# EDGAR Filing Document

**Accession Number:** 0001789972
**File Stem:** 0001193125-26-229173
**Filing Date:** 2026-5
**Character Count:** 23198
**Document Hash:** fcebbc42a5e2d96c0bea9e08d96c2bcc
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001193125-26-229173.hdr.sgml**: 20260518

**ACCESSION NUMBER**: 0001193125-26-229173

**CONFORMED SUBMISSION TYPE**: 8-K

**PUBLIC DOCUMENT COUNT**: 10

**CONFORMED PERIOD OF REPORT**: 20260518

**ITEM INFORMATION**: Regulation FD Disclosure

**ITEM INFORMATION**: Other Events

**ITEM INFORMATION**: Financial Statements and Exhibits

**FILED AS OF DATE**: 20260518

**DATE AS OF CHANGE**: 20260518

**FILER**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Cullinan Therapeutics, Inc.
- **CENTRAL INDEX KEY:** 0001789972
- **STANDARD INDUSTRIAL CLASSIFICATION:** BIOLOGICAL PRODUCTS (NO DIAGNOSTIC SUBSTANCES) [2836]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 813879991
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** 8-K
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 001-39856
- **FILM NUMBER:** 26995081

**BUSINESS ADDRESS:**
- **STREET 1:** ONE MAIN STREET
- **STREET 2:** SUITE 1350
- **CITY:** CAMBRIDGE
- **STATE:** MA
- **ZIP:** 02142
- **BUSINESS PHONE:** 617-410-4650

**MAIL ADDRESS:**
- **STREET 1:** ONE MAIN STREET
- **STREET 2:** SUITE 1350
- **CITY:** CAMBRIDGE
- **STATE:** MA
- **ZIP:** 02142

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Cullinan Oncology, Inc.
- **DATE OF NAME CHANGE:** 20210225

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Cullinan Management, Inc.
- **DATE OF NAME CHANGE:** 20210107

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Cullinan Oncology, LLC
- **DATE OF NAME CHANGE:** 20191001

?xml version='1.0' encoding='ASCII'? 8-K

**UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549**

------

## FORM 8-K

------

**CURRENT REPORT**

**Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934**

**Date of Report (Date of earliest event reported):** May 18, 2026<br>

------

CULLINAN THERAPEUTICS, INC.

**(Exact name of Registrant as Specified in Its Charter)**

------

---

| | | |
|:---|:---|:---|
| Delaware | 001-39856 | 81-3879991 |
| **(State or Other Jurisdiction<br>of Incorporation)** | **(Commission File Number)** | **(IRS Employer<br>Identification No.)** |
| One Main Street<br>Suite 1350 |  |  |
| Cambridge**,** Massachusetts |  | 02142 |
| **(Address of Principal Executive Offices)** |  | **(Zip Code)** |

---

**Registrant's Telephone Number, Including Area Code:** 617 410-4650<br>

**(Former Name or Former Address, if Changed Since Last Report)**

------

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

**Securities registered pursuant to Section 12(b) of the Act:**

---

| | |
|:---|:---|
| **<br>Title of each class** | **<br>Name of each exchange on which registered** |
| Common Stock, $0.0001 par value per share<br> CGEM | The Nasdaq Global Select Market |

---

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

------

## Item 7.01 Regulation FD Disclosure.
On May 18, 2026, Cullinan Therapeutics, Inc. (the "Company") issued a press release announcing that the Company will present initial clinical data from its Phase 1 OUTRACE Program for CLN-978 in patients with treatment-refractory rheumatoid arthritis ("RA") and treatment-refractory moderate to severe systemic lupus erythematosus ("SLE") at the European Alliance of Associations for Rheumatology European Congress of Rheumatology ("EULAR") in June. A copy of the press release is furnished as Exhibit 99.1 to this Current Report on Form 8-K and is incorporated herein by reference.

The information in this report furnished pursuant to Item 7.01, including Exhibit 99.1 attached hereto, shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the "Exchange Act") or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

## Item 8.01 Other Events.
On May 18, 2026, the Company announced initial clinical data from its Phase 1 OUTRACE Program for CLN-978 in patients with treatment-refractory RA and in patients with treatment-refractory moderate to severe SLE.

As of a January 14, 2026 cutoff date, 14 patients were dosed across the RA (cohorts 1-3, n=5) and SLE (cohorts 1-3, n=9) clinical trials. All day 1 step up doses were 10 micrograms ("mcg") and day 8 target doses were either 20 mcg (cohort 2) or 30 mcg (cohort 3).

Following 10 mcg dosing, 9 out of 11 patients exhibited depletion of B cells >75% relative to baseline levels. Following 20 mcg dosing, three out of six patients had depletion of B cells below the level of quantification, and the other three patients exhibited decreases of 98.5%, 77%, and 64%, respectively, relative to baseline levels.

Transient decreases in peripheral blood T cell levels were observed, consistent with a known pharmacodynamic effect of T cell activation by T cell engagers.

Among patients with at least four weeks of follow up data post-baseline, four out of five RA patients had decreases in DAS28-ESR (including four out of four patients decreasing from high activity (>5.1) to moderate activity (three patients) or remission (one patient)), and five out of six patients had a decrease in SLEDAI score of <u>></u>4 points. Ultrasound synovitis scores decreased in three out of four RA patients.

CLN-978 was well tolerated and demonstrated a favorable safety profile in both RA and SLE patients. A single target dose of CLN-978 induced robust B cell depletion in both peripheral blood and tissues, with promising clinical efficacy in RA and SLE patients at the initial dose levels tested. Dose escalation continues in these studies, and the Company will present updated data, including in additional patients, at EULAR in June 2026.

**Forward-Looking Statements**

This Current Report on Form 8-K contains forward-looking statements within the meaning of the U.S. Private Securities Litigation Reform Act of 1995. Any statements in this Current Report on Form 8-K that are not historical facts may be considered "forward-looking statements," including statements regarding the efficacy and safety data from the Company's ongoing Phase 1 OUTRACE Program for CLN-978, the clinical and therapeutic potential of CLN-978 and the Company's plans regarding future data presentations. The clinical trials referenced in this Current Report on Form 8-K are ongoing, and the data described are interim, subject to change, and based on data available as of a specified date. As patient enrollment continues and additional follow-up data is obtained, the reported safety profile and other clinical outcomes may change materially. There can be no assurance that the interim results will be predictive of final study results or that additional data will confirm or support these observations. Forward-looking statements are typically, but not always, identified by the use of words such as "estimate," "expect," and other similar terminology. Any forward-looking statements in this Current Report on Form 8-K are based on management's current expectations and beliefs of future events and are subject to known and unknown risks and uncertainties that may cause the Company's actual results, performance or achievements to be materially different from any expressed or implied by the forward-looking statements. Such risks and uncertainties include, but are not limited to, the risks detailed in the Company's recent filings on Forms 10-K and 10-Q with the SEC. While the Company may elect to update such forward-looking statements at some point in the future, the Company disclaims any obligation to do so, even if subsequent events cause its views to change, except to the extent required by law. These forward-looking statements should not be relied upon as representing the Company's views as of any date subsequent to the date of this Current Report on Form 8-K. Any forward-looking statement included in this Current Report on Form 8-K speaks only as of the date on which it was made.

## Item 9.01 Financial Statements and Exhibits.
(d) Exhibits

------

---

| | |
|:---|:---|
| <u>Exhibit No.</u> | <u>Description</u> |
| 99.1 | [<u>Press release issued by Cullinan Therapeutics, Inc. on May 18, 2026, furnished herewith</u>](cgem-ex99_1.htm) |
| 104 | Cover page from this Current Report on Form 8-K, formatted in Inline XBRL |

---

------

**SIGNATURES**

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

---

| | | | |
|:---|:---|:---|:---|
|  |  |  | **CULLINAN THERAPEUTICS, INC.** |
| Date: | May 18, 2026 | By:  | /s/ Mary Kay Fenton |
|  |  |  | Mary Kay Fenton<br>Chief Financial Officer |

---

------

## Exhibit 99.1

**Exhibit 99.1**

**Cullinan Therapeutics to Present Initial Clinical Data for CLN-978 in Treatment-Refractory Rheumatoid Arthritis and Systemic Lupus Erythematosus at EULAR 2026 Congress**

CAMBRIDGE, Mass., May 18, 2026 (GLOBE NEWSWIRE) -- Cullinan Therapeutics, Inc. (Nasdaq: CGEM), a clinical-stage biopharmaceutical company accelerating potential first- or best-in-class, high-impact therapies in autoimmune diseases and cancer, today announced that initial clinical data from two ongoing Phase 1 studies evaluating CLN-978, a subcutaneously administered CD19xCD3 T cell engager, will be presented at the European Alliance of Associations for Rheumatology (EULAR) European Congress of Rheumatology being held June 3-6, 2026 in London, United Kingdom.

The presentation will feature data from the Phase 1 OUTRACE RA and OUTRACE SLE studies which are evaluating CLN-978 in patients with active, treatment-refractory rheumatoid arthritis (RA) and moderate to severe systemic lupus erythematosus (SLE), respectively. The abstract reports that single target doses of CLN-978 demonstrate a favorable safety profile at the initial dose levels. Robust B cell depletion in both peripheral blood and tissue was observed, along with early signals of promising clinical activity in patients with RA and SLE. Updated data beyond the available published abstract, including additional patients, will be presented at the EULAR Congress.

**Poster Presentation Details**

**Title:** CLN-978, a bispecific CD19 x CD3 T cell engager, induces robust B cell depletion in patients with rheumatoid arthritis and systemic lupus erythematosus<br>**Session Name:** Poster View VIII<br>**Session Date:** Saturday, June 6, 2026<br>**Session Time:** 10:15 a.m. - 11:15 a.m. BST<br>**Room:** Poster View<br>**Poster Number:** POS1179

**About CLN-978** 

CLN-978 is a novel, differentiated and highly potent CD19xCD3 bispecific T cell engager. CLN-978 triggers T cell-redirected lysis of CD19-expressing target cells *in vitro* and *in vivo*. CLN-978 is engineered to achieve very high affinity binding to CD19 to efficiently target B cells, including those with very low CD19 levels. Small in molecular size (65 kDa), CLN-978 contains two single-chain variable fragments, one binding with very high affinity to the CD19 target and the other binding to CD3 on T cells, and a single-domain antibody binding to human serum albumin to extend half-life. CLN-978 was developed by an internal Cullinan team and is a wholly owned asset. CLN-978 has the potential to offer a convenient, off-the-shelf, subcutaneously delivered therapeutic option for patients with autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, and Sjögren's disease.

**About OUTRACE RA and OUTRACE SLE**

------

OUTRACE RA and OUTRACE SLE are global Phase 1 studies of CLN-978 evaluating safety, as well as effects on disease activity and the immune system. Both studies are currently recruiting.

OUTRACE RA enrolls patients with active rheumatoid arthritis (DAS28-ESR ≥3.2) who have been treated with ≥2 prior targeted treatments and have evidence of B cell driven disease. Assessments include DAS28, synovial ultrasound, and optional synovial and lymph node biopsies.

OUTRACE SLE enrolls patients with active systemic lupus erythematosus (hSLEDAI ≥6) who have been treated with at least one biologic or immunosuppressive agent and are seropositive. Assessments include hSLEDAI, CLASI, and physician global assessment.

**About Rheumatoid Arthritis (RA)**

Rheumatoid arthritis is a chronic autoimmune disease primarily characterized by inflammation of the joints, which can lead to pain, swelling, stiffness, and permanent joint damage.<sup>1,2</sup> The disease often affects multiple joints simultaneously, commonly the hands, wrists, and feet, but it can also involve other organ systems.<sup>2</sup> Roughly 5.3 million adults live with rheumatoid arthritis across the U.S., France, Germany, Italy, Spain, the UK, Japan, and Australia, and the disease is more common in women than men.<sup>3-10</sup> While disease-modifying antirheumatic drugs (DMARDs) have improved treatment outcomes, many patients continue to rely on chronic immunosuppression, have inadequate responses, experience disease flares, and face significant impairments in quality of life.<sup>11</sup>

**About Systemic Lupus Erythematosus (SLE)**

Systemic lupus erythematosus (SLE) is a chronic, heterogeneous autoimmune disease in which the immune system attacks a patient's own tissues. The most common manifestations of SLE include skin rashes, arthritis, extreme fatigue, and low fevers. Lupus nephritis (LN) is a kidney disease and the most common severe manifestation of SLE. Approximately 40% of patients with SLE develop LN, which has a 10-year 30% mortality rate.<sup>12,13</sup> The prevalence of SLE in the US is estimated at 160,000 to 320,000 cases and SLE affects approximately 3.4 million individuals globally.<sup>14,15</sup> SLE is more prevalent in women and people of color. It occurs most often in people between the ages of 15 and 45 years but can occur in childhood or later in life as well. Currently available treatments can reduce the signs and symptoms of SLE; however, they do not routinely induce treatment-free remission, and most patients require lifelong immune suppression that treats symptoms without modifying the course of disease.

**Forward-Looking Statements**

This press release contains forward-looking statements within the meaning of The Private Securities Litigation Reform Act of 1995. These forward-looking statements include, but are not limited to, express or implied statements regarding the company's beliefs and expectations regarding: the efficacy and safety data from the Company's ongoing Phase 1 OUTRACE RA and

------

OUTRACE SLE clinical trials; our clinical development plan and timeline for CLN-978, the clinical and therapeutic potential of CLN-978, our plans regarding future data presentations, and other statements that are not historical facts. The clinical trials referenced in this release are ongoing, and the data described are interim, subject to change, and based on data available as of a specified date. As patient enrollment continues and additional follow-up data is obtained, the reported safety profile and other clinical outcomes may change materially. There can be no assurance that the interim results will be predictive of final study results or that additional data will confirm or support these observations. The words "believe," "continue," "could," "estimate," "expect," "intends," "may," "plan," "potential," "project," "pursue," "will," and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words.

Any forward-looking statements in this press release are based on management's current expectations and beliefs of future events and are subject to known and unknown risks and uncertainties that 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. These risks include, but are not limited to, the following: uncertainty regarding the timing and results of regulatory submissions; the risk that any INDs, NDAs or other global regulatory submissions we may file with the United States Food and Drug Administration or other global regulatory agencies are not cleared on our expected timelines, or at all; the success of our clinical trials and preclinical studies; the risks related to our ability to protect and maintain our intellectual property position; the risks related to manufacturing, supply, and distribution of our product candidates; the risk that any one or more of our product candidates, including those that are co-developed, will not be successfully developed and commercialized; the risk that the results of preclinical studies or clinical studies will not be predictive of future results in connection with future studies; and the success of any collaboration, partnership, license or similar agreements. These and other important risks and uncertainties discussed in our filings with the Securities and Exchange Commission, including under the caption "Risk Factors" in our most recent Annual Report on Form 10-K and subsequent filings with the SEC, could cause actual results to differ materially from those indicated by the forward-looking statements made in this press release. While we may elect to update such forward-looking statements at some point in the future, we disclaim any obligation to do so, even if subsequent events cause our views to change, except to the extent required by law. These forward-looking statements should not be relied upon as representing our views as of any date subsequent to the date of this press release. Moreover, except as required by law, neither the company nor any other person assumes responsibility for the accuracy and completeness of the forward-looking statements included in this press release. Any forward-looking statement included in this press release speaks only as of the date on which it was made.

**Contacts:**

**Investors**<br>Nick Smith<br>+1 401.241.3516<br>Nsmith@cullinantx.com

------

**Media**<br>Rose Weldon<br>+1 215.801.7644<br>Rweldon@cullinantx.com

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;1.World Health Organization. (2023). Rheumatoid arthritis. https://www.who.int/news-room/fact-sheets/detail/rheumatoid-arthritis

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2.Johns Hopkins Arthritis Center. Rheumatoid Arthritis Signs and Symptoms. Rheumatoid Arthritis Symptoms: Johns Hopkins Arthritis Center

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.Hunter, T. M., et al. (2017). Prevalence of rheumatoid arthritis in the United States adult population in healthcare claims databases, 2004–2014. *Rheumatology International*, *37*(9), 1551–1557. https://doi.org/10.1007/s00296-017-3726-1

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;4.Guillemin, F., et al. (2005). Prevalence of rheumatoid arthritis in France: 2001. *Annals of the Rheumatic Diseases*, *64*(10), 1427–1430. https://doi.org/10.1136/ard.2004.029199

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;5.Steffen, A., et al. (2017). Epidemiologie der rheumatoiden Arthritis in Deutschland – eine Analyse anhand bundesweiter vertragsärztlicher Abrechnungsdaten. *Zentralinstitut für kassenärztliche Versorgung in Deutschland,* (17), 1–20. https://doi.org/10.20364/VA-17.08

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;6.Rossini, M., et al. (2014). Prevalence and incidence of rheumatoid arthritis in Italy. *Rheumatology International*, *34*(5), 659–664. https://doi.org/10.1007/s00296-014-2974-6

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;7.Fina-Aviles, F., et al. (2016). The descriptive epidemiology of rheumatoid arthritis in Catalonia: A retrospective study using routinely collected data. *Clinical Rheumatology*, *35*(3), 751–757. https://doi.org/10.1007/s10067-014-2801-1

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;8.Abhishek, A., et al. (2017). Rheumatoid arthritis is getting less frequent: Results of a nationwide population-based cohort study. *Rheumatology (United Kingdom)*, *56*(5), 736–744. https://doi.org/10.1093/rheumatology/kew468

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;9.Kojima, M., et al. (2019). Epidemiological characteristics of rheumatoid arthritis in Japan: Prevalence estimates using a nationwide population-based questionnaire survey. *Modern Rheumatology*. Advance online publication. https://doi.org/10.1080/14397595.2019.1682776

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;10.Ackerman, I. N., et al. (2018). Projected burden of osteoarthritis and rheumatoid arthritis in Australia: A population-level analysis. *Arthritis Care & Research*, *70*(6), 877–883. https://doi.org/10.1002/acr.23414

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;11.Radu, A. F., & Bungau, S. G. (2021). Management of rheumatoid arthritis: An overview. *Cells, 10*(11), 2857. https://doi.org/10.3390/cells10112857

------

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;12.Mahajan, A. et al. (2020). Systemic lupus erythematosus, lupus nephritis and end-stage renal disease: A pragmatic review mapping disease severity and progression. *Lupus*, 29(9), 1011–1020. https://doi.org/10.1177/0961203320932219

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;13.Hocaoglu, M. et al. (2023). Incidence, prevalence, and mortality of lupus nephritis: A population-based study over four decades using the Lupus Midwest Network. *Arthritis & Rheumatology*, 75(4), 567–573. https://doi.org/10.1002/art.42375

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;14.Tian, J. et al. (2022). Global epidemiology of systemic lupus erythematosus: A comprehensive systematic analysis and modelling study. *Annals of the Rheumatic Diseases*, 82(3), 351–356. https://doi.org/10.1136/ard-2022-223035

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;15.Dall'Era, M. (2013). Chapter 21. Systemic lupus erythematosus. In J. B. Imboden, D. B. Hellmann, & J. H. Stone (Eds.), *CURRENT Diagnosis & Treatment: Rheumatology* (3rd ed.). McGraw-Hill. https://accessmedicine.mhmedical.com/content.aspx?aid=57272268

------