[424B5] Immuneering Corporation Prospectus Supplement (Debt Securities)

Rhea-AI Filing Summary

Immuneering Corporation (Nasdaq: IMRX) filed a Rule 424(b)(5) prospectus supplement dated June 23, 2025 that updates its existing at-the-market (ATM) offering program.

Key points:

• Public float: Updated to approximately $83.1 million, calculated on 30,016,759 non-affiliate shares at $2.77 on 6/18/25.
• Because float now exceeds $75 million, IMRX is no longer subject to the sales limitation of Form S-3 General Instruction I.B.6, which had capped sales to one-third of public float over any 12-month period.
• ATM activity to-date: 6,155,556 shares sold for gross proceeds of $18.7 million.
• Remaining capacity: Company may now issue up to an additional $31.29 million of Class A common stock through Piper Sandler under the 8/10/22 Equity Distribution Agreement.
• Market context: Last reported share price on 6/20/25 was $2.56, implying potential dilution if new shares are issued near current levels.

Investors should review the “Risk Factors” section referenced in the base ATM prospectus, as the filing states that investing in IMRX shares involves a high degree of risk.

Positive

• Removal of Form S-3 I.B.6 limitation grants IMRX full flexibility to raise capital when market conditions are favorable.
• Additional $31.3 M capacity strengthens potential liquidity runway without the need for a separate underwritten offering, reducing transaction costs.

Negative

• Potential dilution: issuing up to $31.3 M at ~$2.56 could notably expand share count and pressure valuation.
• Low share price context signals limited market appetite and may force IMRX to accept unfavorable pricing to secure funds.

Insights

Equity Capital Markets Analyst

TL;DR: IMRX lifts ATM sales cap; can raise $31.3 M more but shareholders face dilution at ~$2.50 share price.

The updated prospectus is procedurally significant: crossing the $75 M public-float threshold removes Form S-3 I.B.6 restrictions, giving management full flexibility to monetize equity quickly. The ATM has already generated $18.7 M, suggesting an immediate need for working capital typical of clinical-stage biotechs. However, with the stock at $2.56, any sizeable issuance will be dilutive and may pressure the share price. No new financial metrics or strategic updates are provided, so the event primarily affects capital structure rather than fundamentals. Overall, the filing is modestly negative for existing holders due to dilution risk, though positive for liquidity.

As Filed Pursuant to Rule 424(b)(5)

Registration No. 333-266738

PROSPECTUS SUPPLEMENT

(To Prospectus and Prospectus Supplement dated August 19, 2022 and Prospectus Supplement dated March 20, 2025)

Up to $31,293,843.89

IMMUNEERING CORPORATION

Class A Common Stock

This prospectus supplement (this “Current Prospectus Supplement”) supplements the prospectus dated August 19, 2022 (the “Base Prospectus”), the prospectus supplement dated August 19, 2022 (the “Initial Prospectus Supplement”) and the prospectus supplement dated March 20, 2025 (the “Second Prospectus Supplement”, and the Base Prospectus, together with the Initial Prospectus Supplement and Second Prospectus Supplement, the “ATM Prospectus”), relating to the offer and sale of shares of our Class A common stock from time to time pursuant to the terms of the Equity Distribution Agreement, dated August 10, 2022 (the “Agreement”), with Piper Sandler & Co. as sales agent. This Current Prospectus Supplement should be read in conjunction with the ATM Prospectus. This Current Prospectus Supplement is qualified by reference to the ATM Prospectus, except to the extent that the information presented herein supersedes the information contained in the ATM Prospectus. This Current Prospectus Supplement is not complete without, and may only be delivered or utilized in connection with, the ATM Prospectus and any future amendments or supplements thereto.

As of the date hereof, the aggregate market value of our outstanding Class A common stock held by non-affiliates, calculated in accordance with General Instruction I.B.6 of Form S-3 under the Securities Act of 1933, as amended (our “public float”), was approximately $83.1 million, based on 30,016,759 outstanding shares of Class A common stock held by non-affiliates as of June 18, 2025, at a price of $2.77 per share as of June 18, 2025, which was the highest closing sale price of our Class A common stock on The Nasdaq Global Market within 60 days of the filing date of this Current Prospectus Supplement.

We are filing this Current Prospectus Supplement to amend the ATM Prospectus to update our public float and indicate that, since our public float is above $75.0 million, we are no longer subject to the sales limitations of General Instruction I.B.6 of Form S-3 with respect to the registration statement of which the ATM Prospectus, as amended hereby, forms a part. If we become subject to the limitations of such General Instruction I.B.6 in the future, we will file another supplement to the ATM Prospectus.

Since our entry into the Agreement, we have offered and sold 6,155,556 shares of Class A common stock for gross proceeds of $18,706,156.11 pursuant to the Agreement. Accordingly, because we are no longer subject to the sales limitations of such General Instruction I.B.6, we may offer and sell up to an additional $31,293,843.89 of shares of Class A common stock pursuant to the Agreement.

Our Class A common stock is listed on The Nasdaq Global Market under the symbol “IMRX”. On June 20, 2025, the last reported sale price of our Class A common stock on The Nasdaq Global Market was $2.56 per share.

Investing in our Class A common stock involves a high degree of risk. Before making an investment decision, please read the information under the heading “Risk Factors” beginning on page S-6 of the ATM Prospectus and in the documents incorporated by reference in the ATM 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 supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense.

Piper Sandler

The date of this prospectus supplement is June 23, 2025.

FAQ

Why did Immuneering (IMRX) file another prospectus supplement?

To update its public float to $83.1 M and state that it is no longer limited by Form S-3 I.B.6 sales caps.

How much additional stock can IMRX now sell under the ATM program?

Up to $31,293,843.89 worth of Class A common stock through Piper Sandler.

How much has IMRX already raised via the ATM?

It has sold 6,155,556 shares for gross proceeds of $18,706,156.11 since August 2022.

What is Immuneering’s current public float?

Approximately $83.1 million, based on 30,016,759 non-affiliate shares at $2.77 on 6/18/25.

What was the last reported IMRX share price before the filing?

The Nasdaq Global Market closing price on June 20, 2025 was $2.56 per share.

Does the filing include new financial results or guidance?

No. The supplement is limited to ATM mechanics; investors should consult prior filings for operating metrics.