Background: In mice, tumor cryo plus immunologic checkpoint blockade generates tumor antigen release, proliferation of tumor-specific T-cells, and enhanced survival. We previously demonstrated in a pilot study that pre-op cryo+ipi is well tolerated in women with ESBC and did not delay standard of care surgical resection. Here, we analyze pilot study tissue and blood to explore immune response. Methods: 18 ESBC patients (pts) were treated with preop cryo (n=6), single-dose ipi 10mg/kg (n=6), or cryo+ipi (n=6). As a potential surrogate for tumor immunogenicity, baseline T-cell tumor infiltrating lymphocyte (TIL) density was evaluated by T-cell receptor quantitative DNA sequencing. We explored the systemic immune response to cryo and/or ipi using previously described laboratory measures including inducible costimulator (ICOS, a marker of activated CD4+ T-cells) and plasma interferon gamma (IFNγ, a cytokine associated with T-cell activity). Results: Of the 18 study pts, 13 pts had hormone receptor-positive (HR+) disease, 2 pts had HER2+ disease (both treated with ipi alone) and 3 pts had triple-negative (TN) disease (1 ipi alone and 2 cryo/ipi). Baseline TIL density was highly variable overall (range 2-30%), but higher in HER2+ and TN pts (median 15%) compared with HR+ pts (median 5%). Sustained >2-fold elevations in ICOS and IFNγ were observed in the majority of cryo+ipi pts 30 days following treatment (ICOS: 5/6 pts; IFNγ: 4/6 pts), but in the minority of ipi pts (ICOS: 2/6 pts; IFNγ: 2/6 pts) or cryo pts (ICOS: 0/6 pts; IFNγ: 0/6 pts). Sustained ICOS and IFNγ elevations were observed regardless of baseline TIL density. Conclusions: Cryo+ipi was more likely to induce systemic immune activation compared to cryo or ipi alone. These potentially beneficial immune effects were observed in both HR+ and HR- subtypes, as well as in tumors with low or high baseline TIL density. These data support further studies of cryo+ipi in ESBC across HR+ and HR- subtypes, as well as in tumors that do not appear immunogenic at baseline.