Alpine Immune Sciences Completes Enrollment of Phase I Study of ALPN-101 and Announces Third Quarter Conference Call

Company to Discuss Topline Results and Provide Company Update on Third Quarter 2019 Conference Call and Webcast Scheduled for November 13, 2019 at 4:30 p.m. ET

Alpine Immune Sciences, Inc. ALPN, a clinical-stage immunotherapy company focused on developing innovative treatments for cancer, autoimmune/inflammatory, and other diseases, today announced that it has completed enrollment in all planned cohorts of the Phase I study of its lead program, ALPN-101, a first-in-class dual ICOS/CD28 antagonist. Alpine will discuss the preliminary findings during its third quarter 2019 company update conference call and webcast scheduled for November 13, 2019 at 4:30 p.m. ET.

The randomized, placebo-controlled, blinded study was designed to evaluate the safety, tolerability, pharmacokinetics, and pharmacodynamics of single and multiple doses of ALPN-101 in adult healthy volunteers. The results from this trial will help inform further development of ALPN-101 in serious autoimmune and inflammatory diseases.

The company will hold a conference call on November 13, 2019 to discuss third quarter results, recent development progress, and upcoming clinical development plans for both ALPN-101 and ALPN-202, Alpine's lead oncology program. The company will also review new ALPN-101 data presented at the American College of Rheumatology annual meeting and ALPN-202 data presented at the Society for the Immunotherapy of Cancer annual meeting.

Conference Call and Webcast Details

To access the live call by phone, dial (877) 407-0789 (domestic) or (201) 689-8562 (international). To access a live webcast of the call, please visit the Investor Relations section of the Alpine Immune Sciences website at www.alpineimmunesciences.com. The recorded webcast will be available for replay for approximately 30 days following the call.

About ALPN-101

ALPN-101 is a novel Fc fusion protein of a human inducible T cell costimulator ligand (ICOSL) variant immunoglobulin domain (vIgD™), and a first-in-class therapeutic designed to inhibit simultaneously the CD28 and ICOS inflammation pathways. CD28 and ICOS are closely related costimulatory molecules with partially overlapping roles in T cell activation likely connected to multiple autoimmune and inflammatory diseases. In preclinical models of graft versus host disease, inflammatory arthritis, connective tissue disease and multiple sclerosis, ALPN-101 demonstrates efficacy superior to blockade of the CD28 or ICOS pathways alone.

About ALPN-202

ALPN-202 is a first-in-class, conditional CD28 costimulator and dual checkpoint inhibitor, which has the potential to improve upon the efficacy of combined checkpoint inhibition without significant toxicities. Preclinical studies of ALPN-202 have successfully demonstrated superior efficacy in tumor models compared to checkpoint inhibition alone. We anticipate initiation of the first-in-human clinical study of ALPN-202 to begin by the first quarter of 2020.

About Alpine Immune Sciences, Inc.

Alpine Immune Sciences, Inc. is committed to leading a new wave of immune therapeutics, creating potentially powerful multifunctional immunotherapies to improve patients' lives via unique protein engineering technologies. Alpine has two lead programs. The first, ALPN-101 for autoimmune/inflammatory diseases, is a selective dual T-cell costimulation blocker engineered to reduce pathogenic T and B cell immune responses by blocking ICOS and CD28. The second, ALPN-202 for cancer, is a conditional CD28 costimulator and dual checkpoint inhibitor. Alpine is backed by world-class research and development capabilities, a highly-productive scientific platform, and a proven management team. For more information, visit www.alpineimmunesciences.com.

Forward-Looking Statements

This release contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, Section 21E of the Securities Exchange Act of 1934 and the Private Securities Litigation Reform Act of 1995. These forward-looking statements are not based on historical fact and include statements regarding our platform technology and potential therapies, the timing of and results from clinical trials and pre-clinical development activities, clinical and regulatory objectives and the timing thereof, and the potential efficacy, safety profile, future development plans, addressable market, regulatory success, and commercial potential of our product candidates. Forward-looking statements generally include statements that are predictive in nature and depend upon or refer to future events or conditions and include words such as "may," "will," "should," "would," "expect," "plan," "intend," and other similar expressions, among others. These forward-looking statements are based on current assumptions that involve risks, uncertainties, and other factors that may cause actual results, events, or developments to be materially different from those expressed or implied by such forward-looking statements. These risks and uncertainties, many of which are beyond our control, include, but are not limited to: clinical trials may not demonstrate safety and efficacy of any of our product candidates; our ongoing discovery and pre-clinical efforts may not yield additional product candidates; our discovery-stage and pre-clinical programs may not advance into the clinic or result in approved products; any of our product candidates may fail in development, may not receive required regulatory approvals, or may be delayed to a point where they are not commercially viable; we may not achieve additional milestones in our proprietary or partnered programs; the impact of competition; adverse conditions in the general domestic and global economic markets; as well as the other risks identified in our filings with the Securities and Exchange Commission. These forward-looking statements speak only as of the date hereof and we undertake no obligation to update forward-looking statements, and readers are cautioned not to place undue reliance on such forward-looking statements.

"Secreted Immunomodulatory Proteins", "SIP", "Transmembrane Immunomodulatory Protein," "TIP," "Variant Ig Domain," "vIgD" and the Alpine logo are registered trademarks or trademarks of Alpine Immune Sciences, Inc. in various jurisdictions.

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