Zag Bio is a Cambridge, Massachusetts biotechnology company developing thymus-targeting bifunctional antibody medicines to treat and prevent autoimmune diseases. The company's platform engages the body's natural mechanism for T cell tolerance by delivering antigens to the thymus, expanding antigen-specific thymic regulatory T cells (Tregs) while depleting antigen-specific T effector cells (Teff). Founded in 2022 and incubated by Polaris Partners, Zag Bio emerged from stealth in October 2025 with $80 million in financing. Its lead program, ZAG-101, targets Type 1 diabetes, with additional discovery programs aimed at other autoimmune indications. The company's scientific approach was inspired by the research of co-founder Diane Mathis, PhD, of Harvard Medical School.
Company data and valuation marks are estimates and may be incomplete, stale, erroneous, or revised.
Founded
2022
Employees
11–50
Total Funding
$80M
1 rounds
Total raised $80M across 1 rounds
Funding data and valuation marks are estimates and may be incomplete, stale, erroneous, or revised.
Last updated 06-25-2026
Latest Round
Type
Series A
Date
October 28, 2025
Amount
$80M
Valuation
—
Lead Investors
Jason F. Cole
Chief Executive Officer
John Kulman
Co-Founder & Chief Scientific Officer
Diane Mathis
Co-Founder & Scientific Founder
Jo Viney
Co-Founder
Alan Crane
Co-Founder (Partner, Polaris Partners)
Competitor list is illustrative and may be incomplete, stale, or erroneous.
Seismic Therapeutic
Biotech applying machine learning to discover precision immunology medicines for autoimmune and inflammatory disease.
Sonoma Biotherapeutics
Clinical-stage company developing engineered regulatory T cell (Treg) therapies for autoimmune and inflammatory diseases.
Quell Therapeutics
Clinical-stage developer of engineered Treg cell therapies for autoimmune diseases and transplant tolerance.
GentiBio
Biotech engineering autologous regulatory T cell therapies for autoimmune, allergic, and inflammatory diseases including Type 1 diabetes.
Cugene
Biotech developing engineered cytokine therapeutics aimed at selectively expanding regulatory T cells for autoimmune disease.
Pandion Therapeutics
Biotech developing bifunctional antibody therapies for autoimmune disease; acquired by Merck for $1.85B in 2021. Cited as a predecessor in the targeted-Treg space.
No. Zag Bio is a private company and does not have a public stock ticker or trade on a public stock exchange. Its shares are generally held by founders, employees, investors, and other private shareholders. Buyers and sellers may be able to transact in Zag Bio shares through private secondary transactions, but any transaction depends on share availability, buyer and seller agreement, transfer restrictions, company approval rights, and any applicable right of first refusal. There is no guarantee that Zag Bio will complete an IPO or other liquidity event.
Yes, it is sometimes possible to buy Zag Bio shares pre-IPO through private secondary transactions. This depends on finding a willing seller, company approval, and satisfying any transfer restrictions or rights of first refusal.
Buyers interested in buying Zag Bio shares on the secondary market typically do so through SetterVC and other secondary-market platforms, subject to eligibility requirements, share availability, transfer restrictions, and issuer approval. Buyers may need to satisfy sophistication, accreditation, institutional, platform, regulatory, or other eligibility requirements before participating. Once eligible, buyers may be able to view listings, make bids, and work with a licensed broker through the transaction process. Buyers should ensure they have appropriate legal and financial advisors guiding them before completing any transaction.
Zag Bio's latest disclosed funding round was a Series A round in October 28, 2025. The round raised approximately $80M, with Polaris Partners and T1D Fund listed as disclosed lead or major investors. Primary funding rounds are different from secondary transactions: in a primary round, capital goes to the company, while in a secondary transaction, investors buy existing shares from current shareholders. Funding-round data reflects publicly reported or collected information and may be incomplete.
Zag Bio has raised approximately $80M in disclosed funding across 1 round. These figures reflect primary capital raised by the company and do not include every possible secondary transaction, undisclosed round, debt facility, or private transfer. Reported funding totals can change as new rounds are announced or older round details are corrected. Eligible users can use SetterVC to track Zag Bio's funding history alongside private-market activity where available.
Zag Bio's disclosed investors include Polaris Partners and T1D Fund. Investor lists are based on public reporting, company announcements, and collected funding-round data, and may be incomplete. Participation in a prior funding round does not mean those investors are currently buying or selling shares. On SetterVC, eligible users can review Zag Bio's funding history, valuation history, and private-market activity alongside other venture-backed companies.
Zag Bio's most-cited competitors include Seismic Therapeutic, Sonoma Biotherapeutics, Quell Therapeutics, GentiBio, Cugene and Pandion Therapeutics. Investors often compare these companies by sector, product focus, valuation, funding raised, growth signals, investor base, and private-market activity.
Secondary-market demand for Zag Bio shares can be affected by company performance, revenue growth, profitability, funding history, valuation, investor interest, sector momentum, public-market conditions, expected timing of a liquidity event, and the availability of shares for sale. Demand can also be affected by transfer restrictions, company approval rights, right of first refusal processes, limited information, and the price expectations of buyers and sellers. Strong demand does not guarantee strong pricing, liquidity, or investment returns. Weak demand does not necessarily reflect the company's long-term prospects. Demand signals should not be treated as a recommendation or prediction of investment performance. Buyers and sellers should treat demand signals as informational and conduct their own diligence before transacting.
Sellers often rely on intermediaries and platforms, such as SetterVC and other secondary-market platforms, to identify potential buyers. The exact process varies by company and transaction, but sellers often begin by confirming their ownership, desired price, transferability, and any company approval or notice requirements. If the seller agrees with a buyer on acceptable price and terms, the company may need to be notified through a share transfer notice or similar process. If a right of first refusal, company approval right, or other transfer restriction applies, the seller may need to wait until that process is completed. The parties may then execute a purchase and sale agreement, complete required transfer documentation, and close if all required conditions are satisfied. Sellers should always seek proper legal and financial advice before completing the transaction.
Yes, current and former Zag Bio employees, early investors, and other existing shareholders may be able to sell vested shares before an IPO through a private secondary sale. This is not automatic; it depends on whether the shareholder has transferable shares, whether there is buyer demand, and whether the company's governing documents permit the transfer. Many companies require prior notice, company approval, or a right of first refusal before shares can be sold. Sellers should also seek proper legal and financial advice before proceeding.
A Zag Bio secondary transaction usually involves an existing shareholder selling shares to a buyer before a public listing. The buyer and seller typically agree on price, number of shares, share class, and closing conditions. The seller may then need to notify Zag Bio through a share transfer notice or similar process. If Zag Bio or existing investors have approval rights, transfer restrictions, or a right of first refusal, those steps may need to be completed before the transfer can close. The parties typically enter into a purchase and sale agreement, complete any required transfer documentation, and close only if the necessary conditions are satisfied. Timing and certainty can vary by company and transaction.
In most private secondary transactions, parties commonly use a purchase and sale agreement that outlines price, terms, and conditions. They may also use share transfer documentation, often a stock transfer notice, share transfer notice, transfer instruction, or similar document, along with any required company approval or right of first refusal materials. Proof of ownership, such as a cap table entry, share certificate, brokerage statement, issuer confirmation, or administrator confirmation, may also be important. Buyers often request recent company financials, but private companies may limit disclosure. Since every deal varies, buyers and sellers should consult legal and financial advisors to understand which documents are needed.
Buying Zag Bio shares pre-IPO is risky. Shares are illiquid, no IPO or liquidity event is guaranteed, valuations can change, transfers may require company approval, and private companies may provide limited financial disclosure. Be prepared for total loss. SetterVC and Setter Capital do not provide due diligence, legal, tax, accounting, valuation, or investment advice. Buyers must conduct their own due diligence, verify information, and seek independent legal and investment advice before proceeding.
Private secondary shares are typically illiquid. Unlike public stocks, there is no active public market, so selling them can be difficult and time-consuming. Sales depend on finding a willing buyer and often require company approval. Investors should be prepared to hold the shares for an extended period, with no guarantee of a future sale. Always assess your need for liquidity before investing.
SetterVC and Setter Capital do not provide due diligence, legal, tax, accounting, valuation, or investment advice. Buyers must conduct their own due diligence, including verifying ownership, transferability, legal structure, company approval, and assessing the company's prospects. SetterVC and Setter Capital do not provide advice on whether an investment is good, what price to pay, or what the best bid or ask is. SetterVC and Setter Capital may share documents in some circumstances, but it does not guarantee their accuracy or completeness. Due diligence is essential. Seek legal and investment advice as needed.
Before buying Zag Bio shares, a buyer should try to review the share class, price per share, implied valuation, transfer restrictions, ROFR process, company approval rights, seller ownership evidence, recent financing or tender-offer information, available financial information, information rights, resale restrictions, tax considerations, and expected liquidity paths. Not all information may be available for a private company. Buyers should confirm available diligence, process details, and information needs with their own legal, tax, and investment advisers.
SPVs carry risks. Examples include the need to confirm the company allows SPV-based transfers, verify that the SPV truly owns the shares or interests it claims to own, and ensure it has not sold more interests than it holds. Due diligence is essential. Seek legal and investment advice as needed.
Forward contracts carry risks. Examples include the seller refusing to transfer the shares at the future date, even if the seller owns them, the seller going bankrupt with creditors claiming the shares, or the seller committing the same shares to multiple parties. Due diligence is essential. Seek legal and investment advice as needed.
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