PSGL-1 blockade delays relapse to BRAF/MEK inhibition in cutaneous melanoma

Authors

El Naggar, O. S., Ha, B. N., Rakoto, M. L., Cort, L., Amirfallah, A., Haglund, E. A., Urquiza, P., Hetrick, H. A. F., Bradley, L. M., Hartsough, E. J., Hope, J. L., Romano, G.

Abstract

Advanced BRAF-mutant cutaneous melanoma can be treated with targeted therapy when immune checkpoint inhibitors (ICIs) fail or are not a feasible option. Nevertheless, most patients do not achieve a durable response, highlighting the critical need for therapeutic partners that enhance the long-term efficacy of targeted therapy. Transcriptomic analysis of a BRAF-mutant melanoma model of acquired resistance identified P-selectin glycoprotein ligand-1 (PSGL-1) as a top-upregulated immune mediator upon resistance acquisition. PSGL-1 is a key regulator of CD8+ T cell exhaustion and differentiation, and its inhibition has been shown to enhance T cell function across multiple disease models. Based on these observations, we hypothesized that combined targeting of BRAF/MEK and PSGL-1 would improve anti-tumor responses. Here, we demonstrate that dual inhibition of BRAF/MEK and PSGL-1 elicits durable tumor control in a preclinical model of PD-1-refractory cutaneous melanoma. Single-cell RNA sequencing of the tumor microenvironment reveals robust reprogramming of intratumoral CD8+ T cells toward a less terminally differentiated, memory-like phenotype following combined BRAF/MEK and PSGL-1 targeting. Consistent with these findings, CD8+ T cells in the tumor-draining lymph nodes of PSGL-1-/- mice exhibit enhanced functionality and a less differentiated state of exhaustion when compared with wild-type mice. To extend these observations to a translationally relevant setting, we further show that antibody-mediated blockade of PSGL-1, in combination with BRAF/MEK inhibition, yields superior anti-tumor activity compared with either monotherapy. Collectively, these findings identify PSGL-1 as a promising therapeutic target to enhance the durability of targeted therapy and provide a strong rationale for future clinical evaluation.

Preprint server: bioRxiv
The authors list and abstract were imported from bioRxiv on 09 Jul 2026.

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