Background: Antibodies targeting PD-1/PD-L1 combined with vascular endothelial growth factor (VEGF) inhibitors are a front-line standard of care for metastatic RCC. Neoadjuvant use of these combinations is associated with tumor downsizing, but dynamic effects on key immune biomarkers are uncertain. We report early dynamic changes in the tumour immune environment after neoadjuvant treatment with avelumab/axitinib. Methods: Neoavax is an open label, single arm, phase II trial, investigating 12 weeks of neoadjuvant avelumab/axitinib prior to nephrectomy in patients with high-risk non-metastatic clear-cell (cc) RCC (cT1b-4N0-1M0). Partial primary tumour response (RECIST 1.1) occurring in ≥25% is the primary endpoint. Biomarker analysis on sequential tissue is an exploratory endpoint. Expression of PD-L1 (SP263), CD8+, CD8-granzyme-B (CD8/GZMB)+, Foxp3+ cells, CD8/CD39+ and major histocompatibility complex class I (MHC-I) were compared on paired samples (pre-treatment biopsy and nephrectomy) (NCT03341845). Results: Paired, sequential tissue from the first 24 patients was analysed for immune biomarker expression. Of these patients, 70% were ≥pT3a, 30% pN1, 58% had ISUP/WHO grade ≥3 with 8% sarcomatoid features. Compared to pre-treatment biopsy there was a significant increase in PD-L1 (p = 0.0002) and CD8+ expression (p = 0.0003) after therapy, whereas changes in CD8/GZMB+, MHC-I and CD8/CD39+ were not significant. Furthermore, neoadjuvant avelumab/axitinib therapy was associated with a significant decrease in Foxp3+ cells (p = 0.009). Conclusions: 12 weeks of neoadjuvant axitinib/avelumab treatment in ccRCC leads to significant dynamic changes in the tumour microenvironment for CD8+, PD-L1 and Foxp3+ expression. High baseline Foxp3+ infiltration is associated with an unfavorable outcome in the majority of solid tumours. The significant on-treatment decrease in Foxp3+ may account for the positive interaction seen between VEGF targeted therapy and immune checkpoint inhibitors in mRCC. If these cells represent regulatory T cells (Tregs), activated CD4 T cells or fragile Tregs remains to be determined. Clinical trial information: NCT03341845