Company: IOBT
Filing Date: 2025-07-24
Form Type: S-3
Source: 0001193125-25-164495
Chunk: 3

Company: IO Biotech, Inc.
Filing Date: 2025-07-24
Form: S-3
Chunk 3
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 sale price of our
common stock was $1.93.

We are an “emerging growth company” and a “smaller reporting company” under the U.S. securities laws and as
such, have elected to comply with reduced public company reporting requirements for this prospectus and the documents incorporated by reference herein and may elect to comply with reduced public company reporting requirements in future filings. See
“Summary — Implications of Being an Emerging Growth Company and Smaller Reporting Company.”

Investing in our securities involves significant risks. We strongly recommend that you read carefully the risks we describe in this prospectus and in any accompanying prospectus supplement, as well as the risk factors that are incorporated by reference into this prospectus from our filings made with the Securities and Exchange Commission. See “ Risk Factors” beginning on page 6 of this prospectus.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy
or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus is , 2025.

TABLE OF CONTENTS

| ABOUT THIS PROSPECTUS                 |     |  1 |
| SUMMARY                               |     |  2 |
| THE OFFERING                          |     |  5 |
| RISK FACTORS                          |     |  6 |
| FORWARD-LOOKING STATEMENTS            |     |  7 |
| USE OF PROCEEDS                       |     | 10 |
| SELLING STOCKHOLDERS                  |     | 11 |
| PLAN OF DISTRIBUTION                  |     | 13 |
| LEGAL MATTERS                         |     | 16 |
| EXPERTS                               |     | 17 |
| WHERE YOU CAN FIND MORE INFORMATION   |     | 18 |
| INFORMATION INCORPORATED BY REFERENCE |     | 19 |

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ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement on Form S-3 that we filed with the Securities and Exchange
Commission (the “SEC”), using a “shelf” registration process. The selling stockholders may resell, from time to time, in one or more offerings, shares of our common stock offered by this prospectus. Information about the selling
stockholders may change over time. When the selling stockholders sell shares of our common stock under this prospectus, we will, if necessary and required by law, provide a prospectus supplement that will contain specific information about