Galinpepimut-S
A four-peptide cancer vaccine against the WT1 protein, tested to keep leukaemia and mesothelioma from coming back
Galinpepimut-S is a vaccine made of four synthetic peptides from Wilms tumour 1 (WT1), a protein that many blood cancers and some solid tumours make in large amounts. Some of the peptides are heteroclitic, meaning one amino acid was changed so the immune system reacts to them more strongly than to the natural sequence. It is injected under the skin with immune-boosting adjuvants. Small trials found it well tolerated and able to raise T-cell responses against WT1; whether it keeps cancer in remission is the question of the REGAL phase 3 trial in acute myeloid leukaemia, which had not reported when this page was written.
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What is it?
Cancer vaccines of this kind try to teach T cells to recognise a protein that tumour cells carry and normal cells mostly do not. WT1 is a strong candidate: a National Cancer Institute exercise that ranked cancer antigens put it first, and the REGAL protocol paper notes that it is overexpressed in leukaemic blasts and nearly absent from normal blood-forming cells. Galinpepimut-S packs four WT1 peptides into one injection. Because some were altered by a single residue to provoke a stronger response, and together they are not tied to one tissue type, the vaccine can be given to patients regardless of their HLA type.
Its main use has been after treatment, when cancer is in remission but likely to return. In a phase 2 trial in 22 adults with acute myeloid leukaemia in first remission (median age 64), patients had six injections over ten weeks and up to six more monthly. Fourteen completed at least six, and nine had all twelve. Side effects were mostly mild injection-site reactions, fatigue and skin hardening. Nine of the 14 patients tested made a T-cell response to WT1. Fifteen of the 22 relapsed; median disease-free survival was 16.9 months, and the authors estimated survival from diagnosis at more than 67 months, which they considered encouraging but which a single-arm study cannot attribute to the vaccine.
In malignant pleural mesothelioma, a randomised phase 2 after surgery and other treatment compared the vaccine plus adjuvants with the adjuvants alone. It enrolled 41 of 78 planned patients before a futility rule closed the control arm. One-year progression-free survival was 45% with the vaccine and 33% without, and median overall survival 22.8 against 18.3 months, differences the trial was not powered to test. Later phase 1 studies paired it with the checkpoint inhibitor nivolumab: in 11 women with ovarian cancer in second or third remission, ten made WT1 T-cell responses and the one-year progression-free rate among those treated more than twice was 70%; in 10 people with previously treated mesothelioma, three made vaccine-specific responses, none had a tumour shrink by half, and median survival was 7.4 months.
The deciding trial is REGAL, an international open-label phase 3 comparing galinpepimut-S with the investigator's choice of best available therapy as maintenance for acute myeloid leukaemia in second remission, in patients who cannot go straight to a stem-cell transplant. The registry lists 127 participants and the study as active, not recruiting. In August 2026 its sponsor said the final analysis would follow the 80th event and had not yet been run. Until it reports, there is no randomised evidence that the vaccine prevents relapse, and it is not approved anywhere.
At a Glance
Every value in this table is printed from the Grey Peptides dataset, the same record the compound explorer and comparison tool read, so the three can never disagree.
Mechanism of Action
What the trials measured about how the vaccine works.
A target on leukaemia cells
WT1 is overexpressed in leukaemic blast cells and nearly absent from normal blood-forming cells, so an immune response against it should spare most healthy tissue (REGAL protocol, 2025).
Altered peptides for a stronger response
The four peptides include heteroclitic versions, changed by one residue, and are not restricted to one HLA type (2023, 2025 studies).
T cells and antibodies
Trials measured CD4 T-cell proliferation, CD8 interferon-gamma release and, in ovarian cancer, IgG antibodies against WT1; most patients tested made at least one of these responses (2018, 2023).
Published Research
These are all six records PubMed holds for galinpepimut-S, read from their abstracts on October 30, 2026: four trials in people, a 2021 review and the REGAL protocol.
Phase 2 in AML in first remission
22 adults received six injections over ten weeks and up to six more monthly. The vaccine was well tolerated, mostly with grade 1-2 injection-site reactions (46%), fatigue (32%) and skin induration (32%). Nine of 14 tested had a WT1 immune response; 15 relapsed and median disease-free survival was 16.9 months.
Randomised phase 2 in mesothelioma
After multimodality treatment, 41 patients were randomised to the vaccine with GM-CSF and Montanide or the adjuvants alone. Adverse events were mild. One-year progression-free survival was 45% against 33%, median overall survival 22.8 against 18.3 months; the trial closed early and was not powered to compare arms.
With nivolumab in ovarian cancer
Eleven women with WT1-expressing ovarian cancer in second or third remission had six vaccinations every two weeks with nivolumab. One had a dose-limiting grade 3 or worse event. Ten had T-cell responses to WT1, seven of eight evaluable had WT1 antibodies, and the one-year progression-free rate was 70% in those treated more than twice.
With nivolumab in mesothelioma
Ten patients with progressive mesothelioma after chemotherapy had two vaccine doses, then six with nivolumab every two weeks. Two had grade 3 or worse events; three made vaccine-specific T-cell responses. No tumour responded; median progression-free survival was 3.9 months and overall survival 7.4 months.
Review of its development in AML
Summarises the vaccine's structure and the phase 1 and 2 safety and efficacy data in acute myeloid leukaemia, and the move to a phase 3 trial in second remission against best available therapy.
The REGAL phase 3 design
Describes REGAL, an international open-label randomised trial of the vaccine against best available therapy as maintenance in AML in second remission (NCT04229979), and the rationale of WT1 as a target.
Side Effects & Contraindications
Reported Side Effects
From the trials above.
Contraindications & Cautions
There is no label. These cautions follow from how it was studied.
Legal Status
Galinpepimut-S is investigational.
Frequently Asked Questions
?What is galinpepimut-S?
A cancer vaccine made of four synthetic peptides from the WT1 protein, some altered to provoke a stronger immune response, injected under the skin with adjuvants.
?Does it work?
It is not yet known. Small trials show it is well tolerated and that most patients make an immune response to WT1, but survival comparisons so far come from single-arm or underpowered trials. The REGAL phase 3 will decide.
?What is the dose?
The abstracts read do not state the amount of peptide per injection. The schedules were six injections over ten weeks, then monthly, or every two weeks alongside nivolumab.
?Is it a peptide you can buy?
No. It is an investigational vaccine given in trials or expanded access, with adjuvants that are part of the treatment.
References
- [clinical-trial] Maslak PG, et al. "Phase 2 trial of a multivalent WT1 peptide vaccine (galinpepimut-S) in acute myeloid leukemia." Blood Adv, 2018;2(3):224-234. PMID: 29386195.
- [rct] Zauderer MG, et al. "A Randomized Phase II Trial of Adjuvant Galinpepimut-S, WT-1 Analogue Peptide Vaccine, After Multimodality Therapy for Patients with Malignant Pleural Mesothelioma." Clin Cancer Res, 2017;23(24):7483-7489. PMID: 28972039.
- [clinical-trial] Manning-Geist BL, et al. "Phase I Study of a Multivalent WT1 Peptide Vaccine (Galinpepimut-S) in Combination with Nivolumab in Patients with WT1-Expressing Ovarian Cancer in Second or Third Remission." Cancers (Basel), 2023;15(5). PMID: 36900251.
- [clinical-trial] Agrawal P, et al. "Combining a WT1 Vaccine (Galinpepimut-S) With Checkpoint Inhibition (Nivolumab) in Patients With WT1-Expressing Diffuse Pleural Mesothelioma: A Phase 1 Study." JTO Clin Res Rep, 2025;6(1):100756. PMID: 39802820.
- [review] Jain AG, et al. "Galinpepimut-S (GPS): an investigational agent for the treatment of acute myeloid leukemia." Expert Opin Investig Drugs, 2021;30(6):595-601. PMID: 34053383.
- [review] Jamy O, et al. "REGAL: galinpepimut-S vs. best available therapy as maintenance therapy for acute myeloid leukemia in second remission." Future Oncol, 2025;21(1):73-81. PMID: 39606837.
- [registry] ClinicalTrials.gov API v2, read October 28, 2026: NCT04229979 (phase 3, REGAL, active, not recruiting); NCT05593185 (expanded access); NCT01266083 (phase 2, AML or ALL in remission) and NCT01265433 (phase 2, mesothelioma), completed; NCT04040231 (phase 1, mesothelioma with nivolumab, completed); NCT01827137 (phase 1/2, myeloma after autologous transplant, completed).
- [manufacturer] SELLAS Life Sciences. "SELLAS Life Sciences Reports Second Quarter 2026 Financial Results and Provides Corporate Update." Company release, August 11, 2026: REGAL final analysis to follow the 80th event; no result reported. https://ir.sellaslifesciences.com/news/News-Details/2026/SELLAS-Life-Sciences-Reports-Second-Quarter-2026-Financial-Results-and-Provides-Corporate-Update/default.aspx. Read October 30, 2026.
Sources & Citations
Every study on this page was read from its PubMed record on October 30, 2026; trial status is from ClinicalTrials.gov and the sponsor's August 11, 2026 release. Grey Peptides sells nothing and links to no vendor.
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