- Cemdisiran Treatment Resulted in a 37 Percent Mean Reduction in 24-Hour Urine Protein to Creatinine Ratio, Relative to Placebo – a Key Prognostic Marker of Progression to End-Stage Kidney Disease in Patients with IgA Nephropathy -

- Acceptable Safety Profile, Supporting Continued Clinical Development -

- Full Results to Be Presented at Future Medical Congress -

Alnylam Pharmaceuticals, Inc. (Nasdaq: ALNY) announced today topline results from the Phase 2 study of cemdisiran, an investigational RNAi therapeutic targeting the C5 component of the complement pathway that is in development in collaboration with Regeneron Pharmaceuticals for the treatment of immunoglobulin A nephropathy (IgAN). At Week 32, treatment with cemdisiran resulted in a 37 percent mean reduction from baseline in the 24-hour urine protein to creatinine ratio relative to placebo – the primary endpoint of the study and an important prognostic marker of disease progression. The results of secondary endpoints were also consistent with a therapeutic benefit of cemdisiran in IgAN. There were no significant drug-related safety signals. We believe these collective efficacy and safety data support continued clinical development of cemdisiran monotherapy in patients with IgAN.

“We are encouraged by these topline results with cemdisiran demonstrating what we believe to be clinically meaningful reductions in proteinuria – an important prognostic factor in IgA nephropathy. IgAN is the most common inflammatory disease affecting the glomerulus of the kidney. It can progress to end-stage kidney disease, if left untreated,” said Sonalee Agarwal, Ph.D., Vice President and Program Leader for the Cemdisiran program at Alnylam. “Given the limited treatment options and significant unmet need in IgAN, we, together with our partners at Regeneron, are formulating our plans for the Phase 3 clinical development of cemdisiran.”

The Phase 2 study enrolled a total of 31 patients who were on stable doses of angiotensin converting enzyme (ACE) inhibitor or angiotensin II receptor blocker (ARB); nine were randomized to placebo and 22 to cemdisiran. The primary endpoint of the study was the percent change in the 24-hour urine protein to creatinine ratio (UPCR) at Week 32. Secondary endpoints at Week 32 included:

• Percent of patients with partial clinical remission (urine protein <1g/24-hours)
• Percent of patients with >50% reduction in 24-hour proteinuria
• Percent change from baseline in 24-hour proteinuria (g/24-hours)
• Change from baseline in UPCR as measured in spot urine
• Change from baseline in hematuria
• Frequency of adverse events (AEs)

This Phase 2 study was descriptive only and did not include statistical hypothesis testing. Treatment with cemdisiran led to a 37 percent (90% CI: 0, 61) mean reduction in 24-hour urine protein to creatinine ratio relative to placebo. All secondary efficacy endpoints trended in favor of cemdisiran, supporting the therapeutic hypothesis. There were no serious or severe adverse events (AEs) related to study drug, and the overall safety and tolerability profile of cemdisiran supports continued clinical development. One death was reported in the cemdisiran arm due to a post-surgical complication; this was not considered related to study drug by the investigator. There were no discontinuations from study drug due to AEs. Two of nine (22 percent) patients on placebo and 12 of 22 (55 percent) of patients on cemdisiran experienced treatment emergent AEs that were related to study drug.

About Phase 2 Study

The Phase 2 trial is a randomized, double-blind, placebo-controlled multicenter study to evaluate the efficacy and safety of cemdisiran in adult patients with immunoglobulin A nephropathy (IgAN). Thirty-one adult patients (≥18 years and ≤ 65 years of age) with a clinical diagnosis of primary IgAN were randomized in a 2:1 cemdisiran to placebo ratio. The study was conducted in three periods. The first was an observational 14-week run-in period during which patients’ blood pressure, kidney function, degree of hematuria, and proteinuria were measured and the standard of care remained unchanged. Patients did not receive study drug (cemdisiran or placebo) during this time. The second period was a 32-week treatment period, during which patients were dosed with 600 mg of cemdisiran or placebo every 4 weeks in combination with standard of care (angiotensin converting enzyme (ACE) inhibitors or angiotensin II receptor blockers (ARB)). The third period is a 52-week open-label extension (OLE) period to further evaluate the long-term safety and clinical activity of cemdisiran. During the OLE, all patients (including those initially on placebo) are treated with cemdisiran in combination with standard of care. The primary endpoint of the study is the percent change from baseline in 24-hour urine protein to creatinine ratio at week 32. Secondary endpoints include additional measures of proteinuria, changes in hematuria, percent of patients with partial clinical remission, and frequency of adverse events.

About Immunoglobulin A Nephropathy (IgAN)

Globally, IgAN is the most common inflammatory disease affecting the glomerulus of the kidney often progressing to kidney failure. IgAN impacts approximately 2.5 out of 100,000 individuals per year, with a peak incidence in the third and fourth decades of life. Proteinuria, particularly > 1 g/day, is a strong risk factor for disease progression, with 20-40 percent of patients progressing to end-stage kidney disease (ESKD). While the exact cause of IgAN is incompletely understood, biochemical, genetic, and clinical data suggest IgAN is an autoimmune disease that may originate from overproduction of aberrantly modified immunoglobulins (otherwise known as antibodies) that results in the activation of the complement pathway and subsequent promotion of inflammatory mediators.

About Cemdisiran

Cemdisiran (ALN-CC5) is a subcutaneously administered, investigational RNAi therapeutic targeting the C5 component of the complement pathway in development for the treatment of complement-mediated diseases. Cemdisiran utilizes our Enhanced Stabilization Chemistry (ESC)-GalNAc delivery platform.

About RNAi

RNAi (RNA interference) is a natural cellular process of gene silencing that represents one of the most promising and rapidly advancing frontiers in biology and drug development today. Its discovery has been heralded as "a major scientific breakthrough that happens once every decade or so," and was recognized with the award of the 2006 Nobel Prize for Physiology or Medicine. By harnessing the natural biological process of RNAi occurring in our cells, a new class of medicines, known as RNAi therapeutics, is now a reality. Small interfering RNA (siRNA), the molecules that mediate RNAi and comprise Alnylam's RNAi therapeutic platform, function upstream of today’s medicines by potently silencing messenger RNA (mRNA) – the genetic precursors – that encode for disease-causing or disease pathway proteins, thus preventing them from being made. This is a revolutionary approach with the potential to transform the care of patients with genetic and other diseases.

About Alnylam Pharmaceuticals

Alnylam (Nasdaq: ALNY) has led the translation of RNA interference (RNAi) into a whole new class of innovative medicines with the potential to transform the lives of people afflicted with rare and prevalent diseases with unmet need. Based on Nobel Prize-winning science, RNAi therapeutics represent a powerful, clinically validated approach yielding transformative medicines. Since its founding 20 years ago, Alnylam has led the RNAi Revolution and continues to deliver on a bold vision to turn scientific possibility into reality. Alnylam’s commercial RNAi therapeutic products are ONPATTRO® (patisiran), GIVLAARI® (givosiran), OXLUMO® (lumasiran) and Leqvio® (inclisiran) being developed and commercialized by Alnylam’s partner, Novartis. Alnylam has a deep pipeline of investigational medicines, including six product candidates that are in late-stage development. Alnylam is executing on its “Alnylam P5x25” strategy to deliver transformative medicines in both rare and common diseases benefiting patients around the world through sustainable innovation and exceptional financial performance, resulting in a leading biotech profile. Alnylam is headquartered in Cambridge, MA. For more information about our people, science and pipeline, please visit www.alnylam.com and engage with us on Twitter at @Alnylam, on LinkedIn, or on Instagram.

Alnylam Forward Looking Statements

Various statements in this release concerning Alnylam's future expectations, plans and prospects, including, without limitation, the safety and efficacy of cemdisiran as demonstrated by the Phase 2 topline results in patients with IgA nephropathy, plans for continued clinical development of cemdisiran, Alnylam’s aspiration to become a leading biotech company and the planned achievement of its “Alnylam P5x25” strategy, constitute forward-looking statements for the purposes of the safe harbor provisions under The Private Securities Litigation Reform Act of 1995. Actual results and future plans may differ materially from those indicated by these forward-looking statements as a result of various important risks, uncertainties and other factors, including, without limitation: the direct or indirect impact of the COVID-19 global pandemic or any future pandemic on Alnylam’s business, results of operations and financial condition and the effectiveness or timeliness of Alnylam’s efforts to mitigate the impact of the pandemic; the potential impact of the recent leadership transition on Alnylam’s ability to attract and retain talent and to successfully execute on its “Alnylam P5x25” strategy; Alnylam's ability to discover and develop novel drug candidates and delivery approaches and successfully demonstrate the efficacy and safety of its product candidates, including cemdisiran; the pre-clinical and clinical results for its product candidates, including cemdisiran; actions or advice of regulatory agencies and Alnylam’s ability to obtain and maintain regulatory approval for its product candidates, as well as favorable pricing and reimbursement; successfully launching, marketing and selling its approved products globally; delays, interruptions or failures in the manufacture and supply of its product candidates or its marketed products; obtaining, maintaining and protecting intellectual property; Alnylam’s ability to successfully expand the indication for OXLUMO or ONPATTRO (and vutrisiran, if approved) in the future; Alnylam's ability to manage its growth and operating expenses through disciplined investment in operations and its ability to achieve a self-sustainable financial profile in the future without the need for future equity financing; Alnylam’s ability to maintain strategic business collaborations; Alnylam's dependence on third parties for the development and commercialization of certain products, including Novartis, Sanofi, Regeneron and Vir; the outcome of litigation; the potential impact of current and the risk of future government investigations; and unexpected expenditures; as well as those risks more fully discussed in the “Risk Factors” filed with Alnylam's most recent Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission (SEC) and in its other SEC filings. In addition, any forward-looking statements represent Alnylam's views only as of today and should not be relied upon as representing its views as of any subsequent date. Alnylam explicitly disclaims any obligation, except to the extent required by law, to update any forward-looking statements.

This release discusses an investigational RNAi therapeutic and is not intended to convey conclusions about its efficacy or safety or potential use. There is no guarantee that this investigational therapeutic will successfully complete clinical development or gain health authority approval.

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