Arcellx Presents Continued Robust Long-Term Responses from its CART-ddBCMA Phase 1 Expansion Trial in Patients with Relapsed or Refractory Multiple Myeloma at the 63rd ASH Annual Meeting and Exposition

— Two dose levels studied (100 and 300 million CAR+ T-cells); MTD not reached —

— 100% ORR at both dose levels; deep and durable responses observed in patients with poor prognostic factors —

— Pivotal Phase 2 trial planned to initiate by YE 2022 —

FOSTER CITY, Calif., Dec. 13, 2021 (GLOBE NEWSWIRE) — Arcellx, Inc., a privately held clinical-stage biopharmaceutical company, today announced new positive clinical data from the ongoing Phase 1 expansion study of its novel, autologous, CART-ddBCMA for the treatment of patients with relapsed or refractory multiple myeloma. The clinical results are being presented at the 63^rd American Society of Hematology Annual Meeting and Exposition.

Of the 24 patients who have been dosed, 22 are evaluable for safety analysis and 19 are evaluable for efficacy analysis, based on follow-up of at least 1 and 3 months, respectively, following treatment. These evaluable patients comprised the dose escalation cohorts for the first dose level (100 million CAR+T cells, n=6) and the second dose level (300 million CAR+T cells, n=6) and a dose expansion cohort of (100 million CAR+T cells, safety n=10, efficacy n=7). All patients enrolled in the study have poor prognostic factors with 17 of 24 patients penta-refractory and all 22 patients having had at least three prior treatments.

CART-ddBCMA clinical results (November 4, 2021, cutoff date) demonstrate deep and durable responses observed in patients with poor prognostic factors:

• Median follow-up of 283 days (Min-Max: 115-640)
  • 100% overall response rate (ORR) achieved in 19 patients per International Myeloma Working Group criteria
  • 68% (13/19) patients achieved complete response (CR) or a stringent complete response (sCR)
  • 16% (3/19) patients achieved a very good partial response (VGPR)
  • 16% (3/19) patients achieved a partial response (PR)
• 4 responses ongoing >15 months (67% of 6 treated >1 year ago)
• CART-ddBCMA expansion at 100 million CAR+T cells continues to be well-tolerated
  • Toxicities including CRS and ICANS have been manageable, and all resolved with standard management at both dose levels
    • Only 1 grade 3 (or greater) CRS or ICANS event at DL1, ~6% of evaluable cases.
    • No off-target toxicities observed

Matthew J. Frigault, M.D., CART-ddBCMA study investigator and assistant director of the Cellular Therapy Service at Mass General Cancer Center and Instructor at Harvard Medical School said, “These data continue to be impressive at both doses and the safety profile continues to be manageable. Patients enrolled in this clinical trial were heavily pre-treated with poor prognostic factors. It is encouraging to see that this one-time treatment has the potential to be a meaningful therapy for patients suffering from this incurable disease.”

Presentation of New CART-ddBCMA Data:
Session Name: 704 Cellular Immunotherapies: Clinical: Poster III
Title: Phase 1 Study of CART-ddBCMA: a CART-Therapy Utilizing a Novel Synthetic Binding Domain for the Treatment of Subjects with Relapsed or Refractory Multiple Myeloma
Date: Monday, December 13, 2021
Time: 6:00 – 8:00 P.M. ET
Location: Georgia World Congress Center, Hall B5
Presenter: Matthew J. Frigault, M.D., Assistant Director of the Cellular Therapy Service at Mass General Cancer Center and Instructor at Harvard Medical School

About Multiple Myeloma
Multiple Myeloma is a type of hematological cancer in which diseased plasma cells proliferate and accumulate in the bone marrow, crowding out healthy blood cells and causing bone lesions, loss of bone density and bone fractures. These abnormal plasma cells also produce excessive quantities of an abnormal immunoglobulin fragment called a myeloma protein (M protein) causing kidney damage and impairing the patient’s immune function. Multiple myeloma is the third most common hematological malignancy in the United States and Europe, representing approximately 10% of all hematological cancer cases and 20% of deaths due to hematological malignancies. The median age of patients at diagnosis is 69 years with one-third of patients diagnosed at an age of at least 75 years. Because MM tends to afflict patients at an advanced stage of life, patients often have multiple co-morbidities and toxicities that can quickly escalate and become life-endangering.

About CART-ddBCMA
CART-ddBCMA is Arcellx’s BCMA-specific CAR-modified T-cell therapy utilizing the company’s novel BCMA-targeting binding domain for the treatment of patients with relapsed or refractory multiple myeloma that is currently in a Phase 1 study. Arcellx’s proprietary binding domains are novel synthetic proteins designed to bind specific therapeutic targets. CART-ddBCMA has been granted Fast Track, Orphan Drug, and Regenerative Medicine Advanced Therapy Designations by the U.S. Food and Drug Administration. Additional information about the trial can be found at https://www.clinicaltrials.gov/ct2/show/NCT04155749.

About Arcellx, Inc.
Arcellx is a clinical-stage biopharmaceutical company developing adaptive and controllable cell therapies for the treatment of patients with cancer and autoimmune diseases. By advancing its novel proprietary platform through the clinic, Arcellx is focused on delivering superior cell therapies to patients through the care of academic and community practices worldwide. More information can be found at www.arcellx.com.

Investor Contact:
Myesha Lacy
Arcellx, Inc.
510-418-2412
mlacy@arcellx.com

Media Contact:
Zara Lockshin
Solebury Trout
646-378-2960
zlockshin@soleburytrout.com