Phase 1 trial of the anti-LAG3 antibody favezelimab plus pembrolizumab in advanced gastric cancer

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Background: In the dose-confirmation phase of this multicohort trial (NCT02720068), the anti-LAG-3 antibody favezelimab had a manageable safety profile and promising antitumor activity in patients (pts) with advanced solid tumors, confirming preliminary RP2D. Here we present results on the safety of favezelimab (fave) plus pembrolizumab (pembro) in all treated pts and efficacy in pts with advanced gastric cancer. Methods: In this phase 1b trial eligible pts aged ≥ 18 years were enrolled into 7 cohorts across 3 tumor types: Cohorts A (3L+ CRC), B (1L/2L CRC), C (PD-1 naïve HNSCC), D (PD-1 refractory HNSCC), E (PD-1 naïve gastric cancer), F (all solid tumors), and G (PD-1 naïve 3L CRC). Pts with gastric cancer in cohort E received either 200 mg fave + 200 mg pembro, or 700 mg fave + 200 mg pembro Q3W up to 35 cycles. Treatment continued until progression, unacceptable toxicity, or pt withdrawal. Primary endpoint was safety and tolerability of fave + pembro. Secondary endpoint was ORR per RECIST 1.1 by investigator assessment. Exploratory endpoints were PFS per RECIST 1.1, and OS. Data cutoff date was March 21, 2022. Results: At data cutoff, 397 pts were enrolled: 38 to fave, 368 to fave + pembro including 9 who crossed over from fave alone. Of these, 80 pts had gastric cancer; 50 (62.5%) of which had ≥2 lines of treatment, and 48 (60.0%) had PD-L1 CPS≥ 1. Among 368 pts treated with fave + pembro, treatment-related adverse events (TRAEs) occurred in 232 (63.0%) with fave + pembro. Grade ≥3 TRAEs occurred in 66 (17.9%) pts with fave + pembro. There were no grade 5 TRAEs. Immune-mediated adverse events (AEs) occurred in 121 (32.9%) pts with fave + pembro. Grade ≥3 immune-mediated AEs occurred in 27 (7.3%) pts with fave + pembro. No grade 5 immune-mediated AEs occurred. In pts with gastric cancer, the overall ORR was 11.3% (95% CI, 5.3-20.3 [3.8% CR; 7.5% PR]) with fave + pembro. In 2 arms, higher dose of fave (700mg) showed increased ORR and 12 months PFS rate. The table summarizes antitumor activity in the gastric cancer cohort. Conclusions: Favezelimab alone or in combination with pembrolizumab had an acceptable safety profile. The combination therapy showed antitumor activity in line with other checkpoint inhibitors in advanced gastric cancer though higher antitumor activity was seen in PDL1 CPS≥ 1 tumors, particularly at higher dose. Clinical trial information: NCT02720068 . [Table: see text]

Preclinical characterization and clinical translation of pharmacodynamic markers for MK-5890: a human CD27 activating antibody for cancer immunotherapy

Background

Immune checkpoint inhibitors (ICI) have radically changed cancer therapy, but most patients with cancer are unresponsive or relapse after treatment. MK-5890 is a CD27 agonist antibody intended to complement ICI therapy. CD27 is a member of the tumor necrosis factor receptor superfamily that plays a critical role in promoting responses of T cells, B cells and NK cells.

Methods

Anti-CD27 antibodies were generated and selected for agonist activity using NF-кB luciferase reporter assays. Antibodies were humanized and characterized for agonism using in vitro T-cell proliferation assays. The epitope recognized on CD27 by MK-5890 was established by X-ray crystallography. Anti-tumor activity was evaluated in a human CD27 knock-in mouse. Preclinical safety was tested in rhesus monkeys. Pharmacodynamic properties were examined in mouse, rhesus monkeys and a phase 1 dose escalation clinical study in patients with cancer.

Results

Humanized anti-CD27 antibody MK-5890 (hIgG1) was shown to bind human CD27 on the cell surface with sub-nanomolar potency and to partially block binding to its ligand, CD70. Crystallization studies revealed that MK-5890 binds to a unique epitope in the cysteine-rich domain 1 (CRD1). MK-5890 activated CD27 expressed on 293T NF-κB luciferase reporter cells and, conditional on CD3 stimulation, in purified CD8+ T cells without the requirement of crosslinking. Functional Fc-receptor interaction was required to activate CD8+ T cells in an ex vivo tumor explant system and to induce antitumor efficacy in syngeneic murine subcutaneous tumor models. MK-5890 had monotherapy efficacy in these models and enhanced efficacy of PD-1 blockade. MK-5890 reduced in an isotype-dependent and dose-dependent manner circulating, but not tumor-infiltrating T-cell numbers in these mouse models. In rhesus monkey and human patients, reduction in circulating T cells was transient and less pronounced than in mouse. MK-5890 induced transient elevation of chemokines MCP-1, MIP-1α, and MIP-1β in the serum of mice, rhesus monkeys and patients with cancer. MK-5890 was well tolerated in rhesus monkeys and systemic exposure to MK-5890 was associated with CD27 occupancy at all doses.

Conclusions

MK-5890 is a novel CD27 agonistic antibody with the potential to complement the activity of PD-1 checkpoint inhibition in cancer immunotherapy and is currently undergoing clinical evaluation.

Introducing a new reporter gene, membrane-anchored Cypridina luciferase, for multiplex bioluminescence imaging

Bioluminescence reporter gene imaging is a robust, high-throughput imaging modality that is useful for tracking cells and monitoring biological processes, both in cell culture and in small animals. We introduced and characterized a novel bioluminescence reporter—membrane-anchored Cypridina luciferase (maCLuc)—paired with a unique vargulin substrate. This luciferase-substrate pair has no cross-reactivity with established d-luciferin- or coelenterazine-based luciferase reporters. We compare maCLuc with several established luciferase-based reporter systems (firefly, click beetle, Renilla, and Gaussia luciferases), using both in vitro and in vivo models. We demonstrate the different imaging characteristics of these reporter systems, which allow for multiplexed-luciferase imaging of 3 and 4 separate targets concurrently in the same animal within 24 h. The imaging paradigms described here can be directly applied for simultaneous in vivo monitoring of multiple cell populations, the activity of selected signal transduction pathways, or a combination of both constitutive and inducible reporter imaging.

Phase I Study of MK-4166, an Anti-human Glucocorticoid-Induced TNF Receptor Antibody, Alone or with Pembrolizumab in Advanced Solid Tumors

PURPOSE

In this first-in-human phase I study (NCT02132754), we explored MK-4166 [humanized IgG1 agonist mAb targeting glucocorticoid-induced TNF receptor (GITR)] with and without pembrolizumab in advanced solid tumors.

PATIENTS AND METHODS

MK-4166 was tested alone (0.0015-900 mg i.v. every 3 weeks for four doses) or with pembrolizumab (200 mg i.v. every 3 weeks for ≤35 doses) in patients with metastatic solid tumors (dose escalation/confirmation) and advanced melanoma (expansion). Primary objectives were to evaluate the safety and tolerability and establish the MTD of MK-4166. Exploratory endpoints were objective response rate (ORR) and T cell-inflamed gene expression profile (GEP) analysis using RNA from baseline tumor samples.

RESULTS

A total of 113 patients were enrolled [monotherapy, n = 48; combination therapy, n = 65 (20 in the expansion)]. Forty-six patients (40.7%) had grade ≥3 adverse events, 9 (8.0%) of which were treatment related. No treatment-related deaths were observed. One dose-limiting toxicity event with monotherapy (bladder perforation in patient with neobladder) was considered related to study drug. MTD was not reached. MK-4166 pharmacodynamics showed decreased GITR availability on circulating T cells with increasing doses. One objective response (ORR, 2.2%) was achieved with combination therapy in the dose escalation/confirmation (n = 45). In the expansion, 8 of 13 patients with immune checkpoint inhibitor (ICI)-naïve melanoma achieved a response (ORR, 62%; 95% confidence interval, 32-86; 5 complete responses and 3 partial responses). None of the ICI-pretreated patients (n = 7) responded. High response rates were observed in ICI-naïve patients irrespective of GEP status.

CONCLUSIONS

MK-4166 900 mg i.v. every 3 weeks as monotherapy and with pembrolizumab was tolerable. Responses were observed with combination therapy, mostly in patients with ICI-naïve melanoma.

First-in-human phase 1 study of MK-1248, an anti-glucocorticoid-induced tumor necrosis factor receptor agonist monoclonal antibody, as monotherapy or with pembrolizumab in patients with advanced solid tumors

BACKGROUND

Ligation of glucocorticoid-induced tumor necrosis factor receptor (GITR) decreases regulatory T cell-mediated suppression and enhances T-cell proliferation, effector function, and survival. MK-1248 is a humanized immunoglobulin G4 anti-GITR monoclonal antibody agonist.

METHODS

In patients with advanced solid tumors, MK-1248 (starting dose, 0.12 mg) was tested alone and with pembrolizumab (200 mg) according to a 3 + 3 dose escalation design (ClinicalTrials.gov identifier NCT02553499); both treatments were administered intravenously every 3 weeks for ≤4 and ≤35 cycles, respectively. The safety and tolerability, maximum tolerated dose, and pharmacokinetics/pharmacodynamics were explored.

RESULTS

Twenty patients received MK-1248 monotherapy; 17 received combination therapy. The most frequent tumor types were colorectal cancer (n = 8), melanoma (n = 6), and renal cell carcinoma (n = 4). MK-1248 was generally well tolerated at the maximum tested doses of 170 (monotherapy) and 60 mg (combination). No dose-limiting toxicities (DLTs) or treatment-related deaths occurred. Adverse events (AEs) occurred in 36 of the 37 patients (97%); the most common were vomiting (n = 13 [35%]), anemia (n = 10 [27%]), and decreased appetite (n = 10 [27%]). Grade 3 to 5 AEs occurred in 19 of the 37 patients (51%). Treatment-related AEs occurred in 18 of the 37 patients (49%): 9 of the 20 patients (45%) on monotherapy and 9 of the 17 patients (53%) on combination therapy. Among the 17 patients receiving combination therapy, 1 achieved a complete response and 2 achieved a partial response, for an objective response rate of 18%; no patients achieved an objective response with monotherapy. The disease control rate (stable disease or better) was 15% with monotherapy and 41% with combination therapy.

CONCLUSIONS

MK-1248 was generally well tolerated at doses up to 170 (monotherapy) and 60 mg (combination), with no DLTs or treatment-related deaths. Combination therapy provided limited antitumor responses.

O83 Phase 1 study of an anti-CD27 agonist as monotherapy and in combination with pembrolizumab in patients with advanced solid tumors

Background

MK-5890 is a humanized agonist monoclonal antibody that binds to CD27 to provide a costimulatory signal that enhances T-cell–mediated responses. This first-in-human phase 1 study of MK-5890 evaluated the safety and efficacy of escalating doses of MK-5890 as monotherapy and in combination with pembrolizumab in patients with advanced solid tumors.

Methods

Key eligibility criteria included histologically or cytologically confirmed advanced solid tumor, measurable disease by RECIST v1.1, and ECOG PS ≤1. MK-5890 was tested alone (dose range, 2-700 mg) or with pembrolizumab (fixed dose, 200 mg). Patients with disease progression following MK-5890 monotherapy were eligible to cross over to combination treatment. The primary objective was safety and tolerability. Objective response rate by investigator per RECIST v1.1 was also evaluated. The database cutoff for this analysis was May 30, 2019.

Results

Of 44 patients enrolled, 25 received MK-5890 and 19 received MK-5890 plus pembrolizumab; their median age was 59.0 years, 61.4% were female, 47.7% had ECOG PS 1, and 13.6% previously received immune checkpoint inhibitor therapy. In the initial phase, dose-limiting toxicities (DLTs) were reported in 3 patients receiving MK-5890 and 1 patient receiving MK-5890 plus pembrolizumab; all DLTs were associated with infusion-related adverse events. Maximum tolerated dose was defined. Treatment-related adverse events (TRAEs) were reported in 40 patients (90.9%): 22 patients (88.0%) receiving MK-5890 and 18 patients (94.7%) receiving MK-5890 plus pembrolizumab. The most common TRAEs were fatigue (28.0%) and infusion-related reactions (28.0%) with MK-5890 and fatigue (36.8%) and pruritus (31.6%) with MK-5809 plus pembrolizumab. Grade 3-4 TRAEs were reported in 10 patients (22.7%): 6 patients (24.0%) receiving MK-5890 and 4 patients (21.1%) receiving MK-5890 plus pembrolizumab; no grade 5 events were observed. One patient (4.0%) achieved a partial response (PR) with MK-5890 and 1 patient (5.3%) achieved a PR with MK-5890 plus pembrolizumab. Fourteen patients entered the crossover phase to receive MK-5890 plus pembrolizumab. In the crossover phase, no DLTs were reported. TRAEs were reported in 12 patients (85.7%); the most common were pruritus (21.4%), rash (21.4%), and headache (14.3%). One patient (7.1%) reported grade 3-4 TRAEs of increased amylase and increased lipase; no grade 5 events were observed. Two patients (14.3%) achieved a complete response and 2 patients (14.3%) achieved a PR.

Conclusions

Treatment with MK-5890, alone and in combination with pembrolizumab, demonstrated an acceptable safety profile. Early antitumor activity was observed in patients with advanced solid tumors in both monotherapy and combination therapy arms.

Phase 1 study of MK-4166, an anti-human glucocorticoid-induced tumor necrosis factor receptor (GITR) antibody, as monotherapy or with pembrolizumab (pembro) in patients (pts) with advanced solid tumors

9509

Background: Ligation of GITR on immune cells decreases Treg-mediated suppression and enhances T cell proliferation. MK-4166 is a humanized IgG1 agonist monoclonal antibody targeting GITR. Data from the first-in-human phase 1 study (NCT02132754) of MK-4166 as monotherapy (mono) or in combination with pembro (combo) are presented. Methods: MK-4166 was tested alone (0.0015 mg IV-900 mg Q3W ×4 doses) or with pembro (fixed dose 200 mg IV Q3W up to 35 doses) in the absence of toxicity or progression. Study included a dose escalation/confirmation cohort (metastatic solid tumors) and an expansion cohort (treatment-naive and pretreated melanoma). A T cell–inflamed gene expression profile (GEP) was assessed using RNA from baseline tumor samples. End points – primary: safety/tolerability, maximum tolerated dose (MTD) of MK-4166; secondary: pharmacokinetics (PK), pharmacodynamics (PD); exploratory: objective response rate (ORR) per irRECIST1.1. Results: Of 113 pts, 48 received mono and 65 combo; 20 were in the melanoma expansion. Common AEs ( > 20%) were fatigue, infusion-related reaction, nausea, abdominal pain, and pruritus; 43 pts had grade ≥3 AEs (38.1%); 6 (5.3%) were treatment-related. One dose-limiting toxicity (bladder perforation in a urothelial pt with a neobladder) possibly related to study drug was observed with mono. MTD was not reached. No treatment-related deaths were observed. MK-4166 PK/PD showed target-mediated drug disposition concomitant with decreased GITR availability on T cells in blood with increasing doses. Four objective responses (4/45; ORR, 9%) were seen with combo in dose escalation. For ICI-naive melanoma pts (n = 13) in expansion, ORR was 69% (95% CI, 38-91), including 4 CRs and 5 PRs. No response was observed in 7 pts previously treated with ICI. High ORRs were observed in noninflamed and inflamed ICI-naive melanoma pts. Conclusions: MK-4166 at a dose up to 900 mg as monotherapy and in combination with pembro was well tolerated, with dose-related evidence of target engagement. Responses were observed with MK-4166 900 mg plus pembro, particularly in pts with melanoma naive to ICIs. Clinical trial information: NCT02132754.

Bispecific antibody does not induce T-cell death mediated by chimeric antigen receptor against disialoganglioside GD2

Chimeric antigen receptors (CAR) and bispecific antibodies (BsAb) are two powerful immunotherapy approaches for retargeting lymphocytes toward cancer cells. Despite their success in lymphoblastic leukemia, solid tumors have been more recalcitrant. Identifying therapeutic barriers facing CAR-modified (CART) or BsAb-redirected T (BsAb-T) cells should facilitate their clinical translation to solid tumors. Novel lentiviral vectors containing low-affinity or high-affinity 4-1BB second-generation anti-GD2 (disialoganglioside) CARs were built to achieve efficient T cell transduction. The humanized anti-GD2 × CD3 BsAb using the IgG-scFv platform was described previously. CART and BsAb-engaged T cells were tested for viability, proliferation, and activation/exhaustion marker expression, and in vitro cytotoxicity against GD2(+) tumor cells. The antitumor effect of CAR-grafted and BsAb-T cells was compared in a human melanoma xenograft model. The majority of high CAR density T cells were depleted upon exposure to GD2(+) target cells while the BsAb-T cells survived. The in vitro cytotoxicity of the surviving CART cells was inferior to that of the BsAb-T cells. Using low-affinity CARs, inclusion of the 4-1BB co-stimulatory domain or exclusion of a co-stimulatory domain, or blocking PD1 did not prevent CART cell depletion. Both CART cells and BsAb-T cells penetrated established subcutaneous human melanoma xenografts; while both induced tumor regression, BsAb was more efficient. The fate of T cells activated by BsAb differs substantially from that by CAR, translating into a more robust antitumor effect both in vitro and in vivo.

Oncotargets GD2 and GD3 are highly expressed in sarcomas of children, adolescents, and young adults

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/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, 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 to 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 patients with sarcoma, these gangliosides can be potential targets for antibody-based therapies.

GD2-targeted immunotherapy and radioimmunotherapy

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 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 antibodies, cytokines, cells, and genetically engineered products all directed at GD2 are rapidly moving into the clinic. In this review, past and present immunotherapy trials directed at GD2 will be summarized, highlighting the lessons learned and the future directions.

Malignant rhabdoid tumor of the liver presented with initial tumor rupture

Malignant rhabdoid tumor (MRT) of the liver is a rare, highly aggressive tumor of early childhood. We report a 6-month-old boy who was diagnosed with MRT of the liver and presented with spontaneous tumor rupture. The patient underwent intensified chemotherapy and a radical surgical procedure. Twenty four months from the time of the diagnosis, he is alive without evidence of disease. This is the second report of prolonged survival after initial rupture of hepatic MRT.

A new pyrimidine-specific reporter gene: a mutated human deoxycytidine kinase suitable for PET during treatment with acycloguanosine-based cytotoxic drugs

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 2'-deoxy-2'-fluoroarabinofuranosylcytosine, 2'-fluoro-2'-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.

PET imaging of HSV1-tk mutants with acquired specificity toward pyrimidine- and acycloguanosine-based radiotracers

PURPOSE

The aim of this study was to create an alternative mutant of the herpes simplex virus type 1 thymidine kinase (HSV1-tk) reporter gene with reduced phosphorylation capacity for acycloguanosine derivatives, but not pyrimidine-based compounds that will allow for successful PET imaging.

METHODS

A new mutant of HSV1-tk reporter gene, suitable for PET imaging using pyrimidine-based radiotracers, was developed. The HSV1-tk mutant contains an arginine-to-glutamine substitution at position 176 (HSV1-R176Qtk) of the nucleoside binding region of the enzyme.

RESULTS

The mutant-gene product showed favorable enzymatic characteristics toward pyrimidine-based nucleosides, while exhibiting reduced activity with acycloguanosine derivatives. In order to enhance HSV1-R176Qtk reporter activity with pyrimidine-based radiotracers, we introduced the R176Q substitution into the more active HSV1-sr39tk mutant. U87 human glioma cells transduced with the HSV1-R176Qsr39tk double mutant reporter gene showed high (3)H-FEAU pyrimidine nucleoside and low (3)H-penciclovir acycloguanosine analog uptake in vitro. PET imaging also demonstrated high (18)F-FEAU and low (18)F-FHBG accumulation in HSV1-R176Qsr39tk+ xenografts. The feasibility of imaging two independent nucleoside-specific HSV1-tk mutants in the same animal with PET was demonstrated. Two opposite xenografts expressing the HSV1-R176Qsr39tk reporter gene and the previously described acycloguanosine-specific mutant of HSV1-tk, HSV1-A167Ysr39tk reporter gene, were imaged using a short-lived pyrimidine-based (18)F-FEAU and an acycloguanosine-based (18)F-FHBG radiotracer, respectively, administered on 2 consecutive days.

CONCLUSION

We conclude that in combination with acycloguanosine-specific HSV1-A167Ysr39tk reporter gene, a HSV1-tk mutant containing the R176Q substitution could be used for PET imaging of two different cell populations or concurrent molecular biological processes in the same living subject.

Monitoring the efficacy of adoptively transferred prostate cancer-targeted human T lymphocytes with PET and bioluminescence imaging

Noninvasive imaging technologies have the potential to enhance the monitoring and improvement of adoptive therapy with tumor-targeted 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 prostate-specific 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 2'-(18)F-fluoro-2'-deoxy-1-beta-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.

A new acycloguanosine-specific supermutant of herpes simplex virus type 1 thymidine kinase suitable for PET imaging and suicide gene therapy for potential use in patients treated with pyrimidine-based cytotoxic drugs

The herpes simplex virus type 1 thymidine kinase (HSV1-tk) gene is widely used as a suicide gene in combination with ganciclovir (GCV) and as a nuclear imaging reporter gene with an appropriate reporter probe. Wild-type HSV1-tk recognizes a variety of pyrimidine and acycloguanosine nucleoside analogs, including clinically used antiviral drugs. PET of HSV1-tk reporter gene expression will be compromised in patients receiving nucleoside-based antiviral treatment. With the use of an acycloguanosine-specific mutant of the enzyme, PET of HSV1-tk reporter gene expression can be successfully performed with acycloguanosine-based radiotracers without interference from pyrimidine-based antiviral drugs.

METHODS

The levels of expression of wild-type HSV1-tk and HSV1-A167Ytk, HSV1-sr39tk, and HSV1-A167Ysr39tk mutants fused with green fluorescent protein (GFP) and transduced into U87 cells were normalized to the mean fluorescence of GFP measured by fluorescence-activated cell sorting. The levels of enzymatic activities of wild-type HSV1-tk and its mutants were compared by 2-h in vitro radiotracer uptake assays with (3)H-2'-fluoro-2'-deoxy-1-beta-d-arabinofuranosyl-5-ethyluracil ((3)H-FEAU), (3)H-pencyclovir ((3)H-PCV), and (3)H-GCV and by drug sensitivity assays. PET with (18)F-FEAU and (18)F-9-[4-fluoro-3-(hydroxymethyl)butyl]guanine ((18)F-FHBG) was performed in mice with established subcutaneous tumors, expressing wild-type HSV1-tk and its mutants, followed by tissue sampling.

RESULTS

FEAU accumulation was not detected in HSV1-A167Ysr39tk-expressing cells and xenografts. Lack of conversion of pyrimidine derivatives by the HSV1-A167Ysr39tk supermutant was also confirmed by a drug sensitivity assay, in which the 50% inhibitory concentrations for thymine 1-beta-d-arabinofuranoside and bromovinyldeoxyuridine were found to be similar to those in nontransduced cells. In contrast, we found that HSV1-A167Ysr39tk could readily phosphorylate (3)H-GCV at levels similar to those of wild-type HSV1-tk and HSV1-A167Ytk but showed enhanced activity with (3)H-PCV in vitro and with (18)F-FHBG in vivo.

CONCLUSION

We developed a new reporter gene, HSV1-A167Ysr39tk, which exhibits specificity and high phosphorylation activity for acycloguanosine derivatives. The resulting supermutant can be used for PET with (18)F-FHBG and suicidal gene therapy protocols with GCV in patients treated with pyrimidine-based cytotoxic drugs.

Tumor-draining lymph nodes of primary lung cancer patients: a potent source of tumor-specific killer cells and dendritic cells

BACKGROUND

The tumor-draining lymph node tissue (TDLT) of lung cancer patients generated killer cells specific to autologous tumor cells when cultured with low dose IL-2. This production of killer cells lasted as long as 2 months after the initiation of the culture (productive phase). Even after this productive phase, TDLT supported the generation of the killer cells when these were co-cultured with peripheral blood lymphocytes (PBL) from the same patients. We tried to analyze the mechanisms of this production of killer cells from TDLT.

MATERIALS AND METHODS

TDLT, tumor tissues as well as PBL were obtained from primary lung cancer patients and cultured in vitro. Cell growth, cell surface markers and specific cytotoxic activity of the lymphocytes were examined.

RESULTS

The majority of the cells from TDLT or TDLT+ PBL co-culture (TDL-Pb) were CD3-positive T cells (89-99%) and a 51Cr-releasing assay showed that these cells had a stronger cytotoxic activity against autologous tumor cells than cells from PBL cultured with IL-2. Their activity against allogeneic MHC incompatible target cells was not, however, elevated. Cytotoxic activity against autologous tumor cells was blocked by anti-HLA class 1 (52.0%), class 11 (47.9%) and CD8 (46.8%) antibodies, but not by anti-CD56 antibody. The treatment of TDLT with anti-CD8, CD4, CD80 and CD83 all together completely abrogated the ability of TDLT to generate killer cells, with one of these antibodies it did so partially, while treatment with anti-CD56 antibody failed to do so at all.

CONCLUSION

These results collectively suggest that TDLT contains tumor antigen-pulsed DCs as well as precursors of specific killer T cells and gives rise to the generation of killer cells when cultured in a low dose of IL-2.