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 2022 ASCO Annual Meeting

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

-- 22 of 31 (71%) evaluable patients reached CR/sCR --

-- 13 of 16 patients (81%) dosed more than 12 months ago reached CR/sCR; 8 (50%) with EMD; 9 (56%) remain in ongoing response with a median follow up of 17.7 months --

-- No cases of Grade ≥3 CRS and no delayed neurotoxicity or parkinsonian-like events observed at RP2D (n=25) --

-- Phase 2 pivotal study on track to initiate by YE 2022 --

-- Management to host live webcast event on Sunday, June 5, 2022, at 7:00 p.m. CDT to discuss new positive CART-ddBCMA data with a panel of clinician experts --

FOSTER CITY, Calif., June 3, 2022 /PRNewswire/ -- Arcellx, Inc. (NASDAQ: ACLX), a biotechnology company reimagining cell therapy through the development of innovative immunotherapies for patients with cancer and other incurable diseases, today announced new positive clinical data from the ongoing Phase 1 expansion study of its novel, autologous, CART-ddBCMA therapy for the treatment of patients with relapsed or refractory multiple myeloma. The clinical results are being presented during an oral presentation at the 2022 American Society of Clinical Oncology (ASCO) Annual Meeting.

Evaluable for efficacy and safety analysis were 31 patients, based on follow-up of at least one month, following treatment. These evaluable patients comprised the dose escalation cohorts for the first dose level (100 million CAR+ T cells, n=6), the second dose level (300 million CAR+T cells, n=6), and a dose expansion cohort at the recommended Phase 2 dose (RP2D) of 100 million CAR+T cells (n=19). All patients enrolled in the study have poor prognostic factors with 21 of 31 (68%) patients penta-refractory, 12 of 31 (39%) extramedullary disease (EMD), and all 31 patients having had at least three prior treatments.

The interim CART-ddBCMA clinical results (May 3, 2022 cutoff date) demonstrate deep and durable responses in patients with poor prognostic factors.

• Of the 31 evaluable patients with median follow-up of 12.1 months
• 100% overall response rate (ORR) achieved in all patients per International Myeloma Working Group criteria
• 22 of 31 (71%) evaluable patients achieved complete response (CR) or a stringent complete response (sCR)
• 29 of 31 (94%) patients achieved > very good partial response (VGPR)
• 2 of 31 (6%) patients achieved a partial response (PR)
• 12 of 31 (39%) with extramedullary disease
• 13 of 16 patients (81%) dosed more than 12 months ago reached CR/sCR; 8 (50%) with EMD; 9 (56%) remain in ongoing response with a median follow up of 17.7 months
• Conversions to sCR have occurred as early as 1 month and also at ≥12 months
• CART-ddBCMA dosed at RP2D (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
• No cases of delayed neurotoxicity events or parkinsonian symptoms
• No cases of grade 3 (or greater) CRS and only one case (4%) of grade 3 ICANS event with no additional cases from previously reported.

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, "The demand for clinically meaningful and safe CAR-T therapies outweighs what's currently available to multiple myeloma patients. It is encouraging to see these data continue to demonstrate deep responses and provide a benefit to patients. I look forward to enrolling patients in the Phase 2 pivotal study."

"We're excited by these long-term results, particularly given the challenging patient demographics, and believe these promising results reflect the potential for our lead program, CART-ddBCMA, to be a best-in-class treatment for patients with multiple myeloma," said Rami Elghandour, Arcellx's Chairman and Chief Executive Officer. "We believe there's a significant unmet need for cell therapies and we're committed to providing physicians with a safe and effective treatment option for multiple myeloma patients. We're honored to have our data presented at ASCO by Dr. Frigault and look forward to beginning enrollment in our Phase 2 pivotal study by the end of this year as the next step in the path towards regulatory approval." 

The presentation can be accessed on the company's corporate website here. 

Title: Phase 1 Study of CART-ddBCMA in Relapsed or Refractory Multiple Myeloma
Speaker: Matthew J. Frigault, M.D., Assistant Director of the Cellular Therapy Service at Mass General Cancer Center, and Instructor at Harvard Medical School
Session Type/Title: Oral Abstract Session/Hematologic Malignancies—Plasma Cell Dyscrasia
Session Date: Sunday, June 5, 2022
Session Time: 8:00 a.m. – 11:00 a.m. CDT
Location: McCormick Place Convention Center, Chicago, Illinois 
Abstract Number: 8003

Arcellx will host a live webcast event with an expert panel of clinicians to discuss the clinical results on Sunday, June 5, 2022, at 7:00 p.m. CDT. The event will be accessible from Arcellx's website at www.arcellx.com in the Investors section. A replay of the webcast will be archived and available for 30 days following the event.

Multiple Myeloma (MM) 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.

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. CART-ddBCMA 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.

Arcellx, Inc. is a clinical-stage biotechnology company reimagining cell therapy by engineering innovative immunotherapies for patients with cancer and other incurable diseases. Arcellx believes that cell therapies are one of the forward pillars of medicine and Arcellx's mission is to advance humanity by developing cell therapies that are safer, more effective, and more broadly accessible. Arcellx's lead product candidate, CART-ddBCMA, is being developed for the treatment of relapsed or refractory multiple myeloma (r/r MM) in an ongoing Phase 1 study. CART-ddBCMA has been granted Fast Track, Orphan Drug, and Regenerative Medicine Advanced Therapy designations by the U.S. Food and Drug Administration.

Arcellx is also advancing its dosable and controllable CAR-T therapy, ARC-SparX, through two programs: a Phase 1 study of ACLX-001 for r/r MM, initiated in the second quarter of 2022; and ACLX-002 in relapsed or refractory acute myeloid leukemia and high-risk myelodysplastic syndrome, expected to enter the clinic in the second half of 2022.

Visit www.arcellx.com for more information.

Forward-looking Statements
This press release contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. All statements in this press release that are not purely historical are forward-looking statements. The forward-looking statements contained herein are based upon Arcellx's current expectations and involve assumptions that may never materialize or may prove to be incorrect. These forward-looking statements are neither promises nor guarantees and are subject to a variety of risks and uncertainties, including those set forth in Part I, Item 1A (Risk Factors) of Arcellx's Annual Report on Form 10-K and in other reports, such as Quarterly Reports on Form 10-Q and Current Reports on Form 8-K, that Arcellx may file from time to time with the Securities and Exchange Commission. These forward-looking statements are made as of the date of this press release, and Arcellx assumes no obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by law.

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

Media Contact
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Sam Brown Inc.
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