Geometric parameters that affect the behavior of logic-gated CAR T cells

Clinical applications of CAR-T cells are limited by the scarcity of tumor-specific targets and are often afflicted with the same on-target/off-tumor toxicities that plague other cancer treatments. A new promising strategy to enforce tumor selectivity is the use of logic-gated, two-receptor systems. One well-described application is termed Tmod™, which originally utilized a blocking inhibitory receptor directed towards HLA-I target antigens to create a protective NOT gate. Here we show that the function of Tmod blockers targeting non-HLA-I antigens is dependent on the height of the blocker antigen and is generally compatible with small, membrane-proximal targets. We compensate for this apparent limitation by incorporating modular hinge units to artificially extend or retract the ligand-binding domains relative to the effector cell surface, thereby modulating Tmod activator and blocker function. By accounting for structural differences between activator and blocker targets, we developed a set of simple geometric parameters for Tmod receptor design that enables targeting of blocker antigens beyond HLA-I, thereby broadening the applications of logic-gated cell therapies.

122 A powerful, precise targeting system controlled by tumor deletions transforms CEA and MSLN CAR-T cells into tumor-selective agents

Background

Mesothelin (MSLN) and carcinoembryonic antigen (CEA) are classic tumor-associated antigens that are expressed in many solid tumors including the majority of lung, colorectal and pancreatic cancers. However, both MSLN and CEA are also expressed in vital normal organs. This normal expression creates risk of serious inflammation for CEA- or MSLN-directed therapeutics. To date all active CEA- or MSLN-targeted investigational therapeutics have been toxic when administered systemically.

Methods

We have developed a safety mechanism to protect normal tissues without abrogating sensitivity of cytotoxic T cells directed at MLSN(+) or CEA(+) tumors in a subset of patients with defined loss of heterozygosity (LOH) in their tumors (figure 1). This dual-receptor (Tmod< sup >TM</sup >) system exploits common LOH at the HLA locus in cancer cells, allowing T cells to recognize the difference between tumor and normal tissue.1 2 T cells engineered with specific Tmod constructs contain: (i) a MSLN- or CEA-activated CAR; and, (ii) an inhibitory receptor gated by HLA-A*02. HLA-A*02 binding blocks T cell cytotoxicity, even in the presence of MSLN or CEA. The Tmod system is designed to treat heterozygous HLA class I patients, selected for HLA LOH. When HLA-A*02 is absent from tumors selected for LOH, the CARs are predicted to mediate potent killing of the A*02(-) malignant cells.

Results

The Tmod system robustly protects surrogate normal cells even in mixed-cell populations in vitro while mediating robust cytotoxicity of tumor cells in xenograft models (see example in figure 2). The MSLN CAR can also be paired with other blockers, supporting scalability of the approach to patients beyond HLA-A*02 heterozygotes.

Abstract 122 Figure 1

Illustration of the Tmod T cell engaging with tumor cells with somatic loss of HLA-A*02 and with normal cells.

Abstract 122 Figure 2

Bioluminescence measurements show the average difference between the size of the MSLN(+)A*02(+) ‘normal’ graft compared to the MSLN(+)A*02(-) tumor graft on the two flanks of mice after T cell infusion. Both tumor and normal grafts are destroyed by CAR-Ts (CAR-3 and M5 benchmark) while the MSLN Tmod cells kill the tumor but not the normal graft.

Conclusions

The Tmod mechanism may provide an alternative route to leverage solid-tumor antigens such as MSLN and CEA in safer, more effective ways than previously possible.

References

Hamburger AE, DiAndreth B, Cui J, et al. Engineered T cells directed at tumors with defined allelic loss. Mol Immunol 2020;128:298–310.

Hwang MS, Mog BJ, Douglass J, et al. Targeting loss of heterozygosity for cancer-specific immunotherapy. Proc Natl Acad Sci U S A 2021;118(12):e2022410118.

HLA-A*02:01-directed chimeric antigen receptor/forkhead box P3-engineered CD4+ T cells adopt a regulatory phenotype and suppress established graft-versus-host disease

BACKGROUND AIMS

To investigate the feasibility of using CD4 + T cells genetically modified to express an allo-HLA directed CAR and FOXP3 to suppress T cell proliferation and cytokine secretion in GvHD.

METHODS

Human CD4+ T cells from A*02:01 negative donors were transduced to express A*02 CAR and FOXP3 and co-cultured in mixed lymphocyte reaction assays to demonstrate T cell suppression. A*02- CAR/FOXP CD4+ T cells were then injected into mice engrafted with allogeneic T cells in a GvHD mouse model.

RESULTS

CD4+ T cells genetically modified to express allo-HLA-directed CAR and FOXP3 proliferate rapidly, downregulate CD127 and interferon-γ, express high CD25 and Helios and convert to a stable antigen-dependent suppressive phenotype. In mixed lymphocyte reaction assays, these cells potently suppressed T-cell proliferation and secreted IL-10. In a graft-versus-host disease model, A*02-CAR/FOXP3 CD4+ T cells outperformed polyclonal Tregs by reducing liver and lung inflammation, inhibiting pro-inflammatory cytokine production and limiting grafted CD3+ T-cell expansion.

CONCLUSIONS

CD4 + T cells expressing allo-antigen directed HLA-specific CAR and FOXP3 act as potent, specific and stable suppressors of inflammation that out-perform their Treg counterparts both in vitro and in vivo.

115 Engineered T cells directed at tumors with defined allelic loss

Background

Cell therapy, with all its promise as a powerful solid-tumor modality, is still hampered by the fundamental obstacle of cancer therapy: the acute shortage of truly tumor-specific targets. It is well known that an average tumor contains loss of heterozygosity (LOH) at an astonishing frequency: ~20% genome wide. These losses are irreversible and absolutely distinguish the cancer from normal cells.

Methods

We describe a novel approach to cancer immunotherapy that draws on LOH as a large, so far untapped source of cancer targets. To exploit such allelic losses, we focus on polymorphic loci and target the remaining allelic product of a locus that has LOH. We engineer T cells with a modular signal-integration circuit designed to be activated only by tumor cells that have lost expression of one specific allele on their surface.

Results

We use the HLA locus which undergoes LOH at a frequency of 13%, and the HLA-A*02 allele specifically, as proof of concept. We present a large body of quantitative in vitro data, along with in vivo data, that support the use of a synthetic signal-integration circuit called Tmod as a cancer therapy. We also describe Tmod’s mechanistic properties, including thorough structure/function analysis of its components.

Conclusions

LOH is a rich source of new targets, provided a system of sufficient power can be devised to exploit them. Our Tmod signal integration system confers on engineered T cells the capacity to discriminate effectively between normal and tumor cells that contain specific allelic losses.

Ethics Approval

The animal study was approved by Explora BioLabs’ Ethics Board, protocol number EB17-010-059

Creation of a High-Yield AAV Vector Production Platform in Suspension Cells Using a Design-of-Experiment Approach

Recombinant adeno-associated virus (rAAV) vectors are a leading gene delivery platform, but vector manufacturing remains a challenge. New methods are needed to increase rAAV yields and reduce costs. Past efforts to improve rAAV production have focused on optimizing a single variable at a time, but this approach does not account for the interactions of multiple factors that contribute to vector generation. Here, we utilized a design-of-experiment (DOE) methodology to optimize rAAV production in a HEK293T suspension cell system. We simultaneously varied the transgene, packaging, and helper plasmid ratios, the total DNA concentration, and the cell density to systematically evaluate the impact of each variable across 52 conditions. The results revealed a unique set of parameters with a lower concentration of transgene plasmid, a higher concentration of packaging plasmid, and a higher cell density than previously described protocols. Using this DOE-optimized protocol, we achieved unpurified yields approaching 3 × 10¹⁴ viral genomes (VGs)/L of cell culture. Additionally, we incorporated polyethylene glycol (PEG)-based virus precipitation, pH-mediated protein removal, and affinity chromatography to our downstream processing, enabling average purified yields of >1 × 10¹⁴ VGs/L for rAAV-EGFPs across 13 serotypes and capsid variants.

Engineered IL-21 Cytokine Muteins Fused to Anti-PD-1 Antibodies Can Improve CD8+ T Cell Function and Anti-tumor Immunity

Inhibitors that block the programmed cell death-1 (PD-1) pathway can potentiate endogenous antitumor immunity and have markedly improved cancer survival rates across a broad range of indications. However, these treatments work for only a minority of patients. The efficacy of anti-PD-1 inhibitors may be extended by cytokines, however, the incorporation of cytokines into therapeutic regimens has significant challenges. In their natural form when administered as recombinant proteins, cytokine treatments are often associated with low response rates. Most cytokines have a short half-life which limits their exposure and efficacy. In addition, cytokines can activate counterregulatory pathways, in the case of immune-potentiating cytokines this can lead to immune suppression and thereby diminish their potential efficacy. Improving the drug-like properties of natural cytokines using protein engineering can yield synthetic cytokines with improved bioavailability and tissue targeting, allowing for enhanced efficacy and reduced off-target effects. Using structure guided engineering we have designed a novel class of antibody-cytokine fusion proteins consisting of a PD-1 targeting antibody fused together with an interleukin-21 (IL-21) cytokine mutein. Our bifunctional fusion proteins can block PD-1/programmed death-ligand 1 (PD-L1) interaction whilst simultaneously delivering IL-21 cytokine to PD-1 expressing T cells. Targeted delivery of IL-21 can improve T cell function in a manner that is superior to anti-PD-1 monotherapy. Fusion of engineered IL-21 variants to anti-PD1 antibodies can improve the drug-like properties of IL-21 cytokine leading to improved cytokine serum half-life allowing for less frequent dosing. In addition, we show that targeted delivery of IL-21 can minimize any potential detrimental effect on local antigen-presenting cells. A highly attenuated IL-21 mutein variant (R9E:R76A) fused to a PD-1 antibody provides protection in a humanized mouse model of cancer that is refractory to anti-PD-1 monotherapy. Collectively, our preclinical data demonstrate that this approach may improve upon and extend the utility of anti-PD-1 therapeutics currently in the clinic.

Dickkopf-1 regulates bone formation in young growing rodents and upon traumatic injury

The physiological role of Dickkopf-1 (Dkk1) during postnatal bone growth in rodents and in adult rodents was examined utilizing an antibody to Dkk1 (Dkk1-Ab) that blocked Dkk1 binding to both low density lipoprotein receptor-related protein 6 (LRP6) and Kremen2, thereby preventing the Wnt inhibitory activity of Dkk1. Treatment of growing mice and rats with Dkk1-Ab resulted in a significant increase in bone mineral density because of increased bone formation. In contrast, treatment of adult ovariectomized rats did not appreciably impact bone, an effect that was associated with decreased Dkk1 expression in the serum and bone of older rats. Finally, we showed that Dkk1 plays a prominent role in adult bone by mediating fracture healing in adult rodents. These data suggest that, whereas Dkk1 significantly regulates bone formation in younger animals, its role in older animals is limited to pathologies that lead to the induction of Dkk1 expression in bone and/or serum, such as traumatic injury.

Gene therapy with human recombinant osteoprotegerin reverses established osteopenia in ovariectomized mice

Osteoporosis is a chronic condition that is typically treated by the long-term repeated administration of antiresorptive agents. Gene therapy has the potential to deliver protein-based antiresorptive agents without the need for repeated administration. Osteoprotegerin (OPG) is a naturally occuring protein that prevents bone resorption by inhibiting osteoclast formation, function and survival. We tested whether adeno-associated virus (AAV) could deliver OPG at levels that are sufficient to reverse established osteopenia in ovariectomized (OVX) mice without causing liver toxicity. Tibial bone mineral density (BMD) was measured by peripheral quantitative computed tomography (pQCT) in 12-week-old CDF1 mice prior to OVX or sham surgery. Six weeks later, BMD was significantly reduced in OVX mice compared to sham controls or pre-surgery values. Sham and OVX mice were then injected once IV with an AAV vector carrying cDNA for recombinant hOPG (AAV-OPG) or beta-galactosidase (AAV-betaGal). BMD and bone histomorphometry were assessed 10 weeks after treatment. A single injection of AAV-OPG led to the appearance of human OPG (hOPG) in the serum of mice within 7 days, and high serum levels of hOPG were maintained for the duration of the 10-week study. At the end of the study, OVX mice given AAV-OPG had significantly greater tibial BMD compared to age-matched OVX animals given AAV-betaGal. In sham-operated mice, AAV-OPG also significantly increased tibial BMD compared to AAV-betaGal. The increased BMD in AAV-OPG animals was accompanied by significantly increased bone volume and significantly reduced osteoclast surfaces in the proximal tibial metaphysis. Liver histology was normal, and circulating activities of hepatocyte cytosolic enzymes were unaffected by AAV exposure. In an accompanying experiment, young (3-4 weeks) C57BL/6 mice treated once IV with AAV-OPG maintained pharmacologically active levels of OPG in serum for at least 16 months. In summary, a single AAV-OPG treatment reversed established osteopenia in OVX mice without evidence of liver toxicity. AAV delivery appears to be a safe and effective method for producing sustained systemic exposure to OPG.

Female sterilization: an update

Female sterilization is the most popular form of birth control in the world. It is performed laparoscopically or through a minilap, depending on the timing (postpartum) and where the patient lives. It is a safe and efficacious procedure with few complications that can be performed under local or general anaesthesia. The techniques presently in use are all adequate and the choice should evolve from a discussion between the doctor and the patient.

Adenoviral delivery of osteoprotegerin ameliorates bone resorption in a mouse ovariectomy model of osteoporosis

Osteoprotegerin (OPG) regulates bone resorption by inhibiting osteoclast formation, function, and survival. The current studies employed a mouse ovariectomy (OVX) model of estrogen deficiency to investigate gene therapy with OPG as a means of preventing osteoporosis. Young adult females injected with a recombinant adenoviral (Ad) vector carrying cDNA of either full-length OPG or a fusion protein combining the hOPG ligand-binding domain with the human immunoglobulin constant domain (Ad-hOPG-Fc) developed serum OPG concentrations exceeding the threshold needed for efficacy. However, elevated circulating OPG levels were sustained for up to 18 months only in mice given Ad-hOPG-Fc. Administration of Ad-hOPG-Fc titers between 10(7) and 10(9) pfu yielded dose-dependent increases in serum OPG. Mice subjected to OVX or sham surgery followed by immediate treatment with Ad-hOPG-Fc had significantly more bone volume with reduced osteoclast numbers in axial and appendicular bones after 4 weeks. In contrast, animals given OVX and either a control vector or vehicle had significantly less bone than did comparably treated sham-operated mice. This study demonstrates that a single adenoviral gene transfer can produce persistent high-level OPG expression and shows that gene therapy to provide sustained delivery of OPG may prove useful in treating osteoporosis.

Early amniotomy increases the frequency of fetal heart rate abnormalities. Amniotomy Study Group

OBJECTIVE

To determine whether early amniotomy, when practised as an isolated intervention, increases the hourly rate of fetal heart rate record abnormalities.

DESIGN

This is a secondary analysis of the results of a multicentre randomised trial of early versus late amniotomy in labour.

SETTING

Secondary and tertiary level teaching hospitals.

INTERVENTION

Early amniotomy versus an attempt to conserve the amniotic membranes.

MAIN OUTCOME MEASURES

The hourly rates of early, mild variable, severe variable and late decelerations; caesarean section rates.

RESULTS

Severe variable decelerations, when classified as categorical events (> or = 1/h to 2/h, > or = 2/h to < 4/h, > or = 4/h), were more frequent in the amniotomy group (chi2 for trend = 5.7, P = 0.017). The mean hourly rates of severe variable and late fetal heart rate decelerations were increased in the amniotomy group (severe variable: amniotomy group 1.4/h, control 0.7/h, P = 0.021; late: amniotomy group 3.3/h, control 2.3/h, P = 0.011). Although the overall rate of caesarean was similar in the two groups (OR 1.2; 95% CI 0.8-1.8), there was an increase in caesarean section for fetal distress (OR 2.3; 95% CI 1.1-4.5) associated with amniotomy.

CONCLUSION

Our data suggest that early amniotomy increases the hourly rate of severe variable fetal heart rate decelerations without evidence of an adverse effect on neonatal outcome. In settings where the diagnosis of fetal compromise is based primarily on electronic monitoring, caesarean section for fetal distress may be increased by early amniotomy.