A Phase 1, Open-Label, Multiple-Ascending Dose Study of the Safety and Tolerability of CTX-8371 in Patients With Advanced Malignancies

More details:

Overview

CTX-8371 is an investigational, fully human, tetravalent bispecific antibody from Compass Therapeutics that targets both PD-1 and PD-L1. It is being evaluated as intravenous monotherapy in a Phase 1 trial (NCT06150664) involving patients with advanced cancers that progressed after prior immune-checkpoint inhibitors. Dose-expansion cohorts in non-small-cell lung cancer (NSCLC), triple-negative breast cancer (TNBC), and Hodgkin lymphoma are ongoing. (asco.org)

Mechanism of action

CTX-8371 simultaneously blocks PD-1 and PD-L1 while promoting interactions between PD-1–expressing immune cells and PD-L1–expressing cells. Preclinical studies found that this co-engagement induces proteolytic cleavage and loss of PD-1 from activated T-cell surfaces, potentially providing an additional mechanism beyond conventional checkpoint blockade. CTX-8371 increased T-cell activity and produced greater antitumor effects than benchmark PD-1 or PD-L1 antibodies in several cell and mouse models, but these comparisons have not been established clinically. (pmc.ncbi.nlm.nih.gov)

Efficacy

Initial results from the Phase 1 dose-escalation study were presented at ASCO 2026. Among 15 evaluable, heavily pretreated patients:

• Overall response rate: 20% (3/15)
• Disease-control rate: 60%
• Responses occurred in one patient each with NSCLC, TNBC, and Hodgkin lymphoma
• At doses of 3 or 10 mg/kg, the response rate was 33% (2/6)
• The TNBC patient had a greater than 90% reduction in tumor volume; the Hodgkin lymphoma patient had a metabolic partial response. The NSCLC response followed initial pseudoprogression.

These early, non-randomized results come from a small dose-escalation cohort and do not establish comparative efficacy. (asco.org)

Safety

No dose-limiting toxicities were reported, and the maximum tolerated dose was not reached. Treatment-related adverse events were Grade 1–2 except for one asymptomatic Grade 3 lipase elevation, which caused the study’s only dose interruption. No dose reductions were reported. (asco.org)

Further reading

• ASCO 2026 Phase 1 abstract
• Peer-reviewed preclinical study in OncoImmunology
• Clinical trial record: NCT06150664

Last updated: Sep 2026

Inclusion Criteria:

1. Age 18 years or older

2. Patients must have a histologically or cytologically confirmed diagnosis of locally advanced unresectable or metastatic disease that is relapsed/refractory to standard therapy or for which no effective standard therapy is available, including

1. Malignant Melanoma (MM)

* Patients who have progressed after a minimum of 2 doses of a PD-1/PD-L1 treatment. Study enrollment (C1D1) must be within 12 weeks of the last dose of the anti-PD-1/PD-L1 blocking antibody.

* Patients must have had prior testing for BRAF V600 mutations.- Patients with BRAF V600 activating mutation must have received prior therapy with a BRAF/MEK inhibitor.

* Uveal and mucosal melanoma are excluded.

2. Head and Neck squamous cell carcinoma (HNSCC)

* HNSCC of oral cavity, oropharynx, hypopharynx, or larynx

* Patients who have progressed after a minimum of 2 doses of a PD-1/PD-L1 treatment. Study enrollment (C1D1) must be within 12 weeks of the last dose of the anti-PD-1/PD-L1 blocking antibody.

* Patients must have received prior treatment with platinum-based chemotherapy.

3. Non-Small Cell Lung Cancer (NSCLC)

* Patients who have progressed after a minimum of 2 doses of a PD-1/PD-L1 treatment. Study enrollment (C1D1) must be within 12 weeks of the last dose of the anti-PD-1/PD-L1 blocking antibody.

* Patients must have received prior treatment with platinum-based chemotherapy.

4. Triple Negative Breast Cancer (TNBC)

* ER/PR and HER2 status should be defined by ASCO/CAP guidelines (JCO Allison et al 2020).

* Patients with HER2-low cancers (IHC 1+ or FISH-negative) are excluded.

* Patients must have received prior sacituzumab govitecan and if PD-L1 ≥10% by CPS pembrolizumab with chemotherapy.

5. Classical Hodgkin Lymphoma (HL)

* Patients must have received at least two prior systemic therapies including brentuximab vedotin (if eligible) and a prior PD-1 inhibitor

* Patients must have experienced less than a CR (according to Lugano criteria to anti- PD-1 treatment

3. Patients with NSCLC, MM, TNBC, and HNSCC must have measurable disease per RECIST 1.1. Patients with HL must have at least one measurable lesion \> 1.5 cm for nodal, \> 1.0 cm for extranodal FDG-avid disease by the Lugano (2014) response criteria. Tumor sites that are considered measurable must not have received prior radiation

4. Eastern Cooperative Oncology Group (ECOG) performance status 0-1

5. Adequate bone marrow function defined by absolute neutrophil (ANC) of ≥ 1.5×109/L, platelet count of ≥ 100.0×109/L, and hemoglobin of ≥ 9.0 g/dL (with or without transfusion)

6. Adequate hepatic function defined as serum total bilirubin ≤ 1.5 × ULN, AST/ALT ≤ 2.5 × ULN (or ≤ 5 × ULN in patients with liver metastases)

7. Adequate renal function defined as creatinine clearance ≥ 30mL/min by Cockcroft-Gault equation

8. Female patients must be surgically sterile (or have a monogamous partner who is surgically sterile) or be at least 2 years postmenopausal or commits to use 2 acceptable forms of birth control (defined as the use of an intrauterine device (IUD), a barrier method with spermicide, condoms, any form of hormonal contraceptives) or abstinence for the duration of the study and for 4 months following the last dose of study treatment. Male patients must be sterile (biologically or surgically) or commit to the use of a reliable method of birth control (condoms with spermicide) for the duration of the study and for 4 months following the last dose of study treatment.

9. Female patients who are women of childbearing potential (WOCBP) must have a negative serum pregnancy test at Screening within 7 days of dosing with CTX-8371

10. Last dose of previous PD-1 or PD-L1 therapy ≥ 28 days, other anticancer therapy \> 21 days (or 2 half-lives for proteins, whichever is longer), radiotherapy \>21 days (concurrent localized palliative radiotherapy is allowed during CTX-8371 treatment), or surgical intervention \>21 days prior to the first dose of CTX-8371

11. Resolution of all prior anti-cancer therapy toxicities ≤ Grade 2

12. Capable of understanding and complying with protocol requirements

13. Signed and dated institutional review board (IRB)/independent ethics committee (IEC)-approved informed consent form (ICF) before any protocol-directed screening procedures are performed

Exclusion Criteria:

1. Developed clinically significant adverse reaction to PD-1 or PD-L1 therapy, including immune related adverse reactions, which led to discontinuation of treatment

2. Systemic therapy with immunosuppressive agents within 7 days before the start of CTX-8371 treatment. Topical, intranasal, intraocular, or inhaled corticosteroids and physiologic replacement for patients with adrenal insufficiency are allowed

3. Patient is a pregnant or lactating WOCBP

4. Prior organ transplantation

5. Patients with evidence of active hepatitis B virus (HBV), hepatitis C virus (HCV) or human immunodeficiency virus (HIV) infection. Patients with positive HBsAg and/or detectable HBV DNA are eligible only if adequately controlled on antiviral therapy according to institutional standards and liver function eligibility criteria are also met. HCV patients showing sustained viral response or patients with immunity to HBV infection may enroll.

6. Active autoimmune disease or medical conditions requiring chronic steroid (i.e., \> 10 mg/day prednisone or equivalent) or immunosuppressive therapy. Patients with a prior history of autoimmune disease may be eligible following discussion with the Medical Monitor

7. Other medical condition that in the opinion of the Investigator and/or Sponsor Medical Monitor may interfere with the conduct and/or interpretation of the current study, including:

1. Congestive heart failure (\> New York Heart Association Class II), active coronary artery disease, unevaluated new onset angina within 3 months or unstable angina (angina symptoms at rest) or clinically significant cardiac arrhythmias

2. QTc interval (using Fridericia correction calculation) \> 480 msec