To reject tumors, T cells must overcome poor tumor immunogenicity and an adverse tumor microenvironment. Providing agonistic costimulatory signals to tumor-infiltrating T cells to augment T cell function remains a challenge for the implementation of safe and effective immunotherapy. We hypothesized that T cells overexpressing selected costimulatory ligands could serve as cellular vehicles mediating powerful, yet constrained, anatomically targeted costimulation. Here, we show that primary human T cells expressing CD80 and 4-1BB ligand (4-1BBL) vigorously respond to tumor cells lacking costimulatory ligands and provoke potent rejection of large, systemic tumors in immunodeficient mice. In addition to showing costimulation of bystander T cells (transcostimulation), we show the effect of CD80 and 4-1BBL binding to their respective receptors in the immunological synapse of isolated single cells (autocostimulation). This new strategy of endowing T cells with constitutively expressed costimulatory ligands could be extended to other ligand-receptor pairs and used to enhance any targeted adoptive transfer therapy.

Background GD2 and GD3 are the tumor-associated glycolipid antigens found in a broad spectrum of human cancers. GD2-specific antibody is currently a standard of care for high risk neuroblastoma therapy. In this study, the pattern of GD2 and GD3 expression among pediatric/AYA (adolescent or young adult) tumors was determined, providing companion diagnostics for targeted therapy. Methods Ninety-two specimens of human osteosarcoma (OS), rhabdomyosarcoma (RMS), Ewing family of tumors (EFT), desmoplastic small round cell tumor (DSRCT) and melanoma were analyzed for GD2/GD3 expression by immunohistochemistry. Murine monoclonal antibody 3F8 was used for GD2 staining, and R24 for GD3. Staining was scored according to both intensity and percentage of positive tumor cells from 0 to 4. Results Both gangliosides were highly prevalent in OS and melanoma. Among other tumors, GD3 expression was higher than GD2 expression. Most OS samples demonstrated strong staining for GD2 and GD3, whereas expression for other tumors was highly variable. Mean intensity of GD2 expression was significantly more heterogeneous (p<0.001) when compared with GD3 across tumor types. When assessing the difference between GD2 and GD3 expression in all tumor types combined, GD3 expression had a significantly higher score (p=0.049). When analyzed within each cancer, GD3 expression was significantly higher only in DSRCT (p=0.002). There was no statistical difference in either GD2 or GD3 expression between primary and recurrent sarcomas. Conclusion GD2/GD3 expression among pediatric solid tumors is common, albeit with variable level of expression. Especially for sarcoma patients, these gangliosides can be potential targets for antibody based therapies.

Ganglioside GD2 is a tumor-associated surface antigen found in a broad spectrum of human cancers and stem cells. They include pediatric embryonal tumors (neuroblastoma, retinoblastoma, brain tumors, osteosarcoma, Ewing’s sarcoma, rhabdomyosarcoma), as well as adult cancers (small cell lung cancer, melanoma, soft tissue sarcomas). Because of its restricted normal tissue distribution, GD2 has been proven safe for antibody targeting. Anti-GD2 antibody is now incorporated into the standard of care for the treatment of high risk metastatic neuroblastoma. Building on this experience, novel combinations of antibody, cytokines, cells and genetically engineered products all directed at GD2 are rapidly moving into the clinic. In the review, past and present immunotherapy trials directed at GD2 will be summarized, highlighting the lessons learned and the future directions.

Noninvasive imaging technologies have the potential to enhance the monitoring and improvement of adoptive therapy with tumortargeted T lymphocytes. We established an imaging methodology for the assessment of spatial and temporal distributions of adoptively transferred genetically modified human T cells in vivo for treatment monitoring and prediction of tumor response in a systemic prostate cancer model. Methods: RM1 murine prostate carcinoma tumors transduced with human prostatespecific membrane antigen (hPSMA) and a Renilla luciferase reporter gene were established in SCID/beige mice. Human T lymphocytes were transduced with chimeric antigen receptors (CAR) specific for either hPSMA or human carcinoembryonic antigen (hCEA) and with a fusion reporter gene for herpes simplex virus type 1 thymidine kinase (HSV1tk) and green fluorescent protein, with or without click beetle red luciferase. The localization of adoptively transferred T cells in tumor-bearing mice was monitored with 29-18 F-fluoro-29-deoxy-1-b-D-arabinofuranosyl-5-ethyluracil ( 18 F-FEAU) small-animal PET and bioluminescence imaging (BLI). Results: Cotransduction of CAR-expressing T cells with the reporter gene did not affect CAR-mediated cytotoxicity. BLI of Renilla and click beetle red luciferase expression enabled concurrent imaging of adoptively transferred T cells and systemic tumors in the same animal. hPSMA-specific T lymphocytes persisted longer than control hCEA-targeted T cells in lung hPSMA-positive tumors, as indicated by both PET and BLI. Precise quantification of T-cell distributions at tumor sites by PET revealed that delayed tumor progression was positively correlated with the levels of 18 F-FEAU accumulation in tumor foci in treated animals. Conclusion: Quantitative noninvasive monitoring of genetically engineered human T lymphocytes by PET provides spatial and temporal information on T-cell trafficking and persistence. PET may be useful for predicting tumor response and for guiding adoptive T-cell therapy.

In this article, we describe a series of new human-derived reporter genes based on human deoxycytidine kinase (dCK) suitable for clinical PET. Methods: Native dCK and its mutant reporter genes were tested in vitro and in vivo for their phosphorylation of pyrimidine-and acycloguanosine-based radiotracers including 29-deoxy-29-fluoroarabinofuranosylcytosine, 29-fluoro-29-deoxyarabinofuranosyl-5-ethyluracil (FEAU), penciclovir, and 9-[4-fluoro-3-(hydroxymethyl)butyl]guanine (FHBG) and clinically applied antiviral and anticancer drugs. Results: Cells transduced with dCK mutant reporter genes showed high in vitro and in vivo uptake of pyrimidine-based radiopharmaceuticals ( 18 F-FEAU) comparable to that of herpes simplex virus type-1 thymidine kinase (HSV1-tk)-transduced cells. These mutants did not phosphorylate acycloguanosine-based radiotracers ( 18 F-FHBG) or antiviral drugs (ganciclovir). Furthermore, the mutants displayed suicidal activation of clinically used pyrimidine-based prodrugs (cytarabine, gemcitabine). Conclusion: The mutants of human dCK can be used as pyrimidine-specific PET reporter genes for imaging with 18 F-FEAU during treatment with acycloguanosine-based antiviral drugs. Additionally, the prosuicidal activity of these reporters with pyrimidine-based analogs will allow for the safe elimination of transduced cells. (11)(12)(13). Furthermore, administration of ganciclovir, which is routinely used for antiviral therapy in immunocompromised patients who have received bone marrow (stem cell) transplants, will eliminate the adoptively transferred stem cells or lymphocytes transduced with the HSV1-tk reporter gene. To address this latter concern, we recently assessed a mutant of HSV1-tk bearing an arginine-to-glutamine substitution at position 176 that showed reduced phosphorylation activity toward acyclo-