CD40L stimulates tumor-infiltrating B-cells and improves ex vivo TIL expansion.

Background: Adoptive transfer of tumor-infiltrating lymphocytes (TIL) is now a Food and Drug Administration (FDA)-approved treatment for melanoma. While this is a major milestone, there is room for improvement to increase clinical response rates and to further optimize the manufacturing of TIL products. In this study, we characterized the association of tumor-infiltrating B-cells (TIL-B) and tertiary lymphoid structures (TLSs) with clinical response to TIL therapy and tested whether the presence of B-cells in the tumor can be leveraged to optimize TIL manufacture.

Methods: Tumor sections from TIL responders (R, n=9) and non-responders (NR, n=11) were analyzed by RNA sequencing, and immune cell content was estimated in silico. To study the association between B-cells and TIL expansion, we quantified B-cell subsets and TIL phenotype by flow cytometry. CD40L-induced effects on melanoma-infiltrating B-cells were analyzed by flow cytometry and scRNA-sequencing.

Results: Tumors from TIL clinical responders had greater abundance of class-switched B-cells (p=0.007) and a greater TLS score (p=0.03) than those of NRs. In addition, greater abundance of B-cells (p≤0.05) and switched memory B-cells (CD27⁺ IgD-, p≤0.05) in the tumors were associated with greater TIL expansion. Stimulation of TIL-B through addition of CD40L during TIL ex vivo culture improved their expansion success rate from 33% to 67% (p=0.03). Similarly, the addition of CD40L to non-small cell lung cancer (NSCLC) TIL cultures shortened the manufacturing period by 1 week. Moreover, CD40L-enhanced TIL showed more stem-like T-cells (CD39^- CD69^-, p≤0.05) and an enrichment of neoantigen-reactive T-cell clones in NSCLC TIL. Gene expression analysis showed that CD40L induced gene expression changes in TIL-B after 48 hours in culture (126 differentially expressed genes (DEGs)), with minimal to no changes observed in other immune cell types (including 12 DEG in macrophages, 10 DEG in dendritic cells, and none in monocytes). B-cell DEGs included upregulated co-stimulatory ligands (CD83, CD58), chemokines (CCL22, CCL17), among others. CD40L-induced upregulation of CD58 by melanoma infiltrating B-cells was associated with successful TIL expansion.

Conclusions: Our results show that CD40L-stimulated B-cells can be leveraged to enhance the quality and quantity of TIL. Clinical trial NCT05681780 is currently testing this concept applied to NSCLC TIL.