Abstract 1647: Assessment of a novel tumor model using adult patient mobilized human CD34+ hematopoietic stem cells in NCG mice
Authors: Rowe Jenny , Eberle Christoph , Fiore Ann , Mihalek Robert , Schoen Brianna , Festin Stephen 
Published: June 2022

Background: Inhibitors of the PD-1/PD-L1 checkpoint pathway were among the first FDA approved immunotherapies and are now among the standard of care for cancer patients. In vivo animal models that recreate crucial aspects of human tumor biology and anti-tumor immunity are needed for evaluating new therapy developments across cancer types. In 2019, we reported an animal model using non-adult (cord blood derived) hCD34+ hematopoietic stem cells, considered the standard cell source, for humanizing the immune system of NCG mice. In this study we assessed a mouse model using adult patient mobilized hCD34+ stem cells as an alternative source and evaluated engraftment and tumor modulation using checkpoint inhibitors.

Study Details: We evaluated the anti-tumor effects of an anti-human PD-1 checkpoint inhibitor on basal lung cell adenocarcinoma (A549) in NCGs humanized with adult patient mobilized hCD34+ stem cells. Humanized mice were implanted subcutaneously with A549 cells, and tumor bearing mice (TBM) were randomized into treatment groups when the average tumor size reached a volume of ~80-120 mm3. Vehicle control mice were treated with isotype control IgG antibody, whereas A549 TBM were dosed with anti-hPD-1 antibody biweekly (10 mg/kg) for three weeks. Clinical observations, body weights and tumor growth kinetics were recorded throughout the study. At study termination, whole blood, spleen and tumor tissue were collected and processed for immune profiling by multi-color flow cytometry.

Results: Anti-hPD-1 monotherapy significantly inhibited A549 tumor growth. NCG mice injected with adult patient mobilized hCD34+ stem cells sustained engraftment. At study termination common human leukocytes were distributed in peripheral blood, spleen and tumors of surviving mice. Phenotyping of the cancer microenvironment revealed the presence of lymphoid (T-lymphocytes and subsets including Tregs) and myeloid immune cells (DC, TAM) with the latter lineage less detectable overall. PD-1 checkpoint blockade on average increased CD8+ T-cell infiltration and decreased Treg frequencies among the TIL population. Generally, human cytokines (IFN-γ, IL-2 and TNF-α) were secreted by viable tumor-infiltrating total T-cells (CD3+) and subsets (CD4+ and CD8+) following ex vivo PMA/Ionomycin stimulation in the presence of Brefeldin A, demonstrating the capability to produce polyfunctional responses.

Conclusions: This study demonstrates that adult patient mobilized hCD34+ cells can successfully reconstitute NCG mice. An immune modulating anti-tumor response was elicited with tissue infiltration patterns of human leukocytes overall comparable to those found in cord blood derived hCD34+ humanized NCG mice. These findings make this model utilizing NCG mice engrafted with adult patient mobilized hCD34+ stem cells a viable approach for cell transfer studies when assessing targeted immuno-oncology therapies.

Citation Format: Jenny Rowe, Christoph Eberle, Ann Fiore, Robert Mihalek, Brianna Schoen, Stephen Festin. Assessment of a novel tumor model using adult patient mobilized human CD34+ hematopoietic stem cells in NCG mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1647.