Harpoon presents updated interim clinical data for HPN424 at the 2021 ASCO Annual Meeting

Arix Bioscience PLC (ARIX) 
Harpoon presents updated interim clinical data for HPN424 at the 2021 ASCO Annual Meeting 
04-Jun-2021 / 15:25 GMT/BST 
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Arix Bioscience plc 
 
Harpoon presents updated interim clinical data for HPN424 at the 2021 ASCO Annual Meeting 
 
LONDON, 04 June 2021: Arix Bioscience plc ("Arix", LSE:ARIX), a global venture capital company focused on investing in 
and building breakthrough biotech companies, notes that its portfolio company, Harpoon Therapeutics, Inc. ("Harpoon", 
NASDAQ: HARP), today presented interim data from the ongoing dose-escalation portion of a Phase 1/2a trial for its lead 
programme, HPN424, in patients with metastatic castration-resistant prostate cancer at the 2021 American Society of 
Clinical Oncology (ASCO) Annual Meeting. 
 
Harpoon notes that these interim data for HPN424 show early clinical activity, with a manageable safety profile. 
Harpoon's management will host a webcast and conference call at 4 p.m. ET / 9 p.m. BST today, Friday 4 June, to review 
the data and provide an update on other pipeline programmes. A live webcast of the call will be available on the 
company's website at https://ir.harpoontx.com/events-and-presentations and will be archived there shortly after the 
live event. 
The announcement can be accessed on Harpoon's website at:  https://ir.harpoontx.com/news-releases and full text of the 
announcement from Harpoon is contained below. 
 
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About Arix Bioscience plc 
Arix Bioscience plc is a global venture capital company focused on investing in and building breakthrough biotech 
companies around cutting-edge advances in life sciences. 
We collaborate with exceptional entrepreneurs and provide the capital, expertise and global networks to help accelerate 
their ideas into important new treatments for patients. As a listed company, we are able to bring this exciting growth 
phase of our industry to a broader range of investors. www.arixbioscience.com 
 
Harpoon Therapeutics Presents Updated Interim Clinical Data for the PSMA-targeting TriTAC(R) HPN424 at the 2021 ASCO 
Annual Meeting 
  ? The ongoing dose escalation Phase 1/2a trial has enrolled 89 patients with progressive, metastatic 
    castration-resistant prostate cancer in 13 cohorts. 
 
  ? Safety data continues to show that HPN424 is generally well tolerated, and cytokine-related adverse events have 
    been transient and manageable. 
 
  ? Signals of clinical activity include patients with reductions in serum prostate specific antigen (PSA), a confirmed 
    partial response, and patients remaining on study for more than 24 weeks. 
 
  ? Management to host webcast and conference call to review and update the HPN424 data presented at ASCO and provide a 
    pipeline update today at 4 p.m. ET /1 p.m. PT 
SOUTH SAN FRANCISCO, Calif., June 04, 2021 -- Harpoon Therapeutics, Inc. (NASDAQ: HARP), a clinical-stage immunotherapy 
company developing a novel class of T cell engagers, today presented interim data from the ongoing dose-escalation 
portion of a Phase 1/2a trial for HPN424 in patients with metastatic castration-resistant prostate cancer (mCRPC) at 
the 2021 American Society of Clinical Oncology (ASCO) Annual Meeting. HPN424 targets prostate-specific membrane antigen 
(PSMA) and is based on Harpoon's proprietary Tri-specific T cell Activating Construct (TriTAC(R)) platform designed to 
recruit a patient's own immune cells to kill tumor cells. 
As of April 23, 2021, the data cutoff date for the ASCO presentation, 89 patients have been dosed across 13 cohorts at 
fixed doses of 1.3 to 160 ng/kg and in step dosing cohorts up to 300ng/kg administered as a weekly intravenous 
infusion. These interim data demonstrated: 
  ? HPN424 was active and generally well tolerated 
  ? Antitumor activity included a confirmed PR per RECIST, PSA declines and circulating tumor cell (CTC) reductions 
  ? Treatment duration > 24 weeks observed in 15 of 74 (20%) pts, including 8 of 17 (47%) chemo-naïve patients 
  ? Cytokine release syndrome (CRS) has been transient and manageable with 4% of patients experiencing Grade 3 CRS 
  ? CRS and transaminitis events observed most often in Cycle 1, with diminished frequency and severity in subsequent 
    cycles 
  ? Introduction of step dose regimens has allowed for the administration of higher target doses, currently at 300ng/kg 
"These encouraging data for HPN424 are continuing to show clinical activity, target engagement, and a manageable safety 
profile in this heavily pretreated patient population," stated Jerry McMahon, Ph.D., President and CEO, Harpoon 
Therapeutics. "As our step dose cohorts continue to enroll patients, we believe we are nearing the dose we intend to 
explore in the first expansion cohort that we plan to initiate this year." 
"We are excited to share this clinical update from our HPN424 clinical trial. These data suggest that HPN424 is active 
and that the expected cytokine-mediated adverse events can be managed," said Natalie Sacks, M.D., Chief Medical Officer 
of Harpoon. "Our goal is to develop an effective immunotherapy treatment option for patients with prostate cancer." 
Trial Design and Interim Results from the HPN424 Phase 1/2a Clinical Trial 
This Phase 1/2a trial is a multicenter, open-label study designed to evaluate the safety, tolerability, 
pharmacokinetics and activity of HPN424 in patients with mCRPC who are progressing at the time of enrollment and have 
had at least two prior systemic treatments for metastatic disease. The initial ongoing phase of the trial is dose 
escalation, with the goal of determining a recommended dose for the expansion phase. The escalation phase began with 
single patient cohorts and transitioned to a 3x3 design when Grade 2 toxicity was observed. A step dosing regimen was 
introduced in December 2020. HPN424 is being administered to patients once weekly by intravenous infusion and the 
primary outcome measures are an assessment of safety and tolerability, pharmacokinetics, and pharmacodynamics. 
Secondary endpoints include duration of response, progression free and overall survival. Tumor assessments include PSA, 
CT and bone scans performed every 9 weeks. 
As of the April 23, 2021 cut-off date, 89 patients have been treated in 13 cohorts with fixed doses ranging from 1.3 to 
160 ng/kg and step dosing up to 300ng/kg using various regimens. Enrolled patients had a median of 5 prior therapies, 
including 73% with prior chemotherapy, and a median of two prior novel hormonal agents. Median PSA level was 129, with 
a range of 0.1-5000 ng/ml. The most frequent adverse events were cytokine release syndrome (CRS) ((all grade n=61 
(69%), grade >3 n=4 (4%)), chills ((all grade n=60 (67%), grade >3 n=0 (0%)), and pyrexia ((all grade n=58 (65%), grade 
 >3 n=2 (2%)). The majority of CRS events occurred with the first dose. 
Dose Limiting Toxicities (DLTs) were observed at doses ranging from 96 to 300ng/kg and did not limit escalation and 
Maximum Tolerated Dose has not been reached. The most common DLTs were Transaminitis G4 (n=6) and Cytokine Release 
Syndrome G3 (n=4). The most common reason for study discontinuation was progressive disease; two of 89 (2%) patients 
discontinued treatment due to treatment-related AEs. 
HPN424 demonstrated dose proportional increase in Cmax and AUC. Reduction in CTCs was seen in 36 of 64 (56%) patients 
with available baseline and on-treatment CTC counts. Fifteen of 74 (20%) pts with >1 post-baseline value had PSA 
decreases from baseline ranging from -2% to -76%, including 4 pts with PSA50 response and 2 pts with PSA30 response. A 
confirmed PR was observed in a patient treated at 160 ng/kg and that patient remains on study at 41 weeks. 
Patients continue to be enrolled in the escalation and step dosing phase of the trial, with a goal to identify a dose 
for an expansion phase. The expansion phase of the trial will further evaluate the safety and activity of HPN424 in 
patients with mCRPC. This trial is titled, "Study of HPN424 in Patients with Advanced Prostate Cancer". For additional 
information about the trial, please visit www.clinicaltrials.gov using the identifier NCT03577028. 
Conference Call and Webcast Today 
Harpoon's management will host a webcast and conference call at 4 p.m. ET / 1 p.m. PT on Friday, June 4, 2021 to review 
the data and provide an update on other pipeline programs. The live call may be accessed by dialing 866-951-6894 for 
domestic callers or 409-216-0624 for international callers and using conference ID # 2657278. 
A live webcast of the call will be available from the Events and Presentations section of the company's website at 
https://ir.harpoontx.com/events-and-presentations and will be archived there shortly after the live event. 
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(R)) 
platform, Harpoon is developing a pipeline of novel TriTACs initially focused on the treatment of solid tumors and 
hematologic malignancies. HPN424 targets PSMA and is in a Phase 1/2a trial for metastatic castration-resistant prostate 

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