For patients with advanced melanoma without BRAF mutation who no longer respond to immune checkpoint inhibitors, treatment options remain frustratingly limited. A new study from Vanderbilt researchers led by Professor Emerita of Pharmacology Ann Richmond outlines a promising therapeutic strategy that may re-sensitize these resistant tumors to immunotherapy.
The research introduces a three-drug combination that enhances immune activity and suppresses tumor-promoting immune cells by leveraging a low dose of the MEK inhibitor trametinib and multi-kinase inhibitor rigosertib alongside a CD40 agonist to shift the tumor microenvironment toward immune activation. Notably, all three agents have been either approved by the U.S. Food and Drug Administration or are currently in clinical trials, which may speed their path to patient testing.
“While agonist CD40 therapy can be helpful for treatment of melanoma, this therapy also induces the CD11b+ B regulatory cells that suppress the T cell response to tumors,” Richmond said. “We showed that combining CD40 therapy with trametinib and rigosertib prevents the induction of these B regulatory cells.”
Immune checkpoint inhibitors have become a mainstay of melanoma treatment, working by releasing the molecular “brakes” that prevent T cells from attacking cancer. But resistance to ICI is common in metastatic melanoma, especially in tumors that evolve immune-suppressive microenvironments. While CD40 agonists can activate immune cells, this therapy also unexpectedly expands CD11b+ regulatory B cells.
By combining CD40 activation with MEK and PI3K inhibition, the researchers blocked the expansion of suppressive B cells while retaining the benefits of CD40 stimulation. In preclinical mouse models of melanoma, the triple combination not only suppressed tumor growth but also restored responsiveness to checkpoint blockade.
Key findings
- B cells as a resistance mechanism: CD40 therapy alone induced regulatory B cells that dampen T cell–mediated tumor immunity.
- Triple combination prevents immune suppression: Co-treatment with trametinib and rigosertib blocked the agonist CD40 induction of regulatory B cells, allowing immune responses to proceed.
- ICIs regain effectiveness: The drug cocktail slowed tumor progression and re-sensitized resistant melanomas to anti-PD-1 therapy.
Translational promise
Because trametinib, rigosertib, and CD40 agonists are already in human trials or approved for other indications, this therapeutic strategy may advance more quickly than approaches requiring new drug development. Richmond’s team sees potential for testing the triple therapy in clinical trials for melanoma patients who have progressed on ICI.
“This approach provides a new route to enhance antitumor immunity in patients with tumors that no longer respond to immunotherapy,” Richmond said.
The project was a multidisciplinary collaboration that included fellow Vanderbilt principal investigators Vivian Weiss, Doug Johnson, and Qi Liu. Former Research Assistant Professor of Pharmacology Chi Yan was first author; Yan will continue this work in his new lab at the University of Manitoba.
Go deeper
The paper “RAS/MEK/PI3K pathway inhibition augments response to CD40 agonism by targeting CD11b+ Bregs thereby overcoming melanoma PD1-resistance” was published in Nature Communications in January 2026.
Funding
The National Cancer Institute, the Department of Veterans Affairs, and a Lloyd Foundation Melanoma Research Grant supported this research.
Open access
The study was published open access through a transformative agreement negotiated by Vanderbilt University’s Jean and Alexander Heard Libraries. Transformative agreements eliminate traditional paywalls and remove the obstacle of article processing charges, ensuring immediate and unrestricted access to research worldwide. Vanderbilt authors can learn more about the Heard Libraries’ agreements supporting open access publishing in this research guide.