Background: Persistence of activated CD8 T cells is essential for the durability of tumor immune responses. IL-10 is an anti-inflammatory cytokine, PEGylated IL-10 (AM0010) enhances tumor specific CD8 T cell expansion and cytotoxicity. We evaluated tolerability and efficacy of AM0010 alone, with chemotherapy or anti-PD-1 in a phase 1 study. AM0010 alone induces objective anti-tumor responses without auto-immune toxicities. AM0010 with anti-PD-1 was evaluated in RCC (n=8) or NSCLC (n=5) and showed improved response rates (ORR 50 and 40% respectively) compared to published ORR with anti-PD-1 monotherapy. AM0010 and FOLFOX for 2nd LOT pancreatic cancer increased the ORR compared to FOLFOX. Expansion cohorts for AM0010 and FOLFOX in pancreatic cancer (n=20) or with anti-PD-1 in RCC (n=30) or NSCLC (n=30) were evaluated. Methods: Observed tumor responses were monitored using irRC criteria. Immune responses were analysed for 96 serum cytokines. Activation of PBMC derived CD4 and CD8 T cells were analyzed by FACS. The expansion of the T cell repertoire was measured by deep sequencing of the TCR. Results: AM0010 induced systemic, sustained elevation of Th1 and Th2 type cytokines and cytotoxic products of CD8+ T cells. Th17 related cytokines were reduced. In-vitro, AM0010 inhibits activation induced cell death. Phosphorylated STAT3 (p-STAT3) was induced in activated CD8+ T cells in vitro and in tumors. In addition, PD1+ Lag-3+ KI-67+ CD8+ T cells expanded in the blood, remained Tim-3- CTLA-4-. Expansion of PD-1+ Lag-3+ CD8+ T cells correlate with objective tumor response. AM0010 treatment also resulted in the progressive systemic expansion of novel T cell clones, which were not detectable in the patient prior to treatment. This de-novo expansion coincided with tumor responses in several patients. The magnitude of this expansion correlated with the magnitude of objective tumor responses. The immune activation was similar in monotherapy and in the combination arms, suggesting a AM0010 specific and non-redundant mechanism of action. Conclusions: AM0010 has predominantly immune stimulatory activity in cancer patients, alone and in combination with other immune oncology therapies. Clinical trial information: NCT02009449