Background: Antibodies targeting PDL1 or PD1 have been disappointing so far in the treatment of ovarian cancer (OC). A greater understanding of the complex iTME and of the impact of chemotherapy on immune features could uncover promising immune targets. We previously reported that neoadjuvant chemotherapy (NACT) increased CD4+ and CD8+ immune cells (IC) and depleted FOXP3+ suppressive T-regs in OC iTME. Here we aimed to describe the expression of PDL1 as well as other co-regulatory molecules in OC and their changes under NACT. Methods: Tumor samples and clinical data were prospectively collected from patients (pts) in the randomized CHIVA trial of NACT +/- nintedanib. Samples were evaluable for immune profiling for 116-124 pts at diagnosis and 89-107 at surgery after 3 cycles of NACT. IC stained for CD4, CD8 were scored as number of IC+/mm². Expression of immune co-regulatory molecules PDL1, TIM3, LAG3 and IDO was scored as percentage of positive cells, and tumors were classified as PDL1/TIM3/IDO/LAG3 positive if > 1% of IC and/or tumor cells (TC) were positive. Highly sensitive pts, defined as objective response to NACT and prolonged median progression-free survival (mPFS > 24months), were compared to refractory pts (progressing during or within 3mo of platinum). Results: As expected, about one third (36%) of tumors were PDL1+ at diagnosis. In contrast, the prevalence of other co-regulatory molecules was higher with 52%, 54% and 93% of tumors being positive for IDO, LAG3 and TIM3, respectively. There was no significant change in PDL1 expression with NACT. However, in paired samples NACT significantly increased IDO and LAG3 expression (p < 0.05), such that 60% and 66% of tumors post-NACT were positive for IDO and LAG3, respectively. TIM3 expression remained high post-NACT with 92% of positive tumors. Highly sensitive tumors (vs refractory tumors) had significantly higher IC expression of TIM3 after NACT (24% vs 6%, p = 0.005), and were significantly more infiltrated by CD4+ (441 vs 228 cells/mm2, p = 0.04) and CD8+ (460 vs 225 cells/mm2, p = 0.045) T cells. Conclusions: Other immune targets beyond PDL1 are highly expressed in OC. In addition NACT appears to prime the iTME by increasing effector T cell infiltration and the expression of other relevant co-regulatory molecules (LAG3, TIM3 and IDO). Future studies could be performed by priming the iTME with NACT and testing novel immune therapies based on target expression in samples obtained at interval debulking surgery.