Oncolytic adenovirus Ad5/3-E2F-d24-hTNFa-IRES-hIL2 (TILT-123, igrelimogene litadenorepvec) shows promise as a therapeutic agent capable of causing tumor regression and activating host immunity. A phase I clinical study TUNIMO (NCT04695327) assessed its safety as monotherapy in patients with various solid tumors. Through single-cell profiling of peripheral blood, we identified distinct immunological features distinguishing responders from non-responders. Specifically, at baseline, responders demonstrated enhanced cytotoxic markers and stronger immune cell communication networks. Moreover, higher baseline CD16+ monocytes correlated with improved survival, while elevated regulatory T cells predicted poor response. T and B cell evaluation revealed contrasting patterns: responders showed higher numbers of T cells with predicted specificity to both adenovirus and tumor antigens, while elevated total memory B cells, regardless of specificity, predicted poor survival. Several T and B cell receptor segments matched those previously reported in other viral infections, suggesting possible cross-reactive immune responses. These findings emphasize that comprehensive biomarker analysis of peripheral blood should include not only cell frequencies but also transcriptional changes and distinct patterns of cellular and humoral immunity.