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PITTSBURGH – Call it the CAR of the future – an investigational chimeric antigen receptor–T cell construct targeted against an antigen highly expressed on pediatric solid tumors has shown promising efficacy in preclinical studies.
Investigators found that the antigen, labeled B7-H3, was expressed on 84% of microarrays of pediatric solid tumors. More importantly, a single dose of CAR targeted to B7-H3 caused complete regression of osteosarcoma and Ewing sarcoma xenografts and improved survival over an untransduced, CD19-targeted CAR in mice, Robbie Majzner, MD, reported at the annual meeting of the American Society of Pediatric Hematology/Oncology.
Dr. Majzner was the recipient of an ASPHO young investigator award for his team’s research into developing a CAR T that could be as effective against solid tumors as other CAR Ts have been against hematologic malignancies such as acute lymphoblastic leukemia.
Solid tumors are more challenging to target than leukemias or lymphomas because of the small number of antigens expressed on most pediatric tumors, he said.
“Over 95% of tumors have a very low rate of mutations, which means that they have very few neoantigens which the immune system can recognize in order to attack,” he said.
In the Children’s Oncology Group ADVL1412 trial, single-agent immunotherapy with the anti–programmed death protein 1 (PD-1) inhibitor nivolumab (Opdivo) showed no evidence of efficacy against either Ewing sarcoma, osteosarcoma, rhabdomyosarcoma, or measurable neuroblastoma. PD–ligand 1 was found to be expressed in only a few of the 43 tumors studied, suggesting that checkpoint inhibitor therapy is unlikely to work in these solid tumors, he said.
In contrast, B7-H3 is highly expressed on many different pediatric solid tumors, including rhabdomyosarcoma (95% of tumors stained), Ewing sarcoma (89%), Wilms tumor (100%), neuroblastoma (82%), ganglioneuroblastoma and ganglioneuroma (53%), medulloblastoma (96%), glioblastoma multiforme (84%), and diffuse intrinsic pontine glioma (100%).
To see whether CAR T therapy might have better efficacy than checkpoint inhibitors in this population, the investigators created a B7-H3 CAR using the B7-H3 tumor–specific monoclonal antibody MGA271, which has been shown to be safe in both adults and children in early clinical trials.
In human tumor xenograft models of osteosarcoma, all mice who received a single dose of the B7-H3 CAR survived at least 70 days after tumor engraftment, whereas all control mice, who received the CD19 CAR, died by day 60 (P = .0067). Similarly, in a model of Ewing sarcoma, all mice treated with B7-H3 survived at least 100 days, whereas all controls were dead by day 50 (P = .0015).
The B7-H3 construct also showed good activity against a model of medulloblastoma, showing that it was capable of crossing the blood-brain barrier.
Since B7-H3 has been reported to be expressed on both myeloid and lymphoid leukemia cells, the investigators also tested the CAR against a murine model of leukemia generated by injection of K562, a well-characterized line of myeloid leukemia cells.
“While we found some increase in survival in the mice that received the B7-H3 CAR T cells, compared to mice that received untransduced CAR T cells, this clearly is not as effective as in our solid tumor models,” Dr. Majzner said.
Going back to the cell line, they discovered that expression of B7-H3 was considerably lower in the K562 cells than in either the osteosarcoma or medulloblastoma cell lines used in their other models.
They found that both in vitro and in vivo, high levels of B7-H3 expression were necessary to provoke the immune system into releasing cytokines necessary for an adequate antitumor response.
The investigators are currently planning clinical trials using the B7-H3 CAR T-cell construct in patients with solid tumors.
The work is supported by the Sarcoma Alliance for Research through Collaboration, the St. Baldrick’s Foundation, and Stand Up to Cancer. Dr. Majzner reported having no financial disclosures.
SOURCE: Majzner RG et al. ASPHO 2018, Abstract #PS2003.
PITTSBURGH – Call it the CAR of the future – an investigational chimeric antigen receptor–T cell construct targeted against an antigen highly expressed on pediatric solid tumors has shown promising efficacy in preclinical studies.
Investigators found that the antigen, labeled B7-H3, was expressed on 84% of microarrays of pediatric solid tumors. More importantly, a single dose of CAR targeted to B7-H3 caused complete regression of osteosarcoma and Ewing sarcoma xenografts and improved survival over an untransduced, CD19-targeted CAR in mice, Robbie Majzner, MD, reported at the annual meeting of the American Society of Pediatric Hematology/Oncology.
Dr. Majzner was the recipient of an ASPHO young investigator award for his team’s research into developing a CAR T that could be as effective against solid tumors as other CAR Ts have been against hematologic malignancies such as acute lymphoblastic leukemia.
Solid tumors are more challenging to target than leukemias or lymphomas because of the small number of antigens expressed on most pediatric tumors, he said.
“Over 95% of tumors have a very low rate of mutations, which means that they have very few neoantigens which the immune system can recognize in order to attack,” he said.
In the Children’s Oncology Group ADVL1412 trial, single-agent immunotherapy with the anti–programmed death protein 1 (PD-1) inhibitor nivolumab (Opdivo) showed no evidence of efficacy against either Ewing sarcoma, osteosarcoma, rhabdomyosarcoma, or measurable neuroblastoma. PD–ligand 1 was found to be expressed in only a few of the 43 tumors studied, suggesting that checkpoint inhibitor therapy is unlikely to work in these solid tumors, he said.
In contrast, B7-H3 is highly expressed on many different pediatric solid tumors, including rhabdomyosarcoma (95% of tumors stained), Ewing sarcoma (89%), Wilms tumor (100%), neuroblastoma (82%), ganglioneuroblastoma and ganglioneuroma (53%), medulloblastoma (96%), glioblastoma multiforme (84%), and diffuse intrinsic pontine glioma (100%).
To see whether CAR T therapy might have better efficacy than checkpoint inhibitors in this population, the investigators created a B7-H3 CAR using the B7-H3 tumor–specific monoclonal antibody MGA271, which has been shown to be safe in both adults and children in early clinical trials.
In human tumor xenograft models of osteosarcoma, all mice who received a single dose of the B7-H3 CAR survived at least 70 days after tumor engraftment, whereas all control mice, who received the CD19 CAR, died by day 60 (P = .0067). Similarly, in a model of Ewing sarcoma, all mice treated with B7-H3 survived at least 100 days, whereas all controls were dead by day 50 (P = .0015).
The B7-H3 construct also showed good activity against a model of medulloblastoma, showing that it was capable of crossing the blood-brain barrier.
Since B7-H3 has been reported to be expressed on both myeloid and lymphoid leukemia cells, the investigators also tested the CAR against a murine model of leukemia generated by injection of K562, a well-characterized line of myeloid leukemia cells.
“While we found some increase in survival in the mice that received the B7-H3 CAR T cells, compared to mice that received untransduced CAR T cells, this clearly is not as effective as in our solid tumor models,” Dr. Majzner said.
Going back to the cell line, they discovered that expression of B7-H3 was considerably lower in the K562 cells than in either the osteosarcoma or medulloblastoma cell lines used in their other models.
They found that both in vitro and in vivo, high levels of B7-H3 expression were necessary to provoke the immune system into releasing cytokines necessary for an adequate antitumor response.
The investigators are currently planning clinical trials using the B7-H3 CAR T-cell construct in patients with solid tumors.
The work is supported by the Sarcoma Alliance for Research through Collaboration, the St. Baldrick’s Foundation, and Stand Up to Cancer. Dr. Majzner reported having no financial disclosures.
SOURCE: Majzner RG et al. ASPHO 2018, Abstract #PS2003.
PITTSBURGH – Call it the CAR of the future – an investigational chimeric antigen receptor–T cell construct targeted against an antigen highly expressed on pediatric solid tumors has shown promising efficacy in preclinical studies.
Investigators found that the antigen, labeled B7-H3, was expressed on 84% of microarrays of pediatric solid tumors. More importantly, a single dose of CAR targeted to B7-H3 caused complete regression of osteosarcoma and Ewing sarcoma xenografts and improved survival over an untransduced, CD19-targeted CAR in mice, Robbie Majzner, MD, reported at the annual meeting of the American Society of Pediatric Hematology/Oncology.
Dr. Majzner was the recipient of an ASPHO young investigator award for his team’s research into developing a CAR T that could be as effective against solid tumors as other CAR Ts have been against hematologic malignancies such as acute lymphoblastic leukemia.
Solid tumors are more challenging to target than leukemias or lymphomas because of the small number of antigens expressed on most pediatric tumors, he said.
“Over 95% of tumors have a very low rate of mutations, which means that they have very few neoantigens which the immune system can recognize in order to attack,” he said.
In the Children’s Oncology Group ADVL1412 trial, single-agent immunotherapy with the anti–programmed death protein 1 (PD-1) inhibitor nivolumab (Opdivo) showed no evidence of efficacy against either Ewing sarcoma, osteosarcoma, rhabdomyosarcoma, or measurable neuroblastoma. PD–ligand 1 was found to be expressed in only a few of the 43 tumors studied, suggesting that checkpoint inhibitor therapy is unlikely to work in these solid tumors, he said.
In contrast, B7-H3 is highly expressed on many different pediatric solid tumors, including rhabdomyosarcoma (95% of tumors stained), Ewing sarcoma (89%), Wilms tumor (100%), neuroblastoma (82%), ganglioneuroblastoma and ganglioneuroma (53%), medulloblastoma (96%), glioblastoma multiforme (84%), and diffuse intrinsic pontine glioma (100%).
To see whether CAR T therapy might have better efficacy than checkpoint inhibitors in this population, the investigators created a B7-H3 CAR using the B7-H3 tumor–specific monoclonal antibody MGA271, which has been shown to be safe in both adults and children in early clinical trials.
In human tumor xenograft models of osteosarcoma, all mice who received a single dose of the B7-H3 CAR survived at least 70 days after tumor engraftment, whereas all control mice, who received the CD19 CAR, died by day 60 (P = .0067). Similarly, in a model of Ewing sarcoma, all mice treated with B7-H3 survived at least 100 days, whereas all controls were dead by day 50 (P = .0015).
The B7-H3 construct also showed good activity against a model of medulloblastoma, showing that it was capable of crossing the blood-brain barrier.
Since B7-H3 has been reported to be expressed on both myeloid and lymphoid leukemia cells, the investigators also tested the CAR against a murine model of leukemia generated by injection of K562, a well-characterized line of myeloid leukemia cells.
“While we found some increase in survival in the mice that received the B7-H3 CAR T cells, compared to mice that received untransduced CAR T cells, this clearly is not as effective as in our solid tumor models,” Dr. Majzner said.
Going back to the cell line, they discovered that expression of B7-H3 was considerably lower in the K562 cells than in either the osteosarcoma or medulloblastoma cell lines used in their other models.
They found that both in vitro and in vivo, high levels of B7-H3 expression were necessary to provoke the immune system into releasing cytokines necessary for an adequate antitumor response.
The investigators are currently planning clinical trials using the B7-H3 CAR T-cell construct in patients with solid tumors.
The work is supported by the Sarcoma Alliance for Research through Collaboration, the St. Baldrick’s Foundation, and Stand Up to Cancer. Dr. Majzner reported having no financial disclosures.
SOURCE: Majzner RG et al. ASPHO 2018, Abstract #PS2003.
REPORTING FROM ASPHO 2018
Key clinical point:
Major finding: A single dose of the B7-H3 CAR caused complete regression of osteosarcoma and Ewing sarcoma xenografts and extended survival in mice.
Study details: Preclinical research.
Disclosures: The work is supported by the Sarcoma Alliance for Research through Collaboration, St. Baldrick’s Foundation, and Stand Up to Cancer. Dr. Majzner reported having no financial disclosures.
Source: Majzner RG et al. ASPHO 2018, Abstract #PS2003.