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Abstract Introduction: Turning “cold” tumors “hot” is considered essential for immune-oncology therapies to be effective. Bria-IMT is an allogenic human cancer cell line with antigen presenting cell activity (SV-BR-1-GM) designed to overcome the immune-suppressive tumor microenvironment. However, until now there has not been proof that “cold” tumors can become “hot” with this therapy. Using Zr-89 crefmirlimab berdoxam, a zirconium-89 labelled truncated antibody specific to human CD8α and developed for CD8 ImmunoPET, we image before and after Bria-IMT therapy administration to assess the baseline status as well as changes in CD8 cell presence after initiation of therapy. Here we present the first evidence that cold tumors can become hot on treatment with Bria-IMT combined with an anti-PD-1 checkpoint inhibitor (CPI), showing CD8+ cells increased over baseline using CD8 ImmunoPET. Case: After informed consent, a 61 year-old Hispanic female, enrolled in the ongoing randomized phase 2 Bria-IMT trial in advanced heavily pretreated metastatic breast cancer (MBC) (NCT03328026). Her history included MBC in May 2020, ductal type, grade 3, triple negative breast cancer (TNBC) with 6 prior lines of therapy including a Trop-2-directed antibody-drug conjugate and 6 lines of chemotherapy. Precision medicine testing identified no actionable targets. All prior therapies had progressive disease as their best response. The subject was randomized to start the CPI after 2 cycles of Bria-IMT to “train” the host immune system before proceeding with combination immune-oncology therapy. Baseline testing revealed the subject to be anergic to candida and SV-BR-1-GM inoculation. However, by cycle 3 delayed-type hypersensitivity to SV-BR-1GM developed. Interestingly the subject matched SV-BR-1-GM at 2 HLA loci: DRB3*02:02 and DRB1*11:04 which in previous publications is associated with greater clinical benefit. Tumor markers were stable or decreased slightly including CEA (25% decrease) and CA 15-3 (43% decrease). Circulating Tumor Cells (CTCs) and Cancer Associated Macrophage Like cells (CAMLs) also improved. Standard imaging at baseline showed 3 main sites of disease including a large right breast mass, multiple right axillary lymph nodes and a right lower lobe mass with CD8 ImmunoPET uptake in these areas similar to the blood pool. On the follow-up CT imaging, all of these lesions increased in size with newly appreciated pulmonary nodules. The right lower lobe mass showed increased CD8 ImmunoPET accumulation with an SUV of 5.8 (close to the liver background) as compared to an SUV of 2.2 at baseline. The lesions in the right breast and right axilla remained at blood pool levels. There was an increase in CD8 ImmunoPET uptake in bilateral inguinal lymph nodes reaching an SUV of 4.8 as compared to SUV 2.2 at baseline. In addition, there were non-enlarged lymph nodes in bilateral axillary regions that also showed increased radio-tracer accumulation reaching an SUV of 9.5 as compared to SUV 4.9 at baseline. Conclusion: This subject demonstrated a mixed response of metastatic lesions on CD8 ImmunoPET with encouraging changes in peripheral blood tumor markers and CTCs. The nonspecific nodal localization of CD8 ImmunoPET may indicate a systemic activation of CD8 positive lymphoid cells. This shows the value of CD8 ImmunoPET in identifying lesions that are progressing on treatment versus pseudo progression. It also provides support that the Bria-IMT + CPI combination immune-based therapy can result in an increase of CD8+ tumor infiltrating lymphocytes in breast cancer metastatic sites as well as an increase in lymphoid organs. This advance may aid in triaging patients, adjudicating pseudo-progression and predicting clinical benefit of immune based therapies. Citation Format: Russ Kuker, Frances Valdes-Albini, Giuseppe Del Priore, Aazim Arif, Kristin Schmiedehausen, Carmen Calfa. CD8+ Tumor Infiltrating Lymphocytes Turn a Cold Tumor Hot in Metastatic Breast Cancer abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO1-20-12.
Kuker et al. (Thu,) studied this question.