# EDGAR Filing Document

**Accession Number:** 0001806952
**File Stem:** 0001193125-25-324801
**Filing Date:** 2025-12
**Character Count:** 96443
**Document Hash:** 02472d5ad26868af61a876e8bea03053
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001193125-25-324801.hdr.sgml**: 20251218

**ACCESSION NUMBER**: 0001193125-25-324801

**CONFORMED SUBMISSION TYPE**: 424B5

**PUBLIC DOCUMENT COUNT**: 2

**FILED AS OF DATE**: 20251218

**DATE AS OF CHANGE**: 20251218

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Lyell Immunopharma, Inc.
- **CENTRAL INDEX KEY:** 0001806952
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 833006753
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** 424B5
- **SEC ACT:** 1933 Act
- **SEC FILE NUMBER:** 333-291970
- **FILM NUMBER:** 251583063

**BUSINESS ADDRESS:**
- **STREET 1:** 201 HASKINS WAY
- **CITY:** SOUTH SAN FRANCISCO
- **STATE:** CA
- **ZIP:** 94080
- **BUSINESS PHONE:** 650 695-0677

**MAIL ADDRESS:**
- **STREET 1:** 201 HASKINS WAY
- **CITY:** SOUTH SAN FRANCISCO
- **STATE:** CA
- **ZIP:** 94080

##### [**Table of Contents**](#toc)
**Filed Pursuant to Rule 424(b)(5)<br>Registration No. 333-291970** 

**PROSPECTUS**![LOGO](g72300g25m01.jpg)

**1,900,000** 

**Shares of Common Stock** 

This prospectus relates to the proposed resale from time to time by Innovative Cellular Therapeutics Holdings Limited, a Cayman Island exempted company incorporated with limited liability ("ICT Holdings"), as the selling stockholder, of up to 1,900,000 shares of our common stock, par value $0.0001 per share. The shares of common stock registered for resale pursuant to this prospectus were issued as part of the consideration under an Exclusive License Agreement, dated as of November 6, 2025 (the "License Agreement"), by and among us, ICT Holdings and Innovative Cellular Therapeutics, Inc., a Delaware corporation ("ICT" and together with ICT Holdings, the "ICT Group"), pursuant to which the ICT Group granted us an exclusive license to research, develop, manufacture, commercialize and otherwise exploit certain product candidates and products worldwide except in mainland China, Taiwan, Macau and Hong Kong. On November 6, 2025, we issued a total of 1,900,000 shares of our common stock to ICT Holdings in connection with the effectiveness of the License Agreement.

We are registering the shares of our common stock on behalf of ICT Holdings, to be offered and sold by ICT Holdings from time to time. We are not selling any securities under this prospectus and will not receive any of the proceeds from the sale of shares by ICT Holdings.

This prospectus provides a general description of the common stock ICT Holdings may offer. ICT Holdings may sell the shares of our common stock described in this prospectus in a number of different ways and at varying prices. See the section titled "*Plan of Distribution for Shares Offered by the Selling Stockholder"* on page 21 of this prospectus for more information about how ICT Holdings may sell the shares of common stock being registered pursuant to this prospectus.

We and ICT Holdings have agreed to each be responsible for 50% of the expenses incurred in registering the shares of common stock, including certain legal and accounting fees. ICT Holdings will bear all underwriting discounts, selling commissions and similar fees and arrangements and stock transfer taxes allocable to its sales of the shares of our common stock and certain additional legal and advisor fees.

Our common stock is listed on the Nasdaq Global Select Market under the trading symbol "LYEL." On December 17, 2025, the last reported sale price of our common stock was $32.07 per share.

***Investing in our securities involves a high degree of risk. Before making an investment decision, you should review carefully the risks and uncertainties described under the section titled "[Risk Factors](#toc72300_3)" contained in this prospectus and under similar headings in the documents that are incorporated by reference into this prospectus.***

**Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.** 

**The date of this prospectus is December 18, 2025.** 

------

##### [**Table of Contents**](#toc)
**TABLE OF CONTENTS** 

---

| | |
|:---|:---|
|  [ABOUT THIS PROSPECTUS](#toc72300_1) | i |
|  [PROSPECTUS SUMMARY](#toc72300_2) | 1 |
|  [RISK FACTORS](#toc72300_3) | 4 |
|  [SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS](#toc72300_4) | 5 |
|  [SELECTED FINANCIAL DATA REFLECTING REVERSE STOCK SPLIT](#toc72300_5) | 8 |
|  [USE OF PROCEEDS](#toc72300_6) | 9 |
|  [DESCRIPTION OF CAPITAL STOCK](#toc72300_7) | 10 |
|  [SELLING STOCKHOLDER](#toc72300_8) | 17 |
|  [LEGAL OWNERSHIP OF SECURITIES](#toc72300_9) | 18 |
|  [PLAN OF DISTRIBUTION FOR SHARES OFFERED BY THE SELLING STOCKHOLDER](#toc72300_10) | 21 |
|  [LEGAL MATTERS](#toc72300_11) | 24 |
|  [EXPERTS](#toc72300_12) | 25 |
|  [WHERE YOU CAN FIND MORE INFORMATION](#toc72300_13) | 26 |
|  [INCORPORATION OF CERTAIN INFORMATION BY REFERENCE](#toc72300_14) | 27 |

---

**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"), utilizing a "shelf" registration process under the Securities Act of 1933, as amended (the "Securities Act"). Under this shelf registration process, ICT Holdings, as the selling stockholder, which as used herein include donees, pledgees, transferees, distributees or other successors-in-interest selling shares of our common stock or interests in our common stock received after the date of this prospectus from the selling stockholder as a gift, pledge, partnership distribution or other transfer identified in this prospectus, may offer and sell up to 1,900,000 shares of our common stock. This prospectus provides a general description of the shares of our common stock the selling stockholder may offer. We are not selling any securities under this prospectus and will not receive any of the proceeds from the sale of shares by the selling stockholder. For general information about the distribution of shares of common stock offered by the selling stockholder, see the section in this prospectus titled "*Plan of Distribution for Shares Offered by the Selling Stockholder*."

We urge you to read carefully this prospectus, together with the information incorporated herein by reference as described under the sections titled "*Where You Can Find More Information*" and "*Incorporation of Certain Information by Reference*," before buying any of the shares of our common stock being offered.

You should rely only on the information contained in, or incorporated by reference into, this prospectus. We have not authorized any other person to provide you with different or additional information. If anyone provides you with different or inconsistent information, you should not rely on it. We take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. You should assume that the information appearing in this prospectus and the documents incorporated by reference into this prospectus, is accurate only as of the date of those respective documents. Our business, financial condition, results of operations and prospects may have changed since those dates. You should read this prospectus and the documents incorporated by reference into this prospectus, in their entirety before making an investment decision. You should also read and consider the information in the documents to which we have referred you in the sections of this prospectus titled "*Where You Can Find More Information*" and "*Incorporation of Certain Information by Reference*."

The selling stockholder is offering to sell, and seeking offers to buy, shares of our common stock only in jurisdictions where offers and sales are permitted. The distribution of this prospectus and the offering of our securities in certain jurisdictions may be restricted by law. Persons outside the United States who come into possession of this prospectus must inform themselves about, and observe any restrictions relating to, the offering

i

------

##### [**Table of Contents**](#toc)
of our securities and the distribution of this prospectus outside the United States. This prospectus does not constitute, and may not be used in connection with, an offer to sell, or a solicitation of an offer to buy, any shares of common stock offered by this prospectus by any person in any jurisdiction in which it is unlawful for such person to make such an offer or solicitation.

We obtained the industry and market data included or incorporated by reference in this prospectus from our own research as well as from industry and general publications, surveys and studies conducted by third parties. This data involves a number of assumptions and limitations, and you are cautioned not to give undue weight to such estimates. In addition, projections, assumptions and estimates of our future performance and the future performance of the industry in which we operate is necessarily subject to a high degree of uncertainty and risk due to a variety of factors, including those described in the section of this prospectus titled "*Risk Factors*" and documents incorporated by reference into this prospectus. These and other factors could cause results to differ materially from those expressed in the estimates made by independent parties and by us.

This prospectus, including the information incorporated by reference into this prospectus, includes trademarks, service marks and trade names owned by us or others. All trademarks, service marks and trade names included or incorporated by reference in this prospectus are the property of their respective owners.

This prospectus and the information incorporated herein by reference contain summaries of certain provisions contained in some of the documents described herein, but reference is made to the actual documents for complete information. All of the summaries are qualified in their entirety by the actual documents. Copies of some of the documents referred to herein have been filed, will be filed or will be incorporated by reference as exhibits to the registration statement of which this prospectus is a part, and you may obtain copies of those documents as described in the sections titled "*Where You Can Find More Information*" and "*Incorporation of Certain Information by Reference*."

ii

------

##### [**Table of Contents**](#toc)
**PROSPECTUS SUMMARY** 

*This summary highlights selected information appearing elsewhere in this prospectus or incorporated by reference in this prospectus and does not contain all of the information that you need to consider in making your investment decision. You should carefully read this entire prospectus, including the risks of investing in our securities discussed under the section titled "Risk Factors" and under similar headings in the other documents that are incorporated by reference into this prospectus. You should also carefully read the information incorporated by reference into this prospectus, including our financial statements, and the exhibits to the registration statement of which this prospectus is a part.* 

*Unless the context requires otherwise, references in this prospectus to "Lyell," the "Company," "we," "us" and "our" refer to Lyell Immunopharma, Inc.* 

**Overview** 

We are a late-stage clinical cell therapy company advancing a pipeline of proprietary next-generation autologous chimeric antigen receptor ("CAR") T-cell product candidates for patients with cancer. Our goal is to fully realize the curative potential of cell therapy for patients with hematologic malignancies and solid tumors. To achieve this, we are pioneering novel approaches designed to generate T-cell therapies that drive long-lasting clinical responses. Our investigational CAR T-cell therapies start with the identification of promising cancer targets. We then engineer the patient's own living immune cells and arm them with one or more of our innovative enhancements, including CAR constructs, technologies or manufacturing protocols that are designed to endow T-cells with more potent cancer cell killing capabilities.

**Corporate Information** 

We were incorporated in June 2018 as a Delaware corporation. Our principal executive offices are located at 201 Haskins Way, South San Francisco, California 94080 and our telephone number is (650) 695-0677. Our website address is www.lyell.com. Information found on, or accessible through, our website is not a part of, and is not incorporated into, this prospectus, and you should not consider it as part of this prospectus. Our website address is included in this prospectus as an inactive textual reference only.

The Lyell logo and other trademarks or service marks of Lyell Immunopharma, Inc. appearing in this prospectus are the property of Lyell. Other trademarks, service marks or trade names appearing in this prospectus are the property of their respective owners. We do not intend our use or display of other companies' trade names, trademarks or service marks to imply a relationship with, or endorsement or sponsorship of us by, these other companies.

**Recent Development** 

On November 6, 2025 (the "Effective Date"), we entered into the License Agreement with the ICT Group. Under the License Agreement, (i) the ICT Group granted us an exclusive license to research, develop, manufacture, commercialize and otherwise exploit certain product candidates and products worldwide except in mainland China, Taiwan, Macau and Hong Kong and (ii) we (a) paid to ICT Holdings $40 million in cash and (b) issued to ICT Holdings 1.9 million shares of our common stock. Contingent consideration payable following the Effective Date includes (i) a potential $30 million clinical milestone payment, up to $115 million upon achievement of certain late-stage regulatory milestones and up to $675 million in commercial sales milestones, (ii) up to an additional 1.85 million shares of our common stock (the "ICT Contingent Equity Consideration") upon achievement of certain clinical and regulatory milestones and (iii) tiered royalties ranging from mid-single digits up to 10% on annual net sales in the United States and low to mid-single-digit royalties on annual net sales in other countries within the licensed territory.

------

##### [**Table of Contents**](#toc)
**The Offering** 

---

| | |
|:---|:---|
| **The Securities the Selling Stockholder May Offer**  | The selling stockholder, ICT Holdings, may offer up to 1,900,000 shares of our common stock, from time to time in one or more offerings under this prospectus, at prices and on terms to be determined by market conditions at the time of any offering. This prospectus provides you with a general description of the common stock the selling stockholder may offer. |

---

The selling stockholder may sell shares of our common stock directly to investors or to or through agents, underwriters or dealers. The selling stockholder and its agents or underwriters reserve the right to accept or reject all or part of any proposed purchase of shares our common stock. If the selling stockholder does offer shares of our common stock to or through agents or underwriters, a prospectus supplement, if required, will be distributed, which will include, among other things:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the names of those agents or underwriters;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• applicable fees, discounts and commissions to be paid; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• details regarding options to purchase additional shares, if any.

We may suspend the sale of our shares of common stock by the selling stockholder pursuant to this prospectus for certain periods of time for certain reasons, including if the prospectus is required to be supplemented or amended to include additional material information.

The holders of our common stock are entitled to one vote for each share held of record on all matters submitted to a vote of stockholders. Subject to preferences that may be applicable to any then-outstanding shares of preferred stock, the holders of common stock are entitled to receive ratably such dividends as may be declared by our board of directors out of legally available funds. Upon our liquidation, dissolution or winding up, the holders of our common stock are entitled to share ratably in all assets remaining after payment of liabilities and the liquidation preferences of any then-outstanding shares of preferred stock. Holders of our common stock have no preemptive rights and no right to convert their common stock into any other securities.

There are no redemption or sinking fund provisions applicable to our common stock. The rights, preferences and privileges of the holders of our common stock are subject to, and may be adversely affected by, the rights of the holders of shares of any series of preferred stock that we may designate in the future. In this prospectus, we have summarized certain general features of our common stock under the section titled "*Description of Capital Stock — Common Stock*."

------

##### [**Table of Contents**](#toc)

---

| | |
|:---|:---|
| **Use of Proceeds**  | We are not selling any securities under this prospectus and will not receive any of the proceeds from the sale of shares of our common stock by the selling stockholder. |

---

---

| | |
|:---|:---|
| **Nasdaq Global Select Market Listing**  | Our common stock is listed on the Nasdaq Global Select Market under the symbol "LYEL." |

---

---

| | |
|:---|:---|
| **Risk Factors**  | See "Risk Factors" on page 4 of this prospectus for a discussion of factors you should carefully consider before deciding to invest in our common stock. |

---

------

##### [**Table of Contents**](#toc)
**RISK FACTORS** 

Investing in our securities involves a high degree of risk. Before deciding whether to invest in our securities, you should carefully consider the risks and uncertainties discussed under the section titled "*Risk Factors*" contained in our most recent Annual Report on Form 10-K, as updated by our subsequent Quarterly Reports on Form 10-Q, as well as any amendments thereto reflected in subsequent filings with the SEC, which are incorporated by reference into this prospectus in their entirety, together with other information in this prospectus and the other documents incorporated by reference into this prospectus. The risks described in these documents are not the only ones we face. There may be other unknown or unpredictable economic, business, competitive, regulatory or other factors that could have material adverse effects on our future results. Past financial performance may not be a reliable indicator of future performance, and historical trends should not be used to anticipate results or trends in future periods. If any of these risks actually occur, our business, financial condition, results of operations or cash flow could be seriously harmed. This could cause the trading price of our securities to decline, resulting in a loss of all or a part of your investment. Please also read carefully the section below titled "*Special Note Regarding Forward-Looking Statements*."

------

##### [**Table of Contents**](#toc)
**SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS** 

This prospectus, as well as the documents incorporated by reference in this prospectus, contain "forward-looking statements" within the meaning of Section 27A of the Securities Act, and Section 21E of the Securities Exchange Act of 1934, as amended (the "Exchange Act"). All statements other than statements of historical facts contained in this prospectus, including statements regarding our future results of operations and financial position, business strategy, product candidates, planned nonclinical studies and clinical trials, results of nonclinical studies and clinical trials, research and development costs, planned regulatory submissions, regulatory approvals and the timing and likelihood of success, as well as plans and objectives of management for future operations, are forward-looking statements. These statements involve known and unknown risks, uncertainties and other important factors that are in some cases beyond our control and may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements.

In some cases, you can identify forward-looking statements by terms such as "may," "will," "should," "would," "expect," "plan," "anticipate," "could," "intend," "target," "project," "believe," "estimate," "predict," "potential" or "continue," or the negative of these terms or other similar expressions. Forward-looking statements contained in this prospectus include, but are not limited to, statements about:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the sufficiency of our existing cash to fund our future operating expenses and capital expenditure requirements;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the accuracy and timing of our estimates regarding expenses, revenue opportunities, capital requirements and
needs for additional financing;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the scope, progress, results and costs of developing rondecabtagene autoleucel ("ronde-cel," also known as LYL314), LYL273 (formerly known as GCC19CART) or any other product candidates we may develop or acquire, including both nonclinical studies and clinical trials;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the timing and costs involved in obtaining and maintaining regulatory approvals of ronde-cel, LYL273 or any other product candidates we may develop or acquire, and the timing or likelihood of regulatory filings and approvals, including any expectations or plans regarding seeking or
maintaining special designations, such as Regenerative Medicine Advanced Therapy designation, Orphan Drug designation or Fast Track designation, for our product candidates for various diseases;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our plans relating to the commercialization of ronde-cel, LYL273 or any
other product candidates we may develop or acquire, if approved, including the geographic areas of focus, and our ability to commercially differentiate such product candidates and build a sales force;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the size of the market opportunities for ronde-cel, LYL273 or any other
product candidates we may develop or acquire in each of the diseases we may target;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our reliance on third parties to conduct research activities for ronde-cel, LYL273 or any other product candidates we may develop or acquire;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the characteristics, safety, efficacy and therapeutic effects of ronde-cel, LYL273 or any other product candidates we may develop or acquire;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the advancement of our technology platforms and the effectiveness and expected benefits of any of our
technologies and manufacturing processes;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our estimates of the number of patients in the United States and worldwide who suffer from the diseases we target
and the number of patients that may enroll in our clinical trials;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the progress and focus of the current and planned clinical trials of our product candidates, and the reporting of
data from those trials, including the timing thereof;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the ability of our clinical trials to sufficiently demonstrate the safety and efficacy of ronde-cel, LYL273 or any other product candidates we may develop or acquire, and other clinical trial results;

------

##### [**Table of Contents**](#toc)
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the success of competing therapies that are, or may become, available;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• developments relating to our competitors and our industry, including any existing or future competing product
candidates or therapies;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our plans relating to the further development and manufacturing of ronde-cel, LYL273 or any other product candidates we may develop or acquire, including lines of therapy or additional indications that we may pursue;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• existing regulations and regulatory developments in the United States and other jurisdictions;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our potential and ability to successfully manufacture and supply or our ability to contract with third parties to
manufacture and supply ronde-cel, LYL273 or any other product candidates we may develop or acquire for clinical trials and for commercial use, if approved;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the rate and degree of market acceptance, as well as the pricing and reimbursement, of ronde-cel, LYL273 or any other product candidates we may develop or acquire, if approved;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our continued reliance on third parties to assist us in conducting additional clinical trials of ronde-cel, LYL273 or any other product candidates we may develop or acquire;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the scope of protection we are able to establish and maintain for intellectual property rights, including
covering ronde-cel, LYL273 and other product candidates and technology platforms we may develop or acquire;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our ability to retain the continued service of our key personnel and to identify, hire and retain additional
qualified personnel;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our expectations regarding the impact of inflation, macroeconomic conditions and geopolitical conflicts on our
business and operations, including on our manufacturing suppliers, collaborators, contract research organizations and employees;

USA, Inc. ("ImmPACT"), our acquisition of rights to LYL273 from the ICT Group or any other acquisition or strategic transaction and our success in commercializing any product candidates we acquire in connection therewith;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our expectation that our LyFE Manufacturing
Center<sup>TM</sup> and, if applicable, contract drug manufacturing organizations engaged by us, will provide sufficient drug supply for our ongoing and planned clinical trials and through potential
commercial launch; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our anticipated use of our existing cash, cash equivalents and marketable securities.

We have based these forward-looking statements largely on our current expectations and projections about our business, the industry in which we operate and financial trends that we believe may affect our business, financial condition, results of operations and prospects, and these forward-looking statements are not guarantees of future performance or development. Because forward-looking statements are inherently subject to risks and uncertainties, some of which cannot be predicted or quantified, you should not rely on these forward-looking statements as predictions of future events. The events and circumstances reflected in our forward-looking statements may not be achieved or occur, and actual results could differ materially from those projected in these forward-looking statements. We discuss in greater detail, and incorporate by reference into this prospectus in their entirety, many of these risks and uncertainties under the section titled "*Risk Factors*" contained in our most recent Annual Report on Form 10-K, as updated by our subsequent Quarterly Reports on Form 10-Q, as well as any amendments thereto reflected in subsequent filings with the SEC. Also, these forward-looking statements represent our estimates and assumptions only as of the date of the document containing the applicable statement. Unless required by law, we undertake no obligation to update or revise any forward-looking statements to reflect new information or future events or developments. Thus, you should not assume that our silence over time means that actual events are bearing out as expressed or implied in such forward-looking statements. You should read

------

##### [**Table of Contents**](#toc)
this prospectus together with the documents we have filed with the SEC that are incorporated by reference into this prospectus completely and with the understanding that our actual future results may be materially different from what we expect. We qualify all of the forward-looking statements in the foregoing documents by these cautionary statements.

In addition, statements that "we believe" and similar statements reflect our beliefs and opinions on the relevant subject. These statements are based upon information available to us as of the date of this prospectus, and while we believe such information forms a reasonable basis for such statements, such information may be limited or incomplete, and our statements should not be read to indicate that we have conducted an exhaustive inquiry into, or review of, all potentially available relevant information. These statements are inherently uncertain and investors are cautioned not to unduly rely upon these statements.

------

##### [**Table of Contents**](#toc)
**SELECTED FINANCIAL DATA REFLECTING REVERSE STOCK SPLIT** 

**Reverse Stock Split** 

At 5:00 p.m. Eastern Time on May 30, 2025, we effected a 1-for-20 reverse stock split of our common stock (the "Reverse Stock Split"). Based on such Reverse Stock Split, the total number of outstanding shares of common stock was adjusted from 296,161,570 shares to approximately 14,808,006 shares on May 30, 2025 (after accounting for cash payments made in lieu of fractional shares). The par value per common share remained unchanged at $0.0001. The audited consolidated financial statements of Lyell included in the Annual Report on Form 10-K for the year ended December 31, 2024, which are incorporated by reference into this prospectus, are presented without giving effect to the Reverse Stock Split. Except where the context otherwise requires, all information presented in this prospectus has been adjusted to reflect the Reverse Stock Split.

The following selected financial data has been derived from our audited consolidated financial statements included in our Annual Report on Form 10-K filed with the SEC on March 11, 2025, as adjusted to reflect the Reverse Stock Split for all periods presented. Our historical results are not indicative of the results that may be expected in the future and results of interim periods are not indicative of the results for the entire year.

**AS REPORTED** 

---

| | | | |
|:---|:---|:---|:---|
|  | **Year Ended December 31,** | **Year Ended December 31,** | **Year Ended December 31,** |
| *(in thousands, except per share amounts)* | **2024** | **2023** | **2022** |
|  Net loss available to common stockholders | $(342994) | $(234632) | $(183118) |
|  Net loss per common share, basic and diluted | $(1.31) | $(0.93) | $(0.74) |
|  Weighted average common shares outstanding, basic and diluted | 261480 | 250983 | 247080 |
|  Common shares outstanding at year end | 294876 | 253958 | 249567 |

---

**AS ADJUSTED FOR 1-FOR-20 REVERSE STOCK SPLIT (Unaudited)** 

---

| | | | |
|:---|:---|:---|:---|
|  | **Year Ended December 31,** | **Year Ended December 31,** | **Year Ended December 31,** |
| *(in thousands, except per share amounts)* | **2024** | **2023** | **2022** |
|  Net loss available to common stockholders | $(342994) | $(234632) | $(183118) |
|  Net loss per common share, basic and diluted | $(26.23) | $(18.70) | $(14.82) |
|  Weighted average common shares outstanding, basic and diluted | 13074 | 12549 | 12354 |
|  Common shares outstanding at year end | 14744 | 12698 | 12478 |

---

------

##### [**Table of Contents**](#toc)
**USE OF PROCEEDS** 

All the shares of our common stock to be sold pursuant to this prospectus will be sold by ICT Holdings, as the selling stockholder. We will not receive any of the proceeds from the sale of shares of our common stock by the selling stockholder pursuant to this prospectus.

We and ICT Holdings, the selling stockholder, have agreed to each be responsible for 50% of the expenses incurred in registering the shares of our common stock offered pursuant to this prospectus, including certain legal and accounting fees. ICT Holdings will bear all underwriting discounts, selling commissions and similar fees and arrangements and stock transfer taxes allocable to its sales of the shares of our common stock and certain additional legal and advisor fees.

------

##### [**Table of Contents**](#toc)
**DESCRIPTION OF CAPITAL STOCK** 

As of the date of this prospectus, pursuant to our amended and restated certificate of incorporation (the "Restated Certificate"), our authorized capital stock consists of 500,000,000 shares of common stock, $0.0001 par value per share, and 10,000,000 shares of preferred stock, $0.0001 par value per share. All of our authorized shares of preferred stock are undesignated.

This information may not be complete in all respects and is qualified entirely by reference to the provisions of the Restated Certificate, our amended and restated bylaws ("Bylaws"), our amended and restated investors' rights agreement with certain investors and purchasers, dated as of March 5, 2020 (the "Investors' Rights Agreement"), our Registration Rights Agreement with the Representative and certain former stockholders of ImmPACT, dated as of October 31, 2024 (the "2024 Registration Rights Agreement"), our Securities Purchase Agreement with certain institutional and other accredited investors, dated as of July 24, 2025 (the "Securities Purchase Agreement"), our Registration Rights Agreement with ICT Holdings, dated as of November 6, 2025 (the "2025 Registration Rights Agreement") and the General Corporation Law of the State of Delaware. For information on how to obtain copies of the Restated Certificate, our Bylaws, our Investors' Rights Agreement, our 2024 Registration Rights Agreement, our Securities Purchase Agreement and our 2025 Registration Rights Agreement, which are exhibits to the registration statement of which this prospectus forms a part, see the section in this prospectus titled "*Where You Can Find More Information*."

**Common Stock** 

*Voting Rights.* Our common stock is entitled to one vote per share on any matter that is submitted to a vote of our stockholders. Our Restated Certificate does not provide for cumulative voting for the election of directors. Our Restated Certificate establishes a classified board of directors that is divided into three classes with staggered three-year terms. Only the directors in one class will be subject to election by a plurality of the votes cast at each annual meeting of our stockholders, with the directors in the other classes continuing for the remainder of their respective three-year terms. The affirmative vote of holders of at least 66<sup>2</sup>⁄<sub>3</sub>% of the voting power of all of the then-outstanding shares of capital stock, voting as a single class, will be required to amend certain provisions of our Restated Certificate, including provisions relating to amending our Bylaws, the classified structure of our board of directors, the size of our board of directors, removal of directors, director liability, vacancies on our board of directors, special meetings, stockholder notices, actions by written consent and exclusive jurisdiction.

*Economic Rights.* Except as otherwise expressly provided in our Restated Certificate or required by applicable law, all shares of common stock will have the same rights and privileges and rank equally, share ratably and be identical in all respects for all matters, including those described below.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Dividends. Subject to preferences that may apply to any shares of preferred stock outstanding at the time, the
holders of our common stock are entitled to receive dividends out of funds legally available if our board of directors, in its discretion, determines to issue dividends and then only at the times and in the amounts that our board of directors may
determine.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• Liquidation Rights. On our liquidation, dissolution, or winding-up, the
holders of common stock will be entitled to share equally, identically and ratably in all assets remaining after the payment of any liabilities, liquidation preferences and accrued or declared but unpaid dividends, if any, with respect to any
outstanding preferred stock, unless a different treatment is approved by the affirmative vote of the holders of a majority of the outstanding shares of such affected class, voting separately as a class.

*No Preemptive or Similar Rights.* The holders of our shares of common stock are not entitled to preemptive rights, and are not subject to conversion, redemption or sinking fund provisions.

*Fully Paid and Non-Assessable.* When shares of common stock are issued under this prospectus, the shares will be fully paid and non-assessable.

------

##### [**Table of Contents**](#toc)
**Preferred Stock** 

Under the Restated Certificate, our board of directors has the authority, without further action by the stockholders, to issue up to 10,000,000 shares of preferred stock in one or more series, to establish from time to time the number of shares to be included in each such series, to fix the rights, preferences and privileges of the shares of each wholly unissued series and any qualifications, limitations or restrictions thereon and to increase or decrease the number of shares of any such series, but not below the number of shares of such series then outstanding.

Our board of directors may authorize the issuance of preferred stock with voting or conversion rights that could adversely affect the voting power or other rights of the holders of our common stock. The issuance of preferred stock, while providing flexibility in connection with possible acquisitions and other corporate purposes, could, among other things, have the effect of delaying, deterring or preventing a change in our control that may otherwise benefit holders of our common stock and may adversely affect the market price of the common stock and the voting and other rights of the holders of our common stock.

*Voting Rights.* The Delaware General Corporation Law provides that the holders of preferred stock will have the right to vote separately as a class on any proposal involving fundamental changes in the rights of holders of that preferred stock. This right is in addition to any voting rights that may be provided for in the applicable certificate of designation.

*Economic Rights.* Unless we specify otherwise, the preferred stock will rank, with respect to dividends and upon our liquidation, dissolution or winding up:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• senior to all classes or series of our common stock and to all of our equity securities ranking junior to the
preferred stock;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• on a parity with all of our equity securities the terms of which specifically provide that the equity securities
rank on a parity with the preferred stock; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• junior to all of our equity securities the terms of which specifically provide that the equity securities rank
senior to the preferred stock.

The term "equity securities" does not include convertible debt securities.

*Fully Paid and Non-Assessable.* When we issue shares of preferred stock, such shares will be fully paid and nonassessable.

**Registration Rights** 

Subject to federal securities laws, certain holders of shares of our common stock are entitled to certain rights with respect to registration of such shares under the Securities Act. These shares are referred to as registrable securities. The holders of these registrable securities possess registration rights pursuant to the terms of our Investors' Rights Agreement, our 2024 Registration Rights Agreement, our Securities Purchase Agreement and our 2025 Registration Rights Agreement, as described in additional detail below. The registration of shares of our common stock pursuant to the exercise of such registration rights would enable the holders to trade these shares without restriction under the Securities Act when an applicable registration statement is declared effective by the SEC. In general, we will pay the registration expenses, other than underwriting discounts, selling commissions and stock transfer taxes, of the shares registered in connection with the exercise of such demand rights and piggyback rights, and associated Form S-3 registration statements, as applicable. With respect to the shares held by ICT Holdings, we and ICT Holdings have agreed to each be responsible for 50% of the expenses incurred in registering such shares of common stock, including certain legal and accounting fees, unless the offering is to be effected as an underwritten offering and the total offering price is not reasonably expected to equal or exceed $20 million in the aggregate, in which case such expenses shall be borne solely by ICT Holdings. In all instances,

------

##### [**Table of Contents**](#toc)
ICT Holdings will bear all underwriting discounts, selling commissions and similar fees and arrangements and stock transfer taxes allocable to its sales of the shares of our common stock and certain additional legal and advisor fees in accordance with the 2025 Registration Rights Agreement.

*Investors' Rights Agreement* 

Certain holders of our common stock are entitled to certain demand registration rights at any time after 180 days after June 16, 2021, the effective date of the registration statement for our initial public offering. The holders of 40% of these shares may request that we register all or a portion of their shares. We are not required to file more than two registration statements which are declared or ordered effective by the SEC. Such request for registration must cover shares with an anticipated aggregate offering price of at least $35 million.

Additionally, certain holders of shares of our common stock were entitled to, and the necessary percentage of holders waived, their rights to notice of this offering and to include their shares of registrable securities in this offering.

Further, certain holders of shares of common stock will be entitled to certain Form S-3 registration statement registration rights. Holders of 20% of these shares can make a request that we register their shares on a Form S-3 registration statement if we are qualified to file such registration statement and if the reasonably anticipated aggregate net proceeds of the shares offered would equal or exceed $20 million. We will not be required to file more than two Form S-3 registration statements within any 12-month period.

Generally, in an underwritten offering, the managing underwriter, if any, has the right, subject to specified conditions and limitations, to limit the number of shares the holders may include. The demand, piggyback and Form S-3 registration statement registration rights will expire no later than five years after our initial public offering in June 2021.

*2024 Registration Rights Agreement* 

On October 31, 2024 (the "Closing Date"), we completed our acquisition of ImmPACT pursuant to an Agreement and Plan of Merger, dated October 24, 2024 (the "Merger Agreement"), by and among ImmPACT, us, Inspire Merger Sub Inc., a Delaware corporation and our indirect, wholly owned subsidiary ("Merger Sub"), and WT Representative LLC, a Delaware limited liability company, solely in its capacity as the representative of the Company Securityholders (as defined in the Merger Agreement), pursuant to which we acquired ImmPACT through the merger of Merger Sub with and into ImmPACT (the "Merger"), with ImmPACT surviving the Merger as the surviving entity and our indirect, wholly owned subsidiary.

In connection with the closing of the Merger, on the Closing Date, we entered into the 2024 Registration Rights Agreement, pursuant to which we agreed to provide former ImmPACT stockholders certain registration rights in connection with the shares of our common stock, including to file shelf registration statements to permit resale of closing stock consideration and equity milestone consideration issuable under the Merger Agreement. The closing stock consideration has been issued in connection with the Closing. The equity milestone consideration was issued on July 2, 2025.

Additionally, upon request by the demanding stockholders to sell any registrable shares of our common stock held by such demanding stockholders in an underwritten offering pursuant to any of the shelf registration statements, we are obligated to effect such an underwritten shelf takedown if the total offering price exceeds $25 million. WT Representative LLC, solely in its capacity as the representative of the ImmPACT stockholders, on behalf of the demanding stockholders, is not entitled to request such underwritten shelf takedown (i) more than three times in the aggregate or (ii) more than one time in any single calendar year.

------

##### [**Table of Contents**](#toc)
*Securities Purchase Agreement* 

Pursuant to the Securities Purchase Agreement, we agreed to provide the purchasers thereto certain registration rights in connection with the shares of our common stock, including to file shelf registration statements to permit resale of common stock issuable under the Securities Purchase Agreement and, if applicable, the shares of common stock issuable upon exercise of the pre-funded warrants, and generally to cause the applicable registration statements to promptly become effective.

*2025 Registration Rights Agreement* 

In connection with the License Agreement, on November 6, 2025, we entered into the 2025 Registration Rights Agreement, pursuant to which we agreed to provide ICT Holdings certain registration rights in connection with the shares of our common stock, including to file shelf registration statements to permit resale of upfront equity consideration and the ICT Contingent Equity Consideration issuable under the License Agreement. The upfront equity consideration has been issued in connection with the effectiveness of the License Agreement.

Additionally, upon request by ICT Holdings to sell all or any registrable shares of our common stock held by it in an underwritten offering pursuant to any of the shelf registration statements, we are obligated to effect such an underwritten shelf takedown if the total offering price exceeds $18 million. If the total offering price of such underwritten shelf takedown is not reasonably expected to exceed, in the aggregate, $20 million, the expenses incurred in connection therewith shall be borne and paid by ICT Holdings; in other instances, the expenses incurred therewith shall be borne and paid equally (50/50) by ICT Holdings and us. ICT Holdings is not entitled to request such underwritten shelf takedown (i) more than three times in the aggregate or (ii) more than one time in any single calendar year.

**Anti-Takeover Provisions** 

The provisions of Delaware law, our Restated Certificate and our Bylaws, which are summarized below, may have the effect of delaying, deferring or discouraging another person from acquiring control of our company. They are also designed, in part, to encourage persons seeking to acquire control of us to negotiate first with our board of directors. We believe that the benefits of increased protection of our potential ability to negotiate with an unfriendly or unsolicited acquirer outweigh the disadvantages of discouraging a proposal to acquire us because negotiation of these proposals could result in an improvement of their terms.

*Restated Certificate and Bylaws* 

Because our stockholders do not have cumulative voting rights, stockholders holding a majority of the voting power of our shares of common stock are able to elect all of our directors. Our Restated Certificate and our Bylaws provide that all stockholder actions are required to be taken by a vote of the stockholders at an annual or special meeting, and that stockholders may not take any action by written consent in lieu of a meeting. According to our Bylaws, a special meeting of stockholders may only be called by a majority of our board of directors, the chair of our board of directors, or our chief executive officer or president. Our Bylaws require an advance notice procedure for stockholder proposals to be brought before an annual meeting of our stockholders, including proposed nominations of persons for election to our board of directors. In addition, our board of directors is divided into three classes with staggered three-year terms. Our Restated Certificate also provides that directors may be removed only for cause by the affirmative vote of the holders of at least 66<sup>2</sup>⁄<sub>3</sub>% of the shares then entitled to vote at an annual election of directors. Furthermore, any vacancy on our board of directors, however occurring, including a vacancy resulting from an increase in the size of our board, may be filled by the affirmative vote of a majority of our directors then in office even if less than a quorum.

The foregoing provisions will make it more difficult for another party to obtain control of us by replacing our board of directors. Since our board of directors has the power to retain and discharge our officers, these

------

##### [**Table of Contents**](#toc)
provisions could also make it more difficult for existing stockholders or another party to effect a change in management. In addition, the authorization of undesignated preferred stock makes it possible for our board of directors to issue preferred stock with voting or other rights or preferences that could impede the success of any attempt to change our control.

These provisions are designed to reduce our vulnerability to an unsolicited acquisition proposal and to discourage certain tactics that may be used in proxy fights. However, such provisions could have the effect of discouraging others from making tender offers for our shares and may have the effect of deterring hostile takeovers or delaying changes in our control or management. As a consequence, these provisions may also inhibit fluctuations in the market price of our stock that could result from actual or rumored takeover attempts.

*Section 203 of the Delaware General Corporation Law* 

We are subject to the provisions of Section 203 of the Delaware General Corporation Law ("Section 203"). In general, Section 203 prohibits a publicly-held Delaware corporation from engaging in any business combination with any interested stockholder for a period of three years after the date that such stockholder became an interested stockholder, subject to certain exceptions. A "business combination" includes, among other things, a merger, asset or stock sale or other transaction resulting in a financial benefit to the interested stockholder. An "interested stockholder" is a person who, together with affiliates and associates, owns, or did own within three years prior to the determination of interested stockholder status, 15% or more of the corporation's voting stock.

**Choice of Forum** 

For the avoidance of doubt, these provisions are intended to benefit and may be enforced by us, our officers and directors, the underwriters to any offering giving rise to such complaint and any other professional entity whose profession gives authority to a statement made by that person or entity and who has prepared or certified any part of the documents underlying the offering. While the Delaware courts have determined that such choice of forum provisions are facially valid, a stockholder may nevertheless seek to bring a claim in a venue other than

------

##### [**Table of Contents**](#toc)
those designated in the exclusive forum provisions, and there can be no assurance that such provisions will be enforced by a court in those other jurisdictions. We note that investors cannot waive compliance with the federal securities laws and the rules and regulations thereunder.

Additionally, our Restated Certificate provides that any person or entity holding, owning or otherwise acquiring any interest in any of our securities shall be deemed to have notice of and consented to these provisions. These choice of forum provisions may limit a stockholder's ability to bring a claim in a judicial forum that it finds favorable for disputes with us or any of our directors, officers, other employees or stockholders, which may discourage lawsuits with respect to such claims, but will not waive our compliance with federal securities laws and the rules and regulations thereunder.

**Limitation of Liability and Indemnification Matters** 

Our Restated Certificate contains provisions that limit the liability of our directors for monetary damages to the fullest extent permitted by Delaware law. Consequently, our directors will not be personally liable to us or our stockholders for monetary damages for any breach of fiduciary duties as directors, except liability for:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• any breach of the director's duty of loyalty to us or our stockholders;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• any act or omission not in good faith or that involves intentional misconduct or a knowing violation of law;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• unlawful payments of dividends or unlawful stock repurchases or redemptions as provided in Section 174 of
the Delaware General Corporation Law; or

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• any transaction from which the director derived an improper personal benefit.

Such limitation of liability does not apply to liabilities arising under federal securities laws and does not affect the availability of equitable remedies such as injunctive relief or rescission.

Our Restated Certificate authorizes us to indemnify our directors, officers, employees and other agents to the fullest extent permitted by Delaware law. Each of our Restated Certificate and Bylaws provide that we are required to indemnify our directors and officers, in each case to the fullest extent permitted by Delaware law and may indemnify our other employees and agents. Our Bylaws also obligate us to advance expenses incurred by a director or officer in advance of the final disposition of any action or proceeding, and permit us to secure insurance on behalf of any officer, director, employee or other agent for any liability arising out of his or her actions in that capacity regardless of whether we would otherwise be permitted to indemnify him or her under Delaware law. We have entered and expect to continue to enter into agreements to indemnify our directors, executive officers and other employees as determined by our board of directors. With specified exceptions, these agreements provide for indemnification for related expenses including, among other things, attorneys' fees, judgments, fines and settlement amounts incurred by any of these individuals in any action or proceeding. We believe that these bylaw provisions and indemnification agreements are necessary to attract and retain qualified persons as directors and officers. We also maintain directors' and officers' liability insurance.

The limitation of liability and indemnification provisions in our Restated Certificate and Bylaws may discourage stockholders from bringing a lawsuit against our directors and officers for breach of their fiduciary duty. They may also reduce the likelihood of derivative litigation against our directors and officers, even though an action, if successful, might benefit us and our stockholders. Further, a stockholder's investment may be adversely affected to the extent that we pay the costs of settlement and damages.

**Transfer Agent and Registrar** 

The transfer agent and registrar for our common stock is Equiniti Trust Company, LLC. The transfer agent's address is 28 Liberty Street, Floor 53, New York, NY 10005.

------

##### [**Table of Contents**](#toc)
**Rule 144** 

Pursuant to Rule 144 under the Securities Act ("Rule 144"), a person who has beneficially owned our restricted common stock for at least six months would be entitled to sell their shares of our common stock provided that (i) such person is not deemed to have been our affiliate at the time of, or at any time during the three months preceding, a sale and (ii) we are subject to the Exchange Act periodic reporting requirements for at least three months before the sale and have filed all required reports under Section 13 or 15(d) of the Exchange Act during the 12 months (or such shorter period as required to file such reports) preceding the sale.

Persons who have beneficially owned our restricted common stock for at least six months but who are our affiliates at the time of, or at any time during the three months preceding, a sale would be subject to additional restrictions, by which such person would be entitled to sell within any three-month period only a number of shares of our common stock that does not exceed the greater of:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• 1% of the total number of shares of our common stock then outstanding; or

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the average weekly reported trading volume of our common stock during the four calendar weeks preceding the
filing of a notice on Form 144 with respect to the sale.

Sales by our affiliates under Rule 144 are also limited by manner of sale provisions and notice requirements and by the availability of current public information about us.

**Listing on the Nasdaq Global Select Market** 

Our common stock is listed on the Nasdaq Global Select Market under the symbol "LYEL."

------

##### [**Table of Contents**](#toc)
**SELLING STOCKHOLDER** 

We have prepared this prospectus to allow ICT Holdings, as the selling stockholder, which as used herein includes donees, pledgees, transferees, distributees or other successors-in-interest selling shares of our common stock or interests in our common stock received after the date of this prospectus from the selling stockholder as a gift, pledge, partnership distribution or other transfer, to offer and sell from time to time up to 1,900,000 shares of our common stock (which does not include the ICT Contingent Equity Consideration issuable under the License Agreement upon achievement of certain clinical and regulatory milestones). We are registering the offer and sale of the shares beneficially owned by the selling stockholder to satisfy certain registration obligations that we granted the selling stockholder pursuant to the 2025 Registration Rights Agreement.

The following table set forth, based upon information currently known by us as of the date of this prospectus, (i) the name of the selling stockholder, (ii) the aggregate number of shares of common stock beneficially owned by the selling stockholder, (iii) the aggregate number of shares of common stock that the selling stockholder may offer pursuant to this prospectus and (iv) the number of shares of common stock beneficially owned by the selling stockholder assuming all of the shares covered hereby are sold. We have based percentage ownership of securities beneficially owned prior to this offering on 21,243,954 shares of our common stock outstanding as of December 1, 2025. We do not know how long the selling stockholder will hold the shares before selling them, and we currently have no agreements, arrangements or understandings with the selling stockholder regarding the sale or other disposition of any shares.

We have determined beneficial ownership in accordance with the rules and regulations of the SEC and the information is not necessarily indicative of beneficial ownership for any other purpose. Except as indicated by the footnote below, we believe, based on information furnished to us, that ICT Holdings has sole voting and sole investment power with respect to all shares that they beneficially own, subject to applicable community property laws.

To our knowledge, ICT Holdings does not hold any position or office, or otherwise had a material relationship, with us or any of our subsidiaries within the past three years prior to the date of this prospectus other than as a result of the ownership of our securities.

See the section in this prospectus titled "*Plan of Distribution for Shares Offered by the Selling Stockholder*" for further information regarding the selling stockholder's methods of distributing these securities.

We cannot advise you as to whether the selling stockholder will in fact sell any or all of our shares of common stock. The selling stockholder may sell or otherwise transfer all, some or none of such shares of our common stock in this offering.

---

| | | | | | |
|:---|:---|:---|:---|:---|:---|
|  | **Securities Beneficially Owned<br>Prior to Offering** | **Securities Beneficially Owned<br>Prior to Offering** | **Securities to be Sold in<br>this Offering** | **Securities Beneficially Owned<br>After this Offering** | **Securities Beneficially Owned<br>After this Offering** |
| **Name of Selling Stockholder** | **Shares of<br>Common<br>Stock** | **Percentage** | **Shares of<br>Common<br>Stock** | **Shares of<br>Common<br>Stock** | **Percentage** |
|  Innovative Cellular Therapeutics Holdings Limited<sup>(1)</sup> | 1900000 | 8.9% | 1900000 |  |  |

---

(1) Lei Xiao, as the Chief Executive Officer of Innovative Cellular Therapeutics Holdings Limited, has voting,
investment and dispositive power over the shares held by Innovative Cellular Therapeutics Holdings Limited. The address of Innovative Cellular Therapeutics Holdings Limited is 50 W Gude Dr., Ste. 60, Rockville, MD 20850.

------

##### [**Table of Contents**](#toc)
**LEGAL OWNERSHIP OF SECURITIES** 

We can issue securities in registered form or in the form of one or more global securities. We describe global securities in greater detail below. We refer to those persons who have securities registered in their own names on the books that we or any applicable trustee, depositary or warrant agent maintain for this purpose as the "holders" of those securities. These persons are the legal holders of the securities. We refer to those persons who, indirectly through others, own beneficial interests in securities that are not registered in their own names, as "indirect holders" of those securities. As we discuss below, indirect holders are not legal holders, and investors in securities issued in book-entry form or in street name will be indirect holders.

**Book-Entry Holders** 

We may issue securities in book-entry form only. This means securities may be represented by one or more global securities registered in the name of a financial institution that holds them as depositary on behalf of other financial institutions that participate in the depositary's book-entry system. These participating institutions, which are referred to as participants, in turn, hold beneficial interests in the securities on behalf of themselves or their customers.

Only the person in whose name a security is registered is recognized as the holder of that security. Securities issued in global form will be registered in the name of the depositary or its participants. Consequently, for securities issued in global form, we will recognize only the depositary as the holder of the securities, and we will make all payments on the securities to the depositary. The depositary passes along the payments it receives to its participants, which in turn pass the payments along to their customers who are the beneficial owners. The depositary and its participants do so under agreements they have made with one another or with their customers; they are not obligated to do so under the terms of the securities.

As a result, investors in a book-entry security will not own such security directly. Instead, they will own beneficial interests in a global security, through a bank, broker or other financial institution that participates in the depositary's book-entry system or holds an interest through a participant. As long as the securities are issued in global form, investors will be indirect holders, and not legal holders, of the securities.

**Street Name Holders** 

We may terminate a global security or issue securities in non-global form. In these cases, investors may choose to hold their securities in their own names or in "street name." Securities held by an investor in street name will be registered in the name of a bank, broker or other financial institution that the investor chooses, and the investor will hold only a beneficial interest in those securities through an account he or she maintains at that institution.

For securities held in street name, we or any applicable trustee or depositary will recognize only the intermediary banks, brokers and other financial institutions in whose names the securities are registered as the holders of those securities, and we or any applicable trustee or depositary will make all payments on those securities to them. These institutions pass along the payments they receive to their customers who are the beneficial owners, but only because they agree to do so in their customer agreements or because they are legally required to do so. Investors who hold securities in street name will be indirect holders, not holders, of those securities.

**Legal Holders** 

Our obligations, as well as the obligations of any applicable trustee and of any third parties employed by us or a trustee, run only to the legal holders of the securities. We do not have obligations to investors who hold beneficial interests in global securities, in street name or by any other indirect means. This will be the case whether an investor chooses to be an indirect holder of a security or has no choice because we are issuing the securities only in global form.

------

##### [**Table of Contents**](#toc)
For example, once we make a payment or give a notice to the legal holder, we have no further responsibility for the payment or notice even if that legal holder is required, under agreements with depositary participants or customers or by law, to pass it along to the indirect holders but does not do so. Whether and how the legal holders contact the indirect holders is up to the legal holders.

**Special Considerations for Indirect Holders** 

If you hold securities through a bank, broker or other financial institution, either in book-entry form or in street name, you should check with your own institution to find out:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• how it handles securities payments and notices;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• whether it imposes fees or charges;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• how it would handle a request for the holders' consent, if ever required;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• whether and how you can instruct it to send you securities registered in your own name so you can be a holder, if
that is permitted in the future;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• how it would exercise rights under the securities if there were a default or other event triggering the need for
holders to act to protect their interests; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• if the securities are in book-entry form, how the depositary's rules and procedures will affect these
matters.

**Global Securities** 

A global security is a security that represents one or any other number of individual securities held by a depositary. Generally, all securities represented by the same global securities will have the same terms.

Each security issued in book-entry form will be represented by a global security that we deposit with and register in the name of a financial institution or its nominee that we select. The financial institution that we select for this purpose is called the depositary. Unless we specify otherwise in an applicable prospectus supplement, DTC will be the depositary for all securities issued in book-entry form.

A global security may not be transferred to or registered in the name of anyone other than the depositary, its nominee or a successor depositary, unless special termination situations arise. We describe those situations below under the section titled "*Special Situations When a Global Security Will Be Terminated*" in this prospectus. As a result of these arrangements, the depositary, or its nominee, will be the sole registered owner and legal holder of all securities represented by a global security, and investors will be permitted to own only beneficial interests in a global security. Beneficial interests must be held by means of an account with a broker, bank or other financial institution that in turn has an account with the depositary or with another institution that does. Thus, an investor whose security is represented by a global security will not be a legal holder of the security, but only an indirect holder of a beneficial interest in the global security.

If a prospectus supplement for a particular security indicates that the security will be issued in global form only, then the security will be represented by a global security at all times unless and until the global security is terminated. If termination occurs, we may issue the securities through another book-entry clearing system or decide that the securities may no longer be held through any book-entry clearing system.

**Special Considerations for Global Securities** 

The rights of an indirect holder relating to a global security will be governed by the account rules of the investor's financial institution and of the depositary, as well as general laws relating to securities transfers. We do not recognize an indirect holder as a holder of securities and instead deal only with the depositary that holds the global security.

------

##### [**Table of Contents**](#toc)
If securities are issued only in the form of a global security, an investor should be aware of the following:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• an investor cannot cause the securities to be registered in his or her name, and cannot obtain non-global certificates for his or her interest in the securities, except in the special situations we describe below;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• an investor will be an indirect holder and must look to his or her own bank or broker for payments on the
securities and protection of his or her legal rights relating to the securities, as we describe above;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• an investor may not be able to sell interests in the securities to some insurance companies and to other
institutions that are required by law to own their securities in non-book-entry form;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• an investor may not be able to pledge his or her interest in a global security in circumstances where
certificates representing the securities must be delivered to the lender or other beneficiary of the pledge in order for the pledge to be effective;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the depositary's policies, which may change from time to time, will govern payments, transfers, exchanges
and other matters relating to an investor's interest in a global security;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• we and any applicable trustee have no responsibility for any aspect of the depositary's actions or for its
records of ownership interests in a global security, nor do we or any applicable trustee supervise the depositary in any way;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the depositary may, and we understand that DTC will, require that those who purchase and sell interests in a
global security within its book-entry system use immediately available funds, and your broker or bank may require you to do so as well; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• financial institutions that participate in the depositary's book-entry system, and through which an
investor holds its interest in a global security, may also have their own policies affecting payments, notices and other matters relating to the securities.

There may be more than one financial intermediary in the chain of ownership for an investor. We do not monitor and are not responsible for the actions of any of those intermediaries.

**Special Situations When a Global Security Will Be Terminated** 

In a few special situations described below, the global security will terminate and interests in it will be exchanged for physical certificates representing those interests. After that exchange, the choice of whether to hold securities directly or in street name will be up to the investor. Investors must consult their own banks, brokers or other financial institutions to find out how to have their interests in securities transferred to their own name, so that they will be direct holders. We have described the rights of holders and street name investors above.

Unless we provide otherwise in an applicable prospectus supplement, the global security will terminate when the following special situations occur:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• if the depositary notifies us that it is unwilling, unable or no longer qualified to continue as depositary for
that global security and we do not appoint another institution to act as depositary within 90 days;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• if we notify any applicable trustee that we wish to terminate that global security; or

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• if an event of default has occurred with regard to securities represented by that global security and has not
been cured or waived.

Any applicable prospectus supplement may also list additional situations for terminating a global security that would apply only to the particular series of securities covered by such applicable prospectus supplement. When a global security terminates, the depositary, and not we or any applicable trustee, is responsible for deciding the names of the institutions that will be the initial direct holders.

------

##### [**Table of Contents**](#toc)
**PLAN OF DISTRIBUTION FOR SHARES OFFERED BY THE SELLING STOCKHOLDER** 

We are registering for resale by ICT Holdings, as the selling stockholder, up to 1,900,000 shares of common stock. The selling stockholder, which as used herein include donees, pledgees, transferees, distributees or other successors-in-interest selling shares of our common stock or interests in our common stock received after the date of this prospectus from the selling stockholder as a gift, pledge, partnership distribution or other transfer may, from time to time, sell, transfer, distribute or otherwise dispose of certain of their shares of common stock or interests in our common stock on any stock exchange, market or trading facility on which shares of our common stock are traded or in private transactions. These dispositions may be at fixed prices, at prevailing market prices at the time of sale, at prices related to the prevailing market price, at varying prices determined at the time of sale, or at negotiated prices.

The selling stockholder may use any one or more of the following methods when disposing of its shares of common stock or interests therein:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• ordinary brokerage transactions and transactions in which the broker-dealer solicits purchasers;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• one or more underwritten offerings;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• block trades in which the broker-dealer will attempt to sell the shares of common stock as agent, but may
position and resell a portion of the block as principal to facilitate the transaction;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• purchases by a broker-dealer as principal and resale by the broker-dealer for its accounts;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• an exchange distribution in accordance with the rules of the applicable exchange;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• privately negotiated transactions;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• distributions to its shareholders;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• short sales effected after the date of the registration statement of which this prospectus is a part is declared
effective by the SEC;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• through the writing or settlement of options or other hedging transactions, whether through an options exchange
or otherwise;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• in-market transactions, including transactions on a national securities
exchange or quotations service or over-the-counter market;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• directly to one or more purchasers;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• through agents;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• through agreements with broker-dealers, who may agree with the selling stockholder to sell a specified number of
such shares of common stock at a stipulated price per share; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• a combination of any such methods of sale.

The selling stockholder may, from time to time, pledge or grant a security interest in some shares of our common stock owned by it and, if the selling stockholder defaults in the performance of its secured obligations, the pledgees or secured parties may offer and sell such shares of common stock from time to time, under this prospectus, or under an amendment or supplement to this prospectus to include the pledgee, transferee or other successors in interest as the selling stockholder under this prospectus. The selling stockholder also may transfer shares of our common stock in other circumstances, in which case the transferees, pledgees or other successors in interest will be the selling beneficial owners for purposes of this prospectus.

In connection with the sale of shares of our common stock or interests therein, the selling stockholder may enter into hedging transactions with broker-dealers or other financial institutions, which may in turn engage in short sales of our common stock in the course of hedging the positions they assume. The selling stockholder may

------

##### [**Table of Contents**](#toc)
also sell shares of our common stock short and deliver these securities to close out its short positions, or loan or pledge shares of our common stock to broker-dealers that in turn may sell these securities. The selling stockholder may also enter into option or other transactions with broker-dealers or other financial institutions or the creation of one or more derivative securities that require the delivery to such broker-dealer or other financial institution of shares of our common stock offered by this prospectus, which shares such broker-dealer or other financial institution may resell pursuant to this prospectus (as supplemented or amended to reflect such transaction).

The aggregate proceeds to the selling stockholder from the sale of shares of our common stock offered by it will be the purchase price of such shares of our common stock less discounts or commissions, if any. The selling stockholder reserves the right to accept and, together with its agents from time to time, to reject, in whole or in part, any proposed purchase of shares of our common stock to be made directly or through agents. We will not receive any of the proceeds from any offering by the selling stockholder.

At the time a particular offering of securities is made, a prospectus supplement, if required, will be distributed, which will set forth the name of the selling stockholder, the aggregate amount of securities being offered and the terms of the offering, including, to the extent required, (1) the name or names of any underwriters, broker-dealers or agents, (2) any discounts, commissions and other terms constituting compensation from the selling stockholder and (3) any discounts, commissions or concessions allowed or reallowed to be paid to broker-dealers. We may suspend the sale of securities by the selling stockholder pursuant to this prospectus for certain periods of time for certain reasons, including if the prospectus is required to be supplemented or amended to include additional material information.

The selling stockholder also may in the future resell a portion of our common stock in open market transactions in reliance upon Rule 144 under the Securities Act, provided that they meet the criteria and conform to the requirements of that rule, or pursuant to other available exemptions from the registration requirements of the Securities Act.

The selling stockholder and any underwriters, broker-dealers or agents that participate in the sale of shares of our common stock or interests therein may be "underwriters" within the meaning of Section 2(11) of the Securities Act. Any discounts, commissions, concessions or profit they earn on any resale of shares of our common stock or warrants may be underwriting discounts and commissions under the Securities Act. If the selling stockholder is an "underwriter" within the meaning of Section 2(11) of the Securities Act, then the selling stockholder will be subject to the prospectus delivery requirements of the Securities Act. Underwriters and their controlling persons, dealers and agents may be entitled, under agreements entered into with us and the selling stockholder, to indemnification against and contribution toward specific civil liabilities, including liabilities under the Securities Act.

To the extent required, our common stock to be sold, the purchase prices and public offering prices, the names of any agent, dealer or underwriter, and any applicable discounts, commissions, concessions or other compensation with respect to a particular offer will be set forth in an accompanying prospectus supplement or, if appropriate, a post-effective amendment to the registration statement that includes this prospectus.

To facilitate the offering of shares of our common stock offered by the selling stockholder, certain persons participating in the offering may engage in transactions that stabilize, maintain or otherwise affect the price of our common stock. This may include over-allotments or short sales, which involve the sale by persons participating in the offering of more shares of common stock than were sold to them. In these circumstances, these persons would cover such over-allotments or short positions by making purchases in the open market or by exercising their over-allotment option, if any. In addition, these persons may stabilize or maintain the price of our common stock by bidding for or purchasing shares of common stock in the open market or by imposing penalty bids, whereby selling concessions allowed to dealers participating in the offering may be reclaimed if shares of common stock sold by them are repurchased in connection with stabilization transactions. The effect of these

------

##### [**Table of Contents**](#toc)
transactions may be to stabilize or maintain the market price of our common stock at a level above that which might otherwise prevail in the open market. These transactions may be discontinued at any time.

Under the 2025 Registration Rights Agreement, we have agreed to indemnify the selling stockholder against certain liabilities that they may incur in connection with the sale of the securities registered hereunder, including liabilities under the Securities Act. In addition, we and the selling stockholder may agree to indemnify any underwriter, broker-dealer or agent against certain liabilities related to the selling of the securities, including liabilities arising under the Securities Act.

Under the 2025 Registration Rights Agreement, we have agreed to maintain the effectiveness of this registration statement until all securities covered by the 2025 Registration Rights Agreement have been sold under this registration statement, have been transferred without restrictive legends, may be sold under Rule 144 under the Securities Act or are no longer outstanding.

The selling stockholder may use this prospectus in connection with resales of shares of our common stock. This prospectus and any accompanying prospectus supplement will identify the selling stockholder, the terms of our common stock and any material relationships between us and the selling stockholder. The selling stockholder may be deemed to be underwriters under the Securities Act in connection with shares of our common stock they resell and any profits on the sales may be deemed to be underwriting discounts and commissions under the Securities Act. Unless otherwise set forth in a prospectus supplement, the selling stockholder will receive all of the net proceeds from the resale of shares of our common stock.

The selling stockholder may elect to make an in-kind distribution of common stock to its shareholders pursuant to the registration statement of which this prospectus is a part by delivering a prospectus. To the extent that such shareholders are not affiliates of ours, such shareholders would thereby receive freely tradable shares of common stock pursuant to the distribution through a registration statement.

We and ICT Holdings have agreed to each be responsible for 50% of the expenses incurred in the registration of shares of our common stock to be offered and sold pursuant to this prospectus, including certain legal and accounting expenses. ICT Holdings will bear all underwriting discounts, selling commissions and similar fees and arrangements and stock transfer taxes allocable to its sales of the shares of our common stock and certain additional legal and advisor fees.

------

##### [**Table of Contents**](#toc)
**LEGAL MATTERS** 

Skadden, Arps, Slate, Meagher & Flom LLP has passed upon the validity of the securities offered by this prospectus.

------

##### [**Table of Contents**](#toc)
**EXPERTS** 

Ernst & Young LLP, independent registered public accounting firm, has audited our consolidated financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2024, as set forth in their report, which is incorporated by reference in this prospectus and elsewhere in the registration statement. Our financial statements are incorporated by reference in reliance on Ernst & Young LLP's report, given on their authority as experts in accounting and auditing.

------

##### [**Table of Contents**](#toc)
**WHERE YOU CAN FIND MORE INFORMATION** 

This prospectus is part of the registration statement on Form S-3 we filed with the SEC under the Securities Act and does not contain all the information set forth or incorporated by reference in such registration statement. Whenever a reference is made in this prospectus to any of our contracts, agreements or other documents, the reference may not be complete and you should refer to the exhibits that are a part of the registration statement or the exhibits to the reports or other documents incorporated by reference into this prospectus for a copy of such contract, agreement or other document. Neither we nor any agent, underwriter or dealer has authorized any person to provide you with different information. We are not making an offer of these securities in any state where the offer is not permitted. You should not assume that the information in this prospectus is accurate as of any date other than the date on the front page of this prospectus, regardless of the time of delivery of this prospectus or any sale of the securities offered by this prospectus. Because we are subject to the information and reporting requirements of the Exchange Act, we file annual, quarterly and current reports, proxy statements and other information with the SEC. Our SEC filings are available to the public over the Internet at the SEC's website at http://www.sec.gov.

------

##### [**Table of Contents**](#toc)
**INCORPORATION OF CERTAIN INFORMATION BY REFERENCE** 

The SEC allows us to incorporate by reference information from other documents that we file with it, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus. Information in this prospectus supersedes information incorporated by reference that we filed with the SEC prior to the date of this prospectus, while information that we file later with the SEC will automatically update and supersede the information in this prospectus. We incorporate by reference into this prospectus and the registration statement of which this prospectus is a part the information or documents listed below that we have filed with the SEC (Commission File No. 001-40502):

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our Annual Report on [Form 10-K](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1806952/000162828025011978/lyel-20241231.htm) for the fiscal year ended December 31, 2024, filed with the SEC on March 11, 2025;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our Quarterly Reports on Form 10-Q for the quarters ended March 31,
2025, June 30, 2025 and September 30, 2025, filed with the SEC on [May 13, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1806952/000162828025025135/lyel-20250331.htm) , [August 12, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1806952/000180695225000008/lyel-20250630.htm) and [November 12, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/0001806952/000162828025051619/lyel-20250930.htm) ;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• our Current Reports on Form 8-K and 8-K/A, filed with the SEC on [January 10, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1806952/000162828025001065/lyel-20241031.htm) , [January 24, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1806952/000119312525012249/d884359d8k.htm) , [April 1, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1806952/000119312525070521/d920617d8k.htm) , [May 21, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1806952/000119312525123970/d920680d8k.htm) , [May 28, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1806952/000119312525129448/d944707d8k.htm) , [June 9, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1806952/000119312525137853/d940968d8k.htm) , [June 17, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1806952/000119312525141795/d15114d8k.htm) , [June 26, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1806952/000119312525148897/d917552d8k.htm) , [July 25, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/0001806952/000119312525164853/d24368d8k.htm) , [September 16, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/0001806952/000119312525205020/d948282d8k.htm) , [November 3, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/0001806952/000119312525261753/d73457d8k.htm) , [November 10, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/0001806952/000119312525273269/d57756d8k.htm) , [December 5, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1806952/000119312525309621/d13123d8k.htm) and [December 8, 2025](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1806952/000119312525310469/d35459d8k.htm) , respectively, in each case other than information furnished under Item 2.02 or
7.01 of Form 8-K (and exhibits filed on such form that are related to such items);

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the portions of the Definitive Proxy Statement on [Schedule 14A](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/0001806952/000114036125014721/ny20044209x2_def14a.htm) , filed with the SEC on April 
21, 2025, that are incorporated by reference into our Annual Report on [Form 10-K](http://www.sec.gov/Archives/edgar/data/../../../ix?doc=/Archives/edgar/data/1806952/000162828025011978/lyel-20241231.htm) for the fiscal year ended December 31, 2024; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;• the description of our common stock in [Exhibit 4.3](http://www.sec.gov/Archives/edgar/data/1806952/000162828023005572/ex-43_descriptionxofxsecur.htm) to our Annual Report on Form 10-K for the fiscal year ended December 31, 2024.

We also incorporate by reference any future filings (other than current reports furnished under Item 2.02 or Item 7.01 of Form 8-K and exhibits filed on such form that are related to such items unless such Form 8-K expressly provides to the contrary) made with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act until we file a post-effective amendment that indicates the termination of the offering of the securities made by this prospectus, which will become a part of this prospectus from the date that such documents are filed with the SEC. Information in such future filings update and supplement the information provided in this prospectus. Any statements in any such future filings will automatically be deemed to modify and supersede any information in any document we previously filed with the SEC that is incorporated or deemed to be incorporated herein by reference to the extent that statements in the later-filed document modify or replace such earlier statements. We will furnish without charge to each person, including any beneficial owner, to whom a prospectus is delivered, upon written or oral request, a copy of any or all of the documents incorporated by reference into this prospectus but not delivered with the prospectus, including exhibits that are specifically incorporated by reference into such documents. You should direct any requests for documents to:

LYELL IMMUNOPHARMA, INC.

Attn: General Counsel

201 Haskins Way

South San Francisco, CA 94080

(650) 695-0677

------

##### [**Table of Contents**](#toc)
![LOGO](g72300g25m01.jpg)

**1,900,000** 

**Shares of Common Stock** 

**The date of this prospectus is December 18, 2025**