Flt3L enhances clonal diversification and selective expansion of intratumoral CD8+ T cells while differentiating into effector-like cells.

Abstract

PD-1 blockade enhances anti-tumoral CD8⁺ T cell responses via type 1 conventional dendritic cells (cDC1s), but how cDC1s change the properties of intratumoral CD8⁺ T cells remains to be determined. Here, we identified two populations of intratumoral CD8⁺ T cells distinguished by their expression of asialo-ganglio-N-tetraosylceramide (asGM1). asGM1^neg and asGM1^posCD8⁺ T cells show enriched expression of genes characteristic for precursor exhausted T (Tpex) cells and terminally exhausted T (Tex) cells, respectively. The in situ expression of Flt3L or inhibition of PD-1 each promote the differentiation of asGM1^negCD8⁺ T cells into asGM1^posCD8⁺ T cells via interleukin-12 (IL-12) while also increasing the expression of Tpex and effector-like T cell-associated genes and their effector functions. Both interventions selectively expand CD8⁺ T cells, but only Flt3L expression broadens their T cell receptor (TCR) repertoire. These data indicate the distinct role of Flt3L in diversifying the TCR repertoire, offering potential solutions for immune checkpoint blockade-resistant cancers.