Bispecific CD33/CD123 targeted chimeric antigen receptor T cells for the treatment of acute myeloid leukemia

CD33 and CD123 are expressed on the surface of human acute myeloid leukemia blasts and other noncancerous tissues such as hematopoietic stem cells. On-target off-tumor toxicities may limit chimeric antigen receptor T cell therapies that target both CD33 and CD123. To overcome this limitation, we developed bispecific human CD33/CD123 chimeric antigen receptor (CAR) T cells with an "AND" logic gate. We produced novel CD33 and CD123 scFvs from monoclonal antibodies that bound CD33 and CD123 and activated T cells. Screening of CD33 and CD123 CAR T cells for cytotoxicity, cytokine production, and proliferation was performed, and we selected scFvs for CD33/CD123 bispecific CARs. The bispecific CARs split 4-1BB co-stimulation on one scFv and CD3ζ on the other. In vitro testing of cytokine secretion and cytotoxicity resulted in selecting bispecific CAR 1 construct for in vivo analysis. The CD33/CD123 bispecific CAR T cells were able to control acute myeloid leukemia (AML) in a xenograft AML mouse model similar to monospecific CD33 and CD123 CAR T cells while showing no on-target off-tumor effects. Based on our findings, human CD33/CD123 bispecific CAR T cells are a promising cell-based approach to prevent AML and support clinical investigation.

CD3 engagement as a new strategy for allogeneic “off-the-shelf” T cell therapy

Allogeneic “off-the-shelf” (OTS) chimeric antigen receptor T cells (CAR-T cells) hold promise for more accessible CAR-T therapy. Here, we report a novel and simple way to make allogeneic OTS T cells targeting cancer. By engineering T cells with a bispecific T cell engager (BiTE), both TCRαβ and CD3ε expression on the T cell surface are dramatically reduced. BiTE-engineered T (BiTE-T) cells show reduced reaction to TCR stimulation in vitro and have low risk of graft-versus-host disease (GvHD) in vivo. BiTE-T cells down-regulated CD3ε/TCRαβ on bystander T cells by releasing BiTEs. BiTE-T cells produce much fewer cytokines and are comparable to CAR-T cells on anti-cancer efficacy in xenograft mouse models with pre-existing HLA-mismatched T cells. Co-expressing co-stimulatory factors or T cell-promoting cytokines enhanced BiTE-T cells. Our study suggests CD3ε engagement could be a new strategy for allogeneic T cell therapy worthy of further evaluation.

105 4–1BB and optimized CD28 co-stimulation enhances function of human mono- and bi-specific third-generation CAR T cells

Background

Co-stimulatory signals regulate the expansion, persistence, and function of chimeric antigen receptor (CAR) T cells. Most studies have focused on the co-stimulatory domains CD28 or 4-1BB. CAR T cell persistence is enhanced by 4-1BB co-stimulation leading to NF-κB signaling, while resistance to exhaustion is enhanced by mutations of the CD28 co-stimulatory domain.

Methods

We hypothesized that a third-generation CAR containing 4-1BB and CD28 with only PYAP signaling motif (mut06) would provide beneficial aspects of both. We designed CD19-specific CAR T cells with 4-1BB or mut06 together with the combination of both (BB06). We evaluated their immune-phenotype, cytokine secretion, real-time cytotoxic ability and polyfunctionality against CD19-expressing cells. We analyzed LCK recruitment by the different constructs by immunoblotting. We further determined their ability to control growth of Raji cells in NSG mice. Additionally, we engineered bi-specific CARs against CD20/CD19 combining 4-1BB and mut06 and performed repeated in vitro antigenic stimulation experiments to evaluate their expansion, memory phenotype and phenotypic (PD1+CD39+) and functional exhaustion. Bi-specific CAR T cells were transferred into Raji or Nalm6-bearing mice to study their ability to eradicate CD20/CD19-expressing tumors.

Results

Co-stimulatory domains combining 4-1BB and mut06 confers CAR T cells with an increased polyfunctionality and LCK recruitment to the CAR (figure 1A), after repeated-antigen stimulation these cells expanded significantly better than second-generation CAR T cells (figure 1B). A bi-specific CAR targeting CD20/CD19, incorporating 4-1BB and mut06 co-stimulation, showed enhanced antigen-dependent in vitro expansion with lower exhaustion-associated markers (figure 1C). Bi-specific CAR T cells exhibited improved in vivo anti-tumor activity with increased persistence and decreased exhaustion (figure 1D).

Abstract 105 Figure 1

A. pLCK is increased in h19BB06z CAR T cells and associated with the CAR. CAR T cells were stimulated with irradiated 3T3-hCD19 cells at a 10:1 E:T ratio for 24hr. Cells were lysed and CAR bound and unbound fractions were western blotted. A single-cell measure of polyfunctional strength index (PSI) of CAR T cells. B. h19BB06z CAR T cells have the highest proliferation after repeated antigen stimulations. 5x105 CAR T cells were stimulated with 1x105 irradiated 3T3-hCD19 cells. After 1 week, half of the cells were enumerated by flow cytometry and the other half was re-stimulated with 1x105 fresh irradiated 3T3-hCD19 cells. This was repeated for a total of 4 weeks. C. 5x105 CAR T cells were co-cultured with 5x105 target cells (Raji-CD19High). After 1 week half the cells were harvested enumerated and stained by flow cytometry while the other half was re-stimulated with 5x105 fresh target cells (indicated by arrows). This was repeated for a total of 4 weeks. Frequency of PD1+CD39+ cells within CD8+ CAR T cells. D. Raji-FFLuc-bearing NSG mice were treated with 1x106 CAR T cells 5 days after initial tumor cell injection. Tumor burden (average luminescence) of mice treated with bi-specific or monospecific CAR T cells, UT and tumor control. Each line represents an individual mouse. (n = 7 mice per group).

Conclusions

These results demonstrate that co-stimulation combining 4-1BB with an optimized form of CD28 is a valid approach to optimize CAR T cell function. Cells with both mono- and bi-specific versions of this design showed enhanced in vitro and in vivo features such as expansion, persistence and resistance to exhaustion. Our observations validate the approach and justify clinical studies to test the efficacy and safety of this CAR in patients.

4-1BB and optimized CD28 co-stimulation enhances function of human mono-specific and bi-specific third-generation CAR T cells

Background

Co-stimulatory signals regulate the expansion, persistence, and function of chimeric antigen receptor (CAR) T cells. Most studies have focused on the co-stimulatory domains CD28 or 4-1BB. CAR T cell persistence is enhanced by 4-1BB co-stimulation leading to nuclear factor kappa B (NF-κB) signaling, while resistance to exhaustion is enhanced by mutations of the CD28 co-stimulatory domain.

Methods

We hypothesized that a third-generation CAR containing 4-1BB and CD28 with only PYAP signaling motif (mut06) would provide beneficial aspects of both. We designed CD19-specific CAR T cells with either 4-1BB or mut06 together with the combination of both and evaluated their immune-phenotype, cytokine secretion, real-time cytotoxic ability and polyfunctionality against CD19-expressing cells. We analyzed lymphocyte-specific protein tyrosine kinase (LCK) recruitment by the different constructs by immunoblotting. We further determined their ability to control growth of Raji cells in NOD scid gamma (NSG) mice. We also engineered bi-specific CARs against CD20/CD19 combining 4-1BB and mut06 and performed repeated in vitro antigenic stimulation experiments to evaluate their expansion, memory phenotype and phenotypic (PD1⁺CD39⁺) and functional exhaustion. Bi-specific CAR T cells were transferred into Raji or Nalm6-bearing mice to study their ability to eradicate CD20/CD19-expressing tumors.

Results

Co-stimulatory domains combining 4-1BB and mut06 confers CAR T cells with an increased central memory phenotype, expansion, and LCK recruitment to the CAR. This enhanced function was dependent on the positioning of the two co-stimulatory domains. A bi-specific CAR targeting CD20/CD19, incorporating 4-1BB and mut06 co-stimulation, showed enhanced antigen-dependent in vitro expansion with lower exhaustion-associated markers. Bi-specific CAR T cells exhibited improved in vivo antitumor activity with increased persistence and decreased exhaustion.

Conclusion

These results demonstrate that co-stimulation combining 4-1BB with an optimized form of CD28 is a valid approach to optimize CAR T cell function. Cells with both mono-specific and bi-specific versions of this design showed enhanced in vitro and in vivo features such as expansion, persistence and resistance to exhaustion. Our observations validate the approach and justify clinical studies to test the efficacy and safety of this CAR in patients.

Tumor interferon signaling and suppressive myeloid cells are associated with CAR T-cell failure in large B-cell lymphoma

Axicabtagene ciloleucel (axi-cel) is a chimeric antigen receptor (CAR) T-cell therapy for relapsed or refractory large B-cell lymphoma (LBCL). This study evaluated whether immune dysregulation, present before CAR T-cell therapy, was associated with treatment failure. Tumor expression of interferon (IFN) signaling, high blood levels of monocytic myeloid-derived suppressor cells (M-MDSCs), and high blood interleukin-6 and ferritin levels were each associated with a lack of durable response. Similar to other cancers, we found that in LBCL tumors, IFN signaling is associated with the expression of multiple checkpoint ligands, including programmed cell death-ligand 1, and these were higher in patients who lacked durable responses to CAR-T therapy. Moreover, tumor IFN signaling and blood M-MDSCs associated with decreased axi-cel expansion. Finally, patients with high tumor burden had higher immune dysregulation with increased serum inflammatory markers and tumor IFN signaling. These data support that immune dysregulation in LBCL promotes axi-cel resistance via multiple mechanistic programs: insufficient axi-cel expansion associated with both circulating M-MDSC and tumor IFN signaling, which also gives rise to expression of immune checkpoint ligands.

CD28 Costimulatory Domain-Targeted Mutations Enhance Chimeric Antigen Receptor T-cell Function

An obstacle to the development of chimeric antigen receptor (CAR) T cells is the limited understanding of CAR T-cell biology and the mechanisms behind their antitumor activity. We and others have shown that CARs with a CD28 costimulatory domain drive high T-cell activation, which leads to exhaustion and shortened persistence. This work led us to hypothesize that by incorporating null mutations of CD28 subdomains (YMNM, PRRP, or PYAP), we could optimize CAR T-cell costimulation and enhance function. In vivo, we found that mice given CAR T cells with only a PYAP CD28 endodomain had a significant survival advantage, with 100% of mice alive after 62 days compared with 50% for mice with an unmutated endodomain. We observed that mutant CAR T cells remained more sensitive to antigen after ex vivo antigen and PD-L1 stimulation, as demonstrated by increased cytokine production. The mutant CAR T cells also had a reduction of exhaustion-related transcription factors and genes such as Nfatc1, Nr42a, and Pdcd1 Our results demonstrated that CAR T cells with a mutant CD28 endodomain have better survival and function. This work allows for the development of enhanced CAR T-cell therapies by optimizing CAR T-cell costimulation.

Tumor Microenvironment Composition and Severe Cytokine Release Syndrome (CRS) Influence Toxicity in Patients with Large B-Cell Lymphoma Treated with Axicabtagene Ciloleucel

PURPOSE

One of the challenges of adoptive T-cell therapy is the development of immune-mediated toxicities including cytokine release syndrome (CRS) and neurotoxicity (NT). We aimed to identify factors that place patients at high risk of severe toxicity or treatment-related death in a cohort of 75 patients with large B-cell lymphoma treated with a standard of care CD19 targeted CAR T-cell product (axicabtagene ciloleucel).

EXPERIMENTAL DESIGN

Serum cytokine and catecholamine levels were measured prior to lymphodepleting chemotherapy, on the day of CAR T infusion and daily thereafter while patients remained hospitalized. Tumor biopsies were taken within 1 month prior to CAR T infusion for evaluation of gene expression.

RESULTS

We identified an association between pretreatment levels of IL6 and life-threatening CRS and NT. Because the risk of toxicity was related to pretreatment factors, we hypothesized that the tumor microenvironment (TME) may influence CAR T-cell toxicity. In pretreatment patient tumor biopsies, gene expression of myeloid markers was associated with higher toxicity.

CONCLUSIONS

These results suggest that a proinflammatory state and an unfavorable TME preemptively put patients at risk for toxicity after CAR T-cell therapy. Tailoring toxicity management strategies to patient risk may reduce morbidity and mortality.

Optimization of CAR T cell co-stimulation reduces to MDSC suppression

A major obstacle for continued development of CARs is their suppression by the tumor microenvironment. Clinical data from our lab shows patients that have increased myeloid cells have poorer outcomes to CAR T cell therapy. Based on this we examined MDSC suppression of CARs.

First, we examined the effect of MDSCs on CAR T cell production. We found gene transfer was lower for m1928z CAR T cells co-cultured with MDSCs compared to those that were not (24.1% vs 39.1%). There was also a reduction in total T cell counts for m1928z after MDSC co-culture (88%). We also investigated the effect of MDSCs on CAR T cells when present during antigen stimulation. Co-culture with MDSCs in vitro showed significant reductions in CAR T cell mediated killing and IFNγ secretion. Additionally, CAR T cells stimulated in the presence of MDSCs had lower expression of activation markers PD1 and LAG3. This suggests that MDSCs reduce CAR T cell gene transfer, activation, killing, and cytokine production.

To evaluate if we could create a CAR T cell resistant to MDSC suppression null mutations of YMNM and PRRP were incorporated into a CD28 CAR leaving only PYAP active (mut06). When mut06 and MDSCs were co-cultured there was a reduction in gene transfer (21% vs 38%) and T cell counts (80% vs 88%) compared to m1928z. We also found when in the presence of MDSCs mut06 was significantly better at killing compared to m1928z. To examine this in vivo we co-injected mice with CAR T cells and MDSCs. We found mice given m1928z with MDSCs had reduced CAR T cell function while mut06 was not affected by MDSCs. Overall our data shows that MDSCs can suppress CAR T cell function when present during production as well as CAR stimulation and optimizing CD28 CAR signaling creates CAR T cells that are more resistant to MDSCs.