MaaT Pharma (Euronext Paris: MAAT) has reported preliminary findings from the investigator-sponsored Phase 2a PICASSO trial, showing that adding its investigational microbiome therapy MaaT013, also known as Xervyteg, to ipilimumab and nivolumab met the study’s primary safety and feasibility objective in patients with advanced melanoma. However, the randomised, placebo-controlled trial found comparable tumour response rates between the MaaT013 and placebo groups, leaving the treatment’s potential to improve immunotherapy efficacy unestablished.
The findings, announced on 6 November 2026 following a disclosure in the European Union Clinical Trials Information System, provide controlled clinical evidence concerning the administration of a microbiome ecosystem therapy alongside dual immune checkpoint inhibition. The analysis involved 69 patients from a trial that randomised 70 participants across five French centres.
The results are particularly consequential for MaaT Pharma because they distinguish biological activity from demonstrated clinical benefit. Although the investigational treatment increased gut microbiome richness and diversity, that change did not translate into a clearly superior overall tumour response in the disclosed analysis. The company is now examining whether baseline microbiome characteristics could help identify patients more likely to benefit, while continuing development of its next-generation programme MaaT034.
What did the randomised Phase 2a PICASSO trial establish about the safety of combining MaaT013 with immunotherapy?
PICASSO evaluated MaaT013 alongside the immune checkpoint inhibitors ipilimumab and nivolumab in patients with advanced, unresectable or metastatic melanoma who had not previously received anti-CTLA-4, anti-PD-1 or anti-PD-L1 treatment. The investigator-sponsored study was conducted by Assistance Publique Hôpitaux de Paris in collaboration with INRAE and Gustave Roussy.
A total of 70 patients were randomised, with 69 included in the reported analysis. Of those evaluated, 34 received MaaT013 in combination with ipilimumab and nivolumab, while 35 received placebo alongside the same immunotherapy regimen.
The study’s primary objective was to assess the safety and feasibility of introducing a microbiome ecosystem therapy into treatment with dual immune checkpoint inhibitors. According to the preliminary findings, no statistically significant difference was observed between the two groups in the incidence of Grade 3 or higher adverse events.
This is a relevant finding because combined CTLA-4 and PD-1 inhibition can produce substantial immune-related toxicity. Introducing a microbiome intervention into that setting requires evidence that the additional treatment does not create an unacceptable complication burden.
MaaT Pharma said the observed safety profile of the combination was generally consistent with expectations for ipilimumab and nivolumab treatment. The company characterised the primary study objective as met, supporting the feasibility of administering its microbiome product alongside the immunotherapy regimen.
However, the absence of a statistically significant difference in severe adverse events is not equivalent to demonstrating that the two treatment strategies have identical safety profiles. With 34 and 35 patients in the respective analysed groups, the trial has limited ability to exclude uncommon adverse reactions or modest differences in complication rates.
The announcement did not provide detailed numerical rates for every adverse-event category, nor did it establish long-term safety equivalence. Those distinctions are important when interpreting a trial primarily designed to generate early clinical evidence rather than support marketing authorisation.
Why did improved microbiome diversity fail to establish a clear tumour response advantage?
One of the most scientifically interesting PICASSO findings concerns the separation between measurable microbiome changes and clinical tumour outcomes. MaaT Pharma reported statistically significant increases in gut microbiome richness and diversity among patients receiving MaaT013 compared with placebo.
MaaT013 is a donor-derived microbiome ecosystem therapy designed to restore microbial diversity and influence immune function. The underlying biological rationale is that changes in gut microbial composition may affect immune regulation and potentially modify responses to checkpoint inhibitors.
Research has linked aspects of the gut microbiome with immune checkpoint inhibitor responsiveness, although the relationships are complex and have not established that increasing microbial diversity alone improves cancer outcomes. Different bacterial communities, metabolic functions and host immune characteristics may influence treatment response in ways that cannot be reduced to a single diversity measurement.
PICASSO provides evidence that MaaT013 altered the gut microbiome in the studied patients. However, the company’s preliminary disclosure reported comparable response rates in the experimental and placebo groups, despite the measurable biological changes.
That result weakens any straightforward claim that microbiome enrichment necessarily improves the antitumour activity of dual checkpoint inhibition in an unselected melanoma population. It does not rule out a benefit in a narrower subgroup, but it shows that microbiological activity and clinical efficacy must be evaluated separately.
The disclosed results do not establish whether improvements in microbial diversity were associated with longer progression-free survival, improved overall survival or durable differences in treatment response. Those outcomes would require specific analyses and sufficiently mature clinical follow-up.
The practical implication is that future studies may need more sophisticated patient-selection strategies rather than treating microbiome restoration as a universally beneficial addition to immunotherapy.
Could baseline microbiome composition explain why some melanoma patients respond differently?
MaaT Pharma reported exploratory findings suggesting that the composition of a patient’s gut microbiome before treatment may influence clinical response to MaaT013. The company indicated that these observations warrant further investigation and could help inform its immuno-oncology strategy.
This is potentially important because the biological effects of microbiome interventions may depend on the starting condition of the intestinal ecosystem. Patients with substantially disrupted microbial communities may respond differently from those whose baseline microbiome is already relatively diverse or functionally balanced.
Several factors can influence baseline microbiome composition, including prior antibiotic exposure, diet, comorbidities, previous cancer treatment and other medications. Such variability can complicate attempts to identify a reproducible treatment effect across a heterogeneous patient population.
A microbiome-directed therapy may therefore require a biomarker strategy capable of identifying patients whose microbial characteristics are associated with greater potential benefit. This would resemble the broader movement towards biomarker-guided treatment selection in oncology, although microbiome biomarkers remain considerably less established than many tumour genomic markers.
The PICASSO findings are exploratory rather than confirmatory. The company has not disclosed a validated microbial signature that reliably predicts MaaT013 treatment benefit, and the available announcement does not establish whether the suggested subgroup relationships remained significant after accounting for multiple comparisons.
The relatively small trial population also limits the strength of subgroup conclusions. When several microbiome characteristics are examined against clinical outcomes, apparently favourable patterns can emerge by chance, particularly without prespecified testing and independent validation.
MaaT Pharma generated shotgun metagenomic profiles using its gutPrint research engine, providing a dataset for more detailed investigation of microbial communities. These analyses may help identify patterns worth testing in subsequent studies, but a reproducible predictive biomarker would require evidence from independent patient populations.
The next scientific question is whether baseline microbiome composition can distinguish patients who derive additional clinical benefit from a microbiome intervention, rather than merely identifying patients who are already more likely to respond to immunotherapy.
How could the PICASSO findings influence MaaT034 development in checkpoint inhibitor-refractory cancers?
The findings arrive as MaaT Pharma continues development of MaaT034, a next-generation microbiome ecosystem therapy intended for investigation in patients with solid tumours that have not responded adequately to immune checkpoint inhibitors.
MaaT034 differs from MaaT013 and should not be considered clinically validated by the PICASSO results. The company describes the newer programme as using its co-cultivation technology to develop microbiome interventions designed for combination with immunotherapy.
The distinction in treatment setting is central. PICASSO evaluated patients who had not previously received the specified checkpoint inhibitor classes, whereas MaaT034 is being developed for patients with checkpoint inhibitor-refractory disease, including advanced non-small cell lung cancer and melanoma.
Patients whose cancers progress despite checkpoint inhibitor treatment may have different tumour biology, prior treatment exposure and immune characteristics from treatment-naïve populations. A microbiome-based strategy could therefore produce different results in these settings, although the PICASSO trial does not demonstrate that it will.
MaaT Pharma previously outlined plans for a first-in-human MaaT034 study involving patients with advanced solid tumours, including second-line non-small cell lung cancer and refractory advanced melanoma. The proposed study is intended to investigate dosing, pretreatment requirements and initial clinical proof of concept.
The company said in September 2026 that a chemistry, manufacturing and controls-focused pre-investigational new drug meeting with the United States Food and Drug Administration was scheduled for October. Its previously disclosed development plan contemplated potential study initiation in late 2027, conditional on adequate financing and regulatory clearance.
The PICASSO results may influence the biological rationale and patient-selection approach for MaaT034, particularly if further analyses identify microbiome characteristics linked with treatment outcomes. Nevertheless, data obtained with MaaT013 cannot establish the safety or effectiveness of a distinct investigational product.
The strongest route forward would involve using the PICASSO dataset to generate clearly defined hypotheses, then prospectively testing those hypotheses during MaaT034 development.
Why does the European regulatory setback for Xervyteg remain important to MaaT Pharma’s broader strategy?
MaaT013 remains investigational and has not received marketing authorisation for its intended treatment of steroid-refractory gastrointestinal acute graft-versus-host disease. In September 2026, the European Medicines Agency’s Committee for Medicinal Products for Human Use confirmed its negative recommendation following re-examination of MaaT Pharma’s conditional marketing authorisation application.
The agency had initially recommended refusal in June 2026. Following its September reassessment, the regulator maintained that the evidence was insufficient to reliably establish the product’s safety, efficacy and benefit-risk balance.
A central weakness identified by the agency was the absence of a concurrent comparator in the principal clinical study supporting the application. The open-label, single-arm design made it difficult to determine how much of the observed clinical improvement could be attributed to MaaT013 rather than other factors.
The PICASSO trial addresses a different disease and treatment context, but its randomised, placebo-controlled design illustrates the importance of comparative evidence. It provides a stronger basis for examining the incremental effect of a microbiome intervention than a study in which every participant receives the investigational product.
However, PICASSO does not resolve the European regulator’s concerns about MaaT013 in graft-versus-host disease. The patient populations, endpoints and intended clinical applications are different, and the melanoma study did not demonstrate a clear additional tumour response benefit.
MaaT Pharma has also been developing a proposed Phase 3 programme called PHOENIX for MaaT013 in graft-versus-host disease, with its United States strategy informed by discussions with the FDA. Further development requirements and funding availability remain important considerations.
The company must therefore manage a portfolio in which different programmes face distinct evidentiary challenges. Controlled studies may improve the regulatory foundation, but the clinical outcomes must establish meaningful benefit for each intended indication.
How does MaaT Pharma’s funding position affect the commercial significance of PICASSO?
MaaT Pharma’s financial position adds urgency to decisions about its development priorities. The company reported cash and cash equivalents of €17.1 million at 30 June 2026, compared with €24.9 million at the end of December 2025.
Following the negative European regulatory outcome, MaaT Pharma initiated a strategic portfolio review and implemented cash-preservation measures. In its September financial update, the company estimated that its existing resources would support operations until December 2026, based on its then-current operating assumptions.
That funding horizon is particularly relevant because development of MaaT034, the proposed PHOENIX trial and continued microbiome research all require substantial investment. A successful financing or partnership could support continued development, while a prolonged funding gap could require further adjustments to planned programmes.
The PICASSO study was independently sponsored and publicly funded through French research arrangements, reducing the direct financial burden associated with conducting the investigation. MaaT Pharma supplied the investigational product and placebo and undertook microbiome profiling, while academic investigators retained responsibility for the study.
The company has also explored financing and strategic partnership opportunities to support its priority assets. However, the November PICASSO announcement did not disclose a new capital raise or commercial agreement that would materially extend the previously reported cash runway.
The stock market provides another indication of investor sensitivity. MaaT Pharma shares were trading around €1.13 on 6 November, approximately 13% above the previous close during the observed trading session. Even with that recovery, the shares remained substantially below their level at the beginning of 2026.
The short-term movement is consistent with increased attention to the preliminary clinical disclosure, although it cannot establish that investors have interpreted the results as proof of future commercial success. The broader decline reflects a period in which regulatory setbacks and financing needs have become material considerations for the company’s valuation.
For a development-stage biotechnology business, the distinction between demonstrating biological activity and establishing an approvable, commercially viable product is especially important when financial resources are constrained.
What should clinicians and investors expect from the complete PICASSO dataset?
The next important scientific milestone is presentation of the complete PICASSO results by the study investigators at a future medical congress. MaaT Pharma has emphasised that the currently disclosed findings come from information submitted to the European Union Clinical Trials Information System and should not be treated as a final scientific publication.
More detailed data will be needed to interpret the actual rates of Grade 3 or higher adverse events, the numerical response rates, the durability of tumour responses and the relationships between microbial characteristics and treatment outcomes.
The full analysis may also clarify whether particular baseline microbiome profiles are associated with differential treatment effects. Such findings could be valuable for designing future microbiome-directed oncology studies, provided the signals are sufficiently robust to justify prospective testing.
For MaaT034, the development priorities remain appropriate product characterisation, regulatory engagement, adequate funding and generation of initial human safety and efficacy data in the intended checkpoint inhibitor-refractory population.
PICASSO demonstrates that a microbiome ecosystem therapy can be investigated alongside dual checkpoint inhibition in a controlled clinical setting without a statistically significant increase in the reported severe adverse-event endpoint. It also shows that measurable alterations in gut microbial diversity did not produce a clear overall tumour response advantage in the preliminary analysis.
MaaT Pharma’s next task is to determine whether the exploratory microbiome findings offer a scientifically credible way to identify patients more likely to benefit. With additional clinical research and financing decisions approaching, the value of PICASSO will depend less on its positive safety classification than on whether its findings can improve the design and execution of the company’s remaining oncology programmes.
