HOOKIPA Pharma Announces Positive Preliminary Phase 2 Data on HB-200 in Combination with Pembrolizumab in Patients with HPV16+ Head and Neck Cancers HB-200 in combination with pembrolizumab doubled the objective response

HOOKIPA Pharma Announces Positive Preliminary

Phase 2 Data on HB-200 in Combination with Pembrolizumab in Patients with HPV16+ Head and Neck Cancers

NEW YORK and VIENNA,

May 31st , 2023 - HOOKIPA Pharma Inc. (NASDAQ: HOOK, HOOKIPA'), a company developing a new class of immunotherapeutics

based on its proprietary arenavirus platform, today announced positive preliminary data from its ongoing Phase 2 study of HB-200 in combination

with pembrolizumab in patients with recurrent/metastatic Human Papillomavirus 16-positive (HPV16+) head and neck cancer. New data show

a 43 percent objective response rate (ORR) with HB-200 in combination with pembrolizumab in checkpoint inhibitor (CPI)-na ve patients,

doubling the 19 percent response rate for pembrolizumab alone. HOOKIPA plans to share the full data at a medical conference later this

year and is preparing to start a pivotal trial of HB-200 in combination with pembrolizumab in the 1st-line setting in 2024.

The company will host a webcast call June 1st at 8:00 a.m. EDT.

"Given the unmet medical need for patients

with recurrent/metastatic HPV16+ head and neck cancers, we are thrilled to share the preliminary data on HB-200 in combination with pembrolizumab

as they show a robust improvement in objective response rate and prolonged tumor control compared to pembrolizumab alone," said

Joern Aldag, Chief Executive Officer at HOOKIPA. "Efficacy, immunogenicity and safety data observed in our HB-200 program to-date

support our decision to progress to a pivotal trial of HB-200 in combination with pembrolizumab as 1st-line treatment for these

patients. The data also underscore the scalability of our arenaviral platform across a range of cancers."

HB-200 results (NCT04180215)

As of March 31, 2023, 35 patients with HPV16+

recurrent/metastatic head and neck cancers received HB-200 in combination with pembrolizumab as part of the Phase 2 study: 20 patients

were treated with HB-200 and pembrolizumab in the 1st-line setting and 15 in the 2nd-line setting. All received

HB-200 intravenously every three weeks for the first five doses and every six weeks thereafter. HB-200 means 2-vector therapy with alternating

application of HB-201 (LCMV), HB-202 (PICV) vectors, encoding HPV16 E6/E7 antigens.

in combination with pembrolizumab demonstrated promising anti-tumor activity with a 43 percent objective response

rate (6 of 14 patients with confirmed responses by investigator assessment under RECIST 1.1) among

CPI-na ve patients with recurrent/metastatic HPV16+ PD-L1+ head and neck cancer. These data represent a doubling of the 19 percent

objective response rate reported with pembrolizumab alone.1

As of March 31, 2023, 14 patients with at least two imaging assessments were included in the interim efficacy analysis.

Six patients responded (one with confirmed complete response and five with confirmed partial responses), with a 71 percent disease control

rate (10 of 14 patients), meaning stable disease or a complete or partial response. While recruitment is ongoing, based on these data,

HOOKIPA is preparing to start a pivotal trial of HB-200 in combination with pembrolizumab as 1st-line treatment of recurrent/metastatic

HPV16+ PD-L1+ head and neck cancers in 2024.

plus combination data

on HB-200 in combination with pembrolizumab in the 2nd-line plus setting are trending positively in this small initial cohort,

but they are preliminary and need further maturation. As of March 31, 2023, five patients with at least two imaging assessments were included

in the interim efficacy analysis based on RECIST 1.1. Preliminary results show one confirmed partial response and three patients with

stable disease. Preliminary median progression-free survival in this small cohort was 5.3 months. Enrollment is ongoing, and a decision

on a potential path forward in the 2nd-line plus setting will be made in 2024.

the limited options for heavily pre-treated patients with recurrent/metastatic HPV16+ head and neck cancers, HOOKIPA continues to evaluate

HB-200 as monotherapy among these patients in the ongoing Phase 1/2 trial. Follow-up data show HB-200 monotherapy demonstrated a preliminary

median overall survival of 14.2 months in the intent-to-treat population, indicating potential for prolonged clinical benefit in this

heavily pre-treated population. These data are based on 11 patients who received HB-200 as monotherapy at the same dose being evaluated

in combination with pembrolizumab, with a median follow-up period of 12.8 months. Additional patients are also being followed to continue

to assess median overall survival in a larger cohort.

Importantly, new follow-up data from heavily pre-treated

patients show an association between the induction of unprecedented levels of functional T cells after treatment with HB-200 monotherapy

and clinical benefit. T cell increases were rapid and sustained for at least 8 months, as of data cut-off. Patients who achieved disease

control after treatment with HB-200 monotherapy generally had greater CD8+ T cell infiltration in tumors compared to patients whose disease

progressed, suggesting an association of HB-200-induced T cells and clinical benefit.

Safety and tolerability profile

Results from the Phase 1/2 study showed that HB-200

was generally well tolerated among 132 patients treated. The safety profile was similar for patients who received HB-200 monotherapy or

HB-200 in combination with pembrolizumab. This favorable tolerability profile highlights the potential of HB-200 - and arenaviral

immunotherapies in general - to be combined with other immunotherapies where tumor antigen-specific T cells are needed. Only seven

percent of patients showed serious adverse events related to the treatment with HB-200. Only two percent of patients discontinued due

Harrington et al. Pembrolizumab With or Without Chemotherapy in Recurrent or Metastatic Head

and Neck Squamous Cell Carcinoma: Updated Results of the Phase III KEYNOTE-048 Study. Journal of Clinical Oncology. 2023;41(4);790-802.

Webcast: HOOKIPA will host a live webcast

on June 1, 2023 at 8:00 a.m. EDT. Joern Aldag, Chief Executive Officer, Katia Schlienger M.D., Ph.D., Chief Medical Officer, and Klaus

Orlinger, Ph.D., Chief Scientific Officer will provide an overview of the HB-200 data and future plans for HOOKIPA's oncology program.

Alan Ho, M.D., Ph.D., a study investigator, will also

offer commentary on the unmet medical need for patients with head and neck cancer.

The webcast and the presentation will be available

within the Investors & Media section of HOOKIPA's website at https://ir.hookipapharma.com/events. An archived replay will be

accessible for 30 days following the event.

HB-200 is HOOKIPA's lead oncology candidate

engineered with the company's proprietary replicating arenaviral vector platform. It comprises two single-vector compounds with

arenaviral backbones based on lymphocytic choriomeningitis virus and pichinde virus. Both express the same transgene encoding an E7E6

fusion protein derived from HPV16. HB-200 is an alternating 2-vector immunotherapy designed to further focus the immune response against

the encoded antigen. HB-200 in combination with pembrolizumab received Fast Track Designation from the U.S. Food and Drug Administration

for the treatment of 1st-line recurrent/metastatic HPV16+ head and neck cancers.

About the HB-200 trial (NCT04180215)

This Phase 1/2 clinical trial is an open-label

trial evaluating HB-200 for the treatment of advanced HPV16+ cancers. Phase 1 assessed various dose levels, regimen, and modes of administration

in a post-standard of care setting. Based on safety and tolerability, initial anti-tumor activity and T cell response data, HB-200 advanced

for further development in Phase 2.

The Phase 2 part of the trial is open-label with

primary endpoints of efficacy based on objective response and disease control rate as defined by RECIST 1.1 and iRECIST. The trial is

evaluating HB-200 in combination with pembrolizumab in the 1st-line and 2nd-line plus settings, as well as HB-200

alone in the post-standard of care setting. HOOKIPA anticipates sharing an additional data update at an upcoming medical conference.

Human Papillomavirus-driven Cancers

Human Papillomavirus,

or HPV, is a common viral infection estimated to cause about 5 percent of the worldwide cancer burden. This includes up to 60 percent

of head and neck, 89 percent of cervical, 78 percent of vaginal, 88 percent of anal, 67 percent of vulvar and 50 percent of penile cancers.

While there are numerous HPV types associated

with cancer, HPV16 is the most common cause of cancer. Most HPV infections are cleared from the body with no lasting consequences. However,

in some cases, HPV DNA becomes integrated into chromosomal DNA. When host cells take up this DNA, they express the HPV E6 and E7 proteins.

This uptake can potentially lead to cancer since expression of these proteins leads to alterations in cell cycle control, which in turn

predisposes these cells to become cancerous.

HOOKIPA Pharma Inc. (NASDAQ: HOOK) is a

clinical-stage biopharmaceutical company focused on developing novel immunotherapies, based on its

proprietary arenavirus platform, which are designed to mobilize and amplify targeted T cells and thereby fight or prevent serious disease. HOOKIPA's

replicating and non-replicating technologies are engineered to induce robust and durable antigen-specific CD8+ T cell responses and

pathogen-neutralizing antibodies. HOOKIPA's pipeline includes its wholly owned investigational arenaviral immunotherapies

targeting Human Papillomavirus 16-positive cancers, prostate cancers, and other undisclosed programs. HOOKIPA is collaborating with

Roche on an arenaviral immunotherapeutic for KRAS-mutated cancers. In addition, HOOKIPA aims to develop functional cures of HBV and

HIV in collaboration with Gilead.

Find out more about HOOKIPA online at www.hookipapharma.com.

Forward Looking Statements

statements set forth in this press release constitute "forward-looking" statements within the meaning of the Private Securities