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639 BASECAMP-1: Leveraging HLA loss of heterozygosity in solid tumors by NGS to identify patients with relapsed solid tumors for future CEA and MSLN logic-gated Tmod™ CAR T-cell therapy
  1. Diane Simeone1,
  2. Maria Pia Morelli2,
  3. J Randolph Hecht3,
  4. Sandip Patel4,
  5. Marwan Fakih5,
  6. Kedar Kirtane6,
  7. Theodore Welling1,
  8. Sally Lau1,
  9. Yi Lin7,
  10. Mitesh Borad8,
  11. Edward Garon3,
  12. Sarah Larson3,
  13. Shumei Kato4,
  14. Peter Vu4,
  15. Frederick Locke6,
  16. Dae Won Kim6,
  17. John Sunwoo10,
  18. David Miklos9,
  19. Matthew Frigault10,
  20. Marcela Maus10,
  21. Sarah Nikiforow11,
  22. Caron Jacobson11,
  23. Kirstin Liechty13,
  24. Armen Mardiros12,
  25. Ariane Lozac’hmeur13,
  26. Karl Beutner13,
  27. John Welch12,
  28. Eric Ng14,
  29. William Go12,
  30. David Maloney15,
  31. Scott Kopetz2 and
  32. Julian Molina7
  1. 1New York University Langone Health, New York, NY, USA
  2. 2University of Texas MD Anderson Cancer, Houston, TX, USA
  3. 3University of California at Los Angeles, Los Angeles, CA, USA
  4. 4University of California San Diego, La Jolla, CA, USA
  5. 5City of Hope, Duarte, CA, USA
  6. 6H. Lee Moffitt Cancer Center, Tampa, FL, USA
  7. 7Mayo Clinic, Rochester, MN, USA
  8. 8Mayo Clinic Cancer Center, Scottsdale, AZ, USA
  9. 9Stanford University School of Medicine, Palo Alto, CA, USA
  10. 10Massachusetts General Cancer Center, Boston, MA, USA
  11. 11Dana-Farber Cancer Institute, Boston, MA, USA
  12. 12A2 Biotherapeutics, Inc., Agoura Hills, CA, USA
  13. 13Tempus, Chicago, IL, USA
  14. 14A2 Biotherapeutics, Agoura Hills, CA, USA
  15. 15Fred Hutchinson Cancer Research Center, Seattle, WA, USA


Background Solid tumors comprise >90% of cancers. Non-small cell lung cancer (NSCLC), metastatic colorectal cancer (CRC), and pancreatic cancer are the leading causes of cancer-related mortality (5-year overall survival: 26%, 15%, and 11%, respectively).1

Chimeric antigen receptor (CAR) T-cell therapy has demonstrated clinical efficacy in hematologic malignancies.2,3 However, translating engineered T-cell therapies to solid tumors has proven to be challenging due to a lack of tumor-specific targets that can discriminate cancer cells from normal cells. Previous studies using carcinoembryonic antigen (CEA) T-cell receptors and mesothelin (MSLN) CARs resulted in dose-limiting on-target, off-tumor toxicities.4,5

To create a therapeutic safety window, Tmod CAR T-cell therapy utilizes dual-signaling receptors to create a robust logic gate capable of killing tumor cells, while leaving healthy cells intact.6,7

The 2 receptors in Tmod CAR T-cell therapy comprise an activator that recognizes an antigen on the surface of tumor cells that may also be present on normal cells, such as CEA and MSLN, and a blocker that recognizes a second surface antigen from an allele lost only in tumor cells (figure 1).8,9

Human leukocyte antigen (HLA) loss of heterozygosity (LOH) offers a definitive tumor versus normal discriminator target for CAR T-cell therapy.10 The frequency of HLA LOH among advanced NSCLC, CRC, and pancreatic cancers in the Tempus real-world dataset is 16.3% with a range of 15.6%-23.1%.11 LOH can be reliably detected using the Tempus xT-Onco next-generation sequencing (NGS) assay.12,13 Different activator/blocker combinations can be engineered with the Tmod platform technology and may be applied to T cells and natural killer cells in autologous and allogeneic settings.

BASECAMP-1 is a currently enrolling observational study with key objectives: 1) To identify patients with somatic HLA LOH eligible for Tmod CAR T-cell therapy, and 2) Subsequent apheresis and manufacturing feasibility for the future EVEREST CEA or MSLN Tmod CAR T-cell studies.

Methods BASECAMP-1 (NCT04981119) patient eligibility has 2 parts (figure 2): 1) Patients will be initially screened to identify germline HLA-A*02 heterozygosity by central NGS. If HLA-A*02 heterozygosity is confirmed, primary archival tumor tissue will be analyzed for somatic mutations by xT-Onco NGS testing; 2) If the tumor demonstrates HLA-A*02:01 LOH and the patient is eligible after screening, the patient will undergo apheresis. Banked T cells will be available for the autologous EVEREST Tmod CAR T-cell therapy interventional study to reduce waiting time at relapse.

Trial Registration ClinicalTrials. gov, NCT04981119


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  2. Locke F, Miklos D, Jacobson C, et al. Axicabtagene ciloleucel as second-line therapy for large B-cell lymphoma. N Engl J Med. 2022;386(7):640-654.

  3. Maude S, Laetsch T, Buechner J, et al. Tisagenlecleucel in children and young adults with B-cell lymphoblastic leukemia. N Engl J Med. 2018;378(5):439-448.

  4. Parkhurst M, Yang J, Langan R, et al. T cells targeting carcinoembryonic antigen can mediate regression of metastatic colorectal cancer but induce severe transient colitis. Mol Ther. 2011;19(3):620-626.

  5. Haas AR, Tanyi JL, O’Hara MH, et al. Phase I study of lentiviral-transduced chimeric antigen receptor-modified T cells recognizing mesothelin in advanced solid cancers. Mol Ther. 2019;27(11):1919-1929.

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

  7. DiAndreth B, Hamburger AE, Xu H, Kamb A. The Tmod cellular logic gate as a solution for tumor-selective immunotherapy. Clin Immunol. 2022;241:109030.

  8. Sandberg ML, Wang X, Martin AD, et al. A carcinoembryonic antigen-specific cell therapy selectively targets tumor cells with HLA loss of heterozygosity in vitro and in vivo. Sci Transl Med. 2022;14(634):eabm0306.

  9. Tokatlian T, Asuelime GE, Mock JY, et al. Mesothelin-specific CAR-T cell therapy that incorporates an HLA-gated safety mechanism selectively kills tumor cells. J Immunother Cancer. 2022;10(1):e003826.

  10. 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.

  11. Simeone DM, Hecht JR, Patel SP, et al. BASECAMP-1: Leveraging human leukocyte antigen (HLA) loss of heterozygosity (LOH) in solid tumors by next-generation sequencing (NGS) to identify patients with relapsed solid tumor for future logic-gated Tmod CAR T-cell therapy. Poster presented at: ASCO Annual Meeting; June 3-7, 2022; Chicago, IL. Abstract #TPS2676.

  12. Perera J, Mapes B, Lau D, et al. Detection of human leukocyte antigen class I loss of heterozygosity in solid tumor types by next-generation DNA sequencing. J Immunother Cancer. 2019, 7(suppl 1):P103.

  13. Hecht JR, Kopetz S, Patel SP, et al. Next generation sequencing (NGS) to identify relapsed gastrointestinal (GI) solid tumor patients with human leukocyte antigen (HLA) loss of heterozygosity (LOH) for future logic-gated CAR T therapy to reduce on target off tumor toxicity. J Clin Oncol. 2022;40(4_suppl):190-190.

Ethics Approval The study was approved by site IRBs

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