Harpoon Therapeutics Presents HPN217 Phase 1 Clinical Data in Relapsed/Refractory Multiple Myeloma (RRMM) at ASH 2023 and Announces Selection of Recommended Phase 2 Dose (RP2D)

• HPN217 was well tolerated and demonstrated robust and durable clinical activity at doses ranging from 2.15 to 24 mg in heavily pre-treated patients, including patients with prior exposure to BCMA-targeted therapy

• At the 12 mg dose, cohorts demonstrated favorable activity and safety profile:

- 63% ORR; with 53% VGPR or better -

- CRS reported in 16% of patients, no Grade 3 events, no ICANS -

• Findings support further clinical development at the 12 mg RP2D

SOUTH SAN FRANCISCO, Calif., Dec. 11, 2023 (GLOBE NEWSWIRE) -- Harpoon Therapeutics, Inc. (NASDAQ:HARP), a clinical-stage immunotherapy company developing novel T cell engagers, today reported data from the Phase 1 study of HPN217 in patients with RRMM in an oral presentation at the 65th American Society of Hematology (ASH) Annual Meeting and Exposition in San Diego. Harpoon also announced the selection of 12 mg as the HPN217 RP2D.

During the trial, 97 patients with RRMM who had received at least three prior therapies were enrolled across 15 dose escalation cohorts and three expansion regimens. As of the data cut-off of October 17, 2023, the data demonstrated:

• Clinical activity across a wide dose range (2.15 mg to 24 mg). The maximum tolerated dose (MTD) was not reached at the target dose using a step up approach.
• Optimal activity and safety profile was seen at 12 mg, which was declared the RP2D.
• The Overall Response Rate (ORR) across 12 mg cohorts was 63% (12/19, 95% CI: 38, 84). In addition, the depth of response was most significant at 12 mg, with 53% (10/19) of patients having a Very Good Partial Response (VGPR) or better.
• The median time to first response in the 12 mg and 24 mg cohort was 1.2 months, and the median duration of response for all responders was 20.5 months as of the data cutoff date. Out of all the responders, 58% (22/38) remain on treatment.
• In the 12 mg and 24 mg cohorts, nine patients were previously exposed to BCMA-targeting agents, and six of those patients responded to the HPN217 treatment.
• The incidence of cytokine release syndrome (CRS) was lowest (16%) in the 12 mg cohorts, all Grade 1-2. No immune effector cell associated neurotoxicity syndrome (ICANS) events were observed at the 12 mg dose.

"The data presented at ASH today demonstrates that HPN217 has the potential to provide a meaningful benefit for patients with relapsed/refractory multiple myeloma, even in patients with prior anti-BCMA therapy," said Sumit Madan, M.D., Hematologist and Oncologist at Banner MD Anderson Cancer Center and Associate Professor (Adj) of Myeloma and Lymphoma at UT MD Anderson Cancer Center. "The low rate of CRS seen in this study is noteworthy and can help enable future studies of HPN217 in combination and in earlier lines of therapy."

"The HPN217 Phase 1 data set represents important progress for the program and validates the potential of HPN217 to deliver a wider therapeutic index. We observed a compelling 63% response rate in patients treated with the 12 mg target dose, with only a 16% rate of CRS," said Luke Walker, M.D., Chief Medical Officer for Harpoon Therapeutics. "These data and our interactions with the FDA have enabled us to declare a RP2D that can be used to support further clinical development."

For more details about the ASH Annual Meeting, please visit: https://www.hematology.org/meetings/annual-meeting

For additional information about the trial, please visit www.clinicaltrials.gov using the identifier NCT04184050.

The presentation will also be available on Harpoon's website under Publications following the session.

About HPN217

HPN217 targets B-cell maturation antigen (BCMA) and is based on Harpoon's proprietary Tri-specific T cell Activating Construct (TriTAC^®) platform designed to recruit a patient's own immune cells to kill tumor cells. BCMA, a clinically validated target, is a tumor necrosis factor receptor super family member and is a receptor protein expressed on nearly all multiple myeloma cells.

About Harpoon Therapeutics

Harpoon Therapeutics is a clinical-stage immunotherapy company developing a novel class of T cell engagers that harness the power of the body's immune system to treat patients suffering from cancer and other diseases. T cell engagers are engineered proteins that direct a patient's own T cells to kill target cells that express specific proteins, or antigens, carried by the target cells. Using its proprietary Tri-specific T cell Activating Construct (TriTAC^®) platform, Harpoon is developing a pipeline of novel TriTACs initially focused on the treatment of solid tumors and hematologic malignancies. Harpoon has also developed a proprietary ProTriTAC™ platform, which applies a prodrug concept to its TriTAC platform to create a therapeutic T cell engager that remains inactive until it reaches the tumor. Harpoon's third proprietary technology platform, extended release TriTAC-XR, is designed to mitigate cytokine release syndrome. For additional information about Harpoon Therapeutics, please visit www.harpoontx.com.

Forward-Looking Statements

This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Words such as "continue," "demonstrate," "further," "remain," "potential," "will," and similar expressions (as well as other words or expressions referencing future events, conditions, or circumstances) are intended to identify forward-looking statements. These forward-looking statements are based on Harpoon Therapeutics' expectations and assumptions as of the date of this press release. These forward-looking statements involve risks and uncertainties that could cause Harpoon Therapeutics' clinical development programs, future results, or performance to differ significantly from those expressed or implied by the forward-looking statements. Forward-looking statements in this press release include but are not limited to, statements about the expected progress, results, and plans pertaining to Harpoon Therapeutics' clinical trials, including timing, scope, design, enrollment plans and interim results of clinical trials and the safety and tolerability profile of product candidates, the association of interim clinical data and preclinical results with potential treatment outcomes, achievement of future milestones and other statements that are not historical fact. These and other factors that may cause Harpoon Therapeutics' actual results to differ from those expressed or implied in the forward-looking statements in this press release are discussed in Harpoon Therapeutics' filings with the U.S. Securities and Exchange Commission. Except as required by law, Harpoon Therapeutics assumes no obligation to update any forward-looking statements contained herein to reflect any change in expectations, even as new information becomes available.

Contact:

Ana Kapor

Harpoon Therapeutics

[email protected]