Background PARP inhibitors (PARPi) induce synthetic lethality in BRCA1/2-mutant (BRCA-MUT) tumors and can activate DNA-damage-linked immune pathways. The TALAVE study (NCT03964532) examined the combination of the PARPi (talazoparib) with PD-L1 blockade (avelumab). Here we evaluated spatially resolved immune signaling and remodeling in response to talazoparib alone and with avelumab. Methods 24 patients with advanced HER2-negative breast cancer (12 BRCA-MUT, 12 BRCA-WT) received talazoparib then talazoparib + avelumab. Serial biopsies (baseline, post-PARPi [BX2], post-combination [BX3]) underwent transcriptomic, spatial protein, and multiplex IF. BRCA-dependent TME remodeling and cellular neighborhood (CN) shifts were assessed. Results BRCA-MUT tumors showed 83% objective response and 100% clinical benefit, whereas BRCA-WT tumors exhibited minimal activity. BRCA-MUT tumors became fragmented with increased immune activity, while BRCA-WT tumors remained compact and immunosuppressed. gammaH2AX and pTBK1 were spatially co-expressed and sustained in BRCA-MUT tumors during treatment but declined in BRCA-WT tumors. BRCA-MUT tumors displayed enrichment of CD8 + T cells and CD163 + macrophages after PARPi, whereas CD4 + T cells and CD68 + CD163 + macrophages were depleted in BRCA-WT tumors. PD-1 + CD8⁺ T cells were strongly linked to local CD4⁺ T cell density, and PD-1 + frequency in CD8 + T cells correlated with longer PFS at baseline and BX3 in BRCA-MUT but not BRCA-WT tumors. CN analysis revealed CD4 + and CD8 + enriched neighborhoods with intermediate PD-1 expression that expanded after therapy in BRCA-MUT but not BRCA-WT tumors, and these CNs lacked PD-L1⁺ cells. Between BX2 and BX3, BRCA-MUT tumors sustained immune activity but showed no further T cell activation or infiltration. Spatial mapping identified three PD-L1 + CN types: (1) T cell-dense niches with high PD-1/PD-L1 and gammaH2AX-pTBK1 activity enriched only at baseline, largely lost after PARPi; (2) macrophage-T cell mixtures that were depleted during therapy; and (3) PD-L1 + dying tumor cells lacking pTBK1 activity and T cell engagement. Across contexts, PD-L1 was either lost before PD-L1 blockade or confined to regions isolated from T cells, leaving little opportunity to reinvigorate T cells. Conclusions PARP inhibition reshaped the TME of BRCA-MUT tumors by inducing tumor fragmentation, sustaining gammaH2AX-pTBK1 signaling, and restoring CD4 + and CD163 + immune cells, whereas BRCA-WT tumors remained structurally intact and immunosuppressed. PD-1 + T cells localized to PD-L1-negative neighborhoods, and PD-L1 + tumor/myeloid cells were rapidly lost or confined to dying, immune-excluded regions, limiting the impact of PD-L1 blockade. Although PARPi re-engaged T cell programs in BRCA-MUT tumors, strategies beyond PD-L1 inhibition will be required to further enhance T cell infiltration and activation.