High-Performance T-Cell Activation in CLL: Study Highlights
This Phase 1 clinical trial represents a significant milestone in the development of personalised immunotherapy for Chronic Lymphocytic Leukaemia (CLL). The study’s primary highlights include:
1. High Immunogenicity: T-cell responses targeting multiple leukaemia-specific peptides were induced in 95% (19 of 20) of participants.
2. Sustained Response: Immune activation persisted in 84% of responders at the six-month follow-up, with increasing response intensity observed over time.
3. Safety Profile: The personalised activator was well-tolerated, with no grade 4 adverse events or treatment-related serious adverse events reported.
4. Synergistic Potential: The study successfully combined personalised vaccination with ongoing Bruton’s tyrosine kinase inhibitor (BTKi) therapy, addressing the challenge of minimal residual disease (MRD).
Addressing the Gap in Chronic Lymphocytic Leukaemia Therapy
Chronic Lymphocytic Leukaemia (CLL) remains a clinical challenge despite the transformative impact of Bruton’s tyrosine kinase inhibitors (BTKi). While agents like ibrutinib, acalabrutinib, and zanubrutinib have significantly improved progression-free survival, they rarely achieve complete molecular remission. Most patients remain in a state of minimal residual disease (MRD), necessitating indefinite treatment and increasing the risk of clonal evolution, resistance, and long-term toxicity.
The concept of therapeutic T-cell activation aims to leverage the patient’s own immune system to target and eliminate these residual malignant cells. However, several hurdles have hindered the widespread adoption of this approach. Historically, cancer vaccines have struggled with the low mutational burden of CLL, which results in a shortage of mutation-derived neoepitopes. Furthermore, the logistical complexity of designing truly personalised drugs has often limited clinical scalability. This study, led by researchers at Tübingen University, sought to overcome these barriers using a ‘warehouse-based’ personalised multipeptide activator combined with a novel adjuvant.
The iTAC-XS15-CLL01 Study: Design and Protocol
This open-label, single-centre, phase 1 study (NCT04688385) conducted in Germany focused on a highly specific patient population: those with CLL who had achieved at least partial remission but still harboured MRD after 6 to 8 months of BTKi-based therapy.
The Personalised Warehouse Approach
The intervention, iTAC-XS15-CLL01, utilizes a unique ‘warehouse’ strategy. Rather than creating entirely new peptides for each patient—a process that is both time-consuming and expensive—the researchers developed a library of eight CLL-specific peptides. These peptides were selected based on extensive immunopeptidomics, identifying antigens that are naturally presented on the HLA molecules of CLL cells. For each participant, a personalised subset of peptides was chosen based on their individual HLA allotype, ensuring that the vaccine was tailored to the patient’s specific molecular profile.
The Adjuvant: XS15
A critical component of the formulation is XS15, a Toll-like receptor (TLR) 1/2 ligand. XS15 serves as a potent adjuvant, designed to stimulate the innate immune system and provide the necessary co-stimulatory signals for effective T-cell activation. The vaccine was emulsified in Montanide ISA 51 VG and administered via three monthly subcutaneous injections.
Study Population and Endpoints
The trial enrolled 20 patients (median age 56.5 years) with an ECOG performance status of 2 or lower. The primary endpoints were the induction of T-cell responses (measured by IFNγ ELISpot assays) and the assessment of safety and toxicity from the first application through the end of treatment.
Clinical Efficacy: Unprecedented T-Cell Response Rates
The findings of the study are highly encouraging for the field of haematological oncology. The induction of a T-cell response was observed in 19 out of 20 patients (95%). This high rate of immunogenicity is particularly noteworthy given that CLL is often associated with significant immune dysfunction, which can be further exacerbated by long-term BTKi therapy.
Persistence and Intensity
Beyond the initial induction, the durability of the immune response was a key finding. At the six-month follow-up, 16 of the 19 responders (84%) maintained their T-cell activity. Furthermore, the researchers noted that the intensity of these responses—the magnitude of the T-cell activation—actually increased toward the end of the study period. This suggests that the vaccine may be inducing long-term memory T-cell populations capable of sustained surveillance against residual CLL cells.
Targeting Multiple Peptides
One of the strengths of the multipeptide approach is the induction of polyepitopic responses. By targeting multiple antigens simultaneously, the vaccine reduces the likelihood of ‘immune escape,’ where the tumour evolves to lose a single targeted antigen. In this study, the majority of patients developed responses against more than one of the selected peptides, strengthening the therapeutic pressure on the leukaemia.
Safety and Tolerability: A Manageable Profile
Safety is the paramount concern in any Phase 1 trial. The iTAC-XS15-CLL01 activator demonstrated a favourable safety profile. No grade 4 adverse events or treatment-related deaths occurred.
The most common adverse events were localized to the injection site, which is expected with the use of the Montanide adjuvant. These included:
1. Injection-site erythema (15% of patients)
2. Granuloma formation (10% of patients)
3. Local ulceration (5% of patients)
These local reactions are often considered indicative of a robust immune activation and were manageable within the clinical setting. The lack of systemic toxicity suggests that this multipeptide approach avoids the cytokine release syndromes or severe auto-immune toxicities sometimes seen with other forms of advanced immunotherapy like CAR-T cell therapy.
Expert Interpretation and Translational Significance
The success of this Phase 1 study provides a proof-of-concept for the ‘warehouse’ model of personalised immunotherapy. By pre-manufacturing a library of validated antigens, the time-to-treatment can be significantly reduced, making personalised medicine more accessible for clinical practice.
From a mechanistic standpoint, the study confirms that even in the context of BTKi-induced B-cell depletion and altered T-cell dynamics, the immune system remains capable of mounting a robust response to appropriately presented and adjuvanted antigens. This opens a ‘therapeutic window’ where T-cell activators could be used as a consolidation therapy to eliminate MRD and potentially allow for treatment holidays or the complete cessation of BTKi therapy.
However, researchers and clinicians must remain cautious. While the immunogenicity is clear, the clinical impact on progression-free survival and overall survival remains to be determined in larger, randomised Phase 2 and Phase 3 trials. The study was also limited to a White population and a single centre, necessitating further validation across more diverse cohorts.
Conclusion: Paving the Way for Phase 2 Trials
In summary, iTAC-XS15-CLL01 represents a potent and safe immunotherapeutic agent for patients with chronic lymphocytic leukaemia. By successfully inducing long-lasting, multi-peptide T-cell responses in a high percentage of patients, this study provides a strong rationale for moving toward Phase 2 efficacy trials. If validated, this personalised approach could shift the paradigm of CLL treatment from chronic management toward definitive eradication of the disease.
Funding and ClinicalTrials.gov
This study was funded by the Medical Faculty of Tübingen University.
Registration Number: ClinicalTrials.gov (NCT04688385).
References
Heitmann JS, Maringer Y, Jung S, Wacker M, Hackenbruch C, Polster M, Marconato M, Nelde A, Bauer J, Zwick M, Baur AS, Metzger A, Krolla C, Andrieux G, Köhler N, Boerries M, Denk M, Zieschang L, Kammer C, Hoenisch-Gravel N, Richter M, Oezbek MT, Wirths S, Dengler A, Dubbelaar ML, Pumptow M, Martus P, Brüggemann M, Rammensee HG, Salih HR, Walz JS. Personalised multipeptide-based T-cell activator for chronic lymphocytic leukaemia: an open-label, single-centre, phase 1 study. Lancet Haematol. 2026 Feb;13(2):e74-e85. doi: 10.1016/S2352-3026(25)00323-0. Epub 2026 Jan 14. Erratum in: Lancet Haematol. 2026 Feb;13(2):e58. doi: 10.1016/S2352-3026(26)00012-8. PMID: 41547362.