scRNA-Seq analysis of CSF pre- and post-last-treatment showed Avelumab + WBRT stimulated an adaptive immune response associated with a decrease in regulatory T cells (Tregs), among other changes in the expression of immune checkpoints on CD8 + T cells and macrophages.<h4>Conclusions</h4>The combination of Avelumab and WBRT is safe and demonstrates activity in patients with LMD. Here, CD8A is linked to Langer mesomelic dysplasia.