Molan, Reuben S. Harris, Jose S. Pulido, Phonphimon Wongthida. Cancer immunotherapy with APOBEC3B-induced heteroclitic library tumor cell vaccines and immune checkpoint blockade [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B138.

Abstract Tumor cells are able to evade cytotoxic therapies through the accumulation of genomic mutations and rapid evolution. In the case of oncolytic virotherapy, understanding the mechanisms by which cancer cells develop resistance to infection and lysis is critical to the development of more effective viral-based platforms. Here, we identify APOBEC3 as an important factor involved in the restriction of vesicular stomatitis virus (VSV). We show that VSV infection of B16 murine melanoma cells upregulated APOBEC3 in an IFNβ-dependent manner, which was responsible for the evolution of virus-resistanT-cell populations and suggested that APOBEC3 expression promoted the acquisition of a virus-resistant phenotype. ShRNA knockdown of APOBEC3 in B16 cells diminished their capacity to develop resistance to VSV infection in vitro, and enhanced the therapeutic effect of VSV in vivo. Similarly, overexpression of human APOBEC3B promoted the acquisition of resistance to oncolytic VSV in murine melanoma and glioblastoma lines, as well as in a human melanoma cell line in vitro and in vivo. Finally, we demonstrate that progeny virus obtained after passage through APOBEC3B overexpressing cells contained more defective interfering particles, thereby indicating that APOBEC3B directly affected the fitness of VSV, an RNA virus that has not previously been identified to be restricted by APOBEC3B. This research identifies APOBEC3 enzymes as key players to target in order to improve the efficacy of oncolytic viruses as well as broader nucleic acid-based therapeutic platforms. Citation Format: Amanda L. Huff, Phonphimon Wongthida, Timothy Kottke, Jill Thompson, Christopher B. Driscoll, Matthew Schuelke, Kevin G. Shim, Reuben S. Harris, Amy Molan, Jose S. Pulido, Peter J. Selby, Kevin J. Harrington, Alan Melcher, Laura Evgin, Richard Vile. APOBEC3 confers resistance to oncolytic VSV therapy [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A133.

Abstract Vitreoretinal lymphoma (VRL) management remains a challenge. We present 72 patients with VRL, diagnosed at Mayo Clinic between 1990‐2018. Three nondiffuse large B‐cell lymphoma (DLBCL) histology cases were excluded. Among 69 DLBCL, 33 patients had primary VRL (PVRL), 18 concurrent intraocular and central nervous system (CNS) or systemic disease and 18 secondary VRL. Patients received intraocular chemotherapy (intraocular injections of rituximab or metothrexate or steroids or in combination), radiotherapy, systemic or combined systemic plus intraocular treatment in 9, 10, 35, and 15 cases, respectively. Among primary and concurrent VRL, median failure free survival (FFS), CNS relapse‐free survival (CNS‐RFS) and overall survival (OS) were: 1.8, 4.9, and 4.1 years, respectively; among PVRL, median FFS, CNS‐RFS, and OS were: 2.6 year, Not Reached and 9.3 year, respectively. No CNS relapse occurred beyond 4 years in PVRL. Median OS for patients diagnosed between 1990 and 1999 vs between 2000 and 2018 was 1.5 vs 9.4 years, respectively ( P = .0002). OS was significantly higher in PVRL, as compared with concurrent VRL ( P = .04). Previous immunosuppression and poor performance status were predictive of worse outcome. In PVRL, a combined systemic and intraocular therapy showed higher FFS ( P = .002) and CNS‐RFS ( P = .003), but no differences in OS. Among 18 secondary VRL, at a median follow‐up of 1.1 year after vitreoretinal relapse, median FFS and OS were 0.3 and 1.3 years. An improvement in survival of VRL has been observed over the decades. PVRL should undergo combined systemic and intraocular chemotherapy to prevent CNS progression.

AbstractThe combination of pomalidomide (POM) and dexamethasone (DEX) was evaluated for relapsed/refractory primary central nervous system lymphoma (PCNSL) and primary vitreoretinal lymphoma (PVRL) to determine the maximal tolerated dose (MTD) of POM as the primary objective, and overall response rate (ORR), progression-free survival (PFS), and safety profile as secondary objectives. A cohorts-of-3 study design was used with a dose-escalation schedule consisting of POM (3, 5, 7, or 10 mg) orally daily for 21 days every 28 days and DEX 40 mg orally every week. After 2 cycles, POM was continued alone until disease progression, intolerance, or subject withdrawal. Following MTD determination, the MTD cohort was expanded. Twenty-five of 29 patients with the median of 3 prior treatments were eligible for assessment as per international PCNSL collaborative group criteria. The MTD of POM was 5 mg daily for 21 days every 28 days. Whole-study ORR was 48% (12 of 25; 95% confidence interval [CI], 27.8%, 68.7%) with 6 complete response (CR), 2 complete response, unconfirmed (CRu), and 4 partial response (PR). MTD cohort ORR was 50% (8 of 16; 95% CI, 24.7%, 75.4%) with 5 CR, 1 CRu, and 2 PR. Median PFS was 5.3 months (whole study) and 9 months (for responders). One patient had pseudoprogression. Grade 3/4 hematologic toxicities included neutropenia (21%), anemia (8%), and thrombocytopenia (8%). Grade 3/4 nonhematologic toxicities included lung infection (12%), sepsis (4%), fatigue (8%), syncope (4%), dyspnea (4%), hypoxia (4%), respiratory failure (8%), and rash (4%). POM/DEX treatment is feasible with significant therapeutic activity against relapsed/refractory PCNSL and PVRL. This trial was registered at www.clinicaltrials.gov as #NCT01722305.