Hepatocellular carcinoma (HCC) is the fourth most common cause of cancer-related death in the world, and curative systemic therapies are lacking. Chimeric antigen receptor (CAR)-expressing T cells induce robust antitumor responses in patients with hematologic malignancies but have limited efficacy in patients with solid tumors, including HCC. IL15 and IL21 promote T-cell expansion, survival, and function and can improve the antitumor properties of T cells. We explored whether transgenic expression of IL15 and/or IL21 enhanced glypican-3-CAR (GPC3-CAR) T cells' antitumor properties against HCC. We previously optimized the costimulation in GPC3-CARs and selected a second-generation GPC3-CAR incorporating a 4-1BB costimulatory endodomain (GBBz) for development. Here, we generated constructs encoding IL15, IL21, or both with GBBz (15.GBBz, 21.GBBz, and 21.15.GBBz, respec-tively) and examined the ability of transduced T cells to kill, produce effector cytokines, and expand in an antigen-dependent manner. We performed gene-expression and phenotypic analyses of GPC3-CAR T cells and CRISPR-Cas9 knockout of the TCF7 gene. Finally, we measured GPC3-CAR T-cell antitumor activity in murine xenograft models of GPC3 þ tumors. The increased proliferation of 21.15.GBBz T cells was at least in part dependent on the upregulation and maintenance of TCF-1 (encoded by TCF7) and associated with a higher percentage of stem cell memory and central memory populations after manufacturing. T cells expressing 21.15. GBBz had superior in vitro and in vivo expansion and persistence, and the most robust antitumor activity in vivo. These results provided preclinical evidence to support the clinical evaluation of 21.15.GPC3-CAR T cells in patients with HCC.

ABSTRACT:Mannheimia haemolytica consistently causes severe bronchopneumonia and rapid death of bighorn sheep (Ovis canadensis) under experimental conditions. However, Bibersteinia trehalosi and Pasteurella multocida have been isolated from pneumonic bighorn lung tissues more frequently than M. haemolytica by culture-based methods. We hypothesized that assays more sensitive than culture would detect M. haemolytica in pneumonic lung tissues more accurately. Therefore, our first objective was to develop a PCR assay specific for M. haemolytica and use it to determine if this organism was present in the pneumonic lungs of bighorns during the 2009-2010 outbreaks in Montana, Nevada, and Washington, USA. Mannheimia haemolytica was detected by the species-specific PCR assay in 77% of archived pneumonic lung tissues that were negative by culture. Leukotoxin-negative M. haemolytica does not cause fatal pneumonia in bighorns. Therefore, our second objective was to determine if the leukotoxin gene was also present in the lung tissues as a means of determining the leukotoxicity of M. haemolytica that were present in the lungs. The leukotoxin-specific PCR assay detected leukotoxin gene in 91% of lung tissues that were negative for M. haemolytica by culture. Mycoplasma ovipneumoniae, an organism associated with bighorn pneumonia, was detected in 65% of pneumonic bighorn lung tissues by PCR or culture. A PCR assessment of distribution of these pathogens in the nasopharynx of healthy bighorns from populations that did not experience an all-age die-off in the past 20 yr revealed that M. ovipneumoniae was present in 31% of the animals whereas leukotoxin-positive M. haemolytica was present in only 4%. Taken together, these results indicate that culture-based methods are not reliable for detection of M. haemolytica and that leukotoxin-positive M. haemolytica was a predominant etiologic agent of the pneumonia outbreaks of 2009-2010.

Bibersteinia trehalosi and Mannheimia haemolytica, originally classified as Pasteurella haemolytica biotype T and biotype A, respectively, under Genus Pasteurella has now been placed under two different Genera, Bibersteinia and Mannheimia, based on DNA-DNA hybridization and 16S RNA studies. While M. haemolytica has been the predominant pathogen of pneumonia in ruminants, B. trehalosi is emerging as an important pathogen of ruminant pneumonia. Leukotoxin is the critical virulence factor of these two pathogens. While the leukotoxin of M. haemolytica has been well studied, the characterization of B. trehalosi leukotoxin has lagged behind. As the first step towards addressing this problem, we developed monoclonal antibodies (mAbs) against B. trehalosi leukotoxin and used them to characterize the leukotoxin epitopes. Two mAbs that recognized sequential epitopes on the leukotoxin were developed. One of them, AM113, neutralized B. trehalosi leukotoxin while the other, AM321, did not. The mAb AM113 revealed the existence of a neutralizing epitope on B. trehalosi leukotoxin that is not present on M. haemolytica leukotoxin. A previously developed mAb, MM601, revealed the presence of a neutralizing epitope on M. haemolytica leukotoxin that is not present on B. trehalosi leukotoxin. The mAb AM321 recognized a non-neutralizing epitope shared by the leukotoxins of B. trehalosi and M. haemolytica. The mAb AM113 should pave the way for mapping the leukotoxin-neutralizing epitope on B. trehalosi leukotoxin and the development of subunit vaccines and/or virus-vectored vaccines against this economically important respiratory pathogen of ruminants.

TPS2647 Background: CAR T therapies have been successful against hematologic malignancies, but have benefited only a handful of patients with solid cancers. Glypican 3 (GPC3) is an attractive immunotherapeutic target due to its preferential expression on multiple pediatric and adult solid cancers and lack of expression on non-malignant tissues. GPC3-CAR T cells were tested preclinically and inclusion of the 4-1BB costimulatory endodomain with IL-15 and IL-21 co-expression enabled CAR T cells to expand and persist the most in vitro and in vivo and led to robust antitumor activity in vivo. We are now testing GPC3-CAR T cells with IL15 and IL-21 for the first time in children with relapsed/refractory liver tumors. Methods: In this Phase 1 trial (GAP, NCT02932956), we are evaluating patients in 3 cohorts: 1) GPC3-CAR alone; 2) GPC3-CAR and IL-15; 3) GPC3-CAR with IL-15 and IL-21. We will 1) define the safety and establish the Recommended Phase 2 Dose (RP2D) of GPC3-CAR T cells co-expressing IL-15 and IL-21; 2) determine persistence and anti-tumor activity of GPC3-CAR T cells; 3) examine changes in gene and protein expression in the tumor microenvironment associated with potential immune escape mechanisms. Inclusion criteria are the following: age ≤18; histology proven, GPC3-positive tumor; life expectancy>12 weeks; Child-Pugh-Turcotte score<7; serum AST<5 times ULN; total bilirubin<3 times ULN for age; INR ≤1.7; absolute neutrophil count>500/μl; platelet count>20,000/μl; Hgb≥9.0 g/dl. Toxicity will be monitored using the Common Terminology Criteria of Adverse Events v4. The RP2D will be determined by the standard 3+3 dose escalation method using 5 dose levels. Persistence will be quantified using RT-PCR and flow cytometry. Antitumor activity will be defined by 3D imaging using RECIST 1.1 criteria and the immune-related response criteria. Immune-escape will be examined using single cell RNA sequencing and imaging of paraffin-embedded tissues using codetection by indexing to evaluate candidate proteins. Data will be analyzed via descriptive statistics. Cohort 1 of this study is now open for enrollment. Clinical trial information: NCT02932956.