IO102-IO103

What is IO102-IO103?#

IO102-IO103 (brand name Cylembio) is a first-in-class off-the-shelf therapeutic cancer vaccine developed by IO Biotech (Copenhagen, Denmark). It consists of two synthetic long peptides designed to activate the immune system against two key immunosuppressive mechanisms in the tumor microenvironment:

• IO102: A synthetic peptide derived from indoleamine 2,3-dioxygenase (IDO), an enzyme that suppresses anti-tumor immunity by depleting tryptophan and generating immunosuppressive metabolites
• IO103: A synthetic peptide encoding amino acids 9-27 of human programmed death ligand 1 (PD-L1), the protein that inhibits T cell function through the PD-1/PD-L1 checkpoint

Unlike personalized neoantigen vaccines that require tumor sequencing and patient-specific manufacturing, IO102-IO103 targets universally expressed immunosuppressive proteins present across most tumor types. This enables an off-the-shelf approach with immediate availability and no manufacturing delay.

Mechanism of Action#

IO102-IO103 works by turning the tumor's own immunosuppressive mechanisms into targets for immune attack:

IO102 (IDO-Targeting Peptide)#

IDO is an intracellular enzyme overexpressed by tumor cells and immunosuppressive myeloid cells in the tumor microenvironment. It catalyzes tryptophan degradation via the kynurenine pathway, creating a tryptophan-depleted, kynurenine-rich environment that suppresses T cell function and promotes regulatory T cell (Treg) differentiation. IO102 vaccination:

• Activates IDO-specific cytotoxic T cells that directly kill IDO-expressing tumor cells and myeloid-derived suppressor cells
• Reduces IDO-mediated immune suppression in the tumor microenvironment
• Predominantly reduces myeloid-derived immune suppression

IO103 (PD-L1-Targeting Peptide)#

PD-L1 is expressed on tumor cells and antigen-presenting cells, engaging PD-1 on T cells to inhibit anti-tumor immunity. IO103 vaccination:

• Activates PD-L1-specific T cells that kill PD-L1-expressing cells
• Enhances anti-tumor T effector cell function
• Provides an immune-mediated approach to PD-L1 disruption, complementary to antibody-mediated PD-1/PD-L1 blockade

Dual Mechanism Synergy#

Preclinical data show that IO102 and IO103 cooperatively reduce tumor growth through distinct molecular pathways -- IO102 primarily reducing myeloid suppression and IO103 enhancing T effector function. Combined with checkpoint inhibitor antibodies, this creates a three-pronged attack on tumor immune evasion.

Clinical Development#

IO102-IO103 has been evaluated across multiple cancer types:

• MM1636 Phase 1/2 (Nature Medicine, 2021): 30 melanoma patients treated with IO102-IO103 + nivolumab achieved 80% ORR, 43% CR, and 26-month median PFS (PMID: 34887574)
• 5-Year Follow-Up (Nature Communications, 2025): Median PFS of 25.5 months, median duration of response >53 months, median OS of 60 months, with vaccine-specific immune biomarkers (CCL3, CCL4, TNF-alpha)
• Phase 3 IOB-013/KN-D18 (ESMO 2025): 407 melanoma patients randomized to IO102-IO103 + pembrolizumab vs pembrolizumab alone. Median PFS 19.4 vs 11.0 months (8.4-month improvement). PD-L1-negative subgroup: 16.6 vs 3.0 months. Did not meet pre-specified statistical threshold.
• Phase 2 Basket (NSCLC/HNSCC): IO102-IO103 + pembrolizumab showed ORR of 48.4% in NSCLC and 44.4% in HNSCC
• FDA Breakthrough Therapy Designation: Granted December 2020 for IO102-IO103 + anti-PD-1 in unresectable/metastatic melanoma

Important Considerations#

IO102-IO103 is an investigational biologic that has not been approved by any regulatory authority. Key considerations include:

• The phase 3 melanoma trial improved median PFS by 8.4 months but narrowly missed the pre-specified hazard ratio threshold for statistical significance
• Following a pre-BLA meeting in September 2025, the FDA recommended against filing a Biologics License Application based on the current phase 3 dataset alone
• IO Biotech is evaluating strategic options including additional trials
• The vaccine has shown particular promise in PD-L1-negative patients, a population with limited treatment options, which may inform future trial design
• As a peptide vaccine, IO102-IO103 requires combination with checkpoint inhibitors; it is not designed for monotherapy use

Key Research Findings#

Phase 1/2 MM1636 Trial, published in Nature Medicine (Kjeldsen JW et al., 2021; PMID: 34887574):

• Objective response rate of 80% with 43% complete responses in 30 metastatic melanoma patients
• Median PFS of 26 months with median follow-up of 22.9 months
• Safety profile comparable to nivolumab monotherapy
• Vaccine-specific T cell responses detected against both IDO and PD-L1

Phase 3 IOB-013/KN-D18 presented at ESMO 2025:

• 407 patients with untreated advanced melanoma
• Median PFS: 19.4 months (IO102-IO103 + pembrolizumab) vs 11.0 months (pembrolizumab alone)
• PD-L1-negative subgroup: 16.6 vs 3.0 months median PFS
• No increased immune-mediated or treatment-related side effects with the combination

Related Reading#

• IO102-IO103 research studies and evidence
• IO102-IO103 dosing protocols
• IO102-IO103 side effects profile