Exhibit 99.1 PRESS RELEASE Prothena Reports First Quarter 2024 Financial Results and Business Highlights DUBLIN, Ireland, May 8, 2024 -- Prothena Corporation plc (NASDAQ:PRTA), a late-stage clinical biotechnology company with a robust pipeline of investigational therapeutics built on protein dysregulation expertise, today reported financial results for the first quarter of 2024 and provided business highlights. "We continued to meaningfully advance our wholly-owned and partnered programs across our protein ...

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 ______________________________________ FORM 10-K ______________________________________ (Mark One) ☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the year ended December 31, 2023 (Exact name of registrant as specified in its charter) ______________________________________ (State or other jurisdiction of incorporation or organization) Ireland 98-1111119 (I.R.S. Employer Identification No.) 77 S ...

Prothena Corporation plc (NASDAQ:PRTA) Q4 2023 Earnings Conference Call February 15, 2023 4:30 PM ET Company Participants Mark Johnson - Vice President of Investor Relations Gene Kinney - President and Chief Executive Officer Hideki Garren - Chief Medical Officer Tran Nguyen - Chief Financial Officer and Chief Strategy Officer Brandon Smith - Chief Operating Officer Conference Call Participants Charles Duncan - Cantor Fitzgerald Jay Olson - Oppenheimer Neena Bitritto-Garg - Citi Yasmeen Rahimi - Piper Sandl ...

200 mg n= ~32 (3:1) - ascent-2 • Evaluate the safety, tolerability, immunogenicity, pharmacokinetics, and pharmacodynamics of PRX012 in patients with Alzheimer's disease 16 Anti-α-synuclein Antibody • 10 million patients globally5 Ongoing Phase 2b PADOVA (NCT04777331) • Primary Endpoint: Time to confirmed motor progression event 3-year change from baseline in MDS-UPDRS Part III OFF score7 NNC6019: Potential First-in-Class Treatment for ATTR Amyloidosis Tran Nguyen Chief Strategy Officer and Chief Financial ...

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended September 30, 2023 Or ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Commission file number: 001-35676 ______________________________________ PROTHENA CORPORATION PUBLIC LIMITED COMPANY (Exact name of registrant as specified in its charter) __________________________________ ...

15 PRX012 0.070a >67b Data represent KD values from SPRa (nM) or IC50 from ELISAb (nM). • How does binding to protofibrils compare? PRX012s Binds Aβ Protofibrils With Very High Affinity SPR Binding Kinetics Greater affinity is driven largely by a slower binding dissociation Culture time 72 hours at 37°C PRX012s facilitates concentration-dependent clearance of pyroglutamate-modified Aβ (N3pE-Aβ) at concentrations that may be relevant for PRX012 clinical exposure PRX012s Promotes Simultaneous Microglia-Mediat ...

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 ______________________________________ FORM 10-Q _____________________________________ (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended June 30, 2023 Or ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Commission file number: 001-35676 ______________________________________ PROTHENA CORPORATION PUBLIC LIMITED COMP ...

Ab Tau ✓ Avoids T-cell response observed in other vaccines Rare Peripheral Amyloid Diseases PATHOGENIC PATHWAY Protein Misfolding KIDNEY Proteinuria Kidney failure SOLUBLE AGGREGATES AMYLOID FIBRILS CLONAL PLASMA CELLS INVOLVED IMMUNOGLOBU LIN LIGHT CHAIN HEART Restrictive cardiomyopathy Heart failure The four stages (Mayo Stages I–IV) of AL amyloidosis: life expectancy decreases as the disease progresses4,5 1 American Cancer Society. Available from: https://www.cancer.org/cancer/multiple-myeloma/treating/c ...

Investigational Therapies - Prothena's investigational therapeutic birtamimab has shown a significant survival benefit in patients with Mayo Stage IV AL amyloidosis, a rare disease affecting approximately 200,000 to 400,000 patients globally, with 30% categorized as Mayo Stage IV[156][155]. - The confirmatory Phase 3 AFFIRM-AL study for birtamimab is expected to enroll around 150 newly diagnosed patients, with topline data anticipated in 2024[158][157]. - Prasinezumab, an investigational antibody for Parkinson's disease, is part of a collaboration with Roche, with a Phase 2b PADOVA study enrolling 575 patients and topline data expected in 2024[163][160]. - PRX005, an anti-tau antibody for Alzheimer's disease, has advanced to a Phase 1 study, with topline data from the multiple ascending dose portion expected in 2023[174][173]. - PRX012, targeting Amyloid Beta for Alzheimer's disease, is part of Prothena's pipeline aimed at addressing the underlying causes of neurodegenerative diseases[176]. - The lead candidate PRX012 is advancing through a Phase 1 clinical trial, with topline data expected in 2023[181]. - PRX123, a dual Aβ-tau vaccine, is in preclinical development, with an IND filing anticipated in 2023[186]. Financial Performance - Total revenue for the three months ended March 31, 2023, was $2.2 million, an increase of 88% compared to $1.2 million for the same period in 2022[190]. - Collaboration revenue from BMS for US development services related to the Tau/PRX005 program was $2.1 million for the three months ended March 31, 2023, up from $1.1 million in 2022, representing a 92% increase[191]. - Research and development (R&D) expenses increased by $17.5 million, or 64%, to $44.8 million for the three months ended March 31, 2023, compared to $27.3 million in the prior year[193][196]. - General and administrative (G&A) expenses rose by $1.9 million, or 16%, to $13.7 million for the three months ended March 31, 2023, compared to $11.8 million in 2022[200]. - Interest income surged by $6.6 million, or 12,523%, to $6.7 million for the three months ended March 31, 2023, primarily due to higher interest rates and money market balances[202][203]. - The benefit from income taxes increased to $(2.9) million for the three months ended March 31, 2023, compared to $(1.7) million in 2022, reflecting adjustments to deferred tax assets[204]. Cash Flow and Capital - As of March 31, 2023, working capital decreased to $651.5 million from $668.9 million as of December 31, 2022, primarily due to cash use of $58.5 million for operating expenses[206]. - Cash and cash equivalents stood at $686.2 million as of March 31, 2023, with expectations that this will be sufficient to meet obligations for at least the next twelve months[207]. - Net cash used in operating activities was $47.5 million for the three months ended March 31, 2023, compared to $37.4 million for the same period in 2022[212][213]. - Net cash provided by financing activities was $23.3 million for the three months ended March 31, 2023, primarily from net proceeds of $20.7 million from the issuance of ordinary shares[216]. - The company expects full-year 2023 net cash used in operating and investing activities to be approximately $213 million to $229 million[226]. - The company anticipates requiring additional capital in the future for research and development of drug candidates, which may be raised through various financing methods[207]. Obligations and Expenses - Total contractual obligations as of March 31, 2023, amounted to $35.8 million, including $19.7 million in operating leases and $15.7 million in purchase obligations[220][225]. - A foreign currency exchange loss of approximately $141,000 was recorded for the three months ended March 31, 2023, compared to $70,000 in the same period in 2022[228]. - Cash used in investing activities was $48,000 for the three months ended March 31, 2023, primarily related to purchases of property and equipment[215]. Strategic Collaborations - Prothena has received approximately $100 million from Novo Nordisk for the acquisition of its ATTR amyloidosis business, with potential milestone payments totaling up to $1.23 billion[168]. - The global collaboration with Bristol Myers Squibb for neurodegenerative disease research has resulted in Prothena receiving a total of $230 million, with potential additional payments up to $2.2 billion[175]. - The Phase 1 study of NNC6019 for ATTR amyloidosis has shown safety and tolerability, with further studies being conducted by Novo Nordisk[166][169]. Research Focus - Prothena's pipeline includes multiple investigational therapies targeting neurodegenerative diseases, leveraging deep scientific expertise in protein dysregulation[151]. - The company is focusing on discovery programs that address significant unmet medical needs in neurological diseases, including AD and ALS[182].

UNITED STATES SECURITIES AND EXCHANGE COMMISSION For the year ended December 31, 2022 ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Washington, D.C. 20549 For the transition period from to Commission file number: 001-35676 ______________________________________ PROTHENA CORPORATION PUBLIC LIMITED COMPANY (Exact name of registrant as specified in its charter) ______________________________________ Ireland 98-1111119 (State or other jurisdiction of incorporation or ...