Mechanism of Heterodimeric IL-15 in tumor reduction: Induction of myeloid-lymphoid cell interactions leads to IFN-γ dependent lymphocyte recruitment by dendritic cells into tumors

Background

hetIL-15 is evaluated in on-going immunotherapy clinical trials. We studied the mechanism of hetIL-15 antitumor function in several mouse models (MC38, TC-1, 4T1 and EO771).

Methods

We evaluated tumor immune infiltrate by flow cytometry, multi-color immunohistochemistry (IHC), transcriptomics and proteomics.

Results

hetIL-15 treatment delayed primary tumor growth, induced tumor regression and reduced metastases. Flow cytometry and IHC showed increased intratumoral NK and CD8+ T cell infiltration. Tumor-resident NK and CD8+ T cells were activated with enhanced IFN-γ production, increased proliferation (Ki67+), expression of survival factors (Bcl-2) and cytotoxic potential (Granzyme B+). hetIL-15 therapy resulted in increased IFN-γ and XCL1 levels and enhanced tumor accumulation of conventional type 1 dendritic cells (cDC1) expressing XCR1, IRF-8 and CD103. Production of CXCL9 and CXCL10 chemokines by tumor infiltrating cDC1 was boosted in an IFN-γ-dependent manner. Increased frequency of circulating NK and CD8+ T cells expressing CXCR3 was found, suggesting their migration toward tumors following the CXCL9/10 chemokine gradient.

Conclusions

hetIL-15 inhibits tumor growth by triggering lymphocyte-myeloid cell interactions modifying the tumor chemokine and cytokine milieu. hetIL-15 causes induction of XCL1 by lymphocytes, inducing DC intratumoral number, subsequent IFN-γ dependent CXCL9/10 production by DC and increased attraction of effector lymphocytes.

Regression of murine breast tumors after hetIL-15 monotherapy correlates with a novel population of intratumoral dendritic cells, in addition to increased infiltration of T, NK and cDC1 cells

Background

We studied mechanisms of therapeutic efficacy of the heterodimeric IL-15 (hetIL-15) of human, macaque or mouse in several mouse tumor models, including the murine EO771 orthotopic breast cancer model in syngeneic C57BL/6 mice.

Methods

The effects of hetIL-15 on immune cells were compared in tumors, lymph nodes and spleen by flow cytometry, immunohistochemistry (IHC), gene expression profiling (Nanostring) and metabolic profiling of tumor infiltrating T cells.

Results

hetIL-15 administration resulted in tumor regression in 40% of the treated animals and resistance to tumor rechallenge, inducing long term immunological memory. Activated NK and CD8+ T cells were increased in hetIL-15 treated tumors. hetIL-15 administration resulted in increased intratumoral infiltration of conventional Dendritic cells (cDC1) and also induced a new population of intratumoral DC, (F4/80high DCs), which were correlated negatively with the tumor size. Phenotypic profiling of F4/80high DCs identified expression of several cDC1 specific markers, including CD103, IRF8 and XCR1. tSNE analysis clustered F4/80high DCs close to cDC1s and macrophages.

Conclusion

Complete eradication of EO771 tumors by hetIL-15 treatment correlates with different tumor infiltrating immune cell types. We propose that the anti-cancer activity of hetIL-15 in primary tumors is orchestrated by the interplay of CD8+T cells, cDC1 and a novel subset of antigen presenting cells with a distinct phenotypic profile. Effective hetIL-15 treatment leads to development of long term anti-tumor memory. hetIL-15 supported a favorable metabolic profile of intratumoral effector lymphocytes, important for their function.

Prox1 suppresses the proliferation of neuroblastoma cells via a dual action in p27-Kip1 and Cdc25A

Neuroblastoma is a pediatric tumor that originates from precursor cells of the sympathetic nervous system with less than 40% long-term survival in children diagnosed with high-risk disease. These clinical observations underscore the need for novel insights in the mechanisms of malignant transformation and progression. Accordingly, it was recently reported that Prox1, a homeobox transcription regulator, is expressed in higher levels in human neuroblastoma with favorable prognosis. Consistently, we have recently shown that Prox1 exerts a strong antiproliferative effect on neural precursor cells during embryonic development. Thus, Prox1 is a candidate gene with a critical role in suppressing malignant neuroblastoma transformation. Here, we provide evidence that Prox1 strongly suppresses the proliferation of mouse and human neuroblastoma cell lines and blocks the growth of neuroblastoma tumors in SCID mice. Conversely, short hairpin RNA (shRNA) -mediated knockdown of basal Prox1 expression significantly induces proliferation, genomic instability and the ability of neuroblastoma cells to form tumors. Mechanistically, analysis of an inducible Prox1-overexpressing Neuro2A cell line indicates that Prox1 is sufficient to suppress CyclinD1, CyclinA and CyclinB1, consistent with a role in cell cycle arrest. Surprisingly, Prox1 strongly induces CyclinE1 expression in the same system despite its action on blocking cell cycle progression, which could account for the context dependent oncogenic function of Prox1. Most importantly, Prox1 was sufficient to decrease Cdc25A and induce p27-Kip1, but not p21-Cip1 or p53. By alleviating the Prox1 action in Cdc25A and p27-Kip1 expression, we were able to rescue its effect on cell cycle arrest. Together these data suggest that Prox1 negatively regulates neuroblastoma carcinogenesis through suppression of Cdc25A and induction of p27-Kip1 to counteract CyclinE1 overexpression and block cell cycle progression. Furthermore, these observations render Prox1 a candidate target for the treatment of neuroblastoma tumors.