Background: Regulatory T cells (Tregs) are responsible for maintaining self-tolerance, and inhibit antitumor immune responses. PD-1 blockade was reported to increase resistance of effector T cells to Tregs suppression and directly reduces in vitro Tregs suppressive function. Natural killer cells (NKs) expressed PD-1 and engagement of PD-1 reduces their cytolytic potential. To identify biomarkers informative and predictive of Nivolumab efficacy Tregs and NKs phenotype and function was determined in Nivolumab treated metastatic renal cancer (mRCC) patients (REV). Effect of CXCR4 antagonism are evaluated on ex vivo Tregs and NKs.

Methods: 48 REV, 26 other than ICI treated-mRCC (CTR) and 23 Healthy Donors (HD) were enrolled. To date, the clinical evaluation is available for 42 REV [14 with objective response (OR) and 28 in progression (PD)] and 18 CTR (11 OR and 7 PD). 31 patients (pts) underwent first clinical evaluation at 3 months resulting in 25 pts with OR and 6 in PD. Tregs (CD4+CD25+CD127lowFOXP3+) and NKs (CD3-CD56+CD107a+) phenotype and function were evaluated at day 0, 14, 28, 90, and 180. CFSE-T-effector proliferation-Tregs dependent and CD107a externalization toward K562 as NKs function were evaluated.

Results: Higher NKG2D was reported on CD3-CD56dim cells from OR as compared to PD pts (p=0.0054). Statistically significant low NKs basal activity was detected at T0 in 3 months PD- Nivolumab treated pts (p=0.032). CD107a+/CD53+CD56+ is higher in OR compared to PD pts over time. Percent Tregs CD4+CD25+CD127lowFOXP3+ and CD8/Tregs ratio were respectively low (p<0.001) and high (p<0.001) in 71 mRCC as compared to 23 HD. Significant lower PD-1 was observed in Tregs at 3 months of treatment in OR pts (p= 0.048). Moreover, higher % of CD4+CD25+CD127lowFoxp3+ Tregs were observed in PD compared to OR pts over time (p<0.001) with higher CTLA4 expression in PD group. Tregs function, as evaluated at 2 weeks post treatment, was inhibited in responder and potentiated in PD patients. Moreover, CXCR4 antagonism dramatically reversed Tregs function ex vivo as early as at day 14 of treatment in OR pts (p=0.0024). A statistically significant reduction in peripheral Tregs (Effector/Naïve and nonTregs) was revealed in 14 Long Responder compared to 23 PD pts (> 12 months) (p<0.05; p<0.01 and p<0.05, respectively). In 18 CTR no modification in Treg phenotype and function were detected but a common decrease in NK activity unrelated to the clinical outcome.

Conclusions: Basal NK activity and 2 weeks Tregs evaluation discriminates mRCC Nivolumab responding patients. Ex vivo CXCR4 antagonism inhibits Tregs function in responding patients at early treatment time point (2 weeks). These evidence are not detected in non-immune treated mRCC patients.

Citation Format: Sara Santagata, Anna Maria Trotta, Giuseppina Rea, Maria Napolitano, Anna Capiluongo, Crescenzo D'Alterio, Marilena Di Napoli, Sabrina Rossetti, Sandro Pignata, Stefania Scala. Basal NK activity and early Tregs inhibition predicts nivolumab responsiveness in metastatic renal cancer patients (REVOLUTION) trial [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6675.