Idiopathic Recurrent Pericarditis

– ARCALYST® (rilonacept) Q4 2023 and full-year 2023 net product revenue of $71.2 million and $233.2 million, respectively – – ARCALYST 2024 net product revenue expected to be $360 - $380 million, representing ~59% year-over-year growth at the midpoint – – Abiprubart Phase 2 rheumatoid arthritis data from Cohort 4 and a new development indication expected in April 2024 – – Cash reserves of $206.4 million expected to fund operations into at least 2027 – – Conference call and webcast scheduled for 8:30 am ET today – HAMILTON, Bermuda, Feb. 28, 2024 (GLOBE NEWSWIRE) -- Kiniksa Pharmaceuticals, Ltd. (Nasdaq: KNSA) (Kiniksa), a commercial-stage biopharmaceutical company with a pipeline of immune-modulating assets designed to target a spectrum of cardiovascular and autoimmune diseases, today reported fourth quarter and full-year 2023 financial results and recent portfolio execution. “Kiniksa meaningfully advanced its business in 2023, primarily through robust ARCALYST net product revenue and collaboration profit growth. Significant growth remains with ARCALYST in recurrent pericarditis, and we expect to help an increasing number of patients in the years ahead. Importantly, we anticipate our robust commercial performance to contribute to our strong financial position and ability to drive growth across our business,” said Sanj K. Patel, Chairman and Chief Executive Officer of Kiniksa. “Additionally, abiprubart recently showed clinical effect in the first three cohorts of the Phase 2 trial in rheumatoid arthritis. We now expect to advance the asset into a Phase 2b trial in a new indication, funding for which is included in our current cash runway guidance. Data from the fourth cohort of the abiprubart Phase 2 trial are intended to inform trial design and are expected in April.” Portfolio and Collaboration Execution ARCALYST (IL-1α and IL-1β cytokine trap) ARCALYST net product revenue was $71.2 million and $233.2 million for the fourth quarter and full-year 2023, respectively. Since launch in April 2021, more than 1,700 prescribers have written ARCALYST prescriptions for recurrent pericarditis. As of the end of the fourth quarter of 2023, average total duration of ARCALYST therapy in recurrent pericarditis had increased to approximately 23 months. As of the end of the fourth quarter of 2023, approximately 9% of the target 14,000 multiple-recurrence patients were actively on ARCALYST treatment. A poster entitled Rilonacept Utilization in a Steroid-Sparing Paradigm for Recurrent Pericarditis: Real-World Evidence Demonstrating Increased Adoption is planned to be presented at the upcoming American College of Cardiology Scientific Session (ACC.24) in April 2024. Abiprubart (anti-CD40 monoclonal antibody inhibitor of CD40-CD154 interaction) Kiniksa previously announced topline data from the Phase 2 clinical trial of abiprubart in rheumatoid arthritis, showing that the trial met its primary efficacy endpoint: change from baseline in Disease Activity Score of 28 Joints Using C-reactive Protein (DAS28-CRP) versus placebo. In Cohorts 1 and 2 (pharmacokinetic lead-in), multiple doses of abiprubart were well-tolerated. In Cohort 3, the abiprubart 5 mg/kg subcutaneous (SC) weekly dose level achieved statistical significance. The 5 mg/kg SC biweekly dose level did not achieve statistical significance. Across both dose levels abiprubart reduced Rheumatoid Factor, a clinical marker of disease activity and an autoantibody pharmacodynamic marker of CD40 target engagement. Abiprubart was well-tolerated, with no dose-related adverse experiences observed. Kiniksa expects data from the fourth cohort (Cohort 4) of the Phase 2 clinical trial in April 2024. Cohort 4 will evaluate a fixed dose level administered as a single subcutaneous injection once monthly. Mavrilimumab (monoclonal antibody inhibitor targeting GM-CSFRα) Kiniksa is evaluating potential partnership opportunities to advance development of mavrilimumab, which has generated positive data in mid-stage clinical trials across multiple indications. Vixarelimab (monoclonal antibody inhibitor of signaling through OSMRβ) In the fourth quarter of 2023, Kiniksa recognized a $10.0 million development milestone related to a second new indication under its global license agreement with Genentech, a member of the Roche Group. Financial Results Total revenue for the fourth quarter of 2023 was $83.4 million, compared to $61.9 million for the fourth quarter of 2022. Total revenue for the full-year 2023 was $270.3 million, compared to $220.2 million for the full-year 2022. Total revenue for the fourth quarter of 2023 included $12.2 million in license and collaboration revenue, compared to $21.9 million for the fourth quarter of 2022. Total revenue for the full-year 2023 included $37.1 million in license and collaboration revenue, compared to $97.7 million for the full-year 2022. Total operating expenses for the fourth quarter of 2023 were $83.3 million, compared to $55.8 million for the fourth quarter of 2022. Total operating expenses for the full-year 2023 were $295.5 million, compared to $210.4 million for the full-year 2022. Total operating expenses for the fourth quarter of 2023 included $16.9 million in collaboration expenses, which are driven by ARCALYST collaboration profitability, compared to $7.5 million for the fourth quarter of 2022. Total operating expenses for the full-year 2023 included $56.5 million in collaboration expenses, compared to $24.1 million for the full-year 2022. Total operating expenses for the fourth quarter of 2023 included $7.8 million in non-cash, share-based compensation expense, compared to $6.4 million for the fourth quarter of 2022. Total operating expense for the full-year 2023 included $27.1 million in non-cash, share-based compensation expense, compared to $25.1 million for the full-year 2022. Net income for the fourth quarter of 2023 was $25.2 million, compared to net income of $4.5 million for the fourth quarter of 2022. Net income for the full-year 2023 was $14.1 million, compared to net income of $183.4 million for the full-year 2022. Net income for the fourth quarter of 2023 included a tax benefit of $22.8 million, primarily due to the treatment of non-cash deferred tax assets, compared to a tax expense of $2.4 million for the fourth quarter of 2022. Net income for the full-year 2023 included a tax benefit of $30.7 million, compared to a tax benefit of $172.3 million for the full-year 2022, both primarily due to the treatment of non-cash deferred tax assets. As of December 31, 2023, Kiniksa had $206.4 million of cash, cash equivalents, and short-term investments and no debt. Financial Guidance Kiniksa expects 2024 ARCALYST net product revenue of between $360 million and $380 million. Kiniksa expects that its cash, cash equivalents, and short-term investments will fund its current operating plan into at least 2027. Conference Call Information Kiniksa will host a conference call and webcast at 8:30 a.m. Eastern Time on Wednesday, February 28, 2024, to discuss fourth quarter and full-year 2023 financial results and recent portfolio execution. Individuals interested in participating in the call via telephone may register here. Upon registration, all telephone participants will receive a confirmation email detailing how to join the conference call, including the dial-in number along with a unique passcode and registrant ID that can be used to access the call. To access the webcast, please visit the Investors and Media section of Kiniksa’s website. A replay of the event will also be available on Kiniksa’s website within approximately 48 hours after the event. About Kiniksa Kiniksa is a commercial-stage biopharmaceutical company focused on discovering, acquiring, developing, and commercializing therapeutic medicines for patients suffering from debilitating diseases with significant unmet medical need. Kiniksa’s immune-modulating assets, ARCALYST, abiprubart, and mavrilimumab, are based on strong biologic rationale or validated mechanisms, target a spectrum of underserved cardiovascular and autoimmune conditions, and offer the potential for differentiation. For more information, please visit . About ARCALYST ARCALYST is a weekly, subcutaneously injected recombinant dimeric fusion protein that blocks interleukin-1 alpha (IL-1α) and interleukin-1 beta (IL-1β) signaling. ARCALYST was discovered by Regeneron Pharmaceuticals, Inc. (Regeneron) and is approved by the U.S. Food and Drug Administration (FDA) for recurrent pericarditis, cryopyrin-associated periodic syndromes (CAPS), including Familial Cold Autoinflammatory Syndrome and Muckle-Wells Syndrome, and deficiency of IL-1 receptor antagonist (DIRA). The FDA granted Breakthrough Therapy designation to ARCALYST for the treatment of recurrent pericarditis in 2019 and Orphan Drug exclusivity to ARCALYST in 2021 for the treatment of recurrent pericarditis and reduction in risk of recurrence in adults and pediatric patients 12 years and older. The European Commission granted Orphan Drug Designation to ARCALYST for the treatment of idiopathic pericarditis in 2021. IMPORTANT SAFETY INFORMATION ABOUT ARCALYST ARCALYST may affect your immune system and can lower the ability of your immune system to fight infections. Serious infections, including life-threatening infections and death, have happened in patients taking ARCALYST. If you have any signs of an infection, call your doctor right away. Treatment with ARCALYST should be stopped if you get a serious infection. You should not begin treatment with ARCALYST if you have an infection or have infections that keep coming back (chronic infection). While taking ARCALYST, do not take other medicines that block interleukin-1, such as Kineret® (anakinra), or medicines that block tumor necrosis factor, such as Enbrel® (etanercept), Humira® (adalimumab), or Remicade® (infliximab), as this may increase your risk of getting a serious infection. Talk with your doctor about your vaccine history. Ask your doctor whether you should receive any vaccines before you begin treatment with ARCALYST. Medicines that affect the immune system may increase the risk of getting cancer. Stop taking ARCALYST and call your doctor or get emergency care right away if you have any symptoms of an allergic reaction. Your doctor will do blood tests to check for changes in your blood cholesterol and triglycerides. Common side effects include injection-site reactions (which may include pain, redness, swelling, itching, bruising, lumps, inflammation, skin rash, blisters, warmth, and bleeding at the injection site), upper respiratory tract infections, joint and muscle aches, rash, ear infection, sore throat, and runny nose. For more information about ARCALYST, talk to your doctor and see the Product Information. About Abiprubart Abiprubart is an investigational humanized monoclonal antibody that binds to CD40 and is designed to inhibit the CD40-CD154 (CD40 ligand) interaction, a key T-cell co-stimulatory signal critical for B-cell maturation and immunoglobulin class switching and Type 1 immune responses. Kiniksa believes disrupting the CD40-CD154 co-stimulatory interaction is an attractive approach to addressing multiple autoimmune disease pathologies. About Mavrilimumab Mavrilimumab is an investigational fully human monoclonal antibody that blocks activity of GM-CSF by specifically binding to the alpha subunit of the GM-CSF receptor (GM-CSFRα). Phase 2 clinical trials of mavrilimumab in rheumatoid arthritis and giant cell arteritis achieved their primary and secondary endpoints with statistical significance. Kiniksa is evaluating potential partnership opportunities for mavrilimumab. Forward-Looking Statements This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. In some cases, you can identify forward looking statements by terms such as “may,” “will,” “should,” “expect,” “plan,” “anticipate,” “could,” “intend,” “target,” “project,” “contemplate,” “believe,” “estimate,” “predict,” “potential” or “continue” or the negative of these terms or other similar expressions, although not all forward-looking statements contain these identifying words. All statements contained in this press release that do not relate to matters of historical fact should be considered forward-looking statements, including without limitation, statements regarding: our expectation that ARCALYST 2024 net product revenue will be between $360 million and $380 million; our plan to report data from Cohort 4 of our Phase 2 clinical trial of abiprubart in rheumatoid arthritis and a new development indication for abiprubart in April 2024; our expectation about our cash reserves funding our current operating plan into at least 2027; our expectation that we will help an increasing number of patients in the future; our plan to develop abiprubart in an additional indication; our plan to present a poster at the upcoming American College of Cardiology Scientific Session in April 2024; our beliefs about the mechanisms of our product candidates and potential impact of their approach, including that using abiprubart to disrupt the CD40-CD154 co-stimulatory interaction is an attractive approach to address multiple autoimmune disease pathologies; and our belief that all of our product candidates offer the potential for differentiation. These forward-looking statements are based on management’s current expectations. These statements are neither promises nor guarantees, but involve known and unknown risks, uncertainties and other important factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements, including without limitation, the following: delays or difficulty in enrollment of patients in, and activation or continuation of sites for, our clinical trials; delays or difficulty in completing our clinical trials as originally designed; potential for changes between final data and any preliminary, interim, top-line or other data from clinical trials; our inability to replicate results from our earlier clinical trials or studies; impact of additional data from us or other companies, including the potential for our data to produce negative, inconclusive or commercially uncompetitive results; potential undesirable side effects caused by our products and product candidates; our inability to demonstrate safety and efficacy to the satisfaction of applicable regulatory authorities; potential for applicable regulatory authorities to not accept our filings, delay or deny approval of any of our product candidates or require additional data or trials to support approval; inability to successfully execute on our commercial strategy for ARCALYST; our reliance on third parties as the sole source of supply of the drug substance and drug product used in our products and product candidates; our reliance on Regeneron as the current sole manufacturer of ARCALYST; risks arising from our ongoing technology transfer of ARCALYST drug substance manufacturing; raw material, important ancillary product and drug substance and/or drug product shortages; our reliance on third parties to conduct research, clinical trials, and/or certain regulatory activities for our product candidates; complications in coordinating requirements, regulations and guidelines of regulatory authorities across jurisdictions for our clinical trials; changes in our operating plan, business development strategy or funding requirements; and existing or new competition. These and other important factors discussed in our filings with the U.S. Securities and Exchange Commission, including under the caption “Risk Factors” contained therein, could cause actual results to differ materially from those indicated by the forward-looking statements made in this press release. Any such forward-looking statements represent management’s estimates as of the date of this press release. Except as required by law, we disclaim any intention or obligation to update or revise any forward-looking statements. These forward-looking statements should not be relied upon as representing our views as of any date subsequent to the date of this press release. ARCALYST® is a registered trademark of Regeneron. All other trademarks are the property of their respective owners. Every Second Counts! ® Kiniksa Investor and Media Contact Rachel Frank (339) 970-9437 rfrank@kiniksa.com KINIKSA PHARMACEUTICALS, LTD. CONSOLIDATED STATEMENTS OF OPERATIONS (In thousands, except share and per share amounts) (Unaudited) Three Months Ended Years Ended December 31, December 31, 2023 2022 2023 2022 Revenue: Product revenue, net $ 71,220 $ 39,939 $ 233,176 $ 122,524 License and collaboration revenue 12,175 21,945 37,083 97,656 Total revenue 83,395 61,884 270,259 220,180 Operating expenses: Cost of goods sold 9,584 6,710 33,407 22,895 Collaboration expenses 16,939 7,522 56,524 24,071 Research and development 20,052 14,390 76,097 65,490 Selling, general and administrative 36,739 27,215 129,427 97,951 Total operating expenses 83,314 55,837 295,455 210,407 Income (loss) from operations 81 6,047 (25,196 ) 9,773 Other income 2,369 794 8,544 1,253 Income (loss) before income taxes 2,450 6,841 (16,652 ) 11,026 Benefit (provision) for income taxes 22,787 (2,380 ) 30,736 172,337 Net income $ 25,237 $ 4,461 $ 14,084 $ 183,363 Net income per share attributable to common shareholders—basic $ 0.36 $ 0.06 $ 0.20 $ 2.64 Net income per share attributable to common shareholders—diluted 0.35 0.06 0.20 2.60 Weighted average common shares outstanding—basic 70,371,601 69,609,342 70,058,952 69,382,275 Weighted average common shares outstanding—diluted 72,660,171 71,369,394 71,922,915 70,421,322 KINIKSA PHARMACEUTICALS, LTD. SELECTED CONSOLIDATED BALANCE SHEET DATA (In thousands) (Unaudited) As of December 31, December 31, 2023 2022 Cash, cash equivalents, and short-term investments $ 206,371 $ 190,608 Working capital 212,631 195,994 Total assets 526,322 459,672 Accumulated deficit (477,950 ) (492,034 ) Total shareholders' equity 438,839 396,149 - -

– ARCALYST® (rilonacept) 2023 net product revenue grew ~90% year-over-year to $233.1 million (unaudited) – – ARCALYST 2024 net product revenue expected to be $360 - $380 million – – Abiprubart (KPL-404) Phase 2 rheumatoid arthritis trial met the primary efficacy endpoint in Cohort 3 at the weekly dose level – – Abiprubart Phase 2 rheumatoid arthritis data from Cohort 4 expected in Q2 2024 – – Cash reserves of $206.3 million (unaudited) expected to fund operations into at least 2027– HAMILTON, Bermuda, Jan. 04, 2024 (GLOBE NEWSWIRE) -- Kiniksa Pharmaceuticals, Ltd. (Nasdaq: KNSA) (Kiniksa), a commercial-stage biopharmaceutical company with a pipeline of immune-modulating assets designed to target a spectrum of cardiovascular and autoimmune diseases, today provided a corporate update. "Strong execution to date has laid the foundation for the continued advancement of Kiniksa’s portfolio in 2024. ARCALYST 2023 net product revenue grew ~90% year-over-year to $233.1 million, underscoring our robust commercial performance. We believe there is substantial opportunity with ARCALYST in recurrent pericarditis and expect to drive continued revenue growth and collaboration profitability by reaching an increasing number of patients. In fact, at the end of 2023 Kiniksa penetrated approximately 9% into the multiple-recurrence population, compared to approximately 5% at the end of 2022,” said Sanj K. Patel, Chairman and Chief Executive Officer of Kiniksa. “Additionally, abiprubart showed clinical effect in the first three cohorts of the Phase 2 trial in rheumatoid arthritis. Despite a high placebo response rate, the 5 mg/kg weekly dose level in Cohort 3 achieved statistical significance, but the 5 mg/kg biweekly dose level did not. We look forward to evaluating results from Cohort 4, and we will use the totality of the data to determine next steps for the program. Importantly, our strong financial position provides optionality to continue to invest across our business, including ARCALYST commercialization as well as both pipeline and business development.” Portfolio Execution ARCALYST (IL-1α and IL-1β cytokine trap) ARCALYST net product revenue was $71.2 million and $233.1 million for the fourth quarter and full year 2023, respectively (unaudited). Since launch in April 2021, more than 1,700 prescribers have written ARCALYST prescriptions for recurrent pericarditis. As of the end of the fourth quarter of 2023, average total duration of ARCALYST therapy in recurrent pericarditis increased to approximately 23 months. As of the end of the fourth quarter of 2023, approximately 9% of the target 14,000 multiple-recurrence patients were actively on ARCALYST treatment. Kiniksa increased the size of its salesforce to approximately 85 representatives by the end of 2023 to help drive further physician adoption and patient enrollments in 2024. Kiniksa expects 2024 ARCALYST net product revenue of between $360 million and $380 million. Abiprubart (anti-CD40 monoclonal antibody inhibitor of CD40-CD154 interaction) Kiniksa today announced that the Phase 2 clinical trial of abiprubart in rheumatoid arthritis met its primary efficacy endpoint, change from baseline in Disease Activity Score of 28 Joints Using C-reactive Protein (DAS28-CRP) versus placebo. In Cohorts 1 and 2 (pharmacokinetic (PK)-lead in), multiple doses of abiprubart were well-tolerated and enabled the proof-of-concept portion of the study. Although these cohorts were not powered for DAS28-CRP (Secondary Efficacy Endpoint), the following results were observed: In Cohort 1, in the abiprubart 2 mg/kg subcutaneous (SC) biweekly dosing group (n=6), the mean change from baseline in DAS28-CRP at Week 12 was -3.16 points compared to -1.09 points in pooled placebo recipients (n=4), (Mean Difference = -2.07, p=0.0312). In Cohort 2, in the abiprubart 5 mg/kg SC biweekly dosing group (n=6), the mean change from baseline in DAS28-CRP at Week 12 was -3.44 points compared to pooled placebo recipients (n=4), (Mean Difference = -2.35, p=0.0338). In Cohort 3, in the abiprubart 5 mg/kg SC weekly dosing group (n=27), the Least Squares (LS) mean change [95% confidence interval (CI)] from baseline in DAS28-CRP at Week 12 was -2.21 [-2.62, -1.80] points compared to -1.65 [-2.07, -1.23] points in placebo recipients (n=26), (LS Mean Difference = -0.56, p=0.0487). In Cohort 3, in the abiprubart 5 mg/kg SC biweekly dosing group (n=25), the LS mean change [95% CI] from baseline in DAS28-CRP at Week 12 was -2.00 [-2.43, -1.58] points compared to -1.65 [-2.07, -1.23] points in placebo recipients (n=26), (LS Mean Difference = -0.35, p=0.2140). Abiprubart significantly reduced Rheumatoid Factor (a clinical marker of disease activity and autoantibody pharmacodynamic marker of CD40 target engagement) by over 40% in both Cohort 3 dose levels. Abiprubart was well-tolerated, with no dose-related adverse experiences observed. Kiniksa has now completed enrollment in a fourth cohort (Cohort 4) of the Phase 2 clinical trial of abiprubart in rheumatoid arthritis. Cohort 4 will evaluate a fixed dose level administered as a single subcutaneous injection once monthly. The company expects data from Cohort 4 in the second quarter of 2024. Mavrilimumab (monoclonal antibody inhibitor targeting GM-CSFRα) Kiniksa is now evaluating potential partnership opportunities to advance development of mavrilimumab, which has generated positive data in mid-stage clinical trials across multiple indications. Corporate Update Kiniksa’s year-end 2023 cash, cash equivalents, and short-term investments of $206.3 million (unaudited) are expected to fund its current operating plan into at least 2027. 42nd Annual J.P. Morgan Healthcare Conference Sanj K. Patel, Chief Executive Officer and Chairman of the Board of Kiniksa will provide a corporate presentation at the 42nd Annual J.P. Morgan Healthcare Conference on January 8, 2024, at 1:30 p.m. Pacific Time (4:30 p.m. Eastern Time). A live webcast of Kiniksa’s presentation will be accessible through the Investors & Media section of the company’s website at . A replay of the webcast will also be available on Kiniksa’s website within approximately 48 hours after the event. About Kiniksa Kiniksa is a commercial-stage biopharmaceutical company focused on discovering, acquiring, developing, and commercializing therapeutic medicines for patients suffering from debilitating diseases with significant unmet medical need. Kiniksa’s immune-modulating assets, ARCALYST, abiprubart, and mavrilimumab, are based on strong biologic rationale or validated mechanisms, target a spectrum of underserved cardiovascular and autoimmune conditions, and offer the potential for differentiation. For more information, please visit . About ARCALYST ARCALYST is a weekly, subcutaneously injected recombinant dimeric fusion protein that blocks interleukin-1 alpha (IL-1α) and interleukin-1 beta (IL-1β) signaling. ARCALYST was discovered by Regeneron Pharmaceuticals, Inc. (Regeneron) and is approved by the U.S. Food and Drug Administration (FDA) for recurrent pericarditis, cryopyrin-associated periodic syndromes (CAPS), including Familial Cold Autoinflammatory Syndrome and Muckle-Wells Syndrome, and deficiency of IL-1 receptor antagonist (DIRA). The FDA granted Breakthrough Therapy designation to ARCALYST for the treatment of recurrent pericarditis in 2019 and Orphan Drug exclusivity to ARCALYST in 2021 for the treatment of recurrent pericarditis and reduction in risk of recurrence in adults and pediatric patients 12 years and older. The European Commission granted Orphan Drug Designation to ARCALYST for the treatment of idiopathic pericarditis in 2021. IMPORTANT SAFETY INFORMATION ABOUT ARCALYST ARCALYST may affect your immune system and can lower the ability of your immune system to fight infections. Serious infections, including life-threatening infections and death, have happened in patients taking ARCALYST. If you have any signs of an infection, call your doctor right away. Treatment with ARCALYST should be stopped if you get a serious infection. You should not begin treatment with ARCALYST if you have an infection or have infections that keep coming back (chronic infection). While taking ARCALYST, do not take other medicines that block interleukin-1, such as Kineret® (anakinra), or medicines that block tumor necrosis factor, such as Enbrel® (etanercept), Humira® (adalimumab), or Remicade® (infliximab), as this may increase your risk of getting a serious infection. Talk with your doctor about your vaccine history. Ask your doctor whether you should receive any vaccines before you begin treatment with ARCALYST. Medicines that affect the immune system may increase the risk of getting cancer. Stop taking ARCALYST and call your doctor or get emergency care right away if you have any symptoms of an allergic reaction. Your doctor will do blood tests to check for changes in your blood cholesterol and triglycerides. Common side effects include injection-site reactions (which may include pain, redness, swelling, itching, bruising, lumps, inflammation, skin rash, blisters, warmth, and bleeding at the injection site), upper respiratory tract infections, joint and muscle aches, rash, ear infection, sore throat, and runny nose. For more information about ARCALYST, talk to your doctor and see the Product Information. About Abiprubart (KPL-404) Abiprubart (KPL-404) is an investigational humanized monoclonal antibody that binds to CD40 and is designed to inhibit the CD40-CD154 (CD40 ligand) interaction, a key T-cell co-stimulatory signal critical for B-cell maturation and immunoglobulin class switching and Type 1 immune responses. Kiniksa believes disrupting the CD40-CD154 co-stimulatory interaction is an attractive approach to addressing multiple autoimmune disease pathologies. About the Phase 2 Clinical Trial of Abiprubart in Rheumatoid Arthritis The ongoing Phase 2 rheumatoid arthritis trial is a randomized, double-blind, placebo-controlled trial designed to evaluate pharmacokinetics, safety, and efficacy of chronic subcutaneous administration of abiprubart and to provide optionality to evaluate abiprubart across a range of autoimmune diseases. This trial enrolled patients with active rheumatoid arthritis who had an inadequate response or were intolerant to a Janus kinase inhibitor (JAKi) or at least one biologic disease-modifying anti-rheumatic drug (bDMARD). The multiple ascending-dose PK lead-in portion randomized 8 patients each in a 3:1 ratio to receive abiprubart 2 mg/kg or placebo (Cohort 1) or 5 mg/kg or placebo (Cohort 2), administered subcutaneously biweekly over a period of 12 weeks. The primary objective of this part of the trial was to evaluate pharmacokinetics, safety, and tolerability over 12 weeks. The secondary efficacy endpoint was change from baseline in DAS28-CRP versus placebo. The first part of the proof-of-concept portion of the trial (Cohort 3) randomized 78 patients in a 1:1:1 ratio to receive abiprubart 5 mg/kg SC weekly, abiprubart 5 mg/kg SC biweekly, or placebo over a period of 12 weeks. The final part of the proof-of-concept portion of the trial (Cohort 4) randomized 51 patients in a 3:2 ratio to receive a fixed 600 mg loading dose on Day 1 followed by 400 mg SC every four weeks or placebo over a period of 12 weeks. The primary efficacy endpoint of the proof-of-concept portion of the trial is change from baseline in DAS28-CRP versus placebo. About Mavrilimumab Mavrilimumab is an investigational fully human monoclonal antibody that blocks activity of GM-CSF by specifically binding to the alpha subunit of the GM-CSF receptor (GM-CSFRα). Phase 2 clinical trials of mavrilimumab in rheumatoid arthritis and giant cell arteritis achieved their primary and secondary endpoints with statistical significance. Kiniksa is now evaluating potential partnership opportunities for mavrilimumab. Forward-Looking Statements This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. In some cases, you can identify forward looking statements by terms such as “may,” “will,” “should,” “expect,” “plan,” “anticipate,” “could,” “intend,” “target,” “project,” “contemplate,” “believe,” “estimate,” “predict,” “potential” or “continue” or the negative of these terms or other similar expressions, although not all forward-looking statements contain these identifying words. All statements contained in this press release that do not relate to matters of historical fact should be considered forward-looking statements, including without limitation, statements regarding: our expectation that ARCALYST 2024 net product revenue will be between $360 million and $380 million; our plan to report data from Cohort 4 of our Phase 2 clinical trial of abiprubart in rheumatoid arthritis in the second quarter of 2024; our expectation about our cash reserves funding our current operating plan into at least 2027; our expectation that we will drive continued ARCALYST revenue growth and collaboration profitability by reaching an increasing number of patients; our beliefs about the mechanisms of our product candidates and potential impact of their approach, including that using abiprubart to disrupt the CD40-CD154 co-stimulatory interaction is an attractive approach to address multiple autoimmune disease pathologies; and our belief that all of our product candidates offer the potential for differentiation. These forward-looking statements are based on management’s current expectations. These statements are neither promises nor guarantees, but involve known and unknown risks, uncertainties and other important factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements, including without limitation, the following: delays or difficulty in enrollment of patients in, and activation or continuation of sites for, our clinical trials; delays or difficulty in completing our clinical trials as originally designed; potential for changes between final data and any preliminary, interim, top-line or other data from clinical trials; our inability to replicate results from our earlier clinical trials or studies; impact of additional data from us or other companies, including the potential for our data to produce negative, inconclusive or commercially uncompetitive results; potential undesirable side effects caused by our products and product candidates; our inability to demonstrate safety and efficacy to the satisfaction of applicable regulatory authorities; potential for applicable regulatory authorities to not accept our filings, delay or deny approval of any of our product candidates or require additional data or trials to support approval; inability to successfully execute on our commercial strategy for ARCALYST; our reliance on third parties as the sole source of supply of the drug substance and drug product used in our products and product candidates; our reliance on Regeneron as the current sole manufacturer of ARCALYST; risks arising from our ongoing technology transfer of ARCALYST drug substance manufacturing; raw material, important ancillary product and drug substance and/or drug product shortages; our reliance on third parties to conduct research, clinical trials, and/or certain regulatory activities for our product candidates; complications in coordinating requirements, regulations and guidelines of regulatory authorities across jurisdictions for our clinical trials; changes in our operating plan, business development strategy or funding requirements; and existing or new competition. These and other important factors discussed in our filings with the U.S. Securities and Exchange Commission, including under the caption “Risk Factors” contained therein, could cause actual results to differ materially from those indicated by the forward-looking statements made in this press release. Any such forward-looking statements represent management’s estimates as of the date of this press release. Except as required by law, we disclaim any intention or obligation to update or revise any forward-looking statements. These forward-looking statements should not be relied upon as representing our views as of any date subsequent to the date of this press release. ARCALYST® is a registered trademark of Regeneron. All other trademarks are the property of their respective owners. Every Second Counts! ® Kiniksa Investor and Media Contact Rachel Frank (339) 970-9437 rfrank@kiniksa.com

– ARCALYST® (rilonacept) Q3 2023 net product revenue of $64.8 million, representing ~94% year-over-year growth – – KPL-404 Phase 2 rheumatoid arthritis data from Cohorts 1-3 now expected in Q1 2024 – – Cash reserves of $201 million expected to fund operations into at least 2027 – – Conference call and webcast scheduled for 8:30 am ET today – HAMILTON, Bermuda, Oct. 31, 2023 (GLOBE NEWSWIRE) -- Kiniksa Pharmaceuticals, Ltd. (Nasdaq: KNSA) (Kiniksa), a biopharmaceutical company with a pipeline of immune-modulating assets designed to target a spectrum of cardiovascular and autoimmune diseases, today reported third quarter 2023 financial results and recent portfolio execution. “We continue to advance all aspects of our business, including strong revenue growth with ARCALYST and clinical trial execution with KPL-404, and we have cash runway into at least 2027,” said Sanj K. Patel, Chairman and Chief Executive Officer of Kiniksa. “On the commercial side, we are building the recurrent pericarditis market and are focused on helping as many patients as possible. We are currently tracking to the high end of our previously issued guidance of $220 million to $230 million in product revenue. Within our clinical development portfolio, we have completed enrollment in the third cohort of the Phase 2 trial of KPL-404 in rheumatoid arthritis. We now expect data from Cohorts 1-3 in the first quarter of 2024.” Portfolio ExecutionARCALYST (IL-1α and IL-1β cytokine trap) ARCALYST net product revenue was $64.8 million for the third quarter of 2023.Since launch, more than 1,450 prescribers have written ARCALYST prescriptions for recurrent pericarditis.As of the end of the third quarter of 2023, average total duration of ARCALYST therapy in recurrent pericarditis was approximately 20 months. Average total duration of therapy includes the approximately 45% of patients who restarted ARCALYST, within an average of 8 weeks, after having discontinued therapy. KPL-404 (monoclonal antibody inhibitor of CD40-CD154 interaction) Kiniksa completed enrollment of the third cohort of the Phase 2 clinical trial of KPL-404 in rheumatoid arthritis. The company now expects data from Cohorts 1-3 in the first quarter of 2024.Kiniksa is currently enrolling a fourth cohort (Cohort 4) of the Phase 2 clinical trial of KPL-404 in rheumatoid arthritis. The additional cohort will evaluate a fixed dose level administered as a single subcutaneous injection once monthly. The company expects data from Cohort 4 in the second quarter of 2024. Mavrilimumab (monoclonal antibody inhibitor targeting GM-CSFRα) Kiniksa is pursuing collaborative study agreements to evaluate the potential of mavrilimumab in rare cardiovascular diseases where the granulocyte macrophage colony stimulating factor (GM-CSF) mechanism has been implicated. Financial Results ARCALYST net product revenue for the third quarter of 2023 was $64.8 million, compared to $33.4 million for the third quarter of 2022. Total revenue for the third quarter of 2023 was $67.0 million, including $2.2 million in license and collaboration revenue, compared to total revenue for the third quarter of 2022 of $99.1 million, including $65.7 million in license and collaboration revenue. Total operating expenses for the third quarter of 2023 were $78.0 million, compared to $52.7 million for the third quarter of 2022. Total operating expenses for the third quarter of 2023 included $17.3 million in collaboration expenses, due to increasing ARCALYST profitability, compared to $4.6 million for the third quarter of 2022.Total operating expenses for the third quarter of 2023 included $6.8 million in non-cash, share-based compensation expense, compared to $6.0 million for the third quarter of 2022. Net loss for the third quarter of 2023 was $13.9 million, compared to net income of $224.1 million for the third quarter of 2022.As of September 30, 2023, Kiniksa had $201.1 million of cash, cash equivalents, and short-term investments and no debt. Financial Guidance Kiniksa expects 2023 ARCALYST net product revenue of between $220 million and $230 million.Kiniksa expects that its cash, cash equivalents, and short-term investments will fund its current operating plan into at least 2027. Conference Call Information Kiniksa will host a conference call and webcast at 8:30 a.m. Eastern Time on Tuesday, October 31, 2023, to discuss third quarter 2023 financial results and recent portfolio execution.Individuals interested in participating in the call via telephone may register here. Upon registration, all telephone participants will receive a confirmation email detailing how to join the conference call, including the dial-in number along with a unique passcode and registrant ID that can be used to access the call. To access the webcast, please visit the Investors and Media section of Kiniksa’s website. A replay of the event will also be available on Kiniksa’s website within approximately 48 hours after the event. About KiniksaKiniksa is a biopharmaceutical company focused on discovering, acquiring, developing, and commercializing therapeutic medicines for patients suffering from debilitating diseases with significant unmet medical need. Kiniksa’s immune-modulating assets, ARCALYST, KPL-404, and mavrilimumab, are based on strong biologic rationale or validated mechanisms, target a spectrum of underserved cardiovascular and autoimmune conditions, and offer the potential for differentiation. For more information, please visit www.kiniksa.com. About ARCALYSTARCALYST is a weekly, subcutaneously injected recombinant dimeric fusion protein that blocks interleukin-1 alpha (IL-1α) and interleukin-1 beta (IL-1β) signaling. ARCALYST was discovered by Regeneron Pharmaceuticals, Inc. (Regeneron) and is approved by the U.S. Food and Drug Administration (FDA) for recurrent pericarditis, cryopyrin-associated periodic syndromes (CAPS), including Familial Cold Autoinflammatory Syndrome and Muckle-Wells Syndrome, and deficiency of IL-1 receptor antagonist (DIRA). The FDA granted Breakthrough Therapy designation to ARCALYST for the treatment of recurrent pericarditis in 2019 and Orphan Drug exclusivity to ARCALYST in 2021 for the treatment of recurrent pericarditis and reduction in risk of recurrence in adults and pediatric patients 12 years and older. The European Commission granted Orphan Drug Designation to ARCALYST for the treatment of idiopathic pericarditis in 2021. IMPORTANT SAFETY INFORMATION ABOUT ARCALYST ARCALYST may affect your immune system and can lower the ability of your immune system to fight infections. Serious infections, including life-threatening infections and death, have happened in patients taking ARCALYST. If you have any signs of an infection, call your doctor right away. Treatment with ARCALYST should be stopped if you get a serious infection. You should not begin treatment with ARCALYST if you have an infection or have infections that keep coming back (chronic infection).While taking ARCALYST, do not take other medicines that block interleukin-1, such as Kineret® (anakinra), or medicines that block tumor necrosis factor, such as Enbrel® (etanercept), Humira® (adalimumab), or Remicade® (infliximab), as this may increase your risk of getting a serious infection.Talk with your doctor about your vaccine history. Ask your doctor whether you should receive any vaccines before you begin treatment with ARCALYST.Medicines that affect the immune system may increase the risk of getting cancer.Stop taking ARCALYST and call your doctor or get emergency care right away if you have any symptoms of an allergic reaction.Your doctor will do blood tests to check for changes in your blood cholesterol and triglycerides.Common side effects include injection-site reactions (which may include pain, redness, swelling, itching, bruising, lumps, inflammation, skin rash, blisters, warmth, and bleeding at the injection site), upper respiratory tract infections, joint and muscle aches, rash, ear infection, sore throat, and runny nose. For more information about ARCALYST, talk to your doctor and see the Product Information. About KPL-404KPL-404 is an investigational humanized monoclonal antibody that is designed to inhibit CD40-CD154 (CD40 ligand) interaction, a key T-cell co-stimulatory signal critical for B-cell maturation and immunoglobulin class switching and Type 1 immune responses. Kiniksa believes disrupting the CD40-CD154 interaction is an attractive approach to address multiple autoimmune disease pathologies. About MavrilimumabMavrilimumab is an investigational fully human monoclonal antibody that blocks activity of GM-CSF by specifically binding to the alpha subunit of the GM-CSF receptor (GM-CSFRα). Phase 2 clinical trials of mavrilimumab in rheumatoid arthritis and giant cell arteritis achieved their primary and secondary endpoints with statistical significance. Kiniksa is evaluating the development of mavrilimumab in rare cardiovascular diseases where the GM-CSF mechanism has been implicated. Forward-Looking StatementsThis press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. In some cases, you can identify forward looking statements by terms such as “may,” “will,” “should,” “expect,” “plan,” “anticipate,” “could,” “intend,” “target,” “project,” “contemplate,” “believe,” “estimate,” “predict,” “potential” or “continue” or the negative of these terms or other similar expressions, although not all forward-looking statements contain these identifying words. All statements contained in this press release that do not relate to matters of historical fact should be considered forward-looking statements, including without limitation, statements regarding: our expectation that we will report data from cohorts 1-3 of our Phase 2 clinical trial of KPL-404 in rheumatoid arthritis in the first quarter of 2024 and data from cohort 4 of such trial in the second quarter of 2024; our expectation that our full-year net product revenue will be at the high end of our $220 million to $230 million guidance range; our expectation about our cash reserves funding our current operating plan into at least 2027; our beliefs about the mechanisms of action of our product candidates and potential impact of their approach, including that using KPL-404 to disrupt the CD40-CD154 interaction is an attractive approach to address multiple autoimmune disease pathologies; and our belief that all of our product candidates offer the potential for differentiation. These forward-looking statements are based on management’s current expectations. These statements are neither promises nor guarantees, but involve known and unknown risks, uncertainties and other important factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements, including without limitation, the following: delays or difficulty in enrollment of patients in, and activation or continuation of sites for, our clinical trials; delays or difficulty in completing our clinical trials as originally designed; potential for changes between final data and any preliminary, interim, top-line or other data from clinical trials; our inability to replicate results from our earlier clinical trials or studies; impact of additional data from us or other companies, including the potential for our data to produce negative, inconclusive or commercially uncompetitive results; potential undesirable side effects caused by our products and product candidates; our inability to demonstrate safety and efficacy to the satisfaction of applicable regulatory authorities; potential for applicable regulatory authorities to not accept our filings, delay or deny approval of any of our product candidates or require additional data or trials to support approval; inability to successfully execute on our commercial strategy for ARCALYST; our reliance on third parties as the sole source of supply of the drug substance and drug product used in our products and product candidates; our reliance on Regeneron as the current sole manufacturer of ARCALYST; risks arising from our ongoing technology transfer of ARCALYST drug substance manufacturing; raw material, important ancillary product and drug substance and/or drug product shortages; our reliance on third parties to conduct research, clinical trials, and/or certain regulatory activities for our product candidates; complications in coordinating requirements, regulations and guidelines of regulatory authorities across jurisdictions for our clinical trials; changes in our operating plan, business development strategy or funding requirements; and existing or new competition. These and other important factors discussed in our filings with the U.S. Securities and Exchange Commission, including under the caption “Risk Factors” contained therein, could cause actual results to differ materially from those indicated by the forward-looking statements made in this press release. Any such forward-looking statements represent management’s estimates as of the date of this press release. Except as required by law, we disclaim any intention or obligation to update or revise any forward-looking statements. These forward-looking statements should not be relied upon as representing our views as of any date subsequent to the date of this press release. ARCALYST® is a registered trademark of Regeneron. All other trademarks are the property of their respective owners. Every Second Counts! ® Kiniksa Investor and Media ContactRachel Frank(339) 970-9437rfrank@kiniksa.com KINIKSA PHARMACEUTICALS, LTD.SELECTED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS)(In thousands)(Unaudited) Three Months Ended Nine Months Ended September 30, September 30, 2023 2022 2023 2022Revenue: Product revenue, net$64,802 $33,424 $161,956 $82,585License and collaboration revenue 2,244 65,711 24,908 75,711Total revenue 67,046 99,135 186,864 158,296Costs and operating expenses: Cost of goods sold 9,088 6,937 23,823 16,185Collaboration expenses 17,311 4,623 39,585 16,549Research and development 17,106 16,485 56,045 51,100Selling, general and administrative 34,468 24,677 92,688 70,736Total operating expenses 77,973 52,722 212,141 154,570Income (loss) from operations (10,927) 46,413 (25,277) 3,726Other income 2,428 322 6,175 459Income (loss) before income taxes (8,499) 46,735 (19,102) 4,185Benefit (provision) for income taxes (5,626) 177,358 7,679 174,717Net income (loss)$(14,125) $224,093 $(11,423) $178,902Net income (loss) per share attributable to common shareholders—basic$(0.20) $3.23 $(0.16) $2.58Net income (loss) per share attributable to common shareholders—diluted$(0.20) $3.18 $(0.16) $2.55Weighted average common shares outstanding—basic 70,186,016 69,445,071 69,953,591 69,305,755Weighted average common shares outstanding—diluted 70,186,016 70,552,018 69,953,591 70,286,444 KINIKSA PHARMACEUTICALS, LTD.SELECTED CONSOLIDATED BALANCE SHEET DATA(In thousands)(Unaudited) As of September 30,December 31, 2023 2022 Cash, cash equivalents, and short-term investments$201,084 $190,608 Working capital 202,371 195,994 Total assets 482,794 459,672 Accumulated deficit (503,457) (492,034)Total shareholders' equity 404,857 396,149