ARCHER Trial Explores Vaccine Strategy to Prevent ALK Inhibitor Resistance in Advanced NSCLC

Targeted therapies have transformed outcomes for patients with ALK-positive non-small cell lung cancer (NSCLC), but acquired resistance remains a persistent obstacle. Acquired resistance is often mediated by mutations within the ALK kinase domain, limiting the durability of tyrosine kinase inhibitors (TKIs). Investigators behind the ARCHER trial are pursuing a novel approach aimed not at overcoming resistance after it emerges, but at preventing it from developing in the first place.

Primary results from the first-in-human phase 1b ARCHER study evaluated ALK-Vac, a prophylactic peptide vaccine designed to stimulate immune responses against common ALK resistance mutations. The strategy seeks to complement ongoing TKI therapy by enabling the immune system to recognize resistance-associated alterations before ALK inhibitor resistance emerges.

The trial enrolled patients with advanced ALK-positive NSCLC who had not experienced progression while receiving standard-of-care ALK-directed TKI therapy. Participants continued their existing TKI treatment and received ALK-Vac, which consists of synthetic long peptides targeting seven frequently observed ALK resistance mutations: I1171T, I1171N, I1171S, L1196M, G1202R, D1203N, and E1210K. The vaccine was administered subcutaneously alongside the poly-ICLC adjuvant during a priming phase on days 1, 4, 8, 15, and 22, followed by booster doses at weeks 12 and 20.

Fifteen patients were enrolled, and all completed the planned vaccination schedule. Most participants were receiving first-line TKI therapy at study entry. Concomitant treatments included alectinib in 47% of patients, lorlatinib in 33%, and brigatinib in 20%. Patients had been receiving TKI therapy for a median of 43.7 months at enrollment, with treatment durations ranging from 4.6 to 74.2 months. Notably, two-thirds of participants had no measurable disease at baseline, reflecting a minimal residual disease setting in which the vaccine was intended to function as an immune-interception strategy.

Safety represented a primary objective of the study. ALK-Vac was well tolerated, with treatment-related adverse events occurring primarily as grade 1 events. Injection-site reactions were the most frequently reported adverse event, affecting 93% of patients, followed by fatigue in 60% and flu-like symptoms in 40%. No grade 3 or higher treatment-related adverse events were observed.

The second primary objective focused on vaccine-induced immune responses. Investigators assessed T-cell activity using interferon-gamma ELISpot assays and observed vaccine-specific responses in 71% of evaluable patients. Among the 14 patients assessed, 10 demonstrated at least a twofold increase in spot-forming units, with a median increase of 11.9-fold.

Immune responses were detected across multiple targeted resistance mutations. Responses against G1202R, L1196M, and D1203N were each observed in 71% of evaluable patients, while E1210K responses occurred in 64%. Responses targeting the I1171N, I1171S, and I1171T mutations were each seen in 50% of patients. These findings suggest that ALK-Vac can generate immune recognition against several common ALK resistance mutations encountered during ALK-targeted therapy.

Although efficacy was an exploratory endpoint, early disease-control findings were notable. After a median follow-up of 11.5 months, the disease control rate was 93%, corresponding to 14 of 15 patients.

One patient developed oligoprogression while receiving alectinib approximately 8.5 months after initiating ALK-Vac despite demonstrating robust immune responses against multiple ALK resistance mutations. Molecular profiling of the progressing lesion revealed an emergent KRAS G12D mutation without evidence of an ALK resistance mutation. The finding highlights the potential biological complexity underlying treatment resistance and the possibility that alternative resistance pathways may emerge during treatment.

The ARCHER trial represents an early clinical test of a broader immune-interception concept in oncogene-driven lung cancer. By targeting resistance-associated mutations before they become clinically dominant, investigators hope to delay or prevent the emergence of ALK inhibitor resistance. While larger studies and longer follow-up will be needed to determine whether vaccine-induced immune responses translate into prolonged clinical benefit, the primary analysis demonstrates that ALK-Vac was feasible to administer, well tolerated, and capable of generating mutation-specific T-cell responses in patients receiving ongoing ALK-directed therapy.

The findings support continued exploration of prophylactic immune targeting of resistance mutations as an adjunct to TKI therapy and may provide a framework for similar approaches across other oncogene-driven forms of NSCLC. Comprehensive cfDNA and immune-phenotyping analyses are planned for future reporting.