About 80% of soft-tissue sarcomas are immunologically "cold" — they lack tertiary lymphoid structures and resist checkpoint inhibitors. The REGOMUNE phase 2 trial tested whether the anti-angiogenic regorafenib could prime these tumors for the PD-L1 blocker avelumab in 49 patients selected for absent mature TLS. Profiling paired tumor and plasma samples, the team found the combination significantly raised CD8+ T cell and B cell infiltration and PD-1 expression — yet the objective response rate stayed at 11%, with soluble PD-L1 and tryptophan depletion pointing to why warming a cold sarcoma isn't enough.
Published in Signal Transduction and Targeted Therapy, this phase 2 study — co-led by first authors Maud Toulmonde (Institut Bergonié) and Explicyte’s Jean-Philippe Guégan, with Prof. Antoine Italiano (Institut Bergonié, Gustave Roussy) as corresponding author — asked whether an anti-angiogenic drug could make immunologically “cold” soft-tissue sarcomas responsive to checkpoint blockade. Associated with the study through the RHU CONDOR program, Explicyte profiled paired plasma samples from 32 patients with the Olink Explore HT panel and ran the 7-plex multiplex immunofluorescence on paired biopsies — together tracking how the tumor microenvironment shifted on treatment. The work was funded by Institut National du Cancer, the Association pour la Recherche contre le Cancer, and the Agence Nationale de la Recherche (ANR 21 RHUS 0010).
The REGOMUNE phase 2 cohort enrolled 49 patients with advanced soft-tissue sarcoma confirmed by central pathology review to lack mature tertiary lymphoid structures — the ~80% of sarcomas that derive little benefit from immunotherapy. Leiomyosarcoma (45%) and synovial sarcoma (18%) were the most common subtypes in a heavily pretreated population (median two prior lines). Patients received regorafenib at 160 mg daily on a 3-weeks-on, 1-off schedule, with avelumab added on day 15
Explicyte applied a validated 7-plex multiplex immunofluorescence panel (CD8, CD4, CD20, CD23, CD163, PD-1) to baseline and on-treatment (Cycle 2 Day 1) biopsies from seven consenting patients, imaged on the Akoya PhenoImager HT. On treatment, CD8+ T cell density rose (p = 0.047) alongside CD4+ T cells (p = 0.047) and a trend toward more B cells, and B cells moved into closer contact with CD3+ T cells (p = 0.036). PD-1 expression on T cells increased — but no new tertiary lymphoid structures formed.
Explicyte used the Olink Explore HT panel to measure ≈5,300 plasma proteins at baseline and Cycle 2 Day 1 in 32 patients. Soluble PD-L1 (CD274) was the single most significantly upregulated protein on treatment — a known negative predictor of response to PD-(L)1 blockade — with enrichment of T cell receptor signaling pathways. Immune-cell composition inferred from the proteomic data confirmed the tissue findings, with significant gains in CD8+ T cells (p = 0.00013) and B cells (p = 0.048).
Complementary plasma metabolomics showed treatment depleted L-tryptophan, consistent with immunosuppressive kynurenine-pathway activity. Despite this broad immune activation, the objective response rate was 11.0% (95% CI: 4.0%–22.0%), with median PFS of 1.8 months and median OS of 15.1 months — and the rise in immune infiltration did not correlate with clinical benefit, even in patients with the largest increases in CD8+ T and B cell density.
Regorafenib plus avelumab can measurably warm a "cold" sarcoma — but the trial shows that boosting immune-cell numbers, on its own, does not unlock clinical response.
For developers pairing anti-angiogenics with checkpoint inhibitors, the lesson is that vascular normalization can deliver immune cells to a cold tumor without delivering responses — the functional state of those cells, not their abundance, is the bottleneck. The on-treatment surge in soluble PD-L1 and the depletion of tryptophan nominate concrete resistance mechanisms to target next, and argue for layering TLS-inducing strategies, such as CD40 or LTβR agonists, onto this backbone. Selecting patients by TLS status — central to this trial’s design — remains essential to interpreting any sarcoma immunotherapy combination.
